1. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Transverse momentum and centrality dependence of high-pT non-photonic electron suppression in Au+Au collisions at √s NN =200 GeV D. Arkhipkin, Y. Zoulkarneeva, J. Bielcik, W. Dong, M. M. de Moura, A. A. P. Suaide, STAR Collaboration

2. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Overview ➢ Motivation ➢ Analysis ➢ Electron identification ➢ Electron indentification efficiency ➢ Hadron & Electron background ➢ Trigger bias normalisation ➢ Effect of pT resolution ➢ Results ➢ Summary

3. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Physics Motivation To test and extend QCD theory and its predictions STAR will: – use hard (short wavelength) probes such as Inclusive jets and direct photons back to back jets (correlation of leading particles) direct gamma + leading hadron from jet flavor tagged jets to measure the differential energy loss for gluon, light quark and heavy quark probes which couple differently to the medium spectra and yields of the full range of quarkonia, through the Upsilon family, to measure the thermodynamics of deconfinement – measure very large samples of “soft physics” events to study mechanism of equilibration through heavy quark yields and flow the velocity structure of the medium in complete detail the medium’s temperature using leptons, photons spectrum of extended hadronic matter (resonances) broken / restored symmetries (e.g., CP violation, chiral restoration) Sensitivity to rare probes, plasma radiation, and characterization of bulk matter ( From “STAR Physics in the RHIC II Era” talk by J. Dunlop, RHIC II Science Workshop )

4. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Heavy Quark production at RHIC c, b D, B 1) production 2) medium energy loss 3) fragmentation – Can we learn something from the difference in spectra from light and heavy quarks? – How do heavy quarks interact with the medium? ● Important test of the transport properties of sQGP ● Heavy Quark energy loss is expected to be smaller because of the dead cone ● D,B spectra are affected by energy loss light (M.Djordjevic PRL 94 (2004)) ENERGY LOSS

5. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Electrons and nuclear modification factor R AA Single e- from NLO/FONLL prediction: electron suppression up to 2 prediction: large electron suppression of ~ 5 for c only, medium suppression of ~ 2.5 for c+b

6. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Electron identification in d+Au and p+p collisions (example) The electron identification is done using the TPC dE/dX and the BEMC information. The electron identification consists of the following cuts, in the following order: 1. Select primary tracks with p > 1.2 GeV and number of dE/dX points > 20 2. Check if tracks are projected on a valid (status = GOOD) BEMC tower 3. Make a p/E cut (picture of p/E spectrum is here) 4. Check if we can find both SMD clusters associated to the track 5. Check if the SMD clusters has at least 2 hits on it 1. This is a new cut that is being applied when compared to old analyses and it makes the purity of the electron sample increase. 6. Make a dE/dX selection based on the distribution after the BEMC cuts. The dE/dX cut depends on momentum. dEdX evolution

7. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Electron identification efficiency The electron identification efficiency is a composition of BEMC identification efficiency and the dE/dX cut efficiency (SMD hit selection included in analysis). The BEMC efficiency also includes the detector acceptance

8. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Hadron contamination The amount of hadrons in the electron selection region is not negligible and should ne removed from the data. This is done by calculating the hadon area above the cut and compare that to the electron area. The ratio between the two areas is taken as a correction factor and subtracted from the spectra. Hadron contamination as a function of pT – Fitting dE/dx spectrum in pT slices ● 2 or 3 Gaussians do not show differences – Amount of hadrons misidentified as electrons increase with pT ● - Similar results from p+p to central Au+Au

9. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Hadronic background The hadronic suppression facto is defined as the ratio between the number of original hadrons and the number of hadrons that survive the electron identification cuts. A suppression factor of 100 means that a sample of 100 hadrons will result in 1 hadron identified as electron. hadronic suppression factor from BEMC (including trigger) and dE/dX Both methods agree quite well

10. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Electron Background ➢ Most of the electrons measured in the EMC come from photon conversion ➢ Another important source of electron background is the pi0 dalitz decay that are misidentified as primary

11. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Trigger Bias Normalisation The High tower trigger enhances, in general, the high pT tracks yield in the events. In particular, it also enhances the number of high-pT electrons. We have, in this analysis, 3 different triggers: 1. Minimum bias 2. High tower 1 (threshold > 2.5 GeV) 3. High tower 2 (threshold > 5.0 GeV) The bias is simply the inclusive raw yield ratio between high- tower and minimum-bias triggers. Because the software is the same, efficiencies and background corrections should cancel, remaining only the bias. This Figure shows the ratio between the high tower 1 and minimum bias triggers. The ratio plots were fit by a erf() function and this function was used to correct the electron raw yield

12. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Effects of pT resolution The finite momentum resolution in the TPC and electron Bremsstrahlung (that causes energy loss of electrons in the detector material) causes a change in the shape of the electron spectrum. electron embedding data

13. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Inclusive Electron Spectra a) inclusive electron ((e - +e + )/2) spectra for pp, dAu and AuAu collisions at √s NN =200 GeV. b)inclusive to background ratio for pp and 0-5% most central AuAu collisions c) invariant e + e - mass spectrum ● Non-photonic electrons: ➢ semileptonic charm & beauty decays ➢ Drell-Yan processes ● Photonic electrons: ➢ photon conversion, gamma -> e + e - ➢ pi0, eta dalitz decays, pi0->gamma + e + e - Non-photonic electron spectra for pp, dAu and AuAu collisions at √s NN =200 GeV

14. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Nuclear Modification Factor ➢ Unexpectedly large suppression in Au-Au collisions ➢ All the model calculations overpredict data ➢ Processes other than radiative gluon emission may be important to describe the observed suppression The nuclear modification factor, R AA for dAu, and AuAu collisions at √s NN =200 GeV

15. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Summary ➢ Non-photonic electrons from heavy flavor decays were measured in √s NN =200 GeV p+p, d+Au and Au+Au collisions by STAR up to pT ~ 10 GeV/c ➢ Strong suppression of non-photonic electrons has been observed in Au+Au, increasing with centrality ➢ R AA ~ 0.2-0.3 for pT > 3 GeV/c ➢ Suggests large energy loss of heavy quarks ➢ Review process started (STAR GPC), intended for PRL

16. D.Arkhipkin, Y. Zoulkarneeva, Workshop of European Research Group on Ultra relativistic Heavy Ion Physics March 9 th 2006 Support Slides: future STAR upgrade Heavy Flavor Tracker for STAR LBNL/PUB-5509 (2005) The primary motivation for the HFT is to extend STAR s capability to measure heavy flavor production by the measurement of charm and beauty decays that are displaced from the collision vertex. The primary physics topics to be addressed by the HFT include open charm measurements, light quark thermalization, heavy quark energy loss and flow. HFT will provide tracking information for decaying particles that are displaced by only ~100 microns from the primary vertex.