1. Quark Matter 2006 (2006.11.18) Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX Tatsuya Chujo (University of Tsukuba) for the PHENIX collaboration Tatsuya Chujo (University of Tsukuba) for the PHENIX collaboration

2. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 2 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)  s dependence of p/  ratios Centrality dependence of p/  ratios Nuclear modification factor (R AA ) for charged pions, protons, antiprotons. 4. Conclusions 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)  s dependence of p/  ratios Centrality dependence of p/  ratios Nuclear modification factor (R AA ) for charged pions, protons, antiprotons. 4. Conclusions

3. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 3 Introduction ~ Baryon Anomaly at RHIC ~ PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004), PRC 74, 024904 (2006) In Au+Au  s NN = 200 GeV central collisions: R CP (or R AA ) Pions: Strong suppression of yields above p T ~ 2 GeV/c, due to jet quenching effect. Protons: No suppression for at intermediate p T (2-5 GeV/c). p/  and  p/  ratios More (anti) baryons than pions at intermediate p T (2-5 GeV/c). Strong centrality dependence. Called “Baryon anomaly at RHIC”. Quark recombination models reproduce the data qualitatively.

4. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 4 What is the definition of baryon anomaly at RHIC? p T region of interest is the intermediate p T (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 (R CP or R AA ) between pions and (anti)protons. Pions: suppression. (anti)protons: no suppression. p T region of interest is the intermediate p T (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 (R CP or R AA ) between pions and (anti)protons. Pions: suppression. (anti)protons: no suppression.

5. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 5 Remaining questions Where is the onset of baryon anomaly at RHIC? How p/   and  p/   ratios and R AA 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) Where is the onset of baryon anomaly at RHIC? How p/   and  p/   ratios and R AA 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. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 6 PID charged p T 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. 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. Charged particle identification by TOF Charge x Momentum (GeV/c) 1/  Cu+Cu @ 22.5 GeV

7. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 7 p T spectra at low energy Cu+Cu Antiproton spectra in Cu+Cu 22.5/62.4 GeV. We also measured pions, protons for both systems. * No weak decay feed-down correction applied.

8. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 8 p T spectra in p+p 62.4 GeV Data from Run-6 (2006) at RHIC. Provides an important baseline for p T spectra in Au+Au and Cu+Cu at  s NN = 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 p T spectra. * No weak decay feed-down correction applied.

9. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 9 Compilation of p/  ratios (central) p+p 62.4 GeV, set the baseline for HI data. New PHENIX data agrees with ISR data. * No weak decay feed-down correction applied.

10. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 10 Compilation of p/  ratios (central) Cu+Cu 22.5 GeV,  p/   ratio in central agree with p+p. Many protons, mostly from participant nucleons. * No weak decay feed-down correction applied.

11. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 11 Compilation of p/  ratios (central) Cu+Cu 62.4 GeV,  p/   ratio larger than those in p+p and Cu+Cu 22.5 GeV. * No weak decay feed-down correction applied.

12. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 12 Compilation of p/  ratios (central) Cu+Cu 200 GeV, similar to those in Cu+Cu 62.4 GeV. * No weak decay feed-down correction applied.

13. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 13 Cu+Cu vs. Au+Au

14. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 14 Compilation of p/  ratios (central) Au+Au 62 GeV,  p/  - is unchanged, p/  + getting larger. * No weak decay feed-down correction applied.

15. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 15 Compilation of p/  ratios (central) Au+Au 200 GeV,  p/  - is enhanced, p/  + is similar to  p/  - * No weak decay feed-down correction applied.

16. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 16 Compilation of p/  ratios (peripheral) Peripheral collisions for all systems Conversing to the same line for both  p/  - and p/  + * No weak decay feed-down correction applied.

17. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 17 Centrality dep. of p/  in Cu+Cu 22.5 GeV 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 p T = 2 GeV/c, which is close to the value in p+p. * No weak decay feed-down correction applied.

18. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 18 p/  + ratios are reduced, compared to those in Cu+Cu 22 GeV.  p/  - ratio in central collisions reaches R=~0.6 at p T = 2 GeV/c. Centrality dependence is also seen. Centrality dep. of p/  in Cu+Cu 62.4 GeV * No weak decay feed-down correction applied.

19. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 19  s NN dep. of  p/  - ratio (central) Increasing as a function of  s. * No weak decay feed-down correction applied.

20. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 20  s NN dep. of p/  + ratio (central) decreasing as a function of  s. * No weak decay feed-down correction applied.

21. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 21 R AA for charged pions (by ISR fit) Error notations: - Error bars: statistical error for HI spectra - Boxes: 1) sys. error for p+p reference. 2) sys. error for HI spectra. - Lines: N coll error (1 .) 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 (p T > 2.0 GeV/c). * No weak decay feed-down correction applied.

22. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 22 R AA for antiprotons (by ISR fit) Used ISR data at 63 GeV (Alper. NPB 100, 237) for p+p reference. Similar R AA for all three systems. * No weak decay feed-down correction applied.

23. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 23 R AA for protons (by ISR fit) Used ISR data at 63 GeV (Alper. NPB 100, 237) for p+p reference. Largest R AA for Cu+Cu 22.5 GeV. R AA for Au+Au 62.4 GeV is smaller than that in Cu+Cu 62.4 GeV. * No weak decay feed-down correction applied.

24. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 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 p T. – 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. R AA (by ISR fit, limited p T < 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 R AA, it is important to measure the absolute normalized p T 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. 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 p T. – 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. R AA (by ISR fit, limited p T < 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 R AA, it is important to measure the absolute normalized p T 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. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 25

26. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 26 Backup Slides

27. Tatsuya Chujo Quark Matter 2006 (2006.11.18) 27 p/   ratios in p+p 62.4 GeV