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Vol. 53 - No. 9 March 19, 1999 BROOKHAVEN NATIONAL LABORATORY 344th Brookhaven Lecture Measuring Forces With the Muon g-2 Experiment at the AGS At the Alternating Gradient Syn- own axis. It therefore acts like a tiny chrotron (AGS), an intriguing experi- magnet, with a north and south pole ment, E821, recently completed its and a magnetic moment, which is the first major run. name given to a magnet’s strength. The experimenters, some 70 re- During each muon’s 2.2 millionths searchers from BNL and 11 institu- of a second lifetime, it constantly emits tions in Germany, Japan, Russia and and reabsorbs a cloud of even more the U.S., have built the world’s largest short-lived particles, which modify the superconducting magnet coil in order muon’s electric and magnetic force. to make one of the world’s smallest The complex interactions in the muon measurements. They are measuring cloud are known to contain traces of the energy and time at which the elec- every elementary form of matter. tron particles fly off decaying muon If a muon orbits in a magnetic field particles that are spinning round a created by another magnet, its mag- perfectly circular orbit in a magnetic netic moment and its spin rotate with field. Roger Stoutenburgh about the same frequency around the Why do that? external field. The rotation frequency To give the answer, one of the E821 of the spin is proportional to a factor researchers, Associate Scientist Ralf called “g.” Prigl, AGS, will give the 344th Brook- If g were exactly 2, the spin axis, haven Lecture, “Probing the Nature of initially pointing in the direction of Force: The Muon g-2 Experiment at Ralf Prigl at the muon g-2 experiment at BNL’s Alternating Gradient travel, would always move in step the AGS.” Prigl will be introduced by Synchrotron. with the orbit and thus continue to AGS Chair Derek Lowenstein, begin- point in the forward direction. ning at 4 p.m. in Berkner Hall on holds an atom’s nucleus together; and combination of electric and magnetic However, QED predicts that, by the Wednesday, March 24. the electromagnetic force. These are theory, with the theory of quantum time the muon returns to where it As Prigl will explain, the reason for three of the four forces that physicists mechanics and relativity. started, the spin axis will have moved measuring the energy spectrum of the are investigating as governing all in- Now, however, Prigl will relate how slightly inward, due to the effect of the decay electrons is that its time depen- teractions of matter. new technology has made it possible weak, strong and electromagnetic dence indicates the strength of an ef- Prigl will recall how experiments to refine the old result to an even forces on the muon cloud. At each orbit fect on the muon. at CERN, Switzerland, during the higher level of sensitivity that is ex- of the muon, the shift increases by the This effect, called g-2, deflects the 1960s and 70s, had already made this pected to reveal new information about same amount, until — after 30 orbits muon in a magnetic field, adding to an measurement to an extraordinary pre- the weak and strong forces. in the E821 experiment — the axis already well-known force that acts on cision, helping to establish muon be- again points in the direction of travel. The Moving Muon the bare electric charge of the muon. havior and the validity of quantum This rotation of the muon spin axis The effect is believed to be made by the electrodynamics (QED). QED is the To explain the experiment, Prigl relative to the direction of travel is weak force, which is responsible for scientific theory that joins the theory will describe the muon — an electri- called the “g minus 2” (g-2) frequency. particle decay; the strong force, which of electrodynamics, which itself is a cally charged particle that spins on its (continued on page 2) intricacies of nu- RIKEN BNL Supercomputer clear and other sub- atomic forces.” Already, the su- Wins Gordon Bell Prize percomputer has proved its worth by When, at the first anniversary in the application of supercomputers making it possible celebration of the RIKEN BNL Re- to scientific and engineering problems, for BNL and RBRC search Center (RBRC) last October, with particular emphasis on the ma- scientists to do cal- the world’s fastest multipurpose non- chines’ cost-effectiveness. Gordon Bell, culations that were commercial supercomputer was un- a former National Science Foundation presented in sev- veiled, RIKEN BNL researchers knew division director and now a senior re- eral papers at a re- they had a great machine. search at Microsoft, has been sponsor- cent RBRC work- Capable of the top operating speed ing this prize for over ten years to shop. “Now, we can of 600 billion calculations per second promote practical parallel-processing look forward to hav- (0.6 teraflops) needed for the most research. ing predictions for advanced physics research, the Built economically at a cost of $1.8 the new state of supercomputer is also the world’s 12th million, which was provided by RIKEN, matter that could fastest. the Japanese Institute of Physical & be produced in the It is designed to run in tandem with Chemical Research, the RIKEN-BNL Relativistic Heavy the 0.4-teraflop supercomputer at Co- QCD supercomputer is optimized for Ion Collider [RHIC],” lumbia University, resulting in a one- advanced research into quantum chro- Lee said. teraflop computing partnership that modynamics. Also known as QCD, it is Ed McFadden, is the world’s eighth fastest (see the theoretical model of matter based who led the ITD The RIKEN BNL QCD supercomputer (center), win- Brookhaven Bulletin, October 23, 1998). on the force known as the strong inter- team which in- ner of the Gordon Bell Prize for price performance at Within weeks, everyone else in the action, which binds quarks and glu- stalled and de- the November 1998 SC98 High Performance Net- supercomputing field also knew about ons in the particles that make up the bugged the super- working & Computing Conference, Orlando, Florida. the great new machine — because, at nucleus of every atom in the universe. conductor, said, the November 1998 SC98 High Per- Said RIKEN BNL Research Center “We continue to take great pride in the land firms. formance Networking & Computing Director T.D. Lee of Columbia Univer- success of this supercomputer. It is Said Laboratory Director John Conference, Orlando, Florida, the Co- sity, “The construction of this QCD very gratifying to see a computer that Marburger, “We’re very proud that lumbia-designed, BNL- and RBRC- supercomputer began on February 19 was built with our hands, under the the RIKEN BNL superconductor’s ex- built supercomputer won the Gordon last year, and it was completed on direction of the RBRC scientists, work cellence has been recognized with the Bell Prize for price performance. August 28, which is a very short pe- so well. Winning the Gordon Bell Prize Gordon Bell Prize. This is a typical The Bell prize for price performance riod for constructing such a machine. took us all to a new high.” BNL product, resulting from strong recognizes significant achievements We are delighted that, since then, the The supercomputer’s calculational collaborations, plus local talent and supercomputer has been operating power is provided by a total of 12,288 skills, and a determination to break steadily 24 hours every day. All these processors, or daughterboards, divided new ground in pursuit of basic knowl- successes are due to the strong sup- in groups of 64 to form 192 large struc- edge. It was not a simple matter to port of the BNL Information Technol- tures called motherboards. ITD’s Ed build this computer so quickly during ogy Division [ITD] and the harmoni- Brosnan and the Hardware Mainte- a period when the Lab was under ous working relationship between the nance Group maintain the supercom- many external pressures. Ed Mc- scientists of BNL, the RIKEN BNL Re- puter, which stands almost nine feet Fadden and his team built a beautiful search Center, and Columbia.” high and is mounted in six large wa- machine with the slimmest resources It was necessary to have such a ter-cooled racks. because they knew it was important to computer, Lee said, “because without Over $1 million of the computer’s the Lab’s central mission. The RIKEN it we will not be able to understand $1.8 million price was expended in BNL supercomputer will be extremely and to predict with accuracy all the components purchased from Long Is- important to RHIC.” — Liz Seubert Brookhaven Bulletin March 19, 1999 In Memoriam: Andrew Hull, Senior Health Physicist As was noted in Newsday, the Lab understanding of the environmental- fered technical assistance to the U.S. lost “a big piece of its institutional monitoring activities in the early Lab Nuclear Regulatory Commission, sur- memory” with the death on Saturday, years and the information available veying the monitoring practices of March 6, of Andrew Hull, a BNL re- from that time that his contributions nuclear power reactors. As part of that tiree who had continued at the Lab as were invaluable,” said Gunther. “He work, he assessed the ability to moni- a guest senior health physicist. He was a great asset and a wonderful tor radiological releases from nuclear was 79. person.” power reactors under accident condi- Before his death from pneumonia Hull entered the field of health phys- tions. following gallbladder surgery, Hull ics in mid-life, after working in ground Then, as a member of DOE’s radio- had been working with Bill Gunther of operations for American Airlines, logical assistance program (RAP) team Roger Stoutenburgh the Environmental Management Di- 1945-52, and serving in the U.S.

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