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Heavy flavor Heavy flavor production in production in
STAR.STAR.
What can charm and What can charm and beauty tell us about beauty tell us about matter in heavy ion matter in heavy ion
collisions?collisions?Manuel Calderón de la Barca SánchezUC Davisfor the STAR collaboration
DIS 2006Tsukuba, Japan 21/April/2006
21/April/2006 Manuel Calderón de la Barca2
Light quark sector Light quark sector highlightshighlights
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
Large energy loss of light quarks in the formed nuclear matter
Phys. Rev. Lett. 91, 072304 (2003).
Pedestal&flow subtracted
STARSTAR
Jet quenching Hadron suppression in central AuAu
21/April/2006 Manuel Calderón de la Barca3
Heavy quarks in a hot Heavy quarks in a hot mediummedium
Quenching weights, more Quenching weights, more recent way to study energy recent way to study energy loss of heavy quarks in a loss of heavy quarks in a dense medium.dense medium.
Armesto et al. Armesto et al. hep-ph/0501225hep-ph/0501225
Energy loss depends on properties of medium (gluon densities, size) depends on properties of “probe” (color charge, mass)
c, b D, B
1)
production
2)
quark energy loss
3)
fragmentation
• D,B spectra are affected by energy loss, and might be more sensitive to medium properties than light quarks.
• Heavy quark has less dE/dx due to suppression of small angle gluon radiation
“Dead Cone” effectY. Dokshitzer & D. Kharzeev PLB 519(2001)199
Elastic energy loss for heavy quarks? Might have an effect. M.G.Mustafa Phys. Rev C 72 (2005)
21/April/2006 Manuel Calderón de la Barca4
Measuring heavy flavorsMeasuring heavy flavors
Hadronic decay channels:Hadronic decay channels: DD00KK, D, D**DD00, D, D+/-+/-KK
Non-photonicNon-photonic electrons: electrons: Semileptonic channels:Semileptonic channels:
c c e e++ + anything + anything (B.R.: 9.6%(B.R.: 9.6%)) DD0 0 e e++ + anything + anything (B.R.: 6.87%(B.R.: 6.87%) ) DD e e + anything + anything (B.R.: 17.2%(B.R.: 17.2%))
b b e e++ + anything + anything (B.R.: 10.9%(B.R.: 10.9%)) BB e e + anything + anything (B.R.: 10.2%(B.R.: 10.2%))
Drell-Yan Drell-Yan (small contribution for p(small contribution for pTT < 10 GeV/c at RHIC) < 10 GeV/c at RHIC)
PhotonicPhotonic electron background: electron background: conversionsconversions ( ( e e++ee-- ) ) ’ ’ Dalitz decaysDalitz decays … … decays (small)decays (small) KKe3e3 decays (small)decays (small)
21/April/2006 Manuel Calderón de la Barca5
Charm reconstruction via hadronic Charm reconstruction via hadronic decaysdecays
nucl-ex/0510063
D0
STAR Phys. Rev. Lett. 94 (2005)
dAu: 1.4 0.2(stat.) 0.4(sys.) mbAuAu: 1.11 0.08(stat.) 0.42(sys.) mb
Total charm cross section per NN interaction
Assumes Binary scaling dAu to AuAu Charm produced in initial collisions . Systematics and statistics limited (only 3 pT bins in Au+Au).
21/April/2006 Manuel Calderón de la Barca6
Charm reconstruction via Charm reconstruction via muonsmuons
Use dE/dx at low p.Use dE/dx at low p. Add TOF information Add TOF information
(limited acceptance)(limited acceptance)
e
0.15<pT<0.25 GeV/c, DCA<3cm
All particle
After de/dx cutSTAR Preliminary
1) Data
2) Primary track
3) B.G. (K, decay)
4) Sum of 2),3)
c→ at low pT (no photonic/Dalitz backgrounds)
only limited to very low pT.
21/April/2006 Manuel Calderón de la Barca7
dNg/dy=1000 small suppression RAA ~ 0.7 for c+b
Predictions of electron nuclear modification factor Predictions of electron nuclear modification factor RRAAAA
Beauty predicted to dominate above 4-5 GeV/c
Single e- from NLO/FONLL
scaled to
M. Cacciari et al., hep-ph/0502203
dNg/dy=3500 medium suppression RAA ~ 0.5 for c+b
q=14 GeV2/fm medium suppression RAA ~ 0.4 for c+b ^
Two different theories:
Theory I: Djordjevic et al.:
Theory II: Armesto et al.:
21/April/2006 Manuel Calderón de la Barca8
Electrons at pElectrons at pTT 5-10 GeV. 5-10 GeV.Use trigger detectors:
TPC: tracking, PID ||<1.3 =2 BEMC (tower, SMD): PID 0<<1 =2 TOF patch good for low pT, acc. small, no trigger
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 )
Preliminary results from:
HighTower trigger: Only events with high tower ET>3 GeV/c2
Enhancement of high pT
21/April/2006 Manuel Calderón de la Barca9
hadrons electrons
Electron ID in STAR – EMCElectron ID in STAR – EMC1. 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 in Shower Max to discriminate
85-90% purity of electrons (pT dependent)h discrimination power ~ 103-
104
electrons
K p d
hadrons
electrons
8
21/April/2006 Manuel Calderón de la Barca10
Electron backgroundElectron background Inclusive electron spectra:Inclusive electron spectra: Signal Signal
− HHeavy quarkeavy quarkss semi-leptonic semi-leptonic decaydecayss
DominantDominant backgroundbackground− Instrumental:Instrumental:
- - γγ conversion conversion– Hadronic decays:Hadronic decays:
- Dalitz decays (- Dalitz decays (ππ00, , ηη) )
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
21/April/2006 Manuel Calderón de la Barca11
Electrons, muons, D0 Electrons, muons, D0 resultsresults
At low pt, consistent with binary scalingAt low pt, consistent with binary scaling Large errors still for D0 measurement.Large errors still for D0 measurement.
Higher pt, begin to see suppression…Higher pt, begin to see suppression…
21/April/2006 Manuel Calderón de la Barca12
Non-photonic electron spectra at higher pNon-photonic electron spectra at higher pTT pp,dAu,AuAu pp,dAu,AuAu ssNNNN = 200 GeV = 200 GeV
Photonic electrons subtracted
Excess over photonic electrons observed
Corrected for 10-15% hadron contamination
Beauty contribution, can it be disentangled? pQCD calculations can give a range from 2-10 GeV for the c-b crossover in the e spectra.
21/April/2006 Manuel Calderón de la Barca13
pp
AA
AAAA
dpd
T
dpNd
R
3
3
3
3
RRAAAA nuclear modification factor 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
Curves with c-only match RAA but, of course, not the p+p spectra
Armesto et al. hep-th/0511257van Hess et al. hep-th/0508055Wicks et al. hep-th/0512076
21/April/2006 Manuel Calderón de la Barca14
Large electron suppression is a Large electron suppression is a PUZZLEPUZZLE
Large suppression => large dE/dx of heavy quarks (NOT EXPECTED)
Maybe higher at pT? Where is b contribution?
Elastic energy loss? Important, helps, but not enough!
Not enough, RAA saturates!
Armesto et al. hep-ph/0511257
The low end of c-b overlap
The high end of c-b overlap
Wicks et al nucl-th/0512076
Recent study on 3 body cqq elastic scattering in QGP
No beauty included!
Liu&Ko nucl-th/0603004
Large dNg/dx~ 3500, 2ˆ ~ 14GeV /q fm
21/April/2006 Manuel Calderón de la Barca15
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 Expected to be sensitive to both charm and beauty
Strong suppression of non-photonic electrons has been observed in Au+Au increasing with centrality Suggests large energy loss for heavy quarks
(similar to light quarks )
Theoretical attempts to explain suppression fail if b+c are included What is the contribution of b? Are there other/different
contributions to energy loss? It is desirable to separate contribution b+c
experimentally direct reconstruction of other detector upgrades
displaced vertex in heavy ion environment?! Large acceptance TOF (Ds and c, 2009)
e-h correlations
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