Fukutaro Kajihara

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Heavy Quark Measurement by Single Electrons in
the PHENIX Experiment

• Fukutaro Kajihara
• (CNS, University of Tokyo)
• for the PHENIX Collaboration

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Introduction

• Very large suppression
• and v2 have been observed
• for light quarks and gluons
• at RHIC
• Parton energy loss and
• hydrodynamics explain
• them successfully
• Next challenge light heavy quark (HQ
  charm and bottom)
• HQ has large mass
• HQ has larger thermalization time than light
  quarks
• HQ is produced at the very early time
• HQ is not ultra-relativistic ( gv lt 4 )
• HQ will help systematic understanding of medium
  property at RHIC
• Experimental approach
• Electrons from semi-leptonic heavy flavor decays
  in mid rapidity (?lt0.35)

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Motivations in pp at ?s 200 GeV

• HQ Production Mechanism
• Due to large mass, HQ
• productions are considered
• as point-like pQCD processes
• HQ is produced at the initial
• via leading gluon fusion, and
• sensitive to the gluon PDF
• FONLL pQCD calculation
• describes our single electron
• results in Run-2 and Run-3
• within theoretical uncertainties
• Important References
• RAA calculation of HQ
• Important input for J/y studies

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Motivations in AuAu at ?sNN 200 GeV
Energy loss and flow are related to the transport
properties of the medium in HIC Diffusion
constant (D) Moreover, D is related to
viscosity/entropy density ratio (?/s) which ratio
could be very useful to know the perfect
fluidity HQ RAA and v2 (in Shingos talk) can be
used to determine D
G.D. Moore, D Teaney PR. C71, 064904 (2005)
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Data Analysis
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Electron Signal and Background
Photonic electron Background

• Conversion of photons in material
• Main photon source p0??? ? gg
• In material g ? ee- (Major contribution of
  photonic electron)
• Dalitz decay of light neutral mesons
• p0??? ? g ee- (Large contribution of photonic)
• The other Dalitz decays are small contributions
• Direct Photon (is estimated as very small
  contribution)
• Heavy flavor electrons (the most of all
  non-photonic)
• Weak Kaon decays
• Ke3 K ? p0 e ?e (lt 3 of non-photonic in pT gt
  1.0 GeV/c)
• Vector Meson Decays
• w, ?, f??J?? ? ee- (lt 2-3 of non-photonic in
  all pT.)

Non-photonic electron Signal and minor
background
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Background Subtraction Cocktail Method

• Most sources of background
• have been measured in PHENIX
• Decay kinematics and
• photon conversions can be reconstructed by
  detector simulation
• Then, subtract cocktail of all background
  electrons from the inclusive spectrum
• Advantage is small statistical error.

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Background Subtraction Converter Method
We know precise radiation length (X0) of each
detector material The photonic electron yield can
be measured by increase of additional material
(photon converter was installed) Advantage is
small systematic error in low pT
region Background in non-photonic is subtracted
by cocktail method
Photon Converter (Brass 1.7 X0)
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Consistency Check of Two Methods
Accepted by PRL (hep-ex/0609010)
Both methods were always checked each other Ex.
Run-5 pp in left
Left top figure shows Converter/Cocktail ratio of
photonic electrons Left bottom figure shows
non-photon/photonic ratio
Accepted by PRL (hep-ex/0609010)
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New Results are Available!!

• Run-5 pp result at ?s 200 GeV
• Run-4 AuAu result at ?sNN 200 GeV
• Improvements over QM05
• Higher statistics and smaller systematic error
• pT range is extended 0.3ltpTlt9.0 GeV/c
• Both cocktail and converter methods
• Nonphotonic/Photonic ratio updates v2 calculation
  (in Shingos talk)

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Run-5 pp Result at ?s 200 GeV
Accepted by PRL (hep-ex/0609010)
Heavy flavor electron compared to
FONLL Data/FONLL 1.71 /- 0.019 (stat) /-
0.18 (sys) FONLL agrees with data within
errors All Run-2, 3, 5 pp data are consistent
within errors Total cross section of
charm production 567 mb /- 57 (stat) /- 224
(sys)
Upper limit of FONLL
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Run-4 AuAu Result at ?sNN 200 GeV
Submitted to PRL (nucl-ex/0611018)
Heavy flavor electron compared to binary
scaled pp data (FONLL1.71) Clear high pT
suppression in central collisions S/B gt 1 for
pT gt 2 GeV/c (according to inside figure)
MB
pp
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Nuclear Modification Factor RAA
pp reference Data (converter) for pTlt1.6
GeV/c 1.71FONLL for pTgt1.6 GeV/c
Suppression level is the almost same as p0 and h
in high pT region
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Integrated RAA vs. Npart
Binary scaling works well for pTgt0.3 GeV/c
integration (about 50 of total charm
yield) Clear suppression is seen for pTgt3.0 GeV/c
integration Suppression of D meson is probably
less than p0
Submitted to PRL (nucl-ex/0611018)
Total error from pp
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Comparisons with Theories

• (II) (III) include elastic collision mechanism
  of HQ
• Their models provide diffusion constant D
  (2pTD4-6 in (II))

Submitted to PRL (nucl-ex/0611018)
See combined RAA and v2 discussion in Shingos
talk
Anyway, charm/bottom identification is needed for
more development
0-10 centrality
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Summary

• pp collisions at ?s200 GeV in mid rapidity
• New measurement of heavy flavor electrons for
  0.3 lt pT lt 9.0 GeV/c
• FONLL describes the measured spectrum within
  systematic error (Data/FONLL 1.7)
• AuAu collisions at ?s200 GeV in mid rapidity
• Heavy flavor electrons are measured for 0.3 lt
  pT lt 9.0 GeV/c
• Binary scaling of integrated charm yield (pT gt
  0.3 GeV/c) works well
• RAA shows a strong suppression for high pT
  region
• Outlook
• D meson measurement in pp by electron and Kp
  measurement
• High statistic CuCu analysis
• Single m measurement in forward rapidity
• D/B direct measurement by Silicon Vertex Tracker

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13 Countries 62 Institutions 550
Participants
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Backup slides