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CBM RICH detector

CBM RICH detector. Serguei Sadovsky for CBM RICH team (GSI, IHEP, INR, LIT, PNPI, PNU) CBM RICH meeting GSI, 06 March 2006. Outline. Physics motivation Conceptual design of RICH Radiator gases Mirrors Photo-detector plane PMT FEU-Hive Simulation and reconstruction Conclusion.

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CBM RICH detector

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  1. CBM RICH detector Serguei Sadovsky for CBM RICH team (GSI, IHEP, INR, LIT, PNPI, PNU) CBM RICH meeting GSI, 06 March 2006

  2. Outline • Physics motivation • Conceptual design of RICH • Radiator gases • Mirrors • Photo-detector plane • PMT FEU-Hive • Simulation and reconstruction • Conclusion

  3. Diagnostic probes of compressed baryonic matter and CBM experiment U+U 23 AGeV

  4. Particle identifications with TOF & RICH 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 TOF PID RICH PID N2 e μ p π π K complement each other

  5. The major CBM physics topics and RICH:  Soft electron-positron pairs  RICH  In-medium modifications of hadrons onset of chiral symmetry restorationat 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 D0 K-+  RICH can help  Critical point event-by-event fluctuations  RICH can help discontinuities in ratios and slopes of K mesons

  6. ρ,ω, φ e+e-, electron identification Dominant background: π0-Dalitz decay and gamma conversion. Important: identification of soft electrons/positrons ! D.Adamova et al., PRL 91 (2003) 042301 CERES 2000: 159 AGeV Pb+Au beam intensity: 106 ions / spill 1 spill = 4 s beam and 15 s pause targets: 13 x 25 μm Au ( ~ 1 % interaction) trigger: 8% most central Event rate = 470 / spill (~ 25 Hz = 15 Mio events/week)

  7. J/Ψreconstruction with RICH,cut PS < -1.5 J/ Ψ transverse momentum vs rapidity PSelectrons < -1.5 Pt>1GeV/c && Signal + background Invariant mass spectrum with cuts Pt>1GeV/c && PS<-1.5 Alla Maevskaia INR RAS Moscow CBM collaboration meeting 2 March 2006

  8. Discontinuities in ratios and slopes of K mesons Central Au+Au and Pb+Pb collisions: AGS, CERN-NA49, RHIC onset of phase transition at 30 AGeV ?

  9. Strangeness/pion ratios versus beam energy C. Blume et al., nucl-ex/0409008

  10. Fluctuations from NA49 nucl-ex/0403035 • dynamical fluctuations reported by NA49 • increase towards low energies • K/ : not reproduced by UrQMD • p/ : correlation due to resonance decays

  11. Requirements to the performance of RICH detector in CBM experiment: • Electron identification for momenta p  12 GeV/c • High -rejection power, i.e. > 103 (factor 104is needed for the combine RICH and TRD performance) • Good electron identification efficiency, ε > 95% • K/ separation for momenta above 5-6 GeV/c • Large acceptance ( 25o)

  12. CBM RICH Concepts: • 2.2-m long chemically passivegas radiator at atmospheric pressure, γthr = 33- 41 • Two identical walls of the hexagon or trapezoid spherical mirros, R = 4500 mm • Two photo-detector planeswith aperture 3x0.6 m2 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 budgetX0=3-4%to reduce secondaries and multiple scattering

  13. Radiator gases, properties N2 60% N2+40%CH4 CH4CO2 n 1.000298 1.000356 1.000444 1.000450 gth41 37.5 33.6 33.3 pp,th5.72 GeV/c 5.25 GeV/c 4.69 GeV/c 4.65 GeV/c Qc1.398o 1.53o 1.70o1.72o X0304 m 386 m 650 m 183 m

  14. Radiator gases, transmittances N2 [Y.Tomkiewicz and E.L.Garwin, NIM V114 (1974) pp. 413-416] [L.Fabbietti for HADES, NIM A 502 (2003) 256]

  15. Radiator gases, chromatic dispersions Wavelength dependence of the Cherenkov openig angle for different gases Chromatic dispersions for different gases

  16. Absorption spectra for water, oxygen and CO2 N2 CO2

  17. Mirrors, optical scheme of CBM RICH Vertical Horizontal S=3.5x4.5 m2, R=4500 mm

  18. Upper wall of the mirrors in terms of hexagons, aperture 4.5x1.75 m2

  19. Mirror reflectivity in dependence on photon wave length: • The optical surface roughness σh of mirror is 1.6 nm • Total reflectivity R0 of mirrors with Al coverage is 92% • Specular reflectivity Rsp = R0exp(-4תσ/λ) and defuse reflectivity Rdf =R0- Rsp Measurements A.Braen & M.Kostrikov, Preprint IHEP 93-129

  20. 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 wallsand to fit other sides of the goal surface. ~ 94 hexagon units

  21. 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

  22. COMPASS RICH support structure as the prototype of the CBM RICH mirror support structure • Two spherical nets of the Al triangles connected by means of strings to the support frame

  23. Option of the mirror support based on carbon structures

  24. Calculation of the mirror deformations The possible schema of the CBM mirror wall design, hexagon option

  25. Beryllium mirror substrate 4 mm thickness rotated to 9 degrees around horizontal axe Deviation ~0.15µm Deviation ~1.4µm

  26. Glass mirror 4 mm thickness rotated to 9 degrees around horizontal axe Deviation ~0.8µm Deviation ~7µm

  27. Glass mirror 4 mm thickness rotated to 9 degrees around horizontal axe (rectangular 470×470 mm) Vladimir Khmelnikov Deviation ~2µm Deviation ~14µm

  28. Gravitational surface displacement for different mirrors: are these displacements large?

  29. 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% X0), minimum probably 1.3 mm (1.04% X0) • Al+MgF2 coating for high reflectivity in the UV (small shadowing effects in 4 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 1.5-2.0 kEuro • Carbon mirrors ?

  30. RICH photo-detector plane, aperture optimization UrQMD PLUTO

  31. Photo-detector plane on the base of small diameter PMTs Hexagonal packing of the small diameter PMTs, D=7mm NPMT=(3n-2)(n-1)+2n-1 n=12 D = 7x(2n-1) mm d = 7xn mm PMT FEU-Hive 84 mm 161 mm

  32. Small diameter PMT, conception: • Schema of the small diameter PMT FEU-Hive (7 mm) with glass cathode window

  33. Improvement of the light collection efficiency

  34. PMT FEU-Hive, the first samples:

  35. PMT FEU-Hive, the first signals from LED source: FEU-115 FEU-Hive

  36. Parameters of the PMT FEU-Hive: #1 #2 waiting • External PMT diameter, mm 7.5 7.5 6-7 • Photo-cathode diameter, mm 6 6 5-6 • PMT length is, mm 80 • Photo-cathode: K2CsSb • Quantum efficiency, 410 nm, % 4 5 25 • Effective number of dynodes 12 • Nominal HV, kV 2.8 2.8 2 • Amplification 104 105 106 • Dynamical charge range, pC 0.25-2.5 • Noise current is, e/sec 3000 • Capacitance, pF 15 • Power dissipation, mW 40 • Price, Euro/PMT 5000 5000 25

  37. 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 ?

  38. RICH simulation CbmDetector CbmTask CbmRich CbmRichHitProducer CbmRichRingGuidanceProducer CbmRichRingFinder CbmRichPoint CbmRichHit CbmRichMirrorPoint CbmRichRingGuidances CbmRichRing CbmMCPoint CbmHit TObject

  39. RICH in CBMroot

  40. 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

  41. 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

  42. one quarter of mirror/ photodetector: f = 80o 60o 40o q = 5o 10o 15o 20o 25o 30o 35o 20o Be-mirror wall, optics simulation Claudia Höhne • Rings(q,f) - q polar angle, • f azimuth angle • no diffusion at reflection • no magnetic field, no multiple scattering Simulation result: Optics distortions (eccentricity) for large q,f To do: improve optics of the mirror walls / focussing position of focal planes

  43. Systematic in ring radius reconstruction for ideal mirrors

  44. Single particle response in terms of the PMT number, NPMT 50%N2+50%CH4 N2

  45. Single particle response, ring radii 50%N2+50%CH4 N2 N2 after correction

  46. 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

  47. 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

  48. RICH simulation, RICH ring finder Gennadi Ososkov and Co 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

  49. RICH simulation, RICH ring finder (2) 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.

  50. 1. Ring fitting. Problem of nonlinearity However, due to the obvious relation: M(a,b,R)~ 4R2L(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, 329-333).

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