Literature on particle detectors

Transcription

1 Introduction Introduction Gaseous and solid state tracking devices Scintillators, hoto detectors, scint. fibers, nuclear emulsions, electronic bubble chamber Calorimetry Particle identification Many toics will remain uncovered... Design of detector systems Electronics, trigger and data acquisition Non-article hysics (medical, biological etc.) alications Detector construction Detector oeration (monitoring, calibration, alignment) I/1

2 Introduction Literature on article detectors ext books C. Gruen,, Cambridge University Press, 1996 W. R. Leo, echniques for Nuclear and Particle Physics Exeriments, nd edition, Sringer, 1994 R.S. Gilmore, Single article detection and measurement, aylor&francis, 199 W. Blum, L. Rolandi, Particle Detection with Drift Chambers, Sringer, 1994 K. Kleinknecht, Detektoren für eilchenstrahlung, 3rd edition, eubner, 199 Review articles Exerimental techniques in high energy hysics,. Ferbel (editor), World Scientific, Instrumentation in High Energy Physics, F. Sauli (editor), World Scientific, 199. Many excellent articles can be found in Ann. Rev. Nucl. Part. Sci. Other sources Particle Data Book (Phys. Rev. D, Vol. 54, 1996) R. Bock, A. Vasilescu, Particle Data Briefbook htt:// Proceedings of detector conferences (Vienna WCC, Elba, IEEE) I/

3 Introduction A W + W - decay in DELPHI e + e - ( s=161. GeV) W + W - qqqq 4 hadronic jets 10 m 10 m I/3

4 Introduction A W + W - decay in ALEPH e + e - ( s=181 GeV) W + W - qqµν µ hadronic jets + µ + missing momentum _ I/4

5 Introduction Reconstructed B-mesons in the DELPHI micro vertex detector τ B 1.6 s l = cτγ 500 µm γ Primary Vertex Primary Vertex I/5

6 Introduction Particle identification methods I/6

7 13 m Introduction I/7

8 Introduction A simulated event in ALAS (CMS) H 4µ collision at s = 14 ev σ inel. 70 mb Interested in rocesses with σ fb L = cm - s -1, bunch sacing 5 ns 3 overlaing minimum bias events / BC 1900 charged neutral articles / BC I/8

9 Introduction he ideal article detector for high energy hysics exeriments High energy collisions ( e e, e,, ) roduction of a multitude of articles (charged, neutral, hotons) he ideal detector should rovide. coverage of full solid angle (no cracks, fine segmentation detect, track and identify all articles (mass, charge) measurement of momentum and/or energy fast resonse, no dead time ractical limitations (technology, sace, budget) Particles are detected via their interaction with matter. Many different hysical rinciles are involved (mainly of electromagnetic nature). Eventually we will observe... ionization and excitation of matter. I/9

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11 Introduction Momentum measurement Multile scattering Bethe-Bloch formula / Landau tails Ionization of gases Wire chambers Some derivatives of wire chambers Drift and diffusion in gases Drift chambers Micro gas detectors Chamber aging Gas detector simulation Charge Couled Devices (CCD) Silicon drift detectors Silicon detectors? stris/ixels Radiation hardness I/11

12 Momentum measurement I/1

13 I/13 Momentum measurement Momentum measurement the sagitta s is determined by 3 measurements with error σ(x): for N equidistant measurements, one obtains (R.L. Gluckstern, NIM 4 (1963) 381) ex: =1GeV/c, L=1m, B=1, σ(x)=00µm, N=10 L s B y x B L s B L B L L B qb cos sin 0.3 sin m) ( 0.3 c) (GeV ) ( ) ( ) ( BL x s x s s meas 4) 70/( 0.3 ) (. N BL x meas (for N 10) 0.5%. meas 3 1 x x x s (s 3.75 cm)

14 Multile Scattering Scattering An incoming article with charge z interacts with a target of nuclear charge Z. he cross-section for this e.m. rocess is d d 4zZr e mec sin 1 4 Rutherford formula Average scattering angle 0 Cross-section for 0 infnite! d/d Multile Scattering Sufficiently thick material layer the article will undergo multile scattering. L r lane lane RMS 0 lane lane 1 RMS sace I/14

15 Multile Scattering P Gaussian P lane 1 lane ex 0 0 sin -4 (/) 0 lane Aroximation X 0 is radiation length of the medium (accuracy 11% for 10-3 < L/X 0 < 100) 13.6 MeV 0 z ln c X 0 L L X 0 he lateral dislacement can also be aroximated by RMS RMS a Gaussian distribution with width r lane L lane L 0 I/15

16 Momentum measurement Back to momentum measurements: contribution from multile scattering MS ( ) MS sin lane RMS MS BL L X 0 L X B 1 LX 0 indeendent of! ()/ total error ()/ meas. ()/ MS ex: Ar (X 0 =110m), L=1m, B=1 ( ) MS 0.5% I/16

17 Momentum Measurement Momentum measurement in exeriments with solenoid magnet: y x z B x z y B sin olar angle has to be determined from a straight line fit x=x(z). N equidistant oints with error σ(z) meas. ( z) 1( N 1) /( N( N 1)) L + multile scattering contribution. normally small In ractical cases: In summary: meas ( x) 1. BL N I/17

18 Interaction of charged articles Detection of charged articles How do they loose energy in matter? Discrete collisions with the atomic electrons of the absorber v,m material. 0 de d NE d dx, k 0 de e N : electron density - Collisions with nuclei not imortant (m e <<m N ). If, k are big enough ionization. A hoton in a medium has to follow the disersion relation c n c k c k 0 n n For soft collisions + energy and momentum conservation real hotons: cos v k vk v k 1 n cos 1 Cherenkov hotons if 1 n I/18

19 Interaction of charged articles 1 Re schematically! Im regime: otical absortive X-ray effect: Cherenkov radiation ionisation transition radiation Average differential energy loss de dx Many different aroaches (classical, semiclassical) exist... e.g. Allison+Cobb (Ann.Rev. of Nucl. and Part. Phys, 30 (1988), 53), Photo Absortion Ionization (PAI) model includes Cherenkov + transition radiation PAI model relates dσ/de to emirical atomic hotoabsortion cross-sections σ γ (E) Ionisation only Bethe - Bloch formula I/19

20 Bethe-Bloch formula de dx de/dx in [MeV g -1 cm ] 4N Are m c e z Z A 1 m ln ec I max de/dx deends only on β, indeendent of m Formula takes into account energy transfers 1 I I de I 0 Z max with I 0 I : mean excitation otential 10 ev (rough aroximation, I fitted for each element) Bethe-Bloch formula only valid for heavy articles (m m µ ). Electrons and ositrons need secial treatment (m roj =m target ), in addition Bremsstrahlung! de dx MeV gcm Z/A does not differ much for the various elements, excet for Hydrogen! I/0

21 Bethe-Bloch formula I de/dx first falls 1/β (more recise β -5/3 ), kinematic factor de dx then minimum at βγ 4 (minimum ionizing articles, MIP) 4N Are then again rising due to ln γ term, relativistic rise, attributed to relativistic exansion of transverse E- field contributions from more distant collisions. relativistic rise cancelled at high γ by density effect, olarization of medium screens more distant atoms. Parameterized by δ (material deendent) Fermi lateau many other m c small corrections e z Z A 1 1 mec ln max Measured and calculated de/dx solid line: Allison and Cobb, 1980 dashed line: Sternheimer (1954) data from 1978 (Lehraus et al.) I/1

22 Landau tails Real detectors (limited granularity) do not measure <de/dx>, but the energy E deosited in a layer of finite thickness δx. E is the result of a certain number i of collisions with energy transfers E i, with cross-section dσ/de rel. robability below excitation threshold excitation ionization by distant collision ionization by close collisions -electrons Schematically! (after Gilmore) energy transfer/hoton exchange Problem: Relate F( E,δx) to dσ/de Solutions: Williams(199), Landau(1944), Allison and Cobb(1980) and others. Monte-Carlo aroach: 1.) divide absorber layer into thin slices. Probability for any energy transfer in the slice is low..) Choose energy transfer randomly from above distribution. 3.) Sum over all slices. I/

23 Landau tails For thin layers (and low density materials): Few collisions, some with high energy transfer. Energy loss distributions show large fluctuations towards high losses: Landau tails Argon + 7% CH 4 Argon + 7% CH 4 data: Harris et al. (1977) dotted curve: Landau(1944) dashed curve: Maccabee & Paworth(1969) (Landau s method) solid curve: Allison and Cobb For thick layers and high density materials: Many collisions. Central Limit heorem Gaussian shae distributions. I/3

24 Ionization of gases Primary and total ionization Fast charged articles ionize the atoms of a gas. Primary ionization otal ionisation Often the resulting rimary electron will have enough kinetic energy to ionize other atoms. n n total total E W i 34 de dx W n i x rimary total number of created electron-ion airs. E = total energy loss W i = effective <energy loss>/air Number of rimary electron/ion airs in frequently used (detector) gases. W i (ev) 31 6 (Lohse and Witzeling, Instrumentation In High Energy Physics, World Scientific,199) I/4

25 Ionization of gases remarks: 1. he actual number of rimary electron-ion airs is Poisson distributed m n n e P( m) m! he detection efficiency is therefore limited to det P(0) 1 1 e n For thin layers ε det can then be significantly lower than 1. Examle Ar: d = 1mm n rimary =.5. ε det = 0.9. he total number of electron-ion airs is subject to large, non-oissonian, fluctuations (Landau tails). Detectors which are able to identify rimary clusters, may rovide a better energy resolution. cluster counting (see lecture Particle ID). I/5

26 Proortional Counter 100 electron-ion airs are not easy to detect! Noise of amlifier 1000 e - (ENC)! We need to increase the number of e-ion airs. Gas amlification Consider cylindrical field geometry (simlest case): gas cathode E b E threshold a anode 1/r E r V ( r) CV 0 CV r ln r a a C = caacitance / unit length r Electrons drift towards the anode wire ( sto and go! More details in next lecture!). Close to the anode wire the field is sufficiently high (some kv/cm), so that e - gain enough energy for further ionization exonential increase of number of e - -ion airs. I/6

27 Proortional Counter n 1 E x r x n0e or n n 0 e λ: mean free ath α: First ownsend coefficient (e - -ion airs/cm) For low e - energies ε M n n 0 ex r C a r dr Gain kn M ke CV 0 (F. Sauli, CERN 77-09) (O. Allkofer, Sark chambers, heimig München, 1969) I/7

28 Proortional Counter Choice of gas: Dense noble gases. Energy dissiation mainly by ionization! High secific ionization. (MAGBOLZ) De-excitation of noble gases only ossible via emission of hotons, e.g ev for Argon. his is above ionization threshold of metals, e.g. Coer 7.7 ev. Ar * 11.6 ev e - Cu new avalanches ermanent discharges! cathode I/8

29 Proortional Counter Solution: Add oly-atomic gases as quenchers. Absortion of hotons in a large energy range (many vibrational and rotational energy levels). E Energy dissiation by collisions or dissociation into smaller molecules. r Methane: absortion band ev (MAGBOLZ) I/9

30 Proortional Counter Signal formation (F. Sauli, CERN 77-09) Avalanche formation within a few wire radii and within t < 1 ns! Signal induction both on anode and cathode due to moving charges (both electrons and ions). Q dv dv dr lcv dr 0 Electrons collected by anode wire, i.e. dr is small (few µm). Electrons contribute only very little to detected signal (few %). (F. Sauli, CERN 77-09) Ions have to drift back to cathode, i.e. dr is big. Signal duration limited by total ion drift time! Need electronic signal differentiation to limit dead time. I/30

31 Oeration modes of chambers Oeration modes:. ionization mode: full charge collection, but no charge multilication. Proortional mode: above threshold voltage multilication starts. Detected signal roortional to original ionization energy measurement (de/dx). Secondary avalanches have to be quenched. Gain Limited Proortional Saturated Streamer mode: Strong hoto-emission. Secondary avalanches, merging with original avalanche. Requires strong quenchers or ulsed HV. High gain (10 10 ), large signals simle electronics. Geiger mode: Massive hoto emission. Full length of anode wire affected. Sto discharge by cutting down HV. Strong quenchers needed as well. I/31

32 Multi wire roortional chambers Multi wire roortional chambers (MWPC) (G. Charak et al. 1968, Nobel rize 199) Caacitive couling of non-screened arallel wires? Negative signals on all wires? Comensated by ositive signal induction from ion avalanche. field lines and equiotentials around anode wires yical arameters: L=5mm,d=1mm,a wire =0µm. Normally digital readout: satial resolution limited to d x 1 (d=1mm, σ x =300 µµm) Address of fired wire(s) give only 1-dimensional information. Secondary coordinate. I/3

33 Multi wire roortional chambers Secondary coordinate Crossed wire lanes. Ghost hits. Restricted to low multilicities. Also stereo lanes (crossing under small angle). Charge division. Resistive wires (Carbon,kΩ/m). Q A y track Q B y L Q A Q B Q B y L u to 0.4% L iming difference (DELPHI Outer detector, OPAL vertex detector) CFD y L track CFD ( ) 100s ( y) 4cm (OPAL) 1 wire lane + segmented cathode lanes Analog readout of cathode lanes. σ 100 µm I/33

34 Derivatives of roortional chambers Some derivatives Multiste avalanche chambers low field high field low field high field conversion transfer wire meshes amlification 1 G=10 3 amlification G=10 3 arallel lane avalanche chambers (PPAC), searated by transfer fields, oerated at low gain. Achieve high total gain ( ) by reducing feedback hoton roblem. Electron transarency of wire meshes deends on field ratio E out /E in. (E out /E in = ) Charge amlification by Penning rocess at rel. low field: A* + C A + C + + e - Alication: Single hoto electron detection. I/34

35 Derivatives of roortional chambers hin ga chambers (GC) cathode ads ground lane G10 (suort) grahite 3. mm 50 m mm 4kV Gas: CO /n-entane ( 50/50) Oeration in saturated mode. Signal amlitude limited by by the resistivity of the grahite layer ( 40kΩ/). Fast ( ns risetime), large signals (gain 10 6 ), robust Alication: OPAL ole ti hadron calorimeter. G. Mikenberg, NIM A 65 (1988) 3 ALAS muon endca trigger, Y.Arai et al. NIM A 367 (1995) 398 I/35

36 Derivatives of roortional chambers Resistive late chambers (RPC) sacer 10 kv mm bakelite (melamine henolic laminate) icku stris Gas: C F 4 H, (C F 5 H) + few % isobutane (ALAS, A. Di Ciaccio, NIM A 384 (1996) ) ime disersion 1.. ns suited as trigger chamber Rate caability 1 khz / cm 15 kv Double and multiga geometries imrove timing and efficiency Problem: Oeration close to streamer mode. I/36