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

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 Motivation ➢ STAR Detector and Data Analysis ➢ Results and Discussion ➢ Conclusions QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 2

Introduction ➢ The RHIC Beam Energy Scan (BES) Main Goals: To look for... I. Critical Point II. Phase Transition III.Turn Off of QGP Signatures √s NN (GeV) MB Events (10 6 ) 7.7 4.3 11.5 11.7 19.6 35.8 27 70.4 39 130.4 62.4 67.3 arXiv:1007.2613 QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 3

Nuclear Modification Factors Central AA collisions scaled by peripheral: Central AA collisions scaled by pp: Central AA collisions scaled by pA: QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 4

Motivation ➢ Previous R CP Measurements at RHIC ➢ Clear suppression of high p T particles ➢ Consistent with partonic energy loss models ➢ Key signature of a dense colored medium PhysRevLett.91.172302 QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 5

Motivation ➢ R AA Measurements at LHC ➢ Increased suppression at higher collision energies ➢ Suppression extends to higher transverse momentum arXiv:1012.1004v1 QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 6

Motivation ➢ R CP Measurements at SPS ➢ Attempted to measure R CP at √s NN = 17.3 GeV ➢ Statistics too limited to make a firm statement about the extent of suppression PhysRevC.77.034906 QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 7

The STAR Detector TOF TPC ✔ 2π azimuthal acceptance ✔ |η| < 1 acceptance ✔ Time of Flight measurement ✔ dE/dx measurement QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 8

Particle Identification 1.9 GeV < pT < 2.1 GeV π p K π Particle identification is p K performed using simultaneous TOF (m 2 ) and TPC (dE/dx) fits QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 9

Charged Particle Spectra ➢ Spectra for identified charged particles is extracted at each collision energy STAR Preliminary ➢ Efficiency and energy STAR Preliminary loss corrections are applied QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 10

Positive Charge R CP 0-5% / 60-80% STAR Preliminary QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 11

Negative Charge R CP 0-5% / 60-80% STAR Preliminary QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 12

R AA and R AA/pA 0-5% ➢ Cronin enhancement stronger at high p T STAR Preliminary ➢ Impact on R CP and R AA would be a reduction of apparent suppression p+W reference Phys. Rev. D 19, 764–778 (1979) R AA/pA is meant to be qualitative, the Cronin effect scales in a more complicated way. QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 13

Unidentified R CP STAR Preliminary QM 2012 Poster by Stephen Horvat High p T suppression turns off at lower collision energies. QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 14

Hijing Simulation STAR Preliminary Hijing qualitatively describes trend between energies without jet quenching enabled. QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 15

Discussion ➢ Suppression turns off at lower collision energies ➢ Possible disappearance of QGP? ➢ Cronin effect ➢ Relative contributions of soft STAR Preliminary physics and hard scattering ➢ Model comparisons are necessary QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 16

Conclusions ➢ R CP , R AA , and R AA/pA have been measured over a range of energies ➢ Smooth transition in behavior between energies ➢ Clear turn off of suppression (R CP < 1) has been observed at 27 GeV and below ➢ R CP has varying sensitivity to jet quenching at different collision energies ➢ Further studies are ongoing to disentangle effects QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 17

Backup Slides QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 18

Momentum Resolution ➢ Impact was evaluated using MC events generated from spectra fits to the data The effect is negligible compared to other Most realistic systematics at all energies in the pT region we analyze. QM 2012 Evan Sangaline for the STAR Collaboration (UCD) 19