(->ee) production in d+Au collisions at STAR

Haidong Liu

For the Collaboration

Quark Matter 2009, Knoxville Haidong Liu 2

Outline

Motivations measurements in p+p &

Au+Au STAR detectors and the trigger Electron identification signals in d+Au Cross section and the nuclear

modification factors Summary

Quark Matter 2009, Knoxville Haidong Liu 3

Motivations

hep-ph/0110406

Dissociation temperatures of quarkonia states

Lattice QCD Calculations:

T/TC 1/r [fm-1]

(1S)

J/(1S) ’(2S)

c(1P) ’ (2S)b’(2P)’’(3S)TC

2

1.2

b(1P)

Quarkonia’s suppression patterns

QGP thermometer

For the production at RHIC A cleaner probe compare to J/psi

co-mover absorption negligible recombination negligible at RHIC

Anti-shadowing at midrapidity in dAu

rare rate -> need large acceptance and efficient trigger

At RHIC energy (1S) no melting (2S) likely to melt (3S) melts

A .Mocsy, 417th WE-Heraeus-Seminar,2008

Quark Matter 2009, Knoxville Haidong Liu 4

Measurements in pp & AuAu

preliminary

p+p J. Phys. G: Nucl. Part. Phys. 34(2007)S947

Au+Au J. Phys. G: Nucl. Part. Phys. 35(2008)104153

pb(syst.)(stat.)dy

dσB

Υ''Υ'Υ

y

ee 2228910

3σ signal

The cross section in p+p is consistent with

pQCD

Cross section calculation is in progress

Quark Matter 2009, Knoxville Haidong Liu 5

STAR mass resolution in Run8

w/ inner material w/o inner material

•High material runs •Run6 p+p 200GeV•Run7 Au+Au 200GeV

•Low material run•Run8 d+Au 200GeV

Runs

IntegratedLum. (nb-

1)

p+p 5600

Au+Au

0.3

d+Au 32

It’s a good opportunity to measure in this

high luminosity and low material d+Au run

Quark Matter 2009, Knoxville Haidong Liu 6

STAR detector for measurement

• BEMC

• Acceptance: || < 1 , 0 < < 2• eID (E/p)

• High-energy tower trigger =>essential for the luminosity limited measurement

• TPC

• Acceptance: || < 1 , 0 < < 2• Tracking => momentum

• eID (ionization energy loss)

e+ + e-

Quark Matter 2009, Knoxville Haidong Liu 7

STAR trigger (BEMC L0+L2)

L0 (hardware) Accepting high energy tower of

ET>4.3 GeV L2 (software)

Select high energy tower cluster pair with E1>4.5 && E2>3.0 GeV

Loose cut on cosθ (θ is the 3D opening angle)

Cut on mee=√2E1E2(1-cosθ)

charged tracksLarge acceptance BEMC L0+L2 trigger is a great di-electron trigger for luminosity limited

measurements

Quark Matter 2009, Knoxville Haidong Liu 8

Electron ID with TPC+BEMC

1. Use TPC for charged tracks selection2. trigger enhances electrons 3. Use EMC for hadron rejection4. Electrons identified by dE/dx

ionization energy loss in TPC

preliminary preliminary

Quark Matter 2009, Knoxville Haidong Liu 9

signal in d+Au 200 GeV collisions

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 172 +/- 20 (stat.) Strong signal (8σ significance)

Quark Matter 2009, Knoxville Haidong Liu 10

Efficiencies

dtdy

N

dy

dB

y

eeL

0

acc 0.34

L0+L2 0.71

2(TPC reco) 0.72

2(eID cut ) 0.87

0.15

=acc×L0+L2×2(TPC reco)×2 (eID cut )

1. acc is the efficiency of EMC detector and the geometrical acceptance

2. L0+L2 is the efficiency trigger system3. (TPC reco) is efficiency of e reco in TPC4. (eID cut ) is efficiency of eID cuts

Quark Matter 2009, Knoxville Haidong Liu 11

Cross-section at midrapidity

N 172±20(stat.)

0.15

Ldt 32.66 nb-1

dy 1.0

(nb) 435dy

dσB

Υ"Υ'Υ

0y

ee

Quark Matter 2009, Knoxville Haidong Liu 12

Nuclear modification factors

(stat.) 0.401.15 R

(stat.) 0.330.98R

cp

dAu

42mbσ 2.2bσ ppdAu

Centrality Nbin

0~20% 15.0 +/- 0.3

20%~100% 5.6 +/- 0.3

0~100% 7.5 +/- 0.4

Consistent with Nbin scaling

Υ"Υ'Υ

0y

ppee

Υ"Υ'Υ

0y

dAuee

dAu

dy

dσB

dydσ

B

R

pp

dAubinN

1

STAR Preliminary STAR PreliminarySTAR Preliminary

Not showing Rcp on QM?

Quark Matter 2009, Knoxville Haidong Liu 13

Summary and outlook First midrapidity measurement of ++→e+e-

cross section at RHIC in d+Au collisions at √s=200 GeV Signal significance : 8σ Bee×(dσ/dy)y=0=35±4(stat.)nb RdAu =0.98±0.33 ; Rcp =1.15±0.40 The cross section in dAu follows Nbin scaling

STAR is a powerful detector to measure Large acceptance TPC+EMC Efficient trigger (L0+L2)

measurements in the future RHIC II – high luminosity will allow separation of 1S,

2S, 3S states 50pb-1 200 GeV pp

Quark Matter 2009, Knoxville Haidong Liu 14

Backup

Quark Matter 2009, Knoxville Haidong Liu 15

0~20%

4.02.12.0

1

Υ"Υ'Υ

0y

ppee

Υ"Υ'Υ

0y

dAuee

dAu

dy

dσB

dy

dσB

R

pp

dAubinN

N45+/-12(stat.)

0.15

Ldt32.66*0.548= 17.9nb-1

dy 1.0

42mbσ 2.2bσ ppdAu