Charmed Meson Measurement using Silicon Detectors (SVT+SSD) in Au+Au Collisions at 200GeV in STAR Experiment at RHIC Jaiby Joseph Kent State University 1/26/111

2 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 micro-vertexing code  Monte Carlo studies for online/offline cuts  productions of Micro DSTs and Pico-DSTs  signal extraction, optimization, fitting, pt binning  Embedding QA, Study of Systematics and Physics Analysis

Charm work (D 0 /D 0 -bar) ANALYSIS Run GeV/c (calibration sample) Run GeV/c (last silicon run) estimated/expected a sigma effect based on data sample, resolutions and ctau Analysis done from ‘scratch’ Calibration (Alignment and SVT drift velocity) Tracking Upgrade (Kalman) to use Silicon to have full track info in vacuum (incl. errors) develop sec. vertex fitters (LSM, Kalman) run simulations/determine production cuts run 1-3 productions do Embedding + stability correction factors Physics 1/26/113

Kaon decay angle In cm frame Previous studies showed that abs(cos-theta*)<0.6 cuts most background It also avoids kinematical edges (soft kaon/pion) Example of cut studies 1/26/114

Cuts used in reconstruction code EVENT level triggerId : , , 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: p T >.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), DCA xy <.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 |EtaD 0 | < 1.85 For D 0 - ChargeK 0 for D 0 bar -ChargeK > 0 && ChargePi < 0 Number of Events: ~35M 1/26/115 (First production)

D 0 signal in 2007 (Run-7) Data (2007 Production MinBias Files) Offline Cuts: 50<|decayLength|<400, |D0dcaPV|<300, DcaKpi<200um pKaon > 0.7GeV/c pPion > 0.7GeV/c D 0 mass S/N ~ 5.83 Background subtracted Pol3 + gaus pol3 1/26/116 Before background subtraction K-π+K-π+

D 0- bar signal in 2007 (Run-7) Data (2007 Production MinBias Files) Offline Cuts: 50<|decayLength|<400, |D0dcaPV|<300, DcaKpi<200um pKaon > 0.7GeV/c pPion > 0.7GeV/c S/N ~ 6.51 Background subtracted 1/26/11 7 K+π-K+π-

D 0 +D 0 bar signal in 2007 (run7) Data (2007 Production MinBias Files) Preliminary D0bar/D0 ratio ~ 0.94±0.3 Pol3 + gaus pol3 Background subtracted *same cuts as in previous slide 81/26/11

Stability studies of D 0 bar/D 0 Ratio Cut Sets D0 (raw yield) D0 (S/N) D0bar (log signal) D0bar (S/N) D 0 bar/D <|dL|<400 |D0dcaPV|<300 TrkDca<200 pK, pPi > 0.7GeV/c 152.3± ± ± <dL|<400 |D0dcaPV|<400 TrkDca<200 pK, pPi > 0.7GeV/c 153.9± ± ± <|dL|<400 |D0dcaPV|<300 TrkDca<300 pK, pPi > 0.7GeV/c 250.6± ± ± |D0dcaPV|<300 TrkDca<200 pK, pPi > 0.7GeV/c 113.6± ± ±0.29 * Cut changed 1/26/119

Embedding QA 1/26/1110 Microvertexing code successfully produces a D 0 peak with the same cuts used in real data. Previous embedding productions had problem with SVTHit reconstruction.  Need to complete detector stability studies (Jonathan).  Extract time-dependent correction factors  QA in progress.

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 shows a stable D 0 and D 0 bar signal. The combined signal (D 0 +D 0 bar) has ~10σ significance  Preliminary results on D 0 bar/D 0 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. 1/26/1111

Thank you 1/26/1112

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: D 0  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 D 0 (D 0 )  K -  + (K +  - )BR : 3.8 % D +/-  K  BR : 9.2% Full Topological reconstruction Typically limited to low momentum R AA of non photonic electrons in AuAu STAR Phys. Rev. Lett. 98 (2007) /26/1113 [1] Phys. Rev. Lett. 98 (2007) [2] Phys. Lett. B519 (2001)

1/26/1114 Debugging the code - Optimizing the dE/dx cut  From a previous study it was shown 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]

1/26/1115 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 GeV/c is about 60% due to the cut on daughter momenta > 0.7GeV/c New Cut: (P K +P π ) > 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

D 0- bar signal in 2007 (Run-7) Data (2007 Production MinBias Files) Offline Cuts: 50<|decayLength|<400, |D0dcaPV|<300, DcaKpi<200um pKaon > 0.7GeV/c pPion > 0.7GeV/c S/N ~ 6.51 K+π-K+π- D 0 bar mass Background subtracted Pol3 + gaus pol3 1/26/1116 Before background subtraction fits

D 0 +D 0 bar signal in 2007 (run7) Data (2007 Production MinBias Files) Pol3 + gaus pol3 Preliminary D0bar/D0 ratio ~ 0.94±0.3 Pol3 + gaus fit Background subtracted *same cuts as in previous slide 1/26/1117 Before background subtraction Fit (S+B)