Double Longitudinal Spin Asymmetries of Inclusive Charged Pion Production in Polarized p+p Collisions at 200 GeV

A primary goal of the STAR Spin program at RHIC is the measurement of the polarized gluon distribution function $\Delta G$, which can be obtained from a global analysis incorporating measurements of the double spin asymmetry A_{LL} in various final state channels of polarized p+p collisions. Final states with large production cross sections such as inclusive jet and hadron production are analyzed as the program moves towards the measurement of A_{LL} in the theoretically clean channel of prompt photon production. The channels p+p -> pi^{+/-} + X are unique in that the ordering of the measurements of A_{LL} in these two channels is sensitive to the sign of Delta G. Moreover, STAR has already established the procedure for the identification of charged pions and the calculation of their production cross-sections over a broad kinematic range. This contribution will present first measurements of double longitudinal spin asymmetries for inclusive charged pion production extracted from 3 pb^{-1} of data at sqrt{s}=200 GeV and 50% beam polarizations. The asymmetries are calculated over the transverse momentum region 2<p_T<10 GeV/c and compared with theoretical predictions incorporating several gluon polarization scenarios. A systematic bias introduced by the selection of charged pions from events satisfying electromagnetic energy triggers will be discussed and estimated using Monte Carlo.Comment: 4 pages, 3 figures, contribution to the Proceedings of the 17th International Spin Physics Symposium (SPIN 2006), Kyoto, Japan, October 2-7, 200

Improving the dE/dx calibration of the STAR TPC for the high-pT hadron identification

We derive a method to improve particle identification (PID) at high transverse momentum ($p_T$) using the relativistic rise of the ionization energy loss ($rdE/dx$) when charged particles traverse the Time Projection Chamber (TPC) at STAR. Electrons triggered and identified by the Barrel Electro-Magnetic Calorimeter (BEMC), pure protons and pions from $\Lambda\to p+\pi^{-}$ ($\bar{\Lambda}\to \bar{p}+\pi^{+}$), and $K^{0}_{S}\to\pi^{+}+\pi^{-}$ decays are used to obtain the $dE/dx$ value and its width at given $\beta\gamma=p/m$. We found that the deviation of the $dE/dx$ from the Bichsel function can be up to $0.4\sigma$ ($\sim3$) in p+p collisions at $\sqrt{s_{NN}}=200$ GeV taken and subsequently calibrated in year 2005. The deviation is approximately a function of $\beta\gamma$ independent of particle species and can be described with a function of $f(x) = A+\frac{B}{C+x^{2}}$. The deviations obtained with this method are used to re-calibrate the data sample from p+p collision for physics analysis of identified hadron spectra and their correlations up to transverse momentum of 15 GeV/$c$. The ratio of $e^{-}/e^{+}$ (dominantly from $\gamma$-conversion) is also used to correct the residual asymmetry in the negative and positive charged hadrons due to momentun distortion in the STAR TPC.Comment: 18pages, 10 figure

Measurement of longitudinal double spin asymmetries of charged pion production in polarized proton collisions at 200 GeV at Relativistic Heavy Ion Collider

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.In title on title page [pi], [over-arrow], and [sqrt] appear as symbols. Cataloged from PDF version of thesis.Includes bibliographical references (p. 101-105).Spin dependent measurements provide incisive tests for modern theories of particle physics. The discovery that the integral of the quark helicity distribution is much too small to account for the spin of the proton is an excellent case in point. It inspired an intense period of theoretical scrutiny and a new generation of experiments to study [Delta]g, the helicity distribution of gluons in the nucleon. In particular, the unique polarized proton collider at RHIC enables a class of asymmetry measurements that are directly sensitive to gluon polarization. The STAR experiment at RHIC measures the double spin asymmetry A[subscript LL] for a variety of final states in collisions of longitudinally polarized protons in order to constrain [Delta]g. Asymmetries for mid-rapidity charged pion production benefit from large cross sections and the excellent tracking and particle identification capabilities of the STAR Time Projection Chamber. This thesis presents the first measurements of charged pion A[subscript LL] at STAR. The measurements are compared to predictions based on perturbative QCD calculations and from this comparison model-dependent constraints are placed on the integral gluon polarization [Delta]G.by Adam Kocoloski.Ph.D

Indications of Conical Emission of Charged Hadrons at the BNL Relativistic Heavy Ion Collider

Three-particle azimuthal correlation measurements with a high transverse momentum trigger particle are reported for pp, d+Au, and Au+Au collisions at √s[subscript 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 θ=1.37±0.02(stat)[subscript -0.07][superscript +0.06](syst), independent of p[subscript ⊥].Korea Science and Engineering FoundationPolish State Committee for Scientific ResearchSwiss National Science FoundationCSIR of the Government of IndiaDST of the Government of IndiaDAE of the Government of IndiaFOM of the NetherlandsGA of the Czech RepublicIRP of the Czech RepublicMoE of ChinaMoST of ChinaCAS of ChinaNNSFC of ChinaRussian Ministry of Science and TechnologyFAPESP of BrazilEPSRC of the United KingdomSTFC of the United KingdomEMN of FranceRPL of FranceRA of FranceCNRS/IN2P3 of FranceDFG Excellence Cluster EXC153 of GermanyAlfred P. Sloan FoundationNational Science FoundationDepartment of EnergyOffice of High Energy PhysicsOffice of Nuclear Physic

Beam-energy and system-size dependence of dynamical net charge fluctuations

We present measurements of net charge fluctuations in Au+Au collisions at √[subscript s[superscript [NN]]=19.6, 62.4, 130, and 200 GeV, Cu+Cu collisions at √[subscript s[superscript [NN]]=62.4 and 200 GeV, and p+p collisions at √s=200 GeV using the dynamical net charge fluctuations measure ν[subscript +-,dyn]. We observe that the dynamical fluctuations are nonzero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate 1/N[subscript ch] scaling but display approximate 1/N[subscript part] scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.Korea Science and Engineering FoundationPolish State Committee for Scientific ResearchSwiss National Science FoundationCSIR of the Government of IndiaDST of the Government of IndiaDAE of the Government of IndiaFOM of the NetherlandsGA of the Czech RepublicIRP of the Czech RepublicMoE of ChinaMoST of ChinaCAS of ChinaNNSFC of ChinaRussian Ministry of Science and TechnologyFAPESP of BrazilEPSRC of the United KingdomSTFC of the United KingdomEMN of FranceRPL of FranceRA of FranceCNRS/IN2P3 of FranceDFG Excellence Cluster EXC153 of GermanyAlfred P. Sloan FoundationNational Science FoundationDepartment of EnergyOffice of High Energy PhysicsOffice of Nuclear Physic

Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy-ion collisions

Parity (P)-odd domains, corresponding to nontrivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in noncentral collisions. To study this effect, we investigate a three-particle mixed-harmonics azimuthal correlator which is a P-even observable, but directly sensitive to the charge-separation effect. We report measurements of this observable using the STAR detector in Au+Au and Cu+Cu collisions at [sqrt]sNN=200 and 62 GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators and discuss in detail possible contributions from other effects that are not related to P violation.United States. Dept. of Energy. Office of ScienceNational Science FoundationAlfred P. Sloan FoundationDFG Excellence ClusterInstitut National de Physique Nucleaire et Physique des Particules/CNRSScience and Technology Facilities Council, United KingdomEngineering and Physical Sciences Research CouncilFAPESP of BrazilRussian Ministry of Science and TechnologyNational Natural Science Foundation of ChinaChinese National Science FoundationMinistry of Science and Technology of the People's Republic of ChinaMinistry of Education of the People's Republic of ChinaGA of the Czech RepublicIRP of the Czech RepublicFOM of the NetherlandsDAE of the Government of IndiaDST of the Government of IndiaCouncil of Scientific and Industrial Research of IndiaPolish State Committee for Scientific ResearchKorea Science and Engineering Foundatio