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 production in p+p and Au+Au collisions in STAR

Debasish Das UC Davis (For the STAR Collaboration) ‏.  production in p+p and Au+Au collisions in STAR. Quarkonia and the concept of suppression. Charmonia : J/  ,  ’,  c Bottomonia :  (1S),  (2S),  (3S) ‏. Heavy quarks carry the information of early stage of collisions:

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 production in p+p and Au+Au collisions in STAR

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  1. Debasish Das UC Davis (For theSTAR Collaboration)‏  production in p+p and Au+Au collisions in STAR

  2. Quarkonia and the concept of suppression Charmonia: J/, ’, cBottomonia:  (1S), (2S), (3S)‏ • 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 TC and their binding energy Lattice QCD: Evaluation of spectral functions  Tmelting • Deconfinement  Color screening heavy quarkonia states “dissolved” • Tdiss(’)  Tdiss(c)< Tdiss((3S)) < Tdiss(J/)  Tdiss((2S)) < Tdiss((1S))‏ Their suppression pattern is a thermometer of the QCD matter produced. H. Satz, HP2006 2/17

  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 ’)‏ • 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 Cons • extremely low rate 10-9/min. bias pp interaction • need good resolution to separate three S-states  measurements at RHIC  challenge to understand such rare probes

  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/c2 With Inner Tracker : small X/X0~6% W/o Inner Tracker : Low X/X0

  5. STAR Detectors used for  measurements Au+Au  Event in STAR Trigger. • EMC • Acceptance: || < 1 , 0 <  < 2 • High-energy tower trigger  enhance high-pT 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

  6. STAR  Trigger (p+p 200 GeV 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 • Full EMC acceptance |η|<1 in run 6 • Integrated luminosity ≈ 9 pb-1 in run 6

  7. STAR  Trigger (Au+Au 200 GeV in Run 7)‏ Sample -triggered Event • e+e- • mee = 9.5 GeV/c2 (offline mass)‏ • cosθ = -0.77(offline opening angle)‏ • E1 = 6.6 GeV (online cluster energy hardware trigger)‏ • E2 = 3.2 GeV (online cluster energy software trigger)‏ Electron Momentum > 3 GeV/c • Full EMC acceptance |η|<1 in Run 7 • Integrated luminosity ≈ 300μb-1in Run 7 Challenging analysis!!!!! charged tracks

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

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

  10.  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 RAA: Upper Limit  RAA< 1.3 at 90% CL

  11.  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 • Strong 4 signal • First measurement of  in nucleus-nucleus collisions ever • Too early for RAA but will provide good first measurement • also need re-analysis of p+p

  12. Summary and Outlook • Full EMC + trigger  quarkonium program in STAR • Run 6: firstmid-rapidity measurement of S+2S+3S)→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: We have the first measurement in heavy ion collisions for 200 GeV Au+Au • Strong signal • Soon: • RAA 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!!!

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