Hot QCD Matter: An Experimenter’s Dream and Nightmare B. Jacak Stony Brook October 25, 2009.
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Transcript of Hot QCD Matter: An Experimenter’s Dream and Nightmare B. Jacak Stony Brook October 25, 2009.
![Page 1: Hot QCD Matter: An Experimenter’s Dream and Nightmare B. Jacak Stony Brook October 25, 2009.](https://reader035.fdocuments.net/reader035/viewer/2022070415/5697bfc11a28abf838ca441f/html5/thumbnails/1.jpg)
Hot QCD Matter: An Experimenter’s Dream and Nightmare
B. Jacak
Stony Brook
October 25, 2009
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Hot QCD Matter
Exciting and surprising results from RHICWhat IS the coupling in the plasma?What are the degrees of freedom - point particles? pure
fields? composite quasiparticles?
What are the physical properties of the plasma?Thermal: T,, EOS opacity, fluidityDynamic: viscosity, diffusion, energy transport color screening, correlations inside
Measure the above in a system lasting <10 fm/c!Nature does the time integral, whether we like it or not
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Today (results from PHENIX)
Exciting and surprising results from RHICWhat IS the coupling in the plasma?What are the degrees of freedom - point particles? pure
fields? composite quasiparticles?
What are the physical properties of the plasma?Thermal: TT,, EOS opacityopacity, fluidityDynamic: viscosity, diffusion, energy transportenergy transport color screening, correlations inside
Measure the above in a system lasting <10 fm/c!Nature does the time integral, whether we like it or not
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• Exponential fit in pT:Tavg = 221 ±23 ±18 MeV• Multiple hydro models reproduce data •Tinit ≥ 300 MeV
arXiv:0804.4168v1 [nucl-ex]
Initial State Temperature: direct photons
Low mass, high pT e+e-
nearly real photons
Large enhancement above p+p in the thermal region
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Lepton pair emission EM correlator
Emission rate of dilepton per volume
Boltzmann factortemperature
EM correlatorMedium property
ee decay
From emission rate of dilepton, the medium effect on the EM correlator as well as temperature of the medium can be decoded.
e.g. Rapp, Wambach Adv.Nucl.Phys 25 (2000)
Hadronic contributionVector Meson Dominance
qq annihilation
Medium modification of mesonChiral restoration
q
q
Thermal radiation frompartonic phase (QGP)
Yasuyuki Akiba - PHENIX QM09
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Dilepton emission
Vacuum EM correlatorHadronic Many Body theoryDropping Mass Scenarioq+q annihilation (HTL improved)(q+gq+qee not shown)
Calculation: R. Rapp
dMdydpp
dN
tt
eey=0, pt=1.025 GeV/c
Normally: dilepton emission as spectrum dN/dpTdM.
Mass spectrum at low pT is distorted by virtual photonee decay factor 1/M: steep rise as M0
qq annihilation contribution negligible at low mass due to m**2 factor of the EM correlator
NB: calculation omits partonic photon emission processq+gq+q+e+e-
Dilepton
virtual photon
Prob. *l+l-
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Relation of dileptons and virtual photons
Emission rate of dilepton per volume
Emission rate of (virtual) photon per volume
Relation between them
Virtual photon emission rate can be determined from dilepton emission rate
For M0, n* n(real) so real photon emission rate can also be determined
M x dNee/dM givesVirtual photon yield
Dilepton virtual photon
Prob. *l+l-
This relation holds for the yield after space-time integral
Yasuyuki Akiba - PHENIX QM09
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Virtual photon emission rate
dydpp
dN
dMdydpp
dNM
tttt
ee*∝× at y=0, pt=1.025 GeV/c
dydpp
dN
tt
Vaccuum EM correlatorHadronic Many Body theoryDropping Mass Scenarioq+q annihilaiton (HTL improved)(q+gq+qee not shown)
Same calculation shown as virtual photon emission rate.
Note: steep rise at M=0 is gone, and the virtual photon emission rate is more directly related to the underlying EM correlator.
For M0, n* n(real)
q+gq+* is not shown; is similar to HMBT at this pT
Dilepton
virtual photon
Prob. *l+l-
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Excess of virtual photon
Excess over cocktail ~ constant with mass at high pT.
Convert to virtual photon yield by 1/M factor from the virtual photon decay. distribution is ~flat over 0.5 GeV/c2
Extrapolation to M=0 should give the real photon emission rate.
No indication of strong modification of EM correlator at high pT !
presumably the virtual photon emission is dominated by processes e.g. ++* or q+gq+*
Exc
ess
*M (
A.U
).
Yasuyuki Akiba - PHENIX QM09
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How about low pT ?
0 < pT < 8 GeV/c 0 < pT < 0.7 GeV/c
0.7 < pT < 1.5 GeV/c 1.5 < pT < 8 GeV/c
Low pT shape incompatible with constant virtual photon emission rate…
Enhancement of EM correlator at low mass, low pT? NEED HELP FROM THEORY!!
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Exc
ess
*M (
A.U
).
NEW DATA COMING IN 2010
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Interactions within the plasma
Experimentalist’s simple minded picture
Strong coupling = interactions among multiple neighbors
Of course this must cause correlations within plasmaalso increases opacity
how is the energy loss mechanism affected? is the quark gluon plasma “black”?
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Iconic jet quenching (opacity) result
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Insights somewhat unsatisfying
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S. Bass, et al.Phys.Rev.C79:024901,2009
Put 3 different energy loss schemes into common, realistichydrodynamic calculation
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We can do better!
Extend the pT range
Difficult for 0 because decay ’s merge in the
calorimeter Measuring instead of
0 is the solution
RAA remains flat to at least 22 GeV/c!
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Next step: constrain geometry: high-pT v2
arXiv:0903.4886 (Run-4
data)
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pT
NPart
RA
A
• Out-of plane RAA nearly flat with centrality at low pT
• In- and out-of-plane converge at high-pT (~10GeV/c)
Out-of-plane vs. in-plane
in-plane
intermediate
out-of-
plane
Carla Vale - PHENIX QM09
Run-7
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Calculations by S.Bass et al in arXiv:0808.0908
Differentiate among energy loss models!
Carla Vale - PHENIX QM09
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More differential yet: dijet reaction plane dependence
in-plane
out-plane
AwayPTY
0 πφs
π
π
PTY
= p
er-
trig
ger
yie
ld
Penetrating production in-plane
out-plane
π
π
AwayPTY
0 πφs
Tangential production
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Away side yield
Away side yields drop from in-plane to out-of-plane: jets do penetrate medium
Medium is not totally opaque
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Shocks? Medium spectrum
p+p
centralAu+Au
3<pt,trigger<4 GeV
pt,assoc.>2 GeV
Au+Au 0-10%
preliminary
STAR
Harder than inclusive, softer than jet
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Jet-medium interaction
jet
Jet suppressedmedium
medium
Centrality:40-45%
Central:5-10%
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-jet (-h) correlation: calibrated probe
p+p slope:
6.89 0.64
Au+Au slope:
9.49 1.37
fragmentation of tagged jets in/out of medium
Challenge: understand energy transfer to/from the medium! Coupling properties…
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Next step: full jet reconstruction
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Gaussian filter algorithm optimize signal/background by focusing on jet core stabilizes jet axis in presence of background
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In ion collisions life is tougher
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signalbackground
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In Cu+Cu
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Yikes! RAA flat to > 30 GeV/c pT
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Heavy quark energy loss (large!)
PRELIM.Run-4
Run-7
Rapp & van Hees, PRC 71, 034907 (2005)
minimum-bias
Non photonic electrons
0,
Who ordered that?Mix of radiation + collisions (diffusion)
but collisions with what?AdS/CFT provides an answer, but…
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Not all energy loss is created equal!
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High meff large collisional energy loss
R. Kolevatov &
U.A. Wiedemann
arXiV:0812.0270
The “clumps”?b/c separation allows to test!
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Upgrades over next ~3 years
PHENIX Upgrades
Forward Calorimeter at = 1-3Correlate with mid-y h±
Silicon VTX, FVTX Tag displaced vertex for heavy quark decaysTrack charged hadrons in large acceptance
*In addition to RHIC-II luminosity upgrade x8
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Over next decade: entirely new questions
Precision jet probes of energy transport in medium What degrees of freedom?Heavy quark fragmentation modified?Theory + dynamics: qualitative quantitative
What is the screening length in strongly coupled QCD matter?Experiment: onium spectroscopy in pp, dAu, AuAuTheory: understand production & cold matter effects
Supplement silicon tracker to enhance momentum resolutionEnhance electron ID capabilities inner barrel compact calorimeter?
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Conclusion:
It could be that theorists’ dreams make for the experimenters’ nightmares…The really interesting stuff is hard to measure
Experimenters’ dream results are definitely the stuff of the theorists’ nightmaresWe really want to pin you downExtract properties of hot QCD matter by constraining
theory + phenomenology with data!
But for Al - we wish very sweet dreams!We’ll work hard for those sugarplums
HAPPY BIRTHDAYHAPPY BIRTHDAY
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backup slides
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Tag jet energy with direct photon
M. McCumber WWND ‘09
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Local Slopes of Inclusive mT Spectra
Data have soft mT component not expected from hadron decays
Note: Local slope of all sources!need more detailed analysis
Axel Drees34
Soft component below mT ~ 500 MeV:
Teff < 120MeV independent of mass
more than 50% of yield
Tdata ~ 120 MeV
Tdata ~ 240 MeV
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Mike Leitch - PHENIX QM09
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determined three different ways:• single electron spectra methods:
• cocktail subtraction• converter
• di-electrons
Muon measurement at forward rapidity is consistent
cc
bb
d h
eavy/d
y (
mb
)
Open Heavy Flavor
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b quarks and medium effects…
B meson spectra
e-h correlations totag D vs. B decays
b + c !
Oh oh!
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04/02/2009 Quark Matter '09 Y. Yamaguchi
Should modify low pT direct yield→ Evaluate using d+Au data.
Systematic errors on Run3 d+Au results are still large.At 2-3 GeV/c, data looks in agreement with pQCD calculation.
→ No modification of direct yield by nuclear effects?
Run 8 analysis underway: x30 statistics
37/12Nuclear Effects
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Both ridge & shoulder yields grow
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Away/near to ~ cancel acceptance
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Shoulder and ridge have the same physics!See also Rudy Hwa, Jiangyong Jia recent talks
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From the bulk or jet-like?
arXiv:0712.3033
arXiv:0712.3033
Answer:it’s more like the bulk! QGP-like
PHENIX PRL 101, 082301 (2008)
pT spectra
Particle content
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(shear generallya phenomenonin crystals butnot liquids)
Are shocks in strongly coupled EM plasma.So sQGP could also support shockwaves
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In the most central collisions
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Quantifying the viscosity
Need:3-d viscous hydro calculationsPrecision dataMass dependence of v2
+ other observables for pT transport
pT (GeV/c)
v2/s ~ 0 - 0.8Recall: in ideal hydro mfp=0Conjectured /s bound: 1/4
Work is underway to control: initial state geometry gluon distribution
€
~ n p λ mfp
Romatschke & Romatschke, arXiv:0706.1522
PHENIX Preliminary
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p+p Au+Au (MB)Gluon Compton
q
g q
e+
e-
Dileptons at low mass and high pT
•m<2 only Dalitz contributions•p+p: no enhancement •Au+Au: large enhancement at low pT
•A real source virtual with v. low mass•We assume internal conversion of direct photon extract the fraction of direct photon
PHENIX Preliminary PHENIX Preliminary
1 < pT < 2 GeV2 < pT < 3 GeV3 < pT < 4 GeV4 < pT < 5 GeV
r : direct */inclusive *
Direct */Inclusive * determined by fitting each pT bin
( ) ( ) ( ) ( )eedirecteecocktaileedata MfrMfrMf ⋅+⋅−= 1
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direct photons via e+e-
for low mass, pT > 1 GeV/c
direct * fraction of inclusive *
(mostly , ) is real fraction
of (mostly , )
low mass and pT >> mee
dominated by decay of *
mee
hadron cocktail
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Virtual Photon Measurement
Case of Hadrons
Obviously S = 0 at Mee > Mhadron
Case of direct *
– If pT2>>Mee
2
Possible to separate hadron decay components from real signal in the proper mass window.
Any source of real can emit * with very low mass. Relation between the * yield and real photon yield is known.
α
SdNMM
m
M
m
dM
Nd
eeee
e
ee
e
ee
121
41
3
22
2
2
22
⎟⎟⎠
⎞⎜⎜⎝
⎛+−=
S : Process dependent factor
( )3
2
222 1 ⎟⎟
⎠
⎞⎜⎜⎝
⎛−=
hadron
eeee M
MMFS
1=S
Eq. (1)
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Where does the lost energy go?
Radiated particles still correlated with the jet
Completely absorbed by plasmaThermalized?Collective conservation of momentum?
Excites collective response in plasmaShocks or sound waves?Wakes in the plasma?