Results from first beam tests for the development of a RICH detector for CBM

1. Results from first beam tests for the development of a RICH detector for CBM Jürgen Eschke, GSI Darmstadt For the CBM RICH group: GSI, Darmstadt, Germany HS Esslingen, Germany IHEP Protvino, Russia National University of Pusan, Republic of Korea PNPI Gatchina, St. Petersburg, Russia University of Wuppertal, Germany

2. Physics case of CBM • Compressed Baryonic Matter @ FAIR – high mB, 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 2016 (CBM + HADES) at SIS100 • Observables sensitive to high mB/ phase transition: • r-meson • J/y, y‘ • both → e+e- • physics program complementary to RHIC, LHC • rare probes! (charm, dileptons)

3. The CBM experiment Aim: hadron and lepton identification in large acceptance, good momentum and secondary vertex resolution • tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field • hadron ID: TOF (& RICH) • photons, p0, h: ECAL ECAL TOF TRD RICH • electron ID: RICH & TRD & TOF •  p suppression  104 PSD • PSD for event characterization • high speed DAQ and trigger → rare probes! STS magnet Central Au+Au@25AGeV UrQMD event  GEANT

4. RICH concept • task • clean electron identification for p ≤ 8-10 GeV/c • p-suppression factor ~ 500-1000, 104 if combined with TRD + TOF • large acceptance (± 25°), good efficiency (~20 hits/ring) • challenges • high track density: • central Au+Au collisions, 25 AGeV: ~600 charged tracks within ± 25° • RICH detector positioned behind STS, Magnet (material budget!): • large number of secondary electrons • → high ring & track density in RICH detector: • typical scale: ~100 rings: 30 p, 60 2nd e±, 5-10 e± from target • → fake rings, wrong ring-track matches • interaction rates up to 10 MHz (J/y): fast, self-triggered readout electronics

5. RICH concept (II) • concept • gaseous RICH detector • rather high Cherenkov threshold for pions • → CO2 radiator (gth=33, pp,th=4.65 GeV/c) • glass mirrors (3-6 mm, R=3m, size 11.8 m2) • with vertical separation • → focus to upper & lower part of CBM • → photodetector shielded by magnet yoke • photodetector plane (2.4 m2) : Multi-Anode PMTs • → 860 MAPMTs with 64 channels/piece • 55k channels in total • (e.g. Hamamatsu H8500, 64 channels, • outer dimensions 5.2x5.2cm2 ,pixel size 5.8x5.8mm2) • no further windows • → Cherenkov photons with l ≥ 180 nm • → 1.5 m radiator length (~20 hits/ring)

6. Electron identification with RICH Electrons Pions • RICH characteristics: • radiator: CO2 length 1.5 m • glass mirrorof 6 mm thickness: • radius-3m; size-11.8 m2 • photodetector: Hamamatsu H8500MAPMT: • 860 MAPMTs  2.4 m2 55k channels  HK 41.4 Do 15:00: Electron identification capabilities of the CBM experiment at FAIR (S. Lebedev) Simulation: Mean number of hits per electron ring is21 RICH hits (blue),found rings (red),track projections (green). Radius versus momentum for reconstructedrings

7. Requirements RICH Front End Electronics: • fast self-triggered FEE • (event rate up to 10 MHz, max. ~250k hits/channel/s) • sufficient time resolution • (of a few ns for separation of uncorrelated background) (data push architecture)

8. FEE and read-out chain for the CBM-RICH detector • RICH detector will be based on photomultipliers (MAPMTs) like the H8500 from Hamamatsu • plan for FEE: synergy with CBM developments (CBM-XYter, ROC) • use future CBM-XYter (TRD branch, “Gas-XYter”) •  test concept with currently available n-XYter-FEB • Self-triggered architecture - 128 channels - developed for Silicon detectors (125k electrons dynamical range) - can be used for gas detectors (with attenuation) • Positive and negative front-end polarity. • 32 MHz readout frequency • *Developed within DETNI EU project, A.S. Brogna et al., NIM A 568 (2006) 301–308 n-XYTER readout ASIC • adopt to readout for photomultipliers: need to attenuate PMT gain before MAPMT signal ~ 106 electrons  attenuation by factor 50 required

9. Charge Attenuator board (CAB) factor 50 Read Out Controller (ROC) n-XYTER Front End Board (FEB) RICH test beam set up Aug/Sep 2009

10. Proximity focus setup with plexiglass radiator of 8 (4) mm Cherenkov angle Simulation: S. Bianco proton =44.9° 45° momentum 2.78 GeV/c

11. Test beam set up at GSI Aug/Sep 2009 MAPMT Cherenkov UV photons under 44,9 Degree Proton Beam E kin =2GeV P = 2,78 GeV/c plexiglass

12. CBM Beam Test @ GSI – 28.8.-8.9.2009 TriggerS3+S4 RICH GEM STS DABC + Go4, Slow Control

13. time difference: beam counter coinc. – MAPMT hit beam events ( cut on 100 ns time window) Results: Sept. 2009 beam test at GSI noise events noise events [ns] self triggered – all events no cut on time difference with cut on time difference (beam events) example ADC spectra of one channel: note: ADC values shown in reverse scale ADC value (reversed scale) ADC value (reversed scale)

14. Test beam results - distribution of MAPMT hits event integrated distribution of MAPMT hits  clear ¼ Cherenkov ring image 8 mm plexiglas radiator Number of hits per beam event very good noise suppression by time cut (no other cuts applied)  clean signal single event mean Number of MAPMT hits per event ~ 3.5  single photon counting

15. Comparison of measured number of photons to expectation • Produced number of Cherenkov photons in the wavelength interval • 390-800 nm for 2.78 GeV/c proton in 8 mm plexiglass is ~236 with L=8 mm, n= 1,49, θc= 44,9o Characterictics H8500 MAPMTs • Reduction of measured photons due to • - geometry: less than ¼ sequement: ~¼ * 64/100 • - light transmission in plexiglas: ~ 80% • - Quantuum efficiency weighted with yield of • produced photons per ∆Eν: ~15% • - photon collection efficiency: ~ 80% (assumption) Nphotonsexpected = 3.62 ,NMAPMThitsmeasured = 3.52

16. Conclusions: New self triggered front end electronics successfully adopted for readout of MAPMTs  low background noise level achieved by time cut on beam events Number of detected hits in the MAPMT is consistent with expectations  Yes, we nicely identify single photons! Outlook: Further characterization of MAPMT with LED test setup in lab: - crosstalk between channels - performance with WLS coverage for enhanced UV-sensitivity ( additional crosstalk tolerable?) Further development of readout chain: - first version of CBM-XYter (gas detector branch) available soon (adopt to MAPMT readout) Plan for complete RICH prototype with 16 (or 9) MAPMTs and mirror prototype

17. CBM collaboration China: Tsinghua Univ., Beijing CCNU Wuhan USTC Hefei Croatia: University of Split RBI, Zagreb Univ. Mannheim Univ. Münster FZ Rossendorf GSI Darmstadt Univ. Kashmir, Srinagar Banaras Hindu Univ., Varanasi Korea: Korea Univ. Seoul Pusan National Univ. Russia: IHEP Protvino INR Troitzk ITEP Moscow KRI, St. Petersburg Hungaria: KFKI Budapest Eötvös Univ. Budapest Norway: Univ. Bergen Kurchatov Inst. Moscow LHE, JINR Dubna LPP, JINR Dubna Thank you for your attention! 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 Poland: Krakow Univ. Warsaw Univ. Silesia Univ. Katowice Nucl. Phys. Inst. Krakow Cyprus: Nikosia Univ. LIT, JINR Dubna MEPHI Moscow Obninsk State Univ. PNPI Gatchina SINP, Moscow State Univ. St. Petersburg Polytec. U. Czech Republic: CAS, Rez Techn. Univ. Prague France: IPHC Strasbourg Portugal: LIP Coimbra Romania: NIPNE Bucharest Bucharest University Ukraine: INR, Kiev Shevchenko Univ. , Kiev Germany: Univ. Heidelberg, Phys. Inst. Univ. HD, Kirchhoff Inst. Univ. Frankfurt 55 institutions, > 400 members Split, Oct 2009

18. halo of the proton beam Another peak ADC channel:47 beam