Heavy flavor flow from electron measurements at RHIC

39
Heavy flavor flow from electron measurements at RHIC Shingo Sakai (Univ. of California, Los Angeles)

description

Heavy flavor flow from electron measurements at RHIC. Shingo Sakai (Univ. of California, Los Angeles). Outline. Introduction Non-photonic e v 2 measurement Non-photonic e v 2 D meson v 2 Charm v 2 Outlook (B decay). Elliptic flow. - PowerPoint PPT Presentation

Transcript of Heavy flavor flow from electron measurements at RHIC

Page 1: Heavy flavor flow from electron measurements at RHIC

Heavy flavor flow from electron measurements at RHIC

Shingo Sakai

(Univ. of California, Los Angeles)

Page 2: Heavy flavor flow from electron measurements at RHIC

Outline

Introduction Non-photonic e v2 measurement

Non-photonic e v2

D meson v2

Charm v2

Outlook (B decay)

Page 3: Heavy flavor flow from electron measurements at RHIC

Elliptic flow

In non-central collisions, the initial shape is anisotropic The emission pattern is influenced by mean free path

Mean free path λ = (nσ) -1

    λ>> R ; isotropic λ<< R ; anisotropic

RHIC ; n ~ 4 [1/fm3], σππ = 20mb λ ~ 10-1 fm << R(Au) ~ 6 fm

hydro model ; medium is equilibrium, pressure gradient is larger x than y, and the collective flow is developed in x.

second harmonic of the azimuthal distribution       => “elliptic flow”

      

dN/d() = N (1 + 2v2cos(2(φ)))

λ >> R ; Isotropic

λ << R ; anisotropic

Y

X

Y

X

Page 4: Heavy flavor flow from electron measurements at RHIC

Elliptic flow @ RHIC

In low pT (pT<1.5 GeV/c),

v2 increases with pT, and

show mass dependence

v2(π)>v2(K)>v2(p)

=> hydro model well represents

identified particle v2

assume early time

thermalization

    τ0 = 0.6 fm/c

Hydro;Phys. Rev. C 67 (03) 044903v2; Phys.Rev.Lett.91 182301 (2003)   PHENIX

Page 5: Heavy flavor flow from electron measurements at RHIC

5 2006/5/20

v2 already developed in partonic phase ?

identified hadrons v2 after scaling pT and v2 number of quarks

v2 after scaling fall on same curve

v2 already formed in the partonic phase for hadrons made of light quarks (u,d,s)

charm flow => re-scattering is so intense => quark level thermalization

Page 6: Heavy flavor flow from electron measurements at RHIC

Charm study @ RHIC

Electron measurement photonic

- photon conversion

- Dalitz decay (π0,η,ω ---) nonphotonic

   - Ke3 decay

- primarily semileptonic decay

of mesons containing c & b

D meson measurement => reconstructed from π,K

Page 7: Heavy flavor flow from electron measurements at RHIC

Charm quark yield

Phys.Rev.Lett.94:082301,2005(PHENIX)

QM06, F. Kajihara

Non-suppressed charm yield at low pT => they are initially produced and survived until the end Non-photonic electron v2 @ low pT does not come from energy loss => would reflect collective flow * energy loss also generate non-zero v2

Page 8: Heavy flavor flow from electron measurements at RHIC

Radial flow of charm meson

AuAu Central charm hadron

AuAu Central , K, p

AuAu Central strangeness hadron

Brast-wave fit to D-meson and single electron and muon from D-meson decay spectra

non-zero collective velocity

further information of charm flow obtain v2 measurement SQM06, Y. Yifei

STAR

Page 9: Heavy flavor flow from electron measurements at RHIC

Non-photonic electron v2 measurement

Non-photonic electron v2 is given as;  

v2 γ.e ; Photonic electron v2

Cocktail method (simulation) stat. advantage Converter method (experimentally)

v2e ; Inclusive electron v2

=>   Measure RNP = (Non-γ e) / (γ e)=> Measure

NP

eeNPenon

enonee

R

vvRv

d

dN

d

dN

d

dN

.22.

2

..

)1(

(1)

(2)

Page 10: Heavy flavor flow from electron measurements at RHIC

Photonic e v2 determination

decaye vRv 2.2

compare inclusive e v2

with/without converter (converter only increase photonic component)

photonic electron v2

  => cocktail of photonic e v2

R = N X->e/ Nγe

photonic e v2 (Cocktail)

decay

v2 (π0)

pT<3 ; π (nucl-ex/0608033)pT>3 ; π0 (PHENIX run4 prelim.)

Page 11: Heavy flavor flow from electron measurements at RHIC

Non-photonic electron v2

non-zero non-photonic electron v2 was observed below 3 GeV/c

Non-photonic electron v2

Phys. Rev. Lett. 98, 172301 (2007)

dN/d() = N (1 + 2v2cos(2(φ)))

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12

Non-photonic electron v2 (centrality dep.)

Hydro -> driving force of v2 is pressure gradient (ΔP) ΔP get large with impact parameter (centrality) => v2 get large with centrality

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

0-20% 20-40% 40-60%

Page 13: Heavy flavor flow from electron measurements at RHIC

Non-photonic electron v2 (centrality dep.)

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

RAA =1 @ peripheral collisions but non-zero v2

non-photonic e v2 => result of collective flow

0-20% 20-40% 40-60%

1

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D meson v2

charm →D meson → non-photonic e           non-photonic electron v2

reflect D meson v2 ?

pT<1.0 GeV/c, smeared by the large mass difference

pT > 1.0 GeV/c, decay electrons have same angle of the parents

“non-zero” non-photonic e v2

=> indicate non-zero D meson v2

Line ; D mesonCircle ; electron

Electron pT(GeV/c)

<co

s(φ

e -

φD)>

simulation

simulation

Phys.Lett.B597

Page 15: Heavy flavor flow from electron measurements at RHIC

D v2 estimation

π(PHENIX prelim.) p (PHENIX prelim.) k (PHENIX prelim.) D from scaling(kET=mT-m0) + ・・・ φ

MC simulation (PYTHIA) e v2

Assumptions

non-photonic electron decay from D meson

D meson v2 ; D v2 = a*f(pT)

f(pT) ; D meson v2 shape assume various shapea ; free parameter (pT independent)

f(pT)

compared with measured v2 and find “a” range (Χ2 test)

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Fitting result

fitting result    χ2 / ndf vs. a ndf = 13

χ2 /

nd

f

Pion shape Kaon shape Proton shape

φshape scale shape

χ2 /

nd

f

1

1

a[%]

a[%]

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Expected D meson v2

D meson v2 expected from non-photonic e v2

D meson v2 ; Max 0.09±0.03

D v2 is smaller than pion v2(pT<3 GeV/c)

Page 18: Heavy flavor flow from electron measurements at RHIC

Charm flow ?

RAA for non-photonic electron ;

A large suppression of high pT electron yield

model predict initial parton density > 3500 => high parton dense matter

charm mean free path n > 7 fm-3

σ = 3 mb (pQCD) => λcharm < 0.5 fm shorter than R(Au) ~ 6 fm => would expect charm v2

nucl-ex/0611018 (PRL)

[PLB623]

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Estimation of charm quark v2

(1) Apply coalescence model(2) Assume universal pT dependence of v2 for quark

e

T

q

T

q

T

D

cq

T

D

uq

T

D

vpbvpav

pm

mbvp

m

mavpv

222

222

)6

5()

6

1(~

)()()(

[PRC 68 044901 Zi-wei & Denes]

Quark v2

(3)Quarks which have same velocity coales

charm

u

Dv

v

mu + mc = mD

mu = 0.3 & mc = 1.5 (effective mass) a,b --- fitting parameter simultaneous fit to non-γ e v2 , v2

K, v2p

   

v2,u = a ×v2,q

v2,c = b ×v2,q

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Fitting result (1)

χ2 minimum result

The best fitting (Χ2 minimum) a = 1, b = 0.96 (χ2/ndf = 21.85/27)

v2,u = a ×v2,q

v2,c = b ×v2,q

Kaonv2

k = 2(av2,u(2pT,u))

protonv2

p = 3(av2,u(3pT,u)) Non-photonic

Page 21: Heavy flavor flow from electron measurements at RHIC

Fitting result (1)

χ2 minimum result

the coalescence model well represent low pT v2 shape saturate point and value

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Fitting result (2)

χ2 minimum ; a = 1, b = 0.96 (χ2/ndf = 21.85/27) Quark coalescence model indicate non-zero charm v2

a ; u quark

0.96

1

v2,u = a ×v2,q

v2,c = b ×v2,q

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Charm quark v2

In the assumptions(1)Charm quark v2 is non-zero(2)Charm quark v2 is same as light quarks

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Compare with models

(1) Charm quark thermal + flow(2) large cross section ; ~10 mb (3) Elastic scattering in QGP

[PRC72,024906] [PRC73,034913

]

[Phys.Lett. B595 202-208 ]

models support a non-zero charm v2

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Charm thermalization ?

Theoretical calculation [PRC73 034913]

assume D & B resonance in sQGP

=> accelerate c & b thermalization time=> comparable to τQGP~ 5 fm/c Strong elliptic flow andsuppression for nonphotonicwould indicate early time thermaliation of charm

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Bottom quark contribution

Three independent methods provide B/D @ pp

e-h azm. correlation (STAR) e-D0 azm. correlation (STAR) e-h invariant mass (PHENIX)

Page 27: Heavy flavor flow from electron measurements at RHIC

Bottom quark contribution

Three independent methods provide B/D @ pp

e-h azm. correlation (STAR) e-D0 azm. correlation (STAR) e-h invariant mass (PHENIX)

=> consistent

Bottom contribution is significant B/D = 1 above 5 GeV/c

pQCD (FONLL) calculation well represent B/D ratio as a function of pT

pp 200 GeV

Page 28: Heavy flavor flow from electron measurements at RHIC

Bottom quark contribution

RUN4RUN7

min.bias

B/D = 1.0 (pT>5.0) @ pp but unclear @ AuAu

but their contribution would large at high pT @ AuAu nonphotonic electron decay from B keeps parent direction above 3 GeV/c high pT nonphotonic electon v2 would provide B v2 information SVT will install in STAR & PHNIX

Page 29: Heavy flavor flow from electron measurements at RHIC

Summary Non-photonic electron v2 mainly from charm decay was

measured @ s = 200 GeV in Au+Au collisions at RHIC & non-zero v2 is observed

Non-photonic electron v2 is consistent with hydro behavior

Measured non-photonic electron indicate non-zero D

meson v2

Based on a quark coalescence model, the data suggest non-zero v2 of charm quark.

Page 30: Heavy flavor flow from electron measurements at RHIC

BackUp

Page 31: Heavy flavor flow from electron measurements at RHIC

Comparison with models; RAA & v2

Nucl-ex/0611018

Two models describes strong suppression and large v2

Rapp and Van Hees Elastic scattering -> small τ DHQ × 2πT ~ 4 - 6

Moore and Teaney DHQ × 2πT = 3~12

These calculations suggest that small τ and/or DHQ are required to reproduce the data.

Page 32: Heavy flavor flow from electron measurements at RHIC

Constraining /s with PHENIX data Rapp and van Hees Phys.Rev.C71:034907,2005

Simultaneously describe PHENIX RAA(E) and v2(e) with diffusion coefficient in range DHQ ×2T ~4-6

Moore and Teaney Phys.Rev.C71:064904,2005 Find DHQ/(/(+p)) ~ 6 for Nf=3 Calculate perturbatively,

argue result also plausible non-perturbatively

Combining Recall +p = T s at B=0 This then gives /s ~(1.5-3)/4 That is, within factor of 2 of

conjectured bound

Rapp & Hees private communication

Moore & Teaney private communication

Page 33: Heavy flavor flow from electron measurements at RHIC

Additional Remarks What does DHQ/(/(+p)) ~ 6 mean?

Denominator: DHQ is diffusion length ~ heavy quark diffusion length HQ

Numerator: Note that viscosity ~ n <p>

n = number density <p> = mean (thermal) momentum = mean free path

“Enthalpy” + P ~ n <p> Here P is pressure

So /(+P) = (n <p> / (n <p> ) ~ Note this is for the medium, i.e., light quarks

Combining gives DHQ/(/(+p)) ~ HQ / Not implausible this should be of order 6

Notes Above simple estimates in Boltzmann limit of well-defined

(quasi)-particles, densities and mfp’s The “transport coefficient” /(+p) is preferred by theorists because it

remains well-defined in cases where Boltzmann limit does not apply (sQGP?)

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qc & gc cross section

Page 35: Heavy flavor flow from electron measurements at RHIC

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

Page 36: Heavy flavor flow from electron measurements at RHIC

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

Page 37: Heavy flavor flow from electron measurements at RHIC

Converter method

Separate non-photonic & photonic e v2 by usingNon-converter run & converter run

Non-converter ; Nnc = Nγ+Nnon-γ

Converter ; Nc = R *Nγ+Nnon-γ

(1+RNP)v2nc = v2γ + RNPv2non-γ

(R +RNP) v2c = R v2γ + RNPv2non-γ

v2non-γ(non-photonic) & v2γ(photonic) is “experimentally” determined !

R --- ratio of electrons with & without converter (measured) RNP --- non-photonic/photonic ratio (measured) v2nc --- inclusive e v2 measured with non-converter run (measured)  v2c --- inclusive e v2 measured with converter run (measured)

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Outlook for heavy flavor v2 study @ RHIC

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

[Silicon vertex detector]

Page 39: Heavy flavor flow from electron measurements at RHIC

Photonic electron subtraction

Cocktail subtraction

photonic electrons are calculated

as cocktail of each sources.

[PRL 88, 192303 (2002) ]

Converter subtraction

Photonic electrons are extracted

experimentally by special run with

additional converter

(X = 0.4 + 1.7%)[PRL 94, 082301 (2005) ]

  50 % of e come from non-γ @ high pT (>1.5 GeV/c)