lake louise 2006 jaroslav bielcik, yale/bnl 1 motivation star and electron id analysis results:...

Jaroslav Bielcik, Yale/BNL1Lake Louise 2006

Motivation STAR and electron ID Analysis Results: p+p, d+Au, and Au+Au at sNN = 200 GeV Summary

Jaroslav BielcikYale University/BNL

for the collaboration

Centrality dependence of heavy flavor production

from single electron measurements


STAR is one of the 4 experiments at RHIC in BNL on Long Island

545 Collaborators from 51 Institutions in 12 countries

RHIC has been exploring nuclear matter at extreme conditions over the last few years

STAR:


Phys. Rev. Lett. 91, 072304 (2003).

Pedestal&flow subtracted

• Inclusive yields and back-to-back di-hadron correlations are very similar in p+p and d+Au collisions

• Both are strongly suppressed in central Au+Au collisions at 200 GeV

STARSTAR

Light quarks sectorLight quarks sector

Jet quenching Hadron suppression in central AuAu

• Large energy loss of light quarks in the formed nuclear matter


Heavy quarks sectorHeavy quarks sector

c, b

D, B

1)

production

2)

medium energy loss

3)

fragmentation

• D,B spectra are affected by energy loss

• Can we learn something from the difference between heavy and light quarks? • How do heavy quarks interact with the medium?

– Thermalization in early stage of collision, suppression?

light

M.Djordjevic PRL 94 (2004)

ENERGY LOSS

• Heavy quark has less dE/dx due to suppression of small angle gluon radiation“Dead Cone”

effectY. Dokshitzer & D. Kharzeev PLB 519(2001)199

•Effect of elastic energy loss for heavy quarks M.G.Mustafa Phys. Rev C 72 (2005)


Detecting charm/beauty via semileptonic D/B decays

Detecting charm/beauty via semileptonic D/B decays

Hadronic decay channels: D0K, D*D0, D+/-

K

Non-photonic electrons: Semileptonic channels:

c e+ + anything (B.R.: 9.6%)– D0 e+ + anything (B.R.: 6.87%) – D e + anything (B.R.: 17.2%)

b e+ + anything (B.R.: 10.9%)– B e + anything (B.R.: 10.2%)

Drell-Yan (small contribution for pT < 10 GeV/c)

Photonic electron background: conversions ( e+e- ) ’ Dalitz decays … decays (small) Ke3 decays (small)

D0

Phys. Rev. Lett. 94 (2005)H.Zhang QM2005


Predictions of electron nuclear modification Predictions of electron nuclear modification factor Rfactor RAAAA

Beauty predicted to dominate above 4-5 GeV/c

Single e- from NLO/FONLL

scaled to

M. Cacciari et al., hep-ph/0502203

• electron suppression up to 2 large electron suppression of ~ 5 for c medium suppression of ~ 2.5 for c+b


STAR Detector and Data SampleSTAR Detector and Data Sample

Electrons in STAR: TPC: tracking, PID ||<1.3 =2 BEMC (tower, SMD): PID 0<<1 =2 TOF patch

Run2003/2004 min. bias. 6.7M events with half field high tower trigger 2.6M events with full field (45% of all) 10% central 4.2M events (15% of all )

Processed:

HighTower trigger: Only events with high tower ET>3 GeV/c2

Enhancement of high pT

Lake Louise 2006

hadrons electrons

Electron ID in STAR – EMCElectron ID in STAR – EMC

1. TPC: dE/dx for p > 1.5 GeV/c• Only primary tracks (reduces effective

radiation length)• Electrons can be

discriminated well from hadrons up to 8 GeV/c

• Allows to determine the remaining hadron contamination after EMC

2. EMC: a) Tower E ⇒ p/Eb) Shower Max Detector

(SMD)• Hadrons/Electron

shower develop different shape

• Use # hits cuts

85-90% purity of electrons (pT dependent)h discrimination power ~ 102-

104

electrons

K p d

hadrons

electrons

8


Electron backgroundElectron background

Inclusive electron spectra: Signal

− Heavy quarks semi-leptonic decays

Dominant background− Instrumental:

- γ conversion– Hadronic decays: - Dalitz decays (π0, η)

Rejection strategy: For every electron candidate

Combinations with all TPC electron candidates Me+e-<0.14 GeV/c2 flagged photonic Correct for primary electrons misidentified as background Correct for background rejection efficiency

Background rejection efficiency central Au+Au

M e+e-<0.14 GeV/c2

red likesign


Inclusive electron spectra AuAu sNN = 200 GeV


High tower trigger allows STAR to extend electron spectra up to 10 GeV/c

3 centrality bins: 0-5%

10-40%

40-80%

Corrected for hadron contamination ~10-15%


STAR non-photonic electron spectra pp,dAu,AuAu sNN = 200 GeV


Photonic electrons subtracted

Excess over photonic electrons observed

Consistent with STAR TOF spectra

Beauty is expected to give an important contribution above 5 GeV/c


pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

RAA nuclear modification factorRAA nuclear modification factor

Suppression up to ~ 0.5-0.6 observed in 40-80% centrality

~ 0.5 -0.6 in centrality 10-40%

Strong suppression up to ~ 0.2 observed at high pT in 0-5%

Maximum of suppression at pT ~ 5-6 GeV/c

Theories currently do not describe the data

Only c contribution would describe the RAA but not the p+p spectra


SummarySummary Non-photonic electrons from heavy flavor

decays were measured in s = 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 centralityRAA ~ 0.2-0.3 for pT> 3 GeV/c suggests large energy loss for heavy quarks

Reconsidering of energy loss mechanism needed

(incl. b suppression and centrality dependence)

Finalization of the data e-e correlation (what happens with the other D?)e-h correlation (heavy flavor tagged jets)


Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern University of Birmingham Brookhaven National Laboratory California Institute of Technology University of California, Berkeley University of California - Davis University of California - Los Angeles Carnegie Mellon University Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna University of Frankfurt Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut de Recherches Subatomiques de

Strasbourg University of Jammu Kent State University Institute of Modern Physics. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer PhysicsMichigan State University Moscow Engineering Physics Institute

City College of New York NIKHEF Ohio State University

Panjab University Pennsylvania State University

Institute of High Energy Physics - Protvino Purdue UniversityPusan University

University of Rajasthan Rice University

Instituto de Fisica da Universidade de Sao Paulo

University of Science and Technology of China - USTC

Shanghai Institue of Applied Physics - SINAP SUBATECH

Texas A&M University University of Texas - Austin

Tsinghua University Valparaiso University

Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology

University of Washington Wayne State University

Institute of Particle Physics Yale University

University of Zagreb

545 Collaborators from 51 Institutionsin 12 countries

STAR CollaborationSTAR Collaboration


BACK UP SLIDES


Hadron contamination p/E methodHadron contamination p/E method


Electron reconstruction efficiencyElectron reconstruction efficiency

AuAu200GeV the central collisions

determined from electron embedding in real events

the data are corrected for this effect


Part of the primary electrons is flaged as background

Part of the primary electrons is flaged as background

AuAu200GeV the central collisions

determined from electron embedding in real events

the data are corrected for this effect


Two fake conversion points reconstructed

(picking one closer to primary vertex)


Trigger biasTrigger bias

MB/HT ratio (0-5%)


Dalitz Decays: ee versus eeDalitz Decays: ee versus ee

The background efficiency for Dalitz electrons is evaluated by weighting with the 0 distribution but should be weighted by the true distribution.

Comparing the spectra of this both cases normalized to give the same integral for pT>1 GeV/c (cut-off for electron spectra) we see almost no deviation. The effect of under/over correction is on the few percent level!


Electron/Hadron ratioElectron/Hadron ratio


P/E in momentum binsP/E in momentum bins

momentum [GeV/c]

a.u

.


dEdx for pt 6.5-7.0 GeV/cdEdx for pt 6.5-7.0 GeV/c

•After EMC ID cuts the separation with dEdx is still good for high pT




High tower trigger allows STAR to extend electron spectra up to 10 GeV/c

3 centrality bins: 0-5%

10-40%

40-80%

Corrected for hadron contamination ~10-15%




Photonic electrons subtracted

Excess over photonic electrons observed

Consistent with STAR TOF spectra

Beauty is expected to give an important contribution above 5 GeV/c


pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

RAA nuclear modification factorRAA nuclear modification factor

Suppression up to ~ 0.4-0.6 observed in 40-80% centrality

~ 0.3 -0.4 in centrality 10-40%

Strong suppression up to ~ 0.2 observed at high pT in 0-5%

Maximum of suppression at pT ~ 5-6 GeV/c

lake louise 2006 jaroslav bielcik, yale/bnl 1 motivation star and electron id analysis results:...

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