FN EE RW MS I FERMILAB AU.S. DEPARTMENT OF ENERGY LABORATORY New Matter-Antimatter Asymmetry Established 2 Photo by Reidar Hahn Volume 22 Friday, March 19, INSIDE: 1999 Number 6 6 Homecoming for Witherell f 9 Profile: Janet Conrad 10 Waste Minimization 12 DOEÕs New Office Manager 13 The Talk of the Lab NEW Matter- Antimatter by Judy Jackson Nature, ever chary of her secrets, is seldom more reticent than on the subject of antimatter. We creatures of matter inhabit a world apparently fashioned only of matter, yet we do not know why. Using particle accelerators, we can create the antimatter counterparts of matterÕs leptons and quarks, but when we study these particles of antimatter, we find that instead of behaving like mirror reflections of their material cousins, they can follow rules of their own. Today, although antimatter remains one of the great mysteries of physics, it is slightly less mysterious than it was a month ago. Years of careful experiments by physicists at CERN and Fermilab have at last produced a significant advance in the understanding of the difference between the behavior of matter and antimatter. Moreover, physicists from FermilabÕs KTeV experiment said they were ÒshockedÓ at the size of a long-sought result they reported to a standing-room-only audience at a seminar at Fermilab on February 24. Indeed, there was an audible gasp from the audience of physicists when University of Chicago graduate student Peter Shawhan gave KTeVÕs observed value for a phenomenon called Òdirect CP violation.Ó ÒOur result,Ó Shawhan said, Òis that epsilon prime over epsilon equals 28 plus or minus 4.1 times 10-4.Ó KTeV physicists may have been surprised, but CERN physicists in experiment NA31 were elated. ÒThe CERN physics community offers its congratulations to their colleagues from the KTeV experiment at Fermilab for their exciting new data on the observation of direct CP violation in neutral kaon decays,Ó wrote CERN Director-General Luciano Maiani. ÒThe KTeV result of (2.8 ± 0.4) x 10-3 is particularly pleasing as it is an important step forward in the understanding of CP violation and it confirms with greater precision the earlier result by the NA31 experiment at CERN. The NA31 result was published in May 1988 in Physics Letters B in a paper entitled ÔFirst Evidence for Direct CP ViolationÕ with a result of (3.3 ± 1.1) x 10-3 for the relative decay amplitudes of CP violating to CP conserving decays.Ó Amit Lath, from Rutgers University, checks the active scintillation counter regenerator inside the vacuum tank upstream of the KTeV detector. 2 FERMINEWS March 19, 1999 Asymmetry Established Antimatter has been surprising physicists since its KTeV physicist Yee Bob discovery by physicist Carl Anderson, in the track Hsiung, of Fermilab, inspects the half-built of an antielectron, or positron, in a cloud chamber cesium iodine crystal in 1932. The prevailing theory of the fundamental calorimeter, the heart of structure of matter, the Standard Model, holds that the KTeV detector, every particle of matter has a corresponding during installation in the antiparticle of antimatter. It is believed that early in summer of 1996. The calorimeter measures the evolution of the universe, matter and antimatter the energy and position were equally abundant, but today antimatter has of kaon decay products. only been observed in cosmic-ray interactionsÑ and in high-energy particle collisions at accelerators such as FermilabÕs Tevatron. Photo by Reidar Hahn Among the particles born in high-energy collisions attempting to observe an asymmetry in the decay, are mesons. Mesons are short-lived pairings of a rather than the mixing, of the neutral kaon. To do quark and an antiquark. Certain mesons, called so, they have attempted to measure the ratio ε/ε, neutral kaons, are combinations of a strange quark ' Òepsilon prime over epsilon,Ó a double ratio of or antiquark and a down quark or antiquark. different modes of decay of neutral kaons and their In 1964, a group of physicists led by James Cronin antiparticles into pi mesons, or pions. If they found and Val Fitch were studying neutral kaons in a value different from zero, it would signal a new Ñ experiments at the Department of EnergyÕs directÑform of CP violation. Brookhaven National Lab when they discovered a ÒThe Standard Model, if it correctly accommodates slight but definite asymmetry in the behavior of the CP violation, predicts a non-zero, but small, effect,Ó neutral kaon and its antiparticleÑan asymmetry said University of Chicago physicist and KTeV called charge-parity, or CP, violation. Until that spokesman Bruce Winstein. ÒBut experiments up discovery, physicists had believed that particles until now had not firmly established such an effect. and antiparticles behaved symmetrically, like mirror An experiment at CERN, NA31, led by Heinrich reflections of each other. Wahl, reported a significant effect, 23 x 10-4, with a ÒWe were attempting to make a much better test of precision of 3.5 standard deviations, but that was CP invariance,Ó said Fitch, who with Cronin was not yet enough to say definitively that the effect awarded the Nobel Prize for the discovery, Òand it was non-zero. And a previous Fermilab turned out not to be invariant.Ó experiment, E731, reported a value of 7.4 x 10-4, This original CP-violating effect can be described with a standard deviation of 1.25Ñan effect three as an asymmetry in the quantum-mechanical times smaller than the CERN experiment, and not fluctuation, or ÒmixingÓ of the neutral kaon with its far enough away from zero to confirm the CERN antiparticle. Other manifestations of CP violation effect. Most theorists who calculated ε'/ε in the have been clearly established at many laboratories Standard Model found very small values, closer to in the years since its discovery, but they could all the Fermilab result or even smaller. As a result of be traced to this original effect. Among the theories this situation, both groups designed and proposed to explain CP violation is the Superweak constructed experiments aimed at much more Theory, which posits only mixing effects, with no precise determinations.Ó CP violation in the decays of neutral kaons into KTeVÕs new result establishes the existence of other particles. direct CP violation beyond reasonable doubt Yet ever since 1964, scientists at physics (almost 7 standard deviations). The finding laboratories around the world have been FERMINEWS March 19, 1999 3 Matter- Antimatter definitively rules out the Superweak Theory as the ÒWe are excited to have established direct CP sole source of CP violation. The value for ε'/ε was violation,Ó Winstein said. ÒWe want to emphasize that much larger than many experts had expected. CERNÕs NA31 experiment deserves a share of the credit.Ó ÒOne way of explaining the largeness of the effect, within the Standard Model, is if the strange quarkÕs To try to understand the difference from their mass is smaller than is often assumed,Ó said previous results, the KTeV physics analysis team Andreas Kronfeld, a Fermilab theorist. For example has intensely scrutinized the earlier Fermilab if the strange quark has a mass of 70-80 MeV, as measurement, but, said Winstein, Òwe have found obtained by Fermilab theorists Kronfeld and Paul nothing that could account for the difference, other Mackenzie and collaborators, the Standard Model than an unlikely but still possible fluctuation. We prediction for ε'/ε agrees well with KTeVÕs result. are eagerly awaiting the next results from our Left to right: KTeV colleagues at CERN in experiment NA48. That collaborators Peter Fitch, now professor of physics at Princeton experiment has significant strengths that Shawhan, Yee Bob University, summed up reaction to the announce- Hsiung, Peter Shanahan, complement KTeVÕs, and we expect them to report ment: ÒIt is a most astonishing result. It is quite and Bruce Winstein, just soon on data they have already taken. And the unexpected, and very, very interesting.Ó after posting the KTeV physics community awaits the results of a results on the Web, as KTeVÕs Winstein pointed out that the new result, the penguins look on. completely different approach taken by the KLOE which is based on analysis of only about 20 The penguin symbolizes experiment at ItalyÕs Frascati laboratory.Ó percent of the collaborationÕs total data from a Òpenguin diagrams,Ó Cronin, co-discoverer of CP violation in 1964 and which are important in 1996-1997 physics run, is much more consistent professor of physics at the University of Chicago, the Standard Model for with the earlier CERN result than with previous confirmed the significance of the KTeV CP violation. results from Fermilab. announcement. ÒItÕs been 35 years since CP MATTER WITH A BAR MILESTONES IN THE UNDERSTANDING OF ANTIMATTER Paul Dirac Carl Anderson Emilio Segre and James Cronin and John Ellis, Mary Fred Gilman and predicts the sees the track of Owen Chamberlain Val Fitch discover Kay Gaillard, and M. Wise publish existence of the first observe the CP violation in the D. Nanopoulos the first in long antimatter. antiparticle, the antiproton at the mixing of the calculate for the series of antielectron, or Bevatron neutral kaon and first time the size refinements to positron, in a cloud accelerator at its antiparticle of ε'/ε in the the calculations chamber at Lawrence Berkeley (indirect CP Standard Model, by many authors, Caltech. Laboratory. violation). getting a value of leading to about 0.0022. estimates of ε'/ε below 0.001. up charm top photon down strange bottom gluon electron neutrino muon neutrino tau neutrino Z boson electron muon tau W boson I II III Three Generations of Matter 1929 1932 1955 1964 1976 1979 4 FERMINEWS March 19, 1999 University of California at San Diego, the University of Chicago, the University of Colorado, Elmhurst College, Fermilab, Osaka University, Rice University, Rutgers University, the University of Virginia, and the University of Wisconsin.