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Charmed Meson Measurement using Silicon Detectors (SVT+SSD) in Au+Au

Collisions at 200GeV in STAR Experiment at RHIC

Jaiby JosephKent State University

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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: • D0e++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 reconstructionTypically limited to low momentum

RAA of non photonic electrons in AuAuSTAR Phys. Rev. Lett. 98 (2007) 192301

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[1] Phys. Rev. Lett. 98 (2007) 192301 [2] Phys. Lett. B519 (2001) 199-206

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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.

Microvertexing using STAR Silicon Detectors

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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

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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] http://phys.kent.edu/~margetis/theses/LaHurd.pdf

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Debugging the code - Optimizing the momentum cut

We were applying the cut (wrong cut):pT > 0.5GeV/cp > 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

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Cuts used in reconstruction code

EVENT leveltriggerId : 200001, 200003, 200013Primary vertex position along the beam axis : |zvertex| < 10 cmResolution of the primary vertex position long the beam axis: |zvertex|< 200µm

TRACKS levelNumber of hits in the vertex detectors : SiliconHits>2 (tracks with sufficient DCA resolution)Transverse Momentum of tracks: pT >.5GeV/cMomentum of tracks: p >.5GeV/c Number of fitted: TPC hits > 20 Pseudo-rapidity :||<1 (SSD acceptance)dEdxTrackLength>40 cmDCA to Primary vertex (transverse), DCAxy< .1 cm

DECAY FIT level

Probability of fit >0.1 && |sLength|<.1cm

Particle ID : ndEdx :|nK|<2, |nπ|<2

Cuts used to make a pico root file

Kaon opening angle in the CM frame, |Cos(θ*)|<0.6|EtaD0| < 1.85For D0 - ChargeK<0 && ChargePi>0 for D0bar -ChargeK > 0 && ChargePi < 0

Number of Events:

~35M

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(First production)

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D0 signal in 2007 (Run-7) Data (2007 Production MinBias Files)

Offline Cuts:

50<|decayLength|<400, |D0dcaPV|<300, DcaKpi<200umpKaon > 0.7GeV/cpPion > 0.7GeV/c

K-π+

D0 m

ass

S/N ~ 5.83

Background subtracted

Pol3 + gauspol3

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Before background subtraction

fits

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D0bar signal in 2007 (Run-7) Data (2007 Production MinBias Files)

Offline Cuts:

50<|decayLength|<400, |D0dcaPV|<300, DcaKpi<200umpKaon > 0.7GeV/cpPion > 0.7GeV/c

S/N ~ 6.51

K+π-

D0 ba

r mas

s

Background subtracted

Pol3 + gauspol3

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Before background subtraction

fits

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D0+D0bar signal in 2007 (run7) Data(2007 Production MinBias Files)

Pol3 + gauspol3

Preliminary D0bar/D0 ratio ~ 0.94±0.3

Pol3 + gaus fit

Background subtracted

*same cuts as in previous slide

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Before background subtraction

Fit (S+B)

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Stability of D0bar/D0 RatioCut Sets D0

(raw yield)D0

(S/N)D0bar

(log signal)D0bar (S/N)

D0bar/D0

1. 50<|dL|<400 |D0dcaPV|<300

TrkDca<200pK, pPi > 0.7GeV/c

152.3±26.04 5.83 143.0±21.88 6.51 0.94±0.22

2. 50<dL|<400|D0dcaPV|<400

TrkDca<200pK, pPi > 0.7GeV/c

153.9±26.47 5.82 151.71±22.15 6.87 0.99±0.22

3. 50<|dL|<400|D0dcaPV|<300

TrkDca<300pK, pPi > 0.7GeV/c

250.6±35.08 7.16 209.6±31.86 6.60 0.84±0.17

4. -200<|dL|<400&& |dL|>50|D0dcaPV|<300

TrkDca<200pK, pPi > 0.7GeV/c

113.6±18.18 6.25 150.2±22.68 6.62 1.3±0.29

* Cut changed

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Embedding QA

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• Microvertexing code successfully produces a D0 peak with the same cuts used in real data. • Previous embedding productions had problem with SVTHit reconstruction.

SiHits > 2

Need to increase statistics in new production to draw a conclusion. QA in progress.

♯of Events ~ 2.52K

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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.

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Thank you

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