Transcript Slide 1

Leptonic signatures in
Heavy Ion Collisions
E.Kistenev
Brookhaven National Laboratory
7/17/2015Monday,
February 15, 2010
38th Moscow International Winter
School of Physics, ITEP(Otradnoe)
1
BNL-RHIC
Facility
Also: BNL-AGS, CERN-SPS, CERN-LHC
2
From pp to HI Collisions
PHENIX Au+Au central
STAR Au+Au central
STAR-Jet event in pp
High pT particle
High pT particle
Au+Au
p+p
Bj 
1
1 dET 


R 2 c 0  dy 
PRC 71 (2005) 034908
c0 Bj =5.40.6 GeV fm-2
4%

0.5%
3
Why all of it is of interest to taxpayer




LHC was
built to shed the light on Early Universe;
Our current assumption : The Early Universe was
flooded with matter in a state known under code
name of Quark-Gluon Plasma (E.Shurjak);
Creationism : Our world is the only allowed product
of Quark-Gluon Plasma thermalization;
What we do not know : if it will ever be experimentally
verified.
D.Froidevaux in his first lecture at this school :
4
Astrophysics – experiment on the scale of the
Universe – let’s look around and/or ask our neighbors
they’ve probably been here before us …
HI - attempt to recreate early Universe conditions on
the scale of physics laboratory (no proof that we are
actually doing this)
There is some hope and some sadness in both approaches ….
- a galaxy like ours should host hundreds of intelligent civilizations; the bad news
is that the time between when such a civilization becomes technologically
advanced enough and when it is wiped out by homesun going red giant is too short
on galactic scale – at all times there are, in most simulations, no other such
civilizations (or if there are, they are too far away) … we are likely to be alone –
noone will probably ever answer;
- numerical modeling of this type is generally a shadow of the entity it attempts to
model, in this case the Big Bang and its constituents like Milky Way, stars, planets
and other objects…..
- 30 years of attempts on recreating after BigBang conditions in the lab ended with
5
Pandora box slightly opened but yet no proofs that reaches our original goal.
The original Hubble Diagram
“A Relation Between Distance and Radial
Velocity Among Extra-Galactic Nebulae”
E.Hubble (1929)
It took 80 years to learn
that we are 1010 years old
Freedman, et al.
Astrophys. J. 553,
47 (2001)
Edwin
Hubble
Galaxies
outside Milky
Way
W. Freedman
Canadian
Modern Hubble
constant (2001)
Original
Hubble
diagram
Henrietta
Leavitt
1929: H0 ~500 km/sec/Mpc
Distances via
variable stars
2001: H0 = 727 km/sec/Mpc6
Observational astrophysics
a(t)
Matter-dominated,
structure forms
Acceleration, return cosmological
constant and/or vacuum energy.
Radiation-dominated thermal equilibrium
Inflation, dominated by “inflaton field” vacuum energy
t
a(t)t1/2
7
g*S
1 Billion oK
1 Trillion oK
All entropy is in relativistic species
Density of hadron mass states
dN/dM increases exponentially
with mass.
“…a veil, obscuring our
view of the very
beginning.” Steven
Weinberg, The First Three
Minutes (1977)
Keep adding more hadrons….
8
Replace Hadrons
(messy and
numerous)
by Quarks and
Gluons (simple
and few)
“In 1972 the early universe seemed
hopelessly opaque…conditions of
ultrahigh temperatures…produce a
theoretically intractable mess. But
asymptotic freedom renders
ultrahigh temperatures friendly…”
Frank Wilczek, Nobel Lecture
(RMP 05)
D. Gross
H.D. Politzer
F. Wilczek
QCD Asymptotic
Freedom (1973)
/T4
 g*S
Thermal QCD
”QGP” (Lattice)
Hadron gas
QCD to the rescue!
Karsch, Redlich, Tawfik,
Eur.Phys.J.C29:549-556,2003
9
e+e- Annihilation
Nucleosynthesis
Mesons
freeze out
QCD Transition
Heavy quarks and
bosons freeze out
Thermal QCD -i.e. quarks and
gluons -- makes
the very early
universe
tractable; but
where is the
experimental
proof?
g*S
n Decoupling
“Before [QCD] we could not go back further than 200,000 years after the
Big Bang. Today…since QCD simplifies at high energy, we can extrapolate
to very early times when nucleons melted…to form a quark-gluon plasma.”
David Gross, Nobel Lecture (RMP 05)
Kolb & Turner, “The Early Universe”
10
Electromagentic probes (photon and
lepton pairs) – measure
of temperature
+
e
g*
e-


Photons and lepton pairs are
cleanest probes of the dense
matter formed at RHIC
These probes have little
interaction with the matter so
they carry information from
deep inside of the matter
 Temperature?
 Matter
properties?
 Hadrons inside the
matter?
g
11
Thermal photon from hot matter
Hot matter emits thermal radiation
Temperature can be measured from the
emission spectrum
12
Photons: More Sources, More
Theory
Rate
Hadron Gas Thermal Tf
QGP Thermal Ti
“Pre-Equilibrium”?
Turbide, Rapp, Gale
Jet Re-interaction √(Tix√s)
pQCD Prompt x√s
Eg
Final-state photons are
the sum of emissions
from the entire history
of a nuclear collision.
13
“Direct” vs “hadronic”
Fragmentation
Prompt
Induced


r
g
Thermal
Radiation
QGP / Hadron
Gas
High-energy
counts these
0
EM & Weak
Decay
High-energy nuclear
counts these
14
Thermal photons (theory prediction)


g
q
r
g
q
g





S.Turbide et al PRC 69 014903
High pT (pT>3 GeV/c) pQCD
photon
Low pT (pT<1 GeV/c)
photons from hadronic Gas
Themal photons from QGP is
the dominant source of
direct photons for 1<pT<3
GeV/c
Recently, other sources,
such as jet-medium
interaction are discussed
Measurement is difficult
since the expected signal is
only 1/10 of photons from
hadron decays
15
Direct Photons in Au+Au
Blue line: Ncoll scaled p+p cross-section
Direct photon is measured as
“excess” above hadron decay
photons
Measurement at low pT difficult
since the yield of thermal photons
is only 1/10 of that of hadron
decay photons
PRL 94, 232301 (2005)
Au+Au data consistent with pQCD
calculation scaled by Ncoll
16
Alternative method --- measure virtual photon
Source of real photon should also be able to emit
virtual photon
 At m0, the yield of virtual photons is the same as
real photon
 Real photon yield can be measured from virtual
photon yield, which is observed as low mass e+e- 17

Not exactly a new idea
J.H.Cobb,
C. Albajar,etetal,
al,PL
PLB209,
78B, 519
397
(1978)
(1988)

g/0 = 10%

Dalitz
g/0
= 0.53 ±0.92%
(2< pT < 3 GeV/c)

The idea of measuring direct
photon via low mass lepton pair
is not new one. It is as old as the
concept of direct photon.
This method is first tried at
CERN ISR in search for direct
photon in p+p at s1/2=55GeV.
They look for e+e- pairs for
200<m<500 MeV, and set one of
the most stringent limit on direct
photon production at low pT
Later, UA1 measured low mass
muon pairs and deduced the
direct photon cross section.
18
Relation between dilepton and virtual photon
Emission rate of (virtual) photon
Emission rate of dilepton
EM correlator
Matter property
Relation between them
Prob. g*l+l-
e.g. Rapp, Wambach Adv.Nucl.Phys 25 (2000)
Boltzmann factor
temperature
This relation holds for the
yield after space-time
integral
Dilepton
virtual photon
Virtual photon emission rate can be determined from dilepton emission rate
M ×dNee/dM gives virtual photon yield
For M0, ng*  ng(real); real photon emission rate can also be determined
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Theory prediction of (Virtual) photon emission
M
Theory calculation by Ralf Rapp
dNg *
dNee

at y=0, pt=1.025 GeV/c
pt dpt dMdy pt dpt dy
Real photon yield
The calculation is shown
as the virtual photon
emission rate. The virtual
photon emission rate is a
smooth function of mass.
Turbide, Rapp, Gale PRC69,014903(2004)
Vaccuum EM correlator
Hadronic Many Body theory
Dropping Mass Scenario
q+q annihilaiton (HTL improved)
dNg
pt dpt dy
q+g  q+g*
qqg*
≈M2e-E/T
When extrapolated to
M=0, the real photon
emission rate can be
determined.
q+gq+g* is not in the
calculation; it should be
similar size as HMBT at
this pT
20
20
Electron pair measurement in PHENIX
designed to measure rare probes:
Au-Au & p-p spin
2
+ high rate capability & granularity
+ good mass resolution and particle ID
- limited acceptance
central arms:
electrons, photons,
hadrons
 charmonium J/, ’ ->
e+e vector meson r, w,  > e+e high pT
po, p+, p direct photons
 open charm
 hadron physics

g
e-
e+
DC
PC1
magnetic field &
PC3
tracking detectors
21
e+e- mass spectra in pT slices
arXiv:0912.0244
p+p
Au+Au
• p+p in agreement with cocktail
• Au+Au low mass enhancement concentrated at low pT
22
Enhancement of almost real photon
arXiv:0804.4168
pp
Au+Au (MB)
M
M
1 < pT < 2 GeV
2 < pT < 3 GeV
3 < pT < 4 GeV
4 < pT < 5 GeV
Low mass e+e- pairs (m<300
MeV) for 1<pT<5 GeV/c
p+p:
• Good agreement of p+p data
and hadronic decay cocktail
• Small excess above m at
large mee and high pT
Au+Au:
• Clear enhancement visible
above m =135 MeV for all pT
Excess  Emission of almost
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real photon
Virtual Photon Measurement
Any source of real g can emit g* with very low mass.
Relation between the g* yield and real photon yield is known.
4me2  2me2  1
d 2 N 2

1 - 2 1  2 
S ( M ee , pt )dN g
dM ee 3
M ee 
M ee  M ee
dN g *
Process dependent factor S ( M ee , pt ) 
dN g
 Case of hadrons (0, h) (Kroll-Wada)

2
S  F M ee
Direct g
0
h

2
2

M ee
1 2
M hadron

S = 0 at Mee > Mhadron



3
 Case of direct g*
If pT2>>Mee2 S = 1
 For m>m, 0 background (~80% of
background) is removed
 S/B is improved by a factor of five
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Determination of g* fraction, r
Direct g*/inclusive g* is determined by fitting the following function
f data M ee   1 - r  f cocktailM ee   r  f direct M ee 
r = direct
g*/inclusive
g*
fdirect : direct photon shape with S = 1.
• Fit in 120-300MeV/c2
(insensitive to 0 yield)
• The mass spectrum
follows the expectation for
m > 300 MeV
 S(m) ~ 1
arXiv:0804.4168
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arXiv:0912.0244
Fraction of direct photons
 Fraction
arXiv:0804.4168
arXiv:0912.0244
p+p
Au+Au (MB)
μ = 0.5pT
μ = 1.0pT
μ = 2.0pT
NLO pQCD calculation by Werner Vogelsang
of direct
photons
 Compared to
direct photons
from pQCD
p+p
 Consistent with
NLO pQCD
Au+Au
 Clear excess
above pQCD
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Direct photon spectra
exp + TAA scaled pp
arXiv:0804.4168
arXiv:0912.0244
• Direct photon measurements
– real (pT>4GeV)
– virtual (1<pT<5GeV)
• pQCD consistent with p+p
down to pT=1GeV/c
• Au+Au data are above Ncoll
scaled p+p for pT < 2.5 GeV/c
• Au+Au = scaled p+p + exp:
Tave = 221  19stat  19syst MeV
Fit to pp
NLO pQCD (W. Vogelsang)
27
Summary of the fit
Significant yield of the exponential component
(excess over the scaled p+p)
 The inverse slope TAuAu = 221±19±19 MeV
(>Tc ~ 170 MeV)

fit funciton: App(1+pt2/b)-n
 If power-law fit is used for the p+p spectrum, TAuAu =
240±21 MeV
 p+p
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Theory comparison


Hydrodynamical models are
compared with the data
D.d’Enterria &D.Peressounko
T=590MeV, 0=0.15fm/c
S. Rasanen et al.
T=580MeV, 0=0.17fm/c
D. K. Srivastava
T=450-600MeV, 0=0.2fm/c
S. Turbide et al.
T=370MeV, 0=0.33fm/c
J. Alam et al.
T=300MeV, 0=0.5fm/c
F.M. Liu et al.
T=370MeV, 0=0.6 fm/c
Hydrodynamical models are in
qualitative agreement with the
data
29
Initial temperature
Tave(fit) = 221 MeV
TC from Lattice QCD ~ 170 MeV
From data:
Tini > Tave = 220 MeV
From models: Tini = 300 to 600 MeV
0 = 0.15 to 0.6 fm/c
Lattice QCD predicts a phase transition to quark gluon plasma
at Tc ~ 170 MeV
30
Thermal emission from QGP: Summary






e+e- pairs for m<300MeV and 1<pT<5 GeV/c were
measured
 Excess above hadronic background is observed
 Excess is much greater in Au+Au than in p+p
Treating the excess as internal conversion of direct photons,
the yield of direct photon is deduced.
Direct photon yield in pp is consistent with a NLO pQCD
Direct photon yield in Au+Au is much larger.
 Spectrum shape above TAA scaled pp is exponential, with
inverse slope T=221 ±19(stat)±19(sys) MeV
Hydrodynamical models with Tinit=300-600MeV at 0=0.60.15 fm/c are in qualitative agreement with the data.
Lattice QCD predicts a phase transition to quark gluon
31
plasma at Tc ~ 170 MeV
Quarkonia & Deconfinement
32
Quarkonia & Deconfinement
For the hot-dense medium (QGP) created in A+A collisions at RHIC:
• Large quark energy loss in the medium implies high densities
• Flow scales with number of quarks
• Is there deconfinement?  look for Quarkonia screening
Debye screening predicted to destroy J/ψ’s
in a QGP with other states “melting” at
different temperatures due to different
sizes or binding energies.
Mocsy, WWND08
RHIC: T/TC ~ 1.9 or higher
Different lattice calculations do not agree on whether the
J/ is screened or not – measurements will have to tell!
Satz, hep-ph/0512217
5/25/2009
Mike Leitch
33
33
PHENIX A+A Data and Features
PHENIX Au+Au data shows suppression
at mid-rapidity about the same as seen
at the SPS at lower energy
• but stronger suppression at forward
rapidity.
• Forward/Mid RAA ratio looks flat
above a centrality with Npart = 100
Several scenarios may contribute:
• Cold nuclear matter (CNM) effects
• important, need better constraint
• Sequential suppression
• QGP screening only of C & ’removing their feed-down
contribution to J/ at both SPS &
RHIC
• Regeneration models
• give enhancement that
compensates for screening
5/25/2009
Mike Leitch
Centrality (Npart)
34
34
Reaching Higher pT for J/ - probing for the “hot wind”?
New PHENIX RCuCu out to pT = 9 GeV/c !
• shows large suppression that looks roughly constant up to high pT
• STAR points with their huge uncertainties were misleading
AdS/CFT (“hot wind”) - more
suppression at high pT:
Liu, Rajagopal,Wiedemann
PRL 98, 182301(2007)
Regeneration (2-compenent):
Zhao, Rapp
hep-ph/07122407
& private communication
Equilibrating Parton Plasma:
Xu, Kharzeev, Satz, Wang,
hep-ph/9511331
Gluonic dissoc. & flow:
Patra, Menon, nucl-th/0503034
Cronin – less suppression at higher pT:
use d+Au data as a guide
5/25/2009
Mike Leitch
35
35
New CNM fits using 2008 PHENIX d+Au Rcp
(Tony Frawley, Ramona Vogt, …)
• similar to before, use models with shadowing &
absorption/breakup
• but allow effective breakup cross section to
vary with rapidity
• to obtain good description of data for
projections to A+A
• get “breakup(y)”; compare to E866/NuSea &
HERA-B
• Lourenco, Vogt, Woehri - arXiv:0901.3054
with EKS shadowing
with NDSG shadowing
• common trend, with large increasing effective
breakup cross section at large positive rapidity
• need additional physics in CNM model – e.g.
initial-state dE/dx
5/25/2009
Mike Leitch
36
36
Upsilons at RHIC
37
Quarkonia Production & Suppression – Upsilons in p+p
• Cross section follows world trend
• Baseline for Au+Au
d
46
BR *
|| y|0.35  114-45
pb
dy
5/25/2009
Mike Leitch
38
38
Quarkonia – Upsilons Suppressed in Au+Au
Au+Au
p+p
Au+Au
N[8.5,11.5]
10.5(+3.7/-3.6)
11.7(+4.7/-4.6)
NJ/Ψ
2653 ±70±345
4166 ±442(+187/-304)
RAA(J/Ψ)
---
0.425 ±0.025±0.072
RAuAu [8.5,11.5] < 0.64 at 90% C.L.
--- Includes 1S+2S+3S --5/25/2009
Mike Leitch
39
39
Leptons signals & heavy quarks
e


D, B

c, b quark

Study medium effect in open charm
and bottom production
Ideally, D or B meson should be
measured, but for technical reason
most of the measurement so far is
done through electron decay
channel.
From RAA and v2 of the electrons
from heavy quark decays, the
energy loss and the flow of heavy
quarks are indirectly measured.
So far, ce and be are not
separated
40
Large energy loss and flow of heavy quarks
RAA of b,c e
Strong suppression of electron from c and b
Large energy loss of heavy quark



v2 of b,c e
Large elliptic flow of electrons from c and b!
Heavy quark flows in the medium
These results require very strong interaction between the dense matter and
heavy quarks.
Since the observed electron is mixture of ce (dominant) and be, we cannot
determine the suppression or flow of be.
Theoretical expectation is that the medium-quark interaction becomes weaker
41
for heavier quark. Large energy loss and/or flow are not expected.
Heavy flavor electron RAA and flow
PRL98,172301 (2007)
 Two models describes strong
suppression and large v2
 Rapp and Van Hee
 Moore and Teaney
 From model comparison,
viscosity to entropy ratio h/s
can be estimated

DHQ × 2πT = 4 - 6
DHQ ~ 6 x h/(+p) = 6 x h/Ts
h/s ~ (4/3 – 2)/4
estimate of h/s is close
to the conjectured bound
1/4from AdS/CFT
 The
42
Comparison with other estimates
R. Lacey et al.: PRL 98:092301, 2007
h / s  (1.1  0.2  1.2) / 4
H.-J. Drescher et al.: arXiv:0704.3553
S. Gavin and M. Abdel-Aziz:
PRL 97:162302, 2006
pTfluctuations STAR
h / s  (1.0 - 3.8) / 4
v2 PHENIX
& STAR
v2 PHOBOS
h / s  (1.4 - 2.4) / 4
Estimates of h/s based on
flow and fluctuation data
indicate small value as well
close to conjectured limit
significantly below h/s of
helium (4h/s ~ 9)
conjectured quantum limit
43
Closing comments
-Density > 5 GeV/fm3 (transverse energy
measurements);
-Temperature ~220 MeV (thermal photons);
-Preserves flow (h/s ~0.4)
-Interact strongly with non e/m probes (jet
suppression);
-Quarkonia data are still inconclusive – interplay of
CME and QGP screening;
-Unexpected scale of the heavy quark’s energy loss.
44
Heavy quark (charm and bottom) probe

e

D, B

c, b quark

Study medium effect in
open charm and bottom
production
Ideally, D or B meson
should be measured, but
for technical reason
most of the
measurement so far is
done through electron
decay channel.
From RAA and v2 of the
electrons from heavy
quark decays, the energy
loss and the flow of
heavy quarks are
indirectly measured.
So far, ce and be are
not separated
45
BACKUP
46
Heavy flavor production in pp (base line)
Phys. Rev. Lett 97,252002 (2006)




Single electrons from
heavy flavor
(charm/bottom) decay
are measured and
compared with pQCD
theory (FONLL)
The new data extends
the pT reach to 9 GeV/c
FONLL pQCD
calculation agree with
the data
c e dominant in low
pT
be is expected to be
dominant in high p47T
Bottom Measurement
p+p 200 GeV Charm and bottom extracted via e-h mass analysis


Charm and bottom spectra are both by a factor  above FONLL pQCD
calculations (but within the uncertainty)
STAR studied be/ce ratios in pp and obtained similar b/c ratios
48
Basic
Thermodynamics
Hot
Hot
dE  TdS- PdV
Sudden expansion, fluid fills empty
space
 without loss of energy.
dE = 0
PdV > 0 therefore dS > 0
Hot
Hot
Cool
Gradual expansion (equilibrium maintained),
fluid loses energy through PdV work.
dE = -PdV therefore dS = 0
Isentropic
Adiabatic
49
Velocity
Depending on a taste the history began either 10*10 or 80
years ago
The
original
Hubble
Diagram
“A Relation
Between
Distance and
Radial Velocity
Among ExtraGalactic
Nebulae”
E.Hubble
(1929)
Distance
Edwin Hubble
Galaxies outside
Milky Way
Henrietta
Leavitt
Distances via
variable stars
50