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Particle Production in Au+Au Collisions at 9.2GeV

Particle Production in Au+Au Collisions at 9.2GeV. http://drupal.star.bnl.gov/STAR/starnotes/public/sn0493. Jiayun Chen (for Collaboration) Institute of Particle Physics, CCNU, Wuhan, 430079, P.R.China Brookhaven National Lab, Upton, NY,11973, USA. Outline. Motivation

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Particle Production in Au+Au Collisions at 9.2GeV

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  1. Particle Production in Au+Au Collisions at 9.2GeV http://drupal.star.bnl.gov/STAR/starnotes/public/sn0493 Jiayun Chen (for Collaboration) Institute of Particle Physics, CCNU, Wuhan, 430079, P.R.China Brookhaven National Lab, Upton, NY,11973, USA

  2. Outline • Motivation • STAR preliminary 9.2 GeV results • Particle identification in TPC • Charged multiplicity • Azimuthal anisotropy • PID spectra and ratios：energy, centrality • Charged pion interferometry • Summary and outlook Jiayun Chen for STAR -CPOD2009

  3. Lessons from 200GeV • Strong high pT suppression in hadron production. • Number of Constituent Quark scaling in v2measurements • Indicate the existence of sQGP. Phys. Rev. Lett. 92, 052302 (2004) Phys. Rev. C 72, 014904 (2005) Phys. Rev. Lett. 95, 122301(2005) Phys. Rev. Lett. 92, 112301(2004) Phys. Rev. Lett. 91, 072304 (2003) Jiayun Chen for STAR -CPOD2009

  4. Motivation • QCD theory predicts: • • Low B& High T :Cross-over • • High B& Low T:1st order transition • • Mid B& Mid T :Critical Point • Plan :Access to phase diagram • T and B vary with √sNN • Signatures • Locating the phase boundaries • Locating the critical point NSAC 2007 Long-range Plan Aim of this talk is to discuss the results from successful data taking in STAR with Au+Au collisions at 9.2 GeV. Demonstrate our readiness for the future Beam Energy Scan program at RHIC. Jiayun Chen for STAR -CPOD2009

  5. STAR Detector |η|<1.5 2.5<|η|<4.0 Jiayun Chen for STAR -CPOD2009

  6. Collisions @ 9.2 GeV • STAR TPC display: Au+Au at 9.2GeV Non-central Central • ~ 3000 good events collected at • ~ 0.6 Hz in year 2008 • Data taking period lasted for < 5 hr. • In the future, ToF will further enhance the PID Jiayun Chen for STAR -CPOD2009

  7. Collider Acceptance Fixed Jiayun Chen for STAR -CPOD2009

  8. Charged Multiplicity • Collision Centrality Selection • With more events STAR will map out centrality (system-size) in detail. • Changes in fluctuations with system-size can indicate the presence of a 1st order phase transition. • Track selection for various analysis Jiayun Chen for STAR -CPOD2009

  9. Azimuthal Anisotropy Coordinate-Space Anisotropy Momentum-Space Anisotropy interactions pressure gradient  collective flow • This is believed to be due to pressure gradients in the dense medium which lead to collective motion. • Directed flow (v1) at forward rapidities describes the “side-splash”, the foremost early collective motion of the system; • Elliptic flow (v2) demonstrated the development of collectivity • Provide insights into the EOS. Jiayun Chen for STAR -CPOD2009

  10. Directed Flow v1 • two methods to analyze the data • ‘standard’ event plane method • - v1{FTPC,EP1} • - v1{BBC,EP1} • mixed event plane method • -v1{EP1,EP2} STAR Preliminary STAR Preliminary Results from two methods are consistent. Jiayun Chen for STAR -CPOD2009

  11. Directed Flow v1 At mid-rapidity, all the results have comparable values. At forward rapidity, the trend of v1 from low energy is different from high energies. This is due to early longitudinal collision dynamics. V1 values lie on a common trend. STAR Preliminary STAR : PRL 92 (2004) 062301 PRL101（2008）252301 NA49: PRC68(2003)034903 11 Jiayun Chen for STAR -CPOD2009

  12. Elliptic Flow • STAR and NA49 results seem to be consistent. • STAR 9.2GeV v2 nicely fits into the observed trends. STAR Preliminary STAR Preliminary Lokesh Kumar QM2009, SQM2008 NA49 : PRC 68 (2003) 034903 AGS : PLB 474 (2000) 27 STAR : PRC 77 (2008) 054901 : PRC 75 (2007) 054906, PRC 72 (2005) 014904 PHOBOS : PRC 72 (2005) 051901 : PRL 98 (2007) 242302 PHENIX : PRL 98 (2007) 162301 Jiayun Chen for STAR -CPOD2009

  13. pT Spectra We measure within our pT acceptance ~ 82 % of total  produced ~ 47 % of total K produced ~ 75 % of total p produced • The slope of the identified hadron spectra follow the order p<k<p • These spectra can be further characterized by looking at the dN/dy and <pT> or <mT> STAR Preliminary Jiayun Chen for STAR -CPOD2009

  14. Yield &<mT> vs. Energy • Yield and <mT> beam energy dependence are consistent with the published data • Assuming a thermo-dynamic system : T ~ <mT> - m entropy ~ dN/dy  log(√sNN) NA49 : PRC 66 (2002) 054902, PRC 77 (2008) 024903 PRC 73 (2006) 044910 STAR : PRC 79 (2009) 034909, arXiv: 0903.4702 E802(AGS) : PRC 58 (1998) 3523, PRC 60 (1999) 044904 E877(AGS) : PRC 62 (2000) 024901 E895(AGS) : PRC 68 (2003) 054903 STAR Preliminary Jiayun Chen for STAR -CPOD2009

  15. Particle Ratios vs. centrality p  • K-/K+ & K-/-are lower in 9.2GeV compared to that in 200 and 62.4 GeV; • K+/ +in 9.2 GeV is comparable to that in 200 and 62.4 GeV --K+ production is dominated by associated production in low energy. • p/in 9.2 GeV is larger compared to 200 and 62.4 GeV -- shows large baryon stopping at low energy; • Ratios seem to be almost independent of collision centrality for all energies studied. K K STAR Preliminary STAR Preliminary STAR : PRC 79 (2009) 034909 Jiayun Chen for STAR -CPOD2009

  16. Particle Ratio vs. Energy STAR Preliminary K/K+  _ p/p K/ NA49 : PRC 66 (2002) 054902, PRC 77 (2008) 024903, PRC 73 (2006) 044910 E802(AGS) : PRC 58 (1998) 3523, PRC 60 (1999) 044904, PRC 62 (2000) 024901, PRC 68 (2003) 054903 STAR : PRC 79 (2009) 034909, arXiv: 0903.4702 Jiayun Chen for STAR -CPOD2009

  17. Pion Interferometry Centrality : 0 - 60% Error bars for Au+Au 9.2 GeV are statistical Systematic errors expected to be < 10 % for all radii KT=[0.15,0.25](GeV/c) STAR preliminary - Source parameters : • All are consistent with the previously observed trends D. Das for STAR Collaboration WWND 09 E802 : PRC 66 (2002) 054906 CERES : NPA 714 (2003) 124 E895 :PRL 84 (2000 ) 2798 PHOBOS : PRC 73 (2006) 031901 NA44 : PRC 58 (1998) 1656 E866 : NPA 661 (1999) 439 NA49 : PRC 77 (2008) 064908 WA97 : JPG 27 (2001) 2325 STAR : PRC 71 (2005) 044906, PRL 87 (2001) 082301 PHENIX : PRL 88 (2002) 192302, PRL 93(2004) 152302 Jiayun Chen for STAR -CPOD2009

  18. Summary Azimuthal Anisotropy (v1 and v2) results are similar to those obtained at SPS from collisions at similar energies Identified particle spectra obtained from Au+Au collisions at 9.2 GeV. Centrality and beam energy dependence of the hadron yields and ratios studied. In central collisions anti-proton to proton ratio ~ 0.01 shows significant baryon stopping in these collisions In central collisions K-/K+ ~ 0.4 shows associated production for K+ p/ ratio is higher and K-/- is lower at 9.2 GeV compared to 200 GeV at all collision centralities studied Pion interferometry results follow the established beam energy trends Jiayun Chen for STAR -CPOD2009

  19. STAR BES Program Key measurements: PID hadron spectra, ratios, v2… Fluctuations: - Net-pKurtosis - K/ - <pT>, <N> … See Daniel Cebra’s talk ” STAR plans for the RHIC low energy run” Jiayun Chen for STAR -CPOD2009

  20. Outlook • The results from the lowest beam energy collisions at RHIC demonstrate STAR experiment’s readiness to collect high quality data for the proposed Critical Point Search Program. • Large and uniform acceptance for all beam energies in a collider set up, excellent particle identification (TPC+TOF) and higher statistics will lead to significant advance in the Critical Point search: • Differential analyses of pT and number correlations for identified particles -- vs Df and Dh to identify the source and nature of observed non-statistical fluctuations • System-size dependence of fluctuations (1st order phase transition?) • Charge separation of K/pand P/p fluctuations • Higher moments of net-charge and net-proton distributions • Azimuthal HBT • Critical Point Search Program will allow us to explore the QCD phase diagram. Jiayun Chen for STAR -CPOD2009

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