Jaroslav Bielcik

1
Heavy flavor physics in STAR

• Jaroslav Bielcik
• Yale University/BNL

• Motivation
• Charm via hadronic decays
• STAR and electron ID
• Analysis of nonphotonic electrons
• Results pp, dAu, and AuAu at ?sNN 200 GeV
• Summary

2
Light quarks sector

• Inclusive yields and back-to-back di-hadron
  correlations are very similar in
• pp and dAu collisions
• Both are strongly suppressed in central AuAu
  collisions at 200 GeV

• 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)
3
Heavy quarks sector
D, B

• D,B spectra are affected by energy loss

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

4
Measuring charm and beauty

• Hadronic decay channels D0?Kp, D?D0p,
  D/-?Kpp
• 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 lt 10 GeV/c)
• Photonic electron background
• g conversions (p0 ? gg g ? ee- )
• p0, h, h Dalitz decays
• r, f decays (small)
• Ke3 decays (small)

5
Charm reconstruction via hadronic decays
Total charm cross section per NN interaction
dAu 1.4 ? 0.2(stat.) ? 0.4(sys.) mb
AuAu 1.11? 0.08(stat.) ? 0.42(sys.) mb
Binary scaling dAu to AuAu ? Charm produced in
initial phase of the


collision
6
Expected electron nuclear modification factor
RAA
Two different theories
Single e- from FONLL
scaled to
M. Cacciari et al., Phys.Rev.Lett 95 (2005)
Theory I Djordjevic et al.(DVGL)

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

dNg/dy1000 small suppression RAA 0.7
for cb
dNg/dy3500 medium suppression RAA 0.5 for
cb
Theory II Armesto et al.
7
STAR Detector and Data Sample

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

Preliminary results from
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 )
8
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/E
• 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

8
9
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

• Excess over photonic electrons observed
• for all system and centralities
• gt non-photonic signal

10
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

11
RAA nuclear modification factor
Armesto et al. hep-th/0511257 van
Hess et al. hep-th/0508055 Wicks et
al. (DVGL) hep-th/0512076

• 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
12
Large electrons suppression is a PUZZLE

• Large suppression gt large dE/dx of heavy
  quarks (NOT EXPECTED)

Not enough, RAA saturates!

• Where b starts to play a role?

Maybe higher at pT?

• Elastic energy loss?

Important, helps, but not enough!

• Recent study on 3 body cqq
• elastic scattering in QGP

No beauty included!
13
Summary

• Direct charm reconstruction in dAu and AuAu
  from hadronic decays
• 
  
  (binary scalling)
• Charm is produced in initial phase
  of the collision
• 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
• Strong suppression of non-photonic electrons has
  been observed in AuAu, increasing with
  centrality
• Suggests large energy loss for heavy
  quarks
• 
  (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?

• It is desirable to separate contribution bc
  experimentally
• detector upgrades (displaced vertex)
• e-h correlations