Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session S8: Hadronic Physics III |
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Sponsoring Units: DNP Chair: M.J. Tannenbaum, Brookhaven National Laboratory Room: Delaware B |
Monday, February 15, 2010 3:30PM - 3:42PM |
S8.00001: High $p_{T}$ Single Electrons from Heavy-Flavor Decays in $p$+$p$ Collisions at $\sqrt{s}$ = 200 GeV and 62 GeV in the PHENIX experiment at RHIC Harry Themann The PHENIX experiment at RHIC is a high precision, high rate spectrometer. The cross section of $c\bar{c}$ and $b\bar{b}$ pairs can be determined by measuring the spectra of electrons from the semi-leptonic decays of open charm/bottom mesons. The PHENIX central arm detectors cover $\pi$ in azimuth and $|\eta|<$0.35 with excellent electron identification capability and momentum resolution. We will present the work towards the measurement of $c\bar{c}$ and $b\bar{b}$ decay electron yields from $p$+$p$ collisions at $\sqrt{s}$=200 GeV and 62 GeV. PHENIX published electron yield extends to $p_T$ = 8.5 GeV/c for 200 GeV $p$+$p$ data sample. We propose to extend $p_T$ range of measurement to beyond 10 GeV/c where the source of electrons will begin to be dominated by $b\bar{b}$ decays. Conversely, high $p_T$ electrons in 62 GeV $p$+$p$ collisions should have little contribution from $b\bar{b}$. For this we use a new method to statistically subtract the background from charged pions that start to fire the Ring Imaging CHerenkov detector above 5 GeV/c as well as the addition of data from the higher integrated luminosity in 2006 run. [Preview Abstract] |
Monday, February 15, 2010 3:42PM - 3:54PM |
S8.00002: $J/\psi$ Production Mechanism Measurements at PHENIX Todd Kempel Since the discovery of the $J/\psi$ meson in 1974, several attempts have been made to model the mechanism for its production. No model has yet been able to describe all available data, but experimental progress can be made by making cross section measurements at different energies and polarization measurements for all accessible $J/\psi$ transverse momenta. The capability of the RHIC accelerator to operate at high luminosities for center of mass energies of both 200 and 500 GeV gives an exciting opportunity for the PHENIX experiment to make a significant contribution to the search for a $J/\psi$ production mechanism. The recent RHIC run at 500 GeV provides the first access to $J/\psi$s from p+p collisions at that energy. In addition to cross section and polarization measurements, $J/\psi$ production from transversely polarized $p+p$ collisions provides the potential for new probes of the production mechanism. [Preview Abstract] |
Monday, February 15, 2010 3:54PM - 4:06PM |
S8.00003: Neutral pion single transverse spin asymmetries with the PHENIX experiment John Koster The PHENIX experiment at RHIC probes the proton's transverse spin structure by measuring single spin asymmetries, $A_N$, for inclusive hadron production in proton-proton collisions with transverse proton beam polarization. Single spin asymmetries in $p+p$ arise from combinations of Sivers-like and Collins-like effects. Measurements of a large range of the relevant kinematic variables, $x_F$, $p_T$, will help to clarify the origin of the observed large single spin asymmetries. In PHENIX, the asymmetry, $A_N$ for neutral pions can be measured both at central and at forward rapidity using the large 2008 data set. In this paper we report the status of the single spin asymmetry analysis for inclusive hadrons in PHENIX. [Preview Abstract] |
Monday, February 15, 2010 4:06PM - 4:18PM |
S8.00004: Observation of W decay in 500 GeV p+p collisions J. Haggerty Electrons from W$^{\pm}$ decays have been observed in polarized p+p collisions at $\sqrt{s}$ = 500 GeV in the PHENIX detector at RHIC. The status of the analysis of data from an integrated luminosity of approximately 10 pb$^{-1}$ will be shown. The lepton energy spectrum and background estimate to the W signal from heavy flavor and hard QCD processes will be used to determine the cross section in the PHENIX central arms, which cover $\mid \eta \mid \le 0.35$. W production from polarized beams probes the spin and flavor structure of the proton. The proton beams had a longitudinal polarization of approximately 35\%, and progress on extracting an electron single spin asymmetry will be reported. [Preview Abstract] |
Monday, February 15, 2010 4:18PM - 4:30PM |
S8.00005: Measurement of the Proton Quark Structure from Parity Violating Lepton Asymmetries in W Production in PHENIX at RHIC John Hill A major emphasis of the RHIC scientific program is study of the origin of proton spin carried out by studying collisions of 100 and 250 GeV polarized proton beams. Parity violation of the weak interaction in combination with control over proton spin orientation gives access to the flavor spin structure of the proton. The PHENIX experiment will measure lepton single spin asymmetries in polarized W production from 250 Gev proton-proton collisions to determine helicity distributions for quarks and anti-quarks. This will be done by measurement of high p$_{T}$ muons from W decay using the PHENIX forward muon spectrometers. Determination of the charge of the W-boson allows separation of contributions from various quark flavors. The measurement requires upgrade of the first level muon trigger in the forward spectrometer to reject backgrounds related to the proton beams and decay muons from hadrons produced in collisions. The upgrade consists of new electronics reading information from the muon tracking systems to the level 1 trigger processors and new fast RPC tracking stations inserted upstream and downstream of the PHENIX muon spectrometers. An overview of the expected performance will be given. [Preview Abstract] |
Monday, February 15, 2010 4:30PM - 4:42PM |
S8.00006: Transverse Single Spin Asymmetries of di-Hadron Production in Polarized $p+p$ Collisions at PHENIX Ruizhe Yang Large transverse single spin asymmetries, $A_N$, have been observed in inclusive single hadron production in polarized proton-proton collisions over a broad range of center of mass energies. However, it remains difficult to decompose the observed $A_N$ in contributions from the two possible underlying mechanisms: Collins-like and Sivers-like effects. Transverse single spin asymmetries in di-hadron production provide an alternative probe to study the proton's transverse spin structure. Single spin asymmetries for hadron pairs can be defined such that that no contribution from the Sivers mechanism arises. These asymmetries result from the combination of quark transversity distributions and the spin- dependent di-hadron fragmentation function (IFF). Results from the PHENIX experiment for di-hadron fragmentation at RHIC will be shown. The data used for this measurement were collected during the years 2006 and 2008 with a total integrated luminosity of 7.7 pb$^{-1}$ and an average polarization of 50\%. A new approach to extract quark transversity from a global analysis of di-hadron asymmetries observed in $p+p$, $e+p$ and $e^++e^-$ will be discussed. [Preview Abstract] |
Monday, February 15, 2010 4:42PM - 4:54PM |
S8.00007: Investigating the near-side ridge structure in two particle number correlations at RHIC Chanaka De Silva Two particle number correlation measurements at RHIC have shown an extended near side $\delta_\eta$ correlation in heavy ion collisions relative to p+p for both momentum triggered and untriggered analyses. This phenomenon is also known as the ``ridge.'' A quantitative investigation of the near-side structure as a function of momentum of the correlated particles will be shown for Cu+Cu and Au+Au 200 GeV collisions. A smooth evolution of the ridge properties from the untriggered to the triggered correlations is observed. We try to estimate the jet like correlation contribution to the ridge by comparing the integrals of several of the fit components to the complete two-particle correlation structure as a function of centrality and low cut-off in transverse momentum. Several model calculations that attempts to distinguish between bulk and jet contributions are compared to the data [1], [2]. \\[4pt] [1] S. Gavin et.al., Phys. Rev. C79, 051902 (2009)\\[0pt] [2] E. Shuryak, Phys. Rev. C76, 047901 (2007) [Preview Abstract] |
Monday, February 15, 2010 4:54PM - 5:06PM |
S8.00008: Directed and Elliptic Flow of Charged Hadrons in 22.4 GeV Cu+Cu Collisions Yadav Pandit Measurements of anisotropic flow in heavy-ion collisions provide insight into the early stage of the system's evolution. Anisotropic flow is quantified by the Fourier coefficients $v_{n}$ of the distribution of particles with respect to the reaction plane. This talk reports recent results for directed ($v_{1})$ and elliptic flow ($v_{2})$ at $\surd s_{NN }$= 22.4 GeV. The measurements are done using 0-60{\%} central collision for charged particles at mid-pseudo rapidity region \textit{$\vert \eta \vert $}$<$1.2 and at forward pseudorapidity region 2.5\textit{$<\vert \eta \vert <$}4.0 in the STAR experiment at RHIC. The STAR Beam Beam Counters (BBC) cover the pseudorapidity (\textit{$\eta $}) range 3.3 \textit{$< \quad \vert \eta \vert \quad <$ }5.0 and provide full azimuthal coverage. They are used to reconstruct the first-order event plane for the directed flow analysis. For the elliptic flow measurements, charged tracks in the time projection chamber are used to reconstruct the event plane. Comparisons with other methods and with different energies are presented. [Preview Abstract] |
Monday, February 15, 2010 5:06PM - 5:18PM |
S8.00009: Study of Hadronization Dynamics at JLab Rapha\"el Dupr\'e, Kawtar Hafidi The E02-104 experiment ran in the winter of 2004 in Hall B of Jefferson Lab. The goal of the measurements is to explore the dynamics of the process of hadronization. The experiment measures semi-inclusive deep inelastic scattering events produced on different nuclear targets ($ ^{2}$H, C, Fe and Pb). The multiplicity ratios ($R^{h}_{A}$) and transverse momentum broadening ($\Delta p_{t}^{2}$) have been extracted for various hadrons. Results for negative pions and analysis status on positive kaons and protons will be reported. The high luminosity available at Jefferson Lab and the large acceptance of the CLAS detector allow a multidimensional extraction of $R^h_A$ and $\Delta p_t^2$ for negative pions, which leads to better constraints on the existing models. Those results, along with the ones for positive pions, represent an important step toward the extraction of the characteristic times of hadronization. Finally, comparison between pions and kaons will allow the exploration of the flavor dependence of the hadronization process. [Preview Abstract] |
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