First Results of the Ring Imaging Cherenkov Detectors of the LHCb Experiment

Transcription

1 First Results f the Ring Imaging Cherenkv Detectrs f the LHCb Experiment, University f Edinburgh On behalf f the LHCb RICH Cllabratin LHCb Outline: The LHCb Experiment Ring Imaging Cherenkv Detectrs RICH Cmmissining Preliminary Results with LHC Beam Data Cnclusins RICH1 RICH2 RICH2 HPD panel: phtn hits f single pp-interactin and recnstructed Cherenkv rings IPRD10, Siena,

2 LHCb Experiment Diple Magnet RICH2 b-b angular crrelatin RICH1 VELO cllisin pint ~1 cm B Crucial fr LHCb physics prgramme ptimised gemetry and chice f luminsity Trigger efficient in hadrnic & leptnic mdes excellent tracking and Vertexing (σm, στ) excellent particle ID - RICH 2

3 The RICH Radiatrs cs(θ ) c = 1 n v c Silica Aergel n= t 10 GeV/c C 4 F 10 gas n= Up t ~60 GeV/c CF 4 gas n= Up t ~100 GeV/c Expected phtn yields fr islated saturated particles:. RICH1: mrad vertical mrad hrizntal RICH2: mrad vertical, mrad hrizntal Aergel C 4 F 10 CF A. Alves et al., JINST 3:S08005,

4 RICH1 and RICH2 Layut RICH1 RICH2 Interactin Pint reversible magnetic field Flat mirrrs Spherical Mirrrs Supprt Structure 7.2 m Central Tube Phtn Funnel + Shielding 4

5 RICH Detectr Pictures RICH 1: planar mirrrs RICH 2: supprt structure Beryllium beam pipe VELO exit windw and seal Aergel: as tile & full radiatr (16 tiles) magnetic shielding entrance windw central tube 5

6 Requirements fr Phtn Detectin Phtndetectr area: 3.3m 2 Single phtn sensitivity: nm Quantum efficiency: >20% Gd granularity: 2.5 x 2.5 mm 2 LHC rate: 40MHz Radiatin tlerance: 3kRad/yr Slutin: 484 Hybrid Phtn Detectrs RICH1: 14 x 7 x 2 = 196 HPD RICH2: 16 x 9 x 2 = 288 HPD hexagnal dense packed RICH 2 event display: single pp-interactin at 900GeV (Dec 2009) with: Active area fractin: 65% # electrnic channels: 500k 6

7 Hybrid Phtn Detectrs Pixel HPDs: develped in cllabratin with industry (lead partner: Phtnis-DEP) cmbines: vacuum phtn detectr technlgy with silicn pixel readut Quartz windw with S20 phtcathde 20kV perating vltage (~5000 e [eq. Si]) Factr 5 20kV QE: increased during prductin: 25% 32% Readut: encapsulated 256x32 pixel silicn sensr bump-bnded t binary readut chip lw nise f 140 e - 8-fld binary OR effective pixel array pixel size 500µm 500µm sufficient Ande n carrier Vacuum phtn detectr Ande RICH1 HPD panel 7

8 Beam Cllisins at s s = 7 TeV since pixel hit maps RICH1 RICH2 hit multiplicities per event brken data links missing HPDs in repair due t vacuum degradatin (have very lw ccupancy) # f hits # f hits 8

9 HPD Time Alignment Methds: RICH1&2 internal alignment with pulsed laser RICH1 & tracking alignment with csmic rays cnfirmatin and fine-tuning with beam Delay [ns] Efficiency in respnse t 0.1ns laser pulses: plateau: >10ns start, middle, end Delay [ns] Delay [ns] RICH1 RICH2 wrt. LHC clck: = -1.1ns RMS = 1.1ns wrt. LHC clck: = -0.2ns RMS = 0.8ns L0 bard IDs (2 HPD Stephan each) Eisenhardt mid-pint distributin 9

10 Csmic Rays Hrizntal csmic rays 100m undergrund?? 2x2 m 2 trigger scintillatr planes: n Wall (VELO) between RICH1 and TriggerTracker still: nly a few csmic rays / hur August 2009: first RICH rings well islated measured timing relative t tracking nisy pixels phtn hits frm csmic ray lwer RICH1 plane with single csmic ray event Ring radius [mm] 10

11 First Cllisins Nvember 2009: first pp-interactins at s=900gev (450GeV beam energy) ut-f-the-bx data : n crrectin/refinement f calibratin yet applied run trackless ring finder: lk fr islated rings with sme quality criterins applied LHCb data (preliminary) Kan ring LHCb data (preliminary) Kan ring Pin ring RICH1 panel: single pp-interactin event RICH2 panel: single pp-interactin event range pints: phtn hits cntinuus lines: rings fr each particle hypthesis 11

12 Gemetrical Alignment RICH cmpnents t align: RICH1 RICH2 detectr planes 2 2 HPDs spherical mirrrs 4 56 planar mirrrs Effect f misalignment n Cherenkv angle reslutin: θ c ring images relative t tracks & recnstructed θ c aligned misaligned installatin f RICH2 spherical mirrrs 12

13 Alignment Using saturated tracks frm pp-interactins: perfrmed n each pair f mirrrs currently statistics nly sufficient fr centre mirrrs e.g. RICH1 spherical mirrr up-right θ [rad] θ [rad] RICH1 gas misaligned φ [rad] aligned φ [rad] Current prgress: θ c un-aligned currently target (MC expectatin) RICH1 4.0 mrad 2.2 mrad 1.57 mrad RICH2 1.5 mrad 0.9 mrad 0.67 mrad RICH2 gas with mre data: align mre cmpnents 13

14 Phtn Yield Data frm Nv/Dec 2009 s = 900 GeV: Data: p > 5 GeV RICH1 gas Data: p > 15 GeV RICH2 gas # f phtns / ring # f phtns / ring calibratin: wrk in prgress 14

15 Aergel Radiatr Gemetry: 16 tiles f silica aergel, 5 cm thick in C 4 F 10 gas vlume Prperties: refractive index: n ~1.03 excellent hmgeneity: σ(n-1)/(n-1) < 1% very gd clarity: C<0.006 µm 4 /cm 300 µm UV-filter Phtn yield and angular reslutin: wrse than expected under investigatin: uter mirrrs nt yet aligned absrptin f C 4 F 10 increase f frward scattering refractive index: n σ = 7.3 mrad Cherenkv angle [rad]: recnstructed-expected 15

16 Particle Identificatin Recnstructin maximises likelihd f particle identificatin (PID) hypthesis Selectin delta lg likelihd (DLL) between different particle hyptheses tune cut t efficiency, purity, S/B Φ KK? withut PID with PID Φ KK! DLL (K-π) 16

17 Strange Particles at s s = 7 TeV Λ pπ withut PID 65 µb - 1 K* Kπ 65 µb - 1 RICH PID makes peak finding easy Ω Λ( pπ )Κ Ξ Λ( pπ )π φ KK 65 µb nb nb -1 17

18 Charmed Particles at s s = 7 TeV D 0 K - π + D *+ D 0 π + K - π nb nb -1 RICH PID essential fr D 0 D* + and Λ c + D 0 K - K nb -1 Λ c+ K - pπ nb -1 18

19 D s φπ at s s = 7 TeV RICH PID crucial fr D s and D ± facilitated finding first B candidate B + J\ψK + D s? D ±? D s! D ±! D (s)+ φπ + K + K withut RICH particle z is increasing each day: Λ c, Ω -,... PID perfrmance results will appear sn with RICH µb - 1 nb -1 19

20 Cnclusins LHCb RICH detectrs are fully cmmissined all systems wrking Data taking with LHC beams has cmmenced fully time aligned magnetic field calibrated mirrr alignments well underway fr RICH2 and RICH1 gas aergel perfrmance under investigatin Particle Identificatin perfrmance studies have started RICH detectr perfrmance is excellent rings have been bserved immediately after switching n beams, in a RICH detectr at a hadrn cllider in the frward regin many strange and charm particles already bserved Lking frward t analyse 2010/11 LHC data set 20

21 Backup Slides 21

22 First LHCb Events at s s = 7 TeV first day f 7 TeV cllisins RICH2 RICH1 LHCb Event display tp view single event frm pp-interactin 22

23 LHCb Detectr RICH2 RICH1 23

24 HPD Perfrmance Quantum Efficiency increase: increase f average QE: 25% 32% due t tuning f prductin recipe errrs indicate RMS f QE spread Quantum Efficiency vs. prductin batch Excellent pixel chip perfrmance: average threshld: 1065 e - average nise: 140 e - Threshld f pixel chip [e - ] (signal size: 5000 e - ) 24

25 In Feedback Prcess: phtelectrn inises residual gas atm drift f in t pht cathde ( ns) release f secndary pht electrns (~10-40) impact f ph.e. cluster n sensr In-situ mnitring: cw-laser (635nm) recrd IFB frm cluster size evlutin in time high IFB lw IFB cut RICH1 hit map: cw-laser illuminatin typical cluster size distributins example HPD hit maps (dark cunt) phtn yields /event /HPD with cw-laser 25

26 In Feedback Evlutin Evlutin: residual gas seems t increase linear in time illuminatin anneals IFB typically: IFB <0.5% / year fractin f HPD evlve mre quickly Threshld: self-sustained IFB frm IFB > 5% exchange & repair 3 years IFB distributin 03/2010 Replacement: replaced in RICH s far: 73 HPD expect replacements: ~13 HPD / year predictin f HPD replacements 26

27 RICH Cmmissining LHCb RICH detectrs are fully cmmissined: start autumn 2007, finish spring 2009 Experiment & Detectr Cntrl System and Mnitring: fully autmated cntinuus peratin, testing and mnitring RICH detectr cntrl panel Tls: autmated parameter mnitring & lgging dark cunt / cw-laser / pulsed laser csmic rays magnetic distrtin mnitring system / prjectr laser alignment mnitring system RICH1 mnitring panel t be updated t be updated stability f 6 HV channels ver 24hrs 27

28 Gas Systems Mnitring f refractive index: hydrstatic pressure difference: tp-bttm pressure variatin frm atmspheric changes gas cmpsitin frm chrmatgraphy: RICH2 gas residuals during purificatin (03/2010) RICH1: tp-bttm pressure (Nv 2009) t be updated? t be updated? Date Elapsed time (days) April 2010: RICH1 RICH2 C 4 F 10 98% CF 4 98% N 2 1% N 2 1.8% CO 2 0.8% t be updated? O 2 0.2% O 2 0.2% 28

29 Magnetic Field Calibratin RICH1 fringe field after shielding: ~14 Gauss Calibratin f distrtin with high precisin mvable light bar cllimated LEDs, pattern prgrammable retracted during cllisin phtn funnel fr ne RICH1 plane mvable light bar single HPD: respnse t light pattern with field ON/OFF 29

30 First LHC beams First Light August 2008: LHC injectin tests tracks passed thrugh LHCb the wrng way Readut ut f time: sensitive t particles which pass thrugh silicn sensrs stripes f pixel hits RICH1 panel Readut tuned in: sensitive t particles which traverse the HPD Quartz windws large clusters f hits (similar t IFB) RICH1 panel 30

31 Beam Splash Events September 2008: LHC deliberately dumps beam clse t LHCb LHCb recrds massive particle multiplicities L0 bard cnfiguratin prblems all HPD in RICH wrk time alignment already reasnable >2000 hits / HPD (RICH2 C-side) up t phtns / event in RICH2 RICH2 panel: O(30) accumulated events 31

32 Outlk LHCb plans t upgrade detectr fllwing first data taking phase expected ~2016 cllabratin plans t submit Letter f Intend end f 2010 Upgrade strategy: imprve hadrn trigger efficiency t run at 10x design luminsity, i.e. at ~2x10 33 cm -2 s -1 read ut full experiment at 40MHz (currently at 1MHz) RICH phtn detectrs need t be replaced Nvel detectr cncept: TORCH Time-f-Flight fr p < 10GeV Quartz plate with fcusing system t crrect fr phtn time-f-prpagatin in plate Requires time reslutin f O(20 ps) 32