Centrality Determination and Reaction plane reconstruction with MPD D.Dryablov, V. Zhezher, M.Kapishin, G.Musulmanbekov XIV GDRE Workshop, Dubna 12 - 14

Centrality Determination and Reaction plane reconstruction with MPD

D.Dryablov, V. Zhezher, M.Kapishin, G.Musulmanbekov

XIV GDRE Workshop, Dubna 12 - 14 December 2012

TopicsMotivation

Event Generators

MPD Layout

Reaction Plane Reconstruction with ExtZDC

Definitions

MC estimation of efficiency of ExtZDC

Determination of Centrality

by TPC

by ExtZDC

Results of RP reconstruction

Plans for the Future


Motivation: Why do we need RP reconstruction?

Physics Tasks at semi-central nucleus-nucleus collisions:

Elliptic Flow of mesons, nucleons and hyperons, hypernuclei

Direct Flow of nucleons, hyperons and hypernuclei

Femtoscopy Correlations w.r.t. RP

Global polarization (w.r.t. RP) of hyperons (Λ, Ξ, Ω)

Vector mesons alightment w.r.t. RP , measured by dilepton yield asymmety

Charge asymmetry w.r.t. RP, CME

Selection ofSemi-central collisions Centrality Determination


Event Generators: UrQMD vs LAQGSM

QGSMUrQMD

UrQMD QGSM


Event Generators

LAQGSM K. Gudima et al. LA-UR-01-6804

• minbias events: 105 for √s = 3, 5, 7, 9, 11 GeV

• semi-central events: 105 for √s = 7 GeV

GLISSANDO – GlauberMC W. Broniowski et al., CPC, 2008

• any statistics at any energy

In prospect:

UrQMD add-on: A. Polanski, G. Musulmanbekov, ISHEPP’2012• residual nucleus• evaporation• multifragmentation


Length of TPC -340 cm, D=300cm

ExtZDCExtZDC

Last MPD layout


“Old” and Extended ZDC

cell 10 x 10 (cm x cm)XIV GDRE Workshop, Dubna 12 - 14 December 2012

Extended ZDC detector


Simulation of Extended ZDC within mpdroot:

• L ≈ 120 cm

• 5 < R < 61 cm (radius of the inscribe circle)

• dcell = 10x10 cm

• z0 = 365 cm (distance from the int. point to ZDC)

• 0.8o < θ < 9.3o (covered zenith angle)

• 2.5 < η < 5.0 (covered pseudorapidity range)

x

yExtZDC

Reaction Plane: Definitions

initial spatial anisotropy anisotropy in momentum spacex

y z

py

px

y 2 x 2

y 2 x 2

v2 px

2 py2

px2 py

2

-/4

y

x

/43/4

-3/4

“In-plane” region

“Out-of-plane” region

Reaction plane defined by (1) beam direction and (2) impact parameter


Definitions: Flows

1-st Fourier harmonics → directed flow

2-nd Fourier harmonics → elliptic flow

))-cos(φ2v +(12πφ Rn∑ totN

d

dN

ψR


Definitions: Reaction Plane reconstruction

Reactio

n plane

x

y

Reactio

n plane

x

y

Σ wi*sin(2i) tan(22) =

Σ wi*cos(2i)

21

Σ wi*sin(i) tan(1) =

Σ wi*cos(i)

plane with the directed moment

plane with the elliptic moment

(wi: 1 or pT)

i

i

ShinIchi Esumi


Method 1:

2222,

,φcos;φsin;

φcos

φsinarctanφ

∑∑

ii

ii

ii

ii

iivis

iivisLR

xy

x

xy

y

E

E

Method 2:

;

∑∑

,

,arctanφ

iivis

iivisLR

xE

yE

Reaction Plane reconstruction with ExtZDC

x

yExtZDC


Problem of identification:directed flows of pions and nucleons have opposite signs !

So are orientations of RPs defined by them!


ΔΨR vs impact parameter

200 GeV

Selection of Semi-Central Events XIV GDRE Workshop, Dubna 12 - 14

December 2012

Reaction Plane Reconstruction

3 GeV

ExtZDC acceptance



5 GeV

ExtZDC acceptance



7 GeV

ExtZDC acceptance



9 GeV

ExtZDC acceptance



11 GeV

ExtZDC acceptance


Selection of events by centrality in TPC

Impact parameter b: 0 - 3 fm 3 – 6 fm 6 – 9 fm 9 – 12 fm

Fraction of σincltot : 0 - 5% 5 – 15% 15 – 30% 30 – 60%

Total multiplicity of charged tracks is a measure of impact parameter b (and centrality of nucleus-nucleus interaction)

Semi-Central Events XIV GDRE Workshop, Dubna 12 - 14

December 2012


LAQGSM Minbias events, √s = 9 GeV




- 5 – 9 fm, semi-central eventsXIV GDRE Workshop, Dubna 12 - 14

December 2012

Selection of centrality: Nparticipants

GlauberMC Minbias events, √s = 9 GeV


December 2012

Selection of events by centrality in ExtZDC



December 2012







December 2012

RP reconstruction by Extended ZDC detector

• No particle identification

• Geant 4 , QGSP_BIC physics model

• Systematic effect of magnetic field:

~1o at 9 AGeV increases to

~3o at 3 AGeV

x

yExtZDC

∑∑

,

,arctanφ

iivis

iivisLR

xE

yE


Resolution δφRP and <cos δφRP> vs b

M. Kapishin 2012

RP reconstruction by Extended ZDC detector


• Extended ZDC detector (2.2<η<4.8) provides RP measurement at medium b (4<b<10 fm) with resolution of δφRP~22-35o in AuAu collisions at energies 5-9 AGeV, RP resolution deteriorates to δφRP~45-65o at 3 AGeV

• Sensitivity of extended ZDC to RP azimuthal angle in central (b<3 fm) and peripheral collisions (b>12 fm) is much weaker

• QGSM and UrQMD models give consistent results for RP resolution of extended ZDC, model dependence increases at low beam energies

• ZDC cell size and length is not critical: dcell=10x10cm, L=60cm are sufficient for RP measurement. ZDC length is more crucial for energy flow measurement

• Magnetic field systematics to φRP is ~1o at 9 AGeV which increases to ~3o at 3 AGeV. Reduced magnetic field at the lowest energy would decrease systematics

Summary

M. Kapishin 2012


7 GeV

Protons + neutrons +pionsprotons + neutrons

7 GeV

no particle identification

RP reconstruction by MC in Extended ZDC acceptance

7 GeV

<Δψ1> = 34o<Δψ1> = 33.8o R = 0.83 R = 0.83

RP resolution, R = <cos(Δψ1)>


Dependence of RP resolution on size of Extended ZDC


Protons + neutrons

Dependence of RP resolution on size of Extended ZDC


Protons + neutrons+pions

Plans for RP reconstruction:

1. Include ExtZDC channel-by-channel Eloss in DST,

2. Estimate the resolutions needed for the physical tasks.


Thank You!


Reaction plane resolution vs. numbers of particle and value of the flow


Documents

Centrality Determination and Reaction plane reconstruction with MPD D.Dryablov, V. Zhezher, M.Kapishin, G.Musulmanbekov XIV GDRE Workshop, Dubna 12 - 14