Quarkonium Physics with STAR

Mauro Cosentino

(University of Sao Paulo/BNL)

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Why Quarkonia ?

Using F1: S. Digal, P. Petreczky, H. Satz, Phys. Lett. B514 (2001) 57Using V1: C.-Y. Wong, hep-ph/0408020

– Key Idea: Melting in the plasma

• Suppression of states is determined by TC and their binding energy

• Color screening Deconfinement

• QCD thermometer Properties of QGP

Is the sequential suppression pattern the smoking gun?

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The STAR DetectorTPC: || < 1, 0 < < 2ToF: -1 < < 0, = 0.1

EMC: || < 1, 0 < < 2Mag.Field: 0.5 T

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Golden Decay Mode :

Need:Electron IDHadron RejectionTrigger

Typical electron p range for:J/: 1-3 GeV/c: > 3.5 GeV/c

eeQQ

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Electron Identification• Association of TPC and BEMC information

– TPC gives dE/dx and momentum (p)– BEMC gives the energy (E)– Selected particles are within specifics dE/dx and p/E ranges.

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J/ TriggerLevel-0 (topology):

• Φ divided in 6 sections• Find a tower above

threshold (E > 1.2 GeV)• Look for other towers

above threshold on the 3 opposite sections

Level-2 (software): • Full EMC tower data available• Towers clustering → Ee

• CTB matching (veto photons)• Vertex: BBC resolution ~6cm

for Au+Au, 30cm for p+p• Invariant mass assuming

straight tracks: m2inv

2E1E2[1-cos(12)]

• Trigger for minv > 2.5 GeV/c2

• Decision is taking up to 500s

This J/ trigger setup is efficient only for p+pAu+Au will require ToF upgrade

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Trigger Implementation• L0 Trigger

– Simple single high tower trigger ET>3.5 GeV

• L2 Trigger– Use similar L2 to J/

• Very efficient > 80%• Large rejection power

– 100 at L0– 100 at L2

• Luminosity limited • Works in p+p and central

Au+Au• Exploit full STAR

acceptance, 2 & ||<1

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Results J/

J/ data, Gaussian Fit and simulation line shape. Cross-section calculation being reviewed, but preliminary results consistent with

pQCD calculations and PHENIX measurement.

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Results STAR cannot resolve different S states (1S+2S+3S) e+e-

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Cu+Cu analysisThe same analysis for p+p was applied to Cu+Cu@200 GeV data, but without simulations and embedding, no cross-sections quoted

No specific triggers. For the a high-tower threshold of 3.75 GeV mimetized the L0 –trigger.

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STAR Contribution• Large Acceptance at Mid-Rapidity

– ||<1, 0<<2– Pair acceptance~(single acceptance)2

• Electron identification capabilities– TPC dE/dx– EMC E>1-2 GeV (operating full barrel)– TOF p<2-3 GeV/c

• Trigger capabilities on Barrel EMC– Suitable for single electron (see F. Laue’s talk)– Suitable for di-electrons(?)

• Heavy-Quarkonia states are rare : efficient trigger for all systems– J/trigger in p+p only, need large min. bias. dataset in Au+Au

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Efficiency and Purity of the Id

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J/ in Au+Au (Run IV)

• No trigger due to high background

• Dataset: Au+Au@200 GeV

• Just a faint signal• For efficient J/

trigger, full barrel ToF is needed (just patch in Run IV)

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Analysis for Au+Au: Upper Limit

• 90% C.L.: signal < 4.91• B*d/dy C.L. < 7.6 b• Acceptance increase will help (Factor ~4)

Scaling from Au+Au to elementary: =1

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ToF Upgrade

Construction FY 06 – FY 08

23,000 channels covering TPC & Barrel Calorimeter

Will allow to deploy J/ trigger in Au+AuCoincidence: ToF slat + EMC tower

substantially reduces photon background

MRPC Time of Flight Barrel in STAR

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Origin of J/ suppression on SPS

Assume:

1. NJ/(observed) = 0.6 NJ/ + 0.4 Nc (compatible w Hera-B data)

2. J/ doesn’t melt

3. c dissociation = ’ dissociation

Right or wrong, it shows how important

the missing cc measurement is!

F. Karsch, D. Kharzeev, H. Satz, hep-ph/0512239

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EXTRA: trigger pre-calibration for BEMC

• Online energy resolution ~ 17%/√E

• Offline energy resolution ~ 14 %/√E