A Triple-GEM Telescope for the TOTEM Experiment

Transcription

1 A Triple-GEM Telescope for the TOTEM Experiment Giuseppe Latino (Siena University & Pisa INFN) IPRD06 Siena October 4, 2006 TOTEM LHC T2 Telescope 3-GEM Technology Detailed Detector Simulation Test on Production Detector 1

2 CERN Large Hadron Collider (LHC) LHC - p-p collisions at s =14 TeV - L ist ~ cm -2 s -1-5 experiments - start up ~ 2007 TOTEM - total cross section - elastic scattering - diffractive dissociation Total and Elastic Measurement 2

3 TOTEM: Physics Programme Total p-p cross section with uncertainty ~ 1% (L ist ~ cm -2 s -1 ) Elastic p-p scattering on range 10-3 < t < 10 GeV 2 Study of diffractive dissociation processes (with CMS) Total Cross Section Current Situation: Current models predict at s = 14 TeV: σ PP = mb TOTEM goal: absolute error ~ 1mb => possibility to distinguish among different models Luminosity independent method: - elastic scattering (up to t ~ 10-3 GeV 2 ) - inelastic scattering (proper tracking acceptance in forward region) 8π Optical Theorem: σ T = Im F( s, t) t= 0 p s 2 Lσ Lσ T T 16π = 2 1+ ρ = N + N el dn dt inel el t = 0 ρ = Re Im F F t= 0 ~ σ T 16π ( dn / dt) el t =0 = 2 1+ ρ N el + N inel 3

4 TOTEM & CMS CMS Experimental Area (IP5) Leading Protons measured at -147m & -220m from CMS Leading Protons measured at +147m & +220m from CMS TOTEM Experiment 4

5 TOTEM Detectors: Setup in CMS Detectors on both sides of IP5 Inelastic Telescopes: reconstruction of tracks and interaction vertex CMS T1: 3.1 < η < 4.7 T2: 5.3 < η < 6.5 T1: mrad T2: 3 10 mrad η = - log(tg(θ/2)) 10.5 m T1 HF ~14 m T2 Elastic Detectors (Roman Pots): position of p scattered elastically at small angles Active area up mm from beam: 5 10 µrad RP1 (RP2) RP3 147 m (180 m) 220 m 5

6 TOTEM Detectors Technology RP: Edgeless Planar Silicon Detector - sensitive area up to 50 µm from edge - spatial resolution: µm T1: Cathode Strip Chambers (CSC) ~3 m Thin window Secondary Vacuum Detector Bellow Beam Primary Vacuum Beam σ x ~ 0.5mm σ y ~ 0.9mm Vacuum Chamber T2: Triple-GEM Vacuum Chamber ~ 0.4 m Castor Calorimeter (CMS) G. Latino: TOTEM Giornata di Dipartimento, Siena 16/02/2006 6

7 T2 GEM: 70 µm 140 µm Gas Electron Multiplier (GEM) Ions Electrons - Developed at CERN (F. Sauli ~ 1997) - Used in COMPASS, LHCb, - Gas Detector GEM Technology - Rad-hard,, high rate, good spatial and timing resolution - Electrodes: 50 µm kapton + 2x5 µm m Cu - Density: holes/mm 2 - Electric field (channel) ~ 100 KV/cm (V gem = 500 V) electron cascade - Gain: µm Cu 50 µm Kapton 55 µm 70 µm 7

8 T2 Telescope: Triple-GEM Detectors Triple-GEM 3 GEM foils kept in position by thin spacers (2 mm): - high gain (G( gem ~ ) suitable for detecting MIPs - V gem not high (~ 400V) D R IF T G E M 1 G E M 2 G E M 2 R E A D O U T E D E T 1 E I D R I F T T R A N S F E R 1 E T 2 T R A N S F E R 2 I N D U C T I O N Readout (printed) board with pads and strips Pads (trigger, tracking): 65(ϕ) x 24(η) η) = 1560 pads η x ϕ = 0.06 x 0.018π π (~2x2 ( mm 2 ~7x7 mm 2 ) Strips (tracking): 256x2 (width 80 µm, pitch 400 µm) strips pads T2 Telescope - 20 triple-gem detectors combined into 10 planes, to cope with high particle fluxes (5.3 < η < 6.5) - gas: Ar/CO 2 (70/30 %) - digital readout (VFAT) σ R (strips) ~ 70 µm (strips) ~ 70 8

9 Detailed Simulation of T2 Triple-GEM Detectors (I) Software tools (special thanks to Roma/Cagliari LHCb group for precious initial input...) Garfield: main framework Maxwell: electric field map Magboltz: electron/ion drift velocity and diffusion coefficients Imonte: Townsend and attachment coefficients for given gas mixture Heed: energy loss by ionization in gas; cluster production Detailed simulation step by step of: Incoming particle Ionization and diffusion/drift Electric field on GEM foil Avalanche in GEM hole (G GEM ) Signal induction on readout electrodes Spatial and timing properties of collected signal 9

10 Detailed Simulation of T2 Triple-GEM Detectors (II) Drift Zone t & σt drift GEM Foil n - Ionization process - Diffusion and drift toward 1th GEM σxz drift Avalanche in the Gem planes y GEM foil GEM foil GEM foil DRIFT (3 mm) TRANSFER (2 mm) TRANSFER (2 mm) INDUCTION (2 mm) Transfer Zone Diffusion and drift between GEM foils Induction Zone t & σt induction t & σt transfer σxz transfer Gain -Diffusion and drift toward the electrodes -Signal induction σxz induction I(t) 10

11 Detailed Simulation of T2 Triple-GEM Detectors (III) Signal induction: Ramo theorem I k (t) = -q v(x,t) x E k w (x) Weighting field (E( kw (x)):): readout 1V, other 0V Example: timing studies on pad signal DRIFT h e - t d GEM1 GEM2 GEM3 h e - t d t CROSS SIGNAL Signal of electrons not collected by the readout electrode READOU T Readout Pad t i DIRECT SIGNAL Signal of electrons collected by the readout electrode For: Ar-CO 2 STP E d/t ~ 3KV/cm t d t t d Consistent with TB studies on prototype t i 11

12 Detailed Simulation of T2 Triple-GEM Detectors (IV) Example: studies on strip signals studies on cluster size Typical strip cluster size expected: 2 3 strips Consistent with COMPASS TB results 12

13 T2 3-GEM Detector Test CERN Final production detector: design and component CERN Gas Detector Develop. G&A Eng. Radiation source: Cu X-Ray tube (K α = 8 KeV, K β = 8.9 KeV) Test activities: - general functionality - absolute gain - strip/pad charge sharing - energy resolution - time stability - response uniformity 13

14 3-GEM Absolute Gain & Strip/Pad Charge Sharing G T = I tot /n e f n ~ 293: <Ne> for incident γ f : rate of γ interaction G T ~ -4KV consistent with expected detector performances 3-GEM HV (V) Strip cluster charge ~ % of pad cluster charge consistent with design for optimal setup of readout chip (VFAT) 3-GEM HV (KV) 14

15 3-GEM Energy Resolution & Time Stability Energy resolution ~ 20% fwhm (@ 8 KeV Cu) 3-GEM HV (KV) Stability over > 1 h 15

16 Summary & Conclusions TOTEM experiment at CERN LHC will have a very forward tracking detector (T2: 5.3 < η < 6.5) based on triple-gem technology A detailed detector simulation has been developed which allows a complete understanding of its performances by taking into account all of the basic underlying processes Laboratory tests on two final design detectors (assembled by a private company) have been performed at CERN showing detector performances well within expectations A more extensive test on 10 production detectors, coupled to final design electronics (VFAT), is going to be performed at the incoming TOTEM test beam activities scheduled at CERN for November 06 16

17 Spare (I): Signal Intensity & Shape from GEM Simulation MULTIPLICATION FACTORS Number of el. produced per incident particle Mean ~ 27 Most Probable Value ~ 13 RMS ~ 30 Gas & Drift Zone Length <N e > G1 G2 G3 ELECTRONS COLLECTION Number of el. collected by electrode as direct induced current (e - captured by the readout electrode) or cross induced currents (e - captured by the others electrodes) DRIFT GEM1 GEM2 GEM3 ReadOut Geometry & Spatial distribution of the electrons cloud Mean G ~ 15 No outgoing e - ~ 30% 3-GEM G ~ 3.4x10 3 TripleGem Voltage, Gas & GEM foil geometry Readout Pad READOUT Weigthing field lines ReadOut Geometry S1

18 Spare (II): Studies on Pad Signals Studies on Cluster Size Typical pad cluster size expected: 1 2 pads S2

19 Spare (III): Triple-GEM Response Uniformity Studies Study biased by limited channel readout (8 strips) difficult alignment of readout area with X-ray beam S3