Heavy Ion Physics at NICASimulations

G.Musulmanbekov, V. Toneevand the Physics Group on NICA

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV

Motivation

• The main goal of the NICA experiment is to study the behaviour of nuclear matter in vicinity of the QCD critical endpoint.

• To extract information on the equation-of-state of baryonic matter at high densities.

• Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV

Signatures of Possibile Phase Transition :

o Strange particle enhancement

o Hard spectrum of strange mesons

o Charmonium suppression

o Dielectron mass spectrum enhancement at the range 0.2 – 0.6 GeV/c

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV

Observables :

• Global characteristics of identified hadrons, including strange baryons

• Strange to non-strange particles ratio

• Transverse momentum spectra

• Fluctuations in multiplicity and transverse momenta

• Directed and elliptic flows

• Particle correlations (femtoscopy, HBT correlations)

• Dilepton spectra

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV

Simulation Tools :

• UrQMD 1.3, UrQMD 2.2o 104 central events at 3, 3.8, 5, 7, 9 GeVo 105 min bias events at 3, 3.8, 5, 7, 9 GeV

• FastMCo 104 central events at 3, 5, 7, 9 GeV

• PLUTO

o 106 central events at 3, 5, 7, 9 GeV

Mean multiplicities in Au-Au collisions Simulated by UrQMD min.bias events 

Mean multiplicities in Au-Au collisions Simulated by UrQMD central collisions (b ≤ 3 fm) 

Mean multiplicities in Au-Au collisions Simulated by UrQMD central collisions (b ≤ 3 fm) 

Mean multiplicities in Au-Au collisions Simulated by UrQMD central collisions (b ≤ 3 fm) 

Simulated charged multiplicity distributionsin central collisions (b < 3fm)

Simulated charged pseudorapidity distributions in central collisions (b < 3fm)

Simulated charged pseudorapidity distributions in central collisions (b < 3fm)

MPD-2 < η < 2

Simulated charged pseudorapidity distributions in central collisions (b < 3fm)

MPD-1 < η < 1

Strange Baryons Yield

Table: Marked hyperons are accessible through their decays into charged hadrons

Accessible Hyperons

Mass(GeV/c2) Lifetime cτ (cm) Multiplicity Decay channel

BR(%) Registration efficiency (%)|p| > 0.1 GeV/c

-1 < y < 1

ΛΞ-

Ω-

1.1161.3211.672

7.894.912.46

39.81.210.03

p + π-

Λ + π-

Λ + K-

63.999.967.8

1685

Accessible Hyperons

Λ → pπ- Ξ- → Λπ- → pπ- π- Ω- → ΛK- → pK- π-

Strange to non-Strange ratios in central collisions

“Horn” Effect

<π- >/<π+>Au+Au/Pb+Pb, central

<K+ >/<π+>Au+Au/Pb+Pb, central

Strange to non-Strange ratios in central collisions

“Horn” Effect

Strange to nonStrange ratios in central collisions

Strange to nonStrange ratios in central collisions

Strange to nonStrange ratios in central collisions

Transverse Mass Spectra of Mesonsin central collisions

T

m

dm

dN

mT

TT

exp1

T – inverse slope

Transverse Mass Spectra of Mesonsin central collisions

Transverse Mass Spectra of Mesonsin central collisions

Scaled multiplicity variances

i

ii

N

NN22

ω (h+)

ω (h-)

ω (hch)

Scaled multiplicity variancesNA49 results

NA49 result: Measured scaled variances are close to the Poisson one – close to 1!No sign of increased fluctuations as expected for a freezeout near the critical point of strongly interacting matter was observed.

Transverse momentum fluctuations

To exclude trivial fluctuations from consideration the following variable is used:

For the system of independently emitted particles (no inter-particle correlations) Фpt

goes to zero.

Directed flow v1 & elliptic flow v2

x

zNon-central Au+Au collisions:

Interactions between constituents leads to a pressure gradients => spartial asymmetry is converted in asymmetry in momentum space

=> collective flows

22

22

yx

yx2

T

x1

21TTTT

pp

ppv

p

pv

...)cos(22v)cos(2v12π

1

dpdyp

dN

ddpdyp

dN

- directed flow

- elliptic flowV2>0 indicates in-plane emission of

particlesV2<0 corresponds to out-of-plane

emission (squeeze-out perpendicular to the reaction plane)

Direct flow Au + Au collisions at √sNN = 7GeV, b = 5 – 9 fm

Direct flow slopeCollision Energy Dependence

Au + Au, b = 5 – 9 fm

Elliptic flow Au + Au collisions at √sNN = 7GeV, b = 5 fm

Elliptic flow Collision Energy Dependence

Au+Au/Pb+Pb, b = 5 – 9 fm

Sergey Panitkin

qout

qside

qlong

HBT interferometry

Rsi

de

R long

Rout

x1

x2

12 ppq

p1

p2

q

12 pp2

1k

Two-particle interferometry: p-space separation space-time separation

HBT: Quantum interference between identical particles

pairsevent mixed

pairsevent real

)(P)(P

),(P),(

21

2121

pp

ppppC

2long

2long

2side

2side

2out

2out)(1),(

RqRqRqekkqC

q (GeV/c)q (GeV/c)

C (

q)C

(q)

11

22R

1~

– Final-state effects (Coulomb, strong) also can cause correlations, need to be accounted for

Gaussian model (3-d):

HBT interferometry

)qRqRqRexp(1)q,q,q(C 2S

2S

2O

2O

2L

2LLS0

HBT interferometry

HBT interferometry

Dilepton Spectra

Dilepton Spectra

Dilepton Spectra

Dilepton Spectra

Dilepton Spectra

Conclusions

New simulation codes which take into accountphase transitions of deconfinement and/or chiral symmetry restoration are needed.

Thank you!