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CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 1
Suppression of Suppression of light- n’ heavy-flavored hadrons light- n’ heavy-flavored hadrons
from RHIC to LHCfrom RHIC to LHC
Andrea DaineseAndrea Dainese
Padova – University and INFNPadova – University and INFN
based on work in collaboration with:
N.Armesto, C.Loizides, G.Paic, C.Salgado, U.Wiedemann
CERN Heavy Ion ForumCERN Heavy Ion Forum
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 2
LayoutThe discovery of “jet quenching” at RHIC
High-pT particle production in nucleus-nucleus collisions, according to perturbative QCD
Calculating parton energy loss (BDMPS-Z framework)
Light-flv hadron suppression in the Parton Quenching Model
versus RHIC data
predictions for LHC
Energy loss for heavy quarks
PARTON ENERGY LOSS
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 3
Discovery at RHIC:high-pT suppression
Nuclear modification factor of pT distributions:
PHENIX 0 (0-10%)
dd/d
dd/d1)(
2
2
Tpp
TCAA
CcollTAA pN
pN
NpR
factor 5suppression!
compilation by D.d’Enterria
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 4
What about jets?
Jets via di-hadron correlations:
trigger: highest-highest-ppTT track track, (4--6 GeV)
distribution: 2 GeV < pT < pTtrigger
pp 2 back-to-back jets
STAR Coll., PRL 90 (2003) 082302.slide courtesy of P.Jacobs
near side away side
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 5
Discovery at RHIC:no away-side jet in central Au-Au
Quantified via ratio of integrals:
awayaway
AA ppAAI ~1 in peripheral AA
~0 in central AA
STAR Coll., PRL 90 (2003) 082302.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 6
Is it final-state energy loss?
… or saturation of the parton densities in the initial nuclei?
Control experiment, without medium: d-Au
no high-pT suppression the away-side jet is there
Final-state effectPHENIX Coll., PRL 91 (2003) 072303.STAR Coll., PRL 91 (2003) 072304.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 7
High-pt particle prod. in AA collisionsA schematic view:
Ingredients:pp baseline (pQCD)initial-state effects:PDF (anti)shadowingkT broadening (Cronin)
final-state effects:energy loss in-medium hadronization (coalescence)
medium formed in the collision
Au
Au q
qh
hq
p
p q
q h
hpp h+X
x
fgPb / fg
p
LHC RHIC SPSRAA <1 ~1 >1
Q2 = 5 GeV2
pT
RA
B
1
~2-4 GeV/c
kL kT
Cronin enhancement
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 8
Parton Energy LossPartons travel ~4 fm in the high density medium
Bjorken (`82): energy loss due to elastic scattering
…
Bjorken, FERMILAB-Pub-82/59-THY (1982).
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 9
Parton QCD Energy LossPartons travel ~4 fm in the high color-density medium
Successive calculations (`92 ): a QCD mechanism dominates, medium-inducedmedium-induced gluon radiationgluon radiation
Coherent wave-function gluon acummulates kT due to multiple inelastic scatterings in the medium it decoheres and is radiated
hardparton
path length L
Gyulassy, Pluemer, Wang, Baier, Dokshitzer, Mueller, Peigne’, Schiff, Levai, Vitev, Zhakarov, Salgado, Wiedemann, …
hardparton
path length L
kT
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 10
Calculating Parton Energy Loss
cc
ccRsC
I
for )/(
for /
d
d2
Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291.Zakharov, JTEPL 63 (1996) 952.Salgado, Wiedemann, PRD 68(2003) 014008.
BDMPS-Z formalismpath length L
kT
Radiated-gluon energy distrib.:
2
ˆTk
q transport coefficient
2/ˆ 2Lqc LR c
sets the scale of the radiated energyrelated to constraint kT < , controls shape at << c
Casimir coupling factor: 4/3 for q, 3 for gRC
STATICMEDIUM
(BDMPS case)
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 11
Calculating Parton Energy Loss
2
0 ˆ
d
d d LqCC
IE RscRs
c
Probe the medium
qE ˆ gluons volume-density and interaction cross section
Finite parton energy (qualitatively)
LqECECI
E RscRs
E ˆ
d
d d
0
2/1ˆˆ qqLL 2
If E < c (e.g. small pT parton with large L):
dependence on parton energy : smaller sensitivity to density
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 12
Medium ExpansionThe density of scattering centers is time-dependent:
Dynamical scaling law: same spectrum obtained for equivalent static trasport coefficient
Calculations for a static medium apply to expanding systems
0
0ˆ)(ˆ qq
)(ˆ)(2
ˆ0
002
qd
Lq
L
Salgado and Wiedemann, PRL 89 (2002) 092303
= 1.5, 1.0, 0.5, 0
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 13
Quenching Weights
BDMS, JHEP 0109 (2001) 033.Salgado and Wiedemann, PRD 68 (2003) 014008.
Goal: compute high-pT suppression in BDMPS-Z framework
QW = energy loss probability distributions
Calculated from d/d , in approximation
),ˆ,;( LqCEP R
),,ˆ,;( ELqCEP R + uncertainties
]3/1[ s
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 14
Application: Parton Quenching Model
Dainese, Loizides, Paic, EPJC 38 (2005) 461.
QW + Glauber-based medium geometry and density profile + PYTHIA for parton generation and fragmentation
The procedure in short:1) generate parton (q or g) with PYTHIA (or back-to-back pair)
2) calculate its L and average along the path
3) use quenching weights to get energy loss
4) quench parton and then hadronize it (independent fragm.)
q̂
qL ˆ ,
),ˆ,;( LqCEP RPYTHIA
TR pC ,
Fragm
entat ion
pT
pT – pT
dN/dpT
)]()(ˆ[ sTTsq BA
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 15
Model vs RHIC dataDensity ( ) “tuned” to match RAA in central Au-Au at 200 GeV
Note:
No initial-state effects nor “reco”: results given for pT > 5 GeV
Band represents theoretical uncertainty
/fmGeV 14ˆ 2q
q̂
matches pT-indepence of suppression at high pT
Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 16
Model vs RHIC dataCentrality dependence of RAA
pT > 4.5 GeV
Centrality evolution according to Glauber-model collision geometry );();(ˆ bsTTkbsq BA
Dainese, Loizides, Paic, EPJC 38 (2005) 461.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 17
Model vs RHIC dataDisappearence of the away-side jet
near side away side
STAR Coll., PRL 90 (2003) 082302.STAR Coll., nucl-ex/0501016.
awayaway
AA ppAAI
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 18
Extrapolation in c.m.s. energyIntermediate RHIC energy s = 62 GeV
/fmGeV 72/ˆˆ 2GeV 200GeV 62 qq
energy extrapolation works reasonably well
Extrapolation in s: assuming Ngluons/volume (s)0.6 (EKRT saturation model)
First test:
q̂
EKRT: Eskola, Kajantie, Ruuskanen, Tuominen, NPB 570 (2000) 379.PHENIX Coll., JPG 31 (2005) S473.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 19
Model prediction for LHCExtrapolation to LHC according to saturation model gives:
/fmGeV 100ˆ 7ˆ 2GeV 200TeV 5.5 qq
2
GeV 200TeV 5.5 AA
AA
RR
indep. of pT
h
?!?
Dainese, Loizides, Paic, EPJC 38 (2005) 461.Vitev and Gyulassy, PRL 89 (2002) 252301.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 20
Why RAA is flat Surface effectMost partons from inner part are totally absorbed
Energy loss is “saturated”: many partons radiate all their energy before getting outLong path lengths exploited only by high energy partons effectively, RAA doesn’t increase at high pT
Exercise: RAA increases with pT
Prod. points in (x,y) for partons giving hadrons with pT > 5 GeV:
increasing s
10.5 with , EE
LL
Loizides, PhD Thesis, nucl-ex/0501017
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 21
Open points (1): limited sensitivity of RAA
Strong suppression requires very large density
Surface emission scenario
RAA determined by geometry rather than by density itself
Limited sensitivity to
Need more differential observables:
massive partons
RAA vs reaction plane
study of jet shapes
…
q̂
large RAA indep. of q̂ q̂
Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511.
?
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 22
Further handle on L-dependence*
First RAA vs appearing …(see talk by d’Enterria)
= 0
= /2PHENIX 0 prel. vs PQM
Data show stronger dep. than PQM model
PQMPQM
STAR Coll., PRL 93 (2004) 252301
Note: model is not E L2, rather E L * Beware: effect of collective flow on RAA vs !?!
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 23
Open points (2): the opacity problem
Can we really probe the medium?
Need to relate extracted to an energy density QCD estimate for ideal QGP:
A recent analysis* of RHIC data, similar to that presented, extracts energy density 5 larger than that estimated from produced transverse energy dET/dy (Bjorken estimate)
Opacity problem: the interaction of the hard parton with the medium is much stronger than expected
q̂
)(2)(ˆ 4/3 q (Baier)
Baier, NPA 715 (2003) 209.* Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 24
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 25
Lower E loss for heavy quarks ?In vacuum, gluon radiation suppressed at < mQ/EQ
“dead cone” effect
Dead cone implies lower energy loss (Dokshitzer-Kharzeev, 2001):energy distribution d/d of radiated gluons suppressed by angle-dependent factor
suppress high- tail
Q
Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602.Dokshitzer and Kharzeev, PLB 519 (2001) 199.
1
1d
d
d
d2
2
2
Q
Q
LIGHTHEAVY E
mII
Dokshitzer
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 26
Lower E loss for heavy quarks ?Detailed massive calculation shows that:
Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003.
Medium-induced gluon radiation fills the dead cone
Still, kT-integrated radiation is suppressed, but only for quite large m/E (i.e. large m, low pT)*
R = 105
*Warning: large uncertainties
kT
)0.1/( / 2 cdddI
)( 22Tk
m/E = 0.1
massive
massless
dead cone
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 27
Charm Energy Loss at RHICCompute RAA for c, D, e (from D)
Baseline: PYTHIA, with EKS98 shadowing, tuned to match pT-shape of D cross section measured in d-Au by STAR
c-quark E loss as for light-flv hadrons, but using (mc/Ec)-dependent QW
extracted from 0,h RAA (central)
Thermalize charms that lose all energy dN/dmT mT exp(-mT/T), T = 300 MeV
Use a range in to visualize limited sensitivity of RAA to itself
Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.EKS: Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61.
q̂
q̂q̂
baseline dN/dpT
baseline RAA
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 28
Charm RAA at RHIC
effect of the mass
thermalized component
/fmGeV 144ˆ 2q
Small effect of mass for charm (~50% for D, ~30% for e) at low pT [large uncertainties!]Basically no effect in “safe” pT-region
Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 29
Charm Electron RAA from PHENIX
RAA down to 0.3 at pT ~ 4 GeV,where effect of c masspredicted ~20-30%
Reasonable agreementof prediction with data,
however …
RAA
pT (GeV)
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 30
Charm+Beauty e RAA from PHENIX
PHENIXFONLL pQCDCacciari, Nason, Vogt, hep-ph/0502203
PHENIX e spectrum may be ~50% charm + ~50% beauty for 3 < pT < 8 GeV
For pT < 3 GeV, computed RAA depends on T used for thermalized charm
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 31
The heavy-to-light ratio:What enters the game:
1) (c) quark vs gluon (Casimir factor) RD/h > 1
2) harder charm pT distribution: RD/h up
3) harder charm fragm. RD/h down
4) mass effects RD/h up
)(
)()(/
ThAA
TDAA
ThD pR
pRpR
1) dominates > 12-13 GeV2) and 3) ~ compensate4) dominates below 12 GeV
Warning: significant non-pert. effects (e.g. reco) below 6-7 GeV
RHIC
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 32
Heavy Quark Energy Loss at LHCCharm (beauty) production expected to increase from RHIC to LHC by factor 10 (100)
~100 cc pairs and ~5 bb pairs per central Pb-Pb collision
Experiments will measure with good precision RAA for D and
B, and for their decay leptons (see talk by R.Turrisi)
What can we learn from a comparative quenching study of
massive and massless probes at the LHC?
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 33
Heavy Flavor RAA at LHCBaseline: PYTHIA, with EKS98 shadowing, tuned to reproduce c and b pT distributions from NLO pQCD (MNR)
E loss with (m/E)-dep. QW and
MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295.
/fmGeV 10025ˆ 2q
Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 34
Heavy-to-light ratios at LHC: charm
(Small) mass effect limited to pT < 8-10 GeV, where shadowing and “reco” may be significantFor 10 < pT < 20 GeV, charm behaves like a m=0 quark,light-flv hadrons come mainly from gluonsRD/h enhancement probes color-charge dep. of E loss
gq EE
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 35
Heavy-to-light ratios at LHC: beauty
For 10 < pT < 20 GeV, dominant effect due to b mass
RB/h enhancement probes mass dep. of E loss
mass effect
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 36
SummaryOne of the most exciting discoveries at RHIC !We are dealing with energy loss in an extremely opaque medium, but … theoretically, we are just starting to learn how to probe the
medium; still large uncertainties experimentally, already going to more differential observables
vs azimuthal angle i.e. path-length -- (not understood, flow?)
vs parton species and quark mass -- c (b) SUPPRESSED!
The LHC will be a `hard probes machine’ and quenching studies will play a central roleExample: Heavy-to-light ratios as probes of E loss…… color-charge dependence (RD/h)… parton-mass dependence (RB/h)
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 37
EXTRA SLIDES
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 38
Comparison to massive GLV
Djordjevic, Gyulassy, Wicks,hep-ph/0410372
CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese 39
RAAD at LHC, step by step