Open Heavy Flavor in Heavy Ion Collisions

James C. Dunlop

Brookhaven National Laboratory04/02/2009 1J.C. Dunlop, QM2009

10/30/2007 BNL Colloquium James Dunlop 2

Motivation: Grey Probes

• Problem: interaction with the medium so strong that information lost: “Black”

• Significant differences between predicted RAA, depending on the probe

• Experimental possibility: recover sensitivity to properties of the medium by varying probe

Wicks et al, Nucl. Phys. A784 (2007) 426

10/30/2007 BNL Colloquium James Dunlop 3

Charm/Beauty: No shade of gray

• Unexpectedly strong suppression of non-photonic electrons• Tool to study mechanism of energy loss

STAR, PRL 98 (2007) 192301 PHENIX, PRL 98 (2007) 172301

STARSTAR

Measurement: a wealth of decay

• 4 pages D0, 10 pages of B+ decay modes in PDB• Most promising modes:

– Leptons: B.R. ~10% per lepton species of B and D• Electrons: triggerable in calorimeters

• Muons: no Bremsstrahlung, photonic background

• Neither have full kinematic reconstuction

– Pure hadronic: full kinematics• D K➝ π, D* K➝ ππ

• Not easily triggerable

– B J/➝ Ψ + X• Clean from D contamination

• B.R. ~1%, triggerable

04/02/2009 J.C. Dunlop, QM2009 4

K-

bb

B-D*0

D0

+

e

e-

B+

-

K+

D0

Non-photonic electrons in p+p: the baseline

• Factor ~2 discrepancy between STAR and PHENIX • How to resolve this?

04/02/2009 J.C. Dunlop, QM2009 5

STAR, PRL 98 (2007) 192301

Open Charm Cross-section

04/02/2009 J.C. Dunlop, QM2009 6

• Large discrepancy between extracted total cross-section from STAR and PHENIX

• Large theoretical uncertainties

STAR: D0, electrons

PRL 94(2005) 062301

D0, muonsarXiv:0805.0364

PHENIX:Single electrons

PRL 97(2006) 252002

Electron pairs544 ± 39(stat) ± 142 (syst) ± 200 (model)

PLB 670 (2009) 313

Poster F. Jin

PHENIX: Extrapolation issues

04/02/2009 J.C. Dunlop, QM2009 7

Even worse: Additional x2 uncertainty in σ beyond FONLL

Uncertainty driven by low pT, where theory poorly constrained

Single electrons: FONLL shape to extrapolate x1.8Quoted error: 10%

Dileptons:PYTHIA to convert and extrapolateQuoted error: 33%

Measured region

Point not used in extrapolation PHENIX: PRL 97 (2006)252002FONLL: arXiv:0709.252301

STAR: Minimal Extrapolation

• STAR: dominated by muons,pT ~0.17-0.21 GeV/c, and direct reconstruction of D0 which fall less steeply

• Total extrapolation 10%: not the dominant uncertainty 04/02/2009 J.C. Dunlop, QM2009 8

STAR:arXiv:0805.0364STAR: PRL 94(2005) 062301

STARSTAR

But extrapolation isn’t the issue at high pT

• Cross section dominated by low pT, theory not well constrained

• High pT not extrapolated AND theory better constrained

04/02/2009 J.C. Dunlop, QM2009 9

STAR, PRL 98 (2007) 192301

Main difference: material

• PHENIX: low material, so low conversion background– New detectors are changing this

• STAR: before run 8, Silicon Vertexing detectors– Reduces background for D, but increases background for electrons– Reconstruct conversion background, so in principle not an issue, but…– Decision: remove until higher precision silicon can be built

04/02/2009 J.C. Dunlop, QM2009 10

See poster, S. Lapointe

STAR STAR PreliminaryPreliminary

11Jörn Putschke for the STAR Collaboration, QM09, Knoxville

STAR: status of low material run

Material in front of TPC reduced by an order of magnitudeThe final results are not ready in time for this conference

Inclusive e/π ratio Run-3 and Run-8STAR Preliminary

Beam pipe + SVT + SSD+ Dalitz Beam pipe + Dalitz

TPC Inner Field cage

Cou

nt

Analysis status Fu Jin & Xin Li, poster presentations

R [cm]

Run-8

Run-3

But electrons won’t answer the question

Even when we resolve discrepancy in electrons:

Both charm and beauty contribute in an unpredicted way

Quenching can, hopefully will, change eB/eD

J/Ψ are important, according to PHENIX

What is the RAA of high pT J/Ψ?04/02/2009 J.C. Dunlop, QM2009 12

A. Dion, 5D

1/3 of e from J/Ψ decays!

pT [GeV/C]1 9

B. Biritz, 5D

Towards eB/eD

Until we have precise vertexing: correlation measurements provide constraints

Exclude original radiative calc.04/02/2009 J.C. Dunlop, QM2009 13

pT [GeV/C]1 9

B. Biritz, 6D

PHENIX, arXiv:0903.4851

J/Ψ Feeddown into electrons

• PHENIX: J/Ψ e ~1/3 of non-photonic electrons for p➔ T>5 GeV

• Large uncertainties for both STAR and PHENIX at high pT

– At face value, consistent within uncertainties

– Expect large improvements (x5) in STAR statistics runs 9 and 10

• Uncertainties further complicate the interpretation of electrons04/02/2009 J.C. Dunlop, QM2009 14

D. Kikola, 2D E. Atomssa, 2D

The other way: B feeddown into J/Ψ

• B→J/Ψ the “golden channel” for B with vertex detectors• Until we have precision vertexing, constrained by correlations

– STAR p+p: B→J/Ψ/All J/Ψ (13 ± 5)%, in agreement with CDF at this pT

– Model dependence: depends on tuned PYTHIA

04/02/2009 J.C. Dunlop, QM2009 15

STAR Preliminary

d+Au

D. Kikola, 2D C. Perkins, 1D

p+p

Other correlations

• Electron-muon: low backgrounds• Electron-hadron in heavy systems: away-side modification?• Proof-of-principle, await higher statistics, better background

rejection for conclusion

04/02/2009 J.C. Dunlop, QM2009 16

T. Engelmore, 6D B. Biritz, 6D

Outlook: Precision Vertexing

Entering prime years for heavy flavor with precision vertexing

Complementary capabilities and systems

ALICE: LHC, where c becomes a “light” quark

PHENIX: Focus on electrons and muons

STAR: Focus on fully reconstructed kinematics04/02/2009 J.C. Dunlop, QM2009 17

STARSTAR Heavy Flavor Tracker VTX

The “simple”: eB vs. eC

• At ALICE, c a “light quark”, eB/eC sensitive to B energy loss

• Main focus of PHENIX VTX: isolation of eB from eD

– Expected DCA resolution ~50 μm, STAR SVT had achieved ~200 μm

• Warning: cτ of D+~ cτ of B and what matters is βγcτ– More discriminating: multi-hadron correlations, mB>>mD, or B→J/Ψ

04/02/2009 J.C. Dunlop, QM2009 18

A. Dainese, 5D

Expected with VTX (0.4/nb)PHENIX Projection

The other lepton: muons

• Muons an independent check BUT limited by systematics – PHENIX FVTX to reduce backgrounds

• ALICE: muon detectors with clean B signal, pT<~20 GeV/c

• STAR studying upgrade: mid-rapidity Muon Telescope Detector

04/02/2009 J.C. Dunlop, QM2009 19

A. Dion, 5D PHENIX Projection with FVTX

The harder: direct reconstruction

• Direct reconstruction with full kinematic information

• Only possible for charm:

– D+, D0, Λc

• No ambiguities04/02/2009 J.C. Dunlop, QM2009 20

B e + X

RAA D+ K

mC = 1.2 GeV

mC = 0

STARSTAR

A. Dainese, 5D

D0

Poster, J. Bouchet

Λc

Charm Elliptic Flow

Current measurements: large elliptic flow of electrons• Ambiguities: B vs D fraction, decay kinematics

• Are electrons even in the pT region where hydro is applicable?

Solution: direct reconstruction at low pT 04/02/2009 J.C. Dunlop, QM2009 21

STARSTAR

A. Dion, 5D STAR Projection

D0e

Summary

• Current open heavy flavor measurements– Total cross-section: need to measure where the yield is– Non-photonic electrons: ongoing program to increase

precision, decrease systematics, and resolve the STAR/PHENIX discrepancy

– Correlations to constrain contribution of charm– J/Ψ may affect B, and B may affect J/Ψ

• Future: entering the age of precision vertex detectors– Separate charm and beauty contributions to electrons– Direct reconstruction of charm– Elliptic flow: need to measure where hydro is

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10/30/2007 BNL Colloquium James Dunlop 23

Heavy Flavor Correlations

Isolate b from c

Isolate production mechanism

In medium: what is losing energy, and how much?

K-

bb

B-D*0

D0

+

e

e-

B+

-

K+

D0

c

c

g

g

gluon splitting/fragmentation

g

g

g

g

c

c

0

Flavor creation