 (  ->ee) production in d+Au collisions at STAR Haidong Liu For the Collaboration

Quark Matter 2009, KnoxvilleHaidong Liu2 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, KnoxvilleHaidong Liu3 Motivations hep-ph/ Dissociation temperatures of quarkonia states Lattice QCD Calculations: T/T C 1/  r  [fm -1 ]  (1S) J/  (1S)  ’(2S)  c (1P)  ’(2S)  b ’(2P)  ’’(3S) TCTC  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, KnoxvilleHaidong Liu4  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) σ signal The cross section in p+p is consistent with pQCD Cross section calculation is in progress

Quark Matter 2009, KnoxvilleHaidong Liu5 STAR  mass resolution in Run8 w/ inner materialw/o inner material High material runs Run6 p+p 200GeV Run7 Au+Au 200GeV Low material run Run8 d+Au 200GeV Runs Integrated Lum. (nb -1 ) p+p5600 Au+Au0.3 d+Au32 It’s a good opportunity to measure  in this high luminosity and low material d+Au run

Quark Matter 2009, KnoxvilleHaidong Liu6 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, KnoxvilleHaidong Liu7 STAR  trigger (BEMC L0+L2) L0 (hardware) Accepting high energy tower of E T >4.3 GeV L2 (software) Select high energy tower cluster pair with E 1 >4.5 && E 2 >3.0 GeV Loose cut on cosθ (θ is the 3D opening angle) Cut on m ee =√2E 1 E 2 (1-cosθ) charged tracks Large acceptance BEMC L0+L2 trigger is a great di-electron trigger for luminosity limited measurements

Quark Matter 2009, KnoxvilleHaidong Liu8 Electron ID with TPC+BEMC 1. Use TPC for charged tracks selection 2.  trigger enhances electrons 3. Use EMC for hadron rejection 4. Electrons identified by dE/dx ionization energy loss in TPC preliminary

Quark Matter 2009, KnoxvilleHaidong Liu9  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 m ee distribution 172 +/- 20 (stat.) Strong signal (8σ significance)

Quark Matter 2009, KnoxvilleHaidong Liu10 Efficiencies  acc 0.34  L0+L  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 system 3.  (TPC reco) is efficiency of e reco in TPC 4.  (eID cut ) is efficiency of eID cuts

Quark Matter 2009, KnoxvilleHaidong Liu11  Cross-section at midrapidity NN 172±20(stat.)  0.15  L dt nb -1 dy1.0

Quark Matter 2009, KnoxvilleHaidong Liu12 Nuclear modification factors CentralityN bin 0~20%15.0 +/ %~100%5.6 +/ ~100%7.5 +/- 0.4 Consistent with N bin scaling STAR Preliminary Not showing Rcp on QM?

Quark Matter 2009, KnoxvilleHaidong Liu13 Summary and outlook First midrapidity measurement of  +  +  → e + e - cross section at RHIC in d+Au collisions at √s=200 GeV Signal significance : 8σ B ee ×(dσ/dy) y=0 =35±4(stat.)nb R dAu =0.98±0.33 ; R cp =1.15±0.40 The cross section in dAu follows N bin 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 GeV pp

Quark Matter 2009, KnoxvilleHaidong Liu14 Backup

Quark Matter 2009, KnoxvilleHaidong Liu15  0~20% NN 45+/-12(stat.)  0.15  L dt 32.66*0.548= 17.9nb -1 dy1.0