HOT QUARKS 2006
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jaroslav.bielcik@yale.edu1Hot Quarks 2006
Suppression of high-pT non-photonic electrons in Au+Au collisions at √sNN = 200 GeV
HOT QUARKS 2006
Jaroslav BielcikYale University/BNL
jaroslav.bielcik@yale.edu2Hot Quarks 2006
• Inclusive yields are strongly suppressed in central Au+Au collisions at 200 GeV
Hadron suppression in central AuAuHadron suppression in central AuAu
STARSTAR
Hadron suppression in central AuAu
• Large energy loss of light quarks in the formed nuclear matter
Energy loss depends on properties of medium (gluon densities, size) depends on properties of “probe” (color charge, mass)
Probing the medium with heavy quarks => need to measure heavy quark mesons p+p (d+Au) and Au+Au
jaroslav.bielcik@yale.edu3Hot Quarks 2006
Measuring charm and beauty Measuring charm and beauty
Hadronic decay channels: D0K, D*D0, D+/-
K
(Haibin’s talk) 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)
jaroslav.bielcik@yale.edu4Hot Quarks 2006
Heavy flavor electrons from FONLLHeavy flavor electrons from FONLL
Beauty predicted to dominate above 4-5 GeV/c
heavy flavor e- from FONLL
scaled to
Cacciari, Nason, Vogt, Phys.Rev.Lett 95 (2005)
• Large uncertainty on b/c crossing point in pT: from scales/masses variation it changes from 3 to 9 GeV/c
jaroslav.bielcik@yale.edu5Hot Quarks 2006
Energy loss of heavy quarksEnergy loss of heavy quarks
D, B (electrons)
1)
production
in hard scattering
c, b
2)
quark energy loss
3)
fragmentation
• D,B (electrons) spectra are affected by energy loss
light
M.Djordjevic PRL 94 (2004)
ENERGY LOSS
• Heavy quark has less dE/dx due to suppression of small angle gluon radiation
“Dead Cone” effect
Y. Dokshitzer & D. Kharzeev PLB 519(2001)199Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003
•Effect of collisional energy loss for heavy quarks M.G.Mustafa Phys. Rev C 72 (2005) M.Djordjevic nucl-th/0630066
jaroslav.bielcik@yale.edu6Hot Quarks 2006
Heavy quark energy loss BDMPS case
Heavy quark energy loss BDMPS case
2
ˆTk
q BDMPS: Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003
Dainese, Loizides, Paic, EPJC 38 (2005) 461.
•Model: pQCD + E loss probability (quenching weights) + Glauber collision geometry
Density ( ) “tuned” to match RAA in central Au-Au at 200 GeV/fmGeV 144ˆ 2q q̂
0.4
0.1
hep-ph/0510284
0.20.3
light
heavy
=14 GeV2/fm
RAA ~ 0.2 light mesons
RAA ~ 0.4 for electrons from c+b
q̂
jaroslav.bielcik@yale.edu7Hot Quarks 2006
Heavy quark energy loss DGLV caseHeavy quark energy loss DGLV case
Wicks et al nucl-th/0512076
ignore the data for the moment
DGLV: Djordjevic, Guylassy Nucl.Phys. A 733, 265 (2004)
dNg/dy=1000 gluon density of produced matter
+ Elastic energy loss (Wicks et al nucl-th/0512076)
light
heavy
RAA ~ 0.2 light mesonsRAA ~ 0.4-0.6 for electrons from c+b
Djordjevic et al. Phys.Lett B 632, 81 (2006)
jaroslav.bielcik@yale.edu8Hot Quarks 2006
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 (Haibin talk)
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
Hot Quarks 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/E~1 for e-
b) Shower Max Detector • Hadrons/Electron
shower develop different shape
• Use # hits cuts
85-90% purity of electrons (pT dependent)h discrimination power ~ 103-
104
electrons
K p d
jaroslav.bielcik@yale.edu10Hot Quarks 2006
Photonic electrons backgroundPhotonic electrons background Background: Mainly from conv and Dalitz 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 ~50-60% for central AuAu
M e+e-<0.14 GeV/c2
red likesign
Excess over photonic electrons observed for all system and centralities => non-photonic signal
Inclusive/Photonic:
jaroslav.bielcik@yale.edu11Hot Quarks 2006
STAR non-photonic electron spectra pp, dAu, AuAu sNN = 200 GeV
STAR non-photonic electron spectra pp, dAu, AuAu sNN = 200 GeV
pp, dAu: up to 10 GeV/c AuAu: 0-5%, 10-40%,
40-80% up to 8 GeV/c
Photonic electrons subtracted
Corrected for 10-15% hadron contamination
Beauty is expected to give an importantcontribution above 5 GeV/c
jaroslav.bielcik@yale.edu12Hot Quarks 2006
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 well
Only c contribution would be consistent with the RAA but not the p+p spectra
Armesto et al. hep-th/0511257van Hess et al. Phys. Rev. C 73, 034913 (2006)Wicks et al. (DVGL) hep-th/0512076
jaroslav.bielcik@yale.edu13Hot Quarks 2006
RECENT ELECTRON RAA BY D. TEANEYRECENT ELECTRON RAA BY D. TEANEY
D.Teaney (Moriond 2006) Input: spectrum of c+b from Cacciari et. al.
Weak coupling Boltzmann-Langevin Model Phys.Rev.C71;064904 (2005)
Only collisional energy loss Neglect radiative energy loss (v<6) Hadronization: according to measured fragmentation functions
diffusion coefficientD=3/2T corresponds to dNg/dy~2000
jaroslav.bielcik@yale.edu14Hot Quarks 2006
Large electrons suppression is a PUZZLELarge electrons suppression is a PUZZLE
Large suppression => large dE/dx of heavy quarks (NOT EXPECTED)
Maybe higher at pT? Where b starts to play a role?
Elastic energy loss? Important, helps, but not enough!
Not enough, RAA saturates! Large dNg/dy~ 3500, q ~14 GeV2/fm ?^
Armesto et al. hep-ph/0511257
Recent study on 3 body cqq elastic scattering in QGP
No beauty included!
jaroslav.bielcik@yale.edu15Hot Quarks 2006
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 have contribution from 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 ( RAA similar to light quarks )
Theoretical attempts to explain it seem to fail if both 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
• detector upgrades (displaced vertex)
• e-h correlations
jaroslav.bielcik@yale.edu16Hot Quarks 2006
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
Hot Quarks 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 ~ 103-
104
electrons
K p d
hadrons
electrons
jaroslav.bielcik@yale.edu18Hot Quarks 2006
Charm Total Cross Section
1.13 0.09(stat.) 0.42(sys.) mb in 200GeV minbias Au+Au collsions
1.4 0.2(stat.) 0.4(sys.) mb in 200GeV minbias d+Au collisions
Charm total cross section per NN interaction
Charm total cross section follows roughly Nbin scaling from d+Au to Au+Au considering errors
Indication of charm production in initial collisions
jaroslav.bielcik@yale.edu19Hot Quarks 2006
What is v2?What is v2?
Non-central Au-Au collisions azimuthally anisotropic source of matter in coordinate space azimuthally anisotropic (isotropic) of particles in momentum space, given enough particle interactions Non-zero (zero) v2
v2 is built up at the early stage of the collision so it is a nice probe of the hot and dense medium created at RHIC energy!
)](2cos[
)](cos[212
1
2
1
2
3
3
r
nrn
tt
v
nvdydpp
Nd
dp
NdE
jaroslav.bielcik@yale.edu20Hot Quarks 2006
1 2 3
4 5
1: inclusive
2: OSLM
3: SSLM
4: 2-3
5: 1-(2-3)/eff
OSLM: Opposite Sign Low Invariant Mass; SSLM: Same Sign Low Invariant Mass
Charm electron v2 determination
AFTER SUBTRACTING BACKGOUND CONTRIBUTION – LARGE SYSTEMATIC ERRORS
jaroslav.bielcik@yale.edu21Hot Quarks 2006
The detector material in STAR caused too much photonic background, which caused huge systematic and statistical uncertainties. Our result is not sensitive enough to make any conclusion about heavy quark v2 so far.
Electron v2 with new method – large systematic errors
jaroslav.bielcik@yale.edu22Hot Quarks 2006
Charm energy lossCharm energy loss
Strong suppression observed! Indicates charm energy loss in medium.
For D0 RAA, stat. error only.
STAR Preliminary
jaroslav.bielcik@yale.edu23Hot Quarks 2006
Hadron contamination p/E methodHadron contamination p/E method
jaroslav.bielcik@yale.edu24Hot Quarks 2006
Electron reconstruction efficiencyElectron reconstruction efficiency
AuAu200GeV the central collisions
determined from electron embedding in real events
the data are corrected for this effect
jaroslav.bielcik@yale.edu25Hot Quarks 2006
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
jaroslav.bielcik@yale.edu26Hot Quarks 2006
Two fake conversion points reconstructed
(picking one closer to primary vertex)
jaroslav.bielcik@yale.edu27Hot Quarks 2006
Trigger biasTrigger bias
MB/HT ratio (0-5%)
jaroslav.bielcik@yale.edu28Hot Quarks 2006
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!
jaroslav.bielcik@yale.edu29Hot Quarks 2006
Electron/Hadron ratioElectron/Hadron ratio
jaroslav.bielcik@yale.edu30Hot Quarks 2006
jaroslav.bielcik@yale.edu31Hot Quarks 2006
P/E in momentum binsP/E in momentum bins
momentum [GeV/c]
a.u
.
jaroslav.bielcik@yale.edu32Hot Quarks 2006
dEdx for pt bins dEdx for pt bins
jaroslav.bielcik@yale.edu33Hot Quarks 2006
Inclusive electron spectra AuAu sNN = 200 GeV
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%
jaroslav.bielcik@yale.edu34Hot Quarks 2006
STAR non-photonic electron spectra pp,dAu,AuAu sNN = 200 GeV
STAR non-photonic electron spectra pp,dAu,AuAu sNN = 200 GeV
Photonic electrons subtractedExcess over photonic electrons observedConsistent with STAR TOF spectra
Beauty is expected to give an important contribution above 5 GeV/c
jaroslav.bielcik@yale.edu35Hot Quarks 2006
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
jaroslav.bielcik@yale.edu36Hot Quarks 2006
Inclusive electron spectra sNN = 200 GeVInclusive electron spectra sNN = 200 GeV
TOF electrons
STAR Preliminary
Excess of electrons over photonic background in all centralities and systems Corrected for 10-15% hadron contamination
jaroslav.bielcik@yale.edu37Hot Quarks 2006
STAR non-photonic electron spectra pp,dAu,AuAu sNN = 200 GeV
STAR non-photonic electron spectra pp,dAu,AuAu sNN = 200 GeV
Photonic electrons subtracted
Consistent with STAR TOF spectra
Consistent with PHENIX
Beauty is expected to give an important contribution above 5 GeV/c
STAR Preliminary
jaroslav.bielcik@yale.edu38Hot Quarks 2006
jaroslav.bielcik@yale.edu39Hot Quarks 2006
Hadron suppressionHadron suppression
jaroslav.bielcik@yale.edu40Hot Quarks 2006
Au+Au
Systematical uncertainity
d+Au and p+p 40-80% 10-40% 0-5% Notes
electron id and track efficiency
(including dE/dx cut efficiency)
0.25 + 0.05 (2 GeV/c)
0.50 + 0.05(8 GeV/c)
0.16 + 0.05 (2 GeV/c)
0.47 + 0.05(8 GeV/c)
0.14 + 0.05 (2 GeV/c)
0.47 + 0.05(8 GeV/c)
0.13 + 0.05 (2 GeV/c)
0.45 + 0.05(8 GeV/c)
Obtained from embedding, using different cluster finder and
electron cuts.See a plot here of the efficiency variationsfor 0-5% most central Au-Au
Hadronic contamination
(0.50 + 0.03)% (2 GeV/c)
(20 + 4)% (8 GeV/c)
(2.0 + 0.1)%(2 GeV/c)
(20 + 4)%(8 GeV/c)
(2.0 + 0.1)%(2 GeV/c)
(20 + 4)%(8 GeV/c)
(2.0 + 0.1)%(2 GeV/c)
(22 + 5)%(8 GeV/c)
Obtained from changing dE/dx fit parameters
Background finding efficiency
0.65 + 0.06 0.67 + 0.06 0.62 + 0.06 0.56 + 0.06From different photon weigthfunctions and systematical
differences between Alex/Jaro/Yifei/Weijiang and Frank analysis
Bremsstrahlung
0.86 + 0.14 (2 GeV/c)
1.05 + 0.05 (8 GeV/c)
0.9 + 0.1 (2 GeV/c)
1.1 + 0.1(8 GeV/c)
0.9 + 0.1 (2 GeV/c)
1.1 + 0.1(8 GeV/c)
0.9 + 0.1 (2 GeV/c)
1.1 + 0.1(8 GeV/c)
Use the size of the correction as suggested by Jamie
Acceptance 0.84 + 0.050.75 + 0.15 0.75 + 0.15 0.75 + 0.15
from the EMC database tables
Click here for details
Trigger bias uncertainty 8% 6% 6% 5%
From the trigger bias fit parameters
Normalization uncertainty 14% for p+p Overall normalization for p+p
jaroslav.bielcik@yale.edu41Hot Quarks 2006
for the collaboration
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