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Experiments at RHIC:Exciting Discoveries & Future Plans
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outline
introductionplasmas and strong coupling
collective effectshydrodynamics and viscosity
transmission of probes by the quark-gluon plasma heavy quark probes
diffusion
color screening Color Glass Condensate (discussed by Dima) Plasma Physics of the Quark Gluon Plasma at RHIC II
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required conditions (per lattice)
T/Tc
Karsch, Laermann, Peikert ‘99
/T4
Tc ~ 170 ± 10 MeV (1012 °K)
~ 3 GeV/fm3
~15% from ideal gas of weakly interacting quarks & gluons
We now know this leaves room for a big deviation from weak coupling
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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
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Screening: Debye Length
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 D
D = 0kT
-------
nee2
Debye sphere = sphere with radius D
number electrons inside Debye sphere is typically largeND= N/VD= VD VD= 4/3 D
3
1/2
in strongly coupled plasmas it’s 1
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Debye screening in QCD: a tricky concept
in leading order QCD (O. Philipsen, hep-ph/0010327)
vv
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don’t give up! ask lattice QCD
run
nin
g co
up
ling
coupling drops off for r > 0.3 fm
Karsch, et al.
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Implications of D ~ 0.3 fm
can use to estimate Coupling parameter, = <PE>/<KE> but also = 1/ND
for D = 0.3fm and = 15 GeV/fm3
VD = 4/3 D3 = 0.113 fm3
ED = 1.7 GeVto convert to number of particles, use gT or g2T
for T ~ 2Tc and g2 = 4
get ND = 1.2 – 2.5 ~ 1
NB: for ~ 1plasma is NOT fully screened – it’s strongly coupled!other strongly coupled plasmas behave as liquids, even
crystals for ≥ 150dusty plasmas, cold atoms+ions , warm dense matter
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to study experimentally:look at radiated & “probe” particles
as a function of transverse momentumpT = p sin with respect to beam direction)
90° is where the action is (max T, )midway between the two beams!
pT < 1.5 GeV/c
“thermal” particles radiated from bulk of the mediuminternal plasma probes
pT > 3 GeV/c
jets (hard scattered q or g)heavy quarks, direct photons produced early→“external” probe
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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
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4 complementary experiments
STAR
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collective effects
a basic feature distinguishing plasmas from ordinary matter
simultaneous interaction of each charged particle with a considerable number of others
due to long range of (electromagnetic) forces
magnetic fields generated by moving charges give rise to magnetic interactions
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search for collectivity in QGPuse “internal” probes – emitted particles
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
• large pressure buildup • anisotropy happens fast • fast equilibration!
Kolb, et al
Hydrodynamics reproduces elliptic flow of q-q and 3q states Mass dependence requires softer than hadronic EOS!!
NB: these calculations have viscosity ~ 0“perfect” liquid (D. Teaney, PRC68, 2003)
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Elliptic flow scales with number of quarks
implication: quarks are the relevant degrees of freedom when the pressure is built up.Hadronization: quark coalescence
Greco, Ko, Levai: PRC 68 (2003)034904
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D. Morrison, SQM’06
at high pT v2 reflects opacity of medium
approximately expected level from jet quenching
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hadrons
q
q
hadronsleadingparticle
leading particle
schematic view of jet production
.
Al
D2
time (ns)
shock front
Al pusher
dista
nce (µ
m)
0.0 5.01.0 2.0 3.0 4.0 6.0 7.0 8.0
0
100
200
300
x
L
for QGP: fast g and quarks probes must carry color charge
transmission of probes which interact with plasma
EM plasma: x-ray transmission
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nuclear modification factor
photons escape plasma pions and other hadrons: strong interaction, absorbed
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
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flat RAA via radiative energy loss only
(Quark Matter 05)
Dainese, talk at PANIC05AMY
A, Majumder
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RAA wrt reaction plane – more discriminating
Energy loss depends on the path-length, expansion, collisions(?)
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dihadrons: away side suppressed (low pT)
Pedestal&flow subtracted
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some away side particles “reappear” at higher pT
STAR nucl-ex/0604018
pT trigger > 8 GeV/c
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away side yield: some jets escape, some eatenSTAR nucl-ex/0604018
Note similarity ofaway side jetfragmentation.Only yield changes
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how does plasma respond to deposited energy?
M.Miller, QM04
(1/N
trig)d
N/d
()
STAR Preliminary
cGeVp
cGevpassocT
trigT
/42.0
/64
CAN WE DO THIS????? +/-1.23=1.91,4.37 → cs ~ 0.33 (√0.33 in QGP, 0.2 in hadron gas)
PHENIX
dN
/d()
E. Shuryak: g radiates energykick particles in the plasma, acceleratethem in jet direction: a sound wave
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not an experi-mental
artefact!
PHENIX preliminary
PHENIX preliminary
J. Jia
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generallya phenomenonin crystals butnot liquids
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3 particle correlations support cone-like structure
Au+Au Central 0-12% Triggered
Δ1
Δ2
d+Au
Δ1
J. Ulery, HP06
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to further test interaction: heavy quarks
~ same E loss as u,d quarks energy loss not all radiativeneed collisions!
charm also flows
thermalization with the light quarks?not so easy!
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RAA of e± from heavy flavors was a shock
Inclusion of collisional energy loss leads to better agreement with single electron data, even
for dNg/dy=1000.
Wicks, Horowitz, Djordjevic, & Gyulassy, nucl-th/0512076
NB: effect of collisional energyloss for light quarks…
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diffusion = transport of particles by collisions
PHENIX preliminary
Moore & TeaneyPRC71, 064904, ‘05
D ~ 3/(2T) is small! → strong interaction of c quarks
larger D →less charm e loss fewer collisions, smaller v2
D = 1/3 <v> mfp = <v>/ 3D collision time → relaxation time
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aim to measure the screening length
J/bound state of c and cbar quarks)
Tests screening & confinement: do bound c + c survive the medium?
or does QGP screening kill them?
Look at RAA for J/
different bound states probe different lengths
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At RHIC:
CuCu
200 GeV/c
AuAu
200 GeV/c
dAu
200 GeV/c
J/ muon arm
1.2 < |y| < 2.2
mea
sure
d/e
xpec
ted
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At RHIC:
CuCu
200 GeV/c
AuAu
200 GeV/c
dAu
200 GeV/c
AuAuee
200 GeV/c
CuCuee
200 GeV/c
J/ muon arm
1.2 < |y| < 2.2
J/ eeCentral arm
-0.35 < y < 0.35
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At RHIC:
CuCu
200 GeV/c
AuAu
200 GeV/c
dAu
200 GeV/c
AuAuee
200 GeV/c
CuCu
62 GeV/c
J/ muon arm
1.2 < |y| < 2.2
J/ eeCentral arm
-0.35 < y < 0.35
Factor ~3suppression
in central events
CuCuee
200 GeV/c
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RAA
vs Npart
: PHENIX and NA50
NA50 data normalized at NA50 p+p point.
Suppression similar in the two experiments, although the collision energy is 10 times higher (200GeV in PHENIX & 17GeV in NA50)
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What suppression should we expect?
Models that were successful in describing SPS datafail to describe data at RHIC
- but lattice QCD says bound states until ~2Tc -
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regeneratio
n
dire
ct
Rec
ombi
ned
only
Regeneration Narrowing of pT and y?
pT broadening in between Thews direct & in-medium formation: some regeneration
Recombination → narrower rapidity distribution with increasing Npart
BUT: From p+p to central Au+Au : no significant change in y distribution.
No Recombination
Thews et al.
slide from T. Ullrich, HP06
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Karsch, Kharzeev, Satz, hep-ph/0512239
Probe experimentally: onium spectroscopy
40% of J/ from and ’ decays
they are screened but direct J/ not?
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moments of the distribution function of particles f(x,v)0th moment → particle density (n)higher moments are <velocity> & temperature,
pressure tensor, heat flux tensoropacity/transmission is a probe of choice
Transport properties (e.g. diffusion, viscosity) Screening Collective Effects
hydrodynamic expansion, shock propagation, plasma waves→ density correlations inside plasma
Radiationbremsstrahlung, blackbody, collisional and recombination
Plasma oscillations, instabilities
Plasma Physics of the QGP with RHIC IIplasma diagnostics:
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moments of the distribution function of particles f(x,v)0th moment → particle density (n)higher moments are <velocity> & temperature,
pressure tensor, heat flux tensoropacity/transmission is the first probe
Transport properties (e.g. diffusion, viscosity) Screening Collective Effects
hydrodynamic expansion velocity, shock propagation→ density correlations inside plasma
Radiationbremsstrahlung, blackbody, collisional and recombination
Plasma oscillations, instabilities
Plasma properties & “diagnostics”
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next step in transmission study: jet tomography
jet quenching vs. system size, energy→ parton & energy density for EOS→ vary pT to probe medium coupling,
early development of system golden channel: -jet correlations fixes jet energy
flavor-tagged jets to sort out g vs. q energy loss
need detector upgrades (calorimeter coverage, DAQ) must have RHIC II’s increased luminosity x10 for:
statistics for clean -jet & multi-hadron correlationssystem scan in a finite time
tool of choice to study medium response/conductivity
small , low rate
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measure D & B decays; onium spectroscopy
inner trackers for PHENIX and STAR
STAR
PHENIX
+ RHIC II luminosity!
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need high luminosity to scan energy & system
pin down viscosity (and the collision dynamics)sort out via 3D hydro +measure v2 vs. v3, v4c, flows to separate late stage dissipation
from early viscous effects thermalization
plasma temperature via radiated *c, flows can we identify signals of early plasma instability?
probe 2q correlations via baryon production?direct search for density correlations poses a
challenge to experiment & theory both!
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conclusion - discoveries
The matter created shows collective flowsdeveloped early, with quarks/gluons the likely d.o.f.magnitude implies very low viscosityQGP behaves as a liquid
similar to other strongly coupled plasmas! Very opaque to color charged probes
even charm quarks lose energy and flow!another result of strong coupling
J/ suppressed, but only partiallyperhaps screening + recombination from thermal bath?or sequential melting of and `
Evidence of CGC initial state The matter behaves as expected for a plasma!
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conclusion – future plans
figure out the plasma physics of this new kind of matter:temperaturetransport propertiescollective excitations
expansion dynamicsdensity wavesinstabilities?
screening length
needdetector upgrades (planning, construction underway)high luminosity of RHIC II (x10 via electron cooling)
low probes, scan properties with system & energy
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Energy density of matter
high energy density: > 1011 J/m3
P > 1 MbarI > 3 X 1015W/cm2 Fields > 500 Tesla
QGP energy density > 1 GeV/fm3
i.e. > 1030 J/cm3
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backup slides
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conclusions
the matter formed at RHIC is a “perfect” fluidshows collective flows with small viscosityhuge interaction cross sections, very opaque multiple collisions affect even heavy charm quarks
color is partially, but not completely, screened this is like other strongly coupled plasmas
as it should be → it is a plasma!neutrality scale > interparticle distance
How does this super high energy density plasma work?□ map properties of the new stuff at RHIC
how does the plasma transport the “lost” energy? radiation rate? initial temperature achieved? (theory says ~380 MeV)
□ collide Pb+Pb at the LHC for higher Tinitial reach ~ 800 MeV: is coupling strong or weak?
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collective effects
a basic feature distinguishing plasmas from ordinary matter
simultaneous interaction of each charged particle with a considerable number of others
due to long range of the forcesEM plasma: charge-charge & charge-neutral interactions
charge-neutral dominates in weakly ionized plasmasneutrals interact via distortion of e cloud by charges
very sensitive to coupling, viscosity…
magnetic fields generated by moving charges give rise to magnetic interactions
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not an experi-mental
artefact,part I
PHENIX preliminary
PHENIX preliminary
J. Jia
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the ridge
Au+Au 0-10%preliminary
3<pt,trigger<4 GeV
pt,assoc.>2 GeV
J. Putschke
preliminary“jet” sloperidge slopeinclusive slope
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STAR preliminary
Jet + Ridge
STAR preliminary
Jethadrochemistry of jet-associated particles
jet & ridge similar but not identical for Npart<50K trigger typical meson??
J. Bielcikova
jet core yields unchangedchemistry constant
jet + (less) ridgev. central: baryon+meson drops toward reco expectation
A. Sickles
meson-meson
baryon-meson
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plasma properties known, so far
Extract from models, constrained by data
Energy loss <dE/dz> (GeV/fm) 7-10 0.5 in cold matter
Energy density (GeV/fm3) 14-20 >5.5 from ET data
above hadronic E density!
dN(gluon)/dy ~1000 From energy loss, hydro huge!
T (MeV) 380-400
Experimentally unknown as yet
Equilibration time0 (fm/c) 0.6 From hydro initial condition; cascade agrees very fast!
NB: plasma folks have same problem & use same technique
Opacity (L/mean free path) 3.5 Based on energy loss theory
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can get better agreement with data
if add formation of “extra” J/ by coalescence of c and anti-c from the plasma
caveat: not necessarily unique or correct explanation!
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baryon puzzle…
baryons enhanced for pT < 5 GeV/c
RAA
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NA50 and NA60 show suppression in Pb+Pb & In+In
suppression follows system size
Normal nuclear absorption from p+A data: = 4.18±0.35 mb
At CERN (√s = 17 GeV):
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Is the energy density high enough?
5.5 GeV/fm3 (200 GeV Au+Au) well above predicted transition!
PRL87, 052301 (2001)
R2
2c
Colliding system expands:
dy
dE
cRT
Bj 22
11
02
Energy tobeam direction
per unitvelocity || to beam
value is lower limit: longitudinal expansion rate, formation time overestimated
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Saturation of gluons in initial state(colored glass condensate)
Wavefunction of low x (very soft) gluons overlap and the self-coupling gluons fuse.
Saturation at higher x at RHIC vs. HERA due to nuclear size
suppressed jet cross section; no back-back pairsr/ggg
Mueller, McLerran, Kharzeev, …
d + Au collisionscent/periph. (~RAA)
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Why no energy loss for charm quarks?
“dead cone” predicted by Kharzeev and Dokshitzer, Phys. Lett. B519, 199 (1991)
Gluon bremsstrahlung:kT
2 = 2 tform/transverse momentum of radiated gluon
pT in single scatt. mean free path
~ kT / gluon energy But radiation is suppressed below angles 0= Mq/Eq
soft gluon distribution is
dP = sCF/ d/ kT2 dkT
2/(kT2+ 2 0
2) 2not small forheavy quarks!causes a dead cone
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FONLL Predictions
Mateo Cacciari provided a prediction using the Fixed Order Next Leading Logarithm pQCD approach
His calculation agrees perfectly with our “poor man’s” HVQLIB+PYTHIA predictions
Data exceed the central theory curve by a factor of 2-3
Possible explanations:NNLO contribution Fragmentation mechanisms
need to be studied in more details
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use this technique to measure viscosity
melt crystal with laser lightinduce a shear flow (laminar)image the dust to get velocitystudy: spatial profiles vx(y) moments, fluctuations → T(x,y) curvature of velocity profile → drag forces viscous transport of drag in direction from lasercompare to viscous hydro. extract shear viscosity/mass densityPE vs. KE competition governs coupling & phase of matterCsernai,Kapusta,McLerran nucl-th/0604032
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can get better agreement with data
if add formation of “extra” J/ by coalescence of c and anti-c from the plasma
caveat: not necessarily unique or correct explanation!
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screening and thermal masses
Screening mass, mD, defines inverse length scaleInside this distance, an equilibrated plasma is sensitive to
insertion of a static sourceOutside it’s not.
T dependence of electric &magnetic screening massesQuenched lattice studyof gluon propagator
figure shows: mD,m= 3Tc, mD,e= 6Tc at 2Tc D ~ 0.4 & 0.2 fm
magnetic screening mass significantnot very gauge-dependent, but DOESgrow w/ lattice size (long range is important)
Nakamura, Saito & Sakai, hep-lat/0311024
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use to get & compare to molecular dynamics
B. Liu and J. Goree, cond-mat/0502009
minimum arises because kinetic part of decreases with & potential part increases
MD: solve theequations of motionfor massive particlessubject to (screened)interaction potential
follow evolution ofparticle distributionfunction (&correlations)
solve coupled diff.eq’sover nearby space
density-densitycorrelations →
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RHIC’s “perfect fluid”
one that exhibits ideal, non-dissipative hydrodynamics“not-quite-ideal” = can support a shear stress, ≠ 0Viscosity is
~ <v>/ ~ √kT/so viscosity increases with T
decreases with
yv
AF xx
Ideal hydrodynamics ( ~ 0) reproduces data at RHICdoes this make sense to QCD? → ≥h S : conjectured quantum mechanical limit
“A Viscosity Bound Conjecture”, P. Kovtun, D.T. Son, A.O. Starinets, hep-th/0405231 entropy density
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mesons show common pT dependence
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Fast equilibration, high opacity (even for charm): how?
multiple collisions using free q,g scattering cross sections doesn’t work! need x50 in the medium
Molnar
Lattice QCD shows qqresonant states at T > Tc, also implying high interaction cross sections
Hatsuda, et al.
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Color glass condensate?
Hadron Punch Through
Better agreement with BRAHMS data“normal” shadowing cannot explain (R. Vogt hep-ph/0405060)
…sign of CGC?
Kharzeev, hep-ph/0405045
Centrality, pT
dependence
~ correct
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Compare with BRAHMS
Overall consistent.
nucl-ex/0411054
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deposited energy doesn’t thermalize so fast
T. Renk
distribution +longitudinal expansion depopulate region & shift Mach peak