A RICH detector for CLAS12 CLAS12 European Workshop February 25-28, Genova, Italy Evaristo Cisbani INFN Rome and ISS Patrizia Rossi INFN- Laboratori Nazionali di Frascati Hall B Central Detector Forward Detector

Hadron PID in CLAS12 Baseline GeV/c  /K TOF LTCC HTCC  /p TOF LTCC HTCC K/p TOF LTCC  / K PID rely on LTCC performance in 3-5 GeV/c No K/p PID in 5-8 GeV/c  Ratio K/  ~  If we assume a 10%  inefficiency for Cerenkov  rejection factor  /k ~1:1 RICH detector

r L 22  (deg) r(cm) = Ltan   K p P = 2 GeV/c L= 1m n=1.28 (liquid freon) Good separation  /K/p

Which RICH? Liquid Radiator (Freon) –May cover up to 5 GeV/c –Relatively inexpensive (proximity focusing RICH) Aerogel + Gas Radiators –May cover up to 10 GeV/c –Very expensive (cost Aerogel RICH ~ 5x Proximity Focusing RICH)

Location of the RICH Replace part of LTCC: -No impact on baseline design -Nobody will probably complain -Large space available (and to be covered!) Replace HTCC: -Impact on baseline design -Impact on tracking recontruction Simulation done for LTCC

LTCC sector ~ 6.2 m 2 entrance window 1 m depth

A proximity Focusing RICH (~1 m 2 surface) is working in Hall A and being used in the Transversity experiment Same RICH type used by ALICE experiment ( ~10 m 2 surface) Hall A Proximity RICH

Proximity Focusing RICH The Proximity Focusing RICH consists of 3 basic components: Cherenkov Liquid Radiator The Radiator must be in a container (vessel) with UV transparent window (QUARTZ window) The Photon Detector must detect and localize the photon that hits on a given surface: we assume a “pads like” detector Gap (gas filled space) Photon Detector

Hall A Proximity RICH The Freon vessel (radiator) is the most fragile component of the detector The Freon pressure is partially compensated by the glued spacers Quarz planarity and parallelism 0.1 mm Evaporation facility CsI is evaporated on the pad panel in the evaporation chamber: 120h x 110r cm 2 (vacuum mbar) The evaporation facility - cost ~ 0.5 M$ has been built by the INFN Rome group (now at Stony Brook University)

Hall A RICH: QE measurements (July ‘08) 25 ~ 25% Quantum Efficiency has been measured

 K/  rejection ~ 1/1000 F. Garibaldi et al. NIM A502 (2003) Hall A RICH in Hypernuclear Exp. ( )

Estimate the optimal radiator thickness – Larger the thickness, higher the number of photons, higher the uncertainties on photon emission – Larger the thickness more challenging is the vessel technology (and more expensive the system) Estimate the optimal Gap length – Larger the gap, better the ‘focusing’, but larger must be the detection plane Monte Carlo studies: purpose

 Old GEANT3/Fortran/PAW based MonteCarlo framework the same used the for the development of the Hall A Proximity RICH but with different geometry and size!  Charged particles phase space at the LTCC-RICH entrance window assumed uniformly distributed with +/- 10 degree divergence  Use arcs as radiator and detector geometries (see next)  Limitation on photon production (~3000) old memory constraint. This becomes relevant for radiator thickness > cm Main output parameter:  k  = mean error on Cherenkov angle reconstruction of k and  Monte Carlo studies: framework CC CKCK    K-  = (  K +   )/2

Working Point Assume: Two radiators (only 1 simulated); one per sector Detector span up to 2 sectors (detect photons from both radiators) Radiator Polar acceptance: 5° ÷ 30°  fix radiator size ~ 4 m 2 Max gap length = 80 cm Not to scale Unit: mm and degree

Particles uniformely distributed in the phase space Black dots are charged particle positions at RICH entrance (the envelope is the radiator) Contour lines are positions at the detector level of all photons generated in the radiator The large arc is the detector surface (photons out of there are not detected) Geometry is rotated respect to the previous drawing … but represent basically the same idea Monte Carlo Result: Example x/y are not to scale

Points: MonteCarlo, Curves: analytical functions ~ 1 mr difference  C 5 F 12 mandatory! Geometry from the previous example Radiator Type C 5 F 12 C 6 F 14 CC CC   nn

Simulation with realistic phase space To detemine the best photon detector size, ,K,p have been generated at the LTCC-RICH entrance window according with a realistic phase space distribution of reconstructed momenta and angles. (GeV/c)

K-  Separation Radiator= 2 cmRadiator= 1.5 cmRadiator= 3 cm Radiator Thickness = 1.5, 2, 2.5, 3, 3.5 cm Gap length = 80 cm Pad/Pixel size = 0.75 cm Angle reconstruction error vs: 100k events

K-  Separation Radiator Thickness = 2 cm Gap length = 60, 80 cm Pad/Pixel size = 0.75 cm Gap Length= 60 cm Gap Length= 80 cm Separation at 5 GeV/c: 3  = 1/100 / 75% efficiency 1/10 / 95% efficiency Angle reconstruction error vs: 100k events

Radiation thickness Thickness (cm)X 0 (%) Entrance window Al Rohacell5152 Al Radiator Neoceram0.43 C 5 F Quartz0.54 Gap CH Photon Detector Pad NEMAG GEM chamber10.6 Total radiation thickness of the proposed RICH: ~20% X 0

Phenix Replace MWPC with GEM Chamber  faster,  higher gain,  stability at high rate Photon Detector

Hall A RICHFactorClass12 RICH Readout (15%) MWPC: Pads Planes (8%) MWPC: Parts (Macor Insulator) (6%) Freon (C6F14) (33%) Quartz+Neoceram (24%) Mechanical Structure (12%) Evaporation Fac (exist) Freon Recirculation System20 (?)1.530 (?) Total Class12/Hall A Radiator:36-48 (min.-max. volume), 24 (surface) Detector:13 (surface), 4 (chs) GEM ~ 1.2 x MWPC k$ (estimation from Lire, CHF, $ and Euro) Costs - Very Preliminary!!

Monte Carlo simulations have been started to study the feasibility to replace 2 sectors of LTTC with a proximity focusing RICH detector From very preliminary results it seems that:  The best choice is to use Freon C 5 F 12 but it must be cooled! (it evaporate at 29 C at STP !!)  At present stage the Cherenkov angle resolution is not impressive  a careful analysis and design is required to improve both the performance and the detector size  orientation of radiator  pad size  …  work is in progress Conclusions and outlook

K-  Separation_old Radiator Thickness = 3 cm Gap length = 80 cm Pad/Pixel size = 0.75 cm Angle reconstruction error vs: 10K generated events

Approved Experiments requiring a RICH PR Studies of partonic distributionsusing semi-inclusive production of kaons. PR – Studies of the Boer-Mulders Asymmetry in Kaon Electroproduction with Hydrogen and Deuterium Targets. PR Studies of Spin-Orbit Correlations in Kaon Electroproduction in DIS whit polarized hydrogen and deuterium targets.

Optimal combination: Freon Thickness ~ 3 cm GAP Length ~ 80 cm PAD size < 1 cm C 5 F 12 Single sector radiator 2 sectors photon detector (26 m 2 ) Angle reconstruction error vs: Radiator Thickness, Gap length Pad/Pixel size Radiator Thickness / Proximity GAP  Note: MC statistics is poor! CC CC KK KK

The drawings inside the plot represent different detector sizes simulated Black dots: represent the black arc at different external radius Red triangle: corresponds to the red single sector Blue square: corresponds to the blue single sector with optimal external radius Green Triangle: Optimal sector (± 45 degree) and external radius Photon Detector Size

K-  Separation 80_1.5 80_280_2.5 80_3 80_3.5

K-  Separation Separation at 5 GeV/c: best case (green): 1:100 / 90% worst case (black):1:100 / 75%