Upload
nathaniel-shields
View
217
Download
4
Embed Size (px)
Citation preview
Jet quenching: what's next? 1ETD-HICJuly 16-19, 2007
Jets quenching: what’s next?Peter Jacobs
Lawrence Berkeley National Laboratory
Jet quenching: what's next? 2ETD-HICJuly 16-19, 2007
LRP Phases of QCD: Recommendation #11. Our central goal is a dramatic advance in our understanding of QCD Matter, through quantitative comparison of theory and experiment to determine the properties of the strongly coupled Quark-Gluon Plasma discovered in the initial phase of RHIC operations, and through further exploration of the QCD phase diagram at non-zero baryon density where a critical point has been predicted. The essential requirements for the success of this scientific program are therefore our highest priority:
• Effective utilization of the RHIC facility and completion of the ongoing detector upgrade program;• The RHIC II luminosity upgrade, which will enable quantitative study of rare processes;• Strong support for the ongoing theoretical studies of QCD matter, including finite temperature and finite baryon density lattice QCD studies and phenomenological modeling, and an increase of funding to support new initiatives enabled by experimental and theoretical breakthroughs.
What does
this mean
?
Jet quenching: what's next? 3ETD-HICJuly 16-19, 2007
GLV
ASW
χ2 fit to RAA
1-pv
alue
Towards precision: measuring
PHENIX QM06 B. Sahlmueller et al, nucl-ex/0701060
q̂
RAA constrains theory parameters to ~factor 2
Jet quenching: what's next? 4ETD-HICJuly 16-19, 2007
Quantitative jet quenching: 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
Jet quenching: what's next? 5ETD-HICJuly 16-19, 2007
Zhang, Owens, Wang and Wang nucl-th/0701045
from inclusive and di-hadon suppression
fmq 2GeV3.08.2~ˆ
Consistent minima for two independent measurements
q̂
Jet quenching: what's next? 6ETD-HICJuly 16-19, 2007
RHIC Performance: Run 7
slopeRun7 ~ 2 X slopeRun4
Jet quenching: what's next? 7ETD-HICJuly 16-19, 2007
Transport Coefficients
RHIC I AuAu 2nb-1
(Recorded?)
Systematics dominated.
Run-4AuAu 0.2 nb-1
10%)ty (Probabili
/fmGeV 24ˆ6 2
q
RHIC I ++
Jet quenching: what's next? 8ETD-HICJuly 16-19, 2007
Jet in LHC Heavy Ions
Pb+Pb at 5.5 TeV: huge kinematic reach
P. Jacobs and M. van LeeuwenNucl. Phys A774, 237 (2006)
Jet quenching: what's next? 9ETD-HICJuly 16-19, 2007
Jets at RHIC in the fb era (from Jamie Dunlop’s talk on Monday)
Jet reco under optimization
Data in hand: p+p, Cu+Cu, Au+Au
From LHC studies should work for Et>~20-30 GeV
Nbin projection from p+p# Jets in bin at 40 GeV
Run 6 Cu+Cu: ~50Run 7 Au+Au: ~1000
600 ub-1
, 23 pb-1
p+p equiv. RHIC II: ~50, 000 Precise
D(z)
2 pb/GeV
40% precision with 0.3 pb-1, half barrel
STAR PRL 97 (2006) 252001
Jet quenching: what's next? 10ETD-HICJuly 16-19, 2007
• Fully reconstructed single jets
– much reduced geometric bias
– Jet shape and fragmentation modified by the medium
• Observables
– “RAA” of jets
– Fragmentation function
– Acoplanarity of dijets
– Jet-– Jet-Z0
– Multi jets
– …
c
d
a b
ATLAS
Jet observables
Jet quenching: what's next? 11ETD-HICJuly 16-19, 2007
Jet reconstruction: generic issues
Two broad classes of algorithms:“kT/Durham”: merge all tracks/energy clusters that
are nearby in phase space“cone”: fixed shape; stable energy-weighted maxima around seeds; special rules for merging/splitting
colinear safety: finite calorimeter threshold misses jet on left?
infrared safety: one or two jets?
Jet quenching: what's next? 12ETD-HICJuly 16-19, 2007
Jet reconstruction in heavy ion collisions100 GeV jet in central Pb+Pb
En
erg
y (
Ge
V)
Large backgrounds optimal resolution using small jet cones R~0.3?
Complex underlying event fluctuations in heavy ion events:• full jet reconstruction is difficult• jet trigger is tricky (large background fluctuations)
Jet quenching: what's next? 13ETD-HICJuly 16-19, 2007
Soft Background in Jet Cones
ET = 100 GeV, R = 0.4
(TPC+EMCal)
(TPC)
(TPC – like RHIC)
Cone radius R=√(Δη2+ΔΦ2)
Large cone radius large background
Radius cut of .4 + pT cut lowers background > 80% of Ejet
R
Energy in cone R: background and jets
Central Pb+Pb
Preserve “most” of jet while strongly suppressing bkgd:
pT>2 GeV/cR~0.4
Jet quenching: what's next? 14ETD-HICJuly 16-19, 2007
Small cones and jet splittingET = 100 GeV, R = 0.4
(TPC+EMCal)
(TPC)
(TPC – like RHIC)
But why this huge tail for a mono-energetic jet sample with Ejet
T=100 GeV?
Jet quenching: what's next? 15ETD-HICJuly 16-19, 2007
Input Jet Energy [GeV]
fraction of events with Nreconstructed>1
Jet splitting/Sub-jet summing
Jet Energy [GeV]#
Je
ts
all particles, R=0.3, pt>2GeV
- input - Njets,rec=1- Njets,rec>=1 highest jet- Njets,rec>=1 mid-cone- Njets,rec>=1 sum
• Small cone radius splits jets - need a correction pass to sum sub-jets and recover jet energy accurately• Internal structure of jet and its modification may also be of great interest…
Work in
progress
Jet quenching: what's next? 16ETD-HICJuly 16-19, 2007
kT at a hadron collider: CDF inclusive jets
…same performance as modern cone algorithms
Jet quenching: what's next? 17ETD-HICJuly 16-19, 2007
2
222
,min ijTjTiij
jijiij
Rkkd
R
• Infrared safe measure area using zero-energy ghost particles• Potential advantage over cone: smaller effective area, lower integrated background
PhysLett B641, 57 (2006)
Fast kT
Jet quenching: what's next? 18ETD-HICJuly 16-19, 2007
Fast kT for LHC Heavy Ions: ATLAS
Jet quenching: what's next? 19ETD-HICJuly 16-19, 2007
Benchmark measurement: modified fragmentation function
• MLLA: good description of vacuum fragmentation (basis of PYTHIA)• introduce medium effects at parton splitting Borghini and Wiedemann, hep-ph/0506218
Jet quenching fragmentation strongly modified at pT
hadron~1-5 GeV
=ln(EJet/phadron)
pThadron~2 GeV
Jet quenching
Jet quenching: what's next? 20ETD-HICJuly 16-19, 2007
Measuremement of modified fragmentation
Ratio of purple/red
Kinematic reach beyond ~200 GeV
175 GeV jets in ALICE acceptance
Jet quenching
Dashed line = no jet quenching
Jet quenching: what's next? 21ETD-HICJuly 16-19, 2007
So what?
What is learned by probing it with ~200 GeV jets?
is a transport property of a medium at T=200 MeV q̂
22
2~ˆ TT
trT q
dq
ddqq
Jet quenching: what's next? 22ETD-HICJuly 16-19, 2007
Evolution of qhat
2 2 22
2 2ˆ( , ) ( ) ( , )
1 (2 ) 2R T T
Tc
g C d q qq E dx x x q
N Ep
High energy jet small x
Large momentum transfer large scale
22
4 ( )1
s AT T
c
Cx G x
N
2 22
2
( , ) 1( , )
ln(1/ ) ln 2
xG xxG x
x
(DLA)
k=E
p
q
Casalderrey-Solana and Wang, arXiv 0705.1352
Jet quenching: what's next? 23ETD-HICJuly 16-19, 2007
Evolution of qhat cont’d
Casalderrey-Solana and WangarXiv:0705.1352
Consider jet quenching similar to DIS jet energy variation probes QGP structure at small and varying x…
Jet quenching: what's next? 24ETD-HICJuly 16-19, 2007
Frag Fn modification via elastic scattering
H. Pirner et al (LHC Final Predictions workshop): • Frag Fn modified by scattering in a screened gluon gas (ng~T3)• “evolution” is kinematic in origin
ln(1/x)
dN/d
ln(1
/x)
Virtuality Q2Je
t mul
tipl
icit
y
Jet quenching: what's next? 25ETD-HICJuly 16-19, 2007
Direct measurement of qhat: dijet acoplanarity
X.-N. Wang
2 ˆ( , )T q Edy yq jet,
jetT Eq ~
Jet quenching: what's next? 26ETD-HICJuly 16-19, 2007
q,g
+ jet : photon ET = parton ET at LO
Detailed measurement of modified fragmentation
needs RHIC II luminosity
Phys.Rev.C74:034906,2006.Phys.Rev.Lett.77:231-234,1996.
Run-4 AuAu 0.2 nb-1RHIC I AuAu 2 nb-1RHIC II AuAu 20 nb-1
Direct Photons at RHIC II
Jet quenching: what's next? 27ETD-HICJuly 16-19, 2007
p+p
Pb+Pb/
hep-ph/0311131
Direct Photons in LHC Heavy Ions
104/year
This is a difficult and limited measurementcannot be the flagship of the LHC heavy ion program
Jet quenching: what's next? 28ETD-HICJuly 16-19, 2007
Final remarks
Jet quenching is well-established• multiple high-pT signatures with large experimental effects enables detailed quantitative study• theory: qualitative successes but quantitative gaps
New provocations and speculations: AdS/CFT, Mach cones/whatever,...
Qualitatively new opportunities at RHIC II and LHC
But the Gee-Whiz Era of RHIC Physics is overnow vital to turn our qualitative successes into solid quantitative measurements of hot QCD matter with credible error bars
ongoing, intensive collaboration of experiment and theory