production in p+p and Au+Au collisions in STAR

Debasish DasUC Davis

(For the STAR Collaboration)

2/17

Charmonia: J/, ’, c Bottomonia: (1S), (2S), (3S)

Quarkonia and the concept of suppression

Heavy quarks carry the information of early stage of collisions:

• Charm and bottom quarks are massive.• Formation takes place early only in the collision.

Proposed Signature : QCD phase transition Color screening of static potential between heavy quarks: J/suppression: Matsui and Satz, Phys. Lett. B 178 (1986) 416

– Suppression of states is determined by TC and their binding energyLattice QCD: Evaluation of spectral functions Tmelting

Deconfinement Color screening heavy quarkonia states “dissolved”

Tdiss(’) Tdiss(c)< Tdiss((3S)) < Tdiss(J/) Tdiss((2S)) < Tdiss((1S))

Their suppression pattern is a thermometer of the QCD matter produced.

H. Satz, HP2006

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States in RHIC

S), S), S)• (1S) no melting at RHIC standard

candle (reference)• (2S) likely to melt at RHIC (analogous

to J/)• (3S) melts at RHIC (analogous to ’)

measurements at RHIC challenge to understand such rare probes

Cons– extremely low rate 10-9/min.

bias pp interaction– need good resolution to

separate three S-states

Pros– co-mover absorption is very

small ( C.M.Ko PLB 503, 104)

– recombination negligible at RHIC (

bb <<

cc)

– STAR has efficient trigger and large acceptance

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STAR Mass Resolution

• STAR detector is able to resolve individual states of albeit Bremsstrahlung• With current low statistics, yield is extracted from combined (1S+2S+3S) states• FWHM ~ 400 MeV/c2

W/o Inner Tracker : Low X/X

0

With Inner Tracker : small X/X0~6%

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• EMC

• Acceptance: || < 1 , 0 < < 2• High-energy tower trigger

enhance high-pT sample

• Essential for quarkonia triggers

trigger enhances electrons– Use TPC for charged tracks

selection– Use EMC for hadron rejection– Electrons identified by dE/dx

ionization energy loss in TPC– Select tracks with TPC, match to

EMC towers above 3 GeV

STAR Detectors used for measurements

Au+Au Event in STAR Trigger.

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STAR Trigger (p+p 200 GeV in Run 6)

• Full EMC acceptance |η|<1 in run 6• Integrated luminosity ≈ 9 pb-1 in run 6

Sample -triggered Event• e+e-

• mee = 9.5 GeV/c2

• cosθ = -0.67• E1 = 5.6 GeV• E2 = 3.4 GeV

charged tracks

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STAR Trigger (Au+Au 200 GeV in Run 7)

•Full EMC acceptance |η|<1 in Run 7•Integrated luminosity ≈ 300 μb-1 in Run 7

Sample -triggered Event• e+e-

• mee = 9.5 GeV/c2 (offline mass)• cosθ = -0.77(offline opening angle)• E1 = 6.6 GeV (online cluster energy hardware trigger)• E2 = 3.2 GeV (online cluster energy software trigger)

charged tracks

Electron M

omentum > 3 GeV/c

Challenging

analysis!!!!!

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• Signal + Background unlike-sign electron pairs• Background like-sign electron pairs (1S+2S+3S) total yield:

integrated from 7 to 11 GeV from background-subtracted mee distribution

• Peak width consistent with expected mass resolution• Significance of signal is 3σ• Note: Contribution from Drell-Yan (~9%) ignored

preliminary

pre

limin

ary

QM 2006: in Run 6 p+p at √s=200 GeV: Invariant Mass

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STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data

pre

limin

ary

QM 2006 : STAR vs. Theory and World Data

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RAA : Upper Limit RAA< 1.3 at 90% CL

in Au+Au at √s = 200 GeV (Run 7)

First Rough Look: Using identical cuts as in p+p analysis. Pros : allows “apples-to-apples” comparison with p+p Cons : not optimal for Au+Au

– larger background, different trigger thresholds

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• Strong 4 signal• First measurement of in nucleus-nucleus collisions ever• Too early for RAA but will provide good first measurement

– also need re-analysis of p+p

in Au+Au at √s = 200 GeV (Run 7)Improved Analysis: Pros: improved EMC-track-trigger handling

strong signal and enhanced S/BCons: trigger efficiency and systematic checks not completed yet

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Summary and Outlook

• Full EMC + trigger quarkonium program in STAR

• Run 6: first mid-rapidity measurement of S+2S+3S)→e+e- cross section at RHIC in p+p collisions at √s=200 GeV

– Bee×(dσ/dy)y=0=91±28(stat.)±22(syst.) pb

– STAR in p+p measurement is consistent with pQCD and world data

• Run 7: We have the first measurement in heavy ion collisions

for 200 GeV Au+Au

– Strong signal

• Soon:

– RAA of

– Run 8: measurement in d+Au

– Absolute cross-section in p+p, d+Au, and Au+Au

• RHIC II : 20 nb-1 will allow separation of 1S, 2S, 3S states

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Thanks!!!