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Heavy Quark Measurement by Single Electrons in the PHENIX Experiment. Fukutaro Kajihara (CNS, University of Tokyo) for the PHENIX Collaboration. Dir. g. p 0 h. Introduction. Very large suppression and v2 have been observed for light quarks and gluons at RHIC

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Heavy Quark Measurement by Single Electrons in the PHENIX Experiment

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Heavy quark measurement by single electrons in the phenix experiment

Heavy Quark Measurement by Single Electrons in the PHENIX Experiment

Fukutaro Kajihara

(CNS, University of Tokyo)

for the PHENIX Collaboration


Dir. g



  • 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 < 4 )

    • HQ will help systematic understanding of medium property at RHIC

  • Experimental approach:

    Electrons from semi-leptonic heavy flavor decays in mid rapidity (||<0.35)

Motivations in p p at s 200 gev

Motivations in p+p 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

Motivations in au au at s nn 200 gev

Motivations in Au+Au 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 Shingo’s talk) can be used to determine D

G.D. Moore, D Teaney PR. C71, 064904 (2005)

Data analysis

Data Analysis

Electron signal and background

Electron Signal and Background

[Photonic electron] … Background

  • Conversion of photons in material

    Main photon source: p0 → gg

    In material: g → e+e- (Major contribution of photonic electron)

  • Dalitz decay of light neutral mesons

    p0 → g e+e- (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 (< 3% of non-photonic in pT > 1.0 GeV/c)

  • Vector Meson Decays

    w, , fJ → e+e-(< 2-3% of non-photonic in all pT.)

[Non-photonic electron] … Signal and minor background

Heavy quark measurement by single electrons in the phenix experiment

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.

Background subtraction converter method

Ne Electron yield





With converter


W/O converter

Dalitz : 0.8% X0 equivalent radiation length



Material amounts: 0

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)

Consistency check of two methods

Consistency Check of Two Methods

Accepted by PRL (hep-ex/0609010)

Both methods were always checked each other

Ex. Run-5 p+p 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)

New results are available

New Results are Available!!

  • Run-5 p+p result at s = 200 GeV

  • Run-4 Au+Au result at sNN = 200 GeV

  • Improvements over QM05:

    • Higher statistics and smaller systematic error

    • pT range is extended: 0.3<pT<9.0 GeV/c

    • Both cocktail and converter methods

    • Nonphotonic/Photonic ratio updates v2 calculation (in Shingo’s talk)

Run 5 p p result at s 200 gev

Run-5 p+p 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 p+p data are

consistent within errors

Total cross section of charm

production: 567 mb

+/- 57 (stat) +/- 224 (sys)

Upper limit of FONLL

Run 4 au au result at s nn 200 gev

Run-4 Au+Au Result at sNN = 200 GeV

Submitted to PRL (nucl-ex/0611018)

Heavy flavor electron

compared to binary scaled

p+p data (FONLL*1.71)

Clear high pT suppression

in central collisions

S/B > 1 for pT > 2 GeV/c

(according to inside figure)



Nuclear modification factor r aa

Nuclear Modification Factor: RAA

p+p reference:

Data (converter) for pT<1.6 [GeV/c]

1.71*FONLL for pT>1.6 [GeV/c]

Suppression level is the almost same as p0 and h in high pT region

Integrated r aa vs n part

Integrated RAA vs. Npart

Binary scaling works well for pT>0.3 GeV/c integration (about 50% of total charm yield)

Clear suppression is seen for pT>3.0 GeV/c integration

Suppression of D meson is probably less than p0

Submitted to PRL (nucl-ex/0611018)

Total error from p+p

Comparisons with theories

  • (I) pQCD calculation with radiative energy loss

  • Large parton densities and strong coupling ( ~ 14 GeV2/fm)

  • Light hadron suppression is also described with the same value

Comparisons with Theories

  • (II) (III) include elastic collision mechanism of HQ

  • Their models provide diffusion constant D (2pT*D=4-6 in (II))

Submitted to PRL (nucl-ex/0611018)

See combined RAA and v2 discussion in Shingo’s talk

Anyway, charm/bottom identification is needed for more development

0-10 % centrality



  • p+p collisions at s=200 GeV in mid rapidity

    New measurement of heavy flavor electrons for0.3 < pT < 9.0 GeV/c

    FONLL describes the measured spectrum within systematic error (Data/FONLL = 1.7)

  • Au+Au collisions at s=200 GeV in mid rapidity

    Heavy flavor electrons are measured for 0.3 < pT < 9.0 GeV/c

    Binary scaling of integrated charm yield (pT > 0.3 GeV/c) works well

    RAA shows a strong suppression for high pT region

  • Outlook

    D meson measurement in p+p by electron and Kp measurement

    High statistic Cu+Cu analysis

    Single m measurementin forward rapidity

    D/B direct measurement by Silicon Vertex Tracker

Heavy quark measurement by single electrons in the phenix experiment

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