Charged Hadron Nuclear Modification Factors in the Beam Energy Scan data from STAR Stephen Horvat for the STAR collaboration Yale University Stephen HorvatCPOD 2013, Napa, California, March 20131

Contents Stephen HorvatCPOD 2013, Napa, California, March STAR Detector Beam Energy Scan Nuclear Modification Factors (R CP ) Physics –jets as probes –Cronin enhancement R CP Results –charged hadrons –identified hadrons x T scaling Conclusions

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

Is there a critical point and if so where? Is there evidence for a first order phase transition? At what energy do key QGP signatures turn off? nuclear modification factor dihadron correlations ncq scaling Beam Energy Scan 4CPOD 2013, Napa, California, March 2013Stephen Horvat

Data YearN event MB M M M M M M M 5Stephen HorvatCPOD 2013, Napa, California, March 2013

Nuclear Modification Factor p + p Au + Au Peripheral 6 Au + Au Central N bin ≡ number of binary collisions (from Glauber) hard scatterings produce early high p T probes CPOD 2013, Napa, California, March 2013Stephen Horvat

Suppression of high p T Phys. Rev. Lett. 91, (2003) 7 ‘Suppression’ ≡ R CP < 1 ‘Quenching’ ≡ loss of energy for high momentum particles CPOD 2013, Napa, California, March 2013Stephen Horvat STAR AuAu200

The ‘Cronin Effect’ is the experimentally observed enhancement of spectra in asymmetric collisions relative to a p+p reference d+Au for Cold Nuclear Matter (CNM) Physics Letters B 637 (2006) 161–169 The suppression observed at 200GeV is not a CNM effect Protons are more enhanced than pions  maybe pions are better probes? 8CPOD 2013, Napa, California, March 2013Stephen Horvat Protons Pions dAu200

Expectations for the BES 9CPOD 2013, Napa, California, March 2013Stephen Horvat

Results - Spectra STAR Preliminary Peripheral spectra shows stronger dependence on beam energy % 60-80% CPOD 2013, Napa, California, March 2013Stephen Horvat CentralPeripheral Statistical errors only slopes ~ equalslopes different

Results - R CP 11CPOD 2013, Napa, California, March 2013Stephen Horvat h + + h -

To Measure Quenching This motivates alternative methods to investigate quenching 1.species dependence through identified-particle R CP 2.comparison to models 3.variations from scaling patterns 12CPOD 2013, Napa, California, March 2013Stephen Horvat

PID Spectra STAR Preliminary Statistical errors only 13CPOD 2013, Napa, California, March 2013Stephen Horvat 0-5% 60-80% π+π+ p K+K+ π+π+ K+K+ p p T (GeV/c)

PID R CP Positive particles QM CPOD 2013, Napa, California, March 2013Stephen Horvat STAR Preliminary

PID R CP Negative particles QM CPOD 2013, Napa, California, March 2013Stephen Horvat STAR Preliminary

PID R CP Pions are less enhanced than protons A higher p T reach may reveal suppression for additional beam energies Anti-proton R CP is lower than protons at low momentum –annihilation? Kaon behavior is complex (or strange☺) –no obvious mass ordering for all energies Stephen HorvatCPOD 2013, Napa, California, March

Models HIJING –jet quenching on or off –modeled as -dE/dx within the medium –default Lund splitting parameters a=0.5,b=0.9 AMPT v1.21/v2.21(uses HIJING 1.383) –string melting (SM) off uses Lund string fragmentation for hadronization (v1.21) –SM on uses quark coalescence for hadronization (v2.21) –default Lund splitting parameters a=2.2, b=0.5 Stephen HorvatCPOD 2013, Napa, California, March Lund fragmentation formula:

HIJING quenching on Similar behavior to data 200GeV has odd low p T behavior Generally overestimates R CP 18CPOD 2013, Napa, California, March 2013Stephen Horvat DATAHIJING N bin

HIJING quenching off 200GeV better behaved at low p T 7.7GeV barely changed from quenching on 19CPOD 2013, Napa, California, March 2013Stephen Horvat DATAHIJING N bin

AMPT SM off Minimal beam energy dependence Sharp turn over near 2.5GeV/c 20CPOD 2013, Napa, California, March 2013Stephen Horvat DATAAMPT N bin

AMPT SM on Recovers beam energy dependence Limited p T reach (same number of simulated events for SM on/off) 21CPOD 2013, Napa, California, March 2013Stephen Horvat DATAAMPT N bin

HIJING quenching on, alt HIJING with AMPT’s Lund splitting parameters Small effect to R CP from different parameters 22CPOD 2013, Napa, California, March 2013Stephen Horvat HIJING N bin N coll

HIJING quenching on, alt 23CPOD 2013, Napa, California, March 2013Stephen Horvat central spectra ratio peripheral spectra ratio R CP HIJING Lund values ____________________________________________ R CP AMPT Lund values Spectra for central and peripheral are altered by similar amounts when fragmentation parameters are changed

Model summary HIJING captures beam energy dependence of spectra Jet quenching as modeled in HIJING has a greater effect on higher beam energies For AMPT, lower beam energies are better matched by SM off, while SM on better captures the beam energy dependence –physics of hadronization shifts from coalescence to fragmentation? Stephen HorvatCPOD 2013, Napa, California, March

Alternative Scaling 25 Physics Letters B 637 (2006) 161–169 CPOD 2013, Napa, California, March 2013Stephen Horvat

x T scaling STAR Preliminary Stat. errors only 26CPOD 2013, Napa, California, March 2013Stephen Horvat There may be centrality dependence to the exponent (6.5±0.8)

Scaling the y-axis STAR Preliminary Stat. errors only 27CPOD 2013, Napa, California, March 2013Stephen Horvat

Outlook Triggered dihadron correlations provide another method to detect jet-quenching and give another signature for the formation of a QGP p+p data from several BES energies would provide a cleaner reference. Combined with d+Au data, the relative contributions from CNM effects and quenching may be disentangled Additional models and tunes may improve our understanding of the data by quantifying the relative contributions of quenching and enhancement 28CPOD 2013, Napa, California, March 2013Stephen Horvat

Conclusions 29CPOD 2013, Napa, California, March 2013Stephen Horvat

CPOD 2013, Napa, California, March Thank you!

Model statistics YearN event MBAMPTAMPT SMHIJINGHIJING QoffHIJING alternate Lund M1.2M 5.2M2.2M4.3M M1.2M 2.5M500k9.3M M1.2M 970k1.7M1M M1.2M 1M1.4M950k M1.2M1.0M1M 800k M1.2M1.0M1M M1.3M1.0M1M 31Stephen HorvatCPOD 2013, Napa, California, March 2013

PHENIX QM2012 PHENIX and STAR results are not completely consistent STAR sees greater enhancement of central pion spectra for p T <5GeV/c T. Sakaguchi, D.C. STAR PHENIX

Cronin’s result Some beam energy dependence for the Cronin Effect was previously observed PRL 68, 452 (1992) Straub et al. 33 R(p+W)/(p+Be) p T (GeV/c) CPOD 2013, Napa, California, March 2013Stephen Horvat

Effect of quenching in HIJING Stephen HorvatCPOD 2013, Napa, California, March

HIJING quenching on/off Central 0-5% ratioPeripheral 60-80% ratio Spectra Ratios As might be expected, quenching mostly effects central spectra Stephen HorvatCPOD 2013, Napa, California, March

HIJING quenching on/data 36CPOD 2013, Napa, California, March 2013Stephen Horvat central spectra ratio peripheral spectra ratio R CP HIJING Quenching on _______________________________________________ R CP Data Spectra for central and peripheral from data disagree with model

HIJING quenching off/data 37CPOD 2013, Napa, California, March 2013Stephen Horvat central spectra ratio peripheral spectra ratio R CP HIJING Quenching off _______________________________________________ R CP Data Spectra for central and peripheral from data disagree with model

HIJING quenching Lund/data 38CPOD 2013, Napa, California, March 2013Stephen Horvat central spectra ratio peripheral spectra ratio R CP HIJING w/ AMPT Lund par. _______________________________________________ R CP Data Spectra for central and peripheral from data disagree with model

AMPT SM off/data 39CPOD 2013, Napa, California, March 2013Stephen Horvat central spectra ratio peripheral spectra ratio R CP SM off _________________________________ R CP Data Spectra for central and peripheral from data disagree with model

AMPT SM on/data 40CPOD 2013, Napa, California, March 2013Stephen Horvat central spectra ratio peripheral spectra ratio R CP SM on ____________________________ R CP Data Spectra for central and peripheral from data disagree with model

Stephen HorvatCPOD 2013, Napa, California, March

Stephen HorvatCPOD 2013, Napa, California, March