Spring 1998, Vol

S T A N F O R D L I N E A R A CCELERATOR CENTER

Spring 1998, Vol. 28, No.1 A PERIODICAL OF PARTICLE PHYSICS

SPRING 1998 VOL. 28, N UMBER 1

Editors RENE DONALDSON, BILL KIRK

Contributing Editors MICHAEL RIORDAN, GORDON FRASER JUDY JACKSON, PEDRO WALOSCHEK

Editorial Advisory Board GEORGE BROWN, LANCE DIXON JOEL PRIMACK, NATALIE ROE ROBERT SIEMANN, GEORGE TRILLING KARL VAN BIBBER

Illustrations TERRY A NDERSON

Distribution

Lake CRYSTAL TILGHMAN Soudan Superior

Duluth

The Beam Line is published quarterly by the MN Lake Stanford Linear Accelerator Center WI Michigan PO Box 4349, Stanford, CA 94309. Telephone: (650) 926-2585 Madison INTERNET: [email protected] MI FAX: (650) 926-4500 IA Issues of the Beam Line are accessible electronically on the World Wide Web at http://www.slac.stanford.edu/ Fermilab pubs/beamline IL IN SLAC is operated by Stanford University under contract with the U.S. Department of Energy. The opinions of the authors do not necessarily reﬂect the policy of the MO Stanford Linear Accelerator Center.

Cover:The cover photo was taken in 1917, plus or minus about one year. The photographer is unknown or unre- membered. The young lad shown in the photo with his telescope in the garden of his home in Pretoria, South Africa, is Alan Cousins, at the age of about fourteen (he was born in 1903). Dr. Cousins’ ﬁrst contribution to the astronomical literature was published in 1924. Seventy-four years have passed since then, but Alan William James Cousins is still at work at his home base, the South African Astronomical Observatory (SAAO), having recently published his latest paper (“Atmospheric Extinc- tion,” The Observatory, April 1998). He will be 95 in August of this year, continuing a long life among the stars. Happy birthday!

SPRING 1998 CONTENTS

FEATURES

2 ALL WE WANT IS THE WORLD’S BIGGEST MACHINE! One of our Contributing Editors follows up on his article in the last issue on the origins of international collaboration in Europe to describe the creation of CERN. Gordon Fraser

9 SEARCHING FOR NEUTRINO OSCILLATIONS The author describes why understanding neutrino oscillations might be critical to the question of whether neutrinos have mass. Maury Goodman

17 PHYSICS WITH CHARM A Fermilab physicist describes why the study of the charm quark might open the way to physics beyond the Standard Model. Jeffrey A. Appel

DEPARTMENTS

22 THE UNIVERSE AT LARGE This Was the Year That Was (Astrophysics in 1997) Virginia Trimble

31 CONTRIBUTORS

DATES TO REMEMBER

BEAM LINE Contributing Editor Gordon Fraser follows All We Want Is th up on his piece on the origins of international collaboration in Europe (Winter 1997) to describe the creation of CERN. This article is adapted from a chapter in his book The Quark Machines on the politi- cal history of particle physics and the parallel evolution of its big machines.

Isidor Rabi had proposed the idea of a European physics laboratory at a UNESCO conference in Florence in June 1950. The signatories to the initial 1952 agreement to establish CERN sent him this letter.

2 SPRING 1998 World’s Biggest Machine! by GORDON FRASER

ETWEEN 1949 AND 1959, the dream of an international European laboratory for particle physics—‘CERN’—became a reality, brieﬂy sporting the world’s highest energy proton synchrotron. In those ten years, scientists from countries that had been Bat war only a few years earlier set aside their differences and collaborated in a dramatic demonstration of what could be achieved when national characteristics dovetail smoothly in the achievem ent of a com mon goal. The ideals and insights of CERN ’s founding fathers provide vital lessons in the continued quest for wider international collaboration in particle physics.

Scientific objectivity is a com mon bond between winner of the 1929 Nobel prize for his elucidation nations. In every country, scientists address the of particle waves. De Broglie maintained that sci- same problems. If one nation hushes up its research entific collaboration between European countries findings, the knowledge will ultimately be acquired could open up projects that were beyond the means elsewhere. Scientific curiosity cannot be quenched. of individual nations. Following up with his own In the after math of World War II, science was seen ideas, Dautry affirmed that astronomy and astro- as a potential olive branch. However the war had physics on one hand, and atomic energy on the oth- shifted much of the scenery. Major efforts to har- er, would be ideal vehicles for such international ness fission and microwaves had demonstrated the collaboration. value of large-scale collaboration. Militant nation- Dautry could call on powerful colleagues in al pride had given way to new international aware- France. One was Pierre Auger, who had made im- ness. Embarrassed by having caused so much strife portant contributions to atomic and nuclear physics and inflicting it on the rest of the planet, Europe in the 1930s and became Director of Exact and Nat- felt it had to present a more united front. ural Sciences of the new United Nations Educa- The United States, as the leading postwar sci- tional, Scientific and Cultural Organization entific power, attracted scientific emigrants from (UNESCO). Another prominent French figure was Europe in what would eventually be called the nuclear fission pioneer Lew Kowarski, who had “brain drain.” This leak first had to be stemmed worked in Britain during the war and understood if the Continent was not to find itself starved of tal- the special position of the United Kingdom, which ent. Following the Congress of Europe in The Hague was trying to “go it alone.” in May 1949, the European Cultural Conference At the UNESCO General Conference held in in Lausanne in December 1949, attended by 170 in- Florence in June 1950, however, the seed planted at fluential people from 22 countries, helped set the Lausanne still lay dormant. In the U.S. delegation stage. was Isidor Rabi, winner of the 1944 Nobel physics At Lausanne, the Swiss writer Denis de Rouge- prize who had supervised research at the MIT Ra- mont, founder of the European Cultural Centre, de- diation Laboratory during the war. After the war plored an increasing trend towards secrecy in nu- Rabi, with Norman Ramsey, had pushed for the es- clear physics and advocated a “European centre for tablishment of a major new U.S. research labora- atomic research.” Then Raoul Dautry, Adminis- tory, Brookhaven, on New York’s Long Island. In trator-General of the French Atomic Energy Rabi’s mind this was a role model for what could Commission, read a message from Louis de Broglie, be achieved elsewhere.

BEAMLINE3 Upon arriving at Florence, Rabi for Europe at a meeting of a United was surprised to discover that the Nations agency had opened a new agenda included no mention of the door. European physics collaboration The two men who took Rabi’s ba- mooted at Lausanne. Setting up phys- ton and sprinted with it were just ics laboratories was something Rabi those who had helped him draft the knew well, but international com- Florence resolution—Amaldi and mittee work was not. The first thing Auger. Just a few weeks later, Amaldi was to get an item onto the agenda, was stimulated by a visit to Brook- overcoming the apparent indifference haven, where the Cosmotron was of his American colleagues. More already taking shape. Few Europeans helpful were Auger and the Italian had ever seen a physics effort of such physicist Edoardo Amaldi, who had proportions. “Colossale,” he re- worked in Enrico Fermi’s Rome lab- marked. oratory before the war. Invited to the Under the auspices of the Euro- United States by Fermi, Amaldi pre- pean Cultural Centre, a meeting was ferred to stay in Italy and help restore organized in Geneva in December Italian physics after the chaos of the 1950 with delegates from Belgium, war. Amaldi went on to become one France, Italy, the Netherlands, Nor- Edoardo Amaldi in 1971 at the age of 63. of Europe’s great postwar scientific way, and Switzerland. Auger un- One of Europe’s leading postwar statesmen, his achievements appear- veiled a plan for a new laboratory scientific statesmen, he played a key administrative role in the founding of ing to stem from a deep sense of duty dedicated to the physics of elemen- CERN. (Courtesy CERN) rather than personal ambition. tary particles. He knew that in- Drafted with the assistance of triguing new discoveries had already Auger and Amaldi, the proposal from been made in cosmic rays, but that Rabi at Florence requested UNESCO this windfall sprouting could become “to assist and encourage the forma- a major harvest once the big new U.S. tion and organization of regional accelerators were up and running. research centres and laboratories in Initial contacts with Britain had order to increase and make more established that while its physicists fruitful the international collabora- were not against the idea of a Euro- tion of scientists in the search for pean laboratory, they still wanted to new knowledge in fields where the go their own way. Their support was effort of any one country in the re- vital to get the idea off the ground, gion is insufficient for the task.” Rabi however, as in Europe only Britain pointed out that the initiative “was had experience in major projects. Pos- primarily intended to help countries sible sites mentioned for the new which had previously made great European laboratory included Gene- contributions to science,” and va and Copenhagen. that “the creation of a centre in The resolution passed at the Europe . . . might give the impetus Geneva meeting was startling. It to the creation of similar centres in recommended the creation of a lab- other parts of the world.” The oratory for the construction of a motion was unanimously accepted. particle accelerator whose energy Where Europeans had failed to reach should exceed those of machines cur- a consensus, an American resolution rently under construction elsewhere

4 SPRING 1998 (which meant the mighty 3 GeV Cos- machine, a new motron and the even bigger 6 GeV plan envisioned Berkeley Bevatron). In a field where, a smaller initial apart from Britain, Europe had no tra- machine to launch dition and little expertise, the plan the new laborato- was simply to jump into the lead by ry. Proposals were cash and enthusiasm. These bold pro- put forward for a posals were enthusiastically endorsed 500 MeV synchro- in Italy, Belgium, France, Norway, cyclotron and a 5 Sweden, and Switzerland. In Britain, GeV proton syn- where physicists were busy building chrotron, with de- several new accelerators, there was sign and construc- astonishment and skepticism. “Who tion proceeding in is behind the scheme?” thundered parallel. European P. M. S. Blackett, “Is it serious?” physicists seemed A study group to define the new optimistic about accelerator included Cornelis Bakker government fund- from the Netherlands, who had built ing. On the question of the site, new In 1951, before a site for the new labora- a synchrocyclotron at Amsterdam, criteria, designed to undermine tory had been chosen, Odd Dahl of Odd Dahl from Norway, a talented Copenhagen’s case, stipulated the use Norway (standing) was appointed head of CERN’s proton synchrotron group and engineer responsible for the first nu- of a major language. Cornelis Bakker of the Netherlands clear reactor to be built outside the A November 1951 meeting in (seated) head of the synchrocyclotron original “nuclear club,” and Frank Paris suggested that the energy goal group. After a trip to the U.S. in 1952 Goward, a British physicist who had of the new synchrotron could be as where he learned of the invention of graduated into wartime radar work. high as 10 GeV, but to defuse the strong focusing, Dahl wisely pushed for In a flush of modesty after the initial thorny siting issue, the respective the CERN synchrotron to adopt the new, strident proclamation, the new ad- group leaders would remain at their as yet untested technique. But with the decision to build the machine in vertised goal was to copy the 6 GeV home bases—Dahl in Norway work- Geneva, Dahl retired from the project in Berkeley machine instead of the orig- ing on the synchrotron, Bakker in 1954. In 1955, following the resignation of inal idea of building the world’s The Netherlands on the synchrocy- CERN’s first Director General, Felix largest machine. clotron, Kowarski in France on in- Bloch, Bakker succeeded him. One suggestion was to use Niels frastructure, and Bohr in Copenhagen (Courtesy CERN) Bohr’s laboratory in Copenhagen as on theory, with Amaldi’s adminis- a home for the new institute, an idea trative hub in Rome. that also found favor in Britain, and A meeting at Paris that December naturally stimulated interest in Nor- brought representatives together way and Sweden. Bohr, who had not from thirteen European nations, in- been party to the previous discus- cluding West Germany. The Nether- sions around the Auger-Amaldi axis, lands delegation put forward a five- began to exert his considerable in- fold plan, with two points designed fluence. Others thought that he was to appeal to the Northern faction, ex- past his prime. The remoteness of pressing interest in using the exist- Copenhagen and the difficulty of the ing Copenhagen center and Britain’s Danish language were also a deterrent. accelerators, and the remaining To sidestep the challenge of going points designed to appeal to Franco- straight for the world’s largest Italian sentiment, covering the

BEAMLINE5 An early CERN Council meeting in 1953. construction of two new machines longer appropriate. However nobody Left to right, Jean Bannier representing and the establishment of a “Euro- could think of a better acronym, es- The Netherlands, and Pierre Auger and pean Council for Nuclear Research” pecially when it had to have multi- Jean Mussard of UNESCO. (Courtesy —in French “Conseil Européen pour lingual appeal, and CERN has stuck CERN) la Recherche Nucléaire.” The ever since. With the four groups dis- acronym CERN was born. persed and Amaldi still in Rome, the The meeting was continued in organization advanced only slowly. February 1952 in Geneva, where the A major international physics provisional CERN Council was asked meeting at Copenhagen in June 1952 to prepare plans for a laboratory. The heard that the ﬁrst beams had been proposal was immediately accepted produced by the new Cosmotron. A by Germany, the Netherlands and CERN Council meeting immediately Yugoslavia, and accepted subject to advocated that Dahl’s group aim for ratification by Belgium, Denmark, a scaled-up Cosmotron to operate in France, Greece, Italy, Norway, Swe- the energy range 10–20 G e V. den, and Switzerland. Denmark of- To make their scaled-up version fered the new Council the use of the of the Cosmotron, the group need- premises at the Institute of Theo- ed to go to Brookhaven and inspect retical Physics of the University of the new machine. That August, Dahl Copenhagen. While this meeting was and Goward made the trip. Also pass- a major step forward, the enigmatic ing through was accelerator pioneer British were not even present. Rolf Wideröe, then working on Emphasis switched from negoti- betatrons. To receive their European ation to organization and planning. visitors, M. Stanley Livingston had With the new organization open for organized a think tank. The Cos- business, the word “Council” was no motron’s C-shaped magnets all faced

6 SPRING 1998 outwards, making it easy for nega- prospect of at least 20, and possibly tively charged particles to be ex- 30 GeV, and save money. The only tracted, but not positive ones. “Why problem was that nobody had built not have the magnets alternately fac- one yet. Although a gamble, taking ing inward and outward?” suggested this unexplored strong-focusing route Livingston. Ernest Courant, Hartland turned out to be one of the most im- Snyder, and John Blewett seized on portant decisions in CERN’s history. the suggestion and quickly realized In Britain, the strong-focusing pro- that this increased the focusing posal gave a new appeal to the Euro- power of the magnets. The new sug- pean project. The traditional national gestion, variously called “strong fo- approach and the more ambitious in- cusing” or “alternating gradient,” ternational venture became com- might allow the proton beam to be plementary. However before Britain squeezed into a pipe a few centime- could be persuaded to join CERN, key ters across, instead of the 20×60 cen- figures had to be convinced, includ- timeters of the Cosmotron beam ing the formidable Lord Cherwell, pipe. The relative cost of the sur- Winston Churchill’s staunch friend rounding magnet, the most expen- and scientific advisor. sive single item in synchrotron con- In December 1952 Edoardo struction, would be greatly reduced. Amaldi was given a frosty reception The European visitors arrived at by Cherwell in London. Within min- Brookhaven prepared to learn how to utes, Cherwell told Amaldi in no un- make a replica of the Cosmotron and certain terms that he was skeptical discovered instead that the design of the CERN idea. Undeterred, had suddenly become outdated. This Amaldi wanted to meet some of the Fate led British engineer John Adams to 1952 visit set the tone for the young Britons who might be inter- become head of CERN’s proton relationship between the new ested in joining Dahl’s group. Dele- synchrotron project in 1954 at the age of European generation of physicists and gated to drive Amaldi from London 34. Under his inspired leadership, CERN their American counterparts. Based to Harwell was John Adams, a young was to fulfill the dreams of its founding on mutual respect and colored by a engineer who had moved to syn- fathers. (Courtesy CERN) healthy spirit of competition, this re- chrotron development after wartime lationship was to work to their mu- radar work. At Harwell, Amaldi met tual advantage. Untempered, com- others who were working on both the petition can lead to jealousy and CERN machine design and a major secrecy, but in particle physics this new British machine. has rarely occurred. Although each With the national machine com- side has striven to push its own pet mitted to the old weak-focusing de- projects, collaboration and assistance sign, Adams and colleagues had been have always been available, and the taking a close look at strong focus- community as a whole welcomes and ing, and discovered that the initial admires breakthroughs and develop- idea was optimistic. Small errors in ments, wherever they may be made. the magnets—tiny misalignments Dahl was adamant that the new and field variations—would be nat- strong-focusing technique had to be urally amplified and might cause the used for the CERN machine they beam to blow up. To allow for this were planning. It would open up the possibility, the aperture of the strong

BEAMLINE7 focusing machines would have to be on both cheeks. The laconic Adams larger than the Brookhaven physi- phoned Alec Merrison, who later re- cists had initially suggested. To called, “He did not tell me in highly accommodate a larger tube, the en- excited tones. He said ‘Remember veloping magnet had to be much those scintillation counters you and larger too, and the design energy of Fidecaro put in the ring? Will they the CERN machine was compro- detect 20 GeV protons?’ I paused long mised to 25 G e V. enough to grab a bottle of whisky and In parallel with these technical Professor Fidecaro, in that order, and advances, the British suddenly came along to celebrate.” switched from aloofness and for- The following day, at a special mally joined CERN, which finally de- news meeting for CERN staff, Adams cided on Geneva as the site for the showed a vodka bottle he had been new laboratory. On the map, the can- given several months earlier on a trip ton of Geneva appears as a curious to Russia with strict instructions that appendage at the extreme west of it should be drunk when the CERN Switzerland. Almost totally sur- synchrotron surpassed Dubna’s en- rounded by France, it is joined to the ergy. The bottle was now empty. rest of Switzerland by an umbilical But Dubna’s vodka bottle was not cord a few kilometers across. Begin- the only unfilled thing at CERN. Also ning with the Red Cross in 1863, the very empty were the experimental city of Geneva has become the home halls around the new synchrotron. In of many international organizations. the rush to build the new machine, An advance party of the proton On November 24, 1959, CERN’s proton few people had paid attention to the synchrotron group arriving in Geneva synchrotron accelerated protons to instrumentation needed to carry out was joined by John and Hildred 25 GeV and briefly became the world’s experiments. At Brookhaven, the highest energy accelerator. Here a Blewett from Brookhaven. After be- jubilant Gilberto Bernardini from Italy new Alternating Gradient Synchro- stowing crucial insights, Dahl pre- embraces John Adams. tron (AGS), the twin of the new CERN ferred to remain in Bergen, first ap- machine, did not accelerate a beam pointing Goward as his on-site Dubna Synchrophasotron attaining until six months later. But this delay supervisor, and finally resigning from 10 GeV, and even by Britain’s 1 GeV was more than compensated by the the new project. Just a few months synchrotron at Birmingham. Eyes enthusiasm and ingenuity that went later, in March 1954 and only 33 years were focused on the race between the into planning experiments. U.S. old, Goward died of a brain tumor. At two proton synchrotron teams at physicists had cut their high energy the tender age of 34, Adams became Brookhaven and CERN. accelerator teeth on the Cosmotron leader of CERN’s proton synchrotron On November 4, 1959, CERN’s and the Bevatron. Within a few years project. Fate had provided the new new proton synchrotron unexpect- of its commissioning, the AGS reaped project with its leader. John Adams edly accelerated protons all the way an impressive harvest of important was to be the Moses who would take to 25 GeV, becoming the world’s new physics results. CERN into the Promised Land. highest energy machine, easily out- CERN had risen to the challenge CERN’s first machine, the 600 stripping Dubna’s 10 GeV. The CERN of building the world’s most power- MeV synchrocyclotron, was com- team was jubilant, and emotional ful machine from scratch in just a missioned in 1957 and soon began and dramatic scenes offered a sharp few years, but developing research producing useful physics. However contrast in national stereotypes. infrastructure and fostering experi- it was far outgunned by the Cos- Gilberto Bernardini from Italy jubi- mental prowess was to take some- motron and Bevatron, by the big new lantly kissed a disconcerted Adams what longer.

8 SPRING 1998 Searching for Neutrino Oscillations by MAURY GOODMAN

Experiments of the past forty years have revealed three families of the ghostly particles called neutrinos. Continuing studies hint that a neutrino of one family might sometimes change into a neutrino of a different family, by a mechanism known as neutrino oscillation. The author describes why understanding this phenomenon might be critical to the question of whether neutrinos have mass.

HYSICISTSFROM AROUND the world are engaged in a wide variety of experiments to determine whether neutrinos have mass. This possibility has intrigued physicists and cosmologistsP for two decades, ever since neutrinos emerged as a leading candidate for the dark matter thought to inhabit the Universe. A comprehensive new experiment is being built in Illinois and Minnesota to study neutrinos from an intense new Fermilab beam impinging on a detector 500 miles away. It is one of the most ambitious of a new round of experiments being planned and proposed to search for neutrino oscillations, a process in which neutrinos can transform from one kind into another—if they have mass. A positive result could have implications for the density of the Universe, as well as for the generation of energy by the Sun. Often, given a well-deﬁned physics problem, one or two well-designed experiments can answer the question one way or the other. But this is not the case for neutrino mass, because there are three different kinds of neutrinos and a wide range of possible mass scales. This situation has led physicists to at- tempt a large number of experiments that are quite different from each other. In this article, I relate why so many physicists are excited by neutrino- oscillation experiments. First, I describe the properties of neutrinos themselves. Then I cover some of the experimental hints supporting neutrino oscillations. Finally, I close with a description of the Fermilab-to-Soudan, Minnesota, long-baseline neutrino project, an ambitious program to search for changes in the properties of a neutrino beam as it speeds silently beneath the farms and prairies of the American Midwest.

BEAMLINE9 Melvin Schwartz in front of the Brookhaven detector that showed experimenters in 1962 that the muon had its own neutrino, different from the electron neutrino. Schwartz, Leon Lederman, and Jack Steinberger won the Nobel Prize in 1987 for this discovery. (Courtesy Brookhaven National Laboratory)

HERE ARE THREE source of copious neutrinos, but I am “flavors” of neutrinos, the not aware of any experiment that has electron neutrino ν , the detected them.) Neutrinos are either T e massless or far lighter than the muon neutrino νµ, and the tau neu- quarks and other leptons. This dif- trino ντ. Each is closely related to the corresponding lepton: the electron, ference might be related to the fact muon, and tau lepton. These six lep- that neutrinos have no electric tons together with six quarks con- charge, while the quarks and other stitute the fundamental “matter” leptons do have charge. The question particles of the Standard Model of of mass remains one of the big mys- high energy physics. teries remaining in particle physics. The three neutrinos interact very There is no clear prediction relat- weakly with ordinary matter. Physi- ing the masses of the nine charged cists originally thought that the great fermions, and none for whether the weakness of the interaction would neutrino masses are zero or just very make them impossible to detect, but small. neutrinos have been seen coming However, most physicists expect from accelerators, from nuclear re- that if neutrinos do have mass, even actors, from cosmic-ray interactions a tiny amount, the phenomenon of in the atmosphere, from the sun, and neutrino oscillations should exist from Supernova 1987A. (Nuclear (see the box on the opposite page). weapon explosions are also the These transformations are closely related to the quantum-mechanical phenomenon of mixing. If neutrinos oscillate, they can be produced in one

flavor, such as νµ, and be detected as another flavor, such as ντ, some distance away. When Pauli predicted the existence of the neutrino in 1930, he did not suppose there would be more than one kind. He was only trying to explain the wide distribution of electron energies observed in nuclear beta decay. The idea that neutrinos come in different ﬂavors became accepted in 1962, when an experiment at Brookhaven National Laboratory

I s I n directed neutrinos from pion decay I o ti ra at a target and found that almost all I e r I n e e tt of the events had a muon, and not an G a e M I re f electron, emerging from the point of h o T the neutrino interaction. This result led to the idea that each lepton flavor (e, µ, τ) has a conserved quantity— something that doesn’t change in an

10 SPRING 1998 Probability of Neutrino Oscillations

IN ORDERTOMEASURE neutrino oscillations, the experimenter wants the probability that one neutrino transforms into another to be as large as possible. This probability is given by

P = sin2(2θ )sin2(1.27∆m2 L/E ), interaction—associated with it. The two factors affecting neutrino ν1→ ν2 12 12 ν When the pion decays, it almost al- oscillations (see adjacent box) that 2 ways becomes a muon and a neutri- are under the control of the experi- where sin (2θ12) is the mixing angle, ∆m2 = m2 − m2 is the difference in no and hardly ever an electron and menter are the neutrino energy Eν 12 1 2 a neutrino. The Brookhaven National and the distance L between their mass squares of the two neutrinos, L Laboratory result could be explained source and the detector. These ap- is the distance (in km) from the + + neutrino production point to the ex- if the π decays into a µ and a νµ; pear in the ratio L/Eν, so an experi- when they interact with the target ment designer needs a large distance periment, and Eν is the neutrino ener- 2 nuclei, the ν ’s generate muons, not and low energies in order to measure gy in GeV. If either sin (2θ) = 0 or µ 2 electrons. small values of the mass difference ∆m = 0, the phenomenon of neutrino When the third lepton, the tau, between two neutrino types. This re- oscillations does not exist. If all three 2 was discovered at the Stanford Lin- quirement must be balanced against neutrinos are massless, ∆m = 0. ear Accelerator Center in 1975, it was the fact that large distance and low As a result of the above equation, natural to conjure up a third neutri- energy both make it more difficult the neutrino “oscillates” with a strength sin2(2θ) and an “oscillation no, the ντ, to account for missing en- to detect a large number of neutrino ergy in tau decays. In the 1980s physi- events. length” ______πEν cists discovered and began producing Let’s go back to the Brookhaven Losc = 1.27∆m2 copious numbers of Z bosons; this experiment that discovered the particle served as a neutrino counter muon neutrino. If the mixing The oscillation probability varies as 2 because its decay rate is proportion- strength and mass difference had sin (πL/Losc). It is the sinusoidal na- al to the number of fundamental par- both been large enough, that exper- ture which gives the name to ticles with less than half its mass. iment would not have been able to “neutrino oscillations.”

Measurements of this rate at CERN discover the νµ. It would have seen and SLAC confirmed that there are both electrons and muons coming only three neutrino-like particles in from the point of the neutrino in- the elementary particle zoo—a result teractions! We can use the success of that had been predicted by cosmolo- that experiment to place limits on gists. So far, there has not been any the combination of the two parame- convincing evidence that the ντ in- ters. We usually do this by making a teracts with nuclei to make taus in graph in the parameter space called a manner equivalent to the other two the “∆m 2 − sin2 (2θ) plane,” these be- neutrinos. But a current Fermilab ex- ing two parameters that specify the periment is expected to ﬁnd these ντ mixing strength and mass difference interactions. (see the box on the next page). An

BEAM LINE 11 Relevant Neutrino Parameter Space

experiment that is consistent with Simply put, five solar-neutrino 3 10 small or no neutrino oscillations cor- experiments have measured a responds to a curve in that plane that signiﬁcantly smaller number of neu- Missing Matter? excludes the values of mixing trino interactions than expected, strength and mass difference above based on the measured heat output and to the right of the curve. of the Sun and nuclear physics mod- 100 LSND Since the early 1960s, neutrino ex- els of both the Sun and the detectors. periments at Brookhaven, Fermilab, Each experiment observed fewer neu- ) 2

V CERN, and the Institute for High En- trinos than expected, but the actual e ( Atmospheric

2 ergy Physics at Serpukhov, Russia, deﬁcit each measures depends on the Ratio m –3 ∆ 10 have grown from tens to thousands detecting medium and energy thresh- , e

c to millions of neutrino events. None old. While it is not possible to explain

n Up/Down e

r of these experiments has witnessed the data with alternate models of the e f f i evidence for νµ → νe or νµ → ντ os- Sun, one can account for all the data D

s MSW cillations. And at the same time, ex- within the framework of neutrino s a 10–6

M periments at nuclear reactors have oscillations.

found no evidence for νe oscillations As discussed in the box on in detectors situated up to a kilo- page 11, the length scale of an ex- meter from the reactor. The pub- periment provides a possible oscil- lished limits have steadily crept to lation length. There are two possible –9 10 lower values of the neutrino mix- scales for solar neutrinos: the dis- Vacuum ing strength and mass difference. tance from the Sun to the Earth and the radius of the Sun. Each length 10–5 10–4 10–3 10–2 10–1 1 UT THE STORY by no scale leads to a separate neutrino- Mixing Strength, sin2(2θ) means ends there. While ex- oscillation solution for the solar neu- Bperiments at reactors and high trino deficit. One (labeled “vacuum” energy accelerators have found no in the illustration on the left) arises This graph shows the regions of neutrino mass 2 2 evidence for them, four hints have from a straightforward solution of (∆m ) and mixing strength [sin (2θ)] which are emerged suggesting the real possi- the relationship between neutrino suggested and ruled out by present data. The bility of neutrino oscillations and mass and oscillations (see the box on shaded regions are ruled out above and to the hence mass. These are the solar neu- the left). The other solutions (labeled right of the curves labeled νµ → νe and νµ → ντ. trino deficit, the atmospheric neutri- “MSW” after Stanislav Mikheyev, The hatched areas are suggested regions of pa- no deficit, the Liquid Scintillator Neu- Alexei Smirnov, and Lincoln Wolfen- rameter space from the LSND, atmospheric, and trino Detector (LSND) experiment at stein, who formulated the relevant solar neutrino experiments. The band labeled Los Alamos National Laboratory, and theory) obey more complicated equa- “Missing Matter” is where one might expect to the missing matter problem. These tions that take into account the huge find neutrino oscillations if neutrinos contribute hints suggest the existence of neutri- density and density gradients of mat- significantly to the Dark Matter problem. New no oscillations in regions of the ter in the Sun, and how they can af- long-baseline experiments will explore the re- parameter space that have not been fect neutrinos emerging from its core. gion of parameter space suggested by the at- completely ruled out by accelerator Both of these solutions involve os- mospheric ratio and up/down results. experiments. cillations of electron neutrinos into The solar-neutrino deficit has other kinds. been around for thirty years. (See The atmospheric neutrino deficit “What Have We Learned About Solar takes us underground to experiments Neutrinos” by John Bahcall in the that were originally built for another Fall 1994 issue of the Beam Line.) purpose—to search for proton decay.

12 SPRING 1998 These massive detectors, which weigh from one to fifty thousand tons, haven’t discovered proton decay, but they do observe about a hundred interactions of atmospheric neutrinos per year for every thousand tons of detector mass. These neutrinos are created near the top of the atmosphere when cosmic-ray protons initiate a particle cascade, making one or more charged pions, each of which decays into a muon and a

νµ. The muon subsequently decays into an electron, a νµ, and a νe. Thus, the ratio of νµ flux to the νe flux observed in an underground detector should be about two. This is quite a strong prediction, regardless of cosmic-ray rates and the subtleties of calculating the number of parti- would be between 25 km and The LSND detector is designed to search cles produced in the cosmic-ray cas- 12,000 km. There is strong evidence for the presence of electron anti- cades. Underground detectors seem from the SuperKamiokande experi- neutrinos with great sensitivity. Over to be measuring the expected num- ment this is the case. This “up/down 1200 photomultiplier tubes line the inner surface of the oil tank, shown above with ber of electron neutrinos, but only asymmetry” observed seems to favor 2 −4 −2 LSND physicist Richard Bolton of Los sixty percent of the expected muon a value of ∆m between 10 and 10 Alamos. (Courtesy Los Alamos National 2 neutrinos. This νµ deficit could be ex- eV (region labeled “Up/Down” in Laboratory) plained by νµ → ντ oscillations, with the illustration). the ντ too low in energy to produce The LSND experiment at Los a tau lepton by interacting with a nu- Alamos, unlike the solar and atmos- cleus. This deficit seems to indicate pheric neutrino experiments, was ex- a value of ∆m2 betyween 10−3 and plicitly built to look for neutrino os- 1 eV2 (see region labeled “Atmos- cillations. Operating near the target pheric Ratio” in the illustration on of the LAMPF accelerator, it uses a page 12). very intense π+ beam. The pions stop + The distance that atmospheric in the target, decay into a µ and a νµ, + + neutrinos travel before hitting a de- and the µ decays in to an e , a νµ, and tector varies from 25 kilometers for a νe. Except for a small and calcula- those coming from overhead to ble background from negative pion – 12,000 kilometers for those coming decays, there are no ν e’s in the beam. from the other side of the Earth. This So if excess numbers of these parti- provides an opportunity to determine cles are detected, they probably arose – – whether there is any difference in the from νµ → ν e’s oscillations. The ex- signal between the up-going and the periment has a 170 ton tank of min- down-going neutrinos. If so, the os- eral oil that can detect the reaction – + cillation length for typical atmos- νep → ne by measuring a 15–30 MeV pheric neutrino energies (500 MeV) positron in coincidence with a signal

BEAM LINE 13 from neutron capture, which yields density should just equal the critical a 2.2 MeV gamma ray. The experi- value, though there are recent ob- ment has reported a signal that could servational data which suggest only be explained by neutrino oscillations twenty percent of that value. Ordi- nary baryons, the stuff that makes with a strength P(νµ→νe) = 0.003. Unlike the atmospheric and solar up stars and stuffed pizza, is only neutrino deficits, the LSND signal has about five percent of the critical val- been observed in only one experi- ue, based on both observational data ment. In fact, other experiments that and the rates of light element pro- are sensitive to these oscillations duction during the Big Bang. Some over similar regions of parameter of this missing matter may well be space have obtained negative results. neutrinos; there are hundreds of The region favored by LSND but not them in every cubic centimeter of ruled out by other experiments the Universe. If they had a mass of (labeled “LSND” in the figure on just 5 eV, neutrinos would outweigh page 12) suggests a value of ∆m2 all the stars and pizza in the around 1 eV2. Universe. The final hint, the missing mat- Experimenters want to confront ter problem, is really suggestive of these hints of neutrino oscillations neutrino mass rather than oscilla- with more definitive measurements. tions. There is a critical density of New solar neutrino experiments are matter in the Universe (see article by determining the size, time depen- Alan Guth in the Fall 1997 issue of dence, and energy dependence of the the Beam Line, Vol. 27, No. 3), about solar neutrino deficit. New short- one hydrogen atom per cubic me- baseline oscillation experiments are ter, above studying mass differences in the re- Select Present/Future Neutrino Experimentsa which the gion of the missing matter problem. Universe is The reported LSND effect will be Neutrino closed and sought by another collaboration at Experiments Energy Location Status will some- the Rutherford Laboratory in Britain, Solar and there is a proposal for a future SuperKamiokande 7 MeV Kamioka, Japan Current day collapse Sudbury (SNO) 4 MeV Ontario, Canada Beginning back into a follow-up detector at Fermilab (see Atmospheric single point. table on the left for a small selection Soudan 2 600 MeV Minnesota Current If the densi- of these experiments). MACRO 5 GeV Gran Sasso, Italy Current ty is at or Reactor below this HILEUNDERGROUND Chooz 5 MeV France Current critical den- experiments will continue Palo Verde 5 MeV Arizona Future to study the atmospheric Short-baseline sity, the Uni- W NOMAD 50 GeV Geneva, Switzerland Current verse is open neutrino deficit, there is another plan LSND 40 MeV Los Alamos Current and will ex- to study possible neutrino oscilla- Long-baseline pand forev- tions in the same region of parame- MINOS 20 GeV Fermilab to Minnesota Future er. There ter space. These are the long-baseline ICARUS 30 GeV Switzerland to Italy Future are strong experiments. While short-baseline K2K 1 GeV Tsukuba to Kamioka, Japan Future theoretical experiments are typically one kilo- a A more complete list of neutrino experiments can be found at arguments meter from the point where the neu- http://www.hep.anl.gov/ndk/hypertext/nu_industry.html that the trinos are produced, long-baseline

14 SPRING 1998 Lake Soudan Superior

Duluth

MN Lake WI Michigan

Madison experiments in the United States and the pion decay results in an average MI Europe will be located 730 km away angle between a neutrino and the IA from the source. And another exper- original beam of about 1/20th of a Fermilab iment in Japan will have 250 km be- degree. tween neutrino production and de- One obvious concern in aiming IL IN tector. All three of these choices are a beam at a target so far away is the matters of convenience—the dis- precision required to hit it, but this MO tances between existing accelerators turns out to be only a minor prob- and existing underground facilities. lem. Hitting the target is a similar to As luck would have it, however, all aiming a flashlight at the moon. three projects will substantively ad- Most people could hold the ﬂashlight dress the possibility that the and point accurately enough. The Fermilab 10 km Soudan atmospheric neutrino deﬁcit is due problem comes in seeing the flash- 730 km to neutrino oscillations. light while standing on the moon. As an example of one of the most This could only be accomplished 12 km ambitious new neutrino oscillation with a powerful enough light. The Map showing long-baseline neutrino projects, I will now focus on the long-baseline neutrino problem is experiment planned from Fermilab in Fermilab-to-Soudan long-baseline similar. The neutrino beam spreads Illinois to Soudan in Minnesota. project (see map on the right). There out as it recedes from Fermilab, los- are three elements to the project: the ing its intensity. And, neutrinos are neutrino beam, a near detector at Fer- very weakly interacting, so one needs milab, and a far detector at the a very massive target in order to de- Soudan underground physics labora- tect just a few of them. In order to tory in northern Minnesota. study such long oscillation lengths, A high-intensity neutrino beam the detectors must be far away from from Fermilab will be made possible the source and can only intercept a by a new high-intensity 120 GeV pro- small fraction of the beam. Thus it The home of the MINOS detector—a ton source called the Main Injector. is necessary to make the beam very cavern in Soudan, Minnesota—being Scheduled for completion in 1999, intense at its origin. installed in the 1980s. this facility is being built to replace The far detector will be located in (Courtesy Fermilab) the present Main Ring as one stage an old iron mine beneath the Soudan of acceleration. The Main Injector State Park in Minnesota. A half mile will also allow a very high-intensity beneath the surface—at the deepest neutrino program, known as NuMI level of a historic iron mine—is the for “Neutrinos at the Main Injector,” existing Soudan 2 fine-grained de- to be run simultaneously with other tector. The mine, which operated for experiments . The intense proton almost one hundred years, is currently beam makes a neutrino beam by hit- being maintained for tourists by the ting a target to make the maximum State of Minnesota Department of number of pions and kaons, which Natural Resources. Scientists plan to are focused forward to give a beam bring ten thousand tons of iron to with as little divergence as possible. build the MINOS detector, which will Then they travel through a one kilo- join the one thousand tons already in meter pipe where many of them de- Soudan 2, to study neutrinos from cay into neutrinos, which continue Fermilab. It’s a bit like taking coal to moving forward. The kinematics of Newcastle.

BEAM LINE 15 The headframe atop a former iron mine at Soudan in northern Minnesota. (Courtesy Fermilab)

The new MINOS (for “Main In- new MINOS detector in 2002. Given jector Neutrino Oscillation Search”) all the other neutrino experiments detector will measure about twelve around the world, I can promise that thousand neutrino interactions per there will be substantial progress in year out of the five trillion that pass understanding neutrinos and the pos- through. It will consist of six hundred sibility of neutrino oscillations dur- layers each of scintillation counters ing the next decade. But I suspect and magnetized iron. If the atmos- that progress will come slowly and pheric neutrino deficit is due toνµ → gradually. The large and growing ντ oscillations, MINOS will observe effort being devoted to neutrino ex- different rates of events, different periments is indicative not only of fractions of events with muons, and the interest in these ghostly particles different energy distributions from but also the difficulty of doing pre- those seen in the near detector. cision work in this field. Even if we A small version of the MINOSde- definitively show that neutrino os- tector at Fermilab is a necessary part cillations exist, there will be a large of the experiment. This detector will set of neutrino mass and mixing be used to understand the beam and parameters to determine. And if neu- calibrate its intensity, by measur- trino oscillations do not turn up, we ing the interactions of neutrinos will need alternative explanations for before they have had any chance to the present observational hints. In oscillate into other species. one form or another, the experimen- Physicists hope to begin taking tal study of neutrino oscillations will data with the existing Soudan de- probably continue for the next tector and the first sections of the twenty years!

16 SPRING 1998 Physics with Charm by JEFFREYA.APPEL

Physicists recognize that the Standard Model conceals as much as it AYBE WE SHOULD CALL IT something different. “The Standard Model” sounds so def- reveals about the ulti- inite, so final. Perhaps another name would M better describe the part-monument, part- mate workings of punching-bag nature of the world’s best theory of how matter is put together at the smallest scale. The Standard Model matter. Might the study is a monument—a monument to the power of theory and experiment to explore and explain the seemingly trackless in- of the charm quark help ner reaches of the matter around us. But it is a punching bag, open the way to the too, the so-far intact target of experimental jabs and thrusts attempting to expose its weaknesses. The punches have physics beyond the included searches for forbidden processes, neutrino mass, and other symmetry violation. Now, in a dizzying mix of Standard Model? metaphor, the Standard Model has become something else as well—a curtain that physicists know is about to go up, re- vealing the true drama on the stage behind it: The Physics Beyond the Standard Model. For we know that the Standard Model conceals as much as it reveals about the ultimate workings of matter. We know that marvelous scenes will un- fold before us, if only we can find which rope to pull to make the curtain rise. Most of the theoretical and experimental energy of the field of particle physics at the end of the twentieth century is concentrated on raising the Standard Model curtain on the drama that will be twenty-first century physics. And most of these efforts are devoted to pulling on two ropes: high-energy searches for the origin of mass and the quest to find matter- antimatter asymmetry in the behavior of mesons containing the bottom quark. But besides these mainstream efforts, might there be another way to raise the curtain? Might we at least lift its corner by using—charm?

BEAM LINE 17 The charm quark has

intrigued particle

physicists as a Since its famous discovery almost “softer,” that is they keep closer to a quarter century ago, the charm the quarks. Charm particles interest quark has intrigued particle physi- the experimenter because they allow cists as a unique particle, the first unique particle, the the identification of well-defined glu- of the heavy quarks—and more. It on interactions and give us a window is the only quark with charge +2/3 into what is going on in the main- that is both unstable (unlike the up first of the heavy stream matter of the Universe. quark) and yet survives long enough In the story of charm, as in the (unlike the top quark) to bind with story of all particle physics, tech- other quarks and form observable quarks—and more. nology is the deus ex machina that particles. Thus the charm quark of- moves the plot forward. Advances in fers a unique way to discover effects accelerator, detector, and computing that may occur only in this “up- technology have let us make the ac- quark” neighborhood of the parti- quaintance of charm, and advances cle world. Such effects might never at fixed-target experiments (where in technology will take us still fur- show up in the down, strange and beams of moving particles hit sta- ther in the study of its character. bottom quarks, with their −1/3 tionary matter, instead of colliding Learning more about charm will not charges. Charm might give us a with beams of particles coming the only help us understand the gluons, longed-for peek beyond the Standard other way) has elucidated the dis- but illuminate the differences be- Model curtain. tribution of the gluons inside garden- tween the quarks and—and!—get to variety hadrons containing up and that physics beyond the You-Know- FASCINATION OF CHARM down quarks, and even within less What. For charm particles may hold ordinary hadrons containing strange clues to why, for example, charm is Until 1974, three kinds of quarks had quarks. (A hadron is a particle made one of only six quarks, and why those appeared in experiments: up, down of quarks held together by gluons.) six come two by two, like creatures and strange. But theorists, reasoning The fusion of a photon with a from Noah’s Ark. that quarks should come in even gluon from a target hadron is the numbers, predicted a fourth kind, dominant process for producing THE DISCRETE CHARM dubbed charm. If it existed, besides charm-anticharm pairs with a pho- OF FERMILAB FIXED-TARGET evening up the quark score, charm ton beam. The fusion of two gluons EXPERIMENTS would explain a puzzle: why do neu- in hadron-hadron interactions is the tral kaons decay only very rarely into dominant process for creating charm The fixed-target run that ended in a pair of muons? Charm did indeed quarks in that environment. Both September 1997 may have seen the materialize, simultaneously on the of these processes depend on the dis- last dedicated charm experiment at east and west coasts of the United tributions of gluons in hadrons. By Fermilab. This moment—the end of States, and it proved to have the prop- carefully studying the characteristics an era of charm—is a good time to erties the theorists had said it would. of charm production, we work back- look at where we have come so far in Since its appearance, the charm ward to the way gluons are distrib- charm research and at where we quark has taught physicists much uted in target neutrons and protons, might be going. about the strong and weak nuclear as well as in beam hadrons, such as Today, precision results on charm forces and how they interact. pions, kaons and protons. Gluon dis- physics come from electron-positron Charm also teaches us about or- tributions in pions and kaons (each collision experiments at Cornell’s dinary matter. Most of the matter comprising a quark and an antiquark CESR and from Fermilab’s fixed- that we see is made of quarks, held held together by gluons) appear to be target experiments. Where Fermilab’s together by gluons, in neutrons and similar. In protons, which are made precision measurements come to the protons. Producing charm particles of three quarks, the gluons are fore, we can credit the large numbers

18 SPRING 1998 of fully reconstructed decays ob- they then examine only those par- – served and the cleanliness (with re- ticles coming from single vertices. K+ π K– spect to background) of the experi- The combination of these steps –18 mental signals. The Fermilab helps to select the precious charm – 0

) D experiment with the most prodigious events from the more copious, un- m π+ m sample of clean, reconstructed charm interesting false candidate events. ( e

decays now has 200,000; but it will Applying selection criteria using ver- t

a –20 n soon relinquish its title to a charm tex separation and particle identiﬁ- i – 0 d D

r π experiment from the last ﬁxed-target cation reduces background much o σZ2 o

C ∆Z run that projects a million or more, faster than signal. The more certain - 12 Z all told. When we consider that we are that a charm decay vertex can- –22 charm appears only once in every 200 didate is separated cleanly from the relevant photon interactions and event’s interaction vertex, the more σZ1 once in every thousand hadron in- certain we can be that we have ob- teractions, and add in the fact that served a real charm decay. –10.4 –10.2 –10.0 experiments typically reconstruct The methods developed for these Y-Coordinate (mm) only about half a percent of these, we fixed-target experiments have not realize that experimenters are look- only bagged many a charm particle, A charm production event from Fermilab ing for one clean decay in about but have influenced the design for experiment E691. The two white areas represent regions from which tracks emerge 100,000 interactions. hadron colliders doing bottom and and are separated from the initial collision The nature of fixed-target experi- top quark research and for asym- point. This indicates that charm particles D0 – ments can lead to clean charm sig- metric B factories where we need to and D0 were produced and decayed in these nals. Most of the charm particles pro- measure the separation between the regions. duced move rapidly in the direction decay sites of the particles contain- of the incident beam. They live long ing bottom quarks. enough (about a picosecond) to move a few millimeters beyond their pro- TECHNOLOGY OF CHARM duction point before they decay. Experimenters can observe this dis- Advances in three areas of tech- tance, but it requires precision mea- nology have produced today’s large, surement of the trajectories of the clean samples of charm in fixed- decay products, uncluttered by a lot target experiments. Silicon micro- of distracting “junk” in the way. strip detectors (SMDs), videotape Depending on how the charm par- storage, and computer farms—all ticle decays, knowing the identity of linked together—have taken charm the decay products leads to the clean- physics to new levels. est signals. In the electron-positron The figure above right shows how machines used so far to study charm, the history of production and decay the charm particles are at rest or of charm particles in one event can moving slowly at production, so they be reconstructed from the trajectories decay on top of the production of the resulting charged particles. point—a much messier situation. In Tracks (the records of particle tra- fixed-target experiments, physicists jectories) emerging from the primary can use the decay topology to select interaction vertex and the two charm only those interactions that could decay vertices (one for the charm and contain charm particles. For those, one for the simultaneously produced

BEAM LINE 19 Silicon Microstrip Detectors

MODERNMICROELECTRONICTECHNIQUES make possible anticharm) appear to emerge from the silicon microstrip detectors that have brought charm physics such a distinct vertices. This is only possible long way. How do SMDs work? When a charged particle traverses a thin if the charm particles live long crystal of pure silicon, it deposits energy that frees electric charges to enough, if they are moving fast migrate. enough, and if the tracking resolu- If an appropriate voltage is applied across the crystal, the migrating tion is sufficiently fine. A charm me- son that decays after one typical life- charges will produce signals on metal electrodes. The signals, suitably time has traveled several millimeters amplified by sensitive electronics off the silicon plate, are digitized and in the direction parallel to the inci- recorded for later analysis. On SMDs, the electrodes are closely spaced dent beam and 150 microns in the transverse direction. SMDs provide resolutions about ten times more precise than these distances. This provides powerful separation be- ~ 1000 tween combinations of tracks that Collecting Strips emerge from charm decay vertices and background. Over the past fifteen years, the 5 cm raw data from fixed-target experiments has gone from a few gigabytes to 50,000 gigabytes. It would have cost a fortune to handle so much data using the old open-reel magnetic tape system. Fortunately, new technology Particles A silicon microstrip in the form of 8 mm videotape came

detector. to the rescue with greater capacity at m a far lower price. However, because

c of the less-than-lightning speed of an 5 individual 8-mm tape-writing device, one fixed-target charm experiment used 42 of the tape drives writing out 50 µm Pitch events in parallel. The data-acquisition architecture supported this parallel tape writing, along with parallel-path m data accumulation from the front- 0 µ 30 end electronics. Massive new data sets also re- strips, typically 25 to 50 microns from center to center, with amplifiers quired greater economy in analysis attached to each strip. The large number of strips allows experimenters to computing. Charm experiment E691 record the passage of manycharged particles through each detector, first used massive parallel-processing reduces the capacitative load on the fronts of the amplifiers, and improves computer farms at Fermilab for this the achievable spatial resolution. The SMD signal collection takes just a purpose. At that time, experimenters used laboratory-designed, single- few billionths of a second, making SMDs useful in the intense, high-rate en- board computers (over a hundred in vironments that characterize more and more particle physics experiments. one system) with commercial CPU chips and home-built control software.

20 SPRING 1998 8 Millimeter Tape Technology

Later, commercial workstations tied that will study CP violation in asym- s r

together with custom software be- metric B factories all used, use or will e m m

came more cost effective. This ap- use these techniques. Charm showed u S n

proach of using large data sets com- the way. o bined with simple early event But now, whither charm physics D selection offers certain advantages, itself? Have the present technologies THE FIRST 8 MM videotapes held the including the ability to do analysis run their course for charm? A look equivalent of thirteen of the old open-reel after detector calibrations are tuned at the likely landscape of future tapes in use before 1990, and current ver- up and sophisticated computer codes physics experiments shows few if sions hold two times that amount. To put are debugged. The analysis can then any long runs of sufficiently ener- it in perspective, a typical weekend of apply final track- and vertex-finding. getic beams to produce great num- data-taking in experiment E769 resulted in This approach works better than the bers of charm particles. Would-be a forklift of open-reel tapes (see photo use of only the cruder information charm investigators will need some above). In the next series of fixed-target available at data-taking time, which sort of new environment to pursue runs, E791 recorded a comparable necessarily throws away some of the their explorations. Two possibilities amount of data in three hours and stored interesting charm events. It also suggest themselves: asymmetric helped that the price of computing electron-positron colliders and the it in a tray of 8 mm tapes (see photo power dropped rapidly in the inter- forward regions of hadron colliders. below). val between the purchase of systems Both remain to be explored, although for on-line and those for off-line use. both offer the promise of opening new realms of charm. CHARM OF THE FUTURE As in the past, we will need new technologies to deepen our knowl- Massive data storage, massively par- edge of charm. But if we are inven- allel computing and silicon micro- tive enough, and alert to new tech- strip detectors have all become part nical opportunities, it is possible that of the standard tool box for modern we may look to charm for its unique high-energy physics experiments. potential to raise the curtain on the The experiments that discovered the opening act of that riveting all-star top quark at Fermilab’s Tevatron col- production, “Physics Beyond the lider, the experiments that study bot- Standard Model,” coming soon to a s tom quark physics in Z decay at theater near you. e c i v r

SLAC and CERN, and experiments e S a i d e M l a u s i V b

Growth of Data Acquisition Parallelism a l i m r

at Fermilab’s Tagged Photon Laboratory e F Number Data Set Number Fermilab physicist Catherine James holds a Events Size Reconstructed tray of 8 mm tapes. Year Experiment (M) (GB) Charm Decays 1980–81 E516 20 70 100 1984–85 E691 100 400 10,000 1987–88 E769 400 1500 4000 1991–92 E791 20,000 50,000 200,000

BEAM LINE 21 THE UNIVERSE AT LARGE

by VIRGINIA TRIMBLE This Was the Year That Was HE PROGRESS of (Astrophysics in 1997) science is not generally Tmuch like that of a kangaroo. Rather, we tend to advance amoeba-like, cautiously extending pseudopods in some directions and retracting them in others. 1997 witnessed at least its share of advances and retreats, with perhaps a leap or two. The following sections are meant to be logically independent and readable (or at least no less readable) in any order.

MICRO- AND MACRO-MARS: WATER, WATER, EVERYWHERE Readers my age may remember when “I don’t think so” was an expression of genuine doubt. Last year’s announcement of possible microfossils in a meteorite that had come to us (or anyhow to Antarctica) from Mars provided an opportunity to try out the X- generation meaning of the phrase. Our curmudgeonly pessimism has been justiﬁed. After several months of rat-like gnawings on the edges of the evidence by other experts, the original proponents have essentially with- drawn the suggestion. Tactfully, they switched from Science to Nature for the recantation.

22 SPRING 1998 Meanwhile, a number of Martians have acquired personal names. But it’s no use calling them, because, like cats and Victor Borge’s children, they don’t come anyhow. In fact, they all seem to be rocks. And while reports from the Sagan Memorial Station indicate that the said rocks have carefully washed their hands for dinner, there doesn’t seem to be anything to eat. Continued analysis of Pathfinder data will probably yield additional information on Martian geology,* but more advanced probes will be needed to dig below the surface and look for possible relics of early pre-biological Mars Pathfinder. The view is not so very different from that or biological evolution. If you happen to have some recorded by the Viking lander a couple of decades ago, but old slides of the Viking lander site lying around, you can the device itself, including the rover, is clearly much more check my impression that the topography of Mars has elaborate. Additional data on additional particular rocks changed less in the last twenty years than that of our makes clear that Mars, like Earth, has experienced a variety of processes, leading to a variety of minerologies and faces. petrologies. (Courtesy Jet Propulsion Laboratory, California Liquid water continues its role as the probable lim- Institute of Technology, and NASA) iting factor for the development of chemically based life. It may, however, not be so very rare. Besides the Earth terrestrial ice crystals and water vapor molecules. It sees and Mars, wet places in the solar system appear to in- H2O emission and absorption features in star forma- clude subsurface regions of two moons of Jupiter, Europa tion regions, in shells around evolved stars, in external and Ganymede. Lots of images are already in from the galaxies, in the planets, and just about anyplace where Galileo mission, which, after staring at Jupiter for a it is cool enough for molecules to remain bound and per- while, has begun contemplating the moons, and will haps clump together. The water features are often so continue to do so into 1998. strong and numerous that they in effect constitute the Gaseous and solid water are all over the place. We noise in investigations of other species that emit and ab- have always suspected this from their prominence in sorb primarily at infrared wavelengths. Just what you comets and other reservoirs of local volatile material, would have expected in retrospect. but the inventorying has not been very easy. The prob- Nevertheless, not all water is created equal, at least lem is terrestrial water—a very good thing in its way, not in its ratio of deuterium to hydrogen. That ratio has but given to smearing its absorption features across any now been measured in three bright comets, Halley, spectrogram you take from Earth’s surface. ISO, the In- Hyakutake, and Hale Bopp. In all three cases, D/H is frared Space Observatory, a mostly-European effort with about twice the ratio in terrestrial ocean water. This good resolution in both wavelength and position on means that water supplies from comet impacts cannot the sky, has finally climbed above even the very highest be the primary source of terrestrial water, unless there is a comet reservoir not yet probed by the observations. *Areology would seem to be the obvious word, but it just The old-fashioned source of volatiles was outgassing hasn’t caught on. of material trapped when the Earth formed.

BEAM LINE 23 40 THE FAT LADY BURSTS

I have been told on equal authority (that is, none) that the pulchritudinous person in question was either Kate 30 Smith rendering “God Bless America” to end a baseball

) game or a Sutherland-like soprano expressing the desire 1 – z to leave Paris shortly before the end of La Traviata (not H 1 –

s at all a bad thing to do, particularly if the performance 2 –

m happens to be in Paris). I would not presume to choose

c 20 g

r between them. But we were told with equal authority e 9 2

– about three years ago* that the gamma-ray bursters were 0 1 (

ν located either in the halo of our own galaxy or in oth- F er galaxies at distances comparable with the size of 10 the observable Universe. This choice is now easy. They are at cosmological distances. GRBs are, tautologically, bursts of gamma rays (meaning anything above 50 keV or so) that come to us at com- 0 4,200 4,600 5,000 pletely unpredictable times from completely random di- ° rections in the sky, at a rate of about one per day (given λ (A) the sensitivity of the detectors now orbiting on the Spectrum of the GRB 970508 in blue light. The features Compton Gamma Ray Observatory). Most last from a marked are absorption lines due to singly ionized iron and tenth of a second to a few hundred seconds, show sub- magnesium in intervening gas clouds. The fact that the lines structure and complex spectra, and dump from 10−8 to are doublets makes them fairly easy to recognize, and similar 10−4 erg/cm2 at the top of the Earth’s atmosphere, with lines are common in the spectra of quasars with redshifts of the faintest ones being commonest. Oh yes. And until one or more. The more redshifted of the two systems in the GRB is at z = 0.83, telling us that the event itself must have February 1997, none of them had ever been caught do- occurred at still larger distance. The visible source has faded ing anything detectable at any other wavelength. enormously since May 1997, and the spectrogram could not CGRO data had additionally confounded expectations now be duplicated. (Reprinted with permission from Nature © by showing that we see the edge of the GRB distribution 1997 Macmillan Magazines Ltd. and the GRB team, Palomar in space, despite seeming to be at the center of it (see Observatory.) box on the next page). Thus the edge was supposed to be This is perhaps as good a place as any to tell you either the edge of an enormous halo of our own galaxy that the animal pictures come from a Dover volume called Animals, whose cover speciﬁcally declares the images to be (not host to any other known sort of object) or an opti- free of copyright restrictions. cal illusion, introduced by the redshifting of the energy of sources far enough away that cosmic expansion is important. In the last year, a suitable satellite, the mostly- European BeppoSAX, began picking up X-ray tails to the

*At a 75th anniversary restaging of the Curtis-Shapley debate, whose proceedings appear in the December 1995 issue of Publications of the Astronomical Society of the Paciﬁc.

24 SPRING 1998 events are and roughly how much energy each must put into gamma rays (1051 ergs or more, unless the pho- COUNTING SOURCES OF RADIATION tons are strongly beamed) has triggered a new round of simulating . Most of the simulees involve at least one neutron star or black hole, or sometimes two in a binary I HAVEN’T SUBJECTED YOU to a calculation for a system. Given the sub-second time scales of many bursts, long time, and this one is just too much fun to miss out. there aren’t really a lot of other possibilities. Suppose static space is littered uniformly with candles of a fixed, standard intrinsic luminosity. Count all the ones PEOPLE AND PLACES you can see down to apparent brightness S. You will get N(S) ~S −3/2, where the 3 is the dimensionality of space, This can only be a “good news/bad news” section. The and the 2 is the inverse square law. Add a second popu- astronomical community lost more members than ever lation with a different intrinsic luminosity. It, too, will contribute a power-law N(S), and, no matter how many before (not surprising; we are, like most of the sciences, classes you add together, N(S) is always proportional to an aging community), but Alan Cousins, a South African S−3/2. Counts of GRBs rise toward faint S, but not as stellar observer (see cover photo), set what appears to be steeply as S −3/2. Thus either distant events are rare (we a new world record for longevity in publication, with are in the center of a finite distribution, and Copernicus is papers in 1924 and 1998. unhappy), or the bursts are being redshifted so that the S The SAGE detector for solar neutrinos managed to re- we see is the Newtonian one cut down by a factor (1+z)2, sist for another year having its gallium resold for com- and distant events are lost from the sample equally in all mercial purposes, but the HEGRA detector for extensive directions. air showers partially burned soon after it had confirmed the second extragalactic source of TeV gamma rays, a quasar previously seen from the Whipple Observatory. bursts fast enough and with good enough angular pre- SAGE also survived a calibration run with a radioac- cision to swing other telescopes toward their locations tive source, showing that, if neutrinos get to it in their before all the fireworks were over. Three events, in Feb- electron-flavored garments, it sees them, while ruary, May, and December, have been recorded— SuperKamiokande came on line in Japan and confirmed briefly!—in visible light, and the May one as a radio that, for the highest energy neutrinos expected from the source. They are not all the same. The February loca- sun, only about half the predicted flux is arriving in due tion has an underlying steady, fuzzy visible object that order and technically correct. is probably a distant faint galaxy. Most important, the Some important satellite launches failed, including May event (see figure on page 24) had sharp absorption what was to have been the High Energy Transient Ex- lines in its spectrum that could be identified as being plorer (HETE) , left looking up the rear end of its launch produced by Mg II and Fe II in clouds of gas between it partner after they failed to separate. Others did just what and us. The lines had a redshift of0.83, meaning that the they should, including the Japanese X-ray mission that source had to be further away than that (but not beyond carries both the acronym HALCA and the name Haruka a redshift of about 2). And no, I am not going to tell (a type of bird).* you how much that is in light years because it depends *Yes, they really are nearly identical in pronunciation. The VERY much on your favorite values of the Hubble con- unvoiced vowel “u” may be familiar from “sukiyaki.” As stant and other cosmological fudge factors. for the seemingly-double-valued consonant, about all I can suggest is that you try saying “rocket flights” and Theorists had, of course, modeled most of the pos- “locket frights” quickly, in alternation, until they start sibilities long before February. But knowing where the to sound the same.

BEAM LINE 25 The literature contemplated itself, with conclusions Accretion disks around proto-stars, white dwarfs, neu- that Einstein (a) really did write down “his” equations tron stars, black holes, and prominent theorists appear before David Hilbert and (b) had tackled calculations in every year’s highlights of astrophysics because they of gravitational lensing as early as 1912, but thought the are part of the standard models of quasars,X-ray sources, nova results hardly worth publishing. A couple of colleagues explosions, bipolar molecular outflows, and all sorts of other introduced into the literature the words “isopedic” and (real, observed) phenomena. The first, persuasive data-based “enstrophy.” Yes, of course you could look them up, but proposal came in 1956 from John Crawford and Robert Kraft, isn’t it more fun to guess “having the same feet” and “a who concluded that nourishing thermodynamic quantity?” And the grem- AEAqr (a nova-like lins of typography and copy editing brought us many variable) must be a treats, of which my favorite is the acknowledgment “to binary system with the TIRGO tune allocation committee for the award of an accretion disk of telescope time. At most observatories, TAC is an acronym material from its for “time allocation committee,” but having once shared normal star swirling nights at Mt. Palomar with a colleague who kept awake around the white by singing music of the old Polish church, I can see that dwarf. The latest the other might sometimes also be needed. If only they word is that AEAqr had allocated me “99 bottles of beer on the wall” (those is actually a net ex- were long winter nights), or even La Traviata. cretor. Accretion of course persists for DON’T GIVE UP YOUR DAY JOB most of the other ad- One of the dwarf spheroidal galaxies that just barely belongs gravitationally vertised objects, pre- Non-Hollywoodites may need reminding that, along to our Local Group (or just misses). ferentially this past with “don’t call us, we’ll call you,” these are words spo- Perhaps the most remarkable point is year in the form of ken to an aspiring actor or musician who may not be that anybody can succeed in finding “advection domi- quite ready for the big time. Here I have in mind cases and recognizing little smears like nated accretion,” where somebody went out on a limb (often a very sturdy- Antlia as galaxies in the first place. meaning that it car- looking, oak one) only to have some portion of it sawed (Courtesy Mike Irwin, Royal ries a good deal of Greenwich Observatory, UK) off from under him. Additional examples include the heat and kinetic en- Martian micro-fossils and Type I supernovae as distance ergy with it down the tubes. The concept, then unnamed, indicators mentioned in other sections. can be traced in the literature at least back to 1977. Our own Local Group of galaxies consists of two big Planetary companions to nearby stars, mostly with ones (us and the Andromeda Nebula) and a whole bunch masses like Jupiter but shorter orbit periods, glimmered of little ones, whose number has seemed to increase at out of press releases from the October 1995 announce- about one per year of late. But the 1992 and 1996 “dis- ment of 51 Peg onward. Perversely, much of the com- coveries,” small, faint galaxies a million or two light munity embraced with enthusiasm a late 1996 sugges- years away in the directions of the constellations Tu- tion that no such planets were orbiting. Instead, said cana and Antlia were actually catalogued back in 1977. David Gray of Western Ontario, we were merely seeing New at least as confirmed LG members? Perhaps not winds and waves in the atmospheres of (unaccompanied) even that. Antlia is probably further away than the stars. These would perturb profiles of stellar absorption million-parsec limit of gravitational binding to the Local lines and mimic the effects of small, orbiting compan- Group. ions. A pair of January 1998 papers, from him and from an

26 SPRING 1998 independent group at University of Texas, will have shift (that is, its distance) and its angular motion across given us back our planets by the time you read this. the plane of the sky (that is, two-dimensional velocity, Yes, we live in a screwy Universe, but is it also chi- if you know the distance). The community had been ral? Theorists have predicted and observers not seen for counting on Hipparcos for quite some time to improve decades any indication that space-time is rotating or our knowledge of the brightnesses and kinematics of a skewed on cosmic scales. This spring, aPhysical Review number of kinds of stars that are either interesting for Letter, from theorists in Kansas, announced net rotation, their own sake or based on details of polarization of radio emission from important in sources at redshifts exceeding 0.3. The announcers had, climbing up the however, relied on data that they had not collected them- “distance ladder” selves (always risky) and that were mostly well over a to far away galax- decade old, non-uniformly collected around the sky, and ies and the Uni- of sufficiently poor angular resolution that bits of the verse. sources with different intrinsic polarization were The splashiest smeared together. Owners and operators of more recent, press release be- more suitable data sets rapidly ﬁred back upper limits longed to a prob- to the twisting of space considerably below the positive lem that has been value claimed in the Letter. around for half a In fact (pause for the modest cough of a minor poet) century, “the age the previous year had seen a published upper limit slight- of the Universe.” ly below the PRL number, which, naturally, went uncit- The time scale of ed. Probably only two people in the world noticed this, the Universe im- Maurice Goldhaber and yours truly, the authors of the plied by its mea- limit paper! sured expansion Some things really do have net chirality, including, un- rate (the Hubble expectedly, some of the amino acids in the Murchison constant) has spo- meteorite. Contamination by the sticky ﬁngers of me- radically seemed teoriticists, you will say? Apparently not, for the5–10 per- to be rather less The Hipparcos satellite. Its launch was cent excess of L-enantiomers occurs both in some amino than the ages of almost a failure (owing to maloperation acids that terrestrial creatures don’t use and in associa- the oldest stars we of nearly the only part on it of U.S. manu- tion with non-terrestrial values of nitrogen isotope ratios. see. And this par- facture), leading to an elliptical rather ticular example of than circular orbit; but close to100 per- HIP, HIP, HIPPARCOS SAVES THE UNIVERSE, “old wine in less cent of the expected data were obtained OR, TWO AND A HALF CHEERS FOR OUR SIDE old bottles” has over several years. Hipparcos established its own coordinate system on the never been one we sky by swinging back and forth from star Hipparcos is an acronym (origins lost in the mists of were happy with. to star to (more than 105 stars), and this time), a slight misspelling of the name of a Greek com- Fifty years ago, it needs to be tied to other systems of piler of star catalogues, Hipparchus, and a (mostly led to the inven- earth-centered coordinates. (Courtesy European) satellite that scanned the skies for several tion of the Steady European Space Agency) years, establishing a coordinate system made up of pre- State model of the Universe. More recently, the faint cise positions for more than 100,000 stars. In the process, at heart had been driven to invoking Einstein’s notori- it also determined for each star its annual parallactic ous cosmological constant or even to doubting the

BEAM LINE 27 correctness of the basic picture of a universe expand- gamma-ray burster was one of these. Some other 1997 ing out of a hot dense state (a.k.a. Big Bang). examples follow: Two solutions are possible—make the Universe older • Radio pulsations from Geminga. This gamma-ray (that is the Hubble constant smaller, by deciding that source in Gemini was long a mystery because it seemed the galaxies you used to calibrate it are further away (like the bursters) to have no counterpart at any other than you had thought) or make the stars younger (also wavelength. Sensitive X-ray and optical detectors reme- achieved by shoving them away from you, so that they died this several years ago and also showed that it was are brighter and use up their fuel faster). One way of look- a rotation-powered neutron star (“true” pulsar), with a ing at stars measured by Hipparcos seemed to do exactly period of 0.237 seconds. But all proper pulsars should these two things. Parallaxes of a set of stars called beep radio signals at us (that is, after all, how they were Cepheid variables (a traditional distance calibrator) were discovered in 1967), and Geminga seemed to be a failure. a bit smaller than expected, nominally both increas- Three groups, all centered in Russia, have finally found ing the time l/H and decreasing stellar ages. Unfortu- the radio pulses, more or less simultaneously (and each nately, equally valid ways of looking at the data, using has published the discovery at least twice, once in the young clusters of stars to calibrate the Cepheids and sta- Russian literature and once elsewhere). The problem was tistics of stellar motions to get brightnesses of the old that the source is simply very faint and steep-spectrumed, ones, have precisely the opposite effect. 1/H gets small- so that the best bet for catching it was at lower radio fre- er, and the stars get older. Some assembly is apparently quencies than are usually used for the purpose. still required. • A spiral wave in the accretion disk of a cataclysmic Any astronomer who had planned ahead by asking in variable. Theorists have been predicting these for some 1982 was entitled to some slice of Hipparcos data. My pro- time, because a spiral or m = 2 perturbation is the nat- posal (with George Herbig, then of Lick Observatory) was ural consequence of having a large point mass off to inspiringly titled “parallaxes and proper motions of pro- the side of a disk (hence the particularly spectacular arms totypes of astrophysically interesting classes of stars,” but in spiral galaxies with close companions like M51). IP you must read the archival literature to find out what Peg is the first cataclysmic where the wave has been spot- we learned (other than that fifteen years is a long time ted, via a clever mapping technique that uses changes in even to the middle aged). The hundreds of astronomers shapes of spectral lines through the orbit period of the who were also 1982 proposers have thus far probably pro- system to locate bits of gas with different densities and duced an average of one paper each, and many more are velocities. expected, clarifying the evolutionary status of Barium II Reconstructed distribution of density stars and other problems you never even knew you had. in the disk surrounding the white dwarf in IP Peg. The central star is blacked WE KNEW YOU HAD IT IN YOU out and contrast somewhat enhanced. (Courtesy D. Steeghs, E. Harlaftis, K. Some discoveries were bound to be made eventually and Horne, Astronomy Group, Univ. St. fall largely by luck to the first person who happens to Andrews, UK) turn the right sort of telescope or equation in the right direction, much like the case in Moby Dick, where Cap- • Central black holes in galaxies. These have become tain Ahab nails a gold doubloon to the mast for the so common they no longer make the Ne w York Times. first person to spot the whale, or, said Richard Armour, Whoever happens to get the first HST images and spec- the first person up on deck after dark with a claw-headed tra of the center of a nearby galaxy is just about guar- ham mer. Finding the optical counterpart of the May 8th anteed to find a black hole somewhere in the range

28 SPRING 1998 106–109 solar masses. In a few cases, where more than enough to stop the expansion of the Universe in the (very one technique has been brought to bear on a particular remote) future, while a number of other methods that galaxy, the results for BH mass are in clear disagreement. looked at masses of clusters of galaxies or their distri- You can argue about whether this constitutes progress, bution in space were finding perhaps 30 percent of that but it does at least guarantee employment for future gen- critical density. But the result came from a very small erations of astronomers. Our Milky Way is part of the number of distant Ia’s. With a larger sample of abou t fif- great majority with a central black hole of 2–3×106 so- teen events, the best fit is a smaller deceleration para- lar masses as the only possible explanation of the details m eter, or a density of 30–40 percent of the critical value, of the motions of stars and gas near its center. agreeing with the other methods. • Broad absorption lines in a radio quasar. Proper • A new class of pulsating variable star. This is a beau- quasars are strong sources of radio emission (the oth- tiful case of theory and observation rising to meet each ers are QSOs or quasi-stellar-objects, unless you are feel- other. Even as a group of French Canadian modelers of ing lazy). BALs or broad absorption lines are saturated stars were predicting that a particular kind should be un- ones with redshifts just a smidge less than the redshift stable to pulsations with periods near one hour, a group of the emission lines. They are attributed to gas being of South African observers of stars were serendipitously blown out of or around the QSO nucleus. Until 1997, the discovering a handful of stars whose brightnesses vary radio-loud and BAL sets were disjoint. And it took a sur- with several modes near one hour, in just the part of vey of something like 105 radio sources to find the first, luminosity-temperature space where they were predicted. faint overlap (this is a pun; the survey is called FIRST). So far, they are merely called pulsating sdB stars (where The source’s telephone number is 1551+3517 (actually its “sd” says they are faint, compact, and evolved, and “B” location in the sky) in case you want to call. says they have surface temperatures of 15–20,000 K), and • The most distant galaxy. There is a new one of these my efforts to coin the term SubDued Bumpers has met practically every year, and quite often it is really a QSO. with resounding failure. The 1997 queen for a day, at a redshift of 4.92, is an ordinary galaxy. It is visible at that distance partly because EVERY DOG IS it is forming stars like mad (and new, massive stars are ENTITLED TO the brightest kind) and partly because it is gravitation- ONE BITE ally lensed and amplified by a foreground cluster at z = 0.23. This is my attitude, as • The most distant supernova. Here too records are one of the adjectival editors falling constantly, and the current one at z = 0.9 or there- of a fairly prestigious jour- The fact that the parts of a pic- abouts is not very important for its own sake. Distant nal, toward authors bear- ture can be made to fit together galaxies contain heavy elements, so we know they must ing papers about which does not guarantee this is the already have had supernova explosions. But the mem- one is tempted to quote way Nature actually does things. bers of one class of supernova (called Type Ia) all seem Pauli, “It isn’t even wrong.” Because there are lots of to have the same intrinsic luminosity and so can be used journals, many of these ideas turn up as “new” year to measure very large distances and get global values for after year. Still, isn’t it a sort of relief from the serious- the cosmic expansion rate (H) and its change with time, ness of transverse optical phonons to contemplate. the deceleration parameter, q0. These, in turn, are al- a. A model of star formation that produces cylindri- gebraically related to the mean density of the Universe. cal stars. Through most of 1997, the supernova method seemed to b. A universe whose metric oscillates with a period be the one hold-out in finding a q0 or density value large of 160 minutes, and so accounts both for that period

BEAM LINE 29 in the sun and for the peak mode of the variable star Delta Scuti (actually 162 minutes). READ ON c. A scenario for making gamma-ray bursters in the heliosphere. The complete text of “Astrophysics in 1997” by V. Trimble d. Dark matter candidates in the form of a vector- and L. A. McFadden appears in the March 1998 is- based theory of gravity or solid hydrogen. sue of Publications of the Astronomical Society of e. Redshifts quantized by “giving up the arbitrary hy- the Pacific. pothesis of the differentiability of space-time.” The proceedings of the 75th anniversary restaging of the Curtis-Shapley debate, with contributions from R. J. ACKNOWLEDGMENTS Nemiroff (organizer), V. Trimble (on the original C-S event), G. J. Fishman (on observations of gamma- I asked the editor to perch the amoeba atop the kanga- ray bursters), D. Q. Lamb (arguing for events in the roo in the first picture so as to have an excuse for men- halo of our own galaxy), and B. Paczyn´ski (arguing tioning Robert K. Merton, author of On the Shoulders for events in very distant galaxies) appear in PASP of Giants (no, Newton was not the first to say it), who 107, 1131-1176, with a summary by M. J. Rees, the has been an occasional, generous reader of these maun- moderator. derings for some time. Reviewers, even more than oth- The announcement of cosmic chirality is found in B. Nod- er scientists, are indeed supported by their colleagues. land and J. P. Ralston, Phys. Rev. Lett. 78, 3143 The series, Astrophysics in 199x, arose from a sug- (1997). One of the refutations is J. F. C. Wardle et al. gestion by Howard E. Bond, the immediate past editor Phys. Rev. Lett. 79, 1801 (1997); and the premature of Publications of the Astronomical Society of the upper limit appears in M. Goldhaber and V. Trimble, Pacific, who must often have felt like the parent of Rose- J. Astrophys. Astron. 17, 17 (1996) . . . and next time mary’s baby, and who also just happens to have been the we’re going to publish in a prestigious journal too! chap who first spotted the optical counterpart of the May 8th, 1997, gamma-ray burst—that was the one that had a measurable redshift, but he couldn’t measure it, because he was using a 0.9 meter telescope (it took the Keck 10-meter). I am grateful both to him and to my some-time co-authors, Peter Leonard and Lucy-Ann McFadden, for their contributions to the series (and also to the IRS for the schedule C deduction that has enabled me to pay the page charges for its publication most years).

30 SPRING 1998 CONTRIBUTORS

GORDON FRASER studied at JEFFREY A. APPEL has been a London’s Imperial College in the physicist at Fermilab since 1975. mid-1960s, when theoretical physi- Most recently he has been spokesper- cists were attacking spontaneous son for Fermilab experiment E769 and symmetry breaking under Tom Kib- MAURY GOODMAN is a cospokesperson for E791. For eight ble and relativistic SU(6) theory un- physicist in the High Enery Physics years ending in March of this year, der Abdus Salam and Paul Matthews. Division of Argonne National Lab- he headed the Physics Section and Fraser also wrote short-story ﬁction oratory. He received his BS from the follow-on Experimental Physics Pro- and became side-tracked into jour- Massachusetts Institute of Technol- jects. Appel received his PhD from nalism. He returned to physics as a ogy. His 1979 PhD from the Univer- Harvard University. He is a Fellow science writer, eventually transfer- sity of Illinois at Urbana came on a of the American Physical Society and ring to CERN. He is editor of the photoproduction experiment with has coauthored over 120 articles in monthly CERN Courier; co-author, Al Wattenberg. After a postdoc at professional journals. with Egil Lillestol and Inge Sellevag, MIT working on a Fermilab neutrino Appel's interests extend beyond of The Search for Inﬁnity(New York, experiment, he joined the Soudan the purely scientific and technical. Facts on File, 1995) which has been group at ANL, where he studies at- For many years he chaired the Fer- published in ten other languages; and mospheric neutrinos and is search- milab Auditorium Committee that author of The Quark Machines (Bris- ing for evidence of nucleon decay. He organized the arts, lectures, and ex- tol, Institute of Physics Publishing, was an early advocate of a long-base- hibition series there. He also initi- 1997). He is also editor of Particle line neutrino program at Fermilab ated a special Illinois Research Cor- Century, a collection of contribu- and is now a member of the MINOS ridor summer jobs program for tions to be published by Institute of collaboration. outstanding science and math teach- Physics Publishing later this year. ers. His present interests are radiation-hard vertex detectors and the BTeV research and development program.

BEAM LINE 31 VIRGINIA TRIMBLE is not sure that she was a turtle in a previous lifetime or deserves to be one in the next, but members of the genera testudo and pseudymis (order Chelonia) are her favorite companion animals. Her graduate days at Caltech (1964–68) were brightened by the silent sympathy of Triton (a snapper who more than earned his name), Beauregard (a button turtle), Aragorn (a red- eared slider), Golum (a Lousiana soft-shell), and others. Each entered our home about the size of the silver dollar that was the hourly salary of a graduate student in those days, and each somewhat out- weighed the printed thesis by the time we came to a parting of the ways. Oscillating yearly between the University of California and the University of Maryland is too hard a lifestyle for a turtle (and sometimes marginal for a human being), but someday I hope to have another opportunity to listen for the voice of the turtle in the bathtub.

32 SPRING 1998 DATES TO REMEMBER

Jul 22–30 29th International Conference on High-Energy Physics, Vancouver, Canada (ICHEP 98) ([email protected])

July 31 Sid Drell Symposium, Stanford, California ([email protected])

Aug 3–14 26th SLAC Summer Institute on Particle Physics: Gravity—From the Hubble Length to the Planck Length (SSI 98), Stanford, California (Lilian DePorcel: Conference Coordinator, SLAC, MS 62, PO Box 4349, Stanford, CA 94309, or [email protected])

Aug 4–8 6th International Conference on Biophysics and Synchrotron Radiation, Argonne, Illinois (Susan Strasser, Conference Coordinator, APS, [email protected])

Aug 10–14 10th International Conference on X-ray Absorption Fine Structure, Chicago, Illinois (Tim Morrison, Conference Chairman, [email protected])

Aug 23–28 19th International Linear Accelerator Conference (LINAC 98), Chicago, Illinois ([email protected])

Aug 23–Sep 5 1998 European School of High-Energy Physics, St. Andrews, Scotland (Miss Susannah Tracy, School of Physics, CERN/DSU, 1211 Geneva 23, Switzerland, or Susannah.Tracy@cern.ch)

Aug 31–Sep 4 International Conference on Computing in High-Energy Physics (CHEP 98), Chicago, Illinois ([email protected] or [email protected])

Sep 6–19 1998 CERN School of Computing (CSC 98), Funchal, Madeira, Portugal (Miss Jacqueline Turner, CERN School of Computing, 1211 Geneva 23, Switzerland, or [email protected])

Sep 7–12 17th International Conference on High-Energy Accelerators (HEACC 98), Dubna, Russia (Natalia Dokalenko, Intern. Department JINR, Dubna, Moscow Region, RU-141980, Russia, or [email protected])

Sep 14–18 International Computational Accelerator Physics Conference (ICAP 98), Monterey, California ([email protected])

Oct 13–14 9th Users Meeting for the Advanced Photon Source, Argonne, Illinois (Susan Strasser, Confer- ence Coordinator, APS, [email protected])

Oct 14–15 Advanced Photon Source Users Organization Workshops, Argonne, Illinois (Susan Strasser, Conference Coordinator, APS, [email protected])

Oct 19–20 25th Annual SSRL Users Conference, Stanford, California (Suzanne Barrett, SSRL, PO Box 4349, Stanford, CA 94309, or [email protected])

Oct 22–23 ALS Users Association Annual Meeting, Berkeley, California (Ruth Pepe, Lawrence Berkeley National Laboratory, Advanced Light Source, MS 80-101, Berkeley, CA 94720, or [email protected])