CBM RICH detector Serguei Sadovsky for CBM RICH team (GSI, IHEP, INR, LIT, PNPI, PNU) CBM RICH meeting GSI, 06 March 2006 B M C Outline Physics motivation Conceptual design of RICH Radiator gases Mirrors Photo-detector plane PMT FEU-Hive Simulation and reconstruction Conclusion B M C Diagnostic probes of compressed baryonic matter and CBM experiment U+U 23 AGeV B M C TOF PID Simulations, UrQMD central Au + Au at 25 AGeV 160 p, 400 -, 400 +, 44 K +, 13 K -,.... TOF: GEANT4 with B-field, geometry and material time resolution 80 ps, 10 m distance Particle identifications with TOF & RICH K p e RICH PID N2N2 complement each other B M C The major CBM physics topics and RICH: In-medium modifications of hadrons onset of chiral symmetry restoration at high B measure: , , e + e - RICH open charm (D mesons) Strangeness in matter production and propagation of strange particles measure: K, , , , RICH can help Indications for deconfinement at high B production and propagation of charm measure: J/ e + e - RICH D 0 K - + RICH can help Critical point event-by-event fluctuations RICH can help discontinuities in ratios and slopes of K mesons Soft electron-positron pairs RICH B M C , , e+e-, electron identification D.Adamova et al., PRL 91 (2003) Dominant background: 0 -Dalitz decay and gamma conversion. CERES 2000: 159 AGeV Pb+Au beam intensity: 10 6 ions / spill 1 spill = 4 s beam and 15 s pause targets: 13 x 25 m Au ( ~ 1 % interaction) trigger: 8% most central Event rate = 470 / spill (~ 25 Hz = 15 Mio events/week) Important: identification of soft electrons/positrons ! B M C J/ reconstruction with RICH, cut PS < -1.5 Signal + background Invariant mass spectrum with cuts Pt>1GeV/c && PS1GeV/c && PS electrons < -1.5 cutsS/BJ/ eff Pt 10 3 (factor 10 4 is needed for the combine RICH and TRD performance) Good electron identification efficiency, > 95% K/ separation for momenta above 5-6 GeV/c Large acceptance ( 25 o ) B M C CBM RICH Concepts: 2.2-m long chemically passive gas radiator at atmospheric pressure, thr = Two identical walls of the hexagon or trapezoid spherical mirros, R = 4500 mm Two photo-detector planes with aperture 3x0.6 m 2 each on the base of PMT FEU-Hive with WLS films or CsJ UV detectors Gas vessel with vacuum beam pipe in the center, maximal length along the beam is 3 m Overall material budget X 0 =3-4% to reduce secondaries and multiple scattering B M C N 2 60% N 2 +40%CH 4 CH 4 CO 2 n th p ,th 5.72 GeV/c5.25 GeV/c 4.69 GeV/c 4.65 GeV/c c o 1.53 o 1.70 o 1.72 o X m386 m650 m 183 m Radiator gases, properties B M C [Y.Tomkiewicz and E.L.Garwin, NIM V114 (1974) pp ][L.Fabbietti for HADES, NIM A 502 (2003) 256] Radiator gases, transmittances N2N2 B M C Chromatic dispersions for different gases Radiator gases, chromatic dispersions Wavelength dependence of the Cherenkov openig angle for different gases B M C Absorption spectra for water, oxygen and CO 2 N2N2 CO 2 B M C Mirrors, optical scheme of CBM RICH VerticalHorizontal S=3.5x4.5 m 2, R=4500 mm B M C Upper wall of the mirrors in terms of hexagons, aperture 4.5x1.75 m 2 B M C Mirror reflectivity in dependence on photon wave length: The optical surface roughness h of mirror is 1.6 nm Total reflectivity R 0 of mirrors with Al coverage is 92% Specular reflectivity R sp = R 0 exp(-4/) and defuse reflectivity R df =R 0 - R sp A.Braen & M.Kostrikov, Preprint IHEP Measurements B M C CBM RICH, hexagon mirrors Hexagon effects (large mirrors and small radius, R=4500 mm): Lack of exact geometrical description -> impossible to divide a goal spherical surface into hexagons exactly, one can only to approximate manually the surface by hexagons with irregular gaps between them (0.5-12mm); the technological gaps between mirrors is of the order of 3mm Completion efficiency of the surface by hexagons is ~ 96%; Cutting of hexagons (if necessary) to fit a line between 2 mirror walls and to fit other sides of the goal surface. ~ 94 hexagon units B M C CBM RICH, trapezoid mirrors The main idea latitude/longitude division: the division of the goal spherical surface into units has the precise geometrical description; minimal gaps between mirror units, the only technological gaps of 3 mm are needed; the only 2 variants of the unit dimensions, the length of side is about 450 mm; no fitting cuts for units. 72 trapezoid units B M C COMPASS RICH support structure Two spherical nets of the Al triangles connected by means of strings to the support frame as the prototype of the CBM RICH mirror support structure B M C Option of the mirror support based on carbon structures B M C Calculation of the mirror deformations The possible schema of the CBM mirror wall design, hexagon option B M C Beryllium mirror substrate 4 mm thickness rotated to 9 degrees around horizontal axe Deviation ~0.15m Deviation ~1.4m B M C Glass mirror 4 mm thickness rotated to 9 degrees around horizontal axe Deviation ~0.8m Deviation ~7m B M C Glass mirror 4 mm thickness rotated to 9 degrees around horizontal axe (rectangular 470470 mm) Deviation ~2m Deviation ~14m Vladimir Khmelnikov B M C Gravitational surface displacement for different mirrors: Mirror substrate Rotation +3Rotation +9Rotation -9 topbottomtopbottomtopbottom Beryllium hexagonal 500 mm 4mm thickness 0.35m0.89m0.15m1.4m-- Glass hexagonal 500 mm 4mm thickness 1.8m4.5m0.8m7.0m 0.8m Glass hexagonal 500 mm 3mm thickness 3.0m6.5m0.9m10.0m-- Glass rectangular 470 470 mm 4mm thickness --~2m ~ 14m -- are these displacements large? B M C CBM mirrors, discussion Shapes and materials: two mirror shapes are under consideration, i.e. hexagons and trapezoid, we have to chose the best to give inputs for engineering design of the mirror support structure several options of the mirror material/technology are now considered, i.e. Be, Glass, Floating glass mirrors, Carbon, we have to chose the base lines Mirror R & D: Float glasses: Company FLABEG GmbH & Co. KG, Technical Glass Products (made the first set of mirrors for HADES) standard size 580mm x 580mm could then be cut down to any shape standard thickness 2 mm (1.6% X 0 ), minimum probably 1.3 mm (1.04% X 0 ) Al+MgF 2 coating for high reflectivity in the UV (small shadowing effects in4 edges), wavelength and angle dependent reflection have to be measured Be-mirrors: LTD Company Compozit, Moscow, D=400mm, t=4mm, price 15 kE Glass mirrors: St.Peterburg company, negotiations, D=540mm, t=4mm, preliminary price kEuro Carbon mirrors ? B M C UrQMD PLUTO RICH photo-detector plane, aperture optimization B M C Photo-detector plane on the base of small diameter PMTs N PMT =(3n-2)(n-1)+2n-1 n=12 D = 7x(2n-1) mm d = 7xn mm 84 mm 161 mm PMT FEU-Hive Hexagonal packing of the small diameter PMTs, D=7mm B M C Small diameter PMT, conception: Schema of the small diameter PMT FEU-Hive (7 mm) with glass cathode window B M C Improvement of the light collection efficiency B M C PMT FEU-Hive, the first samples: B M C PMT FEU-Hive, the first signals from LED source: FEU-115FEU-Hive B M C #1 #2 waiting External PMT diameter, mm Photo-cathode diameter, mm PMT length is, mm 80 Photo-cathode: K 2 CsSb Quantum efficiency, 410 nm, % Effective number of dynodes 12 Nominal HV, kV Amplification Dynamical charge range, pC Noise current is, e/sec 3000 Capacitance, pF 15 Power dissipation, mW 40 Price, Euro/PMT Parameters of the PMT FEU-Hive: B M C RICH photo-detector options, discussion: PMT FEU-Hive is one of the options, R&D is in progress CsI photo-detector is another promising option, see table Hamamatsu H8500 ? GEM like detectors ? Something else ? RadiatorPhotodetector N 0 [cm-1]N hits /ring (e-) N 2 Protvino PMT CsI Hamamatsu (H8500) CO 2 Protvino PMT B M C RICH simulation CbmDetector CbmMCPointCbmHit CbmTask CbmRich CbmRichPoint CbmRichHit CbmRichHitProducer CbmRichMirrorPoint CbmRichRingGuidanceProducer CbmRichRing CbmRichRingFinder CbmRichRingGuidances TObject B M C RICH in CBMroot B M C RICH geometry macro with simple ASCII file input for fast calculation of new geometries (geometry/create_RICH_geo_file.C, geometry/RICH_readme.txt) e.g. easily change tilting angles of mirror, photodetector... optimize optical layout of RICH detector B M C Test macro for simulation test macro in macro/rich CbmRichTestSim.C output of relevant information (ps-file, A4) in order to check whether the simulation is ok B M C Be-mirror wall, optics simulation Rings( ) - polar angle, azimuth angle no diffusion at reflection no magnetic field, no multiple scattering Simulation result: Optics distortions (eccentricity) for large To do: improve optics of the mirror walls / focussing position of focal planes = 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: Claudia Hhne B M C Systematic in ring radius reconstruction for ideal mirrors B M C Single particle response in terms of the PMT number, N PMT N2N2 50%N 2 +50%CH 4 B M C Single particle response, ring radii 50%N 2 +50%CH 4 N 2 after correctionN2N2 B M C RICH simulations: ring radius resolution vs lower limit of the UV photon region We have no reason to go in the UV region below 150 nm B M C RICH simulations: ring radius resolution vs PMT radius Taking into account effect of chromatic distortion the PMT diameter of 6-7 mm is close to the optimal B M C RICH ring recognition algorithm was elaborated. It starts from the coarse histogramming of source data. Then all areas corresponding to separate or overlapped rings are found by clustering. A fragment of this histogram is shown here. One can see that clustering splits this frgment into three areas corresponding to one or two overlapped rings RICH simulation, RICH ring finder Gennadi Ososkov and Co B M C Ring centers and radii are found by 2D Hough transfom (HT). It is done by calculating centers {xc, yc} and radii of circles drawn through every possible triplet of points from the selected group. Each time distances between points and obtained radii of a triplet are tested to be within prescribed limits. A fragment of HT histogram for ring centers. Two maxima are seen corresponding to two rig centers. RICH simulation, RICH ring finder (2) B M C 1. Ring fitting. Problem of nonlinearity However, due to the obvious relation: M(a,b,R)~ 4R 2 L(a,b,R), it fails for cases when hits are forming a circular arc as it shown here Thus the minimization of L(a,b,R) is equivalent to minimizing M(a,b,R)/ 4R2, which can be realized as the very fast algorithm named as COP (Chernov- Ososkov-Pratt, see CPC v. 33, ). B M C 2. Ring fitting. Robustness aspect Robust fitting approach consists in providing every point by a functional weight, which depends on the distance e of this point from the fitted circle. It can be shown that optimal weights Robust version of COP with Tukeys functional weights implemented by Sasha Airiyan faster than MINUIT version on the order of magnitude. The remarkable stability of robust fit allows to use it in TB finders directly instead of conventional radius histograming. e p [GeV/c] radius [cm] After their approximation by the 4th order polynomial one obtains famous Tukey bi-square weights: B M C Efficiency for electrons. Normalize to MC data Number of true and MC rings ( with >=10 hits and track projection on photodetector plane) vs momentum. Elastic net Hough transform Mean efficiency: Hough transform 83% Elastic net 60% Efficiency for electrons (with >=10 hits and track projection on photodetector Plane) vs momentum. Ring reconstruction soft is in a fast development B M C Conclusion We have presented the status of CBM RICH The aim of talk is only an introduction for discussion Any critical remarks, comments, objections and proposals will be greatly appriciated