3 運動量測定 飛跡検出器 3.1 ガス検出器 3.2 シリコン測定器 運動量測定 磁場中の荷電粒子の運動 F = qv × B 遠心力 mv = qrB PT x B ρ ローレンツ力 v2 F =m r pc = mc2 βγ pc β= mvcγ = pc = qcrB E 相対論的な効果としてγをかける E γ= mc2 B=1T, r=1m の場合を考えよう！ pc = 1.6 × 10−19 (C) · 3 × 108 (m/sec) · 1(m) · 1(T esla) 1T esla = 1N A−1 m−1 1C = 1As = 1.6 × 10−19 · 3 × 108 (N m) 1N m = 1J = 1/(1.6 × 10−19 )eV = 3 × 108 eV = 0.3GeV PT(GeV/c)= 0.3 B(Tesla)ρ(m) 運動量を測定するには飛跡の半径を測る！ 運動量測定には磁場が必要だ！ 高エネルギー実験の歴史 ー＞電磁石の開発 加速器はもちろん、 ダイポール（2極：偏向）電磁石 4極（収束、逆収束）電磁石 6極、８極など 様々な電磁石 測定器でも 固定ターゲット実験 ダイポール電磁石 衝突型加速器実験 ソレノイド電磁石 アクセプタンスの増大 超伝導電磁石 低物質化、MultipleScattering showe cal. の分解能向上 1 ~ 1.5 T -> 3 ~ 5 T at ILC 飛跡検出器 大昔は、シンチレーションカウンター（ホドスコープ）で飛跡検出 位置分解能 数cm かつ 磁場中では使用不可 ガスを使った検出器 ガイガー計数管 円筒電極ないに芯線を張り、希ガスを満たしたものに 高電圧を印加 スパークチェンバー 平行電極版間にガスを満たし、荷電粒子が通った時に高電圧を印加する 比例計数管（ワイヤーチェンバー） MWPC ドリフトチェンバー スモールセル ジェットセル TPC Time Expansion Chamber MPGD ガス検出器の中で何が起こっているか？ Introduction of Gas Detector 1. Primary Ionization ( interaction of charged/photonic particle with matter ) 2. Drift of ionized electrons/ions 3. Gas multiplication Charged particle ++1 +- +- ++- 2 1. is the most basic part for any detector and common to all. charged particle dE/dx, Cerenkov, Trans. radiation photon Photo-electric effect, Compton, Pair creation 2. and 3. are unique to gas detector yield variety of gas detectors 3 Amp. Charged particle in gas Z ρ dE 2mc2 β 2 EM 2 =K − 2β − [ln ] dx A β2 I 2 (1 − β 2 ) 2πN z 2 e4 K= mc2 EM 2mc2 β 2 = 1 − β2 non-relativistic region ∝ 1 β2 relativistic rise pol. effect/density effect Gas : Noble gas (Ar, Ne, Xe, Kr, (He)) is used as main component of gas ( not always ) as noble gas doesn’t have any vibration/rotation modes for energy absorption quencher is also necessary to absorb photon from electron avalanche process. basic parameter of typical gas He Ar Kr CH4 C4H10 Z A 4 18 36 16 34 2 ρ 0.17 I0 24.6 Wi 41 1.94 39.9 83.8 1.66 3.49 15.8 14.0 26 24 16 58 0.67 2.42 13.1 10.8 x10-3g/ eV cm3 dE/dx 0.32 nP 5.9 nT 1.47 1.32 2.44 4.60 29.4 22 94 192 28 23 2.21 1.86 1.48 4.50 16 46 53 195 eV MeV/ keV/ cm /cm /cm gcm-2 7.8 M.I.P. drop energy to medium ~2 MeV/density produce 30 primary ion pairs / 100 total ion pairs in Ar every cm. ion pair is produced discretely primary process sometime produces energetic electron -- delta ray(a few keV) produce large number of secondary -> deteriorate dE/dx info. emitted perpendicular to incident -> deteriorate position info. 2. Drift of electron electrons are drifted by E field macro view accelerated by E field and collide to atom microscopic τ: mean time between collisions drift velocity(w) is average velocity of electron E mv = 1 eEτ w =< v >= vmax = 2 2m CH4 electron get energy from E -> σ becomes large -> τ becomes shorter => drift velocity saturation Drift Vel.(cm/usec) e w is proportional to E ( smaller E ) w is ~constant ( E > Eo) eEdt = eEτ C2H6 Ar E field(kV/cm) Diffusion electron is not at rest even without E field, due to thermal energy (3/2kT) electron can move to transverse direction randomly determined in each coll.. electron spatial distribution x2 1 dN − 4Dt dx follows Gaussian low e =√ N 4πDt √ √ σx = 2Dt = 2D/w L L: drift length defocusing effect for position information 3. Gas multiplication In high E field, electron can receive enough energy to ionize atom before collision e dn = nαdx n = n0 exp[ e x2 e α(x)dx] x1 α: Geiger-Muller streamer 10^6 proportional e e e first Townsend coefficient semiproportional e 10000 100 1 gain e during avalanche, excited/ionized atom emit photon when it become stable state. This photon may ionize another atom around avalanche. Never stopping avalanche (Geiger-Muller mode) happen without quenching these photon. Quencher( CnHm,,,) gas has a role to absorb these photon by vibration/rotation mode. Wire Chamber principle of wire chamber: Proportional Counter using sense wire (diameter 20-30 micron) to make high E field wire can make uniform symmetric field gas multiplication starts @very close to sense wire (<100um) gain doesn’t depend on where electron produced dE/dx measurement -+ -+ -+ -+ MWPC sense wire is aligned on the same layer cathode plane sandwich sense plane individual many pc wire provide discrete position information (depend on wire spacing; 1mm is minimum) Drift Chamber more accurate position information can be provided by drift time when drift velocity is known. btw. trk thr and sig. Today’s Wire Chamber small cell type DC BELLE, Babar good for high rate exp. typ. res. ~150um Jet chamber SLD,JLC high resolution ~80um Merit and weak point of Wire Chamber TPC Limitation of wire length is limited (gravitational sag, tension ,, ) high rate capability ( cell size is limited ) 1-dim. readout ExB effect MPGD( Micro Pattern Gas Detector ) MPGD development has been initiated from ~1990 MSGC ( Micro strip gas detector ) analogy of wire chamber narrow anode electrode produce high E field shape of anode 200um pitch Si substrate | \/ PCB tech. difficulties stability fatal discharge E field in MSGC very high!! >>20~30kV/cm Field produced by ions will not be decreased streamer evolution Micro Gap Chamber 1 dim. structure -> 2 dim. structure Micro dot Chamber Gas Electron Multiplier GEM 50 micron thick Kapton covered by 5 micron copper both sides 75 micron holes are made in 140 micron pitch( by chemical etching ) 5 um Cu 50 um Kapton insulator 50 μm 5 um Cu 75 μm 45 μ m 140 μm triple GEM operation 10MΩ E3 GEM3 E2 VGEM HV3 HV2 GEM2 E1 GEM1 E0 Readout Pad HV1 it’s better to use 6 indiv. HV and prec. current monitors but too many HV sys. are compli. and not easy to control. GEM gas gain depends on not only VGEM but E0,E1,,, typical En is 1 ~ 2 kV/cm GEM is transparent @ VGEM> 250 V E3 drift gap E2,E1 transfer gap ~2kV/cm E0 induction gap ~3kV/cm Signal from Fe 5.9keV X-ray Gain vs. VGEM triple GEM P-10 double GEM 100000 Ar-CO2 Gain vs. HV 10000 1000 saturation due to amp. 100 10 260 300 340 VGEM 380 (Volts) Micromegas Chamber 35 micron First Results Ar:DME=9:1 gas feb4_04gaincurve, Ar:DME=9:1, Drift=-500 V 10 5 Gas gain Gas gain 104 1000 100 280 300 320 340 360 380 Mesh voltage (-V) 400 420 GEM and Micromegas are the most probable candidates for ILC TPC sensor GEM can provide small gain/foil O(10) to avoid discharge multiple layers are necessary less sensitive to geometrical alignment Micromegas can give us large signal ( as it is like a controlled discharge ) sometime signal is too large ( damage to readout electronics ) sensitive to gap Readout pad for both 2 dim determination -> large number of channel THis is new thing for this year !!! We had a experience of Micromegas for this year !! that is more than we expected The gap between foil and readout is matter if the distance between foil and readout small ; E->large ==> high gain @ shorter distance large ; E->small There are optimums for each gases . They are more durable than we expected may have more ability μPIC this is like a Microdot detector made by micro-electronics tech. PCB technology large scale cheap Application to ILC detector DHCAL with GEM Tracker/TPC senser Absorber strong back Gas inlet/outlet (example) Cathode layer Non-porous, double-sided adhesive strips 1 mm 1 mm 9-layer readout pc-board TESLA design Fishing-line spacer schematic 3 mm (NOT TO SCALE) UTA Application to other fields Scintillating GEM for medical imaging detect photon emitted from Gas multiplication alpha track neutron detector Single photon detector using CsI converter X-ray polarimeter Astrophysics photo-electron emitted to E field dir. What I am recently interested in is Dark Matter search using MPGD TPC We have spent much time for ILC TPC Do we have any other use of this kind of TPC ? Dark Matter: exist everywhere in the galaxy like “ether” earth moving around the sun : relative motion of the earth to dark matter modulation must be observed Merit of tracking device for Dark Matter search direction of recoiled particle(nuclei) by Dark Matter collision => modulation ! is a big evidence as Dark Matter but we need large volume to detect DM -> long drift distance -> large diffusion -> smear direction MPGD + Negative Ion Drift has been studied with wire chamber very low diffusion !
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