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X Workshop on Particle Correlation and Femtoscopy 25-29 August, 2014

Higher flow harmonics and ridge effect in PbPb collisions with HYDJET++ model
Czech Technical University in Prague & SINP MSU, Russia V.L. Korotkikh, I.P. Lokhtin, S.V. Petrushanko, A.M. Snigirev SINP MSU

Gyulnara Eyyubova,

Project OPVK CZ.1.07/2.3.00/30.0034

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Outline
HYDJET++ model (hydro + jet) Description of elliptic flow v
2

Triangular flow v3 and higher flow harmonics Dihadron angular correlations Conclusions

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I.Lokhtin, L.Malinina, S.Petrushanko, A.Snigirev, I.Arsene, K.Tywoniuk, Comp. Phys. Comm. 180 (2009) 779

HYDJET++ model

The model combines hard and soft physics. 1. Soft part Hadronization from freez-out surface with distribution function:

p is the hadron energy in the fluid element rest frame, s is strangeness suppression factor
0

2. Hard part Initial parton configuration parton rescattering & energy loss
PYTHIA w/o hadronization



Hadronization
PYTHIA w hadronization

PYQUEN I.P.Lokhtin, A.M.Snigirev, Eur. Phys. J. 45 (2006) 211

Parton collisional loss Radiative loss

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HYDJET++ model
The contribution of soft and hard components into total multiplicity depends on a model parameter: minimal pT of hard process.
I. Lokhtin et al., Eur. Phys. J C72 (2012) 2045

0-5% PbPb collisions at sNN= 2.76 TeV.

The points are ALICE data, histogram dashed is hard component, dotted is soft component of HYDJET++. 4


HYDJET++ model: elliptic flow

Soft part: Space modulation of freeze-out surface; Modulation of liquid velocities on the surface Space asymmetry: Momentum asymmetry:

R(b) is radius of the freeze-out surface

u : azimuthal angle of liquid velocity vector : space azimuthal angle

Parameters (b0), (b0) are tuned to describe experimental data. Hard part: Parton energy loss depends on the path length in the medium: v2(jet) 0
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HYDJET++: triangular flow
Space modulation of the freeze-out surface with independent phase 3 and parameter 3 is introduced in the model:

Particle densities in the transverse plane for v2 and v2+ v3 harmonics.

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HYDJET++ model: flow
Hydrodynamics Jet part +quenching Typical flow pattern

+

Even vn appear in the model because of v Odd vn appear in the model because of v3

2

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HYDJET++ : elliptic flow v
2

The closed circles: ATLAS data (Phys.Rev. C 86, (2012) 014907), vn{EP}, PbPb collisions, 2.76 TeV, open circles: vn{EP} for HYDJET++ , histograms: vn(RP) for HYDJET++ 8

Discrepancy in an intermediate pt region.

L. Bravina et al., Eur. Phys. J C74 (2014) 2807


HYDJET++ : elliptic and quadrangular flow

v4 arising from v2 (w.r.t 2 ) is described well.
In order to describe v4 {4} additional modulation of flow velocity is introduced currently, no independent 4.

L. Bravina et al., Pgys.Rev.C78 (2013) 034901
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HYDJET++ : triangular flow
The simple parametrization: 3 (b ) 01/3 (b )

v

3

The closed circles: ATLAS data (Phys.Rev. C 86, (2012) 014907), vn{EP}, PbPb collisions, 2.76 TeV, 10 open circles: vn{EP} for HYDJET++, histograms: vn(RP) for HYDJET++

L. Bravina et al., Eur. Phys. J C74 (2014) 2807


HYDJET++ : higher order harmonics v
5
L. Bravina et al., Eur. Phys. J C74 (2014) 2807

The closed circles: CMS data vn{EP}, PbPb collisions, 2.76 TeV, open circles: vn{EP} for HYDJET++ ; histograms: vn(RP) for HYDJET++ central collisions the possible presence of the additional pentagonal flow parameter
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HYDJET++ : higher order harmonics v
6
L. Bravina et al., Eur. Phys. J C74 (2014) 2807

The closed circles: CMS data v6{EP}, PbPb collisions, 2.76 TeV, histograms: v6(2) for HYDJET++ ; v6(6) in progress
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V6 also has a contribution from v3 (only contribution from v2 is shown).


Two-plane correlators
2 , 3 are known in the model, 6 is reconstructed with EP method.

Contribution from v3 increases for more central collisions.

Behavior of the plane correlators is in line with the experimental observations.

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Dihadron angular triggered correlations
Signal: correlations of a pair in the same event: Background: correlations of two particles from different events:

Correlation function, definition 1

definition 2

N
CMS, PbPb 2.76TeV arXiv:1107.0032

trig

: number of trigger particles.

Away-side peak from jet is broad on Flow, cos(2)

Short range correlations (small ): hadrons inside jets, clusters, resonances
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Dihadron angular correlation in HYDJET++, PbPb 2.76 TeV
0% centrality 0-5% centrality, v2 only
3
0-5% centrality, v2 & v3

Ridge region, 1D
v2 & v
3

The ridge effect appears in the model because of flow v2 and v3 v3 leads to double-peak structure at away-side on
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Dihadron angular correlation in HYDJET++, PbPb 2.76 TeV
0% centrality 0-5% centrality, v2 only
3
0-5% centrality, v2 & v3

Ridge region, 1D
v2 & v
3

The ridge effect appears in the model because of flow v2 and v3 v3 leads to double-peak structure at away-side on
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HYDJET++ data comparison
Ultra-central collisions, 0-2%

DATA: PLB 708, 249 (2012) ALICE

The ridge is smaller than in data Away-side structure is discribed well

Coefficients V2 , V3 are smaller and V4 , V are negligible compared to data
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HYDJET++ data comparison
Central collisions, 0-5%
EPJC 72 (2012) 2012

EPJC 72 (2012) 2012

Singular particle flow:

v

2

v

3

v

4

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pt assocpt trig .


HYDJET++ data comparison
Mid-central collisions, 30-35%
CMS, EPJC 72 (2012) 2012

Singular particle flows are described well in this region.
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HYDJET++ data comparison
More peripheral collisions, 50-60%
CMS, EPJC 72 (2012) 2012

Coefficients V

2

is much smaller compared to data.
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HYDJET++ data comparison, momentum dependence
Central collisions, 0-5%

Short range correlations, ||<1
flow+non-flow p
t
tr

non-flow (jets)+jet quenching
CMS, JHEP 07 (2011) 076

At 0-5% centrality, HYDJET++ does not reproduce flow harmonics v n (n>2) very well, neither it reproduces dihadron correlations at low pttr. At high pttr HYDJET++ describes data.
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Test of factorization: V

n

vn{2}(pttr)*vn{2}(pta)
)=Vn(p
low

At low pt one neglects non-flow and estimates: vn(p

t

low

t

,p

t

lo w

) ; vn(pt)=Vn(pt ,ptlow) / vn(ptlow)
V3 factorization

V2 factorization

Factorization in HYDJET++ breaks due to hard component (non-flow). Factorization for V2 breaks in data at lower pt compared to HYDJET++.

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Conclusion
Flow in the model: Uncorrelated EbE reaction planes 2 and 3 are introduced, independent on and pt. Multiplicity fluctuation at the same impact parameter flow v2 and v3 fluctuations (no additional fluctuations due to eccentricity fluctuations) Higher flow harmonics appear from v2 and v3 interference in final state (at freeze-out) Data on higher flow harmonics and dihadron angular correlations are described well in mid-central collisions The mechanism of interference of v2 and v3 is not enough to describe data in central collisions

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Backups

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HYDJET++ : quadrangular flow v
4

L. Bravina et al., Eur. Phys. J C74 (2014) 2807
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CMS data, v4{2} -- circles, v4{LYZ} -- squares


Correlation pattern in AA
CMS, PbPb 2.76 TeV, Eur. Phys. C 72 (2012) 10052, Central collisions: The back jet is quenched Small flow v2 ridge Peripheral collisions: Back jet peak Small flow v2 Small ridge ridge Jet region, 2D vs 1D Ridge region 3 assoc

<1.5 GeV/c

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HYDJET++, hard component
Parton collisional loss (high momentum transfer approximation)

t is momentum transfer,E and mp : energy and mass of a hard parton, C is color factor

Radiative loss (coherent gluon radiation in Baier-Dokshitzer-Mueller-Schiff formalism) ­ For massless parton

w is gluon energy

­ For heavy quark (dead cone approximation)

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HYDJET++, hard component
Geometry of QGP
Radial profile of energy density

Jet production vertexes distribution:

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HYDJET++, hard component
Halting the rescattering if: (a) the parton escapes the hot QGP zone, i.e. the temperature in the next point T(i+1, ri+1, i+1) becomes lower than Tc (b) the parton loses so much of energy that its transverse momentum pT (i+1) drops below the average transverse momentum of the "thermal" constituents of the medium.

Three model parameters: initial QGP temperature T0, QGP formation time 0 and number of active quark flavors in QGP Nf (+ minimal pT of hard process Ptmin)

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HYDJET++, soft component
N.S.Amelin, R.Lednisky, T.A.Pocheptsov, I.P.Lokhtin, L.V.Malinina, A.M.Snigirev, Yu.A.Karpenko, Yu.M.Sinyukov, Phys. Rev. C 74 (2006) 064901 N.S.Amelin, R.Lednisky, I.P.Lokhtin, L.V.Malinina, A.M.Snigirev, Yu.A.Karpenko, Yu.M.Sinyukov, I.C.Arsene, L.Bravina, Phys. Rev. C 77 (2008) 014903

Starting point: chemical freeze-out of fireball with the distribution functions in the fluid element rest frame
p is the hadron energy in the fluid element rest frame, s is strangeness suppression factor, quantum statistics is accounted for
0

The mean multiplicity Ni of a hadron species i:

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HYDJET++ data comparison, Integrated yield
CMS data, PAS HIN 11-006

Integrated associated yields in the near-side jet and ridge regions around, minus constant background (ZYAM method).

HYDJET++

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