Status Report particle identification with the RICH detector Claudia Höhne - GSI Darmstadt, Germany general overview focus on ring radius/ Cherenkov angle resolution Boris Polichtchouk: results from simulation

Claudia Höhne CBM collaboration meeting particle identification with RICH ring finding ring finder: Hough Transform, Elastic Net to be implemented in framework → efficiencies... determination of center and radius of ring/ Cherenkov angle matching of rings with tracks → tracking (momentum and position resolution), information from other detectors pid by combining ring radius and momentum information  detailed knowledge of resolution necessary!

Claudia Höhne CBM collaboration meeting main contribution ! ring radius resolution N 2 radiator Cherenkov angle/ ring radius resolution limited by: multiple scattering magnetic stray field in RICH emission point: particle trajectories do not pass through the center of curvature of the mirror  smeared projection in dependence on ( ,  ) mirror surface: enlargement of focal spot in focal plane due to a deviation of the mirror surface from the ideal spherical curvature pixel size: resolution limited due to finite granularity of photodetector chromatic dispersion investigate single rings! resolution for overlapping rings different!

Claudia Höhne CBM collaboration meeting single photon – ring resolution distinguish between Cherenkov angle resolution for single photons   and the resolution for a ring  R consisting of N measured photons table 1 from RICH-TDR of LHCb: aim at doing a similar study 2% of  c max  single = 2.5mrad

Claudia Höhne CBM collaboration meeting multiple scattering momentum dependent error of form with [T. Ypsilantis, J.Seguinot, NIM A343 (1994) 30, P. Glaessel, NIM A 433 (1999) 17] typical value for a N 2 radiator of 1m and p=1GeV: → for 2.5 m N 2

Claudia Höhne CBM collaboration meeting magnetic stray field momentum dependent error of form with being the particle angle relative to the magnetic field direction → [T. Ypsilantis, J.Seguinot, NIM A343 (1994) 30, P. Glaessel, NIM A 433 (1999) 17]

Claudia Höhne CBM collaboration meeting magnetic stray field (II) gaussian shaped field asymmetric field RICH front wall z=170cm → magnetic stray field (B y ) of order 10mT length L=2.5m at maximum z [cm] By [T]

Claudia Höhne CBM collaboration meeting magnetic stray field (III) momentum dependent error of form with being the particle angle relative to the magnetic field direction → L  2.5m, B  =10mT → p=1GeV → [T. Ypsilantis, J.Seguinot, NIM A343 (1994) 30, P. Glaessel, NIM A 433 (1999) 17]

Claudia Höhne CBM collaboration meeting emission point rings(  ) -  polar angle,  azimuth angle no diffusion at reflection no magnetic field, no multiple scattering to do: quantify and correct for distortions at large  improve focussing/ position of focal plane correct for remaining distortions  = 80 o 60 o 40 o 20 o  = 5 o 10 o 15 o 20 o 25 o 30 o 35 o one quarter of mirror/ photodetector: → restrict investigation of resolution to "good" area in central region and wait for optimized setup

Claudia Höhne CBM collaboration meeting mirror surface Be-mirror prototype: optical surface roughness  h = 1.6nm (after glass polishing, Al covering and SiO 2 coating) → diffuse reflection of only 12% of total for = 150nm image diameter of a point source D 0 = 0.4mm (contains 95% of reflected light) → angular deviation from nominal curvature  R = 0.03mrad resulting radius resolution to be determined Ph.D. thesis of G. Hering (2002), CERES: ring center resolution of same order as local mirror deviation →   < 0.1mrad

Claudia Höhne CBM collaboration meeting pixel size finite granularity of photodetector restricts resolution simple estimate can be made from comparing padsize d and ring radius R / Cherenkov angle  → Boris Polichtchouk d=0.6cmpadsize R=5.5cmring radius L=225cmradiator length

Claudia Höhne CBM collaboration meeting chromatic dispersion [nm]  [mrad] strong increase of n( ) in UV region however, dN/d also increases in UV region and N2:N2: → Boris Polichtchouk [Landolt Boernstein Series, 6 th Edition, volume II/8 Ph.D. thesis of Annick Bideau-Mehu (1982)] N2N2 4mrad   ~2mrad (~0.4cm)

Claudia Höhne CBM collaboration meeting total resolution (I) multiple scattering   ~ 1 mrad (p=1 GeV) magnetic stray field   < 1 mrad (p=1 GeV) emission point   small because of corrections, optimization angular deviation of mirror   < 0.1 mrad chromatic dispersion   > 1 mrad (strongly dependent on min ) pixel size   ~ 1-2 mrad  couple of mrad contributions, independent errors  c =24.4 mrad    ~2-3% of  c

Claudia Höhne CBM collaboration meeting total resolution (II) gaussian distributed Cherenkov angles/ radii → calculate separation power for e and  in terms of   for different   1% 2% 3% 4% 5%

Claudia Höhne CBM collaboration meeting ring – track matching matching: combine track and ring with closest distance ~ 2/3 of all rings from secondary interactions, very often not reconstructed difficulty due to high particle mutiplicities  match ring to track (e.g.  ) which is nearby RR additional source for  -misidentification

Claudia Höhne CBM collaboration meeting pid versus  R 1% momentum resolution 1.3 mrad resolution in azimuth angle 0.8 mrad resolution in deep angle 200  m position resolution in mirror ideal tracking: with of  R –distribution due to method for ring center determination finite tracking: distribution widened cut on  R important for efficiency and purity!

Claudia Höhne CBM collaboration meeting efficiency, misidentification efficiency of e-identification in dependence on a cut on  R  R = 0.8cm: > 95% ideal tracking finite resolution ideal tracking finite resolution  - misidentification in dependence on a cut in  R 35 AGeV: 827  / event   0.3/827 = 4   -misid. (  R = 0.8 cm)  = 6   -misid. (60% acc.)

Claudia Höhne CBM collaboration meeting summary/ outlook particle identification with the RICH detector aim: momentum dependent pid efficiency and purity efficiency: ring finders to come purity: started with detailed analysis of ring radius resolution  for  =3% of  c we have 3  separation between e and  at 13.5 GeV/c  impact on detector layout: granularity of photodetector maximum wavelength range for photodetection purity: extend tracking algorithms for extrapolation of tracks to photodetector plane combine with information from other detectors