Gang Wang, WWND 20091 Non-Photonic Electron-Hadron Correlations at RHIC Gang Wang (University of...

Gang Wang, WWND 2009 1

Non-Photonic Electron-Hadron Correlations at RHIC

Gang Wang(University of California, Los Angeles)


Outline

Motivation

Analysis procedure

Near-side contribution in p+p collisions

Away-side broadness in A+A collisions

Outlook


Conical Pattern in Conical Pattern in 2-Particle Correlations in Au+Au Collisions

pTtrig = 2.5-4.0 GeV/c;

pTasso = 1.0-2.5 GeV/c

Motivations

Mark Horner (for STAR Collaboration): J. Phys. G: Nucl. Part. Phys. 34 (2007) S995

The away-side correlation structure in Au+Au is different than p+p or d+Au.

PHENIX, PRC 78 (2008) 014901





Motivations


Further support by 3-particle correlations

See STAR paper on 3-particle correlations at arXiv:0805.0622v2 (accepted by PRL)

Conical PatternConical Pattern


Away Side in medium: How does B/D lose energy? Via conical emission?




Motivations


Near Side:what’s the contribution of B/D decay to the non-photonic electrons?

trigger

What if we trigger on non-photonic electrons?


Study of heavy flavor via non-photonic electrons

• D mesons have their directions well represented by the daughter electrons, above 1.5 GeV/c.

• Electrons from B decays can represent the B meson momentum direction well if pT > 3 GeV/c.

PYTHIA


Time Projection Chamber (TPC) Barrel Electro-Magnetic Calorimeter (BEMC) Barrel Shower Maximum Detector (BSMD)

Data Sample:

At sNN = 200 GeV,

p+p collisions in run5/6 (2006), d+Au collisions in run8 (2008), Cu+Cu collisions in run5 (2005), Au+Au collisions in run7 (2007).

Electron ID in STARPurity

dAu, CuCu, AuAu: above 98% for 3 < pT < 6 GeV/c

p+p collisions: above 98% for 3 < pT < 6 GeV/c; 80% for 9 GeV/c.


Decay photon conversions→ → e+ e- in materialMain background

Dalitz decays→ e+ e-

Direct photon conversionsSmall but could be significant at high pT

Heavy flavor electronsD/B → e± + X

Weak Kaon decays

Ke3: K± → e± e

< 3% contribution in pT > 1 GeV/c

Vector Meson DecaysJ→ e+e-< 2-3% contribution in all pT

Photonic electronNon-photonic electron

Electron signal and background


Photonic Background

• The invariant masses of the OS and SS e-pairs have different distributions.• Reconstructed photonic electron is the subtraction.• Photonic electron is the reconstructed-photonic/ ε• ε is the background reconstruction efficiency calculated from simulations.

e-

e+

e-

(assigned as primary track)

(global track)

(primary track)dca


All Tracks

Inclusive electron

Pass EID cuts

Non-photonic electron Photonic electron

Reco-photonic electron=OppSign - combinatorics

Not-reco-photonic electron=(1/eff-1)*(reco-photonic)

Procedure to Extract the Signal of e-h Correlations

Semi-inclusive electron

Δφnon-pho = Δφsemi-incl + ΔφSameSign – (1/eff -1)*(ΔφOppSign – ΔφSameSign)Each item has its own corresponding Δφ histogram.

In case of low purity…

– Δφhadron


Near-Side contribution in p+p


Clear azim. correlation is observed around near and away side.

Fitting measured dn/dφ distribution from B and D decays, we can estimate B decay contribution to non-photonic electron. 　

)/(

)1(

BDB

Dhe

Bhehe

eeer

rr

Non-photonic e-h correlations in p+p 200GeV

B

D


Almost half-half B and D contributions to non-photonic e’s at 5.5 < pT < 9 GeV/c, and FONLL prediction is consistent with our data within errors.

B contribution to non-photonic e in p+p 200GeV


RAA for non-photonic electron is consistent with hadron’s.This Indicate large energy loss not only charm quark but also bottom quark.

Large bottom energy loss?

)/(

)1(

)(

)(

)(

ppC

ppB

ppB

ecAA

ebAA

ppC

ppB

ppC

ppCbin

AAC

ppC

ppB

ppB

ppBbin

AAB

ppC

ppBbin

AAC

AAB

AA

eeer

RrrR

ee

e

eN

e

ee

e

eN

e

eeN

eeR

With the measurements of r @ pp and RAA, we can derive a relationship between RAA

ec and RAAeb.

non-γ ehadron


o RAAec & RAA

eb correlation together with models

o Dominant uncertainty is normalization in RAA analysis

o RAAeb < 1; B meson is also

suppressed

o prefer Dissociate and resonance model (large b energy loss)I: Djordjevic, Gyulassy, Vogt and Wicks, Phys. Lett. B 632 (2006) 81; dNg/dy = 1000

II: Adil and Vitev, Phys. Lett. B 649 (2007) 139III: Hees, Mannarelli, Greco and Rapp, Phys. Rev. Lett. 100 (2008) 192301

STAR preliminary

pT > 5 GeV/c

RRAAAAecec & R & RAAAA

ebeb correlation correlation


Summary I Non-photonic e-h correlations have been measured in p+p collisions to retrieve B and D contributions to non-photonic electrons up to pT~9 GeV/c.

Comparable B and D contributions for electron pT 5.5~9 GeV/c.

FONLL prediction and the eB/(eB+eD) results are consistent with each other within errors.

The measured B/D ratio would imply considerable b quark energy loss in medium based on RAA measurement from central Au+Au collisions. One more measurement is needed: RAA

eb, RAAec or r@A+A.


Away-side broadness in A+A

d+Au collisions serve as a reference of the cold nuclear matter…


Non-photonic e-h correlations in d+Au 200 GeV

Non-photonic e-h azimuthal correlation is measured in one π range,and open markers are reflections. The away-side correlation can be well described by PYTHIA calculations for p+p. No medium effects seen here.

3 < pTtrig < 6 GeV/c & 0.15 < pT

asso < 0.5 GeV/c

STAR Preliminary


about 40% non-flow or fluctuation(Gang Wang, Nucl. Phys. A 774 (2006) 515.)

Non-photonic e-h correlations in Cu+Cu 200 GeV

Upper limits of v2 used are 60% of hadron v2 values measured with the v2{EP} method (equivalent to v2{2}).

0 – 20%: 3 < pTtrig < 6 GeV/c & 0.15 < pT

asso < 0.5 GeV/c

On the away side, there’s a broad structure or a possible double-hump feature, even before v2 subtraction. PYTHIA fit has a big χ2.


Possible interpretations

The away side in e-h is similar to what has been observed in h-h correlations, and consistent with Mach Cone calculations etc. The charm jet deflection provides an alternative interpretation.

3 < pTtrig < 6 GeV/c & 0.15 < pT

asso < 0.5 GeV/c


Non-photonic e-h correlations in Au+Au 200 GeV

Upper limits of v2 used are 80% of hadron v2 values measured with the v2{EP} method. Non-photonic e-h correlation is broadened on the away side. PYTHIA fit has a big χ2.

0 – 20%: 3 < pTtrig < 6 GeV/c & 0.15 < pT

asso < 0.5 GeV/c

STAR Preliminary


Non-photonic e-h correlations in PHENIX

More statistics needed …

Anne Sickles, DNP08 talk. Also see the talk after mine ...


Using the d+Au collision as a reference, the shape of non-photonic e-h azimuthal correlation function is found to be modified in central Cu+Cu and Au+Au collisions due to the presence of the dense medium created in these collisions.

Away-side: Hint of a broad structure, similar shape to that from h-h correlations.

Induced by heavy quark interaction with the dense medium?

Quantitative measure and investigation of the nature of the possible conical emission pattern will require more statistics! DAQ1000 will help us there! Should try 3-particle correlations!

Here demonstrated is the feasibility of the analysis on

the jet-medium interaction tagged by a heavy quark.

Summary II


OutlookLarge associated particle yields on the near side leave open questions: collective medium excitation by heavy quarks?

Momentum kick model, Cheuk-Yin Wong


Back up slides


HQ Production Mechanism Due to large mass, HQ

productions are considered as point-like pQCD processes

HQ is produced at the initial via leading gluon fusion, and sensitive to the gluon PDF

NLO pQCD diagrams show that Q-Qbar could be not back-to-back in transverse plane

We need to study this smearing effect with models

0

flavor creation

gluon splitting


PYTHIA simulations

B

DFor each pt bin, the non-photonic e-h correlations B_corr and D_corr are combined according to B’s and D’s relative contributions to the non-photonic electrons:(eB*B_corr + eD*D_corr) / (eB+eD)

Each pt bin is weighted with their relative yields, and then they are summed up.


Electron ID in STAR

With BEMC and BSMD, the electron peak is enhanced in the energy loss distribution, and we obtain a very pure electron sample.

Purity

dAu, CuCu, AuAu: above 98% for 3 < pT < 6 GeV/c

p+p collisions: above 98% for 3 < pT < 6 GeV/c; 80% for 9 GeV/c.

calibrated Log(dE/dx)


PYTHIA simulations weighted with CuCu yields3 < pT

trig < 6 GeV/c & 0.15 < pTasso < 0.5 GeV/c

Here we assume the B/D contribution in CuCu is similar to that in p+p. Even if they are not similar, we don’t expect the double-hump without a medium.

B D


Electron ID in PHENIX

Also see the talk after mine ...

• PHENIX central arm coverage:– || < 0.35– = 2 x π/2– p > 0.2 GeV/c

– typical vertex selection: |zvtx| < 20 cm

• charged particle tracking analysis using DC and PC1

• electron identification based on– Ring Imaging Cherenkov detector

(RICH) – Electro-Magnetic Calorimeter (EMC)

Gang Wang, WWND 20091 Non-Photonic Electron-Hadron Correlations at RHIC Gang Wang (University of...

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