elliptic flow of meson in pb-pb
DESCRIPTION
Elliptic flow of meson in Pb-Pb. Paola Pagano. Elliptic flow. z. y. x. spectators. The flow is a collective motion of the particles produced in the ultrarelativistic nuclear reaction. . A non central collision produces an anisotropic flow in the transverse plane. participants. - PowerPoint PPT PresentationTRANSCRIPT
09/12/2009 Paola Pagano Università di Salerno & INFN
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Elliptic flow of meson in Pb-Pb
Paola Pagano
09/12/2009 Paola Pagano Università di Salerno & INFN
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Elliptic flow
x
z
y
participants
spectators
spectators
The flow is a collective motion of the particles produced in the ultrarelativistic nuclear reaction. A non central collision produces an anisotropic flowin the transverse plane
The anisotropic transverse flow, i.e. elliptic flow, springs from the initial azimuthal asymmetry of the interaction region
09/12/2009 Paola Pagano Università di Salerno & INFN
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Elliptic flow
b=0
It has origin from the anisotropic nature of the overlap region in the plane x-y with impact parameter b>0
The secondary interaction of particles converts the initial spatial anisotropy in an observed momentum anisotropy in the final state
09/12/2009 Paola Pagano Università di Salerno & INFN
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Elliptic Flow
....2cos2)cos(212)( 2221
0
2
vvNd
dN
Elliptic flow coefficient
x
y
2
Poskanzer and Voloshin, Phys. Rev. C58, 1998
To measure the elliptic flow, we need first to estimate the reaction plane. Then the coefficients of the Fourier
expansion of the azimuthal distribution of particles with respect to the reaction plane are evaluated.
09/12/2009 Paola Pagano Università di Salerno & INFN
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Elliptic flow measurement: recent results at RHIC
2007
To describe the observed scaling, two different models have been
used: •Quark recombination models• Hadronic transport models.
In the context of both models, the observed v2 values seem to
indicate that elliptic flow is built up prior to hadronization, in the
partonic phase.
A scaling of the elliptic flow parameter v2 with the number of quarks is observed
09/12/2009 Paola Pagano Università di Salerno & INFN
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meson’s elliptic flow measurement :
recent results at RHIC (I)
v2 of meson increases with the eccentricity of the central region of overlap (i.e. the reduction of the centrality)
2007
09/12/2009 Paola Pagano Università di Salerno & INFN
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meson’s elliptic flow measurement:
recent results at RHIC (II)-mesons are produced via coalescence of seemingly thermalized quarks in central Au+Au collisions.This observation implies that
hot and dense matter with partonic collectivity
has been formed at RHIC
NQ-scaling fit
phi mesonNQ = 2.3 ± 0.4
2007
09/12/2009 Paola Pagano Università di Salerno & INFN
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How can we perform this measurement in ALICE?
Mass invariant method1) Mass invariant histogram for phi meson
2) Estimation of Signal and Background: fit with Breit-Wigner + polynomial
3) Estimation of reaction plane angle for each event:
wi e i for the l’ith particle of a given event
)2cos(
)2sin(tan
21 1
2ii
ii
w
w
09/12/2009 Paola Pagano Università di Salerno & INFN
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4) Estimate of the opening angle for all K+K- pairs for each event
5) Histogram of v2(minv)= <cos2(KK-2)>
6) Fit of the last histogram with the function:v2(minv) = a(minv)v2S+[1-a(minv)]v2B(minv)
where v2(minv) = <cos2(KK-2)> v2S is the v2 we are looking for v2B is the v2 of combinatorial background
a(minv) = N(minv) / NK+ K_ (minv)
How can we perform this measurement in ALICE?
Mass invariant method (cont’d)
09/12/2009 Paola Pagano Università di Salerno & INFN
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Status of the analysis• The analysis tools are ready.• We are still producing a sufficient number of events Estimation: approximately 106 events.• Two Productions: - one official, managed by the collaboration, for the
production of the background, now I’m generating the signal - one private, containing only the generated particles
without recostruction-> ongoing on the Salerno computer cluster
• The time and space needed to perform this analysis, make essential the use of the world computing Grid facility.
• Here we show some preliminary results for the estimation of: - reaction plane angle - v2 for all particles
09/12/2009 Paola Pagano Università di Salerno & INFN
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Reaction Plane Angle estimation: checking the algorithm
Reconstructed Particles
Generated Particles
)2cos(
)2sin(tan
21 1
2ii
ii
w
w
22/04/23 12
v2 estimation: checking the generator
After the determination of reaction plane angle Ψ2 , it’s possible to build a global distribution dN/d(φ-Ψ2) using events with same multiplicity and centrality. This distribution can be interpolated with the function:
dN/dφ = cost.(1/2π) + 2 v2 cos2(φ-Ψ2)
v2: 0.02794 ± 0.0011
Generated Particles
φ-Ψ2 (degree)
v2: 0.03163 ± 0.0011
Reconstructed Particles
φ-Ψ2 (degree)
09/12/2009 Paola Pagano Università di Salerno & INFN
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The End
Back up
Metodo della matrice di sfericità trasversa (I)
• Diagonalizzazione della matrice di sfericità trasversa
2212
1211
sincossincossincos
SSSS
iiiii
iiiii
02212
1211
SS
SS
Metodo della matrice di sfericità trasversa (II)
24)( 2
122
221122112,1
SSSSS
Il rapporto è proporzionale a v2
Dagli autovettori si ricava l’angolo del piano di reazione 2 :
21
21
111
1221 2
SSATan