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STATUS AND CHARACTERIZATION OF COMPASS RICH-1

Silvia Dalla Torre presents on hardware news, detector performance, and muon beam experiments. Detailed overview on Gluon Polarization, spin distribution functions, and physics goals of COMPASS project.

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STATUS AND CHARACTERIZATION OF COMPASS RICH-1

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  1. Playa del Carmen, 30/11-6/12/2004 - 5th RICH Workshop STATUS AND CHARACTERIZATION OF COMPASS RICH-1 OUTLINE: • RICH-1 in COMPASS • recall the main characteristiucs (4 talks in Pylos !) • hardware news • detector performances S. Dalla Torre INFN – TRIESTE on behalf of the COMPASS RICH group INSTITUTIONS: • Trieste, INFN and University, ICTP • Turin, INFNand University • Bielefeld, University • CERN support on-line image from RICH-1 event display Silvia DALLA TORRE

  2. With the muon beam * • Gluon Polarization G/G • transverse spin distribution functions Tq(x) • Flavor dependent polarized quark helicity densities q(x) • L physics • Diffractive VM-Production * Data collected COMPASS understanding thenon-perturbative physics of the nucleon With hadron beams • Primakoff-Reactions * • polarizability of  and K • glueballs and hybrids • charmed mesons and baryons • semi-leptonic decays • double-charmed baryons Silvia DALLA TORRE

  3. COMPASS SPECTROMETER Beam:160 GeV µ+ 2 . 108 µ/spill (4.8 s/16.2s) Pm ~ 80% trigger-hodoscopes DW45 straws SM2 dipole Muon-filter2,MW2 HCAL1 RICH_1 Gem_11 ECAL2,HCAL2 SM1 dipole MWPC Gems Scifi Polarised Target Muon-filter1,MW1 Veto straws,MWPC,Gems,SciFi Gems,SciFi,DCs,straws Silicon SciFi Micromegas,DC,SciFi BMS Silvia DALLA TORRE

  4. 3 m 6 m vessel mirror wall photon detectors: CsI MWPC 5 m radiator: C4F10 COMPASS RICH-1 - DESIGN from the experiment design: • hadron PID up to ~50 GeV/c • LARGE acceptance (large size): H: 500 mrad V: 400 mrad • able to stand trigger rates up to 100 KHz • beam rate up to 108 Hz • minimize material + detector designed in 1996 radiator: C4F10 detection of VUV photons (165-200 nm) Silvia DALLA TORRE

  5. PHOTON DETECTION photon detectors (PD) : 5.3 m2 MWPCs (8 chambers) with CsI photocathode read-out: 84,000 analog read-out ch.s with extended local intelligence MWPCs with CsI photocathodes 2 CsI photocathodes, 60 x 60 cm2 each Silvia DALLA TORRE

  6. MWPCs WITH LARGE SIZE PHOTOCATHODES, COMPASS EXPERIENCE photocathode storing marble tablewith x,y movement and microscope to solde anode wire and for dimensional checks(gaps, planarity within 100 mm) CsI: hygroscopic, water degrades QE never exposed to air (max 50 ppm O2 , routinely: 10 ppm) glove box to handle photocathodes photocathode transportation system Silvia DALLA TORRE

  7. PHOTON DETECTORs behaviour in the experiment some PDs exhibit electrical instabilities when exposed to radioactive rates(*), LONG RECOVERY TIME ! (~ 1 d) Instabilities related to – local tiny defects 2001 - 2 good PDs / 8 2002 - 5 good PDs / 8 2003, 2004 – segmented HV supply: 97% MWPC surface good (*) with m beams : MIP flux : ~ 5 x 105 / s / m2 (similar for all PDs) ph. flux : up to 3 x 105 / s / cm2 wire defect, diameter 20 mm Silvia DALLA TORRE

  8. RICH-1 mirror system ‘VUV mirror wall’, 21 m2,116 mirrors radius: 6.6 m average on 126 mirror units at production reflectance stable in time 2000 = @ COATING 2000 reflectance 2001 2002 wave length Silvia DALLA TORRE

  9. MIRROR WALL MECHANICS:light, stiff and adjustable the elements of this modular structure THICKNESS mechanics: 2.5 % X0 mirrors ~5.5 % X0 STABILITY: after an initial deformation ~1 mrad, stable: 0.1 mrad over ~ 3.5 y individual mirror support assembly jig mirror rear side mirror wall mechanics, assembling regulation for angular alignment, 2 orthog. movements mirror wall mechanics, assembled Silvia DALLA TORRE

  10. RICH-1 C4F10 GAS SYSTEM • Gas System for: • P constant +/- 0.1 mbar • to limit DP on - vessel windows • quartz plates • He beam pipe • gas filtering (remove H2O, O2 ) • filling with / recovering C4F10 liquid storage tank filters vessel liquifier PLC and electrical installation compressors Silvia DALLA TORRE

  11. typical transmission through 1,87 m, corresponding to: H2O:~1 ppm, O2: ~3 ppm transmission wavelength (nm) PRESENT (>2002) GAS PERFORMANCES • very good transparency • (better than design) • gas cleaning, see O. Ullaland’s talk • on-line filters, separate functions: • Cu catalyst, ~ 400C for O2 • 5A molecular sieve, ~ 100C for H2O extremely reduced leak rate vessel volume ~ 85 m3 total o-rings : ~ 100 m C4F10 : N2 = 95 : 5 stabile ! gas (atm. P) leak rate = 90 l/d Silvia DALLA TORRE

  12. PREDICTING ON-LINE (n-1) to allow quasi-online data processing, a must: COMPASS data rate = 3 TB/day (n-1) cal from measured P, T continuous line [(n-1)meas – (n-1) cal] / (n-1) prediction at ‰ level (n-1) meas from off-line data analysis red dots Silvia DALLA TORRE

  13. RICH-1 RAW INFORMATION an event, calibration run low intensity: 107/sec an event, standard run nominal intensity: 4 x107/sec Silvia DALLA TORRE

  14. RICH-1 CENTRAL REGION 2 combinated effects: - beam halo - central dead zones overlap of event images PID efficiency from MonteCarlo (beam halo off) photons generated by the beam halo only photon detector dead zones Efficiency Monitor all dead zones Distance from Beam (mm) Silvia DALLA TORRE

  15. “SINGLE PHOTON” PERFORMANCES • selecting particles according to polar angle and producing qring slices •  information on: • resolution • number of detected photons • background example all particles qring (mrad) qhit (mrad) Silvia DALLA TORRE

  16. NUMBER OF PHOTONS background Qparticle<30 mrad 30-60 mrad n. of ph.s adding up regions 3-6 60-90 mrad 90-120 mrad fit above 36 mrad 120-150 mrad 150-180 mrad rings with < 5 ph.s not reconstructed Silvia DALLA TORRE

  17. IS THE NUMBER OF PHOTONS UNDERSTOOD ? Very low beam intensity ~ 4106/spill threshold at 3 s 75% HV = 2000 V eff. Nph, b=1~ 21 expected: 22 <p>=6.3 <p>=6.5 ring centres of the selected particles <nPH>= 20.5 - 3 <nPH>= 21.3 - 3 Silvia DALLA TORRE

  18. RICH-1 RESOLUTION single photon resolution COMPARISON OF RING RESOLUTION DIRECTLY MEASURED (reconstructed rings) AND CALCULATED FROM SINGLE PHOTON RESOLUTION: FULL DETECTOR UNDERSTANDING sphoton (mrad) ring resolution p (GeV/c) scalculated from single photon resolution sRING (mrad) 2.5 s p/K sep. up to 40 GeV/c smeasured from reconstructed rings Qparticle (mrad) Silvia DALLA TORRE

  19. PID with COMPASS RICH-1 • particle> 25 mrad p (GeV/c) > pthr(K) + 2 GeV/c K p, m p Silvia DALLA TORRE

  20. PID EFFICIENCY MOMENTUM SPECTRA IN qparticle BINS 0-30 mrad 30-60 mrad <p> = 12.4 GeV/c <p> = 9.3 GeV/c EFFICIENCY 0. 0.5 1. 60-90 mrad 90-120 mrad <p> = 7.1GeV/c <p> = 5.8 GeV/c p± from Ks decays p> thr. (= on average 0 photons ) p> thr. + 0.5 GeV/c (=on av. 5 det. ph.s) p> thr. + 1.2 GeV/c (=on av.8 det. ph.s) p> thr. + 2 GeV/c (=in m. 10 det. ph.s) 120-150 mrad 150-180 mrad <p> = 4.9 GeV/c <p> = 4.3 GeV/c 0. 90. 180. Qparticle(mrad) Silvia DALLA TORRE

  21. EFFICIENCY, learning curve gas quality PD stability EFFICIENCY 0. 0.5 1. software upgrade EFFICIENCY 0. 0.5 1. K± from Fdecay (sample purity: 84% ) p> thr. + 2. GeV/c (= on av. 5 det. ph.s) p± da decadimenti Ks (sample purity: 94% ) p> thr. + 0.5 GeV/c (= on av. 5 det. ph.s) 0. 90. 180. Qparticle(mrad) 0. 90. 180. Qparticle(mrad) Silvia DALLA TORRE

  22. RICH-1 in COMPASS PHYSICS A remarkable example:DG/G open charm-signal D0 & D0without microvertex detector 2003: Seff= 674 (17) 2002 : Seff(*)= 151 (8) 2002 2003 (2004) Seff/day * 4.9 Preliminary (*) Seff=S/(1+B/S) Silvia DALLA TORRE

  23. CONCLUSIVE REMARKS • COMPASS RICH-1 is fully operative • plateau performances since 2003 • COMPASS RICH-1 • designed ~ mid 90’s • challenging requirements concerning • transversal sizeand • rates (beam, trigger)  large size VUV gas RICH • limitations for the operation of large size CsI photocathodes coupled to gas detectors in radioactive environments have been encountered • “single photon” resolution is satisfactory (~ parameter design) • “ring resolution” limited by physical background • ring resolution allows 2.5sp / Kseparation up to 40 GeV/c • central for COMPASS physics (demonstrated in polarized DIP) Silvia DALLA TORRE

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