带电粒子多重数在 RHIC 对碰撞 能量的依赖 裴 骅 华中师范大学

Outline  STAR Detector  Beam Energy Scan  Nuclear Modification Factors (R CP )  Charged hadron R CP at STAR  Suppression at high p T  Cronin enhancement at low beam energies  Identified charged hadron R CP results from STAR  Model comparisons 2014 年 4 月 20 日 2 中国物理学会高能物理分会第九届全国代表大会

Is there a critical point? if so, where? Is there evidence for a first order phase transition? Both questions above can benefit from a new one: At what energy do key QGP signatures turn off? Beam Energy Scan at RHIC 2014 年 4 月 20 日 3 中国物理学会高能物理分会第九届全国代表大会

upVPD Magnet TOF BEMC BBC EEMC TPC © Maria & Alex Schmah The Solenoid Tracker At RHIC (STAR) TPC: |η| < 1 & 2π in azimuth TOF: |η| <0.9 & 2π in azimuth 2014 年 4 月 20 日 4 中国物理学会高能物理分会第九届全国代表大会

2014 年 4 月 20 日 5 CentralPeripheral slopes ~ equal at different beam energies slopes different -- stronger dependence on beam energy Charged Particle Spectra 中国物理学会高能物理分会第九届全国代表大会 |  |<0.5

R AA : The Nuclear Modification Factor p + p Au + Au Phys. Rev. Lett. 96, (2006) Phys. Rev. Lett. 91, (2003) Strong suppression at central Au+Au collision Peripheral Au+Au collision shows similar yields as p+p 2014 年 4 月 20 日 6 中国物理学会高能物理分会第九届全国代表大会

R AA : The Nuclear Modification Factor  And so is R CP Phys. Rev. Lett. 96, (2006) Phys. Rev. Lett. 91, (2003) Strong suppression at central Au+Au collision Peripheral Au+Au collision shows similar yields as p+p Applied such observable when we don’t have p+p reference 年 4 月 20 日 7 中国物理学会高能物理分会第九届全国代表大会

h + + h - Result of R AA : Suppression and Enhancement Stephen Horvat and Evan Sangaline, QM2012 Lower energies strongly enhanced Suppressed at large  s NN Enhancement at low  s NN 2014 年 4 月 20 日 8 中国物理学会高能物理分会第九届全国代表大会

Result of R AA : Suppression  Quenching The ‘Cronin Effect’ can be observed as the enhancement of spectra in asymmetric collisions relative to a p+p reference CNM effects depend on the presence of a heavy nuclei A significant QGP is unlikely to be formed in d + Au collisions Can this suppression observed in Au+Au at 200GeV co-exist with a CNM effect ? deuteron + Au at 200GeV ‘Suppression’ ≡ R CP < 1 ‘Quenching’ ≡ loss of energy for high momentum particles Phys. Rev. Lett. 91 (2003) 年 4 月 20 日 9 中国物理学会高能物理分会第九届全国代表大会

Introduction of Models: HIJING HIJING captures the collision-energy dependence 200GeV has odd low p T behavior Generally overestimates R CP DATAHIJING N bin Stephen Horvat: CPOD 年 4 月 20 日 10 中国物理学会高能物理分会第九届全国代表大会

2014 年 4 月 20 日 11 Compare data with AMPT models We know already that AMPT have been successful in reproducing spectra/flow in 200 GeV RHIC data, where QGP is desirable. We are then motivated to test AMPT models in the broad range of BES energy levels, and compare with STAR data. 中国物理学会高能物理分会第九届全国代表大会

Introduction of Models: AMPT (Default) AMPT Default (String-melting off) Fails to match data －－ Minimal beam energy dependence Sharp turn over near 2.5GeV/c, possibly due to AMPT’s hadronic transport model dominating at low p T DATA N bin AMPT 2014 年 4 月 20 日 12 中国物理学会高能物理分会第九届全国代表大会

Introduction of Models: AMPT (String Melting) AMPT String Melting Recovers beam energy dependence But didn’t capture the p T dependence very well DATA N bin AMPT 2014 年 4 月 20 日 13 中国物理学会高能物理分会第九届全国代表大会

Inclusive Spectrum Don’t Cover All Information Positive Charged R CP Evan Sangaline, QM2012 The R CP shows a clear dependency on the PID 2014 年 4 月 20 日 14 中国物理学会高能物理分会第九届全国代表大会

Inclusive Spectrum Don’t Cover All Information Negative Charged R CP 2014 年 4 月 20 日 15 中国物理学会高能物理分会第九届全国代表大会 Evan Sangaline, QM2012 The R CP shows a clear dependency on the PID

10mb “Default model” AMPT “default model” PID:  +/K+/proton Reference from AMPT default The “default” AMPT model shows relatively weaker mass dependence or the collision energy dependence in the identified spectra R CP, either 年 4 月 20 日 16 中国物理学会高能物理分会第九届全国代表大会

10mb “Default model” Reference from AMPT default The “default” AMPT model shows relatively weaker mass dependence or the collision energy dependence in the identified spectra R CP, either. AMPT “default model” PID:  -/K-/anti-proton 2014 年 4 月 20 日 17 中国物理学会高能物理分会第九届全国代表大会

AMPT 10mb “String melting model” PID:  +/K+/proton For pion and Kaon, the “string- melting” AMPT model show the PID (mass?) ordering of R CP as STAR data. However the evolution of proton R CP is less evident than STAR data at p T ~ 2 GeV/c. The string-melting AMPT still does a relatively better job in reproducing the identified hadron R CP result, but far from being satisfying 年 4 月 20 日 18 中国物理学会高能物理分会第九届全国代表大会

For pion and Kaon, the “string- melting” AMPT model show the PID (mass?) ordering of R CP as STAR data. However the evolution of anti- proton R CP is VERY DIFFERENT to STAR data at p T ~ 2 GeV/c. AMPT 10mb “String melting model” PID:  -/K-/anti-proton The string-melting AMPT still does a relatively better job in reproducing the identified hadron R CP result, but far from being satisfying 年 4 月 20 日 19 中国物理学会高能物理分会第九届全国代表大会

Conclusions: Clear energy ordering is observed in the data.  Charged RCP is suppressed in high  s NN RHIC data.  At the lower beam energies the R CP is strongly enhanced. Neither AMPT nor HIJING fully matches the measured spectra  AMPT spectra depends on the specific model selected, i.e., string-melting  HIJING has a strong  s NN dependence, similar to the data Look into PID comparisons model: necessary to do so Outlook: Additional models and tunes may allow us to disentangle the relative contributions of quenching and enhancement See more news the QM2014 talks ! 2014 年 4 月 20 日 20 中国物理学会高能物理分会第九届全国代表大会

Backup 2014 年 4 月 20 日 21 中国物理学会高能物理分会第九届全国代表大会

2014 年 4 月 20 日 22 中国物理学会高能物理分会第九届全国代表大会

Further study of spectra Nucl.Phys.A834:249c-252c,2010  If transition happens from partonic matter to hadronic DOF dominated collision dynamics at low  s NN, the radial flow and/or Cronin effect may play an important role.  In addition to R AA and R CP, we expect an evolution pattern in the relative mean p T and p T 2 as function of center-of-mass collision energy 年 4 月 20 日 23 Note: The sample data shown here is of J/ , not the usual pi/K/proton 中国物理学会高能物理分会第九届全国代表大会

The energy and centrality dependence of p T : and RMS (within [0, 3] GeV) AMPT “default model”  A clear dependence of centrality is observed, but less evident for  s NN.  Relative at 0-5% increases with collision energy.  Proof of stronger radial flow and/or Cronin effect at most-central and high  s NN ?  Relative RMS at 0-5% slightly decreases with collision energy.  Proof of stronger broadening at most-central and low  s NN ? 2014 年 4 月 20 日 24 charged particles inclusive 中国物理学会高能物理分会第九届全国代表大会

2014 年 4 月 20 日 25  pion+  proton  anti-proton AMPT “default model” All charged inclusive 中国物理学会高能物理分会第九届全国代表大会

2014 年 4 月 20 日 26  pion+  proton  anti-proton AMPT “default model” 中国物理学会高能物理分会第九届全国代表大会

The energy and centrality dependence of p T : and RMS (within [0, 3] GeV) AMPT 10mb “string-melting model”  No clear dependence of centrality or  s NN is observed.  Can this be a mismatch with the experimental data? 2014 年 4 月 20 日 27 charged particles inclusive 中国物理学会高能物理分会第九届全国代表大会

2014 年 4 月 20 日 28  pion+  proton  anti-proton AMPT 10mb “string-melting model” All charged inclusive 中国物理学会高能物理分会第九届全国代表大会

2014 年 4 月 20 日 29  pion+  proton  anti-proton AMPT 10mb “string-melting model” 中国物理学会高能物理分会第九届全国代表大会