Date post: | 15-Dec-2015 |
Category: |
Documents |
Upload: | melissa-wilkens |
View: | 218 times |
Download: | 3 times |
Open Questions:Jets and Heavy Quarks
(not a summary)
Barbara Jacak
Stony Brook University
June 15, 2006
Open questions as of June 9
What are the implications of incomplete color screening?collisional vs. radiative energy losstransport properties of quark gluon plasma at RHIC
Where are the B mesons in single electron RAA & flow?
Need to take another look at parton densities extracted from jet quenching – impact of collisional energy loss?
Where DOES the energy lost by jets go?density waves (Mach cones)? caught up in longitudinal
flow? thermalized?
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
Debye screening in QCD: a tricky concept
in leading order QCD (O. Philipsen, hep-ph/0010327)
vv
don’t give up! ask lattice QCD
run
nin
g co
up
ling
coupling drops off for r > 0.3 fm
Karsch, et al.
Implications of D ~ 0.3 fm
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!
Implications for properties & observables
For incomplete screening/strongly coupled QGPrange of interaction remains significantinteraction > pQCD
collisions should be important!
Transport in QGP at RHIC should be very interesting!transport of particles → diffusiontransport of energy by particles → thermal conductivitytransport of momentum by particles → viscositytransport of charge by particles → electrical
conductivity
everyone gets flat RAA via radiative energy loss only
(Quark Matter 05)
Dainese, talk at PANIC05AMY
A, Majumder
open question #1:
can another observable distinguish eloss details?can another observable distinguish eloss details?
RAA vs. reaction plane & dihadron yields
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…
others say maybe collisions not needed
BUT v2 is small…
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
open question #2
how important are collisions?how important are collisions?
strong coupling = incomplete color screening→ interactions longer range than expected from pQCD→ transport processes complicated & important
plasma physicists study with molecular dynamics, Fokker-Planck equation, …
effect of collisions is being studied by all groups (it’s a hard problem)
We are starting to extract transport propertieslow diffusivity & viscosity
and recallresult fromWicks, et alfor light quarks!
open question #3
shouldn’t we revisit the plasma density shouldn’t we revisit the plasma density conclusions from radiative energy loss?conclusions from radiative energy loss?
even if collisions prove unimportant, we need to agree on the meaning/value of qhat and “L”
but perhaps perturbative radiation processes aren’t the full/correct way to study the problem??
use AdS/CFT correspondence ↔ coupling
open question #4
WHERE are the $&#*)^% B mesons ??!!!??WHERE are the $&#*)^% B mesons ??!!!??
Hendrik, Greco, Rappnucl-th/0508055
w.o. B meson (c flow)w. B meson (c,b flow)
need better measurements!
inner trackers for PHENIX and STAR
STAR
PHENIX
+ RHIC II luminosity!
BTW: What IS the charm cross section?
need work by experiment and theory both!
experimentsort out difference between STAR & PHENIX
(factor of ~ 2)beat down the uncertainties
better statistics & better control of systematicsupgrades and luminosity will provide the tools
theorycharm underprediction by pQCD is not newNLO doesn’t fix it all
NNLO? another look at resummation of hard processes?
open question #5
how do we use jets to probe the medium?how do we use jets to probe the medium?
5a: is there evidence that deposited energy produces density waves of some kind?
progress fact 1: “ridge” on the near side fact 2: there is evidence for cone-like emission fact 3: a cone-like emission pattern CAN survive
issue: going from here to physics quantities
5b: what is the fragment chemistry trying to tell us?
the ridge
Au+Au 0-10%preliminary
3<pt,trigger<4 GeV
pt,assoc.>2 GeV
J. Putschke
preliminary“jet” sloperidge slopeinclusive slope
evidence for a density wave in the plasma?
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. Shuryakg radiates energykick particles in the plasmaaccelerate them along the jet
not an experi-mental
artefact,part I
PHENIX preliminary
PHENIX preliminary
J. Jia
not an experimental artefact, part IIAu+Au Central 0-12% Triggered
Δ1
Δ2
d+Au
Δ1
J. Ulery
an experimental artefact
generallya phenomenonin crystals butnot liquids
immediate thermalization in flowing systemU. Heinz
deposited energy doesn’t thermalize so fast
T. Renk
distribution +longitudinal expansion depopulate region & shift Mach peak
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
to get medium properties from jet interactions
Need better data!smaller statistical & systematic uncertaintiesscan in particle type, trigger & associated pT
further explore 3 (& more) particle correlations
on theory side:combine dynamics and hadronization modelsget quantitative
pre- & post-dictions of experimental observablesrelate agreement to medium properties
figure out implications of hadrochemistrycan they reflect correlations in the medium?
the open questions
1)1) can an observable beyond Rcan an observable beyond RAAAA distinguish eloss distinguish eloss
details?details?
2)2) how important are collisions?how important are collisions?
3)3) shouldn’t we revisit the plasma density shouldn’t we revisit the plasma density conclusions from radiative energy loss?conclusions from radiative energy loss?
4)4) where are the B mesons ?where are the B mesons ?
5)5) how do we use jets to probe the medium?how do we use jets to probe the medium?
conclusion
a BIG thank you to the organizers of this
fascinating
stimulating
wonderful
scenic
meeting!
Jet tomography at RHIC II to go beyond <>
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 for:
statistics for clean -jet & multi-hadron correlationssystem scan in a finite time
cross section is small, so rate is low
radiation vs. collisions? consider leptons in matter
electrons stop in matter (bremsstrahlung) radiation
muons have long range radiation is suppressed by the large massdominant energy loss mechanism is via collisions
implication use heavy quarks as second kind of probe collisions should be important for c, b quarks
is light quark energy loss radiation dominated?EM plasmas → noradiation: blackbody, bremsstrahlung, collisional, recombination
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
strong elliptic flow; scales w/ number of quarks
minimum at phase boundary?
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 →
seen in strongly coupled dusty plasma
challenge: can a jet excite a density wave in the plasma?
M.Miller, QM04
(1/N
trig)d
N/d
()
STAR Preliminary
cGeVp
cGevpassocT
trigT
/42.0
/64
PHENIX
d
N/d
()
g radiates energykick particles in the plasmaaccelerate them along the jetnon-equilibrium process
generallya phenomenonin crystals butnot liquids
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
backup slides
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
screening masses from gluon propagator
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 is non-zeronot very gauge-dependent, but DOESgrow w/ lattice size (long range is important)
Nakamura, Saito & Sakai, hep-lat/0311024
data + hydrodynamics → very low viscosity
Kolb, et al
RHIC viscosity has drawn great interest from other fieldsincluding string theorists,
who conjecture a lower bound /S ≥ (h/4)
note: softer than hadronic EOS!!
sort out via 3D hydro +measure v2 vs. v3, v4
scan in system size & energyc, flows to separate late stage dissipation from early viscous effects RHIC II luminosity
Ideal hydrodynamics (/S =0) enough to conclude viscosity=0?Deviations → viscous effects?
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
baryon puzzle…
baryons enhanced for pT < 5 GeV/c
RAA
0-5%
PHENIX preliminary
PHENIX preliminary
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
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
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.
Plasma Coulomb coupling parameter
ratio of mean potential energy to mean kinetic energy
a = interparticle distancee = chargeT = temperature
typically a small number in a normal, fully shielded plasma = 1/(number particles in Debye sphere)
when > 1 have a strongly coupled, or non-Debye plasmamany-body spatial correlations existbehave like liquids, or even crystals when > 150 D < a
estimate using this
use =0.2 fm from electric screening mass
=15 GeV/fm3 from hydro initial conditions constrained by v2
density from dE/dx constrained by RAA
put them together: get 0.5 GeV inside Debye sphere
FEW particles! ~1
→ ~ 1
quark gluon plasma should be a strongly coupled plasmaAs in warm, dense plasma at lower (but still high) Tdusty plasmas, cold atom systems
such EM plasmas are known to behave as liquids!
away side jets are strongly modified by the medium
but it’s not very sensitive to E distribution
T. Renk
v2 becomes smaller at large pT
D. Morrison, SQM’06
Radiative energy loss Collisional energy loss
Collisional energy loss comes from the processes which have the same number of incoming and outgoing particles:
Radiative energy loss comes from the processes which there are more outgoing than incoming particles:
0th order
1st order
0th order
M. Djordjevic
Collisional v.s. medium induced radiative energy loss
Collisional and radiative energy losses are comparable!
M.D., nucl-th/0603066
Complementary approach by A. Adil et al., nucl-th/0606010: consistent results obtained.