High Energy

Our faculty in both theoretical ( Allen, Arnowitt, Katrine Becker, Melanie Becker, Bryan, Dutta, Nanopoulos, Pope, Sezgin), and experimental ( Kamon, McIntyre, Safonov, Toback, Webb, White) high energy physics are playing a major role in current and future efforts to understand the new fields, particles, and principles of nature that await discovery during the coming dedade.

The Higgs boson would complete the Standard Model, but may also lead to new physics, since it is quite unlike the other particles that we know. Supersymmetry (SUSY) would give rise to a new menagerie of particles beyond the Standard Model, and uniquely opens the possibility to directly connect the Standard Model with the unification of the fundamental interactions near the Planck scale (~ 10¹⁹ GeV). Neutrino oscillations would signal a mixing of leptonic flavors and again require new physics beyond the Standard Model. Dark matter is inferred from galactic rotation curves, the cosmic microwave background, and supernova observations.

High Energy Experiment:

We seek signals of these new phenomena wherever there is best sensitivity: in the highest energy colliding beams -- CDF (see detector and data sample) at Fermilab, in long-baseline neutrino oscillations -- MINOS (see image) at Fermilab and Soudan, in muons from supernovae and magnetic monopoles from the Big Bang -- MACRO at Gran Sasso, in the feeble interactions of Milky Way WIMPS as they pass through a cryogenic argon WIMP detector (see image).

Collider Detector at Fermilab (Kamon, McIntyre, Toback) The CDF (or see Fermilab page) features proton-antiproton colliding beams at 2 TeV collision energy, L = 10³² cm^-2 s^-1 luminosity and is the premier hadron collider experiment in the world. The Texas A&M group is leading the analysis for trilepton signals of gauginos, the spin 1/2 supersymmetric analogs of the weak bosons. They have been participating in the installation and commissioning of the silicon microvertex detector (SVX), in particular, of a fiber-optic data acquisition system (DAQ - see image) capable of reading 400,000 channels of track information in 10 microseconds. The DAQ system reads the signals from the SVX that make it possible to identify the secondary decay vertices of b-quarks within an interaction - a key tool in finding top quarks (see decay and data) and in several of the cleanest signatures for supersymmetry. They are also working on adding a timing readout system to the electromagnetic calorimeter to improve photon identification. The system will help to investigate the CDF "ee gamma-gamma + missing ET" event (see image).

Long-Baseline Neutrino Oscillations (Webb) The MINOS (or see Argonne page) Collaboration proposes to conduct a search for nm goes to nt and nm goes to ne oscillations using a new nm beam from the Fermilab Main Injector with neutrino energies well above the t production threshold. Oscillations will be detected by the comparison of signals in a near detector at Fermilab and a far detector situated 730 km away in the Soudan underground laboratory. The experiment will require self-consistency among several tests for oscillations to build a compelling case for any discovery. A new 10 kton far detector will be built at Soudan to explore oscillation parameters down to Dm² ~ 0.002 eV² and sin² 2q ~ 0.01. At this time, the far detector is over half completed(~2.2ktons)and taking cosmic ray data. We expect to begin data taking with the NuMI beam sometime in 2004. Until that time, the collaboration will be using atmospheric neutrinos to debug the detector and search for any evidence of differences between the oscillation behavior for neutrinos and anti-neutrinos.

Cryogenic Argon Detection of WIMPS (White) Dr. James White and his students are developing a new type of particle detector to search for the cold dark matter (CDM) that appears to make up over 90% of the mass in the universe. It is believed that dark matter consists of weakly interacting, massive subatomic particles (WIMPs) that were produced during the big bang. Detection and identification of these particles is one of the fundamental problems in physics today.

The active region of the detector consists of a large mass of solid or liquid argon. Each collision between a WIMP and an argon nucleus results in a small cluster of ions which can be extracted and imaged with single ion quantum sensitivity. Such a detector, with a very large mass (tons) and a very low energy threshold (keV), will be competitive with the most sensitive existing detectors. We plan to stage the detector in the WIPP underground laboratory near Carlsbad, New Mexico. This image shows the ionization from an assortment of cosmic ray tracks, gamma rays, and beta particles extracted from a solid argon crystal. The diameter of the image is 2 cm.

New Technology for Detectors and Accelerators (McIntyre) Prof. Peter McIntyre, in conjuction with the parallel Applied Physics program is involved in the development of new superconducting dipole magnet technology to extend the collision energy in the next generation of hadron colliders. These magnets will triple the energy of the Tevatron, and double that of LHC. He is also developing silicon carbide as a radiation-hard replacement for silicon in particle tracking.

High Energy Theory:

Prof. R. A. Arnowitt has made major contributions to general relativity (ADM canonical formulation), quantum field theory, supergravity, and supersymmetry. Over the next five years new accelerator and non-accelerator experiments in high energy physics, as well as satellite astronomy experiments, will bring forth a wealth of new data that will shed light on new laws of particle physics. He is calculating phenomena that might be expected in these new experiments. This research centers around supersymmetric (SUSY) theories of particle interactions as currently the most likely candidate for new physics. His recent research is concerned with detection of SUSY particles at Fermilab and other accelerators, analysis of predictions of supergravity grand unified models on CP violation and proton decay, analysis of superstring D-brane models, heterotic M-Theory, and predictions concerning the detection of dark matter in the Milky Way.

Prof. D. Nanopoulos is working on problems that arise in the effort to construct a Theory of Everything (TOE). He has done work on the Standard Model, Grand Unified Theories, supersymmetry, supergravity, string/M-theory, and astroparticle physics. His contributions cover very different aspects of high energy physics, from phenomenology (e.g., how to detect the Higgs particle and supersymmetric particles) to model building (e. g. flipped SU(5), one of the leading string candidates for a TOE) to more theoretical issues (such as the discovery of no-scale supergravity, which provides the effective, low-energy limit of string/M-theory) to fundamental issues (e.g. modifications of quantum mechanics due to space-time foam, as expressed by M-theory D-brane dynamics). Of topical importance, he has shown supersymmetry brings the coupling constants of the Standard Model to a single value at GUT-energy scales, a prerequisite for a TOE, and has put strong limits on sparticle masses and couplings (see figure). Currently he is involved in the construction of string/M-theory models that are nonperturbatively compliant, and he is trying to understand the nature of quantum space-time foam, i.e. how space-time looks at Planckian distances (~ 10^-33 cm). The synthesis of quantum theory and gravity has already led, at least in some theoretical approaches, to rather drastic modifications of the conventional picture of physics, e.g. dependence, in vacuo, of the velocity of light on its frequency, that can be tested using gamma ray bursters.

Prof. C. Pope is working on quantum gravity, and the unification of the fundamental forces of nature. It seems that string theory is the only plausible candidate that avoids the uncontrollable infinities that plague all attempts to include gravity in the framework of a more traditional field theoretic approach to quantisation. In string theory, the point-like interactions of particle field theories are replaced by the de-localised interactions of fundamental strings, thereby avoiding the infinities. The theory is partially understood in a weakly-coupled perturbative regime, but there are many indications of fascinating deeper underlying structures, associated with the non-perturbative strong-coupling regime. A picture seems to be emerging of a yet more fundamental theory in eleven dimensions, known as M-Theory, which would describe string theory in certain regimes but which has a wider and richer applicability that would take over in regimes where string theory itself became an inappropriate description. Our current state of understanding has been likened to that in quantum physics before the discovery of quantum mechanics. We can expect that uncovering the mysteries of string theory and M-theory will be very difficult, but correspondingly it promises rewards of immense significance for fundamental physics.

Dr. Pope has worked extensively on Kaluza-Klein dimensional reductions, which can explain how these ten or eleven-dimensional theories can describe our observed four-dimensional world. He has also been studying solitonic string solutions and is currently focused principally on trying to gain insights into the non-perturbative strong-coupling regime of string- and M-theory. Remarkable duality symmetries have been discovered, which allow the strong-coupling limit of one formulation of string theory to be probed via a weak-coupling perturbative analysis in another. For example, microscopic black holes and their Hawking radiation can be viewed also as arising from the states of a string theory. This has provided many new insights into such fundamental questions as the apparent paradox of information loss in black hole evaporation. Ultimately, it is hoped that advances in string theory will be of relevance not only for understanding the microscopic structure of the fundamental interactions, but also for understanding the physics of the Big Bang, and the origins and fate of the universe itself.

Prof. E. Sezgin is an expert on supersymmetry, supergravity, and superbranes. Several of his papers on supergravity can be found in the two reprint volumes with commentaries entitled: Supergravities in Diverse Dimensions (eds. A. Salam and E. Sezgin, World Scientific, 1989). He is the co-discoverer of the eleven dimensional supermembrane theory which is an important ingredient of M-theory, which, in turn, is a revolutionary step towards the Theory of Everything. In recent years, Prof. Sezgin's work has focused on the development of superembedding theory, which provides a supergeometrical framework and a powerful tool for studying the dynamics of all superbranes. He has also been working on the theory of massless higher spin theories, which is expected to play an important role in the description of a new phase of M-theory which is drastically different than any other phase seen so far, thus opening a whole new arena of research for a fuller understanding of the ultimate unified theory.

Prof. R. E. Allen is investigating the implications of a new form of supersymmetry in high-energy physics and astrophysics.

Prof. R. A. Bryan made an important contribution to nuclear and particle theory early in his career with the initial prediction of a hadronic scalar meson responsible for the bulk of nuclear binding. The particle has recently been discovered, after an interlude of decades, through reanalysis of old data. Currently he is modeling quarks and leptons with a soliton-inspired potential in four higher dimensions.