The Newsletter ofthe Fermi National Accelerator Laboratory The search for the top quark THE TOP QUARK MAY HOLD has been underway ever since the bottom quark was THE KEY TO EXCITING discovered at Fermilab in NEW PHYSICS 1977. This search has not been an easy quest. For nearly 20 years it has domi- nated the efforts of thou- sands of people worldwide and has turned out to be one of the greatest chal- lenges faced by experiment- ers in high-energy physics. WHAT'S SO SPECIAL ABOUT THE TOP QUARK? Large international experiments at CERN (Geneva, Switzerland), DESY (Hamburg, Germany), KEK (T sukuba, Japan), SLAC (Stanford, California) THE FERMILAB TEVATRON IS THE ONLY ACCELERATOR and FERMILAB have all searched for ABLE TO WORK AT THE ENERGY LEVELS REQUIRED TO the top quark. Each experiment searched PRODUCE TOP QUARKS. ONE OF THE GOALS OF for many years and involved a large EXPERIMENTERS AT CDF AND D0 IS TO FIND THE TOP number of universities and laboratories. QUARK AND MEASURE ITS MASS. Physicists have made predictions about Fermi News the mass of the top quark based on mathematical models and the experi- Friday, April 1, 1994 Volume 17, Number 6 mental evidence gained from past Peoples Testifies for HEP ................................................................ page three searches. A little over a decade ago, many physicists believed that the top Deer Population on Rise ................................................................... page five quark would be observed in experi- Main Injector Enclosure Contract Awarded ...................................... page five ments then being conducted at DESY. At that time the mass of the top quark People and Events ....................................................... pages six through seven 2 was predicted to be about 15 GeV/c • continued to page two TOP QUARK continued from page one Since the search began, experimental evidence has led to a steady rise in the 2 mass limit of the top quark. Recent PETRA at DESY 1984- 15-22 GeV/c results from the CDF and D0 experi- PEP at SLAC 1985 ments show that the top quark mass 2 must be at least 130 GeV/c • 2 (See Table I) Tristan at KEK 1988 26 GeV/c "Scientists now know that the top quark SLC at SLAC 1989 41 GeV/c2 is at least that heavy because if the top 2 quark were lighter than 130 Gev/c , 2 we would have already discovered it," LEP at CERN 1990 45 GeV/c says G.P. Yeh, CDF. HOW ARE TOP QUARKS PRODUCED? Tevatron at 1988 49 GeV/c2 Today, the Fermilab Tevatron is the PERMILAB and only accelerator able to achieve the SppS at CERN energies necessary to confirm the exist- ence of the top quark. If the mass of the top quark is less than 180 2 2 SppS (UA-1) 1990 60 Gev/c GeV/c , it should be discovered at Fermilab in the near future. One of the at CERN goals of CD F and D0is to find the top quark and determine its mass. SppS (UA-2) 1990 69 GeV/c 2 at CERN Tops are produced in pairs when a light quark in the proton and a light Tevatron (CDP) 1990 72-77 GeV/c 2 antiquark in the antiproton annihilate to form a top-antitop pair. Since the at PERMILAB Standard Model predicts that the top should almost always decay into a W Tevatron (CDP) 1992 91 GeV/c 2 particle and a bottom quark, we expect a top-antitop event to produce a w+w- at PERMILAB pair and bottom and antibottom quarks. This assumption must be T evatron (D0) 1994 131 GeV/c 2 tested. The top is so massive, it might decay in ways not included in the at PERMILAB Standard Model. "Nature is the ulti- mate arbiter; she tells us if we are right Table I: There has been a steady progression in the mass limit ofthe top quark or wrong," says Stephen Parke, RD/ ftom 15 GeV/c2 to the most recent published limit of131 GeV7c2. The Theory Department. Standard Model requires that the top mass be less than about 200-250 Ge V/c2. Ifthis mass range can be completely explored then either the top quark will be discovered or the Standard Model will be shown to be incorrect. If current predictions are correct, the T evatron and its upgrade, the Main continued to page four 2 FermiNews April 1, 1994 PEOPLES TESTIFIES FOR HEP "The United States has a BEFORE SCIENCE superb capability for SUBCOMMITTEE forefront research in elementary-particle phys- OnJanuary26, 1994, the Science Sub- cording to known physical laws. Yet ics for the next decade- committee of the House Science, Space despite its success, this picture also but it can be realized only and Technology Committee held a raises profound questions that only new hearing on the future of high-energy experiments can answer. These ques- if there is sufficient fund- physics research in the United States. tions present great opportunities for ing to make efficient use Director JOHN PEOPLES testified discovery. Throughout most ofthe long before the subcommittee, along with period of its development, the U.S. led of our existing world-class panelists Roberto Peccei, past chair- the world in making contributions to facilities."-john Peoples man of the American Physical Society's the understanding of matter and en- Division of Particles and Fields, and ergy. Today, the U.S. is still one of the Frank S. Merritt of the Enrico Fermi leaders in this global field of research. Institute of the Universtiy of Chicago. In spite of the termination of the SSC, offers the best prospect for U.S. experi- Previously, Martha Krebs, DOE's di- the U.S. can make many important mentalists to work at the energy fron- rector of Energy Research; John Gib- contributions to elementary-particle tier in the next decade," said John. bons, director of the Office of Science physics for the remainder of the de- Krebs agreed and spoke of a "vision of and Technology Policy, and Robert cade. But, afrer that, we will not remain the future" that could include the LHC. Eisenstern ofthe National Science Foun- among the leaders in the ensuing de- dation testified as part of the first panel. cades unless we rebuild our capability John said that U.S. participation in the to construct and operate world-class LHC will probably require a contribu- The panelists emphasized the impor- facilities." tion of roughly $500 million to CERN tance of maintaining sufficient fund- for the construction ofLHC and of the ing for the base high-energy physics John added that the funding for the two detectors. "This would require a program. "The most logical and cur- base program is no longer sufficient to 10 percent increase in high-energy phys- rent steps forthe U.S. program in high- "allow achievement of the great poten- ics funding, in addition to funding for energy physics are to complete in timely tial for discovery in the U.S. and it the base program over the 10-year pe- fashion the Fermilab Main Injector certainly does not allow for new projects. riod between 1995 and 2005-a very and the Stanford B-Factory (and) to Nevertheless, some superb opportuni- small number compared to the funds provide full operational funding for ties exist and they can be realized with previously allocated to the SSC," John these facilities once they are completed a modest increase in funding." commented. in order to achieve the most and best physics research," said Gibbons. There was also general agreement by The future of the program is now being the panelists that the U.S. high-energy assessed by a subpanel of DO E's High John Peoples said, "The United States physics program would benefit from Energy Physics Advisory Panel chaired has a superb capability for forefront the United States participation with by Sidney Orel!. They will issue a re- research in elementary-particle physics CERN in the construction of the Large port in May. for the next decade-but it can be Hadron Collider (LHC). "The SSC realized only if there is sufficient fund- has been terminated and we know that The American Physical Society's Divi- ing to make efficient use ofour existing research at the energy frontier will not sion of Particles and Fields has also world-class facilities. Research in par- proceed by that route in the U.S. for established a series of working groups. ticle physics over the past 60 years has the foreseeable future. The LHC pro- They will issue a report in about a year. produced a remarkably successful theo- posed by CERN is scheduled for retical picture describing matter and completion early in the next century. Full text of John's testimony can be energy as built of certain constituents, While it has only a third of the energy obtained from the Publications Office, interacting through specific forces ac- that had been planned for the SSC, it WH15SW, by requesting TM-1876. April 1, 1994 FermiNews 3 particle. Various models and theories, TOP QUARK including the Standard Model, seek to continued ftom page two It is remarkable that the explain why quarks have mass. Pre- cisely measuring the mass of the top top quark, if it exists, is so Injector, should produce a large sample quark may give us real insight into of top quarks. From these studies physi- massive. The minimum what causes mass. That is why studying cists will be able to test the validity of top quark mass of 130 the top quark is so exciting. "We don't the Standard Model. 'The Standard know if the top is the Yeti or just the Model appears to be true.