 production in p+p and Au+Au collisions in STAR Debasish Das UC 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 T C and their binding energy Lattice QCD: Evaluation of spectral functions  T melting Deconfinement  Color screening  heavy quarkonia states “dissolved” T diss (  ’)  T diss (  c )< T diss (  (3S)) < T diss (J/  )  T diss (  (2S)) < T diss (  (1S))‏ Their suppression pattern is a thermometer of the QCD matter produced. H. Satz, HP2006

3  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 /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

4 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/c 2 W/o Inner Tracker : Low X/X 0 With Inner Tracker : small X/X 0 ~6%

5 EMC Acceptance: |  | < 1, 0 <  < 2  High-energy tower trigger  enhance high-p T 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.

6 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 - m ee = 9.5 GeV/c 2 cosθ = E 1 = 5.6 GeV E 2 = 3.4 GeV charged tracks

7 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 - m ee = 9.5 GeV/c 2 (offline mass)‏ cosθ = -0.77(offline opening angle)‏ E 1 = 6.6 GeV (online cluster energy hardware trigger)‏ E 2 = 3.2 GeV (online cluster energy software trigger)‏ charged tracks Electron Momentum > 3 GeV/c Challenging analysis!!!!!

8 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 Peak width consistent with expected mass resolution Significance of signal is 3σ Note: Contribution from Drell-Yan (~9%) ignored preliminary QM 2006:  in Run 6 p+p at √s=200 GeV: Invariant Mass

9 STAR 2006 √s=200 GeV p+p  +  +  →e + e - cross section consistent with pQCD and world data prelimina ry QM 2006 : STAR  vs. Theory and World Data

10 R AA : Upper Limit  R AA < 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

11 Strong 4  signal First measurement of  in nucleus-nucleus collisions ever Too early for R AA 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/B Cons:trigger efficiency and systematic checks not completed yet

12 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 –B ee ×(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: –R AA 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

13 Thanks!!!