poking at the quark gluon plasma with jets and heavy quarks
TRANSCRIPT
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Poking at the Quark Gluon Plasma with Jets and Heavy Quarks
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Scattered partons propagate:fast quarks & gluons traverse
the interesting stuffradiate gluonsinteract with QGP partons
Fragment into jets - usually described by
phenomenological fragmentation function
- in/outside the medium
coneRFragmentation:
z hadron
parton
p
p
What’s this stuff? let’s poke it with a stick!
follow in the footsteps of Rutherford and friends experimenting with radioactivity…
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lattice QCD F. Karsch
properties of matter
thermodynamic (equilibrium)T, P, EOS (relate T,P,V, )vsound, static screening length
transport properties*particle number, energy, momentum, charge diffusion sound viscosity conductivity
* measuring these is new for nuclear/particle physics!
^ QCD
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plasma
ionized gas which is macroscopically neutralexhibits collective effects
interactions among charges of multiple particlesspreads charge out into characteristic (Debye) length, D
multiple particles inside this lengththey screen each other
plasma size > D
“normal” plasmas are electromagnetic (e + ions)quark-gluon plasma interacts via strong interaction
color forces rather than EMexchanged particles: g instead of gluons self-interacting, number (not fixed) T
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typical plasma diagnostics
X-ray tomography: to get temporal and spatial evolution of plasma mode activity, use 10 soft X-ray cameras with 20 channels each, at 70 kHz max.
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heavy ion collision diagnostics
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
Kpnd,
Hadrons reflect (thermal) properties when inelastic collisions stop (chemical freeze-out).
not possible to measure as a function of time nature integrates over the entire collision history
thermal radiation
(, e+e-,
+
color-screened QGP
pressure builds up
Hard scattered q,g(short wavelength) probes of plasmaformed
time
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study plasma by radiated & “probe” particles
as a function of transverse momentumpT = p sin with respect to beam direction)
90° is where the action is (max T, )pL midway between the two beams:
midrapidity pT < 1.5 GeV/c
“thermal” particles radiated from bulk of the medium
pT > 3 GeV/c
jets (hard scattered q or g)heavy quarks, direct photonsdescribe by perturbative QCDproduced early→“external” probe
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
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RHIC at Brookhaven National Laboratory
Collide Au + Au ions for maximum volumes = 200 GeV/nucleon pair, p+p and d+A to compare
STAR
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Experimenter’s Tools
STARspecialty: large acceptancemeasurement of hadrons
PHENIXspecialty: rare probes, leptons,
and photons
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a bit of geometry, terminology
baseline for heavy ion collisions: p+p collisions peripheral collisions (large impact parameter) are like
a handful of p+p collisions central (small impact parameter) collisions produce
largest plasma volume, temperature, lifetime report centrality as fraction of total A+A cross section
» 0-5% = very central
peripheral:few participant nucleons (small Npart)few NN collisions (Ncoll)
central:large Npart & Ncoll
Ncoll near 1000 in ~ head-on Au+Au
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The matter is opaque! jets are quenched
p-p PRL 91 (2003) 241803
Good agreementwith pQCD
head-on Au+AuN
coll = 975 94
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colored objects lose energy, photons don’t
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
how opaque is hot QCD matter?
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interaction of radiated gluons with gluons in
the plasma greatlyenhances the amount
of radiation
energy loss by induced gluon radiation
opacity expansion analysis shows <medium length traversed>/mean free path ~ 3.5 → ~ 1400 gluons/unit rapidity
I. Vitev
d+Au
Au+Au
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energy transport
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constrain with data
extract transport parameter q from data, get ~ 13 GeV2/fm
but pQCD favors ~1 (Baier, et al)
^
PQM model: C. LoizidesEur.Phys.J. C49 (2007) 339
data & fit: arXiv:0801.1665
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momentum exchange: complicated process
The medium is dense and opaque!Quantifying energy deposit ..ongoingDifferent models include radiation, w/ or w/o collisions some/no transfer medium→probe different level of detail describing collision geometry different handling of fluctuations different description of the expansion dynamics
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medium transport of deposited energy?
study using hadron pairs high pT trigger to tag hard
scattering second particle to probe the
medium
Central Au + Au
opposing jet
collective flowin underlying event
same jet
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at high momentum, jets punch through
STAR
centralcollisions
on away side:same distribution ofparticles as in p+pbut ~5 times fewer!expected for opaque medium
X
Phys.Rev.Lett. 97 (2006) 162301
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2/8/2008Quark Matter 2008
Direct Photon-Hadron Correlations in p+p
2/8/2008Quark Matter 200819
[rad]
1/N
trig
dN
/d
(A
.U.)
M.A. Nguyen
toward jet tomography: Compton scattering
q+g → q+ tags q energy12-15 GeV “monoenergetic jet”
0 - h dir - h right mechanism same jet partners are absentaway jet shows similar modificationnext step: quantify energy/momentum flow
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Where we need to go
tags q energy >12 GeV
“monoenergetic” jets
all we need is:more eventsbigger detector coverage
all those near-by curvesvery different
with no mediumALL use weak coupling!
RHIC II AuAu 20 nb-1
-jet
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lower pT partners look funny! medium responds to the “lost” energy
3<pt,trigger<4 GeV
pt,assoc.>2 GeV
Au+Au 0-10%
preliminary
STAR
1 < pT,a < 2.5 < pT,t <4 GeV/c
peripheralcentral
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jets shock the medium
p+p
centralAu+Au
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lost energy excites a sound (density) wave?
if shoulder is sound wave… LOCATION at +/-1.23=1.91,4.37 → speed of sound cosm=cs~0.35-0.4 (cs
2=0.33 in QGP,~0.19 in hadron gas)
relative excitation of sound and diffusion wake in intense studydata →sound mode large
Gubser,Pufu,Yarom PRL100, 012301’08
Chesler & Yaffe, 0706.0368(hep-th)
strong coupling: ask AdS/CFT answer: yes it does!
machcone
wake
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Diffusion of heavy quarks traversing QGP
How do they interact? Prediction: lower energy loss than light quarks
large quark mass reduces phase space for radiated gluons
Measure via semi-leptonic decaysof mesons containing charm or bottom quarks
D Au
AuD
X e±
K
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c,b decays via single electron spectrum
compare data to “cocktail” of hadronic decays
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sufficient interaction to equilibrate??
Measure correlation of e± with the light hadrons Ask whether they flow along.
NB: rate of equilibration gives
information on the viscosity
of the liquid!PRELIMINARY
Run-4
Run-7
Rapp & van Hees, PRC 71, 034907 (2005)
minimum-bias
Heavy quarks do flow!!Use to probe transportproperties of QGP!
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heavy quarks lose energy too
cannot be dominantly by bremsstrahlung (gluon radiation)
plasmas have collisions among constituents! including it helps
larger than expected scattering → stronger coupling
e± from heavy quark decayWicks et al., NPA 784(2007)426
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heavy quark transport: diffusion & viscosity
diffusion = brownian motion of particles
definition: flux density of particles J = -D grad n integrating over forward hemisphere:
D = diffusivity = 1/3 <v>
so D = <v>/ 3nD collision time, determines relaxation time
Langevin: equation of motion for diffusion thru a medium
drag force random force <pT2>/unit time D*
particle concentration
= mean free path
note: viscosity is ability to transport momentum = 1/3 <v> so D = S → measure D get !
* G. Moore and D. Teaney, hep-ph/0412346
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confronting mechanisms with dataPRL98, 172301 (2007)
Radiative energy loss alone: fails to reproduce v2
Heavy quark transport model (i.e. diffusion) shows better agreement with RAA and v2
Though agreement with data is so-so, slow relaxation ruled out by v2
D ~ 4-6/(2T) for charm /S = (1.3 – 2.0)/ 4
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4/)8.30.1(/ s
S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006
pTfluctuations STAR
Comparison with other estimates
4/)2.12.01.1(/ sR. Lacey et al.: PRL 98:092301, 2007
v2 PHENIX & STAR
4/)4.24.1(/ s
H.-J. Drescher et al.: arXiv:0704.3553
v2 PHOBOS
conjectured quantum limit
estimates of /s based on flow and fluctuation dataindicate small value as wellclose to conjectured limitsignificantly below /s of
helium (s ~ 9)
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What about b quarks?
PRL 98, 172301 (2007)
e± from heavy flavor
b quark contribution tosingle electrons becomessignificant. do they alsolose energy?
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Hard probes tell us:
Energy loss in the plasma is large.
and/or s ~ 0.27. What quantity DO we measure? Eloss mechanism?
Deposited energy shocks the medium. Mach cones?cs ~ (0.35 – 0.4) c (closer to hadron gas than QGP)expected diffusion wake AWOL (baryon enhancement?)
Medium is also opaque to charm quarks
Heavy quark diffusion, hadron flow & fluctuations →viscosity: S = (1 – 3)/ 4 close to conjectured bound
First hint of b decay contributions bottom quarks maybe not gobbled up by medium?
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for further (experimental) progress
STAR HFT
PHENIX VTX
Si vertex detectors separate c from b
-3 -2 -1 0 1 2 3 rapidity
NCCNCCM
PC
MP
C
VTX & FVTX
HBD
EM
CA
LE
MC
AL
RHIC II AuAu 20 nb-1
-jetacceptance and ∫L mechanism of eloss
and do it again at higher T at the LHC!
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backup slides
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long standing baryon puzzle…
baryons enhanced for 1.5 < pT < 5 GeV/c
coalescence of thermal quarks from an expanding quark gluon plasma.
STAR
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baryons come from jets – enhanced by wake?
●the “extra” baryons have jet-like partners●only in central collisions do we see a dilution from thermal baryons
meson-meson
baryon-meson
Near side
●collectively flowing medium boosts quarks to higher pT
●wake of fast quark builds particle density to coalesce●baryon enhancement reflects dynamics…?!
speculate:
Gubser, Pufu, Yarom 0706.4307(hep-th)
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sound wave (shoulder) vs. jet remnant
shoulder (medium response)
jet remnant
away-side total
pp collisions
peripheral central
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sum associated pT observed in charged particles
punch-through decreases vs. p+pshoulder grows with centralitynear & far totals both increase
(line: expected in PHENIX acceptance according to PYTHIA generator)
ratio near/far:nearly constant with centrality! at p+p value!near side increase tracks away sideloss of pT in punch-through balanced by shoulder growth
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Ratio of Away pTasso / near pT
asso
Ratio constant with centrality Consistent with p+p value, also with PYTHIA Even though the total vector sum of nearside/awayside both increase, the ratio
of the two still hold constant , i. e. the total contribution from “head” and “shoulder” part is hold, but the portion between the two is changing.
head
shoulder
Head+shoulder
PYTHIA
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LPM effect up to O(gs) + (3+1)d hydro + collisions
Qin, Ruppert, Gale, Jeon, Moore and Mustafa, 0710.0605
Fix initial state by constraining hydro with particle spectra Reproduce observed energy loss vs. centrality using s = 0.27
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Three particle correlations
Two Analysis Approaches:• Cumulant Method
Unambiguous evidence for true three particle correlations.
• Two-component Jet+Flow-Modulated Background Model
Within a model dependent analysis, evidence for conical emission in central Au+Au collisions
pTtrig=3-4 GeV/c
pTassoc=1-2 GeV/c
off-
diag
onal
pro
ject
ion
d+Au
0-12% Au+Au
=(12)/2
Δ2
Δ1 Δ1
0-12% Au+Au: jet v2=0
Δ2
From J. Dunlop, Montreal Workshop ‘07C. Pruneau, QM2006J. Ulery, HP2006 and poster, QM2006
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more complex jet fragment measurements
3 – particle correlationsconsistent with Mach-cone shoulder
sum of jet fragment momentum▪ increases together on trigger and away sides▪ momentum loss in punch-thru jet balanced by momentum in the shoulder peak▪ evidence for wakes?
d+Au 0-12% Au+AuΔ2
Δ1
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suppression at RHIC very similar to that at SPS!why??more suppressed at y 0
PHENIX PRL98 (2007) 232301
J/
screening length: onium spectroscopy
40% of J/ from and ’ decays they are screened but direct J/ not?
Karsch, Kharzeev, Satz, hep-ph/0512239
y=0
y~1.7
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what does non-perturbative QCD say?
Lattice QCD shows heavyqq correlations at T > Tc, also implying that interactions are not zero
Big debate ongoing whether these are resonant states, or “merely” some interactions
Color screening – yes!but not fully…Some J/ may emerge intact
Hatsuda, et al.
J/ is a mystery at the moment!
Others may form in final state if c and cbar find each other
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are J/’s regenerated late in the collision?
c + c coalesce at freezeout → J/
R. Rapp et al.PRL 92, 212301 (2004) R. Thews et al, Eur. Phys. J C43, 97 (2005)
Yan, Zhuang, Xu, PRL97, 232301 (2006) Bratkovskaya et al., PRC 69, 054903 (2004)
A. Andronic et al., NPA789, 334 (2007)
R. Rapp et al.PRL 92, 212301 (2004) R. Thews et al, Eur. Phys. J C43, 97 (2005)
Yan, Zhuang, Xu, PRL97, 232301 (2006) Bratkovskaya et al., PRC 69, 054903 (2004)
A. Andronic et al., NPA789, 334 (2007)
should narrow rapidity dist. … does it?
central
peripheral
J/ is a mystery at the moment!
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plasma basics – Debye screening
distance over which the influence of an individual charged particle is felt by the other particles in the plasma
charged particles arrange themselves so as to effectively shield any electrostatic fields within a distance of order D
D = 0kT
-------
nee2
Debye sphere = sphere with radius D
number electrons inside Debye sphere is largeND= N/VD= VD VD= 4/3 D
3
1/2 ne = number densitye = charge
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plasma frequency and oscillations
instantaneous disturbance of a plasma → collective motionsplasma wants to restore the original charge neutralityelectrons oscillate collectively around the (heavy) ionscharacterized by natural oscillation frequency
plasma frequencyit’s typically high
restoring force: ion-electron coulomb attraction
damping happens via collisionsif e-ion collision frequency < electron plasma frequency pe/2 then oscillations are only slightly dampeda plasma condition: electron collision time large vs. oscillation
nee2
p = ------me0
1/2
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For all distributions described by temperature T and (baryon) chemical potential :
dn ~ e -(E-)/T d3p
Does experiment indicate thermalization?
Tf ~ 175 MeV
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minimum at phase boundary?
Csernai, Kapusta & McLerran PRL97, 152303 (2006)
quark gluon plasma
B. Liu and J. Goree, cond-mat/0502009
minimum observed in other strongly coupled systems –kinetic part of decreases with while potential part increases
strongly coupled dusty plasma
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Elliptic flow scales with number of quarks
transverse KE
implication: valence quarks, not hadrons, are relevant pressure field builds early → dressed quarks born of flowing field (as strongly interacting liquids
lack well-defined, long-lived quasi-particles)
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The acid test for quark scaling
meson (bound state of s+sbar) mass ~ mproton but flows like the mesons
PHENIX
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dielectron spectrum vs. hadronic cocktail
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R.Rapp, Phys.Lett. B 473 (2000)R.Rapp, Phys.Rev.C 63 (2001)R.Rapp, nucl/th/0204003
low mass enhancement at 150 < mee < 750 MeV3.4±0.2(stat.) ±1.3(syst.)±0.7(model)
Comparison with conventional theory
calculations: min bias Au+Authey include:QGP thermal radiation chiral symmetry restoration
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Direct photon v2
1
* _2
.2.
2
R
vvRv
photonBGphotonincphotondir
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transport in QGP (theoretical approach)
weak coupling limit strong coupling limit
perturbative QCD not so easy!
kinetic theory, cascades gravity supersym 4-d
QCD-like theory resummation of hard thermal loops
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Collectivity: measuring elliptic flow (v2)
dN/d ~ 1 + 2 v2(pT) cos (2) + …
“elliptic flow”
Almond shape overlap region in coordinate space
x
yz
momentum space
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v2 is large & reproduced by hydrodynamics
must begin hydro in < 1 fm/cviscosity must be ~ 0 - 0.1 i.e. “perfect” liquid viscosity decreases longitud. pdV work → higher transverse velocity
First indication of small /S
data constrains hydro: as in plasma physics
D. Teaney, PRC68, 034913 (2003)
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Michael P. McCumber for PHENIX Quark Matter – 5 February 2008
Away-side CompositionarXiv:0712.3033
arXiv:0712.3033
Shapes: - Similar shape in away-side mesons and baryons
Ratios: - Away-side baryon/meson ratios approach inclusive values
- Incompatible with in-vacuum fragmentation
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Michael P. McCumber for PHENIX Quark Matter – 5 February 2008
Connections - Centrality
PHENIX poster (Chin-Hao Chen)
- Away-side shoulder and near-side ridge share a common centrality dependence
- Scale similarity here is largely a factor of pT
selection
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Michael P. McCumber for PHENIX Quark Matter – 5 February 2008
Connections - Balance
0.0 < |Δη| < 0.1 0.5 < |Δη| < 0.7
- Jet & Ridge balances Shoulder & Head
- Ridge & Shoulder balance seperately!