Measurement of elliptic flow of electrons from heavy flavor

decays @ RHIC

Shingo Sakai

(Univ. of Tsukuba / JSPS)

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outline

Introduction Elliptic flow (v2) & Nuclear modification factor (RAA) Motivation

Result Method electron v2 from (Mim. & centrality) Charm v2 　 (compare model) v2 vs. RAA

Summary

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Elliptic flow (v2)

ｘ

ｙ

p

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p ｙ

Initial spatial anisotropy

Momentum space anisotropy

of particle emission

2th harmonic of the Fourier expansion of the azimuthal distribution

Reflect initial spatial anisotropy transfer

=> A powerful probe of the initial state of the high energy heavy ion collision

hydrodynamical interruption => pressure gradient of

early stage of collision

dN/dφ N∝ 0(1+2v2cos(2(φ))

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Elliptic flow vs. hydro model

Identified particle v2 => show mass dependence v2(π) > v2(K) > v2(p)

hydrodynamical model well represent the feature of v2

early time thermalization

τ ~ 0.6 fm/c perfect fluid (no viscosity)

The matter is like fluid

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Nuclear modification factor ; RAA

Nuclear modification factor ; RAA

Yield AuAU

Yield pp*<NColl_AuAu>

RAA =

particle production @ high pT　 => hard process => scale by pp collision 　 (RAA = 1.0)

significant suppression in AuAu

parton energy loss in the dense dense matter

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Quark number scaling

Presented by M. Lamont (QM04)

Baryon

Meson

v2 is scaled with number of quarks quark level elliptic flow Consistent Quark coalescence model (N.Q.S)

N.Q.S well explain other measurement ; Rcp , particle ratio (p/π)

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Motivation ; why charm quark ?

flow ? energy loss ?

Light quarks (u,d,s) flow & energy loss in the matter

Charm is much heavier than u,d,s quarks and believed to be produced in initial collisions via gluon fusion => propagates through medium created in the collisions

Charm interact medium ? => charm energy loss & charm flow ? => if so, indicate strongly coupling in the medium

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Charm study @ PHENIX experiment

PHENIX study charm quark via electron,μ and J/ψ　 Central arm (|η| < 0.35)

semi-leptonic decay c -> D -> e cc -> J/ψ -> ee

Muon Arm (1.15 < |η| < 2.25) semi-leptonic decay c -> D ->μ cc -> J/ψ-> μμ

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Charm quark study via electron

Electron sources photonic

- photon conversion

- Dalitz decay (π0,η,ω ---) non-photonic

　　 - Ke3 decay

- primarily semi-leptonic decay

of mesons containing c & b

background subtraction method cocktail method converter method

B.G

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Cocktail method

estimate background electron with simulation

sum up all background electrons

Input π0 (dominant source) 　　 use measured pT @ PHENIX other source assume mt scale of pi

clear enhancement of inclusive electron w.r.t photonic electron

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Converter method

install “photon converter ”(brass ;X0 = 1.7 %) around beam pipe

increase photonic electron yield

Compare electron yield with & without converter

experimentally separate

Non-converter ; Nnc = Nγ+Nnon-γ Converter ; Nc = R *Nγ+Nnon-γ

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Charm quarks energy loss

clear suppression @ high pT in more central collision

=> charm quarks energy loss

low pT is consistent with binary scaling in large uncertainty

Charm interact medium @ low pT ?

v2 measurement give us answer

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Non-photonic electron v2 measurement

Non photonic electron v2 is given as;

dNe/d = dNpho.e /d + dNnon-pho.e /d

　　　　 v2e = ( v2γ

e + RNP v2non-γe ) / (1 + RNP) 　　

Photonic electron v2

=> Cocktail method (simulation)=> Converter method (experimentally determined)

Inclusive electron v2

=> 　 Measure (Non-photonic e) / (photonic e)=> measure

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Electron v2 measurement @ PHENIX

e-

Electron v2 is measured by R.P. method

R.P. --- determined with BBC Tracking (pT,φ) 　 --- DC + PC electron ID --- RICH & EMCal

dN/d(-) = N (1 + 2v2obscos(2(-)))

eID @ RICH

B.G.

After subtract B.G.

Fig : Energy (EMcal) & momentum matching

of electrons identified by RICH.

Clear electron signals around E-p/p = 0

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Inclusive & photonic electron v2

Inclusive e v2

Photonic e v2

50 % of electrons come from non-photonic @ high pT (>1.5 GeV/c) photonic electron v2 ; converter (pT<1.0) & cocktail (pT>1.0)

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Non-photonic electron v2

clear non-zero non-photonic electron v2 measured ! main source of non-photonic electron ; D->e => D v2 is also non-zero

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Non-photonic electron v2 (centrality dep.)

Hydro -> driving force of v2 is pressure gradient (ΔP)

ΔP is get large with impact parameter (centrality) => v2 get large with centrality

Non-photonic electron v2 seems like get large with impact parameter

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expected D v2 from non-photonic e v2

　 expected D meson v2 from non-photonic electron v2 => would be smaller than pi v2

expected D v2 from non-γ v2

process(1) D v2 = a*f(pT) a ; free parameter f(pT) ; pi,K,p(2) D -> e v2

(3) Calculate χ2

(4) Find χ2 minimum for “a”

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Charm quark flow ?

1 2 30 4

pT[GeV/c]

pT[GeV/c]

Compared with quark coalescence model prediction.with/without charm quark flow(Greco, Ko, Rapp: PLB 595 (2004) 202) - No Bottom contribution - c v2 small u v2 @ low pT - quark v2 flat @ high pT

Below 2.0 GeV/c ;consistent with charm quark flow model. => indicate charm quark flow !

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Non-γ e v2 vs. RAA 　 (1)

Origin of v2 @ high pT => energy loss pi0 yield strongly suppress @ high pT and strong elliptic flow observed

Non-γelectron strongly suppress @ high pT same as pi0 but v2 is smaller than pi0

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Non-γ e v2 vs. RAA 　 (2)

estimate D meson v2 assume charm & u have same v2

D meson v2 get N.Q.S

mass effect for N.Q.S v2M (pT) = v21 (R1 pT) + v22 (R2pT)

Ri = mi / mM

(mi ; effective mass of quark i) (Phys.Rev. C68 (2003) 044901 Zi-wei & Dence Molnar)

v2D(pT) ~ v2u (1/6*pT) + v2c (5/6*pT)

pi0 v2

u quark v2

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Non-γ e v2 vs. RAA 　 (3)

if charm & u has same v2, the maximum v2 = 0.1 => Non-photonic electron v2 is smaller than pi (pi0) v2 though RAA is consistent with pi0

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Summary

Study charm v2 via electron v2 measurement Non-zero non-photonic electron v2, decay electron

v2 from charm, observed. Non-photonic electron v2 consistent with charm flow

model Charm quark study via electron indicate charm flow

& charm energy loss in the matter

=> indicate particles in the matter strongly coupling

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Outlook for heavy flavor v2 study @ PHENIX

single μ v2 new reaction plane detector

good resolution => reduce error from R.P. J/ψ v2 & high pT non-photonic electron v2

silicon vertex detector direct measurement D meson v2

[Reaction plane detector][Silicon vertex detector]