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Theoretical high energy physics research at the University of Chicago. Progress report, October 1, 1992--April 30, 1993

Description: Brief narrative descriptions of work performed are given on numerous topics including the following: CP violation, Cabibbo--Kobayashi--Maskawa matrix, and B physics; radiative corrections and electroweak observables; heavy quark symmetry; heavy meson spectroscopy; composite models of quarks and leptons; supersymmetric quantum mechanics, inverse scattering, and the vertex operator; cosmological constraints on lepton-number violation in SO(10) models; black hole evaporation; the light cone in string theory; surfaces in the 3D Ising model; and conformal field theories.
Date: April 1, 1993
Creator: Rosner, J. L.; Martinec, E. J. & Sachs, R. G.
Partner: UNT Libraries Government Documents Department

Survey of composite particle models of electroweak interaction

Description: Models of composite weak bosons, the top-condensate model of electroweak interaction and related models we surveyed. Composite weak bosons must be tightly bound with a high compositeness scale in order to generate approximate puge symmetry dynamically. However, naturalness argument suggests that the compositeness scale is low at least in toy models. In the top-condensate model, where a composite Higgs doublet is formed with a very high scale, the prediction of the model is insensitive to details of the model and almost model-independent Actually, the numerical prediction of the t-quark and Higgs boson masses does not test compositeness of the Higgs boson nor condensation of the t-quark field. To illustrate the point, a composite t{sub R}-quark model is discussed which leads to the same numerical prediction as the top-condensate model. However, different constraints an imposed on the structure of the Higgs sector, depending on which particles are composite. The attempt to account the large t-b mass splitting by the high compositeness scale of the top-condensate model is reinterpreted in terms of fine tuning of more than one vacuum expectation value. It is difficult to lower, without a fourth generation, the t-quark mass in the composite particle models in general because the Yukawa coupling of the i-quark to the Higgs boson, {sub t}{sub 2}/4{pi} = 0.1 for m{sub t} = 200 GeV, is too small for a coupling of a composite particle.
Date: May 1, 1992
Creator: Suzuki, Mahiko
Partner: UNT Libraries Government Documents Department

Polarization and color transparency

Description: Color transparency offers an interesting experimental test of our understanding of hadronic polarization effects which have been seen at high energy. Large polarization effects have been seen for exclusive high momentum transfer reactions which are incompatible with lowest order pQCD. It is proposed to filter these reactions by scattering inside a nucleus. We expect that only color transparent hadrons would survive, and that these should be products of hard'' scattering. If the polarization arrises from a non-perturbative soft'' effect, the nucleus should filter these reaction products away. We should see no polarization remaining after the reaction is filtered by a large nucleus.
Date: January 1, 1993
Creator: Bunce, G.
Partner: UNT Libraries Government Documents Department

Pion double charge exchange scattering above the delta resonance

Description: Data are presented on pion-nucleus double-charge-exchange scattering at energies between 300 and 500 MeV, the highest energies measured so far, together with a review of results at lower energies. The small-angle excitation functions disagree with predictions based on a six-quark cluster model and on an optical model consistent with single-charge-exchange scattering at these energies, but they are consistent with a distorted-wave calculation. Data on f{sub 7/2}-shell nuclei are in partial agreement with a two-amplitude model which is successful at lower energies. In order to achieve good understanding of this process at these energies, more work, both experimental and theoretical, is needed. 16 refs., 6 figs.
Date: January 1, 1990
Creator: Burleson, G.R.
Partner: UNT Libraries Government Documents Department

Glueballs and topological charge in the presence of dynamical quarks

Description: We have estimated the string tension and the masses of the 0{sup ++} and 2{sup ++} glueballs in lattice QCD with 2 light flavours of staggered quarks. In addition we have measured the topological charge and hence susceptibility of our gauge field configurations. The simulations were performed at 6/g{sup 2}=5.6 and quark masses m=0.01 and 0.025 (lattice units) on lattice sizes ranging from 12{sup 4} to 16{sup 4}. 7 refs., 5 figs.
Date: November 1, 1990
Creator: Bitar, K.M.; Edwards, R.; Heller, U.M.; Kennedy, A.D. (Florida State Univ., Tallahassee, FL (USA). Supercomputer Computations Research Inst.); DeGrand, T.A. (Colorado Univ., Boulder, CO (USA). Dept. of Physics); Gottlieb, S. et al.
Partner: UNT Libraries Government Documents Department

The status of strange meson spectroscopy

Description: The present status of strange meson spectroscopy is reviewed with emphasis on the results obtained with the LASS spectrometer at SLAC. The systematics of the level structure are discussed with respect to quark model expectations, and the impact of the proposed KAON Factory on the future of the subject considered. 12 refs., 14 figs.
Date: December 1, 1990
Creator: Dunwoodie, W.
Partner: UNT Libraries Government Documents Department

A classical instability for black strings and p-branes

Description: We investigate the evolution of small perturbations around black of strings and branes which are low energy solutions of string theory. For simplicity we focus attention on the zero charge case and show that there are unstable modes for a range of time frequency and wavelength in the extra 10 - D dimensions. These perturbations can be stabilized if the extra dimensions are compactified to a scale smaller than the minimum wavelength for which instability occurs and thus will not affect large astrophysical black holes in four dimensions. We comment on the implications of this result for the Cosmic Censorship Hypothesis
Date: January 1, 1993
Creator: Gregory, R. (Chicago Univ., IL (United States). Enrico Fermi Inst.) & Laflamme, R. (Los Alamos National Lab., NM (United States))
Partner: UNT Libraries Government Documents Department

Hadron and photon production at large transverse momentum and the dynamics of QCD jets. [Review]

Description: The phenomenology of hadron and photon reactions at short distances is discussed in terms of perturbative quantum chromodynamics. In addition to large P/sub T/ hadron reactions, predictions are reviewed for jet production in two photon collisions, the relation of photon and gluon jet production, hadronic production and color separation, upsilon decay into hadrons and photons, leading particle distributions in low P/sub T/ hadron collisions, discriminants of quark and gluon jets, and the effects of coherence on gluon distributions in hadrons. A number of new experimental tests of QCD are discussed.
Date: October 1, 1978
Creator: Brodsky, S.J.
Partner: UNT Libraries Government Documents Department

Electroweak interactions

Description: A point of view of the electroweak interaction is presented. It begins phenomenologically and moves in stages toward the conventional gauge theory formalism containing elementary scalar Higgs-fields and then beyond. The purpose in so doing is that the success of the standard SU(2) x U(1) theory in accounting for low energy phenomena need not automatically imply success at high energies. It is deemed unlikely by most theorists that the predicted W/sup + -/ or Z/sup 0/ does not exist or does not have the mass and/or couplings anticipated in the standard model. However, the odds that the standard predictions will work are not 100%. Therefore there is some reason to look at the subject as one would were he forced by a wrong experimental outcome - to go back to fundamentals and ascertain what is the minimal amount of theory necessary to account for the data.
Date: October 1, 1980
Creator: Bjorken, J.D.
Partner: UNT Libraries Government Documents Department

[Mathematics and string theory]

Description: Work on this grant was centered on connections between non- commutative geometry and physics. Topics covered included: cyclic cohomology, non-commutative manifolds, index theory, reflection positivity, space quantization, quantum groups, number theory, etc.
Date: January 1, 1993
Creator: Jaffe, A. & Yau, Shing-Tung.
Partner: UNT Libraries Government Documents Department

Kaons and antiprotons as probes of the nucleus

Description: The K/sup +/ absorption on nuclei as a probe is considered, in particular the extraction of neutron densities from elastic and total cross sections, inelastic scattering to particular residual nuclear states, and quasiparticle properties of more deeply bound nucleon orbitals in the shell model via the (K/sup +/, K/sup +/p) reaction and K/sup +/ scattering with large energy loss (deep inelastic processes). It is noted that the level ordering of clumps of states reveals important features of the ..lambda..N interaction, possible formation of strangeness S = 2 nuclear systems, and hypernucleus formation. A new class of mesons is formed in the particle - antiparticle interactions. This formation may be as loosely bound quasimolecular ensembles of baryon and antibaryon or composed of a diquark and an anti-diquark. (JFP)
Date: January 1, 1978
Creator: Dover, C.B.
Partner: UNT Libraries Government Documents Department

Cosmic strings in an expanding spacetime

Description: We investigate the stability of a static, infinitely long and straight vacuum string solution under inhomogeneous axisymmetric time-dependent perturbations. We find it to be perturbatively stable. We further extend our work by finding a string solutions in an expanding Universe. The back reaction of the string on the gravitational field has been ignored. The background is assumed to be a Friedman-Robertson-Walker (FRW) cosmology. By numerically integrating the field equations in a radiation and matter dominated models, we discover oscillatory solutions. The possible damping of these oscillations is discussed. For late times the solution becomes identical to the static one studied in the first part of the paper. 19 refs., 8 figs.
Date: April 1, 1987
Creator: Stein-Schabes, J.A. & Burd, A.B.
Partner: UNT Libraries Government Documents Department

Antiproton-nucleus interactions

Description: The antiproton beams from LEAR are a means for uncovering a hopefully fertile source of physics in the interactions of antiparticles with nuclei. Bound or resonant states have been searched for in the anti N N system and perhaps one candidate found. Resonances in the anti N-A system may have an independent origin, unrelated to isolated states in the two-body system but nevertheless very revealing of the essential nature of the two-body forces. The use of antiproton projectiles to study conventional, and occasionally exotic nuclear structure warrants some attention because of the extreme peripherality of many anti p-induced reactions and the expected strong iso-spin selectivity for inelastic excitation of say giant resonances. The annihilation channels which generate strong absorption in the nuclear interior, localize direct reactions in the nuclear surface. In this fashion anti p's ressemble heavy-ion projectiles but possess the virtue of being a rather more elementary probe and it should be possible to calculate the average anti p-A interaction (optical potential) from something closer to first principles. Perhaps the most fundamental reason for using antinucleons is as carriers, into the target, of antiquarks. It is not at all clear that the sea quarks in a hadron, i.e. in the form of quark-antiquark pairs, exist on an equal footing with valence quarks. The production of cc states (and even of s anti s) appears highly suppressed in nucleon-nucleon collisions. This suppression must be taken into account in establishing the relative merits of pp or p anti p colliders in producing say the W-meson. By introducing antiquarks directly via anti N N and anti N-A one should surely obtain more definite information about q anti q interactions with LEAR, at the low momenta presumably crucial for hadron structure. (WHK)
Date: January 1, 1982
Creator: Kahana, S.
Partner: UNT Libraries Government Documents Department

Hypernuclear physics

Description: A brief overview of progress made in the study of hypernuclear physics is presented. The use of ..lambda..-hypernuclei to study properties of conventional (nonstrange) nuclei is explored. Our knowledge of the hyperon-nucleon force is reviewed. Anecdotal examples of interesting hypernuclear phenomena are discussed. The status of ..sigma..-hypernuclei is considered along with a search for the ''H'' dibaryon. 30 refs., 10 figs.
Date: January 1, 1987
Creator: Gibson, B.F.
Partner: UNT Libraries Government Documents Department

New anomaly in axial-vector ward identity

Description: It is shown how a new type of anomaly, in addition to the Adler--Bell--Jackiw anomaly, can occur in a gauge theory with ..gamma../sub 5/ couplings. Such an anomaly renders standard theories of quantum flavor dynamics nonrenormalizable. 19 references.
Date: January 1, 1978
Creator: Frampton, P.H.
Partner: UNT Libraries Government Documents Department

New (quark) flavors

Description: Some possible characteristics of the new quark suggested by the discovery of T(9.4) are surveyed. An inverse scattering approach to the interquark potential is summarized. 52 references.
Date: February 1, 1978
Creator: Quigg, C.
Partner: UNT Libraries Government Documents Department

Heavy flavor production at fixed target and collider energies

Description: A review is presented of heavy quark production in /bar p/p, p, and pp interactions at fixed target and collider energies. Calculations of total cross sections are described including contributions through next-to-leading order in QCD perturbation theory. Comparisons with available data on charm and bottom quark production show good agreement for reasonable values of charm and bottom quark masses and other parameters. Open issues in the interpretation of results are summarized. A discussion is presented of signatures, backgrounds, and expected event rates for top quark production. 19 refs., 4 figs.
Date: October 13, 1988
Creator: Berger, E.L.
Partner: UNT Libraries Government Documents Department

Introduction to string and superstring theory II

Description: Conformal field theory is reviewed, then conformal invariance is used to rederive the basic results on the embedding dimensionality for bosonic and fermionic strings. The spectrum of the bosonic and the computation of scattering amplitudes are discussed. The formalism used is extended to clarify the origin of Yang-Mills gauge invariance in the open bosonic string theory. The question of the general-coordinate gauge invariance of string theory is addressed, presenting two disparate viewpoints on this question. A brief introduction is then given of the reduction from the idealized string theory in 10 extended dimensions to more realistic solutions in which all but 4 of these dimensions are compactified. The state of knowledge about the space-time supersymmetry of the superstring from the covariant viewpoint is outlined. An approach for identifying possible 6-dimensional spaces which might represent the form of the compact dimensions is discussed, and the orbifold scheme of compactification is presented. 77 refs., 18 figs. (LEW)
Date: March 1, 1987
Creator: Peskin, M.E.
Partner: UNT Libraries Government Documents Department

Inverse scattering problem for quarkonium systems. I. One-dimensional formalism and methodology. [bound state, algebraic technique]

Description: The inverse scattering formalism for reflectionless potentials is applied to the reconstruction of confining potentials from bound-state properties. An explicit algebraic technique is presented and tested on several one-dimensional examples. The connection with a classical problem of interacting solitons is exhibited. 27 references.
Date: December 1, 1977
Creator: Thacker, H.B.; Quigg, C. & Rosner, J.L.
Partner: UNT Libraries Government Documents Department

Introduction to the theory of strings

Description: These lectures present, from an introductory perspective, some basic aspects of the quantum theory of strings. They treat (1) the kinematics, spectrum, and scattering amplitude of the bosonic string, (2) the spectrum and supersymmetry of Green-Schwarz superstring, and (3) the identification of the underlying gauge invariances of the string theory. 43 refs.
Date: October 1, 1985
Creator: Peskin, M.E.
Partner: UNT Libraries Government Documents Department

Measurement of inclusive production of neutral pions at high transverse momentum. [100 to 300 GeV/c, scaling]

Description: These are the results of a measurement of inclusive production at high transverse momentum (P perpendicular to) of neutral pions (..pi../sup 0/) from protons by beams of proton (p), kaon (K), pion (..pi..), and antiproton (antiproton) particles. The experiment used the Fermilab M2 beam line at momenta of 100, 200 and 300 GeV/c striking a liquid hydrogen target. The data include center of mass (cm) production angles of the ..pi../sup 0/ between 2/sup 0/ and 115/sup 0/ for P perpendicular to greater than 1 GeV/c. A pair of differential Cherenkov counters distinguished the types of beam particles. The photon (..gamma..) detector of a lead and scintillator sandwich measured both photons from the ..pi../sup 0/ ..-->.. 2..gamma.. decay and enabled a reconstruction of the ..pi../sup 0/ kinematics. The measurements show several remarkable features distinguishing the production rates for these different beams, including a forward peak in the cm for ..pi..p collisions and much less ..pi../sup 0/ production at high P perpendicular to in pp than in ..pi..p or Kp collisions. A simple parametrization accurately represents the data over most of its range, showing approximate scaling in the radial variable x/sub R/ = 2P/..sqrt..s (in the cm). Several parton models are compared with the data. A heuristic picture in terms of the quark constituents of the interacting hadrons accounts for many features of the data in an intuitive way. 62 references.
Date: October 1, 1978
Creator: Ogawa, A.
Partner: UNT Libraries Government Documents Department

Multiquark evolution in QCD

Description: We present a formalism for the evolution in Q/sub 2/ of multiquark systems as an application of perturbative quantum chromodynamics (QCD) to asymptotic, exclusive nuclear amplitudes. To leading terms in log Q/sup 2/ our formalism is equivalent to solving the renormalization group equations for these amplitudes. Completely antisymmetric multiquark color-singlet represntations are constructed and their evolution is investigated from the one-gluon exchange kernel. We argue that the evolution equation, together with a cluster decomposition, demonstrates a transition from the traditional meson and nucleon degrees of freedom of nuclear physics to quark and gluon degrees of freedom with increasing Q/sup 2/, or at small internucleon separation. As an example, we derive an evolution equation for a completely antisymmetric six-quark distribution amplitude and solve the evolution equation for a deuteron S-wave amplitude. The leading anomalous dimension and the corresponding eigensolution are found for the deuteron in order to predict the asymptotic form of the deuteron distribution amplitude (i.e., light-cone wave function at short distances). The fact that the six-quark state is 80 percent hidden color at small transverse separation implies that the deuteron form factor cannot be described at large Q/sup 2/ by meson-nucleon degrees of freedom alone. Furthermore, since the N-N channel is very suppressed under these conditions, the effective nucleon-nucleon potential is naturally repulsive at short distances. 20 refs.
Date: September 1, 1985
Creator: Ji, C.R.
Partner: UNT Libraries Government Documents Department

Spin models of the proton

Description: We have constructed a model of the proton spin based on a broken SU(6) parameterization for the spin-weighted valence quark distributions in a longitudinally polarized proton. The polarized sea and gluon distributions are assumed to have simple relations to the corresponding unpolarized structure functions. The sum rules, which involve the non-singlet components of the structure function xg/sub 1/, imply that the valence quarks carry about 78% of the proton spin, while the spin carried by sea quarks is negative. Recent EMC data suggest a model in which the sea quarks carry a large negative polarization, whereas certain theoretical arguments favor a model with a smaller negatively polarized sea. These models are discussed with reference to the sum rules. Experiments are suggested which will discriminate between these models. 24 refs., 4 figs.
Date: October 20, 1988
Creator: Ramsey, G.P.
Partner: UNT Libraries Government Documents Department