p t correlations versus relative azimuth of D-Dbar pairs as a sensitive probe for thermalization

1

pt correlations versus relative azimuth of D-Dbar pairs as a

sensitive probe for thermalization

Tsiledakis Georgios

University of Heidelberg

417th WE-Heraeus-Seminar, June 25 - 28 2008, Bad Honnef

2

Outline• Introduction

• Primordial c-cbar (D-Dbar) correlations for p-p collisions at 14 TeV

• The Average Momentum Correlator

• Contribution of transverse radial/elliptic flow

• Primordial B-Bbar pt correlations

• Charm Production in ALICE

• D-e pt correlations

• e+ - e- pt correlations from D, B decays

• Conclusions

3

Introduction

Total quark mass (MeV)

X. Zhu, M. Bleicher, K.Schweda, H. Stoecker, N. Xu et al., PLB 647 (2007) 366.

1) Higgs mass: electro-weak symmetry breaking. (current quark mass)

2) QCD mass: Chiral symmetry breaking. (constituent quark mass)

Strong interactions do not

affect heavy-quark masses.

Important tool for studying properties of the hot/dense medium at RHIC and LHC.

Test pQCD predictions at RHIC and LHC.

4

Low Energy D-Dbar Meson Pair Correlations

(D-Dbar)

= (D) – (Dbar)

• E791 : Eur. Phys. J. direct C1 (1999) 4• WA92 : Phys. Lett. B385 (1996) 487• NA32 : PLB257 (1991) 519 , PLB302 (1993) 112, PLB353 (1995) 547

Correlation variable studied:

103 /

N *

dN

/d(

)

•At low energies, D-Dbar production correlated!

•Pythia describes these correlations!

How about LHC energies?

For many more details, see:

C. Lourenço & H. K. Wöhri,

Phys. Rep. 433 (2006) 127.

D

Dbar

5

Charm correlations at LHC In p+p:

c-cbar are correlated

• Flavor creation: back to

back

• Gluon splitting: forward

• Flavor excitation: flat

In Pb+Pb:

Correlations vanish

frequent interactions

among partons !

probe light-quark

thermalization !

6

PYTHIA Settings

• PYTHIA (v.6_406)

• 500000 p-p events at √s = 14 TeV

• 1 pair c-cbar/event

• no tracking, 100 % efficiency

• No rapidity cut

• Fragmentation Pv = 0.75 (default)

p

p c

c D

D

ALICE PPR vol. II, J. Phys. G: Nucl. Part. Phys. 32 (2006) 1295-2040

7

D+ D*+ D0 D*0 Ds+ D*s+

Primordial D –no decay

Fragmentation of charm quarks into D mesonsC

ou

nts

PID

N(D0) : N(D+) : N(D*0) : N(D*+) = 1 : 1 : 3 : 3

c-cbar D0 + D0bar (61 %)

D+ + D- (19 %)

Ds+ + Ds

- (12 %)

c+ + c

-bar (8 %)

Large fraction of c goes to

D0 mesons

Measure D0-D0bar correlations!

8

Primordial D-Dbar angular correlations

FC away side correlation FE + GS flat Rather weak dependence

No pt cut

Enhanced correlations FC back to back GS forward FE flat Strong pt dependence

Correlations sensitive to pt regionStudy pt correlations versus(DDbar)

Azimuthal correlations survive fragmentation

9

pt (GeV/c)

0

tt

p

0

tt

t

dpdpdn

dpdpdn

px

t

''

''

x(p

t)

Inclusive pt distribution

D

Cumulant pt variable x

Primordial D-Dbar pt correlations

•Incl. pt-distr. Cumulant x(pt) •2-dim plot (x(pt)1, x(pt)2) for D-Dbar respectively•Is uniform when no correlations are present

10

D-Dbar pt correlations – at full

pt correlations are dominated

by large pt effects (along the diagonal

at xx)

Same event

Mixed event

11

D-Dbar pt correlations – angular dependence

Gluon Spitting

Flavor Creation

12

Measurement of pT Fluctuations using the Average Momentum Correlator

• To quantify dynamical pT fluctuations

– We define the quantity <pt,1pt,2>.

– It is a covariance and an integral of 2-body correlations.

– It equals zero in the absence of dynamical fluctuations

– Defined to be positive for correlation and negative for anti-correlation.

S. Voloshin. V. Koch. H. Ritter, PRC60 (1999)

/ 2/ 2

Ck pt ,i pt pt , j pt j1,ij

Nk

i1

Nk

and pt pt k

k1

Nevent

/ Nevent and pt k pt ,i

i1

Nk

/ Nk

Nevent = number of events

pt i = average pt for i th event

Nk = number of tracks for k th event

pt ,i = pt for i th track in event

where

pt,i for Dpt,j for DbarNk=1

))((1

,,

111

2,1,

tjttit

N

j

N

i

N

kpairstt pppp

Npp

kkevents

13

Average Momentum Correlator - same event analysis

pt (DDbar)~30 GeV/c

At full : <pt,1pt,2> = 0.1995 +/- 0.006 (GeV/c)2

or pt~30 %

Co

un

ts

CERES at SPS has measured ~1% fluctuations for charged particles

<pt,1pt,2> = 22.71+/- 0.32 (MeV/c)2


Nk

i1

Nk

(GeV/c)2

14

Average Momentum Correlator – angular dependence

Enhanced correlations

Only FC produces correlations

at Distinction of the baseline at

middle – flat to 0

Average Momentum Correlator

is a sensitive measure of

back to back correlations

Signal

Background

At full : <pt,1pt,2> ~ 0.20 (GeV/c)2

or pt~30 %

15

Transverse radial flow contribution

ptD

ptDbarptD

ptDbar

ptf = m

= 0, 0.3, 0.6, 0.9

E. Cuautle and G. Paic hep-ph/0604246 v2 24 May 2006

Assume a fireball created in a coll. from PYTHIA

Expansion produces additional momentum ptf

Attribute to each pt a randomized position

Add the radial flow component vectorially

pt (GeV/c)

Co

un

ts

16

Transverse radial flow contribution on <pt,1pt,2>

Radial flow: = 0, 0.3, 0.6, 0.9

Stronger flow introduces

anti-correlations around = 180o

10000 events for = 0.3, 0.6, 0.9

500k events for = 0

D

Dbar

D

Dbarff

17

Elliptic flow contribution

k

k

N

ji

ji

jitjttit

N

jitt

f

fpppp

pp,

,,,

2,1,

))((

)]2cos(21 22

vB

d

dN

We evaluate the elliptic flow expressed in units of (GeV/c)2

•We introduce the measure fi,j

•We calculate the average momentum correlator forDDbar pairs that have flow 10% and 90%

Introduces a cos(2) modulation

|))()(|2cos()()(21 ,2,2, jipvpvf jtitji

18

realistic amount of elliptic flow

does not change correlations !

Elliptic flow contribution on <pt,1pt,2>

19

Full rapidity (500000 events)

Mid-rapidity (200000 events)

Primordial D-Dbar angular correlationsat mid-rapidity

• NLO dominant at LHC

• Weak D-Dbar correlation in

• Measurement of medium modification of

this correlation in heavy ion collisions is

challenging

FC away side correlation FE flat in GS forward

Use of pt correlator

20

Average Momentum Correlator for D-Dbar at mid-rapidity

At full : <pt,1pt,2> = 0.549+/-0.017 (GeV/c)2

or pt~40 %

Stronger signal at mid-rapidity



21

Charm Production in ALICE using D0 K-+

ALICE has a barrel system with high precision

vertexing, PID and electron identification (|| < 0.9)

and a forward muon spectrometer (: 2.5–4.0),

down to low pt.

Charm production can be studied:

• In the electronic and muonic channels D eX (X) •In several hadronic decay channels: D0 K , D± K D0 K, Ds KK, Ds

D* D0, c pK ALICE PPR II, J. Phys. 32 (2006) 1295

TPC: main tracking device

ITS: high spatial resolution

TRD: good electron PID (high pion rejection)

ToF: extend PID to large pt

109 p-p events

Nccbar/event = 0.16 (PPR2)

c-cbar D0 (61 %)

D0 (4 %)

Eff.(acceptance, reconstruction,

selection eff.) ~ 0.005

S/B ~ 10%

#Events with both D0-D0bar < 10

Looking at semileptonic decays

22

Charmed e+/e- correlationsp

t D (

GeV

/c)

pt e- (GeV/c)

De-

•Study e+/e- pt correlations

at the electronic channel D e + X

•BR ~ 15% from D+/-, ~7% from D0

•At low pt the correlation is lost (< 0.5 GeV/c)

•At pt > 1 GeV/c survives

•Need to apply a pt cut:

10% e with pt > 1 GeV/c


•To account the BG from Dalitz,

conversions, B semileptonic

decays…

23

Angular correlation of D-e from D e + X

No pt cut

pt > 1 GeV/c

No pt cut

pt > 1 GeV/c

Semileptonic-decay e are strongly pt

correlated with parent D

e+/e- from D-Dbar decay preserve the

original D-Dbar angular correlation to a

large extent

24

D-e pt correlation

K<—D0<—D*—c – c— D*—> D0—>e- + X

Full rapidity

Mid-rapidity

No pt cut

D-e pt correlations survive charm decay

25

Charmed e+/e- pt correlations

Full rapidity

Mid-rapidity

Mid-rapidity with pt > 0.5 GeV/c

Mid-rapidity with pt > 1 GeV/c

e+ - e- pt correlations at pt > 1 GeV/c survive charm decay

e+ + X<—D0<—D*—c – c— D*—> D0—>e- + X

26

PYTHIA processes for charm/beauty generation

Fra

cti

on

of

each

pro

cess

/All

pro

cess

es

f + f’ f + f’

g + g f + fbar

f + g f + g

g + g g + g

•GS dominant for D-Dbar

•FC dominant for B-Bbar

•FE is flat

D-Dbar

B-Bbar

pt (GeV/c)

27

Primordial B-Bbar angular correlations

•At full : <pt,1pt,2> = 2.97 +/- 0.18

(GeV/c)2 or pt~55 %

•GS flat in dN/d but strong in small

using the Average Momentum Correlator

•FC back to back

•The Average Momentum Correlator is

very sensitive to different PYTHIA

processes for beauty generation

28

e+/e- correlations from B decays

pt e- (GeV/c)

pt > 1 GeV/c

e+/e- from B decays are strongly pt

correlated at small and large

Need to study background BDe

pt B

(G

eV/c

)

e+ + X<—B0<—B*—c – c— B*—> B0—>e- + X

29

Conclusions

In p+p, heavy q-qbar production is correlated

The Average Momentum Correlator is a sensitive measure

Correlations survive hadronization

e+- e- pt correlations at pt > 1GeV/c survive charm/beauty decay

need TRD for electron ID!

need full simulations within ALICE

study changes in correlations and address light quark

thermalization at LHC

e<—D0<—D*—c – c— D*—> D0—>e-

<pt,1pt,2> ~ 0.2 (GeV/c)2 for D-Dbar

30

Backup slides

31

Measure of mean pT fluctuations

T

dynp

dynpp pT

TT

||sgn

2,2

,

N

pM T

pdynp TT

222

,

• Normalized dynamical fluctuation

222TTT ppp

MpT : variance of MpT dist.

p2T : variance of inclusive pT dist.

<N> : mean multiplicity

pT : inclusive (event-averaged) mean pT

= 0 for purely statistical fluctuation > 0(< 0) with positive/negative two-

particle correlation or dynamical EbyE fluctuation

pT

Dimensionless measure

TTT ppp FΣN 2

Proportional to mean covarianceof all particle pairs / eventRobust under change of multiplicity due to changes in beam energy and acceptance

32

c-cbar angular correlations

PYTHIA production

No pt cut

Away side correlation

= (c) – (cbar)

33

D-Dbar pt correlations - Mixed event analysis

Full

Uniform populated – no correlations

34

Gluon splitting

Full

D-Dbar pt correlations - Same event analysis

High pT correlations at small

35

Flavor excitation

Full


Rather flat

36

Pair creation

Full


High pT correlations at big

37

Average Momentum Correlator for same/mixed events


Nk

i1

Nk


Nk

i1

Nk

Mixed events

Same events

GeV2

GeV2

Co

un

ts

Co

un

ts


Nk

i1

Nk

38

Correlation strength for primordial D0 and D0 from D*

Generate D0, D+/-, Ds (no resonances)

with Pv=1 (0.75 default)

Generate D* (only resonances) with

Pv=0 and decay them…

correlations survive resonance decay

50000

39

No flow10% elliptic flow90% elliptic flow

Elliptic flow contribution on dN/d

40

Radial flow contribution on dN/d

= 0, 0.3, 0.6, 0.8, 0.9

With increasing near-side/away-side peaks are enhanced

10000

41

Charm Production in ALICEALICE has a barrel system with high precision

vertexing, PID and electron identification (|| < 0.9)

and a forward muon spectrometer (: 2.5–4.0),

down to low pT.

Charm production can be studied:

• In the electronic and muonic channels D eX (X) •In several hadronic decay channels: D0 K , D± K D0 K, Ds KK, Ds

D* D0, c pK

ALICE PPR II, J. Phys. 32 (2006) 1295

D0 K-+ the cleanest channel

• pair of opposite-charge tracks with large impact parameters• good pointing of reconstructed D0 momentum to the primary vertex

TPC: main tracking device

ITS: high spatial resolution

TRD: good electron PID (high pion rejection)

ToF: extend PID to large pT

42



pt for D-Dbar at full and mid-rapidity

43Mid-rapidity (200000 events)


Fra

ctio

n o

f ea

ch p

roce

ss/A

ll p

roce

sses

pt (GeV/c)

44

Number of charmed electrons 109 p-p events

Nccbar/event = 0.16 (PPR2)

c-cbar D0 (61%)

c-cbar D+/- (20%)

D e + X (15% from D+/-, 7% from D0)


#events with e+/e- from D0 = 0.16*0.612*0.072*109 ~ 300000At pt > 1 GeV = 3000

#events with e+/e- from D+/- = 0.16*0.202*0.152*109 ~ 144000At pt > 1 GeV = 1440

~ 4500 clean e+/e- pairs with pt > 1 GeV at full rapidity

45

e+ - e-

D-e

46

D-Dbar

B-Bbar

At full : <pt,1pt,2> = 2.97 +/- 0.18 (GeV/c)2

or pt~55 %

At full : <pt,1pt,2> = 0.2 +/- 0.006 (GeV/c)2

or pt~30 %

Co

un

tsC

ou

nts


Nk

i1

Nk


Nk

i1

Nk

(GeV/c)2

(GeV/c)2

Documents

p t correlations versus relative azimuth of D-Dbar pairs as a sensitive probe for thermalization