future prospects in qcd bnl, july 17-22, 2006 1 jets and heavy flavors jet and heavy flavor probes...
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1Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Jet and Heavy Flavor Probes of Hot QCD MatterPeter Jacobs, LBNL
2Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Calibrated in p+p and p/d+A
Calculable final state medium effects
Why hard probes? (= perturbative processes)
Calculable interactions of energetic partons with the medium calibrated, penetrating tomographic probes
3Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Outline• jet quenching and radiative energy loss• inclusive hadron suppression • heavy quark suppression• dihadron correlations: modification of jet structure• outlook to the LHC
(not discussed: quarkonium)
Most up-to-date reference:http://hp2006.lbl.gov/source/program.htm
4Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
pQCD in p+p at RHIC
Good agreement with NLO pQCD pQCD should be broadly applicable at RHIC (e.g. heavy flavor production…)
Inclusive jets
5Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Inclusive hadron spectra in 200 GeV Au+Au
pT (GeV)
PHENIX
PHOBOS
6Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Jet quenching I: hadrons are suppressed, photons are not
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
Binary collision scaling
p+p
7Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Jet quenching II: recoiling jets are strongly modified
cos()
pTassoc > 0.15 GeV
STAR, Phys Rev Lett 95, 152301
4< pTtrig < 6 GeV
STAR, Phys Rev Lett 91, 072304
pTassoc > 2 GeV
I & II: conclusive evidence for large partonic energy loss (“jet quenching”) in dense QCD matter
trigger
recoil
?
8Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Radiative energy loss in QCD
CS
coherent
LPM Nq
dzd
dI
ldzd
dI ˆHeitlerBethe
2ˆ~ˆ~ LqLqdzd
dIddzE SCS
LPML
med
C
cformation Lt
BDMPS approximation: multiple soft collisions in a medium of static color charges
E independent of parton energy (finite kinematics E~log(E))E L2 due to interference effects (expanding medium E~L)
Medium-induced gluon radiation spectrum:
Total medium-induced energy loss:
2
2
22ˆ
qd
dqqdq mediumTransport coefficient:
Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000)
9Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Extracting qhat from hadron suppression data
RAA: qhat~5-15 GeV2/fm
10Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
What does measure?q̂
LqxxGN
Nq medium
C
CS ˆ,1
4ˆ
2
2
Equilibrated gluon gas:number density ~T3
energy density ~T4
43
ˆ cq
qhat+modelling energy density
• pQCD result: c~2 (S? quark dof? …)• sQGP (multiplicities+hydro): c~10
R. Baier, Nucl Phys A715, 209c
Hadronic matter
QGP
~RHIC data
Model uncertainties
11Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
EASW BDMPS sCR
4ˆ q L2
ˆ q 2
L2d
0
L
ˆ q ()2 ˆ q 00
L
/log
1
4
92
3
ELdy
dN
R
C
Eg
Rs
GLV
BDMPS(ASW) vs. GLVBaier, Dokshitzer, Mueller, Peigne, Schiff, Armesto, Salgado, Wiedemann, Gyulassy, Levai, Vitev
1800dy
dN g
ˆ q 10GeV 2
fm
Rough correspondence: (Wiedemann, HP2006) 900
dy
dN g
fm
GeVq
2
5ˆ
BDMPS
GLV
Medium-induced radiation spectrum
Salgado and Wiedemann PRD68 (2003) 014008
2ˆLqC
30-50 x cold matter density
12Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Alternatively: AdS/CFT Liu, Rajagopal and Wiedemannhep-ph/0605178
Raj
agop
al, H
P20
06
13Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
RAA only provides lower bound on q̂
The limitations of RAA
14Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Inclusive hadrons and surface bias
?
Inclusive measurementsinsensitive to opacity of bulk
Eskola et al., hep-ph/0406319
RAA~0.2-0.3 for broad range of q̂
Large energy loss opaque core
More differential observables are needed to probe deeper…
15Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Heavy quark energy loss• In vacuum, gluon radiation suppressed at < mQ/EQ
• “dead cone” effect: heavy quarks fragment hard into heavy mesons
QDokshitzer, Khoze, Troyan, JPG 17 (1991) 1602.Dokshitzer and Kharzeev, PLB 519 (2001) 199.
Dead cone also implies lower heavy quark energy loss in matter: (Dokshitzer-Kharzeev, 2001)
1
1
dd
d
d2
2
2
Q
Q
LIGHT
HEAVY
E
m
II
16Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Heavy quarks are “grey probes”Wicks, Horowitz, Djordjevic and Gyulassy, nucl-th/0512076
Origin of surviving jets(radial propagation only)
jets go thataway
Heirarchy of “surface bias” correlated with opacity/suppression differential probes of the medium
RAA
17Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Heavy flavor suppression via b,ce+X
Gluon density/qhat constrained by light quark supression+entropy density (multiplicity) under-predicts electron suppression charm vs beauty? elastic energy loss? …?
RAA(non-photonic electrons) ~ 0.2 ~ RAA() !!
S.Wicks et al., nucl-th/0512076Armesto et al., Phys.Lett.B637:362-366,2006
18Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
b vs c suppression
pT~5 GeV/c: ce suppression ~0.2 puzzle resolved if c e dominates non-photonic electron spectrum - is that permissible?
S.Wicks et al., nucl-th/0512076RAA
19Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
N. P. electrons in p+p vs FONLL
~factor 2
CD
F, P
RL
91, 241804 (2003)
D0
FONLL
M. Cacciari, Hard Probes
State of the art: Fixed-Order Next-to-Leading Log
STAR, nucl-ex/0607012
Tevatron charm and beauty vs FONLL: OK
• RHIC n.p. electrons: factor 3-5 excess(!)• Large ambiguity in relative contribution of ce/be need to resolve b and c explicitly
20Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Elastic (collisional) energy loss revisitedS.Wicks et al., nucl-th/0512076
Elastic E comparable to Radiative E – not negligible
Elastic E important even for light quarks revisit energy density estimates?
21Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Resolution of non-photonic electron suppression puzzle needs
• experiment: explicit measurement of c vs b suppression
• theory: unified framework incorporating both elastic and radiative energy loss
22Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Jet structure via hadron correlationsp+p dijet
Full jet reconstruction in the heavy ion environment is difficult probe jet structure via dihadron correlations
trigger
Phys Rev Lett 90, 082302
23Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
cos()
pTassoc > 0.15 GeV
STAR, Phys Rev Lett 95, 152301
Established results…
4< pTtrig < 6 GeV
STAR, Phys Rev Lett 91, 072304
pTassoc > 2 GeV
24Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Dihadron correlations at higher pT
Recoil jet clearly seen above background but at suppressed ratedifferential measurement of`E upper bound on qhat?
trigger
recoil
?
pTtrigger>8 GeV/c
Yie
ld p
er tr
igge
r
STAR, nucl-ex/0604018
25Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Recoiling hadrons: details
No angular broadening
No modificationof fragmentation
Recoil rate is suppressed but jet features unmodified see only non-interacting jets?
D(z
T)
Recoiling hadron distribution
STAR, nucl-ex/0604018
26Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
STAR preliminary
T. Renk, hep-ph/0602045
High pT dihadrons: detailed dynamical calculation
Trigger direction
Different geometrical biases underly trigger and recoil distributions
~75% of recoils due to non-interacting jets
All bremsstrahlung models: discrete term
27Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Correlations and dynamics (cont’d)
T. Renk, hep-ph/0602045
Calculation ~reproduces recoil yields with params fit to RAA • additional sensitivity to dynamics of the collision? (in progress…)
Suggestive calculation need larger dynamic range in pT
trig and pTassoc to probe energy loss
(not only discrete term)Ultimately: +jet (experimentally challenging, in progress)
T. Renk, HP2006
Various models of bulk expansion
28Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Medium response to jet energy loss I
PHENIX, QM05 and nucl-ex/0507004
Leadinghadrons
Medium
away
near
STAR, Phys Rev Lett 95, 152301
Look at low pT recoils…
• experimentally challenging to discriminate signal/bkgd• new development: 3-particle correlations• Mach cone, Cerenkov radiation,…?
29Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Medium response to jet energy loss II
Au+Au 0-10%preliminary
3<pt,trigger<4 GeV
pt,assoc.>2 GeV
Armesto et al, nucl-ex/0405301
Near-side “ridge” correlated with jet trigger
Induced radiation dragged by longitudinally expanding fluid?
30Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Jet quenching at the LHC
Pb+Pb at 5.5 TeV:• First ion collisions 2008• qualitatively new probes full (~unbiased) jet reconstruction in HI events
31Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
SummaryExperiment • jet quenching is well-established: multiple strong effects• key open issue: how does the medium respond to E?• second generation of high precision measurements:
• heavy flavor, correlations, +jet• RHIC upgrades (charm reco), high luminosity (+jet)• LHC brings qualitatively new physics
Theory• qualitative but not yet quantitative understanding of jet quenching• significant uncertainties in
• underlying mechanism (elastic vs radiative)• heavy quark production• modeling of dynamical evolution
32Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Final comment
Current theoretical uncertainties present the largest barrier to quantitative understanding and full exploitation of RHIC and LHC Heavy Ion measurements
The situation is analogous to the early days of the Solar Neutrino puzzle:
We need a Standard Solar Model for Ultra-relativistic Heavy Ion physics
(The good news: this is in progress)
34Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors
Further limitation of RAA
Can RAA of light quarks/gluons constrain the energy loss distribution?T. Renk (HP2006): accurate geometry/expansion, toy models for P(E)
Can always tune medium density to reproduce RAA: only weak constraint on e-loss distribution
Prob. distributions for parton to lose E
parton with E<0.5 GeV is absorbed by medium
More differential observables are needed to probe deeper…