1. Winter Workshop in Nuclear Dynamics, February 10, 2005 Manuel Calderón de la Barca Sánchez Indiana Unviersity Heavy Flavor in STAR

2. 2 Outline @ Why is heavy flavor interesting? @ Single Electron analysis in STAR H Detectors H Backgrounds H Consistency checks H Results @ Prospects for di-electrons in STAR.

3. 3 Heavy Flavor Production in Hadronic Collisions @ Heavy quark production H Charm produced in early stage, mostly from initial gluon fusion W Sensitive to early conditions: O initial gluon density O nuclear effects O medium effects W Are heavy-quarks mesons suppressed as well as light quarks ones? O Probe of energy loss mechanism W Thermalization probe? O Eliptic flow. beauty charm D mesons,  ’, 

4. 4 Heavy Quark Energy Loss Without medium heavy quark jets differ from light quark/gluon jets due to suppression of gluon radiation at small angles, the Dead Cone Effect (Y. Dokshitzer et al, J.Phys.G17,1481) What will happen in the medium? Reduced medium energy loss? Y. Dokshitzer and D. Kharzeev, Phys.Lett.B519, 199 M. Djordjevic and M. Gyulassy, Phys.Lett.B560, 37 N. Armesto, C. Salgado, U. Wiedemann PRD69, 114003 Q  < m Q /E Q suppressed for

5. 5 Heavy quark suppression? @ Propagation of heavy quarks in QCD matter H Energy loss through gluon radiation H dead cone effect  Gluon radiation suppressed for  < M/E (Dokshitzer & Kharzeev, PLB 519 (2001) 199) H Medium induced radiation reduces effect but still sizeable (Arnesto, Salgado, Wiedemann, hep-ph/0312106)  large enhancement of D/  ratio at moderate high p T (5-10 GeV/c) Arnesto, Salgado, Wiedemann, hep-ph/0312106 Dokshitzer, Kharzeev, PLB 519 (2001) 199

6. 6 Heavy Flavor Production in A+A Collisons @ So far  Production little studied (CERN/SPS low  )  Charmonium suppression (melting of J/  due to color screening) used as signature of QGP @ But: H Low x: heavy quark pair produced over long distances W can exceed the size of the nuclei (even though matrix element of hard processes dominated by short distances)  sensitive to medium  good probe for high density matter @ RHIC and LHC: H gluon density in nucleii ? H energy loss due to interaction with medium ? H shadowing  cannot study J/  suppression without understanding open charm

7. 7 Hidden and Open Charm – Both Needed RHIC  s = 200 GeV SPS  s = 17 GeV At RHIC open charm production provides reference and may be the only mean to understand charmonium suppression (same gluon conditions in the initial stage)

8. 8 Heavy Flavor in STAR Direct reconstruction of open charm hadrons using invariant mass technique: D0 -> K , D+ -> K , D*+ -> D0 , D0 ->K  See Xin Dong’s talk later today (Semi-) leptonic decays into electrons: D+ -> e+ anything (17.2%)B+ -> e+ anything (10.2%) D0 -> e+ anything (6.87%)B0 -> e+ anything (10.5%) J/  -> e+ e- (5.9%)  -> e+ e- (2.38%) Sensitive to both charm and bottom

9. 9 The STAR Detector @ Electron ID @ energy loss in the tracking detectors (TPC dE/dx) @ time of flight measurement (TOF) @ calorimetric measurements (EMC)

10. 10 Electron ID (1) Energy loss (dE/dx) in the tracking detectors (TPC)  e/h ~ 500 (depending on momentum)  Limited to certain momentum windows Time of Flight + dE/dx  allows clear electron ID in large momentum range (0.2 < p < 3)  Only prototype installed: Small coverage (1 unit in eta, 6 in phi)

11. 11 Barrel EMC identification @ Run IV acc:  0<  <1, 0<  <2  @ Tower Energy @ Distance from track to center of a tower @ High-granularity Shower Maximum information

12. 12 Electron ID (2) Calorimetric Measurements (EMC + tracking + dE/dx) large coverage 0 <  < 1, in FY03, -1 <  < 1 after completion -1 <  < 2 including Endcap Provides measurements of energy deposit in towers shower shape electron ID starting at 1.5 GeV/c

13. 13 EMC Trigger The EMC as trigger detector provides fast information on energy deposition in towers up to 3 ADC (~energy) thresholds Gives STAR access to hight pT electrons

14. 14 Inclusive Electrons Large “photonic background”   conversions in the detector material  light meson (  0,  ) Dalitz decays Combining detectors: electron pt spectrum for d+Au collisions  p T coverage 0.2 to 7 GeV/c  nice agreement between different techniques in overlap regions  Time-of-Flight, Calorimetry

15. 15 Misidentified hadron background H Obtained by shifting the TPC dE/dx selection over the hadrons region

16. 16 Photonic Background Measuring the background: electron pair invariant mass reconstruction and pair opening angle   conversions   0 dalitz decays  other decays ( ... ) scaled to  0

17. 17 Other Background sources Obtain via simulation H Pythia/HIJING + GEANT W ratio with respect to π 0 Dalitz decay @ Signal/Background is p T dependent H ~1/1 at 2 GeV/c H ~2/1 at 7 GeV/c

18. 18 “Non-photonic” Electrons @ After correction for electrons from photonic sources and background @ measure up to p T = 8 GeV/c @ EMC, ToF and dE/dX electrons agree within errors @ Systematic uncertainties H Trigger bias ~ 0.5σ sys H Efficiency ~ 0.2σ sys H Other sources ~ 0.3σ sys

19. 19 PYTHIA Electron Sources

20. 20 Consistency with D Measurement Direct reconstruction of open charm mesons using invariant mass technique in d+Au (Xin Dong’s talk!) Is data consistent with the electron measurement?

21. 21 Electrons from D Decays Consistency check Use D mesons p T spectrum Use PYTHIA to decay Ds into electrons Non-photonic Electron spectra seems to be accounted for by decay of open charm.

22. 22 Towards heavy quark energy loss… Nuclear modification of Charged hadrons in dAu And AuAu is well established. First steps: Primary electron RdAu Within errors consistent with binary scaling, some indication of Cronin effect

23. 23 Quarkonium Analysis in STAR @ J/Psi and Upsilon mesons are of great interest in HI collisions @ STAR has some capabilities to detect them through their decay in the e + e - channel H Particle ID: W dE/dx (TPC, maybe SVT) at low p W EM Calorimeter at higher p @ Obstacle: They are rare H Develop triggers to enhance the events H If triggering not possible, need a large data set.

24. 24 Quarkonium LEVEL 0 Trigger in STAR  Divide  into 6 sections @ Find a tower above a threshold  Look in the 3 opposite sections in  @ If another tower above threshold, trigger. @ Level-2: Individual tower information.

25. 25  Trigger: L2 Efficiency and Rejection Using High-Tower at level 0 and L2 fast invariant mass: Minimum Bias Central Efficiency can be kept above 85% Rejection is high, so rates are low. ~100 Hz out of Level-0 (at high luminosity) ~2 Hz out of Level-2 Rejections of 10 3

26. 26 So, How many in Run IV? J/  Yield: ~12 J/   e + e -, p>1.2 GeV per 1M min-bias events ~50 J/   e + e -, p>1.2 GeV per 1M 10% central events  Yield: 0.02   e + e -, p>3 GeV per 1M min-bias events 0.1   e + e -, p>3 GeV per 1M 10% central events (Triggered event ~ central) Include: - f AB (hard fraction) - 1 unit  4  - Acceptance (1/2 Barrel) Assuming 0.5x(3/4 Barrel) - momentum cut Run IV Min bias ~30M 360 J/  Central ~50 M ~1500 J/ 

27. 27 Prospects for Run IV  J/  Analysis will rely on large minbias and central data sets for Au+Au. H 50 x 10 6 minbas + 50 x 10 6 central  3  signal + 5  signal in central (conservative) @ Upsilon Trigger looks promising in Au+Au H Conservative estimate: ~few 10’s Upsilons in 2004   has never been measured in heavy ions before, proof of principle measurement.

28. 28 L0+L2 Trigger Performance

29. 29 Summary @ Electrons allow us to access heavy flavor physics @ Analysis of electrons in STAR is on shell! @ Single electron results in pp, dAu soon to be finalized H RdAu : e scale with binary collisions (small Cronin effect) H Comparisons W PYTHIA: Beauty starts to dominate ~4-5 GeV/c (model dep.) W D meson: can account for full non-photonic spectrum @ Future: dielectrons can be accessed in STAR  Trigger on J/  in pp; offline search in AuAu Run IV  Trigger on  in all systems; caveat small  @ Getting ready for the production of Run IV data

30. 30 Extra Slides

31. 31 Did the trigger work? minimum bias 7854 events Central 26581 Upsilon triggers 1159 With the trigger, we can reach m~10 GeV/c 2

32. 32 L2 Trigger: Get invariant mass quickly @ Use individual calorimeter towers @ Energy & position information p 1 = (E EMC-1 2 -m 2 ) ½  E EMC p 2 = (E EMC-2 2 -m 2 ) ½  E EMC cos  x1  x2/(|x1| |x2|) m 2  2 p 1 p 2 (1 – cos  ) Pro: simple, fast avoids ambiguity 

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