Physics with ALICE-PMD
Basanta K. Nandi
IIT Bombay
For PMD collaboration
Photon Multiplicity Detector (PMD) in ALICE
PMD
 Distance from IP : 367 cm
 Approx. 9 sq.m.
 η Covergae : 2.3 to 3.9
2
Photon Multiplicity Detector
 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)
Honeycomb
chamber
(48×96 cells)
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Principle of Photon Multiplicity Detector
Energy deposition in PMD
Hadron
Photon
Edep (a.u.)
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Particle
CPV
PRE
Photon
No
Yes
Ch Hadron
Yes
Yes
Photon Multiplicity Detector
 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 ???
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Charged Particle pseudo-rapidity Density
Au + Au at mid-rapidity
 Particle production mechanism
 Soft process : Nch/γ scales with Npart
200 GeV
130 GeV
19.6 GeV
 Hard process : Nch/γ scales with Ncoll
dNch/d = A x Npart + B x Ncoll
• Hard processes contribution increases with
centrality from ~30% to 50% in the mid-rapidity
 Rapidity distribution of charged particles and photons gives the input
to the theorist to validate their model
Q. What happens at higher energy?
6
Charged Particle pseudo-rapidity Density
Q. What happens in the forward rapidity for photons?
7
Pseudo-rapidity distributions of Photons
900 GeV p+p
7 TeV p+p
ALICE PRELIMINARY


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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.
 Limiting Fragmentation
 Particle production is independent of beam energy near beam rapidity
Q. Is the limiting fragmentation scenario valid for photons?
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Limiting fragmentation (LF) behavior of photons
 Limiting fragmentation behavior of photons seems to be inline with the
earlier measurement.
10
Elliptic Flow
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.
y
py
x
y
x
z
Reaction plane: z-x plane

2
2

y

x


2
2

y

x



p
y

1
v

cos
2
,
tan
(
)
2
p
x







3


d
N
1
d
N
v

cos
2


2
2
E

1

2
v
cos
n







n
RP
3
d
p
2
p
d
d
p
y


t
t
n

1

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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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Charged particle measurement
FMD 1
FMD 2
FMD 3
Outer ing
Inner ring
PMD
Similar Eta acceptance of FMD2I and CPV
 = 2.3
 = 3.5
FMD2i
IP
FMD1
PRE
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CPV
FMD2
o
Beam line
FMD3i Z-axis
FMD3o
Method to determine primary Charged Particles
I.P. @ z = 0
CPV
FMD
X-Y plane @ z = 0
 Principle – Three point straight line tracking
 Necessity – Magnetic Field OFF data
14
Method to determine primary Charged Particles
Y
X
R = √(x2 + y2)
15
Charged particle measurement using CPV
16
Jet Study using PMD ?
p
p
TPC
17
PMD
Physics studies other than PMD
 Fluctuation in mid-rapidity
 K* measurement
 Anti-Nuclei search
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Centrality Dependence of νdyn
10% Centrality Bins
5% Centrality Bins
Measurement of K*
20
Anti-Nuclei Search in ALICE
pp @ 7 TeV
 Approximately 350 M events are analyzed
 Various nuclei are nicely identified in ALICE
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Summary:
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