Single Spin Asymmetry ANA_N in Polarized Proton-Proton Elastic Scattering at s=200\sqrt{s}=200 GeV

We report a high precision measurement of the transverse single spin asymmetry $A_N$ at the center of mass energy $\sqrt{s}=200$ GeV in elastic proton-proton scattering by the STAR experiment at RHIC. The $A_N$ was measured in the four-momentum transfer squared $t$ range $0.003 \leqslant |t| \leqslant 0.035$ \GeVcSq, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of $A_N$ and its $t$-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this $\sqrt{s}$, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure

Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV

We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive Pi0 production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV. The cross section was measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be in good agreement with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T < 11 GeV/c and excludes a maximal positive gluon polarization in the proton. The mean transverse momentum fraction of Pi0's in their parent jets was found to be around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC

High pTp_{T} non-photonic electron production in pp+pp collisions at s\sqrt{s} = 200 GeV

We present the measurement of non-photonic electron production at high transverse momentum ($p_T >$ 2.5 GeV/$c$) in $p$ + $p$ collisions at $\sqrt{s}$ = 200 GeV using data recorded during 2005 and 2008 by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The measured cross-sections from the two runs are consistent with each other despite a large difference in photonic background levels due to different detector configurations. We compare the measured non-photonic electron cross-sections with previously published RHIC data and pQCD calculations. Using the relative contributions of B and D mesons to non-photonic electrons, we determine the integrated cross sections of electrons ($\frac{e^++e^-}{2}$) at 3 GeV/$c < p_T <~$10 GeV/$c$ from bottom and charm meson decays to be ${d\sigma_{(B\to e)+(B\to D \to e)} \over dy_e}|_{y_e=0}$ = 4.0$\pm0.5$({\rm stat.})$\pm1.1$({\rm syst.}) nb and ${d\sigma_{D\to e} \over dy_e}|_{y_e=0}$ = 6.2$\pm0.7$({\rm stat.})$\pm1.5$({\rm syst.}) nb, respectively.Comment: 17 pages, 17 figure

Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at sNN=200\sqrt{s_{NN}} = 200 GeV

We present first measurements of the evolution of the differential transverse momentum correlation function, {\it C}, with collision centrality in Au+Au interactions at $\sqrt{s_{NN}} = 200$ GeV. {\it C} exhibits a strong dependence on collision centrality that is qualitatively similar to that of number correlations previously reported. We use the observed longitudinal broadening of the near-side peak of {\it C} with increasing centrality to estimate the ratio of the shear viscosity to entropy density, $\eta/s$, of the matter formed in central Au+Au interactions. We obtain an upper limit estimate of $\eta/s$ that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.

Longitudinal scaling property of the charge balance function in Au + Au collisions at 200 GeV

We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at 200 GeV using the STAR detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage [-1.3, 1.3]. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes.Comment: 6 pages, 3 figure

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

We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|<0.5) for 0.4 < pT < 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, normalised 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 \sqrt{s_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.Comment: 20 pages and 5 figure

Measurement of the Bottom contribution to non-photonic electron production in p+pp+p collisions at s\sqrt{s} =200 GeV

The contribution of $B$ meson decays to non-photonic electrons, which are mainly produced by the semi-leptonic decays of heavy flavor mesons, in $p+p$ collisions at $\sqrt{s} =$ 200 GeV has been measured using azimuthal correlations between non-photonic electrons and hadrons. The extracted $B$ decay contribution is approximately 50% at a transverse momentum of $p_{T} \geq 5$ GeV/$c$. These measurements constrain the nuclear modification factor for electrons from $B$ and $D$ meson decays. The result indicates that $B$ meson production in heavy ion collisions is also suppressed at high $p_{T}$.Comment: 6 pages, 4 figures, accepted by PR

J/ψ polarization in p+p collisions at s=200 GeV in STAR

AbstractWe report on a polarization measurement of inclusive J/ψ mesons in the di-electron decay channel at mid-rapidity at 2<pT<6 GeV/c in p+p collisions at s=200 GeV. Data were taken with the STAR detector at RHIC. The J/ψ polarization measurement should help to distinguish between different models of the J/ψ production mechanism since they predict different pT dependences of the J/ψ polarization. In this analysis, J/ψ polarization is studied in the helicity frame. The polarization parameter λθ measured at RHIC becomes smaller towards high pT, indicating more longitudinal J/ψ polarization as pT increases. The result is compared with predictions of presently available models

System size dependence of associated yields in hadron-triggered jets

We present results on the system size dependence of high transverse momentum di-hadron correlations at $\sqrt{s_{NN}}$ = 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 ($\Delta\phi\sim0$, $\Delta\eta\sim0$) 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.Comment: 12 pages, 5 figure

J/ψ Production At Low Pt In Au+au And Cu+cu Collisions At Snn =200 Gev With The Star Detector

The J/ψ pT spectrum and nuclear modification factor (RAA) are reported for pT<5GeV/c and |y|<1 from 0% to 60% central Au+Au and Cu+Cu collisions at sNN=200GeV at STAR. A significant suppression of pT-integrated J/ψ production is observed in central Au+Au events. The Cu+Cu data are consistent with no suppression, although the precision is limited by the available statistics. RAA in Au+Au collisions exhibits a strong suppression at low transverse momentum and gradually increases with pT. The data are compared to high-pT STAR results and previously published BNL Relativistic Heavy Ion Collider results. Comparing with model calculations, it is found that the invariant yields at low pT are significantly above hydrodynamic flow predictions but are consistent with models that include color screening and regeneration. © 2014 American Physical Society.902CNRS/IN2P3; NSF; Arthritis National Research Foundation; NRF-2012004024; ANRF; Arthritis National Research FoundationMatsui, T., Satz, H., (1986) Phys Lett. B, 178, p. 416. , PYLBAJ 0370-2693 10.1016/0370-2693(86)91404-8Digal, S., Petreczky, P., Satz, H., (2001) Phys. Rev. D, 64, p. 094015. , 0556-2821 10.1103/PhysRevD.64.094015Karsch, F., Kharzeev, D., Satz, H., Sequential charmonium dissociation (2006) Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 637 (1-2), pp. 75-80. , DOI 10.1016/j.physletb.2006.03.078, PII S037026930600445XBraun-Munzinger, P., Stachel, J., The quest for the quark-gluon plasma (2007) Nature, 448 (7151), pp. 302-309. , DOI 10.1038/nature06080, PII NATURE06080Abreu, M.C., (1999) Phys. Lett. B, 449, p. 128. , (NA38 Collaboration),. PYLBAJ 0370-2693 10.1016/S0370-2693(99)00057-XAbreu, M.C., (1997) Phys. Lett. B, 410, p. 327. , (NA50 Collaboration),. PYLBAJ 0370-2693 10.1016/S0370-2693(97)00914-3Arnaldi, R., Banicz, K., Castor, J., Chaurand, B., Cicalo, C., Colla, A., Cortese, P., Wohri, H.K., J/ψ production in indium-indium collisions at 158GeV/nucleon (2007) Physical Review Letters, 99 (13), p. 132302. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.99.132302&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.99.132302Adare, A., Afanasiev, S., Aidala, C., Ajitanand, N.N., Akiba, Y., Al-Bataineh, H., Alexander, J., Al-Jamel, A., J/ψ production versus centrality, transverse momentum, and rapidity in Au+Au collisions at s NN=200 GeV (2007) Physical Review Letters, 98 (23), p. 232301. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.98.232301&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.98.232301Adamczyk, L., (2013) Phys. Lett. B, 722, p. 55. , (STAR Collaboration),. PYLBAJ 0370-2693 10.1016/j.physletb.2013.04.010Abelev, B., (2012) Phys. Rev. Lett., 109, p. 072301. , (ALICE Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.109.072301Chatrchyan, S., (2012) J. High Energy Phys., (5), p. 063. , (CMS Collaboration),. JHEPFG 1029-8479 10.1007/JHEP05(2012)063Braun-Munzinger, P., Stachel, J., (2000) Phys. Lett. B, 490, p. 196. , PYLBAJ 0370-2693 10.1016/S0370-2693(00)00991-6Grandchamp, L., Rapp, R., (2002) Nucl. Phys. A, 709, p. 415. , NUPABL 0375-9474 10.1016/S0375-9474(02)01027-8Gavin, S., Vogt, R., (1996) Nucl. Phys. A, 610, p. 442. , NUPABL 0375-9474 10.1016/S0375-9474(96)00376-4Capella, A., (1997) Phys. Lett. B, 393, p. 431. , PYLBAJ 0370-2693 10.1016/S0370-2693(96)01650-4Karsch, F., Petronzio, P., (1988) Z. Phys. C, 37, p. 627. , ZPCFD2 0170-9739 10.1007/BF01549724Adare, A., (2012) Phys. Rev. D, 85, p. 092004. , (PHENIX Collaboration),. 10.1103/PhysRevD.85.092004Charm, beauty and charmonium production at HERA-B (2005) European Physical Journal C, 43 (1-4), pp. 179-186. , DOI 10.1140/epjc/s2005-02308-8Vogt, R., Shadowing and absorption effects on J/ψ production in da collisions (2005) Physical Review C - Nuclear Physics, 71 (5), pp. 1-11. , http://oai.aps.org/oai/?verb=ListRecords&metadataPrefix= oai_apsmeta_2&set=journal:PRC:71, DOI 10.1103/PhysRevC.71.054902, 054902Gavin, S., Gyulassy, M., (1988) Phys. Lett. B, 214, p. 241. , PYLBAJ 0370-2693 10.1016/0370-2693(88)91476-1Noble, J.V., (1981) Phys. Rev. Lett., 46, p. 412. , PRLTAO 0031-9007 10.1103/PhysRevLett.46.412Tram, V., Arleo, F., (2009) Eur. Phys. J. C, 61, p. 847. , EPCFFB 1434-6044 10.1140/epjc/s10052-009-0864-yAlde, D., Baer, H., Carey, T., Garvey, G., Klein, A., (1991) Phys. Rev. Lett., 66, p. 133. , PRLTAO 0031-9007 10.1103/PhysRevLett.66.133Leitch, M., (1992) Nucl. Phys. A, 544, p. 197. , (E772 and E789 Collaboration),. NUPABL 0375-9474 10.1016/0375-9474(92) 90574-4Leitch, M., (2000) Phys. Rev. Lett., 84, p. 3256. , (NuSea Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.84.3256Alessandro, B., Alexa, C., Arnaldi, R., Atayan, M., Baglin, C., Baldit, A., Beole, S., Willis, N., Charmonium production and nuclear absorption in p-A interactions at 450 GeV (2004) European Physical Journal C, 33 (1), pp. 31-40. , DOI 10.1140/epjc/s2003-01539-yAlessandro, B., Alexa, C., Arnaldi, R., Atayan, M., Beole, S., Boldea, V., Bordalo, P., Wu, T., A new measurement of J/ψ suppression in Pb-Pb collisions at 158 GeV per nucleon (2005) European Physical Journal C, 39 (3), pp. 335-345. , DOI 10.1140/epjc/s2004-02107-9Arnaldi, R., (2012) Phys. Lett. B, 706, p. 263. , (NA60 Collaboration),. PYLBAJ 0370-2693 10.1016/j.physletb.2011.11.042Adare, A., (2013) Phys. Rev. C, 87, p. 034904. , (PHENIX Collaboration),. 10.1103/PhysRevC.87.034904Adare, A., (2013) Phys. Rev. Lett., 111, p. 202301. , (PHENIX Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.111.202301Adare, A., (2011) Phys. Rev. Lett., 107, p. 142301. , (PHENIX Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.107.142301Zhao, X., Rapp, R., (2010) Phys. Rev. C, 82, p. 064905. , PRVCAN 0556-2813 10.1103/PhysRevC.82.064905Adamczyk, L., (2013) Phys. Rev. Lett., 111, p. 052301. , (STAR Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.111.052301Ackermann, K.H., Adams, N., Adler, C., Ahammed, Z., Ahmad, S., Allgower, C., Amonett, J., Harris, J.W., STAR detector overview (2003) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 499 (2-3), pp. 624-632. , DOI 10.1016/S0168-9002(02)01960-5Llope, W.J., (2004) Nucl. Instrum. Methods Phys. Res., Sect. A, 522, p. 252. , NIMAER 0168-9002 10.1016/j.nima.2003.11.414Adler, C., Denisov, A., Garcia, E., Murray, M., Strobele, H., White, S., The RHIC zero-degree calorimeters (2003) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 499 (2-3), pp. 433-436. , DOI 10.1016/j.nima.2003.08.112Llope, W., (2012) Nucl. Instrum. Methods Phys. Res., Sect. A, 661, pp. S110. , (Suppl. 1),. NIMAER 0168-9002 10.1016/j.nima.2010.07.086Reed, R., (2010) J. Phys.: Conf. Ser., 219, p. 03020. , 1742-6596 10.1088/1742-6596/219/3/032020Beringer, J., (2012) Phys. Rev. D, 86, p. 010001. , (Particle Data Group),. 10.1103/PhysRevD.86.010001Beddo, M., Bielick, E., Fornek, T., Guarino, V., Hill, D., Krueger, K., LeCompte, T., Suaide, A.A.P., The STAR barrel electromagnetic calorimeter (2003) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 499 (2-3), pp. 725-739. , DOI 10.1016/S0168-9002(02)01970-8Miller, M.L., Reygers, K., Sanders, S.J., Steinberg, P., (2007) Annu. Rev. Nucl. Part. Sci., 57, p. 205. , ARPSDF 0163-8998 10.1146/annurev.nucl.57.090506.123020Abelev, B.I., (2009) Phys. Lett. B, 673, p. 183. , (STAR Collaboration),. PYLBAJ 0370-2693 10.1016/j.physletb.2009.02.037Bichsel, H., A method to improve tracking and particle identification in TPCs and silicon detectors (2006) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 562 (1), pp. 154-197. , DOI 10.1016/j.nima.2006.03.009, PII S0168900206005353Shao, M., (2006) Nucl. Instrum. Methods Phys. Res., Sect. A, 558, p. 419. , NIMAER 0168-9002 10.1016/j.nima.2005.11.251Abelev, B.I., (2009) Phys. Rev. C, 79, p. 034909. , (STAR Collaboration),. PRVCAN 0556-2813 10.1103/PhysRevC.79.034909Adamczyk, L., (STAR Collaboration), arXiv:1402.1791Spiridonov, A., arXiv:hep-ex/0510076Abelev, B.I., (2009) Phys. Rev. C, 80, p. 041902. , (STAR Collaboration),. PRVCAN 0556-2813 10.1103/PhysRevC.80.041902Tang, Z., Xu, Y., Ruan, L., Van Buren, G., Wang, F., Xu, Z., (2009) Phys. Rev. C, 79, p. 051901. , PRVCAN 0556-2813 10.1103/PhysRevC.79.051901Tang, Z., Yi, L., Ruan, L., Shao, M., Chen, H., (2013) Chin. Phys. Lett., 30, p. 031201. , CPLEEU 0256-307X 10.1088/0256-307X/30/3/031201Adare, A., (2010) Phys. Rev. D, 82, p. 012001. , (PHENIX Collaboration),. 10.1103/PhysRevD.82.012001Liu, Y., Qu, Z., Xu, N., Zhuang, P., (2009) Phys. Lett. B, 678, p. 72. , PYLBAJ 0370-2693 10.1016/j.physletb.2009.06.006Heinz, U.W., Shen, C., (private communication)Adare, A., (2008) Phys. Rev. Lett., 101, p. 122301. , (PHENIX Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.101.122301Adams, J., (2003) Phys. Rev. Lett, 91, p. 172302. , (STAR Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.91.172302Adare, A., Afanasiev, S., Aidala, C., Ajitanand, N.N., Akiba, Y., Al-Bataineh, H., Alexander, J., Aoki, K., J/ψ Production versus transverse momentum and rapidity in p+p collisions at s=200GeV (2007) Physical Review Letters, 98 (23), p. 232002. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.98.232002&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.98.232002Zhao, X., Rapp, R., (2008) Phys. Lett. B, 664, p. 253. , PYLBAJ 0370-2693 10.1016/j.physletb.2008.03.06