Post on 17-Dec-2015
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Outline
STAR Detector
Beam Energy Scan
Nuclear Modification Factors (RCP)
Charged hadron RCP at STAR
Suppression at high pT
Cronin enhancement at low beam energies
Identified charged hadron RCP results from STAR
Model comparisons
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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• 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 中国物理学会高能物理分会第九届全国代表大会
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upVPD
Magnet
TOFBEMC
BBC
EEMCTPC
© Maria & Alex Schmah
The Solenoid Tracker At RHIC (STAR)
TPC: |η| < 1 & 2π in azimuthTOF: |η| <0.9 & 2π in azimuth
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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Central Peripheral
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
|h|<0.5 |h|<0.5
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RAA: The Nuclear Modification Factor
p + p
Au + Au
Phys. Rev. Lett. 96, 202301 (2006)
Phys. Rev. Lett. 91, 172302 (2003)
Strong suppression at central Au+Au collision
Peripheral Au+Au collision shows similar yields as p+p
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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RAA: The Nuclear Modification Factor And so is RCP Phys. Rev. Lett. 96, 202301 (2006)
Phys. Rev. Lett. 91, 172302 (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.
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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h+ + h-
Result of RAA: Suppression and Enhancement
Stephen Horvat and Evan Sangaline, QM2012 Lower energies strongly
enhanced
Suppressed at large sNN
Enhancement at low sNN
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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Result of RAA: 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’ ≡ RCP < 1‘Quenching’ ≡ loss of energy for high momentum particles
Phys. Rev. Lett. 91 (2003) 072304
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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Introduction of Models: HIJING
• HIJING captures the collision-energy dependence• 200GeV has odd low pT behavior• Generally overestimates RCP
DATA HIJINGNbin
Stephen Horvat: CPOD2013
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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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.
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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 pT
DATA
Nbin
AMPT
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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Introduction of Models: AMPT (String Melting)
AMPT String Melting
• Recovers beam energy dependence
• But didn’t capture the pT dependence very well
DATANbin
AMPT
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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Inclusive Spectrum Don’t Cover All Information
Positive Charged RCP
Evan Sangaline, QM2012
The RCP shows a clear dependency on the PID
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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Inclusive Spectrum Don’t Cover All Information
Negative Charged RCP
2014 年 4 月 20 日 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 RCP shows a clear dependency on the PID
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10mb “Default model”
AMPT“default model”
PID: p+/K+/proton
Reference from AMPT default
The “default” AMPT model shows relatively weaker mass dependence or the collision energy dependence in the identified spectra RCP, either.
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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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 RCP, either.
AMPT“default model”
PID: p-/K-/anti-proton
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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AMPT 10mb“String melting model”
PID: p+/K+/proton
For pion and Kaon, the “string-melting” AMPT model show the PID (mass?) ordering of RCP as STAR data.
However the evolution of proton RCP is less evident than STAR data at pT ~ 2 GeV/c.
The string-melting AMPT still does a relatively better job in reproducing the identified hadron RCP result, but far from being satisfying.
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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For pion and Kaon, the “string-melting” AMPT model show the PID (mass?) ordering of RCP as STAR data.
However the evolution of anti-proton RCP is VERY DIFFERENT to STAR data at pT ~ 2 GeV/c.
AMPT 10mb“String melting model”
PID: p-/K-/anti-proton
The string-melting AMPT still does a relatively better job in reproducing the identified hadron RCP result, but far from being satisfying.
2014 年 4 月 20 日 中国物理学会高能物理分会第九届全国代表大会
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Conclusions:
• Clear energy ordering is observed in the data.
Charged RCP is suppressed in high sNN RHIC data.
At the lower beam energies the RCP 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 sNN 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 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 sNN, the radial flow and/or Cronin effect may play an important role.
In addition to RAA and RCP, we expect an evolution pattern in the relative mean pT and pT
2 as function of center-of-mass collision energy.
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Note:The sample data shown here is of J/y, 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 pT: <pT
2> and RMS (within [0, 3] GeV)AMPT “default model”
A clear dependence of centrality is observed, but less evident for sNN .
Relative <pT2> at 0-5% increases with collision energy. Proof of
stronger radial flow and/or Cronin effect at most-central and high sNN?
Relative RMS at 0-5% slightly decreases with collision energy. Proof of stronger broadening at most-central and low sNN?
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charged particles inclusive
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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
The energy and centrality dependence of pT: <pT
2> and RMS (within [0, 3] GeV)
AMPT 10mb “string-melting model”
No clear dependence of centrality or sNN is observed.
Can this be a mismatch with the experimental data?
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charged particles inclusive
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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