Study of bottom quark contribution to non-photonic electron

Study of b quark contributions tonon-photonic electron yieldsby azimuthal angular correlations betweennon-photonic electrons and hadronsStudy of b quark contributions tonon-photonic electron yieldsby azimuthal angular correlations betweennon-photonic electrons and hadrons

Shingo Sakai for STAR collaboration

Univ. of California, Los Angeles

OutlineOutline

b/c separation in non-photonic electron

at 200 GeV pp by electron-hadron (e-h &e-D0) azimuthal correlation @ STAR

Discuss heavy flavor energy loss in the

dense matter

Parton energy lossParton energy loss

 Gluon radiation model well

represents RAA for neutral pion

 The model predicts that

heavier quarks lose smaller

energy due to “dead cone” effect

 The model predicts significant

difference between bottom quark

energy loss and light & charm

quark energy loss.

Phys. Lett. B 632, 81 (2006)

Heavy flavor energy lossHeavy flavor energy loss

Phys. Rev. Lett. 98 (2007) 192301

 Heavy flavor production has been

studied by measuring electrons

decay from charm and bottom

(non-photonic electron)

at RHIC

 RAA for non-photonic electron

is strong & consistent with hadrons

 Indicate a large energy loss

for heavy quarks in the dense

matter.

 Uncertainty from bottom quark contribution

not only theory but also experiment

pQCD prediction for BottompQCD prediction for Bottom

 Since charm and bottom

are heavy, their production

have been predicted by pQCD

 FONLL predicts bottom quark

contribution significant (c/b = 1)

around 5 GeV/c in non-photonic

electron yield with

large uncertainty.

 It’s important to experimentally

determine bottom quark

contribution to understand

heavy flavor energy loss.

*Uncertainty comes from mass,

PDF, etc in the calculation

*FONLL

=A Fixed-Order plus Next-

to-Leading-log

charm/bottom separation(1)charm/bottom separation(1)

 Monte Carlo simulation (PYTHIA) for eD-h and eB-h

 Near side width for B decay is wider than

that of D decay due to decay kinematics

 measuring e-h correlation in pp & fit by MC

with B/(B+D) as parameter

eD - h

eB - h

Charm/bottom separation (2)Charm/bottom separation (2)

 e-D0 correlation

 Request like-sign e-K pair

o near-side ; bottom dominant

o away-side ; charm dominant

STAR ExperimentSTAR Experiment

 Large acceptance

Full azimuthal coverage

=> good for azimuthal correlation study

 TPC

measure momentum

measure dE/dx

 EMC + SMD

measure energy

measure shower shape

=> electron identification

 TOF

measure Time of flight

=> particles (π, K, p) identification

Particle IdentificationParticle Identification

/K separation to 1.6 GeV/c

–0.7 for TPC Alone

(+K)/p to p = 3 GeV/c

–1.2 for TPC Alone

electron

Electron purity

98% for pT < 6 GeV/c

80% for 9 GeV/c @ pp

TOF

Photonic electron identificationPhotonic electron identification

 Photonic electron is main background

 Photonic electrons are experimentally reconstructed

by calculating invariant mass at DCA for two electrons

 request mass < 0.1

 # of reconstructed photonic e

 reconstruction efficiency (εreco)

is ~ 70%

m (GeV/c2)

each distributions are experimentally determined.　

combinatorial

electron sample after removing opposite sign electron

(inv. mass<0.1) forms “semi” inclusive electron.

 Non-photonic electron can be calculated as;

Method of Method of eHF - hadron correlation

eHF and hadron correlationeHF and hadron correlation

 Azimuthal correlation between eHF and hadron

 Experimental result is fit by simulation results

eD – h (MC)

eB – h (MC)

fitting

pp@200 GeV

parameter for the fitting

eHF and D0 correlationeHF and D0 correlation

 making Kπ invariant mass for Δφ bins w.r.t trigger electron

(S/B ~ 14% and significance ~ 3.7)

 request same sign Kaon as triggered electron

Near side ; B dominant

Away side ; D dominant

 compared with MC simulations to get B/D ratio

pp@200 GeV

B decay contributionB decay contribution

 B decay contribution to non-photonic electron

 B decay contribution increase with pT

 B/D = 1.0 above 5 GeV/c

 good agreement with pQCD (FONLL) prediction

Large Bottom energy loss ?Large Bottom energy loss ?

 Bottom quark contribution

is ~50% above 5 GeV/c @ pp

=> there would be bottom

contribution in AuAu, too

 RAA for non-photonic electron

consistent with hadrons

 Indicate large energy loss

not only charm quark

but also bottom quark.

C:B ~ 1:1 @ pp

RAAc & RAAb correlation (1)RAAc & RAAb correlation (1)

 RAAC and RAAB are connected B decay contribution @ pp

 With the measurements of r @ pp and RAA,

we can derive a relationship between RAAc and RAAb.

RAAc & RAAb correlation (2)RAAc & RAAb correlation (2)

o RAAc & RAAb correlation

together with models

o Dominant uncertainty is

normalization in RAA analysis

o RAAb < 1 ; B meson suppressed

o prefer Dissociate and

resonance model

(large b energy loss)

I; Phys. Lett. B 632, 81 (2006) ; dNg/dy = 1000

II; Phys. Lett. B 694, 139 (2007)

III; Phys.Rev.Lett.100(2008)192301

STAR preliminary

pT>5 GeV/c

SummarySummary

 Azimuthal correlation between non-photonic electron and

hadron (e-h & e-D0) has been measured at 200 GeV pp

collisions @ RHIC-STAR

 The azimuthal angular correlation differs for non-photonicelectrons from D and B semi-leptonic decays

 We compare our measured azimuthal correlation with thosefrom D and B semi-leptonic decays from PYTHIA p+psimulations to derive the relative ratio of B/(B+D)

 Our result indicates comparable B and D contributions tonon-photonic electrons for pT 2.5-9 GeV/c and it isconsistent with FONLL calculation.

 Our measured B/D ratio would imply considerable b quarkenergy loss in medium based on RAA measurement fromcentral Au+Au collisions