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Study of Cherenkov detectors for high
momentum charged particle identification
in ALICE experiment at LHC
Guy Paic
Instituto de Ciencias Nucleares UNAM
For the VHMPID group
New aspects of physics at LHC
• Hard collisions among partons
collisions SPS: 98% soft, il 2% hard;
collisions RHIC
: 50% soft, 50 % hard;
collisions LHC: 2% soft, 98 % hard.
Results of RHIC @ BNL
RHIC measured an increase
of the production of baryons
and antibaryons with respect to
mesons at momenta pT ≈ 2 –
5 GeV/c,
Predictions for LHC
• The results of RHIC are interpreted in the framework of partonic
recombination or coalescence
•The high density of particles favors the recombination of partons in
baryons
• Some predictions for LHC favor
strongly the production of baryons in
a large momentum range pT ≈ 10 –
20 GeV/c (ref. Rudolph C. Hwa, C. B.
Yang, arXiv:nucl-th/0603053 v2 21 Jun
2006)
The detectors of ALICE
TRD
Electron ID,
Tracking
pioni
HMPID
RICH , PID @ high pT
TOF
PID @ intermediate pT
TPC
Main Tracking,
PID with dE/dx
ITS
Vertexing, low pt tracking
and PID with dE/dx
PHOS
g,p0 -ID
pioni
L3
Magnet
B=0.2-0.5 T
MUON
m-ID
+
T0,V0, PMD,FMD and ZDC
Forward rapidity region
THe experiment
Excellent particle identification: ALICE
 ITS + TPC :
 TOF :
 TRD :
 HMPID : (1÷5 GeV/c).
p/K
TPC + ITS
(dE/dx)
K/p
e /p
p/K
TOF
HMPID
(RICH)
TRD
K/p
p/K
0
1
2
3
K/p
4
5 p (GeV/c)
e /p
1
10
100 p (GeV/c)
VHMPID
 At present there is no identification track by track available in ALICE for p > 5
GeV/c
 We are studying 5÷10 GeV/c  VHMPID (Very High Momentum Particle
Identifier Detector).
 We tried several posibilities of designing a Cherenkov counter which will allow
us to obtain an identification from ~10 to ~30 GeV/c for protons
• Aerogel
• Gas Cherenkov in different geometries
Gas choice
• CF4 produces scintillation photons which produce unwanted background (Nph ≈
1200/MeV),
• C4F10 is no more produced because of the ozone hole
• We therefore continue our work with C5F12.
momentum
CF4
Particle Id.
momentum
C4F10
Particle Id.
< 5 GeV/c
0
e
< 3 GeV/c
0
e
5 < p < 16 GeV/c
1
p
3< p < 9 GeV/c
1
p
5 < p < 16 GeV/c
0
K, p
3< p < 9 GeV/c
0
K, p
16 < p < 30 GeV/c
1
p, K
1
p, K
16 < p < 30 GeV/c
0
p
9 < p < 17 GeV/c
9 < p < 17 GeV/c
0
p
> 30 GeV/c
1
p
> 17 GeV/c
1
p
CF4 (n ≈ 1.0005, gth ≈ 31.6)
Impulso
C5F12
Particle Id.
< 2.5 GeV/c
0
e
2.5< p < 8 GeV/c
2.5< p < 8 GeV/c
1
p
0
K, p
8 < p < 15 GeV/c
1
p, K
8 < p < 15 GeV/c
0
p
> 15 GeV/c
1
p
C4F10 (n ≈ 1.0014, gth ≈ 18.9)
C5F12 (n ≈ 1.002, gth ≈ 15.84)
Momentum intervals for
different particles
Setups
TIC (Threshold Imaging
Cherenkov) setup: the
photons are reflected into
the detector of phoptons by
a mirror – the MIP signal is
absent
Proximity-geometry setup: the
signal from the MIP is present.
The gas length is the same in all
positions
Study of the particle identification with
the focusing geometry
information
Radius of
the blob
Photon detector
Number of
pad in the
blob
25
GeV/c
proton
Topology of the blobs in the TIC setup
Nph(b = 1) ≈ (1.4 eV-1cm-1)*(3 eV)*(115 cm) ≈ 480,
3 GeV/c
<N> ≈ 24
15 GeV/c
<N> ≈ 55
Topology of the blobs – proximity focusing setup
Nph(b = 1) ≈ (1.4 eV-1cm-1)*(3 eV)*(180 cm) ≈ 760, MA
<N> ≈ 43
3 GeV/c
15 GeV/c
Diameter of the photon blob
A special algorithm was developed to determine the photon blob
We consider that the radius R is given
by the circle which contains of the
pads registered.
Separation power
Study of background and occupancy in
ALICE
We have simulated a detector inserted in the ALICE simulation
framework with all the other detector present
Interaction
point
• The coordinates in the ALICE reference
system are C(0, 5.04 m, 4 m).
• we simulated 3000 HIJING events;
• B = 0.5 Tesla;
VHMPID box
Particelle cariche totali
<N> ≈ 47
Particelle cariche con impulso
maggiore dell’impulso di
soglia Cherenkov
<N> ≈ 17
Occupancy
Occupancy ≈ 5.8 %
Conclusions I
We abandon the TIC geometry
1. It is difficult to build large size detectors in this geometry
2. The form of the blob depends from the point of imapact
3. the absence of the MIP signal in conditions of large
background as in PbPb collisions at LHC is making the
tracking difficult
ID for a single particle
ID in Pb-Pb events
Conclusion II
• The proximity focusing design is very
sensitive to background and therefore
difficult to identify without substantial
misidentification
Focussing VHMPID
focusing properties of
spherical mirrors
which have been
successfully used in
many RICH detectors
the photons emitted in
the radiator focus in a
plane that is located
at 120cm from the
mirror center. The
spherical mirror radius
is 240 cm, the
hexagon radius is 30
cm, the radiator tank
is 60 x 60 x 120 cm,
Digitization & Detector Response
The simulations include the CsI quantum
efficiency of the photocathode, the gas
transmittance, and the optical characteristics
of the proposed materials. Plus the response
and digitization of the CsI+MWPC photon
detector
Number of detected photons
Occupancy
PID separation
PID
separation
16 GeV/c
24 GeV/c
26 GeV/c
Background
Conclusions III
• The focusing geometry offers a real
possibility to identify the protons in a large
momentum range
• We are working on deatiled pattern
recognition for this setup
• We are working on the photon detector
design and tests using gas electron
multipliers (GEM)