 production in p + p collisions in

1. STAR  production in p+p collisions in Manuel Calderón de la Barca Sánchez UC Davis STAR Collaboration 23d Winter Workshop on Nuclear Dynamics Big Sky, Montana 2-15-07

2. Goal: Quarkonia states in A+A Charmonia: J/y, Y’, ccBottomonia: (1S), (2S), (3S) Key Idea: Meltingin the plasma • Color screening of static potential between heavy quarks: • J/y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 (next talk!) Sequential disappearance of states:  Color screening  Deconfinement  QCD thermometer  Properties of QGP When do states really melt? Tdiss(y’)  Tdiss(cc)< Tdiss((3S)) < Tdiss(J/y)  Tdiss((2S)) < Tdiss((1S)) H. Satz, HP2006

3.  :Pros for theory interpretation , ’, ’’ sequential suppression (1S) no melting at RHIC (nor LHC?)  standard candle (reference) (2S) likely to melt at RHIC (analog J/y) (3S) melts at RHIC (analog y’) Pros co-mover absorption negligible recombination negligible at RHIC Both of these affect charmonia, but not bottomonia.

4.  : Experimental Pros and Cons Cons • Mass resolution pushed to the limit • Ratio extraction (2S/1S) and (3S/1S) possible, but difficult • extremely low rate • BR x ds/dy(1s+2s+3s)=91 pb • from NLO calculations. • Luminosity limited (RHIC II will substantially help) • pp Run 6 ~ 9 pb-1 (split into 2 triggered datasets) Pros • Efficient trigger • ~80% • works in p+p up to central A+A! • Large acceptance at midrapidity • Run VI = Run IV x 4 • Small background at M~10 GeV/c2.  STAR’s strength are the  states

5. STAR Detectors Used for  Analysis • EMC • Acceptance: || < 1 , 0 <  < 2 • PID : EMC Tower (energy)  p/E • High-energy tower trigger  enhance high-pT sample • Essential for quarkonia triggers • Luminosity limited for  • TPC • Tracking and dE/dx PID for electrons & positrons

6.  Mass Resolution and expected s • STAR detector does not resolve individual states of the  • Finite p resolution (B=0.5 T) • e-bremsstrahlung • Yield is extracted from combined ++ states • FWHM ≈ 0.7 GeV/c2 W.-M. Yao et al. (PDG), J. Phys. G 33, 1 (2006); R. Vogt et al., RHIC-II Heavy Flavor White Paper

7. STAR  Trigger • Sample -triggered Event • e+e- candidate • mee = 9.5 GeV/c2 • cosθ = -0.67 • E1 = 5.6 GeV • E2 = 3.4 GeV Offline: charged tracks + EMC tower • Fast L0 Trigger (Hardware) • Select events with at least one  high energy tower (E~4 GeV) • L2 trigger (Software) • Clustering, calculate mee, cos q. • Very clean to trigger up to central Au+Au • Offline: Match TPC tracks to triggered towers

8.  Acceptance in STAR • Simulations Run 6 Conditions • Including detector variations: • Calorimeter crates removed/recovered • Hot towers masked • Two Trigger setups: • Acc = 0.272±0.01 for |y|<0.5 (set 1) • Acc = 0.263±0.019 for |y|<0.5 (set 2) • Set 2 used in results shown today.

9.  Trigger Efficiency • Simulation of Trigger response • Level-0: Fast, Hardware Trigger, Cut on Single Tower Et • L0 triggered/accepted = 0.928±0.049 • Level-2: Software Trigger, Cut on invariant mass of tower clusters • L2 triggered/L0 triggered= 0.855±0.048 • Acceptance x Trig Efficiency ~19-21%

10.  Analysis: Electron Id with TPC and EMC e d K p π p electrons preliminary preliminary preliminary •  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 consistent with trigger

11. Electron PID Efficiency and Purity • Electron Pair PID+Tracking efficiency= 0.47±0.07 dE/dx cut dE/dx cut dE/dx cut dE/dx cut

12. STAR  Invariant Mass preliminary preliminary • 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 (0.96 of total) • Peak width consistent with expected mass resolution

13.  Cross Section and Uncertainties preliminary =geo×L0×L2×2(e)×mass • geo : geometrical acceptance • L0 : efficiency of L0 • L2 : efficiency of L2 • (e) : efficiency of e reco • mass: efficiency of mass cut

14. STAR  Cross Section at Midrapidity preliminary

15. STAR  vs. theory and world data preliminary STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data trend Only RHIC peeks at √s=200 GeV range

16. Outlook for Run VII Au+Au Run IV Au+Au Events sampled per day • Yield estimate: • 17 Week run ~ 100 days • Run 4 Performance • 4-20 M events/day • For Run VII: • Assume: • 400 – 2000 M events • 60 mb-1 - 0.3 nb-1 •  cross section in Au+Au • Using • with a=0.9, (AB)a ~ 13,500 • dsAuAu/dy|y=0=91 pb x 13500 = 1.2 mb-1 •  produced at y=0 in dy=1 ~ 73 – 368 •  after acc. & eff. ~ 7 – 37 • Yes, its tough!!! 107 106

17. Summary • 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 • BRee×(dσ/dy)y=0=91±28(stat.)±22(syst.) pb • STAR  measurement is consistent with pQCD and world data trend • Next run: Towards a STAR  cross section in Au+Au collisions at √s=200 GeV

18. Extra Slides

19. STAR J/ Trigger Real Data, p+p Run V preliminary • L0 (hardware) • J/ topology trigger: two towers above ET≈1.2 GeV • Separated by 60° in φ • L2 (software) • Match EMC high tower to CTB slat  photon rejection • Tower clustering • Cut on mee=√2E1E2(1-cosθ) • Cut on cosθ • High background contamination ~1.5 GeV/c • Rejection~100  not sampling full luminosity • Challenging analysis!!! • Efficiency × acceptance ≈ 12%

20. STAR J/ Signal preliminary preliminary • Signal in 200 GeV p+p from 2006 • Tested and working trigger in p+p • No trigger for Au+Au until full ToF in 2009 • Integrated luminosity in 2006: 377 nb-1 • Analysis in progress