Transcript The Quenching of Beauty James Dunlop Brookhaven National Laboratory

The Quenching of Beauty
Last Hope for a Grey Probe of the QGP
James Dunlop
Brookhaven National Laboratory
11/1/2007
Heavy Quark Workshop, Berkeley
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The Promise of Jet Tomography
=
+
• Simplest way to establish the properties of a
system
– Calibrated probe
– Calibrated interaction
– Suppression pattern tells about density profile
• Heavy ion collisions
– Hard processes serve as calibrated probe
– Suppression provides density measure
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The Limitations of RAA: “Fragility”
K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511
Central RAA Data
Increasing density
A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461
Surface bias leads effectively to saturation of RAA with density
Challenge: Increase sensitivity to the density of the medium
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Black and White
S.S. Adler et al, Phys. Rev. Lett. 94, 232301 (2005)
• Medium extremely black to hadrons, limiting sensitivity to density
• Medium transparent to photons (white): no sensitivity
• Is there something grey?
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Calibrated Interaction? 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 the
properties of the medium by
varying the probe
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Wicks et al, Nucl. Phys. A784 (2007) 426
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Gluons vs Quarks: Method
200 GeV p+p
1.
q jets or g jets  gluon jet contribution to protons is significantly larger
than to pions at high pT in p+p collisions at RHIC; pbar/ < 0.1 from quark
jet fragmentation at low beam energy . STAR Collaboration, PLB 637, 161 (2006).
2.
From Kretzer fragmentation function, the g/q jet contribution is similar to
AKK. S. Kretzer, PRD 62, 054001 (2000).
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Gluons vs. Quarks: No shade of gray
gluon jet
quark jet
quark jet
STAR Collaboration, PRL 97 (152301) 2006
•
•
•
•
Gluons should lose more energy than quarks
Pions have larger quark contribution than protons
SO, Protons should be more suppressed than pions
Experimentally NOT observed: equal suppression for pT>6 GeV/c
– Perhaps: If medium already black to quarks, can’t be blacker than black
• Other methods to be tried: kinematics in h (as done in e.g. dijet Sivers)
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Charm/Beauty: No shade of gray
STAR, PRL 98 (2007) 192301
PHENIX, PRL 98 (2007) 172301
• Unexpectedly strong suppression of non-photonic electrons a major issue
– Calls into question the calibration of the interaction of the probe with the medium
• Uncertainties in B contribution: need to measure c and b separately
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Mechanisms for Energy Loss
“Passage of Particles through Matter”, Particle Data Book
Bremsstrahlung
Radiative dE/dx
• QED: different momenta, different mechanisms
• Just beginning the exploration of this space in QCD
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Calibrated Probe? Electrons in p+p
STAR, PRL 98 (2007) 192301
b
Crossing from c to b:
anywhere from 3-10 GeV
c
• Large uncertainties in non-photonic electrons, even in p+p
– STAR and PHENIX factor of 2 discrepancy in measurements
•
STAR: runs 8 and 9 low material (same as PHENIX), PHENIX…?
– Theoretical uncertainties, esp. in b vs. c contribution
• Need to measure c and b separately, in all systems, with precision
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Correlations
• RHIC: 10-1 to 10-3 level
• WMAP: 10-5 level
– One sample
– Only photons
– Well-defined separation of
sources
– Multiple samples
– Multiple probes
– Model dependence in separation of
sources
• quite a few “two-component” models,
with different components
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Heavy Flavor Correlations
+
eKe
D0
D*0
B-
Flavor creation
c
g

b
b
D0
B+

Isolate b from c
K+
Isolate production mechanism
In medium: what is losing energy, and how much?
c
g
gluon splitting/fragmentation
c
-
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c
g
g
g
g
0
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Correlations: Can we tell how much beauty?
Xiaoyan Lin, QM2006
• Use e-h Correlation
– Large B mass compared to D
– Semileptonic decay: e gets larger
kick from B.
– Broadened e-h correlation on nearside.
• Extract B contribution
– Use PYTHIA shapes
• Con: Model dependent
• Pro: Depends on decay kinematics
well described
– Fit ratio B/(B+D)
• There is more information from
correlations that is not currently
being used (momentum, charge,
etc.)
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e-h from B
e-h from D
Fit
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B contribution to NP electrons vs. pT
•
Fit e-h correlation with PYTHIA Ds
and Bs
•
Non-zero B contribution
•
Contribution consistent with FONLL
– Model dependent (PYTHIA)
– Depends mainly on kinematics of
D/B decay (not Fragmentation)
•
Xiaoyan Lin, QM2006
p+p 200 GeV
Dominant systematic uncertainty:
– photonic background rejection
efficiency
– Additional uncertainties under study
• There is more information from
correlations that is not currently
being used
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Future at RHIC: “RHIC II” or the fb era
STAR HFT
90
80
Current Au Run, year 7
70
60
Peak Luminosity
Previous Au Run, year 4
50
Ave. Luminosity
40
Beam Current
30
20
10
2014
2012
2010
2008
2006
2004
0
2002
PHENIX VTX
One year at RHIC II ~ 30 nb-1
30 nb-1*1972 =~ 1 fb-1 p+p equivalent
• RHIC: luminosity + upgraded detectors for precision
– Beauty: last hope for a “grey” probe; needs detector upgrades to both
STAR and PHENIX to isolate from charm
– g-jet: precision probe of energy loss
– Upsilon: precision tests of Debye screening with a “standard candle”
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Grey Correlations: Heavy Flavor in the fb era
Heavy flavor
Light Hadrons
Inclusive Spectra
Correlations
From 5 pb-1
Identified heavy flavor correlations: promising, but statistical power still low
RHIC II: many orders of magnitude (>~x1000 with luminosity, S/B improvements)
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Quarkonium: Upsilon
RHIC
Proof of principle measurement: run 6 p+p
Upsilon(1S+2S+3S)→e+e-
Sequential dissociation of quarkonia to measure energy density of plasma
Requires full luminosity of RHIC II for definitive measurements
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Other initiatives: Muons and dileptons
• Muon Tracking Detector: use magnet steel as absorber
– Physics: dileptons from intermediate mass up to quarkonia states
– Best method for separating Upsilon states (a la CDF)
– R+D stage: Brookhaven LDRD 2007-2008
• Dielectrons using TOF for ID and HFT for background rejection
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Conclusion
Idunn’s Apples of Youth, D’Alair’s Book of Norse Mythology
Is Beauty Grey?
We need more apples to tell
Watershed in coming years from RHIC II luminosity and detector upgrades
– Precision studies with g, b, c, and associated multi-hadron correlations
– IF beauty is less suppressed than other parton species, we will be able to probe
the properties of the QGP with exquisite precision
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