Overview of charm physics in STAR

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Overview of charm physics in STAR

• Jaro Bielcik

Yale-Columbia Fest Yale JAN 2007
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CHARM and BEAUTY HOT TOPICS IN STAR

• Open Flavors
• charm mesons D0,Ds
• non-photonic electrons spectra
• muon spectrum
• electron-hadron correlations
• Quarkonia
• J/? reconstruction
• ? reconstruction

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Charm measurements at STAR

• Direct D0 reconstruction
• muon from charm semileptonic decay
• electron from heavy quark semileptonic decay

?-
semileptonic decay
c ? e anything (B.R. 10.3) c ? ? anything
(B.R. 9.5) D0 ? e anything (B.R. 6.9) D0 ?
? anything (B.R. 6.5)
D0 ? K p (B.R. 3.8)
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Charm via hadronic decays
TPC only
D0 in dAu and AuAu at 200GeV (pT 0.1- 3.0
GeV/c)
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Non-photonic electrons I-st part
TPCTOF

• photonic background must
• be constructed and subtracted

• only tiny part of TOF
• pT 0.9-5.0 GeV/c

QM2006
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Muon measurement
TPCTOF

• There are no photonic muons !!!
• pT 0.16-0.26 GeV/c
• it is good that it is so low pT

m2(p/b/g)2
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Charm total cross sections

• 1.4 ? 0.2(stat.) ? 0.4(sys.) mb
• in 200GeV minbias dAu
• 1.26 ? 0.09 ? 0.23 mb
• in 200GeV minbias AuAu
• 1.33 ? 0.06 ? 0.18 mb
• in 200GeV central 12 AuAu

90 of total kinematic range covered
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STAR x PHENIX part I

• FONLL as baseline
• Large uncertainties due to quark masses,
  factorization and renormalization scale
• Phenix about a factor of 2 higher but consistent
  within errors
• Only electrons but less background
• 15 of the total cross section is measured
• STAR data about a factor of 5 higher
• More material but it is the only direct
  measurement of D-mesons
• 90 of the total cross section is measured

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Non-photonic electrons part II
TPCEMC
High-tower EMC trigger gt high pT
electrons Photonic subtracted FONLL describe
shape of pp well we
expect some bottom
STAR nucl-ex/0607012
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STAR x PHENIX part II
pp non-photonic x FONLL FONLL underestimates
measured STAR data by factor
4-5 PHENIX high-pT data differs from
STAR by factor 2
PHENIX electrons are inconsistent with ALL STAR
charm analysis
ALL STAR charm analysis are inconsistent with
PHENIX electrons
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Understanding NPE suppression
PHENIX nucl-ex/0611018 STAR nucl-ex/0607012

• Radiative EL with reasonable gluon densities do
  not explain the observed suppression
• Djordjevic, Phys. Lett. B632 81 (2006)
• Even extreme conditions with high transport
  coefficient do not account for the observed
  suppression
• Armesto, Phys. Lett. B637 362 (2006)
• Other EL mechanisms?

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Understanding NPE suppression
PHENIX nucl-ex/0611018 STAR nucl-ex/0607012

• Collisional EL may be significant for heavy
  quarks
• Wicks, nucl-th/0512076
• van Hess, Phys. Rev. C73 034913 (2006)
• Still marginal at high-pT

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Understanding NPE suppression
PHENIX nucl-ex/0611018 STAR nucl-ex/0607012

• Charm alone seems to describe better the
  suppression at high-pT
• Dead cone more significant for bottom quark ?
  larger collisional (relative) EL

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Understanding NPE suppression
PHENIX nucl-ex/0611018 STAR nucl-ex/0607012

• Other effects may contribute to the observed
  suppression
• What if heavy quarks fragment inside the medium
  and are suppressed by dissociation?
• Adil and Vitev, hep-ph/0611109
• Similar suppression for B and D at high-pT

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e-h correlations in pp bottom vs. charm

• Understand charm and bottom production is a key
  point to understand suppression and flow
• Direct measurement is very complicated
• One possible idea electron-hadron correlations
• Near side peak dominated by decay kinematics
• Preliminary e-h correlations from pp collisions
  in STAR
• Extract relative bottom contribution for
  different electrons pT

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e-h correlations in pp bottom vs. charm

• FONLL has large uncertainties in the b/(cb)
  ratio
• Could the data nail it down?
• First measurement of open-bottom at RHIC
• Non-zero contribution of bottom
• Very close to FONLL predictions

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J/?
L0 (hardware) J/? topology trigger two towers
above ET1.2 GeV Separated by 60 in f L2
(software) Match EMC high tower to CTB slat
? photon
rejection Tower clustering Cut on
meev(2E1E2(1-cos?)) Cut on cos?
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Beauty ? signal in pp

• ee- Minv
• Unlike-Sign Pairs
• Like-Sign Pairs

STAR Preliminary pp 200 GeV
STAR Preliminary pp 200 GeV ee- Minv Background
Subtracted

• Large dataset sampled in Run VI
• Luminosity limited trigger
• Analyzed 5.6 pb-1, with corrections.
• Measure ?(1s2s3s) ds/dy at y0

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Mid-rapidity ?(1s2s3s) Cross section
STAR Preliminary pp 200 GeV
Counts
ds/dy (nb)
y

• Integrate yield at mid-rapidity ylt0.5
• ?(1s2s3s) BR ds/dy
• 91 28 stat 22 syst pb-1 (Preliminary)
• Consistent with NLO pQCD calculations at
  midrapidity.
• Trigger ready for next run and RHIC II
  luminosity limited

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Some considerations

• Heavy flavor is an important tool to understand
  HI physics at RHIC
• First RHIC results are interesting and
  challenging
• Large differences in cross section between Phenix
  and STAR
• Why so much suppression at high-pT?
• Charm and bottom relative production. Where
  bottom starts dominating?
• First attempts from STAR indicates a non-zero
  contribution of bottom to the NPE spectra
• Very first step on the understanding of heavy
  quark EL

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Dielectron Invariant Mass Spectra

• The invariant mass spectra in the 0-20, 20-40,
  40-80, and 0-80 centrality classes are shown
• Number of J/? in each centrality class is
  determined by bin counting
• Gaussian fits (widths are held fixed to the value
  seen in minbias events) are used to estimate
  systematics
• Signal in the 0-20 bin is rather weak, so only
  an upper limit is quoted

STAR Preliminary
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Dielectron Invariant Mass Spectrum

• The (raw) background subtracted dielectron
  invariant mass spectrum is shown
• A signal of 5 sigma significance is clearly
  visible
• The trigger has been successfully commissioned
  and is currently running as we speak

STAR Preliminary
J/??ee- in pp _at_ 200 GeV
More statistics are expected from Run 6
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