Physics with ALICE-PMD

Basanta K. NandiIIT Bombay

For PMD collaboration

PMDPMD

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Distance from IP : 367 cm Approx. 9 sq.m. η Covergae : 2.3 to 3.9

Photon Multiplicity Detector (PMD) in ALICE

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Honeycomb chamber

(48×96 cells)

Cell depth : 0.5 cm Cell cross-section : 0.23 cm2

Total no. of cells : 220 K Sensitive medium : Gas

(Ar+CO2 in the ratio 70:30)

Photon Multiplicity Detector

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Edep (a.u.)

Energy deposition in PMD

Hadron

Photon

Principle of Photon Multiplicity Detector

Particle CPV PRE

Photon No Yes

Ch Hadron Yes Yes

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PMD measures: - Event-by-event number of photons produced in heavy-ion collisions     - Spatial distribution (x,y) or (,) of photons

Physics Capabilities: - Pseudo-rapidity density - Limiting Fragmentation

- Fluctuation in the ratio of N/Nch in the common coverage of PMD & FMD - Azimuthal anisotropy and event plane determination - Charged particle multiplicity - Jet ???

Photon Multiplicity Detector

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Particle production mechanism

dNch/d = A x Npart + B x Ncoll

19.6 GeV

130 GeV

200 GeV

• Hard processes contribution increases with centrality from ~30% to 50% in the mid-rapidity

Q. What happens at higher energy?

Rapidity distribution of charged particles and photons gives the input to the theorist to validate their model

Hard process : Nch/γ scales with Ncoll

Soft process : Nch/γ scales with Npart

Au + Au at mid-rapidity

Charged Particle pseudo-rapidity Density

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Q. What happens in the forward rapidity for photons?

Charged Particle pseudo-rapidity Density

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At 0.9 TeV Phojet explains the data where as Pythia6D6T and Pythia6ATLAS underpredict.

At 7 TeV both Pythia and Phojet under-predict the data.

Pseudo-rapidity distributions of Photons

900 GeV p+p 7 TeV p+p

ALICE PRELIMINARY

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Limiting Fragmentation

Q. Is the limiting fragmentation scenario valid for photons?

Particle production is independent of beam energy near beam rapidity

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Limiting fragmentation (LF) behavior of photons

Limiting fragmentation behavior of photons seems to be inline with the earlier measurement.

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Flow is a phenomenon seen in nucleus-nucleus collisions, which correlates the momentum distributions of the produced particles with the spatial eccentricity of the overlap region.

azimuthal dependence of the pressure gradient.

Ed3N

d3p

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2dN

ptdptdy1 2vn cos n RP

n1

v2 cos 2 2

xzy

px

pyy

x

y 2 x 2y 2 x 2

v2 cos2 , tan 1(pypx

)Reaction plane: z-x plane

Elliptic Flow

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Event Plane Determination from PMD

PMD event plane determination codes are in the repository for global use

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FMD 1 FMD 3FMD 2

Outer ing

Inner ring

Similar Eta acceptance of FMD2I and CPV

FMD1

FMD2i

FMD2o

FMD3o

FMD3i

IP Z-axisBeam line

= 2.3

= 3.5

PMD

PRE CPV

Charged particle measurement

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CPV

X-Y plane @ z = 0

I.P. @ z = 0

FMD

Principle – Three point straight line tracking

Necessity – Magnetic Field OFF data

Method to determine primary Charged Particles

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X

Y

R = √(x2 + y2)

Method to determine primary Charged Particles

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Charged particle measurement using CPV

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Jet Study using PMD ?

pp

TPC PMD

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Physics studies other than PMD

Fluctuation in mid-rapidity

K* measurement

Anti-Nuclei search

10% Centrality Bins 5% Centrality Bins

Centrality Dependence of νdyn

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Measurement of K*

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Approximately 350 M events are analyzed Various nuclei are nicely identified in ALICE

pp @ 7 TeV

Anti-Nuclei Search in ALICE

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Summary: