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...

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

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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


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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


52014 年 4 月 20 日

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


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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.


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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


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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


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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


112014 年 4 月 20 日

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


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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


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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


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Inclusive Spectrum Don’t Cover All Information

Negative Charged RCP


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.


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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


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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.


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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.


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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

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Backup


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.

2014 年 4 月 20 日23

Note:The sample data shown here is of J/y, not the usual pi/K/proton


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?

2014 年 4 月 20 日24

charged particles inclusive


2014 年 4 月 20 日25

pion+

proton

anti-proton

AMPT “default model”

All charged inclusive


2014 年 4 月 20 日26

pion+

proton

anti-proton

AMPT “default model”


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?

2014 年 4 月 20 日27

charged particles inclusive


2014 年 4 月 20 日28

pion+

proton

anti-proton


All charged inclusive


2014 年 4 月 20 日29

pion+

proton

anti-proton



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...

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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...