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Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX

Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX. Tatsuya Chujo (University of Tsukuba) for the PHENIX collaboration. Outline. 1. Introduction (baryon anomaly at RHIC) 2. Data set and analysis 3. Results (from lower energy RHIC data) p T spectra (Cu+Cu/p+p)

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Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX

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  1. Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX Tatsuya Chujo (University of Tsukuba) for the PHENIX collaboration

  2. Outline 1. Introduction (baryon anomaly at RHIC) 2. Data set and analysis 3. Results (from lower energy RHIC data) • pT spectra (Cu+Cu/p+p) • s dependence of p/ ratios • Centrality dependence of p/ ratios • Nuclear modification factor (RAA) for charged pions, protons, antiprotons. 4. Conclusions

  3. Introduction ~ Baryon Anomaly at RHIC ~ PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004), PRC 74, 024904 (2006) • In Au+Au sNN = 200 GeV central collisions: • RCP (or RAA) • Pions: Strong suppression of yields above pT ~ 2 GeV/c, due to jet quenching effect. • Protons: No suppression for at intermediate pT (2-5 GeV/c). • p/ and p/ ratios • More (anti) baryons than pions at intermediate pT (2-5 GeV/c). • Strong centrality dependence. • Called “Baryon anomaly at RHIC”. • Quark recombination models reproduce the data qualitatively.

  4. What is the definition of baryon anomaly at RHIC? • pT region of interest is the intermediate pT (2.0 - 5.0 GeV/c). • p/ (p/) ratios are much larger than the fragmentation expectations (p+p). • Strong centrality dependence in heavy ion data. • Different nuclear modification factor (RCP or RAA) between pions and (anti)protons. • Pions: suppression. • (anti)protons: no suppression.

  5. Remaining questions • Where is the onset of baryon anomaly at RHIC? • How p/ and p/ ratios and RAA evolve as a function of s and colliding system? • The following low energy data sets have been taken by the PHENIX experiment recently, and they may give us an answer to questions above. • Lower beam energy data in PHENIX. • Au+Au 62.4 GeV (2004) • Cu+Cu 62.4 GeV (2005) • Cu+Cu 22.5 GeV (2005) • p+p 62.4 GeV (2006)

  6. Charged particle identification by TOF 1/ Cu+Cu @ 22.5 GeV Charge x Momentum (GeV/c) PID charged pT spectra analysis in PHENIX • Detectors: • Drift Chamber, PC1, BBC and TOF for PID charged analysis. • Centrality: • Subdivided minimum bias triggered events, based on BBC charge (62 GeV), or the number of PC1 hit (22 GeV). • Corrections: • Geometrical acceptance, in flight decay. • NOTE: No weak decay feed-down correction applied for all plots in this presentation.

  7. pT spectra at low energy Cu+Cu * No weak decay feed-down correction applied. • Antiproton spectra in Cu+Cu 22.5/62.4 GeV. • We also measured pions, protons for both systems.

  8. pT spectra in p+p 62.4 GeV • Data from Run-6 (2006) at RHIC. • Provides an important baseline for pT spectra in Au+Au and Cu+Cu at sNN = 62.4 GeV. • Presented the invariant yields here. • Working on the determination of inelastic cross section and trigger bias in PHENIX experiment for the absolute normalization in pT spectra. * No weak decay feed-down correction applied.

  9. Compilation of p/ ratios (central) * No weak decay feed-down correction applied. p+p 62.4 GeV, set the baseline for HI data. New PHENIX data agrees with ISR data.

  10. Compilation of p/ ratios (central) * No weak decay feed-down correction applied. Cu+Cu 22.5 GeV, p/ ratio in central agree with p+p. Many protons, mostly from participant nucleons.

  11. Compilation of p/ ratios (central) * No weak decay feed-down correction applied. Cu+Cu 62.4 GeV, p/ ratio larger than those in p+p and Cu+Cu 22.5 GeV.

  12. Compilation of p/ ratios (central) * No weak decay feed-down correction applied. Cu+Cu 200 GeV, similar to those in Cu+Cu 62.4 GeV.

  13. Cu+Cu vs. Au+Au

  14. Compilation of p/ ratios (central) * No weak decay feed-down correction applied. Au+Au 62 GeV, p/- is unchanged, p/+ getting larger.

  15. Compilation of p/ ratios (central) * No weak decay feed-down correction applied. Au+Au 200 GeV, p/- is enhanced, p/+ is similar to p/-

  16. Compilation of p/ ratios (peripheral) * No weak decay feed-down correction applied. Peripheral collisions for all systems Conversing to the same line for both p/- and p/+

  17. Centrality dep. of p/ in Cu+Cu 22.5 GeV * No weak decay feed-down correction applied. • More protons transported to mid rap. instead of production for Cu+Cu 22GeV. • Almost no centrality dependence in p/. • p/- ratios are ~0.3-0.4 at pT = 2 GeV/c, which is close to the value in p+p.

  18. Centrality dep. of p/ in Cu+Cu 62.4 GeV * No weak decay feed-down correction applied. • p/+ ratios are reduced, compared to those in Cu+Cu 22 GeV. • p/- ratio in central collisions reaches R=~0.6 at pT = 2 GeV/c. • Centrality dependence is also seen.

  19. sNN dep. of p/- ratio (central) • Increasing • as a function of s. * No weak decay feed-down correction applied.

  20. sNN dep. of p/+ ratio (central) • decreasing as a function of s. * No weak decay feed-down correction applied.

  21. RAA for charged pions (by ISR fit) • Used ISR fit (nucl-ex/0411049, D. d’Enteria) for p+p parameterization. • Using ISR fit: Moderate suppression for Au+Au 62.4 GeV, larger than one for Cu+Cu 62/22 GeV (pT > 2.0 GeV/c). • Error notations: • - Error bars: statistical error for HI spectra • - Boxes: 1) sys. error for p+p reference. 2) sys. error for HI spectra. - Lines: Ncoll error (1.) * No weak decay feed-down correction applied.

  22. RAA for antiprotons (by ISR fit) • Used ISR data at 63 GeV (Alper. NPB 100, 237) for p+p reference. • Similar RAA for all three systems. * No weak decay feed-down correction applied.

  23. RAA for protons (by ISR fit) • Used ISR data at 63 GeV (Alper. NPB 100, 237) for p+p reference. • Largest RAA for Cu+Cu 22.5 GeV. • RAA for Au+Au 62.4 GeV is smaller than that in Cu+Cu 62.4 GeV. * No weak decay feed-down correction applied.

  24. Conclusions • Antiproton is a good probe to study the excitation function of baryon anomaly. • Only antiprotons in Cu+Cu 22.5 GeV system is different from others: • No centrality dependence in p/ ratio at the intermediate pT. • Central 0-10% p/ ratio agrees with the value in p+p collisions. • From 62 GeV Cu+Cu/Au+Au data: • p/- ratio: • Baryon anomaly still exists in central Au+Au “AND” Cu+Cu 62 GeV. • RAA (by ISR fit, limited pT < 2.5 ~ 3.0 GeV/c) • : moderate suppression in Au+Au 62 GeV, unity for Cu+Cu 62 GeV. • p: larger in Cu+Cu than that in Au+Au (baryon transportation). • p: small differences between Cu+Cu and Au+Au, close to one. • To conclude on RAA, it is important to measure the absolute normalized pT spectra in p+p 62.4 GeV. • Summary: Data indicates that an onset of baryon anomaly at RHIC is in between 22 GeV and 62 GeV.

  25. Backup Slides

  26. p/ratios in p+p 62.4 GeV

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