Open Heavy Flavor in Heavy Ion Collisions
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Transcript of Open Heavy Flavor in Heavy Ion Collisions
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
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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?
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STAR, PRL 98 (2007) 192301
Open Charm Cross-section
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• 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
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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
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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
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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
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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
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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
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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
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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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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