An overview of the LHCb RICH detectors

1. An overview of the LHCb RICH detectors Neville Harnew University of Oxford On behalf of the LHCb RICH Collaboration RICH 2007Trieste 15-20 Oct 2007

2. Outline of the talk • The LHCb Experiment • The RICH status • RICH1 • RICH2 • The Hybrid Photon Detector (HPD) project • RICH2 commissioning • RICH calibration • Performance • Summary

3. The LHCb Detector Forward spectrometer (running in pp collider mode). A dedicated B-physics experiment at the LHC Acceptance Vertical 250mrad Horizontal 300mrad to 10 mrad Two RICH detectors provide p/K/p identification

4. LHCb detector in place, commissioning is well underway…. RICH2 RICH1

5. The RICH Radiators Expected photon yields – for isolated saturated particles C4F10 gas n=1.0014 Up to ~70 GeV/c CF4 gas n=1.0005 Beyond ~100 GeV/c Silica Aerogel n=1.03 1-10 GeV/c RICH1: 25250 mrad vertical 25 300 mrad horizontal RICH2: 15100 mrad vertical, 15 120 mrad horizontal

6. The LHCb RICH Detectors 4m 1m

7. RICH1 schematic : “vertical” geometry Photon detector plane 14 by 7 Hybrid Photon Detectors (HPDs) Upper Magnetic Shielding Protects HPDs from B field, supports upper HPDs 4m Quartz Window Spherical Mirrors Lightweight carbon fibre mirrors 1.5% radiation length Glass Planar Mirrors VELO Exit Window 2mm aluminium.. Sealed to gas enclosure. No RICH entrance window. Beryllium beampipe (defines RICH1 inner acceptance) RICH1 Exit Window Carbon fibre & PMMI foam Sealed direct to the beampipe. Gas Enclosure supports mirrors and aerogel, contains C4F10 Lower Photon detector plane Mounted on lower shield Lower Magnetic Shielding mounted on cavern floor, supports lower HPDs and Gas Enclosure

8. RICH1 Magnetic shielding RICH1 picture gallary Gas enclosure and mirrors installed in LHCb pit Beryllium beampipe, VELO exit window and seal and planar mirrors Trial installation of the HPD box Gas Enclosure before installation

9. See talk by Fabio Metlica The RICH1 Mirrors Spherical mirrors Glass planar mirrors Carbon Fibre Mirrors:1.5% radiation length

10. See talk by Tito Bellunato and poster by Davide Perego The RICH1 Aerogel Radiator • 16 aerogel tiles for RICH1. Produced by Boreskov Institute of Catalysis Novisibirsk • 200x200x50 mm tiles – the largest ever • n=1.03 ; gives p/K separation up to ~10 GeV/c • Exceptional clarity C ~ 0.005m4cm-1 [I/I0 = A exp –(Ct/l4) for thickness t] • Excellent homogeneity s(n-1)/(n-1) <1% • Tiles have undergone extensive ageing studies Test installation into RICH1

11. 8m RICH2 schematic : “horizontal” geometry Flat Mirrors each made from 20 square glass segments Spherical Mirrors each made from 21 glass hexagonal segments Magnetic Shields protect the HPD planes HPD planes of 9 by 16 HPDs RICH2 entrance / exit windows carbon fibre and foam sandwich Gas Enclosure Contains CF4 gas radiator and the optical system

12. RICH2 to the pit-Nov 2005 • Mirrors aligned to 150 mrad before move • After move, mirror movement ~100 mrad • Stability & alignment verified. No need to re-align in situ • cf. RICH-2 Cherenkov angle resolution ~ 700 mrad

13. Pixel Hybrid Photon Detectors • Pixel HPDs developed in collaboration with industry (Photonis-DEP lead partner) • Combines vacuum technology with silicon pixel readout ( Quartz window with S20 photocathode). • 484 HPDs occupy a total area of 3.3m2 with 2.5 x 2.5 mm granularity • Factor 5 demagnification @ 20kV. • Operates at the LHC bunch crossing frequency (40MHz) • Encapsulated 32x32 pixel silicon sensor Bump-bonded binary readout chip • 200-600 nm wavelength coverage

14. See talk by Stephan Eisenhardt HPD qualification • Two Photon Detector Test Facilities (PDTFs) have qualified all 550 HPDs produced by Photonis/DEP. • 98% of tubes have passed the selection criteria. • Excellent response, QE, dark counts, ion feedback etc.

15. The HPD readout chain • All HPDs arranged in columns with ancillary front-end electronics • LV & HV boards power the HPDs • Level-0 boards pass triggered data to the Level-1 off-detector board via an ~100m optical link • Level-1 off-detector receives and zero-suppresses the data and passes to the DAQ HPD column assembly

16. See talk by Carmelo D’Ambrosio 10kV applied. RICH2 Commissioning Laser photon source. Hit map of 2.4M channels. RICH2 is complete and running • Most of columns have been up to 20kV. Operating RICH2 has now become a routine and safe task. • 10 failed HPDs disconnected (out of 288) – these will be replaced • The detector control/safety systems (DCS and DSS) are operational • RICH2 is ready for global commissioning.

17. HPD box temperature Light level See talk by Mario Sannino University Genoa HPD box humidity <- 5 days -> <- 5 days -> Cooling pressure over 60 days Detector control system in place

18. See talk by Antonis Papanestis RICH calibration procedures in place • Calibration & alignment systems use projected test patterns: • Corrections to HPD trajectories for magnetic field. • RICH alignment monitoring. • Calibration & alignment also with tracks (data): • Alignment with tracks. • Refractive index monitoring. • Cherenkov angle resolution from isolated rings. • Particle ID calibration with D*’s B=0 and B=30G Test pattern with B=0

19. See talk by Sean Brisbane RICH performance (testbeam) • Performance of the RICH system has been verified in a 80 GeV/c charged particle beam at CERN SPS. C4F10 ~1m radiator length. • Realistic 25 ns beam structure • Final RICH hardware and DAQ • RICH specifications for photon yield and θc resolution have been verified. Pixel map of a C4F10 ring integrated with ~50k events over 3 HPDs (preliminary) C4F10 run

20. See talk by Claus Buszello PID Performance • Ring finding - The algorithm uses tracks, and performs a global likelihood fit to particle hypotheses across both RICH detectors. • p – K separation - Excellent efficiency and low mis-ID rate

21. Summary and prospects • LHCb RICH has excellent particle ID - crucial for the B physics programme of LHCb • RICH1 installation almost complete • Ready for commissioning at end of year • Innovative carbon fibre mirror and aerogel technology • RICH2 is almost commissioned • Ready for global commissioning • Hybrid Photon Detectors provide excellent single photon sensitivity. Performance is excellent • LHCb expects its first physics data in 2008, with stable running in 2009. We look forward to data-taking with a completed RICH system !

22. Spare slides

23. RICH Performance Single Cherenkov photon angle resolution (mrad) Chromatic Uncertainty The uncertainty due to the dependence of the refractive index on the wavelength of the photon Emission point Error The uncertainty due to the assumption the photon was emitted at the centre of the track Pixel Uncertainty The uncertainty due to the limited resolution of the pixel detectors Tracking Uncertainty The uncertainty due to the limited accuracy of the tracking stations Combining Uncertainty The CU, EPE and PE are independent but the TU is not and so does not reduce with higher statistics number of photoelectrons

24. HPD test results

25. B┴  B║ • Magnetic fields distort the electron trajectories of the HPDs. • We should expect significant distortions in the LHCb RICHes (max 24 Gauss in RICH1) . • Tubes are individually shielded in mumetal cylinders to mitigate these effects. • Below: RICH2 projection system Magnetic Distortion calibration Axial Transverse

26. LHC “approved” schedule - Aug 2007