Future Prospects in QCD BNL, July 17-22, 2006 1 Jets and Heavy Flavors Jet and Heavy Flavor Probes...

1Future Prospects in QCDBNL, July 17-22, 2006 Jets and Heavy Flavors

Jet and Heavy Flavor Probes of Hot QCD MatterPeter Jacobs, LBNL


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


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


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


Inclusive hadron spectra in 200 GeV Au+Au

pT (GeV)

PHENIX

PHOBOS


Jet quenching I: hadrons are suppressed, photons are not

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Binary collision scaling

p+p


Jet quenching II: recoiling jets are strongly modified

cos()

pTassoc > 0.15 GeV

STAR, Phys Rev Lett 95, 152301

4< pTtrig < 6 GeV


pTassoc > 2 GeV

I & II: conclusive evidence for large partonic energy loss (“jet quenching”) in dense QCD matter

trigger

recoil

?


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)


Extracting qhat from hadron suppression data

RAA: qhat~5-15 GeV2/fm


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


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


Alternatively: AdS/CFT Liu, Rajagopal and Wiedemannhep-ph/0605178

Raj

agop

al, H

P20

06


RAA only provides lower bound on q̂

The limitations of RAA


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…


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


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


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


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


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


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?


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


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


cos()

pTassoc > 0.15 GeV


Established results…

4< pTtrig < 6 GeV


pTassoc > 2 GeV


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



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 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


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


Medium response to jet energy loss I

PHENIX, QM05 and nucl-ex/0507004

Leadinghadrons

Medium

away

near


Look at low pT recoils…

• experimentally challenging to discriminate signal/bkgd• new development: 3-particle correlations• Mach cone, Cerenkov radiation,…?


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?


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


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


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)


Extra slides


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…

Future Prospects in QCD BNL, July 17-22, 2006 1 Jets and Heavy Flavors Jet and Heavy Flavor Probes...

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Transcript of Future Prospects in QCD BNL, July 17-22, 2006 1 Jets and Heavy Flavors Jet and Heavy Flavor Probes...