Jaiby Joseph Kent State University

1. Charmed Meson Measurement using Silicon Detectors (SVT+SSD) in Au+Au Collisions at 200GeV in STAR Experiment at RHIC Jaiby Joseph Kent State University

2. Charm Mesons in Heavy Ion Collisions • Charm quarks are produced during the early stages of collision through gluon fusion, therefore can give insights of the medium created. • Measurement through semi-leptonic decay channel shows suppression of heavy quarks at high pT in central Au+Au collisions[1]. This is in contradiction to theory[2]. The different energy loss mechanisms are not well understood. • Measurement of charm elliptic flow can give us valuable information about thermalization of light quarks and thus about the properties of medium. • D-Meson Measurement • Semi-Leptonic decay channel: • D0e++X , BR : 6.9 % • D+/-e+/-+X BR : 17.2% • Large pT range. • Relative contribution of electrons from B and D mesons are unknown. • Azimuthal correlation of D mesons with e- can be utilized to disentangle the charm contribution. • Hadronic decay channel • D0 (D0)K-+(K+-)BR : 3.8 % • D+/-K BR : 9.2% • Full Topological reconstruction • Typically limited to low momentum RAA of non photonic electrons in AuAu STAR Phys. Rev. Lett. 98 (2007) 192301 [1] Phys. Rev. Lett. 98 (2007) 192301 [2] Phys. Lett. B519 (2001) 199-206

3. Microvertexing using STAR Silicon Detectors • We tried a Full Topological reconstruction of D-Mesons using the pointing capabilities of STAR silicon Drift (SVT) and Silicon Strip (SSD) detectors • The Micorvertexing code uses full track/error matrix information • Code works as expected In simulation data, the reconstructed quantities behave as expected within systematic errors. • My Involvement/contribution to the effort • debugging the microvertexing code • Monte Carlo studies for online/offline cuts • productions of Micro DSTs and Pico-DSTs • signal extraction, optimization, fitting, pt binning • Embedding QA

4. Debugging the code - Optimizing the dE/dx cut • From a previous study it wasshown that a cut on Kaon opening angle, |Cos(θ*)|<0.6 can remove the poorly reconstructed low momenta tracks[1]. • The original dE/dx cut used in the code removed all K and π tracks in the overlapping region. Which are the higher momenta tracks • This means that the cut on dEdx and Kaon opening angle were mutually exclusive! Implementation of the dE/dx correction gave initial results on D0 signal in the 2007 Prod2 files. • [1] http://phys.kent.edu/~margetis/theses/LaHurd.pdf

5. Debugging the code - Optimizing the momentum cut We were applying the cut (wrong cut): pT > 0.5GeV/c p > 0.8GeV/c (Mainly to speed up the code) A look at the pureD0 sample shows that, this cut removed a lot of good K, π tracks. lose of about 60-70% of the total D0 yield. Yifei’s PYTHIA quick simulation also showed that the kinematics lost around 0.5-2.0GeV/c is about 60% due to the cut on daughter momenta > 0.7GeV/c • New Cut: • (PK+Pπ) > 1.5GeV/c • No pT Cut This preserves the phase space of the D0 candidates better. Latest production with modified momentum cut shows a strong signal with no offline track momenta cut

6. Cuts used in reconstruction code (First production) • EVENT level • triggerId : 200001, 200003, 200013 • Primary vertex position along the beam axis :|zvertex| < 10 cm • Resolution of the primary vertex position long the beam axis:|zvertex|< 200µm • TRACKS level • Number of hits in the vertex detectors : SiliconHits>2 (tracks with sufficient DCA resolution) • Transverse Momentum of tracks:pT>.5GeV/c • Momentum of tracks:p>.5GeV/c • Number of fitted: TPC hits > 20 • Pseudo-rapidity :||<1(SSD acceptance) • dEdxTrackLength>40 cm • DCA to Primary vertex (transverse), DCAxy< .1 cm • DECAY FIT level • Probability of fit >0.1 && |sLength|<.1cm • Particle ID : ndEdx :|nK|<2, |nπ|<2 • Cuts used to make a pico root file • Kaon opening angle in the CM frame, |Cos(θ*)|<0.6 • |EtaD0| < 1.85 • For D0 - ChargeK<0 && ChargePi>0 • for D0bar -ChargeK > 0 && ChargePi < 0 Number of Events: ~35M

7. D0 signal in 2007 (Run-7) Data (2007 Production MinBias Files) Before background subtraction Offline Cuts: 50<|decayLength|<400, |D0dcaPV|<300, DcaKpi<200um pKaon > 0.7GeV/c pPion > 0.7GeV/c K-π+ D0mass Background subtracted fits Pol3 + gaus pol3 S/N ~ 5.83

8. D0bar signal in 2007 (Run-7) Data (2007 Production MinBias Files) Before background subtraction Offline Cuts: 50<|decayLength|<400, |D0dcaPV|<300, DcaKpi<200um pKaon > 0.7GeV/c pPion > 0.7GeV/c K+π- D0 bar mass Background subtracted fits Pol3 + gaus pol3 S/N ~ 6.51

9. D0+D0bar signal in 2007 (run7) Data(2007 Production MinBias Files) Before background subtraction *same cuts as in previous slide Pol3 + gaus pol3 Background subtracted Fit (S+B) Pol3 + gaus fit Preliminary D0bar/D0 ratio ~ 0.94±0.3

10. Stability of D0bar/D0 Ratio * Cut changed

11. Embedding QA • Microvertexing code successfully produces a D0 peak with the same cuts used in real data. • Previous embedding productions had problem with SVTHitreconstruction. ♯of Events ~ 2.52K SiHits > 2 • Need to increase statistics in new production to draw a conclusion. • QA in progress.

12. Summary and outlook • We present a method (and Preliminary results) using full track information and secondary vertex fit for charm reconstruction using the capabilities of silicon vertex detectors (SVT+SSD). • Initial analysis of near FULL production of Au+Au (Run 7) data ~ 35Million Events • A stable D0 and D0bar signal has been observed • The combined signal (D0+D0bar) has ~10σ significance • Initial results on D0bar/D0 ratio from real data, is compatible with a ratio close to 1. • pT Spectra Calculation and analysis of Embedding Sample for efficiency correction are in progress. • Currently we are doing a new production with fine-tuned cuts ( can preserve the signal candidates better) and elliptic flow information saved. A strong signal is observed with the statistics achieved and without a cut on daughter momenta. • Analysis of 2005 Cu+Cu data (reprocessed with error matrix saved) in progress • Method developed here is baseline to analyses involving Heavy Flavor Tracker (HFT), the future upgrade of STAR.

13. Thank you