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Fukutaro Kajihara

(CNS, Univ. of Tokyo)

Measurement of Single ElectronMeasurement of Single Electronfrom Semileptonic Decay from Semileptonic Decay of of Charm/Bottom QuarksCharm/Bottom Quarks

in RHIC-PHENIXin RHIC-PHENIX

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IntroductionIntroduction

RHIC で行われた二つの代表的な測定 楕円型フロー ジェット・クェンチング

Next Step は？これまでの成果は Soft probe (, K, p 等 ) による結果反応初期状態を直接的に probe する観測量が必要

「閉じ込めの破れ」の検証

Soft probe から Hard probe へ Heavy quark の測定

高密度状態完全流体性

熱的電磁輻射、 Heavy quarks (charm/bottom)

J/, Y, Heavy quark v2

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hA

hB

g

cg

c_(a)

(b) (c)

Heavy Quark ProductionHeavy Quark ProductionProduction

gg->QQ “gluon fusion”Sensitive to the initial gluon density

Mass is large s(mC2) ~ 0.3

can use pQCD

Cold nuclear matter effect(a) Cronin effect(b) (Anti-) shadowing(c) Absorption

Hot/dense matter effect(c) Energy lossNeed systematic study for entanglement.

p-p, d-Au

Au-Au

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c c

0D

間接測定 :Semileptonic decay からのレプトンを測定

0DK

+

K

How do We Measure Heavy Quarks?How do We Measure Heavy Quarks?

直接測定 :DK, DK

Meson D±,D0

Mass 1869(1865) GeV

BR D0 --> K (3.85 ± 0.10) %

BR --> e +X D±: 17.2, D0: 6.7 %

比較的大きな branching ratio

Single Electron/Prompt muon

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History of Single Electron MeasurementHistory of Single Electron MeasurementSingle electron は 1970 年代の初期に CERN-ISR において測定された . 当時は charm quark がまだ発見されていなかった .

F. W. Busser et al, PLB53, 212F. W. Busser et al, NPB113, 189

後に charm quark の semileptonic decay から生成された電子であると判明

I. Hunchlife and C. H. Llewellyn Smith, PLB61,472M. Bourquin and J.-M. Gaillard, NPB114,334

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Heavy Quark Measurement at RHICHeavy Quark Measurement at RHIC

PHENIXSingle electron measurements in p+p, d+Au, Au+Au sNN = 130,200,62.4 GeV

STARDirect D mesons hadronic decay channels in p+p/d+Au

D0KD±KD*±D0

Single electron measurements in p+p, d+Au

Phys. Rev. Lett. 88, 192303 (2002)

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実験とデータ解析

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A composite detector to measure leptons, photons and hadrons.

Beam

Beam

The PHENIX detectorThe PHENIX detector

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Event trigger is defined by beam-beam counters.

The PHENIX detectorThe PHENIX detector

Beam-beam counters

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Central arms

Tracking chambers

RICH counters Central arm

The PHENIX detectorThe PHENIX detector

EM calorimeters

TOF counters

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Cross-section of PHENIXCross-section of PHENIXPHENIX central arm:

|| < 0.35

= 2 x /2

p > 0.2 GeV/c

vertex: |zvtx| < 20 cm

Charged particle tracking analysis using DC and PC → p

Electron identificationRing Imaging Cherenkov detector (RICH)

Electro- Magnetic Calorimeter (EMC) → energy E

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Electron IDElectron ID

Electrons are identified by RICH and EMCal E/p matching, position matching, shower shape cut.

Energy-Momentum [GeV]

All charged tracks

Accidentalbackground

Net signal

Real

Apply RICH cut

RICH ring shape(signal accumulated)

Au-Au data

z [cm]

r [c

m]

Cerenkov photons from e+ or e- are detected by array of PMTs

mirror

Most hadrons do not emit Cerenkov light

Electrons emit Cerenkov photonsin RICH.

Central Magnet

ＲＩＣＨ

PMT arrayPMT array

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Background for Inclusive ElectronMain source

Random combinations of EMC cluster and RICH ring

pT independent

Minor source

-electrons knocked by the hadron in RICH active volume

h<10-6

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E/p in Au+Au collisionsE/p in Au+Au collisions

Purity of e± sample excellent aftersubtraction of “random association” background

E/p cut

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Singnal and Background

Photon Conversion

Main photon source: → In material: → e+e- (Major contribution of photonic electron)

Dalitz decay of light neutral mesons→ 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± → e± e (< 3% of non-photonic in pT > 1.0 GeV/c) Vector Meson Decays

J → e+e-(< 2-3% of non-photonic in all pT.)

Photonic Electron

Non-photonic Electron

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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

converterCLp

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Consistency Check of Two Methods

Both methods were checked each other

Left top figure shows Converter/Cocktail ratio of photonic electrons

Left bottom figure shows non-photon/photonic ratio

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Results and DiscussionResults and Discussion

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Result of p+p at s = 200 GeV

Heavy flavor electroncompared to FONLL

Data/FONLL = 1.71 +/- 0.019 (stat) +/- 0.18 (sys)

Tevatron の実験結果

PRL, 97, 252002 (2006)

Upper limit of FONLL

~factor 2

D0

CD

F,

PR

L 91

, 24

1804

(2

003)

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Drell-Yan processDrell-Yan process

FONLL calculation: Cacciari, Nason, Vogt, PRL95 (2005) 122001Drell-Yan from: Gavin et al., hep-ph/9502372Comparison: Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257

FONLL: electron spectrum may be ~50% c + ~50% b for 3 < pT < 8 GeV

Drell-Yan component investigated as well: < 10% up to 10 GeV

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Result of d+Au at Result of d+Au at ssNNNN=200 GeV=200 GeV

No strong modification compared to p+p

PHENIX PRELIMINARY

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Result of Au+Au at Result of Au+Au at ssNNNN = 200 GeV = 200 GeV

Heavy flavor electroncompared to binary scaledp+p data (FONLL*1.71)

Clear high pT suppression in central collisions

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

(according to inside figure)

Submitted to PRL (nucl-ex/0611018)

MB

p+p

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Energy Loss of Heavy QuarkEnergy Loss of Heavy Quark

In vacuum, < mQ/EQ では Gluon の制動放射が抑制される

“dead cone” effect

Heavy quark の energy loss は小さい (Dokshitzer-Kharzeev, 2001):放射された gluon のエネルギー分布 d/d は放出角依存性があり、抑制される

Q

Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602.Dokshitzer and Kharzeev, PLB 519 (2001) 199.

1

1d

d

d

d2

2

2

Q

Q

LIGHTHEAVY E

mII

22QQ

2 ])/([

1

Em

Gluonsstrahlung probability

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Nuclear Modification Factor: Nuclear Modification Factor: RRAAAA

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dpNdN

dPNdpR

ppcoll

AATAA

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 0 and in high pT region

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RRAA AA vs. Nvs. Npartpart

横運動量で積分し、 Npart の関数として計算した

Binary scaling works well for pT>0.3 GeV/c integration

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

Total error from p+p

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Dielectron Continuum Measurements Dielectron Continuum Measurements in √sin √sNNNN = 200GeV Au+Au = 200GeV Au+Au

schematic dilepton mass distribution

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Radiative Energy LossRadiative Energy Loss

Radiative Energy Loss with reasonable gluon densities do not explain the observed suppressionDjordjevic, Phys. Lett. B632 81 (2006)Armesto, Phys. Lett. B637 362 (2006)

DGLV Radiative Energy Loss Model

dNg/dy = 1000

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Collisional Energy LossCollisional Energy LossCollisional energy loss may be significant for heavy quarksWicks, nucl-th/0512076van Hess, Phys. Rev. C73 034913 (2006)

DGLV Radiative + Elastic Scattering

dNg/dy = 1000

van Hee & Rapp Elastic Scattering

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Other modelsOther models

Charm alone seems to describe better the suppression at high-pT

Dead cone is more significant for bottom quark Larger collisional (relative) Energy loss

DGLV Radiative + Elastic Scattering For Only Charm

Larger Dead Cone and Larger

Collisional E-loss For Bottom Quark

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Heavy Flavor RHeavy Flavor RAAAA at LHC at LHC>100 cc pairs and >5 bb pairs per central Pb-Pb collision

Baseline: PYTHIA to reproduce c and b pT distributions from NLO pQCD

MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295.Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. Eskola, Kajantie, Ruuskanen, Tuominen,

NPB 570 (2000) 379.

/fmGeV 10025ˆ7ˆ 2 RHICLHC qq

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SummarySummarysNN=200 GeV における Au+Au 衝突実験において、

mid rapidity 0.3 < pT < 9.0 GeV/c

Heavy quark からの寄与と考えられる電子を測定した Integrated yield (pT > 0.3 GeV/c) が Binary scaling している RAA が high pT 領域において強い抑制効果を示した 理論計算との比較

典型的な Radiative Energy Loss の Model が成り立たない 更なる発展には、 D/B の識別測定が必要不可欠

ه OutlookD meson measurement in p+p by electron （ K measurement ）

High statistic Cu+Cu analysisSingle measurement in forward rapidityD/B direct measurement by Silicon Vertex Tracker

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Backup slides