Fukutaro Kajihara(CNS, University of Tokyo)

for the PHENIX Collaboration

Heavy Quark Measurements by Weak-Decayed Electrons

at RHIC-PHENIX

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Introduction

“Strongly interacting, high dense, and perfect fluid has been observed in RHIC”

0

Dir.

Very large jet-quenching and elliptic flow (v2) have been observed for light quarks and gluons at RHIC

Parton energy loss in high dense medium and hydro-dynamics explain them successfully

Next challenge: light → heavy quarks (HQ: charm and bottom)

– HQ has “large mass”– HQ has larger thermalization time than light quarks– HQ is produced at the very early time by hard collisions– HQ is not ultra-relativistic ( < 4 ) at RHIC

HQ provides further insight into medium property at RHIC

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c c

0D

Indirect Measurement via Semileptonic decays

0DK

+

K

Heavy Quark Measurement by Single Electrons

Direct Measurement:DK, DK

Meson D±,D0

Mass 1869 (1865) MeV

BR: D0 → K (3.85 ± 0.10) %

BR: D → e +X D±: 17.2, D0: 6.7 %

Branching ratio is relatively large

F. W. Busser et al, PLB53, 212

Single electrons from semileptonic decays were first measured to extract charm at CERN-ISR in early 1970’s.

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Electron Measurement in PHENIX

e-

Central Arm Detectors: 0.35 (2 arms x /2)

Centrality, Npart, Ncol :

BBC, ZDC + Glauber model

Electron ID : RICH, EMC

Tracking : DC, PC, EMC

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Electron Signal and Background

Photon conversions → → e+ e- in materialMain background

Dalitz decays→ e+ e-

Direct PhotonVery smallMeasured by PHENIX

Heavy flavor electronsD → e± + X

Weak Kaon decays

Ke3: K± → e± e < 3% of non-photonic in pT > 1.0 GeV/c

Vector Meson DecaysJ → e+e-< 2-3% of non-photonic in all pT

Photonic electron Non-photonic electron

Background is subtracted by two independent techniques

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Results

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Run-5 p+p Result at s = 200 GeV

Heavy flavor electroncompared to FONLL

Data/FONLL = 1.71 ± 0.019 (stat.) ± 0.18 (sys.)

Total cross section of charmproduction: 567 b± 57 (stat.) ± 224 (sys.)

All Run-2, 3, 5 p+p data areconsistent within errors

PRL, 97, 252002 (2006)

Upper limit of FONLLProvides crucial reference for heavy ion measurement

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Run-4 Au+Au Result at sNN = 200 GeV

Clear high pT suppression in central collisions

PRL, 98, 172301 (2007)

MB

p+p

Heavy flavor electron in Au+Au compared to p+p reference

Solid lines: FONLL normalized to p+p data and scaled by number of binary collisions

The inside box shows signal to background ratio.S/B > 1 for pT > 2 GeV/c

In low pT, spectra in Au+Au agree with p+p reference

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Nuclear Modification Factor: RAA

Suppression level is the almost same as 0 and in high pT region

Total error from p+p

Binary scaling works well for p’T>0.3 GeV/c integration (Total charm yield is not changed)

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Elliptic Flow: v2

1

Non-zero elliptic flow for heavy-flavor electron → indicates non-zero D v2

Kaon contribution is subtracted

Elliptic flow: dN/dφ N∝ 0(1+2 v2 cos(2φ)) Collective motion in the medium

v2 forms in the partonic phase before hadrons are made of light quarks (u/d/s)

→ partonic level v2

If charm quarks flow, - partonic level thermalization - high density at the early stage of heavy ion collisions

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RAA and v2 of Heavy Flavor Electrons

PRL, 98, 172301 (2007) Only radiative energy loss model can not explain RAA and v2 simultaneously.

Rapp and Van HeesPhys.Rev.C71:034907,2005

Simultaneously describes RAA and v2 with diffusion coefficient in range: DHQ × 2πT ~ 4 – 6

Assumption: elastic scattering is mediated by resonance of D and B mesons. They suggest that small thermalization time τ(~ a few fm/c) and/or DHQ.Comparable to QGP life time.

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Summaryp+p collisions at s = 200 GeV in mid rapidity

　 New measurement of heavy flavor electrons for 0.3 < pT < 9.0 GeV/c.

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

Au+Au collisions at sNN = 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.

Non-zero v2 of heavy flavor electrons has been observed.

Only radiative energy loss model can not explain RAA and v2 simultaneously.

OutlookD meson measurement in p+p by electron and K measurement.

High statistic Cu+Cu analysis.Single measurement in forward rapidity.D/B direct measurement by Silicon Vertex Tracker.

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Thank you

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Backup slides

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Consistency Check of Two MethodsPRL, 97, 252002 (2006)

PRL, 97, 252002 (2006)

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

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Motivations in Au+Au at sNN = 200 GeV

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

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

sTD

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Most sources of backgroundhave 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: Cocktail Method

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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 issubtracted by cocktail method

Photon Converter (Brass: 1.7% X0)

Ne Electron yield

Material amounts:

0

0.4% 1.7%

Dalitz : 0.8% X0 equivalent radiation length

0

With converter

W/O converter

0.8%

Non-photonic

Photonic

converter