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Electroproduction of light quark baryons

Description: The status of electromagnetic excitation of light quark (u, d) baryon states is reviewed and confronted with results of calculations within the framework of microscopic models of the baryon structure and the photon - baryon coupling. Prospects for a qualitative improvement of their knowledge in this sector using photon and electron beams at the new, intermediate energy continuous wave (CW) electron machines are discussed.
Date: April 1, 1992
Creator: Burkert, V.
Partner: UNT Libraries Government Documents Department

Theoretical uncertainties in {Gamma}{sub sl}(b {r_arrow} u)

Description: The author reviews the existing theoretical uncertainties in relating the semileptonic decay width in b {r_arrow} u transitions to the underlying Kobayashi-Maskawa mixing element {vert_bar}V{sub ub}{vert_bar}. The theoretical error bars are only a few percent in {vert_bar}V{sub ub}{vert_bar}, with uncertainties from the impact of the nonperturbative effects nearly negligible.
Date: May 1, 1999
Creator: Uraltsev, Nikolai
Partner: UNT Libraries Government Documents Department

Measuring the {anti u}/{anti d} asymmetry in the proton sea: Fermilab E866

Description: Experiment E866, conducted at the Fermi National Accelerator Laboratory, is a high statistics experiment to measure {anti u}(x)/{anti d}(x) in the proton over a wide range of x. A review of the current evidence for {anti u}(x) {ne} {anti d}(x) in the proton is given and is followed by a short description of the spectrometer and the experimental procedures used in E866. Preliminary results are shown for the ratio of the Drell-Yan cross sections {sigma}{sup pd}/2{sigma}{sup pp}. The preliminary results confirm the conclusions of both the NMC and NA51 collaborations that there is an {anti u}/{anti d}(x) asymmetry in the proton sea.
Date: July 1, 1998
Creator: Hawker, E.A.; Awes, T.; Brown, C. & Collaboration, E866
Partner: UNT Libraries Government Documents Department

Possible new class of dense white dwarfs

Description: If the strange quark matter hypothesis is true, then a new class of white dwarfs can exist whose nuclear material in their deep interiors can have a density as high as the neutron drip density, a few hundred times the density in maximum-mass white dwarfs and 4 {times} 10{sup 4} the density in dwarfs of typical mass, M {approximately} 0.6M{sub {circle_dot}}. Their masses fall in the approximate range 10{sup {minus}4} to 1M{sub {circle_dot}}. They are stable against acoustical modes of vibration. A strange quark core stabilizes these stars, which otherwise would have central densities that would place them in the unstable region of the sequence between white dwarfs and neutron stars.
Date: January 10, 1995
Creator: Glendenning, N.K.; Kettner, C. & Weber, F.
Partner: UNT Libraries Government Documents Department

The Charge asymmetry in W bosons produced in p anti-p collisions at center of mass energy - 1.96 TeV

Description: The primary mode of production of W{sup +} bosons in a p{bar p} collider is u + {bar d} {yields} W{sup +}. The u quark generally carries more momentum than the {bar d} and the resultant W{sup +} tends to be boosted in the proton direction. Similarly, W bosons are boosted in the anti-proton direction. This is observed as an asymmetry in the rapidity distributions of positive and negative W bosons. Measurement of this asymmetry serves as a probe of the momentum distribution of partons within the proton. These distributions are required as input to the calculation of every p{bar p} production cross section. This thesis presents the first measurement at D0 of the charge asymmetry of the W boson production cross section as measured in W {yields} ev decays in 0.3 fb{sup -1} of p{bar p} collisions collected with the D0 Detector. Theoretical predictions made using the CTEQ6.1M and MRST(2004) parton distribution functions are compared with the measurement.
Date: July 1, 2005
Creator: Torborg, Julie M. & U., /Notre Dame
Partner: UNT Libraries Government Documents Department

Search for single production of scalar leptoquarks in p anti-p collisions decaying into muons and quarks with the D0 detector

Description: We report on a search for second generation leptoquarks (LQ{sub 2}) which decay into a muon plus quark in p{bar p} collisions at a center-of-mass energy of {radical}s = 1.96 TeV in the D0 detector using an integrated luminosity of about 300 pb{sup -1}. No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction {beta} into a quark and a muon was determined for second generation scalar leptoquarks as a function of the leptoquark mass. This result has been combined with a previously published D0 search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark-muon-quark coupling, {lambda}. Assuming {lambda} = 1, lower limits on the mass of a second generation scalar leptoquark coupling to a u quark and a muon are m{sub LQ{sub 2}} > 274 GeV and m{sub LQ{sub 2}} > 226 GeV for {beta} = 1 and {beta} = 1/2, respectively.
Date: December 1, 2006
Creator: Abazov, V.M.; Abbott, B.; Abolins, M.; Acharya, B.S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Quarks and gluons at hadron colliders

Description: Data from proton-antiproton collisions at high energy provide important information on constraining the quark and gluon distributions in the nucleon and place limits on quark substructure. The S asymmetry data constrains the slope of the d/u quark distributions and significantly reduces the systematic error on the extracted value of the W mass. Drell-Yan data at high invariant mass provides strong limits on quark substructure. Information on {alpha}{sub s} and the gluon distributions can be extracted from high P{sub T} jet data and direct photons.
Date: August 1, 1996
Creator: Bodek, A.
Partner: UNT Libraries Government Documents Department

Flavor tests of grand unification

Description: How will we ever be convinced that grand unification, or string theory, or some other physics at very high energies, is correct? Two ways in which this could happen are: The structure of the theory is itself so compelling and tightly constrained, and the links to observed particle interactions are sufficiently strong, that the theory is convincing and is accepted as the standard viewpoint. String theory is a candidate for such a theory, but connections to known physics will require much further understanding of the breaking of its many symmetries. The theory predicts new physics beyond the standard model, which is discovered. If the structure of the theory is not very tightly constrained, several such predictions will be necessary for it to become convincing. Grand unification is a candidate for such a theory, but as yet there have been no discoveries beyond the standard model. Supersymmetric grand unified theories do have a constrained gauge structure, and this has led to the successful prediction of the weak mixing angle at the percent level of accuracy While significant, this is hardly convincing. Never-the-less, supersymmetric grand unified theories offer the prospect of many further tests. In this talk I make the case that experiments of this decade, and the next, allow for the possibility that we might become convinced that grand unification is correct.
Date: October 31, 1995
Creator: Hall, L. J.
Partner: UNT Libraries Government Documents Department

Search for flavor changing neutral current decays of the top quark in p{bar p} collisions at {radical}s = 1.8 TeV

Description: The authors search for the Flavor-Changing Neutral Current decays of the top quark t {yields} q{gamma} and t {yields} qZ (here q represents the c and u quarks) in p{bar p} collisions at {radical}s = 1.8 TeV from a dataset with an integrated luminosity of approximately 110 pb{sup {minus}1} collected during the 1992-1995 run of the Collider Detector at Fermilab. They set limits on the branching fractions BF (t {yields} q{gamma}) < 2.9% (at 95% CL) and BF (t {yields} qZ) < 44% (at 90% CL), consistent with the Standard Model.
Date: September 1, 1997
Creator: LeCompte, T.J.
Partner: UNT Libraries Government Documents Department

RHIC spin program. Revision 07/97

Description: Colliding beams of high energy polarized protons at RHIC is an excellent way to probe the polarization of gluons, {anti u} and {anti d} quarks in a polarized proton. RHIC is the Relativistic Heavy Ion Collider being built now at Brookhaven in the ISABELLE tunnel. It is designed to collide gold ions on gold ions at 100 GeV/ nucleon. Its goal is to discover the quark-gluon plasma, and the first collisions are expected in March, 1999. RHIC will also make an ideal polarized proton collider with high luminosity and 250 GeV x 250 GeV collisions. The RHIC spin physics program is: (1) Use well-understood perturbative QCD probes to study non-perturbative confining dynamics in QCD. The author will measure gluon and sea quark polarization in a polarized proton, and polarization of quarks in a transversely polarized proton. (2) Look for additional surprises using the first high energy polarized proton colliders. The author will look for the expected maximal parity violation in W and Z boson production, search for parity violation in other processes, and test parton models with spin. This lecture is organized around a few of the key ideas: Siberian Snakes -- What are they? High energy proton-proton collisions are scatters of quarks and leptons. At high x, a polarized proton beam is a beam of polarized u quarks. Quark and gluon collisions are very sensitive to spin. The author discusses two reactions: how direct photon production measures gluon polarization, and how W{sup {minus}} boson production measures u and {anti d} quark polarization.
Date: July 1, 1997
Creator: Bunce, G.
Partner: UNT Libraries Government Documents Department

Asymmetric quarks in the proton

Description: Asymmetries in the quark momentum distributions in the proton reveal fundamental aspects of strong interaction physics. Differences between {anti u} and {anti d} quarks in the proton sea provide insight into the dynamics of the pion cloud around the nucleon and the nature of chiral symmetry breaking. Polarized flavor asymmetries allow the effects of pion clouds to be disentangled from those of antisymmetrization. Asymmetries between s and {anti s} quark distributions in the nucleon are also predicted from the chiral properties of QCD.
Date: June 1, 2000
Creator: Melnitchouk, W.
Partner: UNT Libraries Government Documents Department

Measurement of the charged multiplicities of b, c and light quark events from Z{sup 0} decays

Description: Average charged multiplicities have been measured separately for {ital b, c} and light quark ({ital u, d, s}) events from Z{sup 0} decays at SLD. Impact parameters of charged tracks were used to select enriched samples of {ital b} and light quark events. We measured the charged multiplicities: {bar {ital n}}{sub {ital uds}} = 19.80 {+-} 0.09 ({ital stat}) {+-} 0.57 ({ital syst}), {bar {ital n}}{sub {ital c}} = 21.17 {+-} 0.44 ({ital stat}) {+-} 1.01 ({ital syst}) and {bar {ital n}}{sub {ital b}}{+-}23.14 {+-} 0.09 ({ital stat}) {+-} 1.03 ({ital syst}) (PRELIMINARY), from which we derived the differences between the total average charged multiplicities of {ital c} or {ital b} quark events and light quark events: {delta}{bar {ital n}}{sub {ital c}} = 1.37 {+-} 0.45 ({ital stat}) {+-} 0.86 ({ital syst}) and {delta}{bar {ital n}}{sub {ital b}} = 3.34 {+-} 0. 13 ({ital stat}) {+-} 0.77 ({ital syst}) (PRELIMINARY). We compared these measurements with those at lower center-of-mass energies and with QCD predictions.
Date: June 1995
Creator: Collaboration, The SLD
Partner: UNT Libraries Government Documents Department

Implications of D^0-\overline D^0 Mixing for New Physics

Description: We provide a comprehensive, up-to-date analysis of possible New Physics contributions to the mass difference {Delta}M{sub D} in D{sup 0}-{bar D}{sup 0} mixing. We consider the most general low energy effective Hamiltonian and include leading order QCD running of effective operators. We then explore an extensive list of possible New Physics models that can generate these operators, which we organize as including Extra Fermions, Extra Gauge Bosons, Extra Scalars, Extra Space Dimensions and Extra Symmetries. For each model we place restrictions on the allowed parameter space using the recent evidence for observation of D meson mixing. In many scenarios, we find strong constraints that surpass those from other search techniques and provide an important test of flavor changing neutral currents in the up-quark sector. We also review the recent BaBar and Belle findings, and describe the current status of the Standard Model predictions of D{sup 0}-{bar D}{sup 0} mixing.
Date: June 8, 2007
Creator: Golowich, Eugene; /Massachusetts U., Amherst; Hewett, JoAnne; /SLAC; Pakvasa, Sandip; U., /Hawaii et al.
Partner: UNT Libraries Government Documents Department

Inclusive Measurements of |V(ub)| From BaBar

Description: The Cabibbo-Kobayashi-Maskawa (CKM) matrix element V{sub ub} is a fundamental parameter of the Standard Model, representing the coupling of the b quark to the u quark. It is one of the smallest and least known elements of the CKM matrix. With the increasingly precise measurements of decay-time-dependent CP asymmetries in B-meson decays, in particular the angle {beta} [1, 2], improved measurements of the magnitude of V{sub ub} will allow for stringent experimental tests of the Standard Model mechanism for CP violation [3]. The extraction of |V{sub ub}| is a challenge, both theoretically and experimentally. Theoretically, the weak decay rate for b {yields} uev can be calculated at the parton level. It is proportional to |V{sub ub}|{sup 2} and m{sub b}{sup 5}, where m{sub b} is the b-quark mass. To relate the B-meson decay rate to |V{sub ub}|, the parton-level calculations have to be corrected for perturbative and non-perturbative QCD effects. These corrections can be calculated using various techniques: heavy quark expansions (HQE) [4] and QCD factorization [5]. They make use of specific assumptions and are affected by different uncertainties. It is therefore important to make redundant measurements by using several experimental techniques, and different theoretical frameworks. Experimentally, the principal challenge is to separate the signal B {yields} X{sub u}ev decays from the 50 times larger B {yields} X{sub c}ev background. This can be achieved by selecting regions of phase space in which this background is highly suppressed. In addition, exploiting the available kinematic variables which discriminate between rare charmless semileptonic decays and the much more abundant decays involving charmed mesons, gives different sensitivities to the underlying theoretical calculations and assumptions. In inclusive measurements, the most common kinematic variables discussed in the literature, each having its own advantages, are the lepton energy (E{sub {ell}}), the hadronic invariant mass (M{sub X}), and ...
Date: April 17, 2006
Creator: Della Ricca, G. & /Trieste U. /INFN, Trieste
Partner: UNT Libraries Government Documents Department

Probing {anti u}/{anti d} asymmetry in the proton via quarkonium and W/Z production

Description: The experimented and theoretical status of the flavor dependence of the sea quark distributions in the proton is summarized. Sensitivities of {ital J}/{Psi}, {Gamma}, and {ital W/Z} production to the {ital {anti u}/{anti d}} asymmetry are then discussed.
Date: December 31, 1995
Creator: Peng, J.C.; Jansen, D.M. & Chen, Y.C.
Partner: UNT Libraries Government Documents Department

Limits on quark-lepton compositeness and studies of W asymmetry at the Tevatron collider

Description: Drell-Yan dilepton production at high invariant mass place strong limits on quark substructure. Compositeness limits from CDF Run 1, and expected sensitivity in Run II and TEV33 are presented. The W asymmetry data constrains the slope of the d/u quark distributions and significantly reduces the systematic error on the extracted value of the W mass.
Date: October 1, 1996
Creator: Bodek, A.
Partner: UNT Libraries Government Documents Department

Top decays and mass with CDF

Description: The authors report preliminary results on top quark decays and measurements of the top mass recently obtained by the CDF collaboration, using a data sample of about 110 pb{sup {minus}1} collected at the Tevatron collider. Upper limits for non Standard model top decays into W + q (non b quark), Z + q and {gamma} + q are given. Top mass measurements are obtained in three topologies for t{anti t} production and decay into W b: lepton + {ge} 4 jets, di-lepton and all hadronic final states. The most precise measurement is obtained in the lepton + {ge} 4 jets topology using 34 events which have at least one jet tagged by the SVX or SLT b-tagging algorithms and a good constrained kinematics fit.
Date: June 1, 1996
Creator: Barbaro-Galtieri, A.
Partner: UNT Libraries Government Documents Department

Precision measurement of charge symmetry breaking in np elastic scattering at 347 MeV

Description: Charge symmetry breaking in np elastic scattering at 347 MeV has been measured with high precision. From fits of the measured asymmetry curves over the angular range 53.4{degree} {le} {theta}{sub cm} {le} 86.9{degree}, the difference in the center-of-mass zero-crossing angles of the analyzing powers was determined to be 0.438{degree} {+-} 0.054{degree} (stat.) {+-} 0.051{degree} (syst.). Using the experimentally determined slope of the analyzing power, dA/d{theta} = ({minus}1.35 {+-} 0.05) {times} 10{sup {minus}2} deg{sup {minus}1}, this is equivalent to {Delta}A = [59 {+-} 7(stat.) {+-} 7(syst.) {+-} 2(syst.)] {times} 10{sup {minus}4}. Predictions of nucleon-nucleon interaction models based on meson exchange agree well with this result.
Date: July 1, 1995
Creator: Abegg, R.; Berdoz, A.R. & Birchall, J.
Partner: UNT Libraries Government Documents Department

Nonperturbative estimates of the Standard Model parameters

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project objectives were (1) to develop highly optimized codes for the simulation of lattice Quantum Chromodynamics (QCD) on the Connection Machine CM-5, (2) to use these codes to carry out a comprehensive analysis of Standard Model phenomenology using a large statistical sample, and (3) to combine the results of numerical simulations with experimental data to estimate the unknown parameters of the Standard Model. We were successful in achieving all these goals. Our highly optimized codes were used to debug both the hardware and software of the CM-5. We carried out a comprehensive study of the hadron spectrum, decay constants for mesons, semi- leptonic form factors, form-factors for the rare decay B {r_arrow} K{sup *} {gamma}, {pi}-{pi} scattering amplitude, and matrix elements of a variety of 4-fermion weak operators. From these observables we were able to predict the masses of light quarks, m{sub u} + m{sub d} and m{sub s}, matrix elements of the Cabibbo-Kobayashi-Maskawa mixing matrix, and the CP violating parameters {epsilon} and {epsilon}{prime}. Our new estimates of light-quark masses are roughly half of commonly believed values, and we predict a much larger value for {epsilon}{prime}/{epsilon}, which will be tested experimentally over the next few years. 15 refs.
Date: August 1, 1997
Creator: Gupta, R.; Bhattacharya, T.; Tamayo, P.; Grandy, T.; Kilcup, G. & Sharpe, S.
Partner: UNT Libraries Government Documents Department