Laboratory for Nuclear Science
The Laboratory for Nuclear Science (LNS) provides support for research by faculty and research staff members in the fields of high energy and nuclear physics. These activities include those at the Bates Linear Accelerator Center and in the Center for Theoretical Physics. Almost half of the faculty in the Department of Physics conduct their research through LNS. During fiscal year 2001, the Department of Energy is expected to provide LNS a total of $28,815,000 in research funding.
LNS researchers in experimental high energy physics are active at a number of laboratories around the world, including CERN (Switzerland), SLAC (California), and Fermilab (Illinois). The overall objective of current research in high energy physics is to test as precisely as possible the Standard Model, which has been very successful in describing a wide variety of phenomena, and to seek evidence for physics beyond the Standard Model. LNS researchers are playing principal roles in much of this research, as described below.
At CERN, an LNS group has led the research program with L3, the largest of four detectors at the Large Electron Positron (LEP) Collider. In the past year, the energy of LEP was raised so as to enhance the probability of detecting the Higgs boson, the particle necessary for the existence of mass in the Standard Model. Despite intriguing hints of the Higgs in data from L3 and the other detectors, LEP was shut down in November, 2000, to make way for the construction of the Large Hadron Collider (LHC). LNS is involved in both large detector projects at the LHC viz., the CMS and ATLAS detectors. In CMS, LNS scientists are engaged in the development of the data acquisition system; in ATLAS the effort is mainly in the development of the muon detection systems. LNS scientists have considerable expertise in both of these areas and expect to be major participants in the U.S. effort at the LHC.
LNS researchers have played leading roles in exploiting the unique properties of the SLD detector at SLAC, which has now completed its data-taking. Final data analysis is underway. An LNS group is now participating in the BaBar experiment at SLAC, which has already produced important insights into the nature of charge symmetry/parity violation in the B-meson system.
The Collider Detector Facility (CDF) Experiment at Fermilab is designed to study the Standard Model and its possible extensions at the highest energy accelerator in the world, the Tevatron collider. Current objectives of CDF include studies of the "bottom" (b) quark, precision measurements of the mass of the W particle (the carrier of the charged electroweak force), and the search for possible quark substructure. After a major upgrade, in which LNS researchers assumed important responsibilities, the multi-year Collider Run II began in the spring of 2001.
The Alpha Magnetic Spectrometer (AMS) experiment had a very successful first flight on the Space Shuttle Discovery in June 1998. AMS is an experiment designed to look for cosmic anti-matter and evidence for dark matter by operating a large magnetic spectrometer above the Earth's atmosphere. The international AMS collaboration is composed primarily of particle physicists and is led by an LNS group. An upgraded version of the AMS spectrometer is under construction, and the experiment is scheduled for a several-year data-taking period on the International Space Station starting in 2004.
Experimental nuclear physics at present has two main thrusts: medium-energy physics and heavy-ion physics. LNS has active, leading groups in both of these sub-fields.
The focus of LNS medium-energy activities is of course the Bates Linear Accelerator Center, which is operated by LNS for the Department of Energy as a national user facility. Bates has been a premier national and international resource for nuclear and particle physics studies for more than two decades. Continuous (as opposed to pulsed) electron beams in the South Hall Ring have been produced in both storage and stretcher modes. Stored beam has been used to test components of the BLAST (Bates Large Acceptance Spectrometer Toroid) detector and internal gas targets, and, with polarized electrons, to commission the beam polarimeter. Extracted beam has been used in two highly successful experiments with the new Out-of-Plane Spectrometer system which probed different aspects of the structure of the proton.
LNS nuclear physics researchers are leading several important efforts at accelerator facilities other than Bates. These facilities include TJNAF (Virginia), LANSCE (New Mexico), DESY (Germany), and Mainz (Germany). The focus of these experiments is a detailed understanding of the properties of the proton, the neutron, and light nuclei.
LNS researchers are prominent in relativistic heavy-ion physics. The principal goal of this field is to probe the existence and properties of the so-called "quark-gluon plasma," a state of matter which is predicted to exist at temperatures and densities higher than those present in normal matter, and which may have been present in the very early universe. An LNS group leads the PHOBOS experiment on the Relativistic Heavy Ion Collider (RHIC) at Brookhaven; this group produced the first publication from this new facility.
Research at the Center for Theoretical Physics (CTP) seeks to extend and unify our understanding of the fundamental constituents of matter. It seeks to advance the conceptual foundations of fundamental physics, especially as applied to the structure and interactions of hadrons and nuclei, new forms of matter which may be created experimentally or observed astrophysically, and the history and large scale structure of the Universe. A few examples of recent work are mentioned below.
String theory aims to unite the strong, electroweak, and gravitational interactions and to explain the observed hierarchy of particles and interactions. The CTP has a strong and diverse group in string theory with important ties to lower energy particle physics. Important work includes the study of instabilities of "branes"-extended objects that occur in string theory-and their implications for field theories of strings. CTP theorists are also very active in the exploration of matrix quantum mechanics, which may be the fundamental structure that unifies various versions of string theory, and the study of tantalizing connections between string theories in anti-de-Sitter space and conformal quantum field theories.
String theories suggest patterns of supersymmetry breaking which may have implications for physics at the energy scales of the next accelerators. CTP researchers have been exploring these patterns. Also, string theory and quantum gravity suggest that space-time may have other dimensions, which influence physical phenomena only indirectly. This has been an extremely active area in the past year, largely led by CTP theorists. Effects include manifestations of extra dimensions at energies quite close to those presently available at accelerators.
MIT theorists have been actively developing new calculational tools for the study of non-perturbative effects in quantum field theories. Variational methods, consistent with renormalization and adapted for easy numerical computation, have been developed and are being applied to problems that arise in the Standard Model.
A major thrust in the CTP has been in the area of lattice gauge theory, which provides a unique tool to solve, rather than model, quantum field theories beyond perturbation theory. The CTP led the development of a major collaboration on high speed computation in QCD, which was recently approved for funding as part of the DOE's SciDAC initiative. These efforts parallel a new thrust in the study of quantum chromodynamics (QCD) at finite density and pressure. CTP researchers have suggested novel effects, such as "color superconductivity," and explained how they may be observed in heavy ion collisions.
CTP researchers continue to lead the exploration of the spin and flavor structure of hadrons, as seen in experiments (many led by MIT faculty) at Bates, Jefferson Lab, DESY, and Brookhaven National Lab.
Finally the CTP has initiated important work in quantum computing. New algorithms that exploit the adiabatic approximation in quantum mechanics offer hope of solving generic problems much faster than classical methods.
Since its founding LNS has placed education at the forefront of its goals. At present approximately 86 graduate students are receiving their training through LNS research programs. A number of undergraduate students are also heavily involved in LNS research. Evidence shows that LNS educates a significant portion of the leaders of nuclear and high-energy physics in this country and abroad.