Development of a RICH detector for electron identification in CBM Claudia Höhne, GSI Darmstadt CBM collaboration CBM-RICH group Bergische Universität Wuppertal, Germany GSI, Germany Hochschule Esslingen, Germany PNPI Gatchina, St. Petersburg, Russia Pusan Natl. University, Korea University Gießen, Germany (joining soon)

Claudia Höhne RICH2010, Cassis, May Outline Introduction: FAIR RICH detector for electron identification RICH detector development photodetector: electronics, wavelength-shifting films mirror prototype(s) Simulations Summary

Claudia Höhne RICH2010, Cassis, May FAIR at GSI high intensity ion beam CBM + HADES starting 2017 SIS 100 p beam 2 – 30 GeV Ca beam 2 – 15 AGeV Au beam 2 – 11 AGeV SIS 300 p beam 2 – 90 GeV Ca beam 2 – 45 AGeV Au beam 2 – 35 AGeV max. beam intensity 10 9 ions/s

Claudia Höhne RICH2010, Cassis, May Physics case of CBM Compressed Baryonic FAIR – high  B, moderate T: searching for the landmarks of the QCD phase diagram first order deconfinement phase transition chiral phase transition (high baryon densities!) QCD critical endpoint in A+A collisions from 2-45 AGeV starting in 2018 (CBM + HADES) physics program complementary to RHIC, LHC rare probes being sensitive to the created matter! (charm, dileptons)  → e+e- J/ ,  ’ → e+e- penetrating probes!

Claudia Höhne RICH2010, Cassis, May The CBM experiment – „electron setup“ tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field hadron ID: TOF (& RICH) photons,  0,  : ECAL PSD for event characterization high speed DAQ and trigger → rare probes! electron ID: RICH & TRD   suppression  10 4 RICH TRD TOF ECAL magnet STS + MVD

Claudia Höhne RICH2010, Cassis, May CBM-RICH detector simulation of di-electrons from a  -meson aim: clean electron identification for momenta below 8 GeV/c.... maybe use also for additional  -suppression in K-id at higher p concept: RICH with gas radiator: stable, robust, fast rely to a large extend on components from industry photodetector (2.4 m 2, 55k Ch.) photomultipliers (MAPMT: H8500 series) enhanced UV sensitivity using wavelength shifting films? fast self-triggered readout: “CBM-XYter” chip development mirror (11.8 m 2 ) glass mirror: R=3m, ≤ 6mm thickness, Al+MgF 2 coverage radiator CO 2 :  th =33, p ,th =4.65 GeV/c → 21 N p.e. /ring (electrons) → N 0 ≈ 130 – 140 cm -1 → ≈ 9-10 % X 0

Claudia Höhne RICH2010, Cassis, May Challenges for Au+Au collisions at 25 GeV/nucleon RICH behind material budget of STS: 2ndary e ± ! → high ring density! high track densities → problem of ring-track mismatches interaction rates up to 10 MHz inner part of PMT plane (currently – might still move PMT plane outwards) energy density < 3krad/year neutron fluence < 3∙10 11 n-eq/cm 2 /year magnetic field < 25 mT (shielding?!) green – track projections blue – hits red – found rings event display of part of photodetector plane ~ 100 rings per central Au+Au collision at 25 GeV/nucleon

Photodetector

Claudia Höhne RICH2010, Cassis, May Photodetector investigate H8500 MAPMT series from Hamamatsu [Hamamatsu Photonics] aim at large number of hits on ring → investigate means to increase q.e. UV extended window Super-/ ultra bialkalkali photocathodes wavelength-shifter films readout electronics → investigate usage of self-triggered FEE based on “n-XYter” chip developed for Si-detectors (input range up to -125∙10 3 e-)

Claudia Höhne RICH2010, Cassis, May WLS films Wavelength shifting films – principle and application Organic molecules absorbing in the short (UV) wavelength region Strong fluorescence in visible region Application via evaporation, spin coating/ dip coating Example: p-Terphenyl [work in cooperation with CERN (C. Joram, A. Braem, P. Solevi)] p-terphenyl (PT)

Claudia Höhne RICH2010, Cassis, May WLS-films (II) strongly enhanced q.e. below 300 nm compared to a bare PMT with borosilicate window gain factor: number of detected photoelectrons normalized to 1 for bare PMT insensitive on film thickness if > 0.8 µm [work in cooperation with CERN (C. Joram, A. Braem, P. Solevi)] p-terphenyl: gain ~ 1.7 Tetraphenyl: gain ~ 1.3 Butadiene

Claudia Höhne RICH2010, Cassis, May GEANT4 simulation (P. Solevi, ETH Zürich): photons generated isotropically in 0.8µm thick p-terphenyl layer on top of 1.5mm thick borosilikate window photons distributed around generation point with  =2.1mm at photocathode (distribution well described by gaussian) degradation of pixel resolution from 1.7 mm ( , pixel length 5.8 mm (H8500)) to 2.3 mm Degradation of position resolution? 0.8 µm PT 1.5 mm PMT glass photocathode [work in cooperation with CERN (C. Joram, A. Braem, P. Solevi)] to be verified experimentally further investigations: application technique long term stability radiation tolerance effect on UV window fluorescence decay time

Claudia Höhne RICH2010, Cassis, May CBM Front End Electronics concept: self-triggered FEE: data push architecture with large computer farm for online event reconstruction and trigger decisions → cope with up to 10 MHz interaction rate, trigger on rare probes current working horse and basis for further developmets: “n-XYter” chip developed for Si-detectors adopt for readout of MAPMT: typical gain of 10 6 → charge attenuator by factor 50 [DETNI EU project, A.S. Brogna et al., NIM A 568 (2006) 301–308] self triggered architecture 128 channels, readout speed up to 250 kHz per channel 32 MHz readout frequency input range +62.5∙10 3 e to -125∙10 3 e see Poster: J. Eschke (GSI)

Claudia Höhne RICH2010, Cassis, May FEE test with MAPMT readout tested in lab test concept in proton beamtime (2.8 GeV/c) under beam conditions together with other detectors and common DAQ proximity focusing setup with plexiglass radiator (8mm) tilted by 45° to overcome internal reflection see Poster: J. Eschke (GSI) RICH

Claudia Höhne RICH2010, Cassis, May time difference: beam counter coinc. – MAPMT hit σ 2 =σ 2 FEE +σ 2 MAPMT +σ 2 BeamCoincPMTs ADC value (reversed scale) with timing cut no cut on timing pedestal (noise) peak σ FEE <3,7 ns noise reduction! Testbeam results ADC spectra with and without timing cut ADC value (reversed scale) see Poster: J. Eschke (GSI) H

Claudia Höhne RICH2010, Cassis, May Testbeam results single photon counting achieved with new self triggered FEE adopted to MAPMT readout → further “CBM-XYter” development ongoing: Si- and gas-detector branch; use synergy; adopt to MAPMT readout good timing essential for clean signal and noise reduction, here  FEE < 3.7 ns see Poster: J. Eschke (GSI) event integrated MAPMT hit distribution with timing cut only → clear ¼ Cherenkov ring image; 3.5 hits/event

Mirror

Claudia Höhne RICH2010, Cassis, May Mirrors glass mirrors: ≤ 6 mm thickness, R ≈ 3 m, Al+MgF 2 coating search for provider from industry with sufficient quality on surface homogenity and reflectivity photography FLABEG GmbH, Germany: d = 6 mm, r 0 = 3.2m size A = 40 x 40 cm 2 Coating: Al: d = 70 nm (55) MgF 2 : d = 90 nm (120) Compas, Czech Republic d = 3 and 6 mm, r 0 = 3 m size R = 30 cm Coating: Al: d = 80 nm MgF 2 : d = 30 nm

Claudia Höhne RICH2010, Cassis, May Reflectivity measurements Measurements done in cooperation with CERN, A. Braem and C. Joram FLABEG: very good reflectivity between 400 nm and 270  nm first drop around 250 nm: influence of aluminum oxide second drop at about 180 nm: interference at MgF 2 layer

Claudia Höhne RICH2010, Cassis, May Reflectivity measurements Measurements done in cooperation with CERN, A. Braem and C. Joram FLABEG: very good reflectivity between 400 nm and 270  nm first drop around 250 nm: influence of aluminum oxide second drop at about 180 nm: interference at MgF 2 layer Compas: good reflectivity in the UV, full range to be measured

Claudia Höhne RICH2010, Cassis, May FLABEG: very broad feature, most of the intensity in the background; pronounced irregularities on the cm-scale Compas: CCD Point source mirror radius of curvature 4 mm 6 mm at CERN – Carmelo D'Ambrosio Radius of curvature and surface homogenity D 0  2.3 mm (95 % intensity) Flabeg Compas

Claudia Höhne RICH2010, Cassis, May Size: D = 60 cm glass: d = 4 mm Radius: r 0 = 3000 mm Compas mirrors Proposed for delivery soon: glass: d = 6 mm Radius: r 0 = 3000 mm coating Al+MgF2 2 samples: round (D=60 cm), rectangular (40x40 cm 2 ) next steps: same type of samples with 5 mm and 4 mm thickness → systematically study distortions from cutting, stability first (ambitious) project: mirrors with thickness of 3 mm → mirrors broke when cut to quadratic tiles and/ or lost shape after cutting meanwhile: simulations show that 6 mm mirrors are well feasible from tracking New sample: uncoated mirror

Claudia Höhne RICH2010, Cassis, May Mirror mount mirror mount design ongoing investigation (simulation, finite element calculations) of influence of placement of mirror mounts on additional distortions on D 0 for mirror+mount due to mount and gravity (6 mm thickness) tilted by -20° Max. deformation [µm] D 0 (95%) [mm] not tilted

RICH prototypes

Claudia Höhne RICH2010, Cassis, May RICH prototype Pusan RICH prototype produced in Pusan, tested in 60 MeV electron beam at Pohang no ring structure seen in event integrated displays experimental setup: no possibility to trigger on single electrons and to record single events! see Poster: J. Yi (Pusan)

Claudia Höhne RICH2010, Cassis, May Simulations of RICH prototype Pusan problem: Pohang delivers 60 MeV electron beam: multiple scattering in air and radiator! → no ring image seen in event integrated MAPMT signals because rings are smeared all over the PMT-plane see Poster: J. Yi (Pusan) simulation → improve beam conditions (select single electrons) → upgrade readout (n-XYter) Planning started for larger RICH prototype with real size CBM modules, (simplified) gas system

Simulations

Claudia Höhne RICH2010, Cassis, May CbmRoot Simulations C++ and ROOT based simulation framework, GEANT3 or GEANT4 usable detector response implemented as realistic as (currently) possible full event reconstruction including RICH algorithms tuned for speed – online event reconstruction: parallelization! systematic studies of detector performance physics feasibility studies for di-electrons show good performance embedded electrons in central Au+Au collisions at 25 GeV/nucleon ~90 rings/event 21 hits/ring 4% fake rings,1% clones  -misidentification 1/500 (p < 7 GeV/c) reconstruction time/ event 5.8 ms (scalar) – 3 ms (parallel)

Claudia Höhne RICH2010, Cassis, May Summary Photodetector investigate H8500 series (Hamamatsu) usage of WLS films for enhanced q.e.? adopt self-triggered readout electronics to MAPMTs Mirror investigate glass mirrors with Al+MgF 2 coating development of mirror mount design Prototype Pusan RICH prototype installed Plans for large prototype with real size CBM modules, gas system Simulations simulation framework established, event reconstruction established, systematic studies of detector performance promising physics feasibility studies

Claudia Höhne RICH2010, Cassis, May CBM collaboration Russia: IHEP Protvino INR Troitzk ITEP Moscow KRI, St. Petersburg China: Tsinghua Univ., Beijing CCNU Wuhan USTC Hefei Croatia: University of Split RBI, Zagreb Portugal: LIP Coimbra Romania: NIPNE Bucharest Bucharest University Poland: Krakow Univ. Warsaw Univ. Silesia Univ. Katowice Nucl. Phys. Inst. Krakow Ukraine: INR, Kiev Shevchenko Univ., Kiev Univ. Mannheim Univ. Münster FZ Rossendorf GSI Darmstadt Univ. Wuppertal Czech Republic: CAS, Rez Techn. Univ. Prague Germany: Univ. Heidelberg, Phys. Inst. Univ. HD, Kirchhoff Inst. Univ. Frankfurt Hungaria: KFKI Budapest Eötvös Univ. Budapest India: Aligarh Muslim Univ., Aligarh IOP Bhubaneswar Panjab Univ., Chandigarh Gauhati Univ., Guwahati Univ. Rajasthan, Jaipur Univ. Jammu, Jammu IIT Kharagpur SAHA Kolkata Univ Calcutta, Kolkata VECC Kolkata Univ. Kashmir, Srinagar Banaras Hindu Univ., Varanasi Norway: Univ. Bergen Kurchatov Inst. Moscow LHE, JINR Dubna LPP, JINR Dubna Cyprus: Nikosia Univ. 56 institutions, > 400 membersSplit, Oct 2009 LIT, JINR Dubna MEPHI Moscow Obninsk State Univ. PNPI Gatchina SINP, Moscow State Univ. St. Petersburg Polytec. U. Korea: Korea Univ. Seoul Pusan National Univ. France: IPHC Strasbourg

Claudia Höhne RICH2010, Cassis, May Additional slides

Claudia Höhne RICH2010, Cassis, May nm surface roughness on 6 nm scale (AFM measurement) however: pronounced irregularities on the cm scale reflection in mirror if standing at a distance equal to the mirror radius Surface homogenity – Flabeg mirrors

Claudia Höhne RICH2010, Cassis, May CBM RICH prototype plan for a larger RICH prototype with “real” modules for the final CBM-RICH: 2x2 (2x1) mirror module with mounts: test effect of mirror distortions, test mirror adjustment, tiles of 40x40 cm 2 3x3 or 4x4 MAPMT supermodule: test different H8500 versions, test WLS coverage, develop concept for electronics integration, PMT module mounting simplified gas system, to be extended/ upgraded later ~1.9 m ~1 m ~1.5 m → scalable to the full RICH detector

Claudia Höhne RICH2010, Cassis, May Physics topics and Observables Onset of chiral symmetry restoration at high  B in-medium modifications of hadrons ( , ,   e + e - (μ + μ - ), D) Deconfinement phase transition at high  B excitation function and flow of strangeness (K, , , ,  ) excitation function and flow of charm (J/ψ, ψ', D 0, D ,  c ) charmonium suppression, sequential for J/ψ and ψ' ? The equation-of-state at high  B collective flow of hadrons particle production at threshold energies (open charm) QCD critical endpint excitation function of event-by-event fluctuations (K/π,...) mostly new measurements CBM Physics Book (theory) in preparation

Claudia Höhne RICH2010, Cassis, May  -meson spectral function [Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1, hep-ph/ ]  -meson couples to the medium: "melts" close to T c and at high  B vacuum lifetime  0 = 1.3 fm/c dileptons = penetrating probe  -meson spectral function particular sensitive to baryon density connection to chiral symmetry restoration? p n  ++  p   e +, μ + e -, μ - 

Claudia Höhne RICH2010, Cassis, May Charm production at threshold [W. Cassing et al., Nucl. Phys. A 691 (2001) 753] HSD simulations CBM will measure charm production at threshold → after primordial production, the survival and momentum of the charm quarks depends on the interactions with the dense and hot medium! → direct probe of the medium! charmonium in hot and dense matter? relation to deconfinement?

Claudia Höhne RICH2010, Cassis, May Parameters for simulation chromatic dispersion [Landolt Boernstein Series, 6 th Edition, volume II/8 Ph.D. thesis of Annick Bideau-Mehu (1982)]

Claudia Höhne RICH2010, Cassis, May Parameters for simulation (II) photon absorption [Y.Tomkiewicz and E.L.Garwin, NIM V114 (1974) pp ] [O. Ullaland, talk at RICH2004 workshop]

Claudia Höhne RICH2010, Cassis, May The CBM experiment tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field hadron ID: TOF (& RICH) photons,  0,  : ECAL electron ID: RICH & TRD   suppression  10 4 PSD for event characterization high speed DAQ and trigger → rare probes! muon ID: absorber + detector layer sandwich  move out absorbers for hadron runs RICH TRD TOF ECAL magnet absorber + detectors STS + MVD

Claudia Höhne RICH2010, Cassis, May Parameters for simulation (III) mirror reflectivity (HADES) [J.Friese for HADES, NIM A 502 (2003) 241]

Claudia Höhne RICH2010, Cassis, May photons distributed around generation point with  =2.1mm at photocathode estimated degradation of resolution from 1.7 mm ( , pixel length 5.8 mm (H8500)) to 2.3 mm distribution of recorded photons around generation point at photocathode [P. Koczon et al., submitted to NIM A] Degradation of position resolution?

Claudia Höhne RICH2010, Cassis, May Degradation of position resolution? (III) first investigations with H (one half covered with PT) pinhole mask: enlight center of one pixel only fraction of hits in neighbouring pixels ~16% no WLS ~31% w WLS consistent with Hamamatsu specification, WLS simulation approx. factor 2 more crosstalk with WLS further measurements planned/ started at GSI (J. Eschke), Wuppertal group [P. Koczon, GSI]

Claudia Höhne RICH2010, Cassis, May WLS-films

Claudia Höhne RICH2010, Cassis, May WLS films (III) application technique, mechanical stability of films? so far evaporated films used homogenous coverage minor formation of crystals not very stable against scratches test dip coating larger mechanical stability due to additional binder

Claudia Höhne RICH2010, Cassis, May WLS films (IV) first explorative studies: comparable fluorescence intensity seen to evaporated films! improve on homogeneous coverage, investigate formation of crystals, influence of binder…? 25 mm further investigations: long term stability effect on UV window fluorescence decay time

Claudia Höhne RICH2010, Cassis, May Simulations of RICH prototype Pusan simulation experimental setup: no possibility to trigger on single electrons! too high beam current (1nA in approx. 1µs bunch) not yet enough electronics channels available for readout of 2(-4) MAPMTs data → improve beam conditions (select single electrons) → upgrade readout (n-XYter) → once running: test gas system specifications see Poster: J. Yi (Pusan)

Claudia Höhne RICH2010, Cassis, May Expected radiation doses (FLUKA) FLUKA calculation (see CBM-Wiki pages) for configuration without MUCH, “MUCH2” is appr. at position of PMT plane of RICH < 3krad/year at max < 3∙10 11 n-eq/cm 2 /year at max appr. PMTplane position Expected radiation doses at the photodetector plane (shielded by the magnet yoke) - not yet done with new magnet design!

Claudia Höhne RICH2010, Cassis, May Expected radiation doses (TGEANT3 + GCALOR) GEANT calculation (see CBM-Wiki pages) for configuration without MUCH, “MUCH2” is appr. at position of PMT plane of RICH appr. PMTplane position < 3krad/year at max < n-eq/cm 2 /year at max Expected radiation doses at the photodetector plane (shielded by the magnet yoke) - not yet done with new magnet design!

Claudia Höhne RICH2010, Cassis, May Magnetic field at PMT plane magnetic field in region of photodetector plane in T (Sim. currently z=170cm) max. ~25mT: need shielding of PMTs! and/ or shifted position of PMT plane sensitivity of electronics (XYter FEBs, ROCs)? new design, see CBM collaboration meeting in Split, Oct. 2009