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Improving the Top Quark Forward-Backward Asymmetry Measurement at the LHC

Description: At the LHC, top quark pairs are dominantly produced from gluons, making it difficult to measure the top quark forward-backward asymmetry. To improve the asymmetry measurement, we study variables that can distinguish between top quarks produced from quarks and those from gluons: the invariant mass of the top pair, the rapidity of the top-antitop system in the lab frame, the rapidity of the top quark in the top-antitop rest frame, the top quark polarization and the top-antitop spin correlation. We combine all the variables in a likelihood discriminant method to separate quark-initiated events from gluon-initiated events. We apply our method on models including G-prime's and W-prime's motivated by the recent observation of a large top quark forward-backward asymmetry at the Tevatron. We have found that the significance of the asymmetry measurement can be improved by 10% to 30%. At the same time, the central values of the asymmetry increase by 40% to 100%. We have also analytically derived the best spin quantization axes for studying top quark polarization as well as spin-correlation for the new physics models.
Date: August 15, 2011
Creator: Bai, Yang; /SLAC; Han, Zhenyu & /Harvard U., Phys. Dept.
Partner: UNT Libraries Government Documents Department


Description: We report BRAHMS results from RHIC d+Au and p+p collisions at {radical}S{sub NN} = 200GeV. A remarkable change in the nuclear modification factor R{sub dAu} is seen as the pseudorapidity of the detected charged hadrons changes from zero at mid-rapidity to 3.2 at the most forward angle studied during the 2003 run. For pseudorapidity {eta} > 1 the suppression of the R{sub cp} factor is more pronounced in the sample of central events in contrast to the behavior at mid-rapidity where the central events show higher enhancement compared to a semi-central sample. These results are consistent with a saturated Au wave function strongly affected by quantum evolution at higher values of rapidity.
Date: March 15, 2004
Partner: UNT Libraries Government Documents Department


Description: We present the first measurement of directed flow (v{sub 1}) at the Relativistic Heavy Ion Collider (RHIC). v{sub 1} is found to be consistent with zero at pseudorapidities {eta} from -1.2 to 1.2, then rises to the level of a couple of percent over the range 2.4 < |{eta}| < 4. The latter observation is similar to that from NA49 if the SPS rapidities are shifted by the difference in beam rapidity between RHIC and SPS. We studied the evolution of elliptic flow from p + p collisions through d + Au collision, and onto Au + Au collisions. Measurements of higher harmonics are presented and discussed.
Date: March 15, 2004
Partner: UNT Libraries Government Documents Department

The PHENIX experiment at RHIC

Description: Later this decade the Relativistic Heavy Ion Collider (RHIC) will be built at Brookhaven National Laboratory. Its goal will be to accelerate and collide Au beams at 100 GeV/c in an attempt to create a Quark Gluon Plasma (QGP). The PHENIX detector aims to detect the QGP through its leptonic and hadronic signatures. We describe here its physics capabilities and the details of the apparatus designed to pick out rare leptonic signatures from among hadronic multiplicities of up to 1500 particles per unit of rapidity.
Date: December 15, 1993
Creator: Tonse, S. R. & Thomas, J. H.
Partner: UNT Libraries Government Documents Department

Energy dependence of transverse momentum fluctuations in Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS) at 20A to 158A GeV

Description: Results are presented on event-by-event fluctuations of transverse momenta p{sub T} in central Pb+Pb interactions at 20A, 30A, 40A, 80A, and 158A GeV. The analysis was performed for charged particles at forward center-of-mass rapidity (1.1 < y*{sub {pi}} < 2.6). Three fluctuation measures were studied: the distribution of average transverse momentum M(p{sub T}) in the event, the {phi}{sub p{sub T}} fluctuation measure, and two-particle transverse momentum correlations. Fluctuations of p{sub T} are small and show no significant energy dependence in the energy range of the CERN Super Proton Synchrotron. Results are compared with QCD-inspired predictions for the critical point, and with the UrQMD model. Transverse momentum fluctuations, similar to multiplicity fluctuations, do not show the increase expected for freeze-out near the critical point of QCD.
Date: April 15, 2009
Creator: Collaboration, NA49 & Anticic, T.
Partner: UNT Libraries Government Documents Department

The study of hadronic matter at the highest density; the search for the deconfined quark-gluon phase using 2 TeV anti p -p collisions; and the exclusive study of nuclear fragmentation using the Lawrence Berkeley Laboratory EOS-TPC

Description: This report discusses the: Fermilab experiment 735, a search for the quark-gluon plasma; an exclusive study of nuclear fragmentation using the EOS-TPC; and a study of the central rapidity region at the relativistic heavy ion collider.
Date: August 15, 1990
Creator: Scharenberg, R.P. & Hirsch, A.S.
Partner: UNT Libraries Government Documents Department

Study of intermittency in e sup + e sup minus annihilations at 29 GeV

Description: Charged particle multiplicity distributions from e{sup +}e{sup {minus}} annihilations at 29 GeV have been analyzed in selected rapidity and azimuthal angle intervals. The data were taken with the High Resolution Spectrometer at PEP. The factorial moments of the multiplicity distributions increase as the rapidity interval is decreased, the so-called intermittency phenomenon. These direct measurements of the moments agree with values derived from negative binomial fits to our multiplicity distributions in various central rapidity windows. The factorial moments are also given for the distribution in azimuthal angle around the beam direction and for the two-dimensional distribution in rapidity and azimuthal angle around the jet directions.
Date: June 15, 1990
Creator: Abachi, S.; Derrick, M.; Kooijman, P.; Musgrave, B.; Price, L.; Repond, J. et al.
Partner: UNT Libraries Government Documents Department

Some TPC (Time Projection Chamber) measurements in an oxygen beam at the AGS

Description: The principal detector for AGS Experiment 810 is a Time Projection Chamber (TPC) in which it is intended to measure momenta and angles of a major fraction of the charged particles from each light ion collision. This report describes the results of a test of a prototype of the TPC in a beam of (14.6 /times/ 16 = 233.6 GeV/c) oxygen ions run in June of this year.
Date: November 15, 1988
Creator: Love, W. A.; Bonner, B. E.; Buchanan, J. A.; Chan, C. S.; Chiou, C. N.; Clement, J. M. et al.
Partner: UNT Libraries Government Documents Department