Proximity Focusing RICH Detector Simulation for CLAS12 Experiment

1. Hall B Central Detector Forward Detector A RICH detector for CLAS12 Evaristo Cisbani INFN Rome and ISS Patrizia Rossi INFN- Laboratori Nazionali di Frascati CLAS12 European Workshop February 25-28, 2009- Genova, Italy

2. Ratio K/ ~ 0.1-0.15 • If we assume a 10%  inefficiency for Cerenkov rejection factor /k ~1:1 RICH detector Hadron PID in CLAS12 Baseline • p/K PID rely on LTCC performance in 3-5 GeV/c • No K/p PID in 5-8 GeV/c

3. 2 L RICH detector r P = 2 GeV/c L= 1m n=1.28 (liquid freon) Good separation /K/p

4. 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)

5. 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 Location of the RICH

6. 1 m depth ~ 6.2 m2 entrance window LTCC sector

7. Hall A Proximity RICH • A proximity Focusing RICH (~1 m2 surface) is working in Hall A and being used in the Transversity experiment • Same RICH type used by ALICE experiment ( ~10 m2 surface)

8. Cherenkov Liquid Radiator Gap (gas filled space) Photon Detector Proximity Focusing RICH The Proximity Focusing RICH consists of 3 basic components: 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

9. Evaporation facility • CsI is evaporated on the pad panel in • the evaporation chamber: 120h x 110r • cm2 (vacuum 10-7 mbar) • The evaporation facility - cost ~ 0.5 M$ has been built by the INFN Rome group (now at Stony Brook University) • 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 Hall A Proximity RICH

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

11. Hall A RICH in Hypernuclear Exp. (2003-2005)  K/p rejection ~ 1/1000 F. Garibaldi et al. NIM A502 (2003)

12. Monte Carlo studies: purpose • 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

13. Monte Carlo studies: framework • 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 > 2.5-3.0 cm Main output parameter: skp= mean error on Cherenkov angle reconstruction of k and p   K-= (K+ )/2 CK C

14. Working Point Not to scale Unit: mm and degree • 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 m2 • Max gap length = 80 cm

15. Monte Carlo Result: Example • 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 x/y are not to scale

16. n   C C Geometry from the previous example Radiator Type C5F12 C6F14 ~ 1 mr difference  C5F12 mandatory! Points: MonteCarlo, Curves: analytical functions

17. (GeV/c) 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.

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

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

20. Radiation thickness Total radiation thickness of the proposed RICH: ~20% X0

21. Photon Detector • Replace MWPC with GEM Chamber • faster, • higher gain, • stability at high rate HBD @ Phenix

22. Costs - Very Preliminary!! Class12/Hall A Radiator: 36-48 (min.-max. volume), 24 (surface) Detector: 13 (surface), 4 (chs) k$ (estimation from Lire, CHF, $ and Euro) GEM ~ 1.2 x MWPC

23. Conclusions and outlook • 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 C5F12 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