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Transverse momentum and centrality dependence of high-ptnon-photonic electron suppression in Au+Au collisions at $\sqrt{s_{NN}}$= 200 GeV

Description: The STAR collaboration at RHIC reports measurements of theinclusive yield of non-photonic electrons, which arise dominantly fromsemi-leptonic decays of heavy flavor mesons, over a broad range oftransverse momenta (1.2<pt<10 gevc) in pp, dAu, and AuAucollisions at sqrt sNN = 200 GeV. The non-photonic electron yieldexhibits unexpectedly large suppression in central AuAu collisions athigh pt, suggesting substantial heavy quark energy loss at RHIC. Thecentrality and \pt dependences of the suppression provide constraints ontheoretical models of suppression.
Date: July 11, 2006
Creator: Abelev, B.I.; Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett,J.; Anderson, B.D. et al.
Partner: UNT Libraries Government Documents Department

Systemsize dependence of associated yields in hadron-triggered jets

Description: We present results on the system size dependence of high transverse momentum di-hadron correlations at {radical}s{sub NN} = 200 GeV as measured by STAR at RHIC. Measurements in d+Au, Cu+Cu and Au+Au collisions reveal similar jet-like correlation yields at small angular separation ({Delta}{phi} {approx} 0, {Delta}{eta} {approx} 0) for all systems and centralities. Previous measurements have shown that the away-side yield is suppressed in heavy-ion collisions. We present measurements of the away-side suppression as a function of transverse momentum and centrality in Cu+Cu and Au+Au collisions. The suppression is found to be similar in Cu+Cu and Au+Au collisions at a similar number of participants. The results are compared to theoretical calculations based on the parton quenching model and the modified fragmentation model. The observed differences between data and theory indicate that the correlated yields presented here will provide important constraints on medium density profile and energy loss model parameters.
Date: July 5, 2010
Creator: Collaboration, STAR & Abelev, Betty
Partner: UNT Libraries Government Documents Department

System-size independence of directed flow at the RelativisticHeavy-Ion Collider

Description: We measure directed flow (v{sub 1}) for charged particles in Au + Au and Cu + Cu collisions at {radical}s{sub NN} = 200 GeV and 62.4 GeV, as a function of pseudorapidity ({eta}), transverse momentum (p{sub t}) and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to v{sub 1} in different collision systems, and investigate possible explanations for the observed sign change in v{sub 1}(p{sub t}).
Date: September 20, 2008
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

The underlying event in large transverse momentum charged jet and Z-boson production

Description: The authors study the behavior of the underlying event in large transverse momentum charged jet and Z-boson production at 1.8 TeV and compare with the QCD Monte-Carlo models. The data indicate that neither ISAJET or HERWIG produce enough charged particles (with p{sub T} &gt; 0.5 GeV/c) from the beam-beam remnant component and that ISAJET produces too many charged particle from initial-state radiation. PYTHIA which uses multiple parton scattering to enhance the underlying event does the best job describing the data.
Date: December 21, 2000
Creator: Field, Rick
Partner: UNT Libraries Government Documents Department

Rapidity gaps in jet events at D0

Description: Preliminary results from the D0 experiment on jet production with rapidity gaps in p{anti p} collisions are presented. A class of dijet events with a forward rapidity gap is observed at center-of-mass energies {radical}s = 1800 GeV and 630 GeV. The number of events with rapidity gaps at both center-of-mass energies is significantly greater than the expectation from multiplicity fluctuations and is consistent with a hard diffractive process. A class of events with two forward gaps and central dijets is also observed at 1800 GeV. This topology is consistent with hard double pomeron exchange.
Date: July 1, 1997
Creator: Abbott, B.; Abolins, M.; Acharya, B.S. & Collaboration, D0
Partner: UNT Libraries Government Documents Department

New new-phenomena results from D-Zero

Description: We have searched for diphoton events ({gamma}{gamma} /E{sub T}) with large missing transverse momentum, {gamma} /E{sub T} events ({gamma} /E{sub T}+{ge} 2 jets) with two or more jets, and diphoton events ({gamma}{gamma}) with high transverse energies in p{anti p} collisions at {radical}s = 1.8 TeV using approximately 100 pb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron in 1992-1996. No excess of events beyond the expected backgrounds is observed. The null results are interpreted in supersymmetric models with a dominant {tilde {xi}}{sup 0}{sub 2} {yields} {gamma}{tilde {xi}}{sup 0}{sub 1} decay and in terms of Dirac pointlike monopole production.
Date: June 1, 1998
Creator: Qian, J.
Partner: UNT Libraries Government Documents Department

Drell-Yan Lepton Pair Azimuthal Asymmetry in Hadronic Processes

Description: We study the azimuthal asymmetry in the Drell-Yan lepton pair production in hadronic scattering processes at moderate transverse momentum region, taking into account the contributions from the twist-three quark-gluon correlations from the unpolarized hadrons. The contributions are found to dominate the asymmetry, and are not power suppressed by qt/Q at small qt where qt and Q are the transverse momentum and invariant mass of the lepton pair. Accordingly, the Lam-Tung relation will be violated at this momentum region, and its violation depends on the twist-three functions. However, at large transverse momentum qt~;;Q, the Lam-Tung relation still holds because all corrections are power suppressed by Lambda2/qt2 ~;; Lambda2/Q2 where Lambda is the typical nonperturbative scale.
Date: January 22, 2009
Creator: Zhou, Jian; Yuan, Feng & Liang, Zuo-Tang
Partner: UNT Libraries Government Documents Department

Energy and system size dependence of phi meson production in Cu+Cu and Au+Au collisions

Description: We study the beam-energy and system-size dependence of {phi} meson production (using the hadronic decay mode {phi} {yields} K{sup +}K{sup -}) by comparing the new results from Cu + Cu collisions and previously reported Au + Au collisions at {radical}s{sub NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from midrapidity (|y| &lt; 0.5) for 0.4 &lt; p{sub T} &lt; 5 GeV/c. At a given beam energy, the transverse momentum distributions for {phi} mesons are observed to be similar in yield and shape for Cu + Cu and Au + Au colliding systems with similar average numbers of participating nucleons. The {phi} meson yields in nucleus-nucleus collisions, normalized by the average number of participating nucleons, are found to be enhanced relative to those from p + p collisions with a different trend compared to strange baryons. The enhancement for {phi} mesons is observed to be higher at {radical}s{sub NN} = 200 GeV compared to 62.4 GeV. These observations for the produced {phi}(s{bar s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems.
Date: October 28, 2008
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

Indications of Conical Emission of Charged Hadrons at the BNL Relativistic HeavyIon Collider

Description: Three-particle azimuthal correlation measurements with a high transverse momentum trigger particle are reported for pp, d + Au, and Au + Au collisions at {radical}s{sub NN} = 200 GeV by the STAR experiment. Dijet structures are observed in pp, d + Au and peripheral Au + Au collisions. An additional structure is observed in central Au + Au data, signaling conical emission of correlated charged hadrons. The conical emission angle is found to be {theta} = 1.37 {+-} 0.02(stat){sub -0.07}{sup +0.06}(syst), independent of p{sub {perpendicular}}.
Date: February 9, 2009
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

Single Spin Asymmetry in Inclusive Hadron Production in pp Scattering from Collins Mechanism

Description: We study the Collins mechanism contribution to the single transverse spin asymmetry in inclusive hadron production in pp scattering p{up_arrow}p {yields} {pi}X from the leading jet fragmentation. The azimuthal asymmetric distribution of hadron in the jet leads to a single spin asymmetry for the produced hadron in the Lab frame. The effect is evaluated in a transverse momentum dependent model that takes into account the transverse momentum dependence in the fragmentation process. We find the asymmetry is comparable in size to the experimental observation at RHIC at {radical}s = 200GeV.
Date: April 14, 2008
Creator: Yuan, Feng & Yuan, Feng
Partner: UNT Libraries Government Documents Department

Sea quark transverse momentum distributions and dynamical chiral symmetry breaking

Description: Recent theoretical studies have provided new insight into the intrinsic transverse momentum distributions of valence and sea quarks in the nucleon at a low scale. The valence quark transverse momentum distributions (q - qbar) are governed by the nucleon's inverse hadronic size R{sup -1} ~ 0.2 GeV and drop steeply at large p{sub T}. The sea quark distributions (qbar) are in large part generated by non-perturbative chiral-symmetry breaking interactions and extend up to the scale rho{sup -1} ~ 0.6 GeV. These findings have many implications for modeling the initial conditions of perturbative QCD evolution of TMD distributions (starting scale, shape of p{sub T}. distributions, coordinate-space correlation functions). The qualitative difference between valence and sea quark intrinsic p{sub T}. distributions could be observed experimentally, by comparing the transverse momentum distributions of selected hadrons in semi-inclusive deep-inelastic scattering, or those of dileptons produced in pp and pbar-p scattering.
Date: January 1, 2014
Creator: Schweitzer, Peter; Strikman, Mark & Weiss, Christian
Partner: UNT Libraries Government Documents Department

In situ calibration of the CMS HCAL detector

Description: One serious challenge for hadron calorimeters is setting the absolute calibration. Electromagnetic calorimeters in a magnetic spectrometer have the momentum of electrons to calibrate against. In addition, at hadron colliders, Z supplies a narrow resonance to determine calibrations. No such well-measured processes have been available in the past for hadron calorimeters. In high energy collisions, high Pt hadrons are not normally isolated, rather appearing as part of jets. Contamination of the energy scale by unmeasured neutrals or by leakage from adjacent particles is always a concern. There are low cross section processes that possess jets of well understood energy, for example a high pt Z recoiling off of a single jet. The high energy and luminosity of the LHC may supply enough of these events for quantities useful for calibration. In this paper we outline the possibility for doing in situ calibration using Z recoiling off of a jet events, and {ital t{anti t}} events. We also comment on the more conventional possibilities of using muons and energy-flow to calibrate.
Date: December 20, 1996
Creator: Freeman, J. & Wu, W.
Partner: UNT Libraries Government Documents Department

Update of the measurement of the t tbar cross section at {radical}s =1.96 TeV

Description: A measurement of the t{bar t} cross section at {radical}s = 1.96 TeV is carried out on a data sample of {approx}100 pb{sup -1} in the dilepton and lepton+jets channels. Overall, 46 events are observed, with an expected background of 23.7 {+-} 3.0. The t{bar t} production cross section is measured to be: {sigma}{sub p{bar p}{yields}t{bar t}} = 8.1 {sub -2.0}{sup +2.2} (stat) {sub -1.3}{sup +1.6} (sys) {+-} 0.8 (lumi) pb. The preliminary measurement of the t{bar t} cross section at a center-of-mass energy of 1.96 TeV presented at the 2003 winter conferences [1] is updated with improved object identification algorithms and a larger data sample of approximately 100 pb{sup -1}. The analyses reported herein are based on data sets taken from August 2002, until July 2003, where {approx}190 pb{sup -1} were delivered to the experiment and {approx}130 pb{sup -1} were recorded and reconstructed. As the various analysis channels have different trigger criteria and quality requirements, the integrated luminosity corresponding to each channel varies. The trigger requirements are the same as those reported in [1]. The run data quality requirements that were applied in [1] are also applied to this larger dataset and are supplemented by additional data quality requirements based on smaller units of data called luminosity blocks ({approx}1 minute of data taking). These requirements reduce the effective data sample by 6%. The most prominent change in the analyses occurred in the identification of electrons, where a likelihood is now used to combine individual criteria, such as electromagnetic cluster x{sup 2} [1], spatial track matching, the E/p matching [1], the fraction of electromagnetic energy of the cluster [1], the distance of closest approach to the primary vertex (DCA) used to select primary high transverse momentum electrons originating from the primary interaction vertex, and the isolation with respect to nearby ...
Date: October 14, 2003
Creator: al., Victor Abazov et
Partner: UNT Libraries Government Documents Department

Transverse instability analysis for the IPNS Upgrade

Description: The proposed 1-MW spallation neutron source upgrade calls for a 2-GeV rapidly-cycling synchrotron (RCS) with an intensity of 1.04{times}10{sup 14} protons per pulse. The potential exists for the excitation of collective, intensity-dependent transverse instabilities. These can normally be controlled by introducing a betatron tune shift or spread, where care is exercised to avoid single-particle resonance effects. Adjusting the chromaticity using sextupoles to vary the head-to-tail phase shift is compared to introducing Landau damping by octupoles. An option for a feedback system is also examined. The momentum spread used for the transverse analysis was obtained from the requirements for longitudinal stability.
Date: July 1, 1995
Creator: Harkay, K. & Cho, Y.
Partner: UNT Libraries Government Documents Department

Measurement of M{sub ital W} using the transverse mass ratio of W and Z

Description: We report on the measurement of W boson mass from a determination of the ratio of the transverse masses of {ital W} and {ital Z} using the DO detector at the Fermilab Tevatron {ital p{anti p}} Collider operating at {radical}{ital s} = 1.8 TeV. The analysis is a preliminary result based on a partial data sample of 13 pb{sup -1} using W {r_arrow} {ital e{sup -}{mu}{sup +}} and Z {r_arrow} {ital e{sup -}e{sup +}} decays. The mass ratio can also be extracted by comparing the shapes of the electron E{sub T} and & distribution from W and Z decays.
Date: December 31, 1996
Creator: Rajagopalan, S.; Rijssenbeek, M. & Collaboration, D0
Partner: UNT Libraries Government Documents Department

Particle beams with uniform transverse distribution

Description: A successfully tested method is described which achieves a more uniform illumination of an extended flat target by the charged particle beam from an accelerator, by proper use of a combination of quadrupole and octupole magneto-optical elements.
Date: October 1, 1996
Creator: Tsoupas, N.; Zucker, M.S.; Snead, C.L. & Ward, T.E.
Partner: UNT Libraries Government Documents Department

The Pomeron beyond BFKL

Description: Conformally invariant reggeon interactions derived from t-channel unitarity are discussed and progress towards understanding the {open_quotes}physical Pomeron{close_quotes}, via massless quark reggeon interactions, is briefly out-lined.
Date: May 12, 1997
Creator: White, A. R.
Partner: UNT Libraries Government Documents Department

QCD results using the k{perpendicular} jet-finding algorithm in p{bar p} collisions at {radical}s = 1800 GeV

Description: An inclusive measurement of the jet mass as a function of jet p{sub {perpendicular}} has been made for jets with {vert_bar}{eta}{vert_bar} < 0.5. This measurement is the first in a hadron collider environment using the k {sub {perpendicular}} jet- finding algorithm. This analysis shows that the HERWIG Monte Carlo well reproduces the average jet mass for high p{sub {perpendicular}} jets. At lower p{sub {perpendicular}}, the data jets are 5-10% more massive. A second analysis has been performed with the same algorithm which measures the distribution of subjets (jets within jets).
Date: May 1, 1997
Creator: Lincoln, D. & Collaboration, DO
Partner: UNT Libraries Government Documents Department

Hadron distributions - recent results from the CERN experiment NA44

Description: Proton distributions at midrapidity have been measured for 158A{circ}GeV/c Pb + Pb collisions in the focusing spectrometer experiment NA44 at CERN. A high degree of nuclear stopping is found in the truly heavy ion collisions. Systematic results of single particle transverse momentum distributions of pions, kaons, and protons, of 200A-GeV/c S+S and 158A{circ}GeV/c Pb+Pb central collisions will be addressed within the context of thermalization. By comparing these data with thermal and transport models, freeze-out parameters such as the temperature parameter T{sub fo} and mean collective flow velocity ({Beta}) are extracted. Preliminary results of the particle ratios of K{sup -}/K{sup +} and p/p are discussed in the context of cascade models of RQMD and VENUS.
Date: September 1, 1996
Creator: Xu, N.
Partner: UNT Libraries Government Documents Department

Fully differential QCD corrections to single top quark final states.

Description: The authors have performed a fully differential calculation of QCD corrections to electroweak production of single top quarks. The method used allows for jet definitions and experimental cuts. The corresponding computer code passes the necessary check of reproducing the previously known total rate. First examination of the rapidity and transverse momentum of the top quark shows the corrections to be flat relative to leading order. Additional phenomenological studies are in order. Further work is in progress on the corrections to t-b-jet final states which will give a comprehensive set of tools for studying single-top-quark production at future hadron-hadron colliders.
Date: November 14, 2000
Creator: Harris, B. W.; Laenen, E.; Phaf, L.; Sullivan, Z. & Weinzierl, S.
Partner: UNT Libraries Government Documents Department

Soft and hard interactions in p {bar p} collisions at {radical}s = 1800 and 630 GeV

Description: Proton-antiproton events collected with the CDF minimum-bias trigger at {radical}(s) = 1800 and 630 GeV are studied splitting the full event sample in a soft subsample of events with no energy clusters above 1.1 GeV and in the subsample of the remaining events. Detailed and precise analyses of the multiplicity and transverse momentum distributions as well as of the correlation of the average pt and of its dispersion with the multiplicity are performed for the two samples. Comparisons of the results and of their dependence from the center of mass energy show clear differences in their behaviors. The results support important and unexpected scaling properties of the soft sample.
Date: October 31, 2000
Creator: Rimondi, Franco
Partner: UNT Libraries Government Documents Department

Transverse momentum distributions of W and Z bosons produced in p {anti p} collisions at 1.8 TeV

Description: The transverse momentum distributions of W and Z bosons produced in p{anti p} collisions at {radical}s = 1.8 TeV are measured with the D0 detector at Fermilab. The results are compared to QCD calculations which include soft gluon resummation. The transverse momentum distribution of the Z boson is consistent with the calculation of Ladinsky and Yuan, and is used to extract their non-perturbative parameter 92-
Date: October 1, 1997
Creator: Abbott, B.
Partner: UNT Libraries Government Documents Department

Transverse spin dependent Drell-Yan in QCD to O({alpha}{sub s}{sup 2}) at arge p{sub T} (I). Virtual corrections and methods for the real emissions

Description: The authors investigate the role of the transverse spin dependence in Drell Yan lepton pair production to NLO in QCD at parton level. In their analysis the authors deal with the large p{sub T} distributions. They give very compact expressions for the virtual O({alpha}{sub s}{sup 2}) corrections to the cross section and show that the singularities factorize. The study is performed in the {ovr MS} scheme in Dimensional Regularization, and with the t'Hooft-Veltman prescription for {gamma}{sub 5}. A discussion of the structure of the real emissions is included, and detailed methods for the study of these contributions are formulated.
Date: September 1, 1997
Creator: Chang, Sanghyeon; Coriano, Claudio & Elwood, John K.
Partner: UNT Libraries Government Documents Department