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Results from hadron colliders

Description: The present status of hadron collider physics is reviewed. The total cross section for {bar p} + p has been measured at 1.8 TeV: {sigma}{sub tot} = 72.1 {plus minus} 3.3 mb. New data confirm the UA2 observation of W/Z {yields} {bar q}q. Precision measurements of M{sub W} by UA2 and CDF give an average value M{sub W} = 80.13 {plus minus} 0.30 GeV/c{sup 2}. When combined with measurements of M{sub Z} from LEP and SLC this number gives sin{sup 2}{theta}{sub W} = 0.227 {plus minus} 0.006, or m{sub top} = 130{sub {minus}60}{sup +40} GeV/c{sup 2} from the EWK radiative correction term {Delta}r. Evidence for hadron colliders as practical sources of b quarks has been strengthened, while searches for t quarks have pushed the mass above M{sub W}: m{sub top} > 89 GeV/c{sup 2} 95% cl (CDF Preliminary). Searches beyond the standard model based on the missing E{sub T} signature have not yet produced any positive results. Future prospects for the discovery of the top quark in the range m{sub top} < 200 GeV/c{sup 2} look promising. 80 refs., 35 figs., 7 tabs.
Date: December 14, 1990
Creator: Pondrom, L.G. (Wisconsin Univ., Madison, WI (USA))
Partner: UNT Libraries Government Documents Department

Nuclear effects on heavy quark production: Results from Fermilab Experiments E772 and E789

Description: Fermilab Experiments E772 and E789 are fixed target experiments with 800 GeV protons incident on nuclear targets corresponding to a center-of-mass energy of {radical}{bar s} {approximately} 39 GeV. Measurements are made with a pair spectrometer which has a solid angle of a few percent and operates at high luminosity with up to {approximately}10{sup 12}(E772) or {approximately}10{sup 11}(E789) protons/spill. Our experimental program explores several types of nuclear medium effects: the modification of quark and gluon structure functions by the nucleus, effects on the production of vector mesons (e.g. J/{psi} and {gamma}), and effects on the production of D mesons. The latter is accomplished with the use of a new silicon vertex detector. E789 also looks at the decays of B mesons including the decay to J/{psi} and searches for the decays to two-charged particles (e.g. B {yields} h{sup +}h{sup {minus}}) but I will not discuss this part of our program in this paper.
Date: January 1, 1991
Partner: UNT Libraries Government Documents Department

Review of the heavy ion physics sessions

Description: The parallel sessions on Heavy Ion Physics covered several areas of recent progress in characterizing the nuclear equation of state and the search for deconfined quark matter. Studies of systems from 1 to several hundred GeV/nucleon have been made in order to map the behavior of nuclear matter over a wide range of temperatures and pressures. We have also considered results from proton-nucleus reactions in the heavy ion physics discussions. This should help untangle nuclear effects'' due to the presence of relatively undisturbed nuclear matter from observables arising in the hot, dense part of the system. Even though heavy ion physics covers a large range of bombarding energies, the same two basic questions must be answered. The first problem is to characterize the system that has been produced. We need to determine the energy density, lifetime, temperature and baryon density reached in the collision before expansion and particle production. Then we may address the second issue and look for evidence of new physics. At this meeting, we heard new results from experiments, and theoretical analyses which strive to explain all available data, including those from proton-nucleus collisions. We explored heavy quark production, which may indicate quark matter through color screening of c{bar c} pairs. We heard new results in strangeness production, which has been predicted to be enhanced if quark matter is formed. There were also discussions of jets and minijets, which may probe the hot, dense matter existing early in the collision.
Date: January 1, 1991
Creator: Jacak, B.V.
Partner: UNT Libraries Government Documents Department

Resonance production in two-photon interactions

Description: Resonance production in two-photon interactions is studied using data collected with the ASP detector at the PEP e/sup +/e/sup /minus// storage ring located at the Stanford Linear Accelerator Center. The ASP detector is a non-magnetic lead-glass calorimeter constructed from 632 lead-glass bars. It covers 94% of 4..pi.. in solid angle, extending to within 20/degree/ of the beamline. Lead-scintillator calorimeters extend the coverage to within 21 mr of the beamline on both sides. Energy resolution of ..sqrt..E/10%, where E is the energy is GeV, is achieved for electrons and photons in the lead-glass calorimeter, and particle trajectories are reconstructed with high efficiency. A total luminosity of 108 pb/sup /minus/1/ was collected with the ASP detector at a center-of-mass energy of 29 GeV. The observed process is e/sup +/e/sup /minus// ..-->.. e/sup +/e/sup /minus//..gamma..*..gamma..* ..-->.. e/sup +/e/sup /minus//X, is a pseudoscalar resonance (J/sup PC/ = 0/sup /minus/+/) and ..gamma..* is a virtual (mass /ne/ 0) photon. The outgoing electrons scatter down the beampipe and are not detected. The observed resonances are the /eta/ and /eta/' mesons, with masses of 549 and 958 MeV, respectively. They are detected in the ..gamma gamma.. decay mode; a total of 2380 +- 49 /eta/ ..-->.. ..gamma gamma.. and 568 +- 26 /eta/' ..-->.. ..gamma gamma.. events are observed. From the number of events, the detection efficiency, and the calculated production cross sections the radiative widths, GAMMA/sub ..gamma gamma../, of the /eta/ and /eta/' were measured and found to be: GAMMA/sub ..gamma gamma../(/eta/) = .481 +- .010 +- .047keV and GAMMA/sub ..gamma gamma../(/eta/') = 4.71 +- .22 +- .70keV. These results are in good agreement with the world average values. 67 refs., 42 figs., 20 tabs.
Date: February 1, 1989
Creator: Roe, N.A.
Partner: UNT Libraries Government Documents Department

Light-cone quantization of quantum chromodynamics

Description: We discuss the light-cone quantization of gauge theories from two perspectives: as a calculational tool for representing hadrons as QCD bound-states of relativistic quarks and gluons, and also as a novel method for simulating quantum field theory on a computer. The light-cone Fock state expansion of wavefunctions at fixed light cone time provides a precise definition of the parton model and a general calculus for hadronic matrix elements. We present several new applications of light-cone Fock methods, including calculations of exclusive weak decays of heavy hadrons, and intrinsic heavy-quark contributions to structure functions. A general nonperturbative method for numerically solving quantum field theories, discretized light-cone quantization,'' is outlined and applied to several gauge theories, including QCD in one space and one time dimension, and quantum electrodynamics in physical space-time at large coupling strength. The DLCQ method is invariant under the large class of light-cone Lorentz transformations, and it can be formulated such at ultraviolet regularization is independent of the momentum space discretization. Both the bound-state spectrum and the corresponding relativistic light-cone wavefunctions can be obtained by matrix diagonalization and related techniques. We also discuss the construction of the light-cone Fock basis, the structure of the light-cone vacuum, and outline the renormalization techniques required for solving gauge theories within the light-cone Hamiltonian formalism.
Date: June 1, 1991
Creator: Brodsky, S.J. (Stanford Linear Accelerator Center, Menlo Park, CA (USA)) & Pauli, H.C. (Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany, F.R.))
Partner: UNT Libraries Government Documents Department

Review of CERN heavy-ion physics

Description: The primary motivation for studying nucleus-nucleus collisions at very high energies is the possibility of forming a quark-gluon plasma (QGP). In these collisions energy and baryon densities are expected to increase and reach critical values where the quark constituents of the incident nucleons, bound in nuclei, form an extended volume of freely interacting quarks, antiquarks and gluons. Various signatures of the existence of a quark-gluon plasma in these collisions have been proposed: suppression of J/Psi production, an enhancement in strange particle production, event-by-event fluctuations in the rapidity distributions of produced particles, observation of direct photons from the plasma and other observables. The system is expected to evolve dynamically from a pure plasma or mixed phase through expansion, cooling, hadronization and freeze-out. To be able to determine that a new, transient state of matter has been formed it is necessary not only to identify QGP signatures but also to determine the space-time evolution of the collision process. This requires an understanding of the microscopic structure of hadronic interactions, at the level of quarks and gluons, at high temperatures and high densities. In this talk I will describe the physical observables important for understanding the dynamics of heavy-ion collisions at high energies and the present status of experimental results covering these observables. I will then describe the various signatures of QGP formation, present experimental results and plausible interpretations of the results. This talk is not meant to be a comprehensive review, it is rather a summary of important background information, current outstanding problems, observations of particular interest and recent results on dynamics and signatures.
Date: December 1, 1990
Creator: Harris, J.W.
Partner: UNT Libraries Government Documents Department

Heavy ion interactions

Description: Nuclear Physics has come a long way since its inception 70 years ago. We have learned a great deal about nuclear structure and nuclear interactions -- and we have a lot to learn yet. Our understanding of the substructure of protons and neutrons in terms of their elementary' constituents has also evolved to the present level of QCD and the Standard Model. Early work on nuclear reactions involving light projectiles did a great deal in elucidating the characteristic nuclear symmetries and the dynamic phenomena associated with nuclei. As accelerator and ion source technologies evolve it has become possible to accelerate heavier nuclei in addition to electrons, protons, and the very light nuclear systems. From these developments in the tools of our science we are deriving new knowledge: learning about otherwise inaccessible nuclear properties, of the dynamic characteristics of nuclear matter, and about the production of mesons, antiparticles, and other exotic objects in the collision of complex nuclear systems. The subject cuts across much of nuclear physics and it is difficult to give a cohesive overview talk. But I would like to attempt giving you the current flavors of the subject. 18 figs.
Date: January 1, 1989
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Relativistic heavy ions physics

Description: Central nuclear collisions at energies far above 1 GeV/nucleon may provide for conditions, where the transition from highly excited hadronic matter into quark matter or quark-gluon plasma can be probed. We review current ideas about the nature of, and signals for, this transition, and we discuss the (hadronic) string model approach to the nuclear collisions dynamics. At even higher energies in the TeV/nucleon range peripheral nuclear collisions may become a laboratory for electroweak physics at the unification scale allowing, e.g., for Higgs boson production. 42 refs., 29 figs.,
Date: January 1, 1989
Creator: Mueller, B.
Partner: UNT Libraries Government Documents Department

Tau Charm Factory physics

Description: Tau Charm Factories proposed for future machines will provide powerful and unique facilities to study a variety of physics topics: the tau lepton, charm mesons, charmonium and the J/{psi} decays. These topics cover the physics of the members of the first and second quark doublets and the third lepton doublet. A workshop held at Stanford Linear Accelerator Center reviewed the physics, the machine and the detector for such a facility. In this paper, highlights of this meeting will be reviewed. We will begin with a short sketch of the machine issues and then briefly describe topics in tau, charm and charmonium-J/{psi} physics. 49 refs., 2 figs., 1 tab.
Date: September 1, 1989
Creator: Toki, W.H.
Partner: UNT Libraries Government Documents Department

Challenges to quantum chromodynamics: Anomalous spin, heavy quark, and nuclear phenomena

Description: The general structure of QCD meshes remarkably well with the facts of the hadronic world, especially quark-based spectroscopy, current algebra, the approximate point-like structure of large momentum transfer inclusive reactions, and the logarithmic violation of scale invariance in deep inelastic lepton-hadron reactions. QCD has been successful in predicting the features of electron-positron and photon-photon annihilation into hadrons, including the magnitude and scaling of the cross sections, the shape of the photon structure function, the production of hadronic jets with patterns conforming to elementary quark and gluon subprocesses. The experimental measurements appear to be consistent with basic postulates of QCD, that the charge and weak currents within hadrons are carried by fractionally-charged quarks, and that the strength of the interactions between the quarks, and gluons becomes weak at short distances, consistent with asymptotic freedom. Nevertheless in some cases, the predictions of QCD appear to be in dramatic conflict with experiment. The anomalies suggest that the proton itself as a much more complex object than suggested by simple non-relativistic quark models. Recent analyses of the proton distribution amplitude using QCD sum rules points to highly-nontrival proton structure. Solutions to QCD in one-space and one-time dimension suggest that the momentum distributions of non-valence quarks in the hadrons have a non-trival oscillatory structure. The data seems also to be suggesting that the intrinsic'' bound state structure of the proton has a non- negligible strange and charm quark content, in addition to the extrinsic'' sources of heavy quarks created in the collision itself. 144 refs., 46 figs., 2 tabs.
Date: November 1, 1989
Creator: Brodsky, S.J.
Partner: UNT Libraries Government Documents Department

Recent heavy ion results from CERN and Brookhaven

Description: Results of the first round of ultrarelativistic heavy ion experiments at CERN and BROOKHAVEN are reviewed. The experiments measure global variables such as transverse energy and multiplicity to characterize the impact parameter of the collisions and compare with geometrical models of heavy ion collisions. Charged particle transverse momentum spectra are measured, and p-nucleus and nucleus-nucleus collisional look rather similar. The hardening of the spectrum at high p/sub t/, previously observed in p-nucleus, is also present in heavy ion collisions. Two-particle interferometry has been used to study the pion source in central collisions. For analysis of all pions pairs, this looks approximately like the tube cut through the target by the projectile, but mid-rapidity pion pairs indicate a large, nearly spherical, very chaotic source. Study of dimuon production in the J//psi/ mass region has shown a suppression of J//psi/ with respect to the continuum in central compared to peripheral collisions. This could be a signal of deconfinement, but careful studies are underway to determine the magnitude of such an effect from nuclear absorption. 28 refs., 14 figs.
Date: January 1, 1988
Creator: Jacak, B.V.
Partner: UNT Libraries Government Documents Department

Topics in nuclear chromodynamics: Color transparency and hadronization in the nucleus

Description: The nucleus plays two complimentary roles in quantum chromodynamics: (1) A nuclear target can be used as a control medium or background field to modify or probe quark and gluon subprocesses. Some novel examples are color transparency, the predicted transparency of the nucleus to hadrons participating in high momentum transfer exclusive reactions, and formation zone phenomena, the absence of hard, collinear, target-induced radiation by a quark or gluon interacting in a high momentum transfer inclusive reaction if its energy is large compared to a scale proportional to the length of the target. (Soft radiation and elastic initial state interactions in the nucleus still occur.) Coalescence with co-moving spectators is discussed as a mechanism which can lead to increased open charm hadroproduction, but which also suppresses forward charmonium production (relative to lepton pairs) in heavy ion collisions. Also discussed are some novel features of nuclear diffractive amplitudes--high energy hadronic or electromagnetic reactions which leave the entire nucleus intact and give nonadditive contributions to the nuclear structure function at low /kappa cur//sub Bj/. (2) Conversely, the nucleus can be studied as a QCD structure. At short distances, nuclear wave functions and nuclear interactions necessarily involve hidden color, degrees of freedom orthogonal to the channels described by the usual nucleon or isobar degrees of freedom. At asymptotic momentum transfer, the deuteron form factor and distribution amplitude are rigorously calculable. One can also derive new types of testable scaling laws for exclusive nuclear amplitudes in terms of the reduced amplitude formalism.
Date: March 1, 1988
Creator: Brodsky, S.J.
Partner: UNT Libraries Government Documents Department

Lepton-pair production in hadron-nucleus collisions

Description: The general features of lepton pair production are reviewed. Physics motivations for precision measurements of lepton pair production in nuclei are discussed. Preliminary results from Fermilab experiment E772 are presented. The relevance of these results to the EMC effects and to J//psi/ suppression in heavy ion collisions is also discussed. 73 refs., 26 figs., 2 tabs.
Date: January 1, 1988
Creator: Peng, J.C.; Alde, D.M.; Baer, H.W.; Carey, T.A.; Garvey, G.T.; Klein, A. et al.
Partner: UNT Libraries Government Documents Department

Large transverse momentum and higher twist phenomena

Description: A brief summary of the physics of large transverse momentum and higher twist phenomena is given. Particle topics discussed are: higher twist effects in deep inelastic scattering; power suppressed effects at kinematic boundaries; heavy flavour production; vector boson production; and the running of the coupling constant. (LSP)
Date: November 1, 1988
Creator: Ellis, R.K.
Partner: UNT Libraries Government Documents Department

Hadronic production of J/[psi] at large [chi][sub F] in 800 GeV p+Cu and p+Be collisions

Description: The differential cross-section d[sigma]/dx[sub F] for J/[psi] production in 800 GeV proton-nucleus collisions has been measured in the kinematic range 0.30 [le] x[sub F] [le] 0.95 and x[sub F] [lt] p[perpendicular] [lt] 5 GeV through the decay mode J/[psi] [yields] [mu][sup +][mu][sup [minus]]. The nuclear dependence of J/[psi] production over this range was measured using copper and beryllium targets. The differential cross sections are in good agreement with the predictions of the symbolical parton duality model. The data show no evidence for an intrinsic charm component in the proton. The ratio of the differential cross sections for copper and beryllium shows a suppression of J/[psi] production in copper which increases with increasing x[sub F].
Date: December 1, 1992
Creator: Kowitt, M.S.
Partner: UNT Libraries Government Documents Department

High energy nucleus-nucleus collisions at CERN: Signatures, physical observables and experimental results

Description: Experimental results on high energy nucleus-nucleus collisions have become available with the recent experiments at CERN utilizing 200 GeV/n oxygen and sulfur beams. Physics motivations for these experiments are presented: a description of predicted signatures for possible formation of a quark-gluon plasma and physical observables that are expected to provide important information for understanding the dynamics of these collisions. A presentation will be made of some of the first experimental results to emerge from this new field. 28 refs., 9 figs.
Date: February 1, 1988
Creator: Harris, J.W.
Partner: UNT Libraries Government Documents Department

PEGASYS/Mark II: A program of internal target physics using the Mark II detector at the PEP storage ring

Description: This document is a proposal to SLAC on behalf of the PEGASYS Collaboration for a program of internal target physics at PEP utilizing the Mark A detector. Having completed its tour of duty at SLC in November 1990, we propose that the Mark A detector be returned to the PEP storage ring, where it will be used in conjunction with a long gas target for studies of QCD with nucleon and nuclear targets, as well as tests of QED in lepton pair production, and a search for new neutral bosons. We expect that the detector in its new configuration could be commissioned by late 1991 and begin taking data by 1992. This document presents the physics to be accomplished with the Mark A, and describes the minimal changes to the detector that we will need to make it function for internal target experiments. We also show a possible timeline for the project, and indicate the makeup of the collaboration that will carry out the work.
Date: November 1, 1990
Partner: UNT Libraries Government Documents Department

PHENIX Conceptual Design Report

Description: The PHENIX Conceptual Design Report (CDR) describes the detector design of the PHENIX experiment for Day-1 operation at the Relativistic Heavy Ion Collider (RHIC). The CDR presents the physics capabilities, technical details, cost estimate, construction schedule, funding profile, management structure, and possible upgrade paths of the PHENIX experiment. The primary goals of the PHENIX experiment are to detect the quark-gluon plasma (QGP) and to measure its properties. Many of the potential signatures for the QGP are measured as a function of a well-defined common variable to see if any or all of these signatures show a simultaneous anomaly due to the formation of the QGP. In addition, basic quantum chromodynamics phenomena, collision dynamics, and thermodynamic features of the initial states of the collision are studied. To achieve these goals, the PHENIX experiment measures lepton pairs (dielectrons and dimuons) to study various properties of vector mesons, such as the mass, the width, and the degree of yield suppression due to the formation of the QGP. The effect of thermal radiation on the continuum is studied in different regions of rapidity and mass. The e[mu] coincidence is measured to study charm production, and aids in understanding the shape of the continuum dilepton spectrum. Photons are measured to study direct emission of single photons and to study [pi][sup 0] and [eta] production. Charged hadrons are identified to study the spectrum shape, production of antinuclei, the [phi] meson (via K[sup +]K[sup [minus]] decay), jets, and two-boson correlations. The measurements are made down to small cross sections to allow the study of high p[sub T] spectra, and J/[psi] and [Upsilon] production. The PHENIX collaboration consists of over 300 scientists, engineers, and graduate students from 43 institutions in 10 countries. This large international collaboration is supported by US resources and significant foreign resources.
Date: January 29, 1993
Partner: UNT Libraries Government Documents Department