1. Instituto de Ciencias Nucleares UNAM
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

2. 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 BNL
RHIC measured an increase of the production of baryons and antibaryons with respect to mesons at momenta pT ≈ 2 – 5 GeV/c,

3. 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/ v2 21 Jun 2006)

4. The detectors of ALICE pioni pioni HMPID RICH , PID @ high pT TRD
Electron ID,
Tracking
pioni
TOF
intermediate pT
TPC
Main Tracking,
PID with dE/dx
MUON
m-ID
ITS
Vertexing, low pt tracking
and PID with dE/dx
PHOS
g,p0 -ID
L3 Magnet
B= T
pioni +
T0,V0, PMD,FMD and ZDC
Forward rapidity region

5. THe experiment ALICE p/K e /p Excellent particle identification:
ITS + TPC :
TOF :
TRD :
HMPID : (1÷5 GeV/c).
p (GeV/c)
TPC + ITS
(dE/dx)
p/K
K/p
e /p
HMPID
(RICH)
TOF
p (GeV/c)
TRD e /p

6. 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

7. Gas choice C4F10 is no more produced because of the ozone hole
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.

8. Momentum intervals for different particles
CF4
Particle Id.
< 5 GeV/c e
5 < p < 16 GeV/c 1 p
K, p
16 < p < 30 GeV/c
p, K
> 30 GeV/c p 1
> 17 GeV/c
p, K
9 < p < 17 GeV/c
K, p
3< p < 9 GeV/c e
< 3 GeV/c
Particle Id.
C4F10
momentum
3< p < 9 GeV/c
9 < p < 17 GeV/c
CF4 (n ≈ , gth ≈ 31.6)
C4F10 (n ≈ , gth ≈ 18.9)
C5F12 (n ≈ 1.002, gth ≈ 15.84) p 1
> 15 GeV/c
p, K
8 < p < 15 GeV/c
K, p
2.5< p < 8 GeV/c e
< 2.5 GeV/c
Particle Id.
C5F12
Impulso
2.5< p < 8 GeV/c
Momentum intervals for different particles
8 < p < 15 GeV/c

9. Setups
Proximity-geometry setup: the signal from the MIP is present. The gas length is the same in all positions
TIC (Threshold Imaging Cherenkov) setup: the photons are reflected into the detector of phoptons by a mirror – the MIP signal is absent

10. Study of the particle identification with the focusing geometry
information
Radius of the blob
Number of pad in the blob
25 GeV/c proton
Photon detector

11. 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
<N> ≈ 55
15 GeV/c

12. Topology of the blobs – proximity focusing setup
Nph(b = 1) ≈ (1.4 eV-1cm-1)*(3 eV)*(180 cm) ≈ 760, MA
15 GeV/c
<N> ≈ 43
3 GeV/c

13. 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.

14. Separation power

15. 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
VHMPID box
The coordinates in the ALICE reference system are C(0, 5.04 m, 4 m).
we simulated HIJING events;
B = 0.5 Tesla;

16. Particelle cariche totali
<N> ≈ 47
Particelle cariche con impulso maggiore dell’impulso di soglia Cherenkov
<N> ≈ 17

17. Occupancy
Occupancy ≈ 5.8 %

18. Conclusions I We abandon the TIC geometry
It is difficult to build large size detectors in this geometry
The form of the blob depends from the point of imapact
the absence of the MIP signal in conditions of large background as in PbPb collisions at LHC is making the tracking difficult

19. ID for a single particle

20. ID in Pb-Pb events

21. Conclusion II
The proximity focusing design is very sensitive to background and therefore difficult to identify without substantial misidentification

22. 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, and the detector 60 x 10 x 2 cm.

23. 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

24. Number of detected photons

25. Occupancy

26. PID separation

27. PID separation
24 GeV/c
16 GeV/c
26 GeV/c

28. Background

29. 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)