Production and Suppression in Heavy Ion Collisions at STAR

Anthony KesichUniversity of California, Davis

STAR Collaboration

February 5, 2013

2

Outline

• Motivation for measuring Upsilons• The Solenoidal Tracker At RHIC and its

triggers• production cross section in p+p• production in d+Au• Nuclear Modification Factor in Au+Au• Suppression Models• Conclusions

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Goal: Quarkonia states in A+ACharmonia: J/Ψ, Ψ’, χc Bottomonia: (1S), (2S), (3S),χB Key Idea: Quarkonia Melt in the plasma

• Color screening of static potential between heavy quarks• Suppression of states is determined by TC and their binding energy• Lattice QCD: Evaluation of spectral functions Tmelting• Originaly proposed by Matsui & Satz (1986)

When do states melt?

February 5, 2013

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Quarkonia at RHIC

• A cleaner probe compared to J/Ψ • co-mover absorption → negligible• recombination → negligible

• σcc = ~800 µb• σbb= ~ 2µb

• Challenge: low rate, rare probe– Large acceptance detector– Efficient trigger

February 5, 2013

Why do at RHIC instead of J/Ψ?

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STAR

EM Calorimeter

•|η| < 1•Full φ coverage•Electron ID via E/p•Event Triggering

Time Projection Chamber

•|η| < 1•Full φ coverage•Tracking and EID via Ionization

February 5, 2013

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Triggering on decays

February 5, 2013

Level 0 Trigger (p+p,d+Au,Au+Au):•Hardware-based•Fires on at least one high tower

Level 2 Trigger (p+p,d+Au):•Software-based•Calculates:• Cluster energies• Opening angle• Mass

High rejection rate allowed us to sample entire luminosity

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in p+p 200 GeV

February 5, 2013

N(total)= 145±26(stat.)

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Statistical error reduced bya factor of 2!

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in p+p 200 GeV, Comparisons

February 5, 2013

STAR √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data trend

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in d+Au 200 GeV

February 5, 2013

∫L dt = 32.6 nb-1

N = 79 ± 17 (stat.) ± 13 (syst.)

Signal has ~8σ significancepT reaches ~8 GeV/c

STAR Preliminary

Efficiency/calibrations under study

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in Au+Au 200 GeV

February 5, 2013

Raw yield of e+e- with |y|<0.5 = 197 ± 36∫L dt ≈ 1400 µb-1

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in Au+Au 200 GeV, Centrality

February 5, 2013

Peripheral Central

STAR Preliminary

STAR Preliminary

STAR Preliminary

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in Au+Au 200 GeV, RAA

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•Strickland uses a dynamic model with fireball expansion and feed-down• Results are consistent with complete 2S and 3S suppression in

this model• Model is assumes a T0 in the range of 428-442 MeV and 1/4π<

η/S < 3/4π•Emerick & Rapp band covers two scenarios:• Binding energy of the Upsilon decreases with T (Weak Binding)• Suppression is due to gluo-dissociation of Upsilon (Strong

Binding)

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Outlook

February 5, 2013

Au+Au @ 200 GeV, 2011• Same setup as in 2010• Double the total luminosity

• Approximately 2.8 nb-1

p+p @ 500 GeV, 2011• High energy doubles Upsilon cross section• Excited-to-ground state ratio• PT spectrum• Approximately 22 pb-1 of data

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Outlook

February 5, 2013

New muon detectors will open up a second, cleaner channelfor Upsilon detection. About 60% of it is currently installed.Important due to increased material in the detector from new vertexer

Statistical Error Projection for Muon Detectors

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Conclusions

• Measured production in p+p, d+Au, and Au+Au collisions at 200 GeV

• Au+Au results consistent with 2S and 3S suppression

• Increased Au+Au statistics from run 11 will further decrease RAA uncertainties

• New muon channel will enhance and compliment our electron measurementsFebruary 5, 2013

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Thank you