Upsilon production in STAR

Pibero DjawothoIndiana University Cyclotron Facility

October 12, 2007

DNP 2007

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

Key Idea: Melting in the plasma• 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 energy

• Lattice QCD: Evaluation of spectral functions Tmelting

– Sequential disappearance of states: Color screening Deconfinement

QCD thermometer Properties of QGP

H. Satz, HP2006

When do states really melt?Tdiss(’) Tdiss(c)< Tdiss((3S)) < Tdiss(J/) Tdiss((2S)) < Tdiss((1S))

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and J/ States in STARJ/, ’• J/ likely to melt at RHIC• ’ melts at RHICPros• moderate rate• J/ and ’ can be separatedCons• co-mover absorption affects

yield• recombination affects yield• trigger only in pp (still low eff.)• moderate electron PID in J/

momentum range

, ’, ’’ (1S) no melting at RHIC

standard candle (reference) (2S) likely to melt at RHIC

(analog J/) (3S) melts at RHIC (analog ’)Pros• co-mover absorption negligible• recombination negligible at RHIC• STAR efficient trigger and large

acceptanceCons• extremely low rate• need good resolution to separate 3

S states

STAR’s strength are the states

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STAR Detectors Used for Quarkonia

• EMC

• Acceptance: || < 1 , 0 < < 2• PID with EMC detectors

• Tower (energy) p/E

• High-energy tower trigger enhance high-pT sample

• Essential for quarkonia triggers

• Luminosity limited for

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STAR Trigger

• Similar L0+L2 triggers– Higher mass state higher energy

threshold

– Pros: Easier and cleaner to trigger

– Cons: Small yield; need large luminosity and acceptance

• 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 Mass Resolution

State Mass [GeV/c2] Bee [%] (dσ/dy)y=0 Bee×(dσ/dy)y=0

9.46030 2.38 2.6 nb 62 pb

10.02326 1.91 0.87 nb 17 pb

10.3552 2.18 0.53 nb 12 pb

++ 91 pb

• STAR detector is able to resolve individual states of the albeit:– Finite p resolution– e-bremsstrahlung

• Yield is extracted from combined ++ states

• FWHM ≈ 1 GeV/c2

W.-M. Yao et al. (PDG), J. Phys. G 33, 1 (2006);R. Vogt et al., RHIC-II Heavy Flavor White Paper

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Analysis: Electron ID with TPC and EMC

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

pre

lim

ina

ry

electrons

K p d

preliminary

preliminary

e

π

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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

preliminary

pre

limin

ary

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

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in Run 6 p+p at √s=200 GeV:Cross Section

dtdy

N

dy

dB

y

eeL

0

geo 0.263±0.019

L0 0.928±0.049

L2 0.855±0.048

2(e) 0.47±0.07

mass 0.96±0.04

0.094±0.018

=geo×L0×L2×2(e)×mass

geo is geometrical acceptanceL0 is efficiency of L0 triggerL2 is efficiency of L2 trigger(e) is efficiency of e recomass is efficiency of mass cut

preliminary

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STAR Run 6 Cross Section in p+p at Midrapidity at √s=200 GeV

N 48±15(stat.)

0.094±0.018

Ldt (5.6±0.8) pb-1

dy 1.0

pb(syst.)22(stat.)2891dy

dσB

Υ"Υ'Υ

0y

ee

pre

limin

ary

11

pb22(syst.)28(stat.)91dy

dσB

'Υ'Υ'Υ

0y

ee

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

pre

limin

ary

STAR vs. Theory and World Data

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Past: in Run 4 Au+Au at √sNN=200 GeV• Cannot resolve different S states

(1S+2S+3S) e+e-

• STAR– Large acceptance (|| < 1, full

EMC) – PID for electrons (EMC, TPC)– Trigger

• Very efficient > 80%– Luminosity limited

triggerthreshold No N+++N--

subtracted

Scaling from Au+Au to elementary: =1

• First look in 2004: ½ EMC, little statistics

• 90% C.L.: signal < 4.91• B·d/dy C.L. < 7.6 b

STAR Preliminary

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Rare Trig Int Lumi Goal=600ub-1

0.00

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3/29/2007

4/8/2007

4/18/2007

4/28/2007

5/8/2007

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5/28/2007

6/7/2007

6/17/2007

6/27/2007

7/7/2007

Future:Run 7 Au+Au at √sNN=200 GeV Trigger

• 605.69 μb-1 integrated luminosity for L2-upsilon during Run 7

• ~37 expected at y=0 for |y|<0.5 or ~70 for |y|<1. Assume:– S/B=48/83 significance

3.3σ from 2006 p+p at √s=200 GeV

– Binary scaling and nuclear effects σAB=σpp(AB)α

preliminary

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Summary and Outlook

• Full EMC + trigger quarkonium program in STAR• Run 6: first midrapidity measurement of

++→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: expect cross section at midrapidity in Au+Au collisions at √s=200 GeV (37-70 raw yield) and nuclear modification factor RAA