Centrality depencence of electron production in AuAu200 GeV

1
Suppression of high-pT non-photonic electrons in
AuAu collisions at vsNN 200 GeV
Jaroslav Bielcik Yale University/BNL
2
Why measure non-photonic electrons?
Non-photonic electrons
indirect way to study heavy quarks

RAA
pp dAu AuAu
how heavy quarks interact with medium
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)
Direct way Hadronic decay channels
e.g. D0?Kp
3
Charm quark production

• Charm is dominantly produced
• in initial hard scattering
• via gluon fusion
• Charm total cross-section should follow
• Nbin scaling from pp to AuAu

STAR scc
Observed binary scaling dAu gt AuAu
4
Heavy flavor electrons in FONLL
heavy flavor e- from FONLL

• FONLL extension of NLO pQCD

scaled to

• Due to mass of heavy quarks its
• production should be calculable in pQCD

Cacciari, Nason, Vogt, Phys.Rev.Lett 95 (2005)

• Beauty predicted to dominate above 4-5 GeV/c

• Crossing point is important because of
• huge c,b mass difference gt
• interactions can be different

5
Uncertainty of c/b contribution

• FONLL
• Large uncertainty on c/b crossing point in
• pT from scales/masses variation it changes
• from 3 to 9 GeV/c

6
Energy loss of quarks in medium
Energy loss depends on properties of medium
(gluon densities, size)
depends on properties of probe (color charge,
mass)
nuclear modification factor
RAA 1 signal of medium
effects RAA hadrons light quarks and
gluons RAA D,electrons heavy quarks c,b
Charm and beauty quarks probe
the nuclear matter in AuAu
7
Energy loss of heavy quarks

• D,B (electrons) spectra are affected by energy
  loss

• 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 case
R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne'
and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997)
291.
ASW Armesto, Salgado, Wiedemann, PRD 69 (2004)
114003
light
time averaged momentum transfer quark-medium per
unit lenght
Dainese, Loizides, Paic, EPJC 38 (2005) 461.
14 GeV2/fm RAA 0.2 light mesons
9
Heavy quark energy loss DVGL case
DVGL Djordjevic, Guylassy Nucl.Phys. A 733, 265
(2004)
Elastic energy loss (Wicks et al
nucl-th/0512076)
dNg/dy1000 gluon density of produced matter
light
RAA 0.2 light mesons
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STAR Detector

• Electrons in STAR
• TPC tracking, PID hlt1.3 f2p
• BEMC (tower, SMD) PID 0lthlt1 f2p
• TOF patch

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Electron ID in STAR EMC

• TPC dE/dx for p gt 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
• EMC
• Tower E ? p/E1 for e-
• Shower Max Detector
• Hadrons/Electron shower develop different shape
• 85-90 purity of electrons
• (pT dependent)
• h discrimination power 103-104

all
pgt1.5 GeV/c2
p/E
SMD
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Photonic electrons background

• Background Mainly from g conv and p0,h Dalitz
• Rejection strategy
• For every electron candidate
• Combinations with all TPC
• electron candidates
• Mee-lt0.14 GeV/c2 flagged photonic
• Correct for primary electrons
• misidentified as background
• Correct for background rejection efficiency
• 50-60 for central AuAu

Inclusive/Photonic
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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

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Electrons from pp x FONLL pQCD
sSTARcc/sFONLL
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

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Electron RAA nuclear modification factor
Armesto et al. hep-th/0511257 van
Hess et al. Phys. Rev. C 73, 034913
(2006) Wicks et al. (DVGL) hep-th/0512076
JB QM2005 nucl-ex/0511005

• 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 pp spectra
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Summary

• Non-photonic electrons from heavy flavor decays
  were measured in ?s 200 GeV pp, dAu and AuAu
  collisions by STAR up to pT10 GeV/c
• Expected to have contribution from
  both charm and beauty
• FONLL underpredicts non-photonic electrons pp
  electrons
• Strong suppression of non-photonic electrons has
  been observed in AuAu, 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 bc 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 bc
  experimentally
• detector upgrades (displaced vertex)
• e-h correlations

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STAR Collaboration
545 Collaborators from 51 Institutions in 12
countries
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 Physics Michigan 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 University Pusan 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 AM 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
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STAR emc x tof x PHENIX
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EMC electrons
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Electron 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
AuAu200GeV the central collisions
determined from electron embedding in real events
the data are corrected for this effect
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Dalitz Decays p0 ? gee- versus (p0,h) ? gee-

• The background efficiency for Dalitz electrons
  is evaluated by weighting with the p0
  distribution but should be weighted by the true
  p0h distribution.
• Comparing the spectra of this both cases
  normalized to give the same integral for pTgt1
  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 bins
a.u.
momentum GeV/c
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dEdx for pt bins
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Hadron suppression
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AuAu AuAu AuAu
Systematical uncertainity dAu and pp 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 0.06 From 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 0.05 0.75 0.15 0.75 0.15 0.75 0.15 from the EMC database tablesClick here for details
Trigger bias uncertainty 8 6 6 5 From the trigger bias fit parameters
Normalization uncertainty 14 for pp Overall normalization for pp


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