suppression of high-p t non-photonic electrons in au+au collisions at √s nn = 200 gev
DESCRIPTION
Suppression of high-p T non-photonic electrons in Au+Au collisions at √s NN = 200 GeV. Jaroslav Bielcik Yale University/BNL. Why measure non-photonic electrons?. Non-photonic electrons indirect way to study heavy quarks. R AA. p+p – d+Au – Au+Au. - PowerPoint PPT PresentationTRANSCRIPT
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Suppression of high-pT non-photonic electrons in Au+Au collisionsat √sNN = 200 GeV Jaroslav BielcikYale University/BNL
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Why measure non-photonic electrons?Why measure non-photonic electrons?
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%)
Non-photonic electrons indirect way to study heavy quarks
p+p – d+Au – Au+Au how heavy quarks interact with medium
Direct way: Hadronic decay channels: e.g. D0K
RAA
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Charm quark productionCharm quark production
Z. Lin & M. Gyulassy, PRC 51 (1995) 2177 Charm is dominantly produced
in initial hard scattering
via gluon fusion:
Charm total cross-section should follow
Nbin scaling from p+p to Au+Au
Observed binary scaling d+Au => Au+Au
STAR cc
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Beauty predicted to dominate above 4-5 GeV/c
heavy flavor e- from FONLL
scaled to
Cacciari, Nason, Vogt, Phys.Rev.Lett 95 (2005)
Heavy flavor electrons in FONLLHeavy flavor electrons in FONLL
• Due to mass of heavy quarks it’s production should be calculable in pQCD
• FONLL: extension of NLO pQCD
• Crossing point is important because of huge c,b mass difference => interactions can be different
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• FONLL: Large uncertainty on c/b crossing point in pT: from scales/masses variation it changes from 3 to 9 GeV/c
Uncertainty of c/b contributionUncertainty of c/b contribution
set PDF,,,mm
m FR varying
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Energy loss of quarks in mediumEnergy loss of quarks in medium
Charm and beauty quarks probe the nuclear matter in Au+Au
Energy loss depends on properties of medium (gluon densities, size) depends on properties of “probe” (color charge, mass)
tpp
tAA
colltAA dpdN
dpdN
NpR
/
/1)(
nuclear modification factor:
RAA 1 … signal of medium effects
RAA hadrons … light quarks and gluons
RAA D,electrons … heavy quarks: c,b
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Energy loss of heavy quarksEnergy loss of heavy quarks
• 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
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Heavy quark energy loss ASW caseHeavy quark energy loss ASW case
2
ˆTk
q
ASW: Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003
Dainese, Loizides, Paic, EPJC 38 (2005) 461.
/fmGeV 144ˆ 2q Density ( ) “tuned” to match RAA in central Au+Au at 200 GeV
q̂
light
=14 GeV2/fm
RAA ~ 0.2 light mesons
q̂
time averaged momentum transferquark-medium per unit lenght
2 ˆ LqCE Rs
0.4
0.1
hep-ph/0510284
0.20.3
heavy
RAA ~ 0.4 for electrons from c+b
R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997) 291.
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Heavy quark energy loss DVGL caseHeavy quark energy loss DVGL case
DVGL: 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
RAA ~ 0.2 light mesons
RAA ~ 0.4-0.6 for electrons from c+b
heavy
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STAR Detector STAR Detector
Electrons in STAR: TPC: tracking, PID ||<1.3 =2 BEMC (tower, SMD): PID 0<<1 =2 TOF patch
HighTower trigger: Only events with high tower ET>3 GeV/c2
Enhancement of high pT
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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
85-90% purity of electrons (pT dependent) h discrimination power ~ 103-
104
electrons
K p d
allp>1.5 GeV/c2
p/E
SMD
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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 Au+Au
M e+e-<0.14 GeV/c2
red likesign
Inclusive/Photonic:
Excess over photonic electrons observed for all system and centralities => non-photonic signal
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STAR non-photonic electron spectra p+p, d+Au, Au+Au sNN = 200 GeV
STAR non-photonic electron spectra p+p, d+Au, Au+Au sNN = 200 GeV
p+p, d+Au: up to 10 GeV/c
Au+Au: 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
JB QM2005 nucl-ex/0511005
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STAR preliminary
Electrons from p+p x FONLL pQCDElectrons from p+p x FONLL pQCD
5.5
FONLL has to be scaled by factor ~5.5 to match the data Ratio Data/FONLL is constant ~ pT: both charm and beauty are needed to get shape both charm and beauty are off in FONLL
STARcc/FONLL
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Electron RAA nuclear modification factorElectron RAA 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
JB QM2005 nucl-ex/0511005
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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
FONLL underpredicts non-photonic electrons p+p electrons
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?
Collisional energy loss, multibody effects…
It is desirable to separate contribution b+c experimentally
• detector upgrades (displaced vertex)
• e-h correlations
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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
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STAR emc x tof x PHENIXSTAR emc x tof x PHENIX
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Electron reconstruction efficiencyElectron reconstruction efficiency
AuAu200GeV the central collisions
determined from electron embedding in real events
the data are corrected for this effect
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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
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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!
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P/E in momentum binsP/E in momentum bins
momentum [GeV/c]
a.u
.
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dEdx for pt bins dEdx for pt bins
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Hadron suppressionHadron suppression
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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
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R.Vogt Slides
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R.Vogt Slides
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R.Vogt Slides
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R.Vogt Slides