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

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 pioni pioni HMPID RICH , PID @ high pT TRD Electron ID, Tracking pioni TOF PID @ 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=0.2-0.5 T pioni + T0,V0, PMD,FMD and ZDC Forward rapidity region

THe experiment ALICE p/K e /p Excellent particle identification: ITS + TPC : TOF : TRD : HMPID : (1÷5 GeV/c). 0 1 2 3 4 5 p (GeV/c) TPC + ITS (dE/dx) p/K K/p e /p HMPID (RICH) TOF 1 10 100 p (GeV/c) TRD e /p

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 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.

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 ≈ 1.0005, gth ≈ 31.6) C4F10 (n ≈ 1.0014, 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

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

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

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

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

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 VHMPID box The coordinates in the ALICE reference system are C(0, 5.04 m, 4 m). we simulated 3000 HIJING events; B = 0.5 Tesla;

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 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

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, and the detector 60 x 10 x 2 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 24 GeV/c 16 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)