Electromagnetic Probes in Heavy-Ion Collisions II ...hees/publ/graz15-2.pdf · Electromagnetic...

Electromagnetic Probes in Heavy-Ion Collisions IIPhenomenology from SIS to LHC energies

Hendrik van Hees

Goethe University Frankfurt and FIAS

November 27, 2015

Hendrik van Hees (GU Frankfurt/FIAS) Electromagnetic Probes November 27, 2015 1 / 54

Outline

1 Heavy-ion collisions on one slide

2 QCD and ultra-hot and -dense matter

3 Electromagnetic probes in heavy-ion collisions

4 Simulations for electromagnetic probes in HICsDileptons at SIS energies (HADES)Dileptons at SPS and RHICDirect photons at RHIC and LHC: “the flow puzzle”

5 Outlook: Signatures of the QCD-phase structure?

6 References


Heavy-Ion collisions in a Nutshelltheory of strong interactions: Quantum Chromo Dynamics, QCDat high densities/temperatures: hadrons dissolve into a QGPcreate QGP in Heavy-Ion Collisions at RHIC (and LHC)GSI SIS: pp, dp, pA, AA collisions at low energies (Ekin = 1.25-3.5 GeV)Dielectrons from HADESCERN SPS: AA collisions with Ekin = 158 GeV per nucleon on a fixed target(center-mass energy:

psN N = 17.3 GeV)

dileptons (particularly µ+µ− in In-In collisions from NA60)BNL RHIC: Au Au collisions with center-mass energy of

psN N = 200 GeV;

“beam-energy scan”p

sN N = 7.7-39 GeVdileptons from STAR and PHENIX; direct photons from PHENIXCERN LHC: Pb-Pb collisions at

ps = 2.76 TeV per nucleon

direct photons from ALICE


Phenomenology and Chiral symmetry

in vacuum: Spontaneous breaking of chiral symmetry

⇒mass splitting of chiral partners

qq-excitations of the QCD vacuum

π

ρ ω

φ

(140)

(770) (782)

(1260)

(1020)

(1285)

(400-

1200)

a f

f

f

1 1

1

0

Energy (MeV)

P-S, V-A splitting

in the physical vacuum

(1420)

0 1 2 3

s [GeV2]

0

0.02

0.04

0.06

0.08

−Im

ΠV

,A/(

πs)

[d

im.−

less

]

V [τ −> 2nπ ντ]

A [τ −> (2n+1)π ντ]

ρ(770) + cont. a

1(1260) + cont.


The QCD-phase diagram

hot and dense matter: quarks and gluons close together

highly energetic collisions⇒ “deconfinement”

quarks and gluons relevant degrees of freedom⇒ quark-gluon plasma

still strongly interacting⇒ fast thermalization!

0.0µ

N

0.05

0.10

0.15

0.20

0.25

T [

Ge

V] SPS

AGS

SIS

RHIC

nuclei

hadron gas

〈q̄q〉 6= 0 〈qq〉 6= 0

quark-gluon plasma

〈q̄q〉= 〈qq〉= 0

crit. point 1 storder


The QCD-phase diagram

at high temperature/density: restoration of chiral symmetrylattice QCD: T χ

c ' T deconfc

Mass

Spec

tral

F

unct

ion

Spec

tral

F

unct

ion

"a1"

"ρ"pert. QCD

Melting Resonances?

"a1"

"ρ"

pert. QCD

Dropping Masses?

mechanism of chiral restoration?two main theoretical ideas

“dropping masses”: mhad∝

ψψ�

“melting resonances”: broadening of spectra through medium effects


Electromagnetic probes in heavy-ion collisions

γ,`±: no strong interactions

reflect whole “history” of collision:from pre-equilibrium phasefrom thermalized mediumQGP and hot hadron gasfrom VM decays after thermalfreezeout

ρ/ω γ∗ e−π, . . .

e+

γ

0 1 2 3 4 5

mass [GeV/c2]

dN

ee / d

ydm

πo,η Dalitz-decays

ρ,ω

Φ

J/Ψ

Ψl

Drell-Yan

DD

Low- Intermediate- High-Mass Region> 10 fm > 1 fm < 0.1 fm

Fig. by A. Drees


Electromagnetic probes from thermal source

photon and dilepton thermal emission rates given by sameelectromagnetic-current-correlation function (Jµ =

∑

f Q f ψ f γµψ f )

McLerran-Toimela formula [MT85, GK91]

Π<µν(q ) =

∫

d4 x exp(iq · x )

Jµ(0)Jν(x )�

T=−2 fB(q ·u ) ImΠ(ret)

µν (q )

q0

dNγd4 x d3 ~q

=−αem

2π2g µν Im Π(ret)

µν (q , u )�

�

�

q0=|~q |fB(q ·u )

dNe +e −

d4 x d4k=−g µν

α2

3q 2π3Im Π(ret)

µν (q , u )�

�

�

q 2=M 2e+e−

fB(q ·u )

manifestly Lorentz covariant (dependent on four-velocity of fluid cell, u)

q ·u = Ecm: Doppler blue shift of qT spectra!

to lowest order in α: 4παΠµν 'Σ(γ)µν

vector-meson dominance model:

Σγµν =

Gρ

`+`−-M spectra⇒ in-med. spectral functions of vector mesons (ρ,ω,φ)!Hendrik van Hees (GU Frankfurt/FIAS) Electromagnetic Probes November 27, 2015 8 / 54

Radiation from thermal QGP: q q̄ annihilation

General: McLerran-Toimela formula

dN (MT)l +l −

d4 x d4q=−

α2

3π3

L (M 2)M 2

gµνIm∑

i

Πµνem,i (M , ~q ) fB(q ·u )

i enumerates partonic/hadronic sources of em. currents

in-medium em. current-current correlation function

Πµνem,i = i

∫

d4 x exp(iq x )Θ(x 0)�

j µem,i (x ), j νem,i (0)��

in QGP phase: q q̄ annihilation

hard-thermal-loop improved electromagnetic current-current correlator

q

q̄

γ∗ γ∗−iΠem,QGP =


Radiation from thermal sources: ρ decays

model assumption: vector-meson dominance

Σγµν =

Gρ

dN (MT)ρ→l +l −

d4 x d4q=

M

q 0Γρ→l +l − (M )

dNρd3 ~x d4q

=−α2

3π3

L (M 2)M 2

m 4ρ

g 2ρ

gµν Im D µνρ (M , ~q ) fB

�

q ·u −2µπ(t )T (t )

�

special case of McLerran-Toimela (MT) formula

M 2 = q 2: invariant mass, M , of dilepton pair

L (M 2) = (1+2m 2l /M

2)q

1−4m 2l /M 2: dilepton phase-space factor

D µνρ (M , ~q ): (four-transverse part of) in-medium ρ propagator

at given T (t ), µmeson/baryon(t )

− Im Dρ in-medium ρ-meson spectral function!

analogous forω andφ


Hadronic many-body theory

hadronic many-body theory (HMBT) for vector mesons[LK95, CS92, CS93, RCW97, UBRW98, UBW02, UBRW00, Her92, HFN93, GR99, RW99, RW00]

ππ interactions and baryonic excitations

effective hadronic models, implementing symmetries

parameters fixed from phenomenology(photon absorption at nucleons and nuclei, πN →ρN )

evaluated at finite temperature and density

self-energies⇒mass shift and broadening of particle in the medium

ρ ρ

π

π B , a , K ,...*1 1

π,...N, K,

ρ ρ

Baryon (resonances) important, even at low net baryon density nB−nB̄

reason: nB+nB̄ relevant (CP inv. of strong interactions)


Meson contributions

0.0 0.2 0.4 0.6 0.8 1.0 1.2

M [GeV]

−30

−20

−10

0

10

20

30

Re Σ

ρ/m

ρ [M

eV

]

−70

−60

−50

−40

−30

−20

−10

0

Im Σ

ρ/m

ρ [M

eV

]

a1

π’h

1K1

ω

f1

sum

T=150MeV

q=0.3GeV

ω

suma

1

K1

[GR99]


In-medium spectral functions and baryon effects

[RW99]

baryon effects importantlarge contribution to broadening of the peakresponsible for most of the strength at small M


Radiation from thermal sources: multi-π processes

use vector/axial-vector correlators from τ-decay data

Dey-Eletsky-Ioffe mixing: ε̂ = 1/2ε(T ,µπ)/ε(Tc , 0)

ΠV = (1− ε̂)z 4πΠ

vacV ,4π+

ε̂

2z 3πΠ

vacA,3π+

ε̂

2(z 4π+ z 5

π)ΠvacA,5π

avoid double counting: leave out two-pion piece and a1→ρ+π(already contained in ρ spectral function)

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

-Im

ΠV

/(π

M2)

M2 (GeV

2)

data: ALEPH at LEP

V [τ→ 2n π ντ]

V [τ→ 2 π ντ]

ρ + cont.

2π (ρ)

4π (fit)

0

0.01

0.02

0.03

0.04

0.05

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

-Im

ΠA

/(π

M2)

M2 (GeV

2)

A [τ→ (2n+1) π ντ]

A [τ→ 3 π ντ]

a1 + cont.

3π (a1)

5π (fit)

Data: [B+98]


Bulk evolution with transport and coarse graining

established transport models for bulk evolutione.g., UrQMD, GiBUU, BAMPS, (p)HSD,...solve Boltzmann equation for hadrons and/or partons

dilemma: need medium-modified dilepton/photon emission rates

usually available only in equilibrium QFT calculations

ways out:use (ideal) hydrodynamics⇒ local thermal equilibrium⇒ use equilibrium ratesuse transport-hydro hybrid model: treat early stage with transport, then coarsegrain⇒ switch to hydro⇒ switch back to transport (Cooper-Frye “particlization”)

here: UrQMD transport for entire bulk evolution⇒ use coarse graining in space-time cells⇒ extract T , µB , µπ, . . .⇒ use equilibrium rates locally


Simulations for em. probesin heavy-ion collisions


Coarse-grained UrQMD (CGUrQMD)

problem with medium modifications of spectral functions/interactions

only available in equilibrium many-body QFT models

use “in-medium cross sections” naively: double counting?!?

way out: map transport to local-equilibrium fluid

use ensemble of UrQMD runs with an equation of state

fit temperature, chemical potentials, flow-velocity fieldfrom anisotropic energy-momentum tensor [FMRS13]

T µν = (ε+P⊥)uµuν−P⊥g µν− (P‖−P⊥)V

µV ν

thermal rates from partonic/hadronic QFT become applicable

extrapolated lattice QGP and Rapp-Wambach hadronic many-body theory

caveat: consistency between EoS, matter content of QFT model/UrQMD!



Tc = 170 MeV; T > Tc ⇒ lattice EoS; T < Tc ⇒HRG EoS

0ε/εEnergy density

0 10 20 30 40 50 60 70 80 90 100

Te

mp

era

ture

[M

eV

]

100

120

140

160

180

200

220

240

260

280

300

=170 MeV)c

Lattice EoS (T

=0)B

µHadron Gas EoS (for



pressure anisotropy (In-In collisions (NA60) at SIS)

Time t [fm]0 2 4 6 8 10 12 14

-310

-210

-110

1

10

210In+In @ 158 AGeV

>=120η/dch

<dN

Central cell (x=y=z=0)

)3

(GeV/fm PPAnisotropy parameter x

Relaxation function r(x)



energy/baryon density⇒ T ,µB (for In+In @ SPS; NA60)

central “fluid” cell!

Time t [fm]0 2 4 6 8 10 12 14

0ρ/

Bρ

an

d

0ε/

ε

-210

-110

1

10

210In+In @ 158 AGeV

>=120η/dch

<dNCentral cell (x=y=z=0)

0ε/εEnergy density

0ρ/ρBaryon density

(a)

Time t [fm]0 2 4 6 8 10 12 14

[M

eV

]B

µT

an

d

0

100

200

300

400

500Lattice EoS Hadron Gas EoS

In + In @ 158 AGeV

>=120η/dch

<dN

Central cell (x=y=z=0)

T

Bµ

πµ

(b)



energy (ε) and baryon (ρ) density profiles (for In+In@SPS; NA60)

x-axis [fm]-8 -6 -4 -2 0 2 4 6 8

]0

ρ/ρ

an

d

0ε/

εE

ne

rgy

an

d b

ary

on

de

ns

ity

[

0

20

40

60

80

100

120Transverse density profilesIn+In @ 158 AGeV

t = 1fm:

t = 3fm:

t = 5fm:

0ε/ε

0ρ/ρ

x 50

ε/ε

x 50

ρ/ρ

x 80

ε/ε

x 80

ρ/ρ

(a)

z-axis [fm]-8 -6 -4 -2 0 2 4 6 8

]0

ρ/ρ

an

d

0ε/

εE

nerg

y a

nd

bary

on

den

sit

y [

0

20

40

60

80

100

120Longitudinal density profilesIn+In @ 158 AGeV

t = 1fm:

t = 3fm:

t = 5fm:

0ε/ε

0ρ/ρ

x 50

ε/ε

x 50

ρ/ρ

x 80

ε/ε

x 80

ρ/ρ

(b)


Dielectrons (SIS/HADES)


CGUrQMD: Ar+KCl (1.76 AGeV) (SIS/HADES)

coarse-graining method works at low energies!UrQMD-medium evolution + RW-QFT rates [EHWB15b]

]2M [GeV/c0 0.2 0.4 0.6 0.8 1

-1]

2 d

N/d

M

[Ge

V/c

×)

0π

1/N

(

-910

-810

-710

-610

-510

-410

-310

-210UrQMD

πη

foωfo

ρφρMedium

ωMedium πMulti

Coarse-Graining

< 1.1 GeV/ce

HADES acceptance, 0.1 < pAr + KCl @ 1.76 AGeV

(a)



dielectron spectra from Ar+KCl(1.76 AGeV)→ e+e− (SIS/HADES)mt spectra [EHWB15b]

Mee < 0.13 GeV

]2 [GeV/ctm0 0.2 0.4 0.6 0.8 1

2/5

]2

[G

eV

/ct

dN

/dm

×)

3/2

t)m

0π

1/(

N(

-610

-510

-410

-310

-210

-110

1

10UrQMD

πη

foωfo

ρφρMedium

ωMedium πMulti

Coarse-Graining

2 < 0.13 GeV/ceeM

(a) Ar + KCl @ 1.76 AGeV




0.13 GeVMee < 0.3 GeV

]2 [GeV/ct

m0 0.2 0.4 0.6 0.8 1

2/5

]2

[G

eV

/ct

dN

/dm

×)

3/2

t)m

0π

1/(

N(

-810

-710

-610

-510

-410

-310

-210

2 < 0.30 GeV/cee0.13 < M

(b)





]2 [GeV/ct

m0.2 0.4 0.6 0.8 1 1.2

2/5

]2

[G

eV

/ct

dN

/dm

×)

3/2

t)m

0π

1/(

N(

-910

-810

-710

-610

-510

-410

-310

2

< 0.45 GeV/cee0.30 < M(c)





]2 [GeV/ct

m0.4 0.6 0.8 1 1.2 1.4

2/5

]2

[G

eV

/ct

dN

/dm

×)

3/2

t)m

0π

1/(

N(

-1010

-910

-810

-710

-610

-510

-410

2 < 0.65 GeV/cee0.45 < M

(d)




Mee > 0.65 GeV

]2 [GeV/ct

m0.6 0.8 1 1.2 1.4 1.6

2/5

]2

[G

eV

/ct

dN

/dm

×)

3/2

t)m

0π

1/(

N(

-1010

-910

-810

-710

-610

-510

-410

2 > 0.65 GeV/cee M

(e)



dielectron spectra from Ar+KCl(1.76 AGeV)→ e+e− (SIS/HADES)

mt spectra [EHWB15b]

rapidity spectrum (Mee < 0.13 GeV)

Radpidity y-0.5 0 0.5 1 1.5 2

dN

/dy

×)

0π

1/N

(

-710

-610

-510

-410

-310

-210

-110

12 < 0.13 GeV/ceeM(f)


CGUrQMD: Au+Au (1.23 AGeV) (SIS/HADES)

]2M [GeV/c0 0.2 0.4 0.6 0.8 1

-1]

2 d

N/d

M [G

eV

/c×

))

0π

(1/N

(

-910

-810

-710

-610

-510

-410

-310

-210

< 1.1 GeV/ce

HADES acceptance, 0.1 < pAu + Au @ 1.23 AGeV (b)

caveat: pp/np acceptance filter with single-e cut, pt < 100 MeVcorrect filter urgently needed!excellent agreement with preliminary HADES data(data points not shown here on request of the HADES collaboration)


What to learn about the “bulk dynamics”?

hadronic observables like pT spectra: “snapshot” of the stage after kineticfreezeout

particle abundancies: chemical freezeout

em. probes: emitted during the whole medium evolutionlife time of the medium⇒ “four-volume of the fireball”

use CGUrQMD to study system-size dependence

study AA collisions for different A

hard to quantify “life time” of the “thermal” medium in transport

here: use time, for which the central cell has T ≥ 50 MeV


Four Volume

V (4)AA /A

V (4)CC /12of cells larger than various T

Mass number A0 20 40 60 80 100 120 140 160 180 200

12

C1

2C

12 4

V /

AA

A4

V

0

1

2

3

4

5

6

7

8

9

10T > 50 MeV

T > 60 MeV

T > 70 MeV

T > 80 MeV

T > 90 MeV

(a)

how to explain “scaling behavior”?


Lifetime of the central cell

consider central collisions from C+C to Au+Au at Ekin = 1.76 AGeV

Mass number A0 20 40 60 80 100 120 140 160 180 200

Tim

e t

[fm

]

0

5

10

15

20

25

30

t∆

1/3A

t∆

T > 50 MeV in central cell (x=y=z=0) (b)

∆t ∝ A1/3

A∝V (3) of nuclei⇒ A1/3∝ dnucl

fireball lifetime∝ time of nuclei to traverse each other


Lifetime of the central cell

yieldAA/AyieldCC/12

Mass number A0 20 40 60 80 100 120 140 160 180 200

12

C1

2C

12

Yie

ld /

A

AA

Yie

ld

0

1

2

3

4

5

60

π

(0.2 GeV < M < 0.4 GeV)-e+

Thermal e

(0.2 GeV < M < 0.4 GeV)-e+

Non-thermal e

(a)

yieldhad∝ A∝V (3)fo

yieldnon-thermal ee∝ A∝V (3)fo⇒ hadronic decays after kinetic freeze-out


Scaling behavior of thermal-dilepton yield

Mass number A0 20 40 60 80 100 120 140 160 180 200

12

C1

2C

/Ra

tio

AA

Ra

tio

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

4/3A

-e+

thermal e

0.2 < M < 0.4 GeVYield

thermal

4V

-e+

thermal e


thermalt⋅A

-e+

thermal e


4/30

πN

-e+

thermal e


(b)

thermal-dilepton yield roughly∝V (4)therm∝ A4/3∝ Attherm∝N 4/3π0


Dimuons (SPS/NA60)


CGUrQMD: In+In (158 AGeV) (SPS/NA60)

dimuon spectra from In+ In(158 AGeV)→µ+µ− (NA60)[EHWB15a]

min-bias data (dNch/dy = 120)note the importance of baryon effects!

M [GeV]0 0.2 0.4 0.6 0.8 1 1.2 1.4

]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-910

-810

-710

-610

-510

ρIn-medium ρNon-thermal

QGP (Lattice)πMulti

Sum

ρThermal (no baryons)

qPerturb. q

For comparison:

In+In @ 158 AGeV

HG-EoS + Lattice EoS

> 0 GeVT

>=120, pη/dch

<dN(a)




min-bias data (dNch/dy = 120)higher IMR: provides averaged true temperature(no blueshifts in the invariant-mass spectra!)

M [GeV]0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8

]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

(b)




min-bias data (dNch/dy = 120)pT < 0.2 GeV

Invariant Mass M [GeV]0 0.2 0.4 0.6 0.8 1 1.2 1.4

]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

ρIn-medium ρNon-thermal

QGP (Lattice)πMulti

Sum

In+In @ 158 AGeV>=120η/dch<dN

< 0.2 GeVT

p(a)




min-bias data (dNch/dy = 120)0.2 GeV < pT < 0.4 GeV


]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 0.4 GeVT

0.2 < p(b)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 0.6 GeVT

0.4 < p(c)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 0.8 GeVT

0.6 < p(d)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 1.0 GeVT

0.8 < p(e)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 1.2 GeVT

1.0 < p(f)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 1.4 GeVT

1.2 < p(a)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 1.6 GeVT

1.4 < p(b)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 1.8 GeVT

1.6 < p(c)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 2.0 GeVT

1.8 < p(d)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 2.2 GeVT

2.0 < p(e)






]-1

) [2

0 M

eV

η/d

ch

)/(d

Nη

/dM

d2

µµ

(dN

-1010

-910

-810

-710

-610

< 2.4 GeVT

2.2 < p(f)



dimuon spectra from In+ In(158 AGeV)→µ+µ− (NA60) [EHWB15a]

min-bias data (dNch/dy = 120)

-M [GeV]t

m0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

]-2

) [G

eV

η/d

ch

)/(d

Nη

d t/d

m2

µµ

)(d

Nt

(1/m

-910

-810

-710

-610

-510

-410ρIn-medium

ρNon-thermal

QGP (Lattice)

πMulti

Sum

0.2 < M < 0.4 GeVIn+In @ 158 AGeVHG-EoS + Lattice EoS

>=120η/dch

<dN

(a)





-M [GeV]t

m0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

]-2

) [G

eV

η/d

ch

)/(d

Nη

d t/d

m2

µµ

)(d

Nt

(1/m

-910

-810

-710

-610

-510

-410 0.4 < M < 0.6 GeV(b)





-M [GeV]t

m0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

]-2

) [G

eV

η/d

ch

)/(d

Nη

d t/d

m2

µµ

)(d

Nt

(1/m

-910

-810

-710

-610

-510

-410 0.6 < M < 0.9 GeV(c)





-M [GeV]t

m0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

]-2

) [G

eV

η/d

ch

)/(d

Nη

d t/d

m2

µµ

)(d

Nt

(1/m

-910

-810

-710

-610

-510

-410 1.0 < M < 1.4 GeV(d)


Dielectrons at RHIC


Dileptons@RHIC: PHENIX (2007)

)2 (GeV/ceem

0 0.2 0.4 0.6 0.8 1 1.2

/Ge

V)

IN P

HE

NIX

AC

CE

PT

AN

CE

2 (

cee

dN

/dm

-510

-410

-310

-210

-110 = 200 GeVNNsmin. bias Au+Au R.Rapp & H.vanHees

cocktail

vacuumρsum w/

broadeningρsum w/

dropping)ρsum/

partonic yield (PY)

ee (PYTHIA)→ cc

ee (random correlation)→ cc

DATA|y| < 0.35

> 0.2 GeV/ce

Tp

model: Rapp, HvH, data [A+10]

here: thermal-fireball evolution instead of CGUrQMD (work in progress)huge enhancement in the LMR explained by new PHENIX results fromSep/2015




here: thermal-fireball evolution instead of CGUrQMD (work in progress)




here: thermal-fireball evolution instead of CGUrQMD (work in progress)


Dileptons@RHIC: STAR (QM 2012)

[Rap13], data: [Zha11]

compatible with medium modifications in model calculation


Direct photons (RHIC/LHC)


Direct Photons at RHICsame model [TRG04] for rates as for dileptonsfireball parametrization with elliptic flow v2

photons inherit v2 from hadronic sources

[HGR11, RHH14, HHR15]


Effective slopes vs. temperatures

effective slopes of photon pT spectra are NOT temperatures!

emission from a flowing medium⇒Doppler effect

Teff '√

√1+ ⟨vT ⟩1−⟨vT ⟩

T

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 2 4 6 8 10 12

qT=2 GeV

t (fm)

Teff (GeV)T (GeV)<vT>/10

[RHH14]


Direct Photons at the LHC

same model, fireball adapted to hadron data from ALICE [HHR15]

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

0 1 2 3 4 5

0-40% Pb-Pb, |y|<0.75

q0 d

N/d

3q [

GeV

-2]

qT [GeV]

hadron gasQGP

primordialtotal

ALICE prelim.

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0 1 2 3 4 5

v2

qT [GeV]

ALICE prelim.total

thermal γ

large direct-photon v2

early buildup of v2; here developed already at end of QGP phase

emission mostly around Tc (dual rates!) ⇒⇒ source has already developed radial flow and v2

large effective slopes include blueshift from radial flow!

still additional (hadronic?) sources (bremsstrahlung?) missing?!?


Signatures of theQCD-phase structure?


Possible signatures of QCD-phase structure?

measurement of thermal-dilepton spectra/yields a la NA60

scaling behavior at low energies studied with one HRG EoS

beam-energy scan like at RHIC⇒ deviations from naive scaling behavior?

possible variations in fireball lifetime due to different phase transitions

cross over at higher RHIC and LHC energies [RH14]

deviations in regions of larger µB?

possible signature of 1st-order line?

possible signature of critical point through “anomalies in fireball lifetime”due to critical slowing-down???

NB: `+`− also “thermometer” from invariant-mass slopes in IMR(needs a good handle on correlated DD decays a la NA60!)


Dilepton systematics in the beam-energy scan

beam-energy scan at RHIC and lower energies at future FAIR and NICAacceleratorsinvariant-mass slope in IMR⇒ true temperature!no blue shift from radial flow as in pT /mT spectra

10 100

s1/2

(GeV)

0

50

100

150

200

250

300

350

400

T (

MeV

)

Ts (M=1.5-2.5 GeV)

Ti

Tpc

Central AA Collisions

[RH14]Hendrik van Hees (GU Frankfurt/FIAS) Electromagnetic Probes November 27, 2015 45 / 54

Dilepton systematics in the beam-energy scan

beam-energy scan at RHIC and lower energies at future FAIR and NICAacceleratorsdilepton yield as fireball-lifetime clock

0

5

10

15

20

25

10 1000

5

10

15

20Nℓ+

ℓ−/

Nch·1

06

τ fb(

fm/

c)

√sNN (GeV)

0.3GeV < M < 0.7GeVhadronicQGPsumτfb

[RH14]


Summary

em. probes, `+`− and γ: neglible final-state interactions

probe in-medium electromagnetic current-current correlatorover entire history of fireball evolution

provide insight into fundamental properties of QCD matter

needs models for electromagnetic radiation from QGP and hadron gas

medium effects on vector mesons in hot and dense matter

hint at chiral-symmetry restoration⇒melting resonances rather than dropping mass

insight into fireball dynamics (temperature, lifetime)

possible hints of QCD-phase structure (equation of state)?

for more details, see website of the HQM Lecture Week spring 2014http://fias.uni-frankfurt.de/~hees/hqm-lectweek14/index.html


http://fias.uni-frankfurt.de/~hees/hqm-lectweek14/index.html

Bibliography I

[A+10] A. Adare, et al., Detailed measurement of the e+e− pair continuum inp+p and Au+Au collisions at

psN N = 200 GeV and implications for

direct photon production, Phys. Rev. C 81 (2010) 034911.http://dx.doi.org/10.1103/PhysRevC.81.034911

[A+15] A. Adare, et al., Dielectron production in Au+Au collisions atpsN N=200 GeV (2015).

http://arXiv.org/abs/1509.04667

[B+98] R. Barate, et al., Measurement of the spectral functions ofaxial-vector hadronic τ decays and determination of αs (M 2

τ ), Eur.Phys. J. C 4 (1998) 409.http://publish.edpsciences.org/abstract/EPJC/V4/P409

[CS92] G. Chanfray, P. Schuck, The rho meson mass spectrum in densematter, Nucl. Phys. A 545 (1992) 271c.http://dx.doi.org/10.1016/0375-9474(93)90325-R


http://dx.doi.org/10.1103/PhysRevC.81.034911

http://arXiv.org/abs/1509.04667

http://publish.edpsciences.org/abstract/EPJC/V4/P409

http://publish.edpsciences.org/abstract/EPJC/V4/P409

http://dx.doi.org/10.1016/0375-9474(93)90325-R

Bibliography II

[CS93] G. Chanfray, P. Schuck, The rho meson in dense matter and itsinfluence on dilepton production rates, Nucl. Phys. A 555 (1993) 329.http://dx.doi.org/10.1016/0375-9474(93)90325-R

[EHWB15a] S. Endres, H. van Hees, J. Weil, M. Bleicher, Coarse-grainingapproach for dilepton production at energies available at the CERNSuper Proton Synchrotron, Phys. Rev. C 91 (2015) 054911.http://dx.doi.org/10.1103/PhysRevC.91.054911

[EHWB15b] S. Endres, H. van Hees, J. Weil, M. Bleicher, Dilepton production andreaction dynamics in heavy-ion collisions at SIS energies fromcoarse-grained transport simulations, Phys. Rev. C 92 (2015) 014911.http://dx.doi.org/10.1103/PhysRevC.92.014911

[FMRS13] W. Florkowski, M. Martinez, R. Ryblewski, M. Strickland, Anisotropichydrodynamics, Nucl. Phys. A 904-905 (2013) 803c.http://dx.doi.org/10.1016/j.nuclphysa.2013.02.138


http://dx.doi.org/10.1016/0375-9474(93)90325-R



http://dx.doi.org/10.1016/j.nuclphysa.2013.02.138

Bibliography III

[GK91] C. Gale, J. I. Kapusta, Vector Dominance Model at FiniteTemperature, Nucl. Phys. B 357 (1991) 65.http://dx.doi.org/10.1016/0550-3213(91)90459-B

[GR99] C. Gale, R. Rapp, Rho Properties in a hot Gas: Dynamics ofMeson-Resonances, Phys. Rev. C 60 (1999) 024903.http://publish.aps.org/abstract/PRC/v60/e024903

[Her92] M. Herrmann, Eigenschaften des ρ-Mesons in dichter Kernmaterie,Dissertation, Technische Hochschule Darmstadt, Darmstadt (1992).http://www-lib.kek.jp/cgi-bin/img_index?200038480

[HFN93] M. Herrmann, B. L. Friman, W. Nörenberg, Properties of rho mesonsin nuclear matter, Nucl. Phys. A 560 (1993) 411.http://dx.doi.org/10.1016/0375-9474(93)90105-7

[HGR11] H. van Hees, C. Gale, R. Rapp, Thermal Photons and Collective Flowat the Relativistic Heavy-Ion Collider, Phys. Rev. C 84 (2011) 054906.http://dx.doi.org/10.1103/PhysRevC.84.054906


http://dx.doi.org/10.1016/0550-3213(91)90459-B

http://publish.aps.org/abstract/PRC/v60/e024903

http://www-lib.kek.jp/cgi-bin/img_index?200038480

http://dx.doi.org/10.1016/0375-9474(93)90105-7


Bibliography IV

[HHR15] H. van Hees, M. He, R. Rapp, Pseudo-Critical Enhancement ofThermal Photons in Relativistic Heavy-Ion Collisions, Nucl. Phys. A933 (2015) 256.http://dx.doi.org/10.1016/j.nuclphysa.2014.09.009

[LK95] G.-Q. Li, C. M. Ko, Can dileptons reveal the in-medium properties ofvector mesons?, Nucl. Phys. A 582 (1995) 731.http://dx.doi.org/10.1016/0375-9474(94)00500-M

[MT85] L. D. McLerran, T. Toimela, Photon and dilepton emission from thequark-gluon plasma: some general considerations, Phys. Rev. D 31(1985) 545.http://link.aps.org/abstract/PRD/V31/P545

[Rap13] R. Rapp, Dilepton Spectroscopy of QCD Matter at Collider Energies,Adv. High Energy Phys. 2013 (2013) 148253.http://dx.doi.org/10.1155/2013/148253



http://dx.doi.org/10.1016/0375-9474(94)00500-M

http://link.aps.org/abstract/PRD/V31/P545

http://dx.doi.org/10.1155/2013/148253

Bibliography V

[RCW97] R. Rapp, G. Chanfray, J. Wambach, Rho meson propagation anddilepton enhancement in hot hadronic matter, Nucl. Phys. A617(1997) 472.http://arxiv.org/abs/hep-ph/9702210

[RH14] R. Rapp, H. van Hees, Thermal Dileptons as Fireball Thermometerand Chronometer (2014).http://arxiv.org/abs/1411.4612

[RHH14] R. Rapp, H. van Hees, M. He, Properties of Thermal Photons at RHICand LHC, Nucl. Phys. A 931 (2014) 696.http://dx.doi.org/10.1016/j.nuclphysa.2014.08.008

[RW99] R. Rapp, J. Wambach, Low mass dileptons at the CERN-SPS:Evidence for chiral restoration?, Eur. Phys. J. A 6 (1999) 415.http://dx.doi.org/10.1007/s100500050364

[RW00] R. Rapp, J. Wambach, Chiral symmetry restoration and dileptons inrelativistic heavy-ion collisions, Adv. Nucl. Phys. 25 (2000) 1.http://arxiv.org/abs/hep-ph/9909229


http://arxiv.org/abs/hep-ph/9702210

http://arxiv.org/abs/1411.4612


http://dx.doi.org/10.1007/s100500050364

http://arxiv.org/abs/hep-ph/9909229

Bibliography VI

[TRG04] S. Turbide, R. Rapp, C. Gale, Hadronic production of thermalphotons, Phys. Rev. C 69 (2004) 014903.http://dx.doi.org/10.1103/PhysRevC.69.014903

[UBRW98] M. Urban, M. Buballa, R. Rapp, J. Wambach, Momentumdependence of the pion cloud for ρ mesons in nuclear matter, Nucl.Phys. A 641 (1998) 433.http://dx.doi.org/10.1016/S0375-9474(98)00476-X

[UBRW00] M. Urban, M. Buballa, R. Rapp, J. Wambach, Modifications of the ρmeson from the virtual pion cloud in hot and dense matter, Nucl.Phys. A 673 (2000) 357.http://dx.doi.org/10.1016/S0375-9474(00)00125-1

[UBW02] M. Urban, M. Buballa, J. Wambach, Temperature dependence of ρand a1 meson masses and mixing of vector and axial-vectorcorrelators, Phys. Rev. Lett. 88 (2002) 042002.http://dx.doi.org/10.1103/PhysRevLett.88.042002



http://dx.doi.org/10.1016/S0375-9474(98)00476-X

http://dx.doi.org/10.1016/S0375-9474(00)00125-1

http://dx.doi.org/10.1103/PhysRevLett.88.042002

Bibliography VII

[Zha11] J. Zhao, Dielectron continuum production fromp

sN N = 200 GeVp+p and Au+Au collisions at STAR, J. Phys. G 38 (2011) 124134.http://dx.doi.org/10.1088/0954-3899/38/12/124134


http://dx.doi.org/10.1088/0954-3899/38/12/124134

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