Some Aspects of Heavy Flavor Physics in ALICE: the “Other” Hard Probe

Oct. 15, 2005 ALICE-USA Collaboration Meeting, LBNL

Some Aspects of Heavy Flavor Physics in ALICE:

the “Other” Hard Probe

V. Ghazikhanian

UCLA


Heavy Quark Production Mechanism

• Sensitive to initial gluon density and gluon distribution

0D

D0

J/

K+

l

l

K-

e-/-

e+/+

e-/-

e+/+

• Energy loss when propagating through dense medium

• Different scaling properties in central and forward region indicate shadowing, which can be due to CGC.

• Suppression/enhancement of charmonium in the medium is

a critical signal for QGP.

• Sensitive to initial gluon density and gluon distribution

to these one needs to add photoproduction mechanism

(see Spencer’s presentation)


Parton Distribution Function

Bx

Ax

2 1 21 2 1 2

1 2

1 21 2

1 2

ˆ

1ln

2

exp ; exp

ppQQ

zQQ

z

QQ QQ

QQ QQpp pp

Z ZM s x x s x x s

A A

E py

E p

M MA Ax y x y

Z Zs s

A. Dainese, PhD. Thesis [arXive:nucl-ex/0311004


2ˆ s RE C q L

Parton Energy Loss

Casimir coupling factor:4/3 for quarks3 for gluons

Medium transport coefficient gluon density and momenta

R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997) 291.

hardparton

path length L

• Due to medium-induced gluon radiation

• Average energy loss (BDMPS model):


ALICE Heavy Flavor Acceptance

arXive:hep-ph/0311048 v1 4 Nov. 2003


Some Heavy flavor quenching observables

• Inclusive:– Suppression of dilepton invariant mass spectrum

– Suppression of lepton spectra– Non-photonic electrons

• Exclusive jet tagging:– High- pT lepton ( ) & displaced vertex– Hadronic decay (ex. D0 K-p+ ) & displaced vertex

B D

+ - + - + -DD , ,BB B


Open Charm Production At LHC/ALICE



Detecting D-Mesons via Hadronic Decays

• Hadronic Channels:– D0 K (B.R.: 3.8%) – D0 K (B.R.: 6.2% 100% () = 6.2%)– D K p (B.R.: 9.1%)– D*± D0π (B.R.: 68% 3.8% (D0 K ) = 2.6%) c p K (B.R.: 5%)

pc

xMxxP

0

0 exp)(

Huan Huang


•Weak decay with mean proper length ct = 124 μm•Impact Parameter (distance of closest approach of a track to the primary vertex) of the decay products d0 ~ 100 μm

•STRATEGY: invariant mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices

–Measurement of Impact Parameters–Measurement of Momenta–Particle identification to tag the two decay products

Detection strategy for D0 K- p+



Hadronic charmCombine ALICE tracking + secondary vertex finding capabilities (sd0~60mm@1GeV/c pT) + large acceptance PID to detect processes as D0K-+ ~1 in acceptance / central event ~0.001/central event accepted after rec. and all cuts

S/B+S ~ 37 S/B+S ~ 8

for 1<pT<2 GeV/c(~12 if K ID required)

significance vs pT

Results for 107 PbPb ev. (~ 1/2 a run)


Initial Signal Significance



D0 Cross section measurement

pp, 14 TeV

mc

scalesPDFs

down ~ 0!down to 1 GeV/c!


A.Dainese nucl-ex/0311004

/1

/AA t

AAcoll pp t

dN dpR

N dN dp

q …medium transport coefficient depends on gluon density, momenta

D quenching (D0 K-p+ )

Ratio D/hadrons (or D/π0) enhanced and sensitive to medium properties


V2 of J/psi

V2 of J/psi can differentiate scenarios !

pQCD direct J/psi should have no v2 !

Recombination J/psi can lead to non-zero v2 !


Detecting Charm/Beauty via Semileptonic D/B Decays

• Semileptonic Channels:– D0 e+ + anything (B.R.: 6.87%) – D e + anything (B.R.: 17.2%)– B e + anything (B.R.: 10.2%)

single “non-photonic” electron continuum

• “Photonic” Single Electron Background: conversions (0 ) 0, Dalitz decays , , … decays (small)– Ke3 decays (small)

mBc

MmD

c

Mpc

xMxxP

/ MeV11)( ; / MeV15)(

exp)(

00

00


Even

ts/1

00 M

eV

103

J/Y

5 10 15

102

dN/d=8000

0

• 1 month statistics of PbPb √sNN=5.5 TeV

c/b Quarkonia



Heavy Flavor Production Yields (I)

Peter J.


Hadron and Lepton Identification

ALICE PPR CERN/LHCC 2003-049


Summary/Outlook • ALICE Heavy flavor Physics is complementary to that of RHIC and will extend x reach where Gluon structure function dominates.

• just as in RHIC (and perhaps even more) one needs to follow a program of complete set of measurements (RAA, RCP, dN/dY, v2, …) for AA systems, and also need yields from pp and pA for open charm (beauty) and quarkonium states. [pp and pA will provide information on basic production rates and nuclear shadowing effects (and nuclear absorption/energy loss), respectively].

• Need to have good control over photonic vs. non-photonic electrons in semileptonic open charm/beauty decay (TRD needed in front of EMC, TOF and EMC to extend pT ~ 3-10 GeV/c in order to extend PID in the region where b contribution dominates that of c quarks)!

• Trigerring on heavy flavor mesons: high pt electrons (high tower trigger in EMC, TRD), also triggering on muons in the muon spectrometer + electrons in EMC (to look for b decay chain proceeding via b -> mu + c -> e (EMC)).

• more studies are needed both on theory front and experimental side [e.g., better energy loss estimates for partons in deconfined nuclear matter/QGP and for quarkonia; need further simulation on detector/trigger performance for TRD+EMC+TOF+ITS].


The End


Nuclear Modification Factors

ddp

Nd

collddpNd

TAA

T

pp

T

AA NpR 2

2

/)(

Use number of binary nucleon-nucleon collisions to scale the colliding parton flux:

N-binary Scaling RAA or RCP = 1 simple superposition of independent nucleon-nucleon collisions !

Peripheralcoll

T

Centralcoll

TTCP

NddpNd

NddpNd

pR

]/[

]/[

)( 2

2

/

( )( )

( )

DAA T

D h T hAA T

R pR p

R p


D mesons quenching reducedRatio D/hadrons (or D/0) enhanced and sensitive to medium properties

Heavy Quarks and Quarkonia

Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202].

For Heavy Quarks with momenta < 20–30 GeV/c v << c

Gluon radiation is suppressed at angles “dead-cone” effect

Contributes to the harder fragmentation of heavy quarks and implies lower energy loss for heavy quarks relative to light quarks

0Qm

E

k

E

M

dP

k

dkkdCdP Fs

,

)/1()(

0

2220

022

022

22

Y. Dokshitzer et al, J Phys G 17, 1602 (1991)


Heavy Flavor Production Yields (II)



Heavy Flavor Production Yields (III)



Charm pT Spectra

Power-law function with parameters dN/dy, <pT> and n to describe the D0 spectrum

D0 and e combined fit

Generate D0e decay kinematics according to the above parameters

Vary (dN/dy, <pT>, n) to get the min. 2 by comparing power-law to D0 data and the decayed e shape to e data

<pT>=1.20 0.05(stat.) GeV/c in minbias Au+Au

<pT>=1.32 0.08(stat.) GeV/c in d+Au


Charm Total Cross Section

1.13 0.09(stat.) 0.42(sys.) mb in 200GeV minbias Au+Au collsions

1.4 0.2(stat.) 0.4(sys.) mb in 200GeV minbias d+Au collisions

Charm total cross section per NN interaction

Charm total cross section follows roughly Nbin scaling from d+Au to Au+Au considering errors

Indication of charm production in initial collisions

Systematic error too large !


Charm and Non-photonic Electron Spectra

1.13 0.09(stat.) 0.42(sys.) mb in 200GeV minbias Au+Au collsions

Total charm Binary Scalingsuppression at high pT


Charm Nuclear Modification Factor

STAR: Phys. Rev. Lett. 91 (2003) 172302

Suppressions!!

RAA suppression for single electron incentral Au+Au similar to charged hadrons at 1.5<pT<3.5 GeV/c

Heavy flavor production IS alsomodified by the hot and dense mediumin central Au+Au collisions at RHIC


electrons

K p d

electrons

hadrons

High pT Electron ID

dE/dx from TPC

SMD from EMC


hadrons electrons

High pT Electron ID

p/E from EMC

After all the cuts


STAR non-photonic electrons from EMC


Does Charm Quark Flow Too ?

Reduce Experimental Uncertainties !!Suppression in RAA Non-zero azimuthal anisotropy v2 !


• J/ – Small: r ~ 0.2 fm

– Tightly bound: Eb ~ 640 MeV

HG

QGP Observed in

dileptons invariant mass spectrum

Other charmonia• ’ ~ 8%• ~ 32%

Color Screening


J/psi Suppression and Color Screening

cdissJ

cdissdiss

TT

TTT

)25.1(

1.1

/

'

QCD Color Screening: (T. Matsui and H. Satz, Phys. Lett. B178, 416 (1986))

A color charge in a color medium is screened similar to Debye screening in QED the melting of J/.

c c Charm quarks c-c may not bindInto J/ in high T QCD medium

The J/ yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050)

Recent LQCD Calculation:

dirdirdirJJ SSSS '// 1.03.06.0


J/ Quark Potential Model


Lattice QCD Calculations


J/psi is suppressed in central Au+Au Collisions !

Factor ~ 3 the same as that at SPS

Satz: Only states are screened both at RHIC and SPS.

Alternative: Larger suppression in J/psi at RHIC due to higher gluon density, but recombination boosts the yield up !


J/ Suppression or NotNuclear Absorption of J/ important at low energy important (SPS) !

Both QCD color screening and charm quarkcoalescence are interesting, which oneis more important at RHIC?

At RHIC the J/ measurement requires highluminosity running!

Centrality and pT dependence important !


Collisions at high pCollisions at high pT T (pQCD)(pQCD)

)ˆˆˆ(),(

ˆˆˆ

),(),( 22

2/

2/3

3

utszDz

s

td

dxfxfdxdx

pd

dE hhc

h

cdab

bpbapaabcd

bah

h

At sufficiently large transverse momentum, let us consider the process:

p + p hadron + x

1) f(x,2) – parton structure function

2) ab->cd – pQCD calculable at large 2

3) D(zh,2) – Fragmentation functionTo produce heavy quark pairs, the CM energy must>2m


~7.6M AuAu 200GeV Run IV P05ia production 0~80% Min. Bias. |Vz| < 30cm

Electrons can be separated from pions. But the dEdx resolution is worse than d+Au

Log10(dEdx/dEdxBichsel) distribution is Gaussian.

2 Gauss can not describe the shoulder shape well. Exponential + Gaussian fit is used at lower pT region. 3 Gaussian fit is used at higher pT region.

2/ndf = 65/46

0.3<pT<4.0 GeV/c

TOF electron measurements

|1/-1|<0.03

2/ndf = 67/70

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Some Aspects of Heavy Flavor Physics in ALICE: the “Other” Hard Probe

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