1. Upsilon production in STAR Pibero Djawotho Indiana University Cyclotron Facility October 12, 2007 DNP 2007

2. 2 Why Quarkonia? Charmonia: J/ ,  ’,  c Bottomonia:  (1S),  (2S),  (3S) Key Idea: Melting in the plasma 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 –Sequential disappearance of states:  Color screening  Deconfinement  QCD thermometer  Properties of QGP H. Satz, HP2006 When do states really melt? T diss (  ’)  T diss (  c )< T diss (  (3S)) < T diss (J/  )  T diss (  (2S)) < T diss (  (1S))

3. 3  and J/  States in STAR J/ ,  ’ J/  likely to melt at RHIC  ’ melts at RHIC Pros moderate rate J/  and  ’ can be separated Cons co-mover absorption affects yield recombination affects yield trigger only in pp (still low eff.) moderate electron PID in J/  momentum range ,  ’,  ’’  (1S) no melting at RHIC  standard candle (reference)  (2S) likely to melt at RHIC (analog J/  )  (3S) melts at RHIC (analog  ’) Pros co-mover absorption negligible recombination negligible at RHIC STAR efficient trigger and large acceptance Cons extremely low rate need good resolution to separate 3 S states  STAR’s strength are the  states

4. 4 STAR Detectors Used for Quarkonia EMC Acceptance: |  | < 1, 0 <  < 2  PID with EMC detectors Tower (energy)  p/E High-energy tower trigger  enhance high-p T sample Essential for quarkonia triggers Luminosity limited for 

5. 5 STAR  Trigger Similar L0+L2 triggers –Higher mass state  higher energy threshold –Pros: Easier and cleaner to trigger –Cons: Small yield; need large luminosity and acceptance 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 = -0.67 E 1 = 5.6 GeV E 2 = 3.4 GeV charged tracks

6. 6 STAR  Mass Resolution StateMass [GeV/c 2 ]B ee [%](dσ/dy) y=0 B ee ×(dσ/dy) y=0  9.460302.382.6 nb62 pb  10.023261.910.87 nb17 pb  10.35522.180.53 nb12 pb  +  +  91 pb STAR detector is able to resolve individual states of the  albeit: –Finite p resolution –e-bremsstrahlung Yield is extracted from combined  +  +  states FWHM ≈ 1 GeV/c 2 W.-M. Yao et al. (PDG), J. Phys. G 33, 1 (2006); R. Vogt et al., RHIC-II Heavy Flavor White Paper

7. 7  Analysis: Electron ID with TPC and EMC  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 preliminary electrons  Kp d preliminary e π

8. 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 preliminary  in Run 6 p+p at √s=200 GeV: Invariant Mass

9. 9  in Run 6 p+p at √s=200 GeV: Cross Section  geo 0.263±0.019  L0 0.928±0.049  L2 0.855±0.048  2 (e) 0.47±0.07  mass 0.96±0.04  0.094±0.018   =  geo ×  L0 ×  L2 ×  2 (e)×  mass  geo is geometrical acceptance  L0 is efficiency of L0 trigger  L2 is efficiency of L2 trigger  (e) is efficiency of e reco  mass is efficiency of mass cut preliminary

10. 10 STAR Run 6  Cross Section in p+p at Midrapidity at √s=200 GeV NN 48±15(stat.)  0.094±0.018  L dt (5.6±0.8) pb -1 dy1.0 preliminary

11. 11 STAR 2006 √s=200 GeV p+p  +  +  →e + e - cross section consistent with pQCD and world data preliminary STAR  vs. Theory and World Data

12. 12 Past:  in Run 4 Au+Au at √s NN =200 GeV 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

13. 13 Future:Run 7 Au+Au at √s NN =200 GeV  Trigger 605.69 μb -1 integrated luminosity for L2-upsilon during Run 7 ~37  expected at y=0 for |y|<0.5 or ~70  for |y|<1. Assume: –S/B=48/83  significance 3.3σ from 2006 p+p at √s=200 GeV –Binary scaling and nuclear effects  σ AB =σ pp (AB) α preliminary

14. 14 Summary and Outlook 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 –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: expect  cross section at midrapidity in Au+Au collisions at √s=200 GeV (37-70  raw yield) and nuclear modification factor R AA