R CP Measurements of Identified and Unidentified Charged Particles - - PowerPoint PPT Presentation

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R CP Measurements of Identified and Unidentified Charged Particles at High p T in Au+Au Collisions at s NN = 7.7 62.4 GeV in STAR Evan Sangaline for the STAR Collaboration UC Davis August 16th, 2012 Outline Introduction and

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RCP Measurements of Identified and Unidentified Charged Particles at High pT in Au+Au Collisions at √sNN = 7.7 – 62.4 GeV in STAR

Evan Sangaline

for the STAR Collaboration

UC Davis

August 16th, 2012

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QM 2012 Evan Sangaline for the STAR Collaboration (UCD)

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Outline

➢ Introduction and Motivation ➢ STAR Detector and Data Analysis ➢ Results and Discussion ➢ Conclusions

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QM 2012 Evan Sangaline for the STAR Collaboration (UCD)

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Introduction

➢ The RHIC Beam Energy Scan (BES)

arXiv:1007.2613

Main Goals:

  • I. Critical Point
  • II. Phase Transition

III.Turn Off of QGP Signatures

To look for... √sNN (GeV) MB Events (106)

7.7 4.3 11.5 11.7 19.6 35.8 27 70.4 39 130.4 62.4 67.3

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QM 2012 Evan Sangaline for the STAR Collaboration (UCD)

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Nuclear Modification Factors

Central AA collisions scaled by peripheral: Central AA collisions scaled by pp: Central AA collisions scaled by pA:

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Motivation

➢ Previous RCP Measurements at RHIC

PhysRevLett.91.172302

➢Clear suppression

  • f high pT particles

➢Consistent with

partonic energy loss models

➢Key signature of a

dense colored medium

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QM 2012 Evan Sangaline for the STAR Collaboration (UCD)

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Motivation

arXiv:1012.1004v1

➢ RAA Measurements at LHC

➢Increased suppression

at higher collision energies

➢Suppression extends to

higher transverse momentum

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Motivation

➢ RCP Measurements at SPS

PhysRevC.77.034906

➢Attempted to measure

RCP at √sNN = 17.3 GeV

➢Statistics too limited to

make a firm statement about the extent of suppression

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The STAR Detector

✔2π azimuthal acceptance ✔|η| < 1 acceptance ✔Time of Flight measurement ✔dE/dx measurement

TOF TPC

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Particle Identification

Particle identification is performed using simultaneous TOF (m2) and TPC (dE/dx) fits

π K p π K p

1.9 GeV < pT < 2.1 GeV

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Charged Particle Spectra

➢ Spectra for identified

charged particles is extracted at each collision energy

➢ Efficiency and energy

loss corrections are applied

STAR Preliminary STAR Preliminary

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Positive Charge RCP

STAR Preliminary 0-5% / 60-80%

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Negative Charge RCP

STAR Preliminary 0-5% / 60-80%

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RAA and RAA/pA

p+W reference

  • Phys. Rev. D 19, 764–778 (1979)

➢ Cronin

enhancement stronger at high pT

➢ Impact on RCP

and RAA would be a reduction

  • f apparent

suppression

STAR Preliminary 0-5%

RAA/pA is meant to be qualitative, the Cronin effect scales in a more complicated way.

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Unidentified RCP

High pT suppression turns off at lower collision energies.

STAR Preliminary QM 2012 Poster by Stephen Horvat

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Hijing Simulation

Hijing qualitatively describes trend between energies without jet quenching enabled.

STAR Preliminary

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Discussion

➢ Suppression turns off at

lower collision energies

➢ Possible disappearance of

QGP?

➢ Cronin effect ➢ Relative contributions of soft

physics and hard scattering

STAR Preliminary

➢Model comparisons are necessary

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Conclusions

➢ RCP, RAA, and RAA/pA have been measured over a

range of energies

➢ Smooth transition in behavior between energies ➢ Clear turn off of suppression (RCP < 1) has been

  • bserved at 27 GeV and below

➢ RCP has varying sensitivity to jet quenching at different

collision energies

➢ Further studies are ongoing to disentangle effects

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Backup Slides

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Momentum Resolution

➢ Impact was evaluated using MC events

generated from spectra fits to the data The effect is negligible compared to

  • ther

systematics at all energies in the pT region we analyze.

Most realistic