1. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20061 J/ ψ measurements in Au+Au and p+p Collisions at 200 GeV Motivation J/ψ in Au+Au J/ψ in p+p Conclusions Outline Johan Gonzalez for the STAR Collaboration

2. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20062 Motivation Charm quarks are primarily produced in the initial stages of the collision via hard scatterings  Can be used to probe the initial conditions of the hot, dense matter produced Screening and scattering mechanisms predicted [1] to destroy the J/ψ in the Quark-Gluon Plasma –This leads to a suppression of J/ψ production, which would imply deconfinement On the other hand, regeneration models [2,3,4] predict an enhanced production of hidden charm states for sufficiently high charm densities –This would imply thermalization of charm quarks, and by extension, the light quarks that comprise the QGP Scrutiny of the centrality dependence and transverse momentum systematics of charmonium production can help distinguish between the two scenarios J/ Ψ regeneration [1] T. Matsui and H. Satz, Phys. Lett. B 178 (1986) 416. [2] Grandchamp, Rapp, Brown hep-ph/0403204 [3] Thews, Schroedter, Rafelski, Phys. Rev. C 63, 054905 [4] P.B.M., Andronic, hep-ph/0402291

3. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20063 Motivation Suppression mechanisms §, such as Debye screening or gluon scatterings, destroy the J/ψ. Magnitude of suppression depends on collision energy and centrality Regeneration mechanisms, such as Statistical Hadronization, are expected to contribute in conditions of high parton densities The two scenarios are not mutually exclusive – regeneration mechanisms may be at play even in the case where only a suppression is observed An illustration of the competition of regeneration and suppression mechanisms suppression regeneration L. Grandchamp and R. Rapp, Phys. Lett. B523 60 (2001) § These exclude “normal” suppression mechanisms, such as collisions with co-movers

4. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20064 The STAR Detector For the Au+Au analysis in run 4, we only used the TPC For the p+p analysis, we used the TPC in conjunction with the BEMC. Schematic side view of the STAR detector

5. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20065 J/ψ  e + e - in Au+Au @ 200GeV

6. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20066 Data & Analysis Cuts Dataset –Run IV Au+Au collisions –Trigger selection: Minbias Analysis Cuts –|vertexZ|<30cm –|η| < 1.0 –p > 500 MeV/c –Selected electron band, skipped hadron bands –Scanned 20M minbias events  12M 0-80% events after cuts p (GeV/c) dE/dx selected tracks

7. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20067 Dielectron Invariant Mass Spectra The dielectron invariant mass spectra are generated using the event mixing technique Subtracted spectrum shows a peak of 3.5 sigma significance in the vicinity of the J/ψ mass Subtracted spectrum 0-80% 12M events STAR Preliminary Zoom Same event Mixed event STAR Preliminary J/ψ  e + e - (BR = 5.93%)

8. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20068 Dielectron Invariant Mass Spectra The invariant mass spectra in the 0-20, 20-40, 40-80, and 0- 80% centrality classes are shown Number of J/ψ in each centrality class is determined by bin counting Gaussian fits (widths are held fixed to the value seen in minbias events) are used to estimate systematics Signal in the 0-20% bin is rather weak, so only an upper limit is quoted STAR Preliminary

9. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 20069 STAR Preliminary 0-80% Centrality Dependence of Scaled J/ ψ yields The N bin -scaled yields are plotted vs number of participants Bars indicate statistical uncertainties and the bands indicate the systematic uncertainties An upper limit is quoted for the most central bin Binary Scaling (black line and grey band) Determined from PHENIX data (nucl-ex/0507032)

10. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200610 Centrality Dependence of Scaled J/ ψ yields Statistical Hadronization Synopsis:  Complete screening of primordial J/ψ’s  J/ψ’s regenerated at chemical freezout from thermalized c-cbars [1] A. Andronic et al., Phys.Lett. B571 (2003) 36-44 [3] STAR, Phys. Rev. Lett. 94 (2005) 062301 pQCD x-section from:Cacciari, Nason, Vogt, PRL 95 (2005) 122001 [2] PHENIX, Phys.Rev.Lett. 96 (2006) 032001 Statistical Hadronization [1] calculations are shown for various values of the differential c-cbar cross section The model appears to overpredict the scaled J/ψ yields for most values of the c-cbar cross section However, it should be noted that the uncertainties in the measured [2,3] c-cbar cross sections are rather large at this time. STAR Preliminary

11. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200611 J/ψ  e + e - in p+p @ 200GeV

12. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200612 Data & Analysis Cuts Dataset –Run V p+p collisions –Trigger selection: J/ψ Level-0 portion require 2 BEMC hits above 1.2 GeV with Δφ> 60 o Level-2 portion acts as a photon veto and also makes an online invariant mass cut of 2<m<15 GeV (m 2 ~2*E 1 *E 2 *(1-cos(θ))) –Scanned 1.6M events Analysis Cuts –|vertexZ|<100cm –TPC tracks were required to match with BEMC towers –0.15 < p/E tower < 2.0 –3.2 < dE/dx < 5.0 keV/cm A typical triggered event Track selection

13. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200613 Dielectron Invariant Mass Spectrum The (raw) background subtracted dielectron invariant mass spectrum is shown A signal of 5 sigma significance is clearly visible The trigger has been successfully commissioned and is currently running as we speak STAR Preliminary J/ψ  e+e- in p+p @ 200 GeV More statistics are expected from Run 6

14. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200614 Summary & Conclusions We have investigated the production of J/ψ  e + e - in Au+Au and p+p collisions at 200 GeV Taking the STAR measured c-cbar cross section, our Au+Au results rule out a model of J/ψ production via Statistical Hadronization A J/ψ trigger in p+p collisions was successfully tested and is now being implemented in this year’s run With the future inclusion of the Barrel Time of Flight detector, electron identification—and by extension J/ψ reconstruction— will be substantially augmented in STAR In future endeavors, we will carry out a detailed analysis of the centrality and transverse momentum dependence of J/ψ in order to fully disentangle regeneration and suppression scenarios

15. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200615 Extra slides

16. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200616 Efficiency Corrections (1/3) Embedded simulated J/ψ’s into “Run 4-like” events: –Full field –|vertexZ|<30cm –J/ψ  e + e - only –Flat in p T and rapidity Quantities having to do with dE/dx are not well simulated  must use data itself to correct spectra: –Isolated electron band using TOF data in order to determine number of pairs lost due to nSigma cuts –Used the correlation* between nHits and nHitsDedx to assess number of pairs lost due to nHitsDedx cuts Folded data-determined corrections into embedding efficiency analysis TPC+TOF

17. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200617 Efficiency Corrections (2/3) Efficiency corrections are shown as a function of transverse momentum Strong centrality dependence is observed Sag in the vicinity of 1.5 GeV/c induced by nSigma cuts 0-20% 40-80% 0-80% 20-40% Centrality dependence of efficiency corrections

18. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200618 Efficiency Corrections (3/3) Correction factors were obtained by embedding J/ψ’s into real data Due to lack of statistics, we had to resort to numerical integration Randomly sampled J/ψ candidates and carried out correction: Σ dN dy = N ( 1 ε(p T ) ) Where N is the number of candidates in a given centrality bin and ε is the efficiency

19. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200619 Systematic Uncertainties Varied kinematic and track quality cuts in embedding. Variation of nHitsDedx cuts done in parallel with nHits variation Assessed uncertainty in correction the correction technique Uncertainty in background subtraction determined to contribute about 10% to overall errors, assumed equal across all centralities The uncertainty in the yield due to nSigma cuts is the dominant contributor to systematic errors, accuracy limited by TOF statistics 0-800-2020-4040-80 nHits>241.81.5 nHits>262.11.81.31.9 |etamax|<0.990.60.40.80.5 |etamax|<1.010.50.30.5 |y_jpsi|<0.490.30.20.10.4 |y_jpsi|<0.510.30.60.10.3 corr. Technique0.50.91.0 bkg. Subtraction10 nSigma cuts11.78.67.915.2 quadratic sum15.713.413.018.4 Error Budget

20. Johan Gonzalez - Strange Quark Matter 2006, UCLA - March 200620 Comparison with PHENIX Results Our data is similar to PHENIX Run 2 data Our results are higher than PHENIX Run 4 data, but error bars should be taken seriously! Comparison with PHENIX Run 2 Comparison with PHENIX Run 4