Quarkonium Physics with STAR Mauro Cosentino (University of Sao Paulo/BNL)

2 Why Quarkonia ? Using F 1 : S. Digal, P. Petreczky, H. Satz, Phys. Lett. B514 (2001) 57 Using V 1 : C.-Y. Wong, hep-ph/ –Key Idea: Melting in the plasma Suppression of states is determined by T C and their binding energy Color screening  Deconfinement QCD thermometer  Properties of QGP Is the sequential suppression pattern the smoking gun?

3 The STAR Detector TPC: |  | < 1, 0 <  < 2  ToF: -1 <  < 0,  = 0.1 EMC: |  | < 1, 0 <  < 2 

4 Golden Decay Mode : Need: Electron ID Hadron Rejection Trigger Typical electron p range for: J/  : 1-3 GeV/c  : > 3.5 GeV/c

5 electrons  Kp d Electron ID Works from p= GeV/c TPC: dE/dx for p > 0.5 GeV/c –Electrons can be discriminated well from hadrons up to 8 GeV/c –Allows to determine the remaining hadron contamination after EMC ToFEMC

6 Electron ID at medium-p T ToF –Cut at |1/  –1| < 0.03 –clean e ± identification with TPC- ToF up to 2.5 GeV/c Downside: only patch (  / <  <0) Future (2008): full barrel (2 , |  |<1.0) will enable J/  physics (also trigger in AA) p T < 2 GeV/c so far EMC+TPC only not sufficient TPC – particle energy loss e  K p

7 Electron ID at high-pT EMC Towers energy & TPC momentum → p/E≈1 for electrons SMD: hadrons and electrons have different shower shapes hadronselectrons

8 J/  Trigger Level-0 (topology): Fast: t ≤ 1ms Φ divided in 6 sections Find a tower above threshold (E > 1.2 GeV) Look for other towers above threshold on the 3 opposite sections Level-2 (software): Full EMC tower data available Towers clustering → E e CTB matching (veto photons) Vertex: BBC resolution ~6cm for Au+Au, 30cm for p+p Invariant mass assuming straight tracks: m 2 inv  2E 1 E 2 [1-cos(  12 )] Trigger for m inv > 2.5 GeV/c 2 Decision is taking up to 500  s This J/  trigger setup is efficient only for p+p L0 rate: ~100 Hz L2 rate: ~ 1 Hz Au+Au will require ToF upgrade

9  Trigger Implementation L0 Trigger –Simple single high tower trigger E T >3.5 GeV L2 Trigger –Use similar L2 to J/  Very efficient > 80% Large rejection power –100 at L0 –100 at L2 Luminosity limited Works in p+p and central Au+Au Exploit full STAR acceptance, 2  & |  |<1

10 Results J/  (Run IV) Just a faint signal For efficient J/  trigger, full barrel ToF is needed (Run V) trigger commissioning (~1.7M events) Results compatible with expectations Run VI (this year): expect S = (work in progress)

11 Au+Au (Run IV): comissioning run ½ EMC Several technical issues upper limit only p+p (Run VI): Expect significant signal Results  trigger threshold No N ++ +N -- subtracted Cannot resolve different S states   (1S+2S+3S)  e+e-

12 Future & Rates SignalRHIC Exp.ObtainedRHIC-I (>2008) RHIC-IIRHIC-II / R2D LHC / ALICE + J/  → e + e  J/  →     PHENIX~80 ~7000 3,300 29,000 45, ,000 4,300,000 9, ,000  → e + e -  →     STAR PHENIX ,200 1,040 39,000 2,600 8,400 B → J/  → e + e  B → J/  →     PHENIX ,700 67,000 N/A  c → e + e    c →  +    PHENIX ,600 2,900* 117,000* 670,000 N/A D→KD→K STAR~0.4×10 6 (S/B~1/60 0) 30,000** N/A8000 Upgrades: DAQ1000: high data taking rate, no trigger dead time ToF full barrel: → J/  PID and trigger (  veto) RHIC-II: e-cooling, 40  nominal luminosity

13 Summary & Conclusion Quarkonia trigger tested successfully J/  –Expect moderate sample in p+p and Au+Au compared to PHENIX Require ToF upgrade  –Large acceptance & clean trigger –Strength of STAR’s quarkonium program Also: –J/  at forward rapidities -> FPD & FMS (upgrade) –Testing  detectors (re-use CTB, magnet=absorber)

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15 J/  e + e - Au+Au √s NN =200 GeV J/  e+e- p+p √s=200 GeV Quarkonia in STAR Slowly getting started with J/  : Signal in 200 GeV p+p from 2005 Tested and working trigger in p+p No trigger for AuAu until full ToF in 2009 Much more from 2006 in the works… Also signal in Au+Au with TPC only Large hadron contamination Need full EMC STAR Preliminary

16  in STAR Cannot resolve different S states   (1S+2S+3S)  e + e - STAR –Large acceptance (|  | < 1, full EMC) –PID for electrons (EMC, TPC) –Trigger Very efficient > 80% –Luminosity limited trigger threshold No N ++ +N -- subtracted Scaling from Au+Au to elementary:  =1 First look in 2004: ½ EMC, little statistics 90% C.L.: signal < 4.91 B·d  /dy C.L. < 7.6  b STAR Preliminary

hadrons electrons Electron ID in STAR – EMC 1.TPC: dE/dx for p > 1.5 GeV/c Only primary tracks (reduces effective radiation length) Electrons can be discriminated well from hadrons up to 8 GeV/c Allows to determine the remaining hadron contamination after EMC 2.EMC: a)Tower E ⇒ p/E~1 for e - b)Shower Max Detector Hadrons/Electron shower develop different shape Use # hits cuts 85-90% purity of electrons (p T dependent) h discrimination power ~

18 Electron Identification Association of TPC and BEMC information –TPC gives dE/dx and momentum (p) –BEMC gives the energy (E) –Selected particles are within specifics dE/dx and p/E ranges.

19 Why Quarkonia? J/  would “melt” in QGP due to screening of static potential between heavy quarks: –Matsui and Satz, Phys. Lett. B 178 (1986) 416 Recent developments shows that the dissociation temperature for heavy quarkonia states are considerably higher than first supposed Using F 1 : S. Digal, P. Petreczky, H. Satz, Phys. Lett. B514 (2001) 57 Using V 1 : C.-Y. Wong, hep-ph/ Feed down from excited states could account for observed suppression [Matsui and Satz, Phys. Lett. B 178 (1986) 416]

20 Achieving our Goals A complete understanding of suppression requires a broad range of systematic studies –p+p, Au+Au, vs. centrality, vs. √s –Measurement of J/  and excited states –Measurement of  and excited states small cross-section  high luminosity  trigger good mass resolution to resolve 1S, 2S, 3S states

21 STAR Contribution Large Acceptance at Mid-Rapidity –|  |<1, 0<  <2  –Pair acceptance~(single acceptance) 2 Electron identification capabilities –TPC dE/dx –EMC E>1-2 GeV (operating full barrel) –TOF p<2-3 GeV/c Trigger capabilities on Barrel EMC –Suitable for single electron (see F. Laue’s talk) –Suitable for di-electrons(?) Heavy-Quarkonia states are rare –  : efficient trigger for all systems –J/  trigger in p+p only, need large min. bias. dataset in Au+Au

22 Efficiency and Purity of the Id

23 J/  Trigger Level-0 (topology) Fast: t ≤ 1  s Φ divided in 6 sections Find a tower above threshold Look for other towers above threshold on the 3 opposite sections If signal above threshold found, issue trigger

24 J/  Trigger Level-2 (software) Looks for e + e - pairs Towers above threshold→ “seeds” → clusters CTB matching (veto photons) cos(  12 ) obtained from clusters and vertex positions Vertex: BBC resolution ~6cm for Au+Au, 30cm for p+p Pairing clusters and neglecting m e : m 2 inv  2E 1 E 2 [1-cos(  12 )] Decision is taking up to 500  s Real Data, p+p Run V

25 Applicability of the trigger J/  Au+Au: –Only peripheral events have good rejection –Most of J/  yield is on central events (98% of signal on top 60% central) –So, J/  trigger not suitable for Au+Au – Alternative is large min. bias dataset J/  trigger efficient only for p+p

26  trigger: L0 + L2  large mass –Simpler L0, requiring one single tower with E T >3.5 GeV – Use similar L2 algo –Can trigger p+p and central Au+Au events Rare triggers go to “express stream” processing But… very low production rate –Less than 100 expected for full Run IV Au+Au dataset –Actually, only a few achieved, for several reasons

27 J/  in Au+Au (Run IV) No trigger due to high background Dataset: GeV Just a faint signal For efficient J/  trigger, full barrel ToF is needed (just patch in Run IV)

28  trigger in Au+Au  →e + e - channel L0: events with E tower > 3.5 GeV L2: events with pair mass > 7 GeV/c 2 High efficiency (80%) Needs full BEMC for that (only ½ in RunIV) Little statistics trigger threshold No N ++ +N -- subtracted

29  Analysis for Au+Au: Upper Limit 90% C.L.: signal < 4.91 B*d  /dy C.L. < 7.6  b Acceptance increase will help (Factor ~4) Scaling from Au+Au to elementary:  =1

30 Run V data sample (p+p) 1.7M events Simulation: yield of J/  Data: yield small but consistent with simulation

31 Data  Simulation Width consistent with detector resolution Mass slightly lower than simulation (2  ) Left tail in simulation due to bremsstrahlung in material at r < 50 cm (beam pipe, SVT, SSD, air, TPC field cage)

32 Run VI p+p (just finished) Barrel EMC full installed L2 widely used (jets, dijets,…) Both triggers are on (J/  and  ) just ended –~3.3M J/  triggered events taken (~800J/  ) –~1.9M  triggered events taken (~80  ) Most of events not reconstructed yet

33 Future perspectives Completed Run VI with sufficient dataset to measure J/  cross-section J/  trigger also deployed for 62.4 GeV Medium-Term Upgrades: –ToF (full barrel) –Heavy Flavor Tracker (HFT) –See next talk (Tony Frawley)

34 ToF Upgrade Construction FY 06 – FY 08 23,000 channels covering TPC & Barrel Calorimeter Will allow to deploy J/  trigger in Au+Au Coincidence: ToF slat + EMC tower substantially reduces photon background MRPC Time of Flight Barrel in STAR

35 Origin of J/  suppression on SPS Assume: 1.N J/  (observed) = 0.6 N J/  N  c (compatible w Hera-B data) 2.J/  doesn’t melt  c dissociation =  ’ dissociation Right or wrong, it shows how important the missing cc measurement is! F. Karsch, D. Kharzeev, H. Satz, hep-ph/

36 EXTRA: trigger pre-calibration for BEMC Online energy resolution ~ 17%/√E Offline energy resolution ~ 14 %/√E

37 J/  in Au+Au (Run IV) No trigger due to high background Dataset: GeV (Minbias) Invariant mass spectra from dE/dx selection (skiping hadron bands) Subtracted spectrum shows a 3.5  signicance peak arount J/  mass Zoom Same event Mixed event J/ψ  e + e - (BR = 5.93%) p (GeV/c) dE/dx Johan Gonzalez, SQM2006

38 Invariant mass spectra vs. centrality Number of J/  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 Johan Gonzalez, SQM2006

39 Centrality dependence of scaled J/  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/ ) Johan Gonzalez, SQM2006

40 Centrality dependence of scaled J/  yields Statistical Hadronization Synopsis: Complete screening of primordial J/ψ’s J/ψ’s regenerated at chemical freezout from thermalized c-cbars Statistical Hadronization[1] calculations are shown for various values of the differential ccbar cross section The model appears to overpredict the scaled J/ψ yields (~Ncc2) for most values of the ccbar 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. [1] A. Andronic et al., Phys.Lett. B571 (2003) [2] PHENIX, Phys.Rev.Lett. 96 (2006) [3] STAR, Phys. Rev. Lett. 94 (2005) pQCD x-section from:Cacciari, Nason, Vogt, PRL 95 (2005) Johan Gonzalez, SQM2006

41  trigger in Au+Au L0: events with E tower > 3.5 GeV L2: events with pair mass > 7 GeV/c 2

42 Trigger performance in Au+Au 4-20 M events sampled per day Variation on daily samples sizes due to several STAR goals Other triggers reduced the  trigger livetime

43  Analysis for Au+Au 34.2  b -1 sampled –200M+ mb events scanned with  trigger –Only 50M off-line –Small dataset processed Only 3 signal counts (no BG) observed Half field running, no BEMC-based triggers.

44 Trigger performance in Run V Online monitoring of the trigger: Extremely fast turnaround No need for offline production to check the trigger Energy (MeV) Invariant mass (MeV/c 2 )

45 Trigger performance for Run VI Trigger monitoring shows consistency with Run V tests

46 Run VI data analysis Only a few hundred k events, for both triggers, are reconstruct so far Besides limited statistcs is available data seem promissing ~270k  trigger events were enough to give a hint of signal

47  Preliminary analysis Subtracted invariant mass spectrum 270k events