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Summary of recent color coherence results

Description: Recent experimental results on color coherence phenomena from e{sup +}e{sup -}, ep, and p{anti p} collisions are presented. The data are compared to analytic perturbative QCD calculations based on the modified leading logarithm approximation and the local parton hadron duality hypothesis.
Date: August 1, 1998
Creator: Varelas, N., University of Chicago
Partner: UNT Libraries Government Documents Department

Exotic leptoquarks from superstring derived models

Description: The H1 and ZEUS collaborations have recently reported a significant excess of e{sup +}p {r_arrow} e{sup +} jet events at high Q{sup 2}. While there exists insufficient data to conclusively determine the origin of this excess, one possibility is that it is due to a new leptoquark at mass scale around 200 GeV. We examine the type of leptoquark states that exist in superstring derived standard-like models, and show that, while these models may contain the standard leptoquark states which exist in Grand Unified Theories, they also generically contain new and exotic leptoquark states with fractional lepton number, {+-}1/2. In contrast to the traditional GUT-type leptoquark states, the couplings of the exotic leptoquarks to the Standard Model states are generated after the breaking of U(1){sub B-L}. This important feature of the exotic leptoquark states may result in local discrete symmetries which forbid some of the undesired leptoquark couplings. We examine these couplings in several models and study the phenomenological implications. The flavor symmetries of the superstring models are found to naturally suppress leptoquark flavor changing processes.
Date: March 1, 1997
Creator: Elwood, J.K. & Faraggi, A.E.
Partner: UNT Libraries Government Documents Department

Moments of the proton F{sub 2} structure function at low Q{sup 2}

Description: The authors review the status of inclusive electron-proton scattering F{sub 2} structure function data in both the nucleon resonance region and the deep inelastic region, at momentum transfers below 5 (GeV/c){sup 2}. From these data they construct moments of F{sub 2}, down to momentum transfers of Q{sup 2}{approx}0.1(GeV/c){sup 2}. The second moment is only slowly varying with Q{sup 2} down to Q{sup 2}{approx}1, which is a reflection of duality. Below Q{sup 2} of 1 (GeV/c){sup 2}, the Q{sup 2} dependence of the moments is predominantly governed by the elastic contribution, whereas the inelastic channels still seem governed by local duality.
Date: May 1, 2000
Creator: Armstrong, C.S.; Ent, R.; Keppel, C.E.; Liuti, S.; Niculescu, G. & Niculescu, I.
Partner: UNT Libraries Government Documents Department

Hard exclusive electroproduction of pions

Description: The authors investigate the exclusive electroproduction of {pi}{sup +} mesons from nucleons. To leading twist, leading order {alpha}{sub s} accuracy the corresponding production amplitude can be decomposed into pseudovector and pseudoscalar parts. Both can be expressed in terms of quark double distribution functions of the nucleon. While the pseudovector contribution is connected to ordinary polarized quark distributions, the pseudoscalar part can be related to one pion t-channel exchange. They observe that the pseudovector part of the production amplitude is important at x < 0.1. On the other hand, for 0.1 < x < 0.4 contributions from one pion exchange dominate.
Date: December 1, 1998
Creator: Mankiewicz, L.; Piller, G. & Radyushkin, A.
Partner: UNT Libraries Government Documents Department

QCD: Challenges for the future

Description: Despite many experimental verifications of the correctness of our basic understanding of QCD, there remain numerous open questions in strong interaction physics and we focus on the role of future colliders in addressing these questions. We discuss possible advances in the measurement of {alpha}{sub s}, in the study of parton distribution functions, and in the understanding of low x physics at present colliders and potential new facilities. We also touch briefly on the role of spin physics in advancing our understanding of QCD.
Date: January 13, 1997
Creator: Burrows, P.; Dawson, S.; Orr, L. & Smith, W.H.
Partner: UNT Libraries Government Documents Department

Recent results for (e,e{prime}p) reactions at Jefferson Lab

Description: Coincidence cross sections for (e, e{prime}p) quasi-elastic scattering were measured at CEBAF with high statistical precision for C, Fe, and Au targets for 0.6 < Q{sup 2} < 3.3 GeV{sup 2}. Missing energy and missing momentum distributions obtained from a preliminary analysis are in reasonable agreement with prior data from SLAC. The preliminary analysis are compared with a PWIA calculation to determine the nuclear transparency as a function of Q{sup 2} and A. A Rosenbluth analysis to extract the longitudinal and transverse cross sections from these data is anticipated.
Date: September 1, 1997
Creator: Potterveld, D.; Cummings, W.J. & Geesaman, D.F.
Partner: UNT Libraries Government Documents Department

Isolated prompt photon plus jet photoproduction at HERA

Description: The cross section for photoproduction of a prompt photon in association with a jet is studied in Next-to-Leading Order at the DESY ep collider HERA. The effect of various cuts imposed on the cross section by the ZEUS collaboration including isolation cuts on the photon is examined. Comparisons with the ZEUS preliminary data using various parametrizations of the photon structure function is made, and good agreement is found. The preliminary data is not yet precise enough to make a distinction between various models for the photon structure function.
Date: June 10, 1997
Creator: Gordon, L.E.
Partner: UNT Libraries Government Documents Department


Description: This paper is an analytical investigation of the trans-verse electron-proton (e-p) two-stream instability in a pro-ton bunch propagating through a stationary electron back-ground. The equations of motion, including the effect of damping, are derived for the centroids of the proton beam and the electron cloud. An approach is developed to solve the coupled linear centroid equations in the time domain describing the e-p instability in proton bunches with non-uniform line densities. Examples are presented for proton line densities corresponding to uniform and parabolic profiles.
Date: June 1, 2001
Partner: UNT Libraries Government Documents Department

E-P instability in the NSNS accumulator ring

Description: It has been speculated that the intensity limitation observed in the Los Alamos Proton Storage Ring (PSR) is caused by a coherent instability induced by the presence of pockets of electrons generated by scattering with the molecules of the vacuum residual gas. A theoretical explanation of the e-p instability of course does exist, and is similar to the one developed for the ion-induced instability in electron storage rings. Considering the large beam power (3 MW) involved in the NSNS Accumulator Ring, and the consequences caused by even a small amount of beam loss, we need to carefully assess the effects of electrons that may be generated in the vacuum chamber.
Date: August 1997
Creator: Ruggiero, A. G. & Blaskiewicz, M.
Partner: UNT Libraries Government Documents Department

Measurements of the strangeness content of the proton through parity violating electron scattering at JLAB

Description: The authors have measured the parity violating asymmetry in the cross section for elastic scattering of longitudinally polarized electrons from protons at 3.36 GeV incident energy and 0.48 GeV/c{sup 2} momentum transfer at Jefferson Lab. This asymmetry is {minus}14.5 {+-} 2.3 ppm, consistent with the Standard Model with no contribution from strange quarks. They extract the combination of strange form factors G{sub E}{sup s} + 0.39G{sub M}{sup s} = 0.023 {+-} 0.034(stat) {+-} 0.022(syst) {+-} 0.026{delta}G{sub E}{sup n}, where the last error arises from the neutron electric form factor.
Date: September 1, 1998
Creator: Michaels, Robert
Partner: UNT Libraries Government Documents Department


Description: In this talk, we discussed the physics case for an eA collider. We emphasized the novel physics that might be studied at small x. The interesting physics at intermediate x's has been discussed elsewhere [3]. Plans for an electron-ion collider include, as a major part of the program, the possibility of doing polarized electron-polarized proton/light ion scattering. A discussion of the combined case for high energy electron nucleus and polarized electron-polarized proton scattering will be published separately [66].
Date: September 14, 2001
Partner: UNT Libraries Government Documents Department

Study of deep inelastic scattering of polarized electrons off polarized deuterons

Description: This thesis describes a 29GeV electron - nucleon scattering experiment carried out at Stanford Linear Accelerator Center (SLAC). Highly polarized electrons are scattered off a polarized ND{sub 3} target. Scattered electrons are detected by two spectrometers located in End Station A (ESA) at angles of 4.5{degrees} and 7{degrees} with respect to the beam axis. We have measured the spin structure function g{sub 1} of deuteron over the range of 0.029 < x < 0.8 and 1. 0 < Q{sup 2} < 12.0(GeV/c){sup 2}. This integral indicates a discrepancy of more than three standard deviations from the prediction of the Ellis-Jaffe sum rule, 0.068{+-}0.005 at Q{sup 2} = 3.0(GeV/c){sup 2} while our result of g{sub 1}{sup d} in good agreement with SMC results. Combined with g{sub 1} of the proton, the measurement of {integral}{sub 0}{sup 1}(g{sub 1}{sup d}-g{sub 1}{sup n}) is 0.169{+-}0.008. We also obtained the strong coupling constant at Q{sup 2} = 3.0(GeV/c){sup 2} to be 0.417{sub -0.110}{sup +0.086}, using the power correction for the sum rule up to third order of {alpha}{sub s}. This result is in agreement with the strong coupling constant {alpha}{sub s}(Q{sup 2}) = 3.0(GeV/c{sup 2}) obtained from various experiments. Using our deuteron results and the axial vector couplings of hyperon decays, the total quark polarization along the nucleon spin is found to be 0.286{+-}.055, implying that quarks carry only 30% of the nucleon spin. The strange sea quark polarization is also determined to be -0.101 {+-} .023. These measurements are in agreement with other experiments and provide the world`s most precise measurement of these quark polarizations. 80 refs., 151 figs., 23 tabs.
Date: March 1, 1996
Creator: Kuriki, M.
Partner: UNT Libraries Government Documents Department

Measurement of the longitudinal deuteron spin-structure function in deep-inelastic scattering

Description: Experiment E143 at SLAC performed deep-inelastic scattering measurements with polarized electrons incident on polarized protons and deuterons. The data for the beam energy of 29 GeV cover the kinematical range of x{sub Bj} > 0.03 and 1 < Q{sup 2} < 12 GeV{sup 2}. From these data, the spin-dependent structure functions g{sub 1} were determined. This dissertation describes the experiment and its analysis and discusses the results. The measured integral of g{sub 1}{sup d} over x from x = 0 to x = 1 is {Gamma}{sub 1}{sup d} = 0.046 {+-} 0.003 (stat){+-}0.004 (syst) at Q{sup 2} = 3 GeV{sup 2} and disagrees by more than three standard deviations with the prediction of the Ellis-Jaffe, sum rule. The data suggest that the quark contribution to the nucleon helicity is 0.35 {+-} 0.05. From the proton data of the same experiment, the integral over the proton spin-structure functional g{sub 1}{sup d} was determined to be {Gamma}{sub 1}{sup p} = 0.127 {+-} 0.003(stat){+-}0.008(syst). By Combining the deuteron data with the proton data, the integral {Gamma}{sub 1}{sup n} was extracted as {minus}0.027 {+-} 0.008 (stat){+-}0.010 (syst). The integral {Gamma}{sub 1}{sup p} {minus} {Gamma}{sub 1}{sup n} is 0.154{+-}0.010(stat) {+-}0.016 (syst) according to the E143 analysis. This result agrees with the important Bjorken sum rule of 0.171 {+-} 0.009 at Q{sup 2} = 3 GeV{sup 2} within less than one standard deviation. Furthermore, results of a separate analysis involving GLAP evolution equations are shown. Data were also collected for beam energies of 16.2 and 9.7 GeV, Results for g{sub 1} at these energies are presented.
Date: September 1, 1996
Creator: Bauer, J.M.
Partner: UNT Libraries Government Documents Department

QCD subgroup on diffractive and forward physics

Description: The goal is to understand the pomeron, and hence the behavior of total cross sections, elastic scattering and diffractive excitation, in terms of the underlying theory, QCD. A description of the basic ideas and phenomenology is followed by a discussion of hadron-hadron and electron-proton experiments. An appendix lists recommended diffractive-physics terms and definitions. 44 refs., 6 figs.
Date: October 1, 1996
Creator: Albrow, M.G.; Baker, W. & Bhatti, A.
Partner: UNT Libraries Government Documents Department

QCD subgroup on diffractive and forward physics

Description: Over the last few years, there has been a resurgence of interest in small-x or diffractive physics. This has been due to the realization that perturbative QCD techniques may be applicable to what was previously thought of as a non-perturbative problem and to the opening up of new energy regimes at HERA and the Tevatron collider. The goal is to understand the pomeron, and hence the behavior of total cross sections, elastic scattering and diffractive excitation, in terms of the underlying theory, QCD. This paper is divided into experiments of hadron-hadron colliders and electron-proton colliders.
Date: September 1, 1997
Creator: Albrow, M.G.; Baker, W. & Bhatti, A.
Partner: UNT Libraries Government Documents Department

From HERA to the Tevatron: A scaling law in hard diffraction

Description: Results on hard diffraction from CDF are reviewed and compared with predictions based on the diffractive structure function of the proton measured in deep inelastic scattering at HERA. The predictions are generally larger than the measured rates by a factor of {approximately} 6, suggesting a breakdown of conventional factorization. Correct predictions are obtained by scaling the rapidity gap probability distribution of the diffractive structure function to the total integrated gap probability. The scaling of the gap probability is traced back to the pomeron flux renormalization hypothesis, which was introduced to unitarize the soft diffraction amplitude.
Date: December 4, 1997
Creator: Goulianos, K. & CDF
Partner: UNT Libraries Government Documents Department

The Drell-Hearn-Gerasimov sum-rule at polarized HERA

Description: The Drell-Hearn-Gerasimov sum-rule for spin dependent photoproduction relates the difference of the two cross-sections for the absorption of a real photon with spin anti-parallel {sigma}{sub A} and parallel {sigma}{sub P} to the target spin to the square of the anomalous magnetic moment of the target nucleon. The authors discuss the potential of polarized HERA to measure the spin dependent part of the total photoproduction cross section at large {radical}(s{sub {gamma}p}).
Date: November 1, 1997
Creator: Bass, S.D.; Brisudova, M.M. & De Roeck, A.
Partner: UNT Libraries Government Documents Department

E{sub 1+}/M{sub 1+} and S{sub 1+}/M{sub 1+} from an analysis of p(e,e{prime}p){pi}{sup 0} in the region of the {Delta}(1232) resonance at Q{sup 2} = 3.2 (GeV/c){sup 2}

Description: In this paper the authors present an analysis of exclusive p(e,e{prime}p){pi}{sup 0} data to determine the electromagnetic and scalar transition multipoles in the mass region of the {Delta}(1232) at the highest Q{sup 2} value where data exist, Q{sup 2} = 3.2(GeV/c){sup 2}.
Date: October 1, 1995
Creator: Burkert, V. & Elouadrhiri, L.
Partner: UNT Libraries Government Documents Department


Description: New results are reported from an R and D program aimed at greater understanding and control of the e-p instability observed at the Los Alamos Proton Storage Ring (PSR). Numerous characteristics of the electron cloud for both stable and unstable beams in PSR were measured with ANL electron analyzers and various collection plates. Strong suppression of the electron flux density by TiN coating of the vacuum chamber in a straight section was also observed, thereby confirming an essential role for secondary emission at the walls. Landau Damping by a variety of techniques including higher rf voltage, transverse coupling, multipole fields in the lattice, and the use of inductive inserts has been effective in controlling the e-p instability. By these methods, the instability threshold has been raised significantly to 9.7 micro Coulombs per stored pulse.
Date: January 1, 2001
Creator: MACEK, R.
Partner: UNT Libraries Government Documents Department

An Energy Recovery Electron Linac-on-Proton Ring Collider

Description: Electron-proton colliders with center of mass energies between 14 GeV and 30 GeV and luminosities at the 10{sup 33} level have been proposed recently as a means for studying hadronic structure [1]. Electron beam polarization appears to be crucial for the majority of experiments. Two accelerator design scenarios have been examined in detail: colliding rings [2] and recirculating linac-on-ring [3]. Although the linac-on-ring scenario is not as well understood as the ring-ring scenario, comparable luminosities appear feasible, while the linac-on-ring option presents a significant advantage with spin manipulations. Rf power and beam dump requirements make the linac-on-ring option viable only if the electron linac recovers the beam energy, a technology demonstrated at Jefferson Lab's IR FEL, with cw current up to 5 mA and beam energy up to 50 MeV [4]. We begin with a brief overview of the Jefferson Lab energy recovery FEL and summarize the benefits of energy recovery. The feasibility of an energy recovery linac-ring collider is investigated and two conceptual point designs are shown. Luminosity projections for the linac-ring scenario based on fundamental limitations are presented. Accelerator physics issues are discussed and we conclude with a list of required R and D for the realization of such a design.
Date: March 1, 2001
Creator: Merminga, L.; Krafft, G. & Lebedev, V.
Partner: UNT Libraries Government Documents Department

CDF results on diffraction from Run I and plans for Run II

Description: Results on soft and hard diffraction obtained by the CDF Collaboration in Run I of the Fermilab Tevatron {bar p}p collider are reviewed and compared with results from the DESY ep collider HERA and with theoretical expectations. In addition, the CDF program for diffractive studies in Run II is briefly reviewed with emphasis on the relevant detector upgrades and physics goals.
Date: October 16, 2001
Creator: Goulianos, K.
Partner: UNT Libraries Government Documents Department