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STAR Open Heavy Flavor Measurements

Gang Wang (UCLA)

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Motivation

D0 / Ds / D*

Non-photonic electron

Summary

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Why heavy quarks?X. Zhu, et al, Phys. Lett. B647, 366(2007).

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

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

Strong interactions do not affect heavy-quark mass.

Initial fusion dominates heavy flavor production.

Study properties of the hot and dense medium at the early stage of heavy-ion collisions.

Light flavor thermalization.

M. Gyulassy & Z. Lin, PRC 51 (1995) 2177

Charm quark

The STAR detector and Particle IDLarge acceptance|| < 1, 0 < < 2

p

TPC dE/dx, momentum

TOF 1/ difference

Run9 ~ 72% of full TOFRun10: 100%

significantly improved PID for final state hadrons, especially for kaons

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Previous D0 measurements

% 83.3~)( 00 KDD

STAR Preliminary ArXiv: 0805.0364

run4

D0

PRL. 94 (2005) 62301

run3

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Nbin scaling Charm x-section ~ Nbin.

STAR Preliminary ArXiv: 0805.0364

run4run3

NPE+D0 NPE+μ+D0

NPE+μ

Difficulties:

Short life time

Low production rate

Large combinatorial bg

D0 in 200GeV p+p

Mass window: 1.72 – 2.1 GeV/c2

~ 4signal observed.

Yifei Zhang, DNP2010 talk

0.4 < pT < 2.2 GeV/c

Mixing event

Track rotation

Same sign

run9

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Ds in 200GeV Au+Au

%5.4~ sD

Preliminary results indicate statistical hadronization.

• Assume pT spectrum shape similar to D0: 47% yield covered.• D± yields estimated from D±

/D0 ratio from e+e- data.

with the help of Silicon Vertex Tracker.

Sarah LaPointe, WWND2010 talk

I.Kuznetsova, J. Rafelski,Eur. Phys. J. C 51 1 (2007) 113-133

run7

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D* in 200GeV p+p

Background combinations:Wrong sign:D0 and -, D0bar and +

Side band:1.72< M(K) < 1.80 or1.92 < M(K) < 2.0 GeV/c2

All triggers included.More than 4 signal at low pT and very significant at high pT - mostly from EMC-based high neutral energy triggers.

%7.67~)()*(* 00 sDDDD

Yifei Zhang, DNP2010 talk

run4

D* in 200GeV p+p

All triggers included.

More than 4 signal at low pT and very significant at high pT - mostly from EMC-based high neutral energy triggers.

Wrong sign and side-band method reproduce background well.

STAR Preliminary

No significant charge asymmetry

Yifei Zhang, DNP2010 talk9

Summary: D mesons

Previous STAR NPE/μ/D0 measurents in Au+Au and d+Au show the Nbin scaling of charm x-section.

STAR Ds measurement in Au+Au tends to support the statistical hadronization model.

Open charm hadrons are reconstructed from STAR run9 p+p 200 GeV data.

4 D0 signal at low pT and more significant D* signal at high pT are observed.

Working on efficiency for pT spectra and cross-section.

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Photon conversions

→ → e+ e- in material

Dalitz decays

→ e+ e-

Heavy flavor electronsD/B → e± + X

Weak Kaon decaysKe3: K± → e± e < 3% contribution in pT > 1 GeV/c

Vector Meson DecaysJ→ e+e-< 15% contribution in all pT

Photonic electron Non-photonic electron

Electron signal and background

11%~anything 10.1%~anything

16%~anything 6.5%~anything 0

0

eDBeB

eDeD

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Long and slowly dying issue on RHIC NPE

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Results differ by a factor of two in pT spectra Total cross section p+p collisions Au+Au collisions

Investigation is underway

STAR PRL 97(2007)192301

PHENIX PRL 98(2007)172301

PRL 94(2005)082301PRL 97(2006)252002

STAR d+Au PRL 94(2005)62301

STAR

run3

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STAR preliminary

R(cm)

Beam pipe + SVT + SSD+ Dalitz

Beam pipe + Dalitz

TPC Inner Field cage

Cou

nt

STAR efforts Significantly Increase the S/B of this analysis (2008-present) Cross check NPE measurements with early runs.

Yield of conversion electrons at different radial location 13

Wei Xie, HP2010 talk

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STAR high pT NPE in 200GeV p+p

Measurement done using TPC+EMC using run08 and run05 data. pT>2.5GeV/c NPE measurement with dramatically different background agree with each other very well

• Combined using “Best Linear Unbiased Estimate”. χ2/ndf = 4.81/7 = 0.69 14

Wei Xie, HP2010 talk

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Comparison with the Published NPE Results

STAR and PHENIX NPE result in 200GeV p+p collisions consistent within errors at pT > 2.5 GeV/c

STAR High pT NPE results are consistent with FONLL in 200GeV p+p collisions15

Wei Xie, HP2010 talk

See Wenqin Xu's talk for details on eB x-section!

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

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

pTtrig = 3-4.0 GeV/c;

pTasso = 0.5-1 GeV/c

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?

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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

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Disentangle Charm and Bottom Production

• Wider φ distribution for B meson because of the larger mass.

•Combined fit on data to obtain the B meson contribution to non-photonic electron.

DheB

BheBhe rr )1(

)/( BDBB eeer

B

D hep-ph/0602067

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~30-60% of non-photonic electron come from B meson in 200GeV p+p collisions.

Assume the same fraction in Au+Au collisions, results indicate B meson is suppressed

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B Meson Suppression in 200 GeV Au+Au

See Andre Mischke's talk for details!

Phys. Rev. Lett. 105 (2010) 202301

run5&6

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Raw NPE-h correlation without pile-up removal in 500GeV p+p collisions.

PYTHIA simulation still shows different near-side peaks for NPE from D and B.

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NPE-h Correlation in 500 GeV p+p

Wei Li (ATHIC2010 talk)

run9

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CuCuAuAu

21.7 / 5 34.4 / 5

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B. Biritz (QM2009)

Away side broadened, beyond PYHTIA fit, in both the Au+Au and the Cu+Cu collisions

Broadened Awayside in the NPE-h Correlations

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

asso < 0.5 GeV/c

run5

run7

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

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

Gang Wang, HP2010 talk

run8

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Above 1.5 GeV/c, D-decay electrons well represent the mother D mesons’ direction.

eD v2 ~ D v2Similarly, above 3 GeV/c,

eB v2 ~ B v2

Partonic Partonic flow flow picture is picture is supported supported for u, d, s.for u, d, s.What What about about heavier heavier quarks?quarks?

Motivations

PHENIX, arXiv:nucl-ex/0604011; STAR, Nucl. Phys. A 830(2009)19c.

NPE v2

Non-photonic e v2 is lower than hadron v2 (or KS0, Λ).

STAR, Phys. Rev. C 77 (2008) 54901

Gang Wang, HP2010 talk 24

run7

Summary: NPE Discrepancy in high pT NPE has been solved!

NPE-h correlations have been measured in p+p collisions to retrieve B and D contributions, and used to study B energy loss.

Using d+Au as a reference, the shape of NPE-h correlation on the away-side 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.

NPE v2 values obtained via fitting the correlations fall in a reasonable range, and are lower than hadron(or KS

0, Λ) v2.

Correlations with heavy flavor tag: jet reconstruction, ridge..

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Future of Heavy Flavor Measurement at STARMTD (MRPC)

See Xin Dong's talk for details!

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backup

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Disentangle Charm and Bottom Production

cc0D0D

eK

K

0D

eK

bb0D

KB B

0*D

• Near side: mostly from B mesons •Away side: charm (~75%), Bottom (~25%)

STAR preliminary

JPG35(2008)104117

JPG35(2008)104117

K* in 200GeV p+p

Three different methods to reproduce combinatorial background.

Very good K*0 and K2*(1430) signal observed.

K*0

K2*(1430)

Run 9 p+p 200 GeV 105M minbias eventsYifei Zhang, DNP2010 talk

0.4 < pT < 2.2 GeV/c

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Energy loss mechanisms of non-photonic Electrons

D0

radiative energy loss

c quark

K+

l

e-/- light

(D. kharzeev, M.Djordjevic et al. )

u

c

“dead cone effect”: gluon radiation suppressed at < mQ/EQ

collision energy loss

c quark

Hot/Dense Medium

Hot/Dense Medium

(Teany, Ralf, Denes et al.)

D0

K+

l

e-/-

D0

meson energy loss

c quark u

c

Hot/Dense Medium

Ivan, et al

u

cD0

K+

l

e-/-

30Wei Xie, HP2010 talk