Muon detector S Tanaka KEK Contents Introduction About
Muon detector S. Tanaka (KEK)
Contents • Introduction • About Muon Spectrometer – ATLAS – CMS • Fundamentals of wire chambers • Performance of Muon Spectrometer • Summary
References • ATLAS Muon TDR – http: //atlas. web. cern. ch/Atlas/GROUPS/MUON/TDR/ Web/TDR_chapters. html • CMS Muon TDR – http: //cmsdoc. cern. ch/cms/TDR/MUON/muon. html
Introduction • How to select the interest muon tracks – Muon spectrometer • Magnets • Trackers • How to optimize the parameters of muon spectrometer – – Efficiency Radiation hardness Long term stability Costs
The ATLAS Muon Spectrometer ATLAS: A Toroidal LHC Apparatu. S Muon Spectrometer: • toroidal magnetic field: <B> = 4 Tm high pt-resolution independent of the polar angle • size defined by large lever arm to allow high stand-alone precision • air-core coils to minimise the multiple scattering • 3 detector stations Trackers: - cylindrical in barrel • fast trigger chambers: TGC, RPC - wheels in end caps • high resolution tracking detectors: MDT, CSC • coverage: | | < 2. 7
CMS Muon Spectrometers CMS: A Compact Muon Solenoidal detector of LHC Muon detector coverage: | | < 2. 4 Magnetic Field =4 Tesla
Difference of 2 type magnetic fields *Large Homogenous field inside coil *Weak opposite field in return yoke *Size limited *Large size area with high magnetic field *Non-uniform field *Field always perpendicular to momentum
6 m ←ATLAS:Troidal magnetic field (y-z view) 3 m CMS: Solenoidal magnetic Field → (r-φview)
Momentum measurement ATLAS 2. 5 %@100 Ge. V CMS 8 % @ 100 Ge. V
How to measure Pt? Measure the transverse component to B field Position resolution s(x) for each Pt resolution depends on B, L and s(x) (not R)!
Important parameters for Pt • Position resolution of Precision chamber • Alignment calibration of chambers • Magnetic field calibration • Distance between chambers • Energy loss by inside materials • Multiple scattering effects • Uniformity of the B field and precision chamber acceptance • Performance stability on high flux irradiation
Interaction of charged particle Rutherford scattering An incoming particle with charge z interacts elastically with a target of nuclear charge Z. The cross-section for this e. m. process is z: Charge of incident particle Z: Atomic number of material Approximation - Non-relativistic - No spins • Scattering does not lead to significant energy loss
Interaction of charged particle • • Multiple scattering (Moliere formula) – Approximates the projected scattering angle of multiple scattering by a Gaussian, with a width Approximation X: charge X 0 : Radiation length (Mean distance over which a high energy electron loses all but 1/e of its energy by bremsstrahlung, and 7/9 of the mean free path for pair production by a high-energy photon. ) Rutherford scattering
Interaction of charged particle • What is the contribution of multiple scattering to Momentum resolution? Independent of Pt More Precisely →
Muon Spectrometer Concept • For reconstructed mass resolution (ex. H → 4μ, Z → 2μ) Need good transverse momentum resolution ~2%: ATLAS , 7~8%: CMS for 5 -100 Ge. V • For charge identification (ex. Z’→mm) – Need Good position resolution • For CP-violation and B and Top physics Trigger selectivity : High Pt (~20 Ge. V) and Low Pt (~ 6 Ge. V) • For bunch-crossing identification (Trigger) Time resolution : < 25 ns ⇒ ・Standalone muon system ・Dedicated chambers each for tracking and triggering ATLAS: MDT+RPC for Barrel, MDT+TGC for End-cap CMS: DT+RPC for Barrel, CSC+RPC for End-cap ・Superconducting magnet
Toroid magnet (ATLAS) • Current=20. 5 k. A • 25. 3 m length • 4 T on superconductor
Magnetic field and Pt resolution (ATLAS) Integrated magnetic field as a function of Pt Resolution Acceptance as a function of
Solenoid magnet (CMS) • 4 T superconducting solenoid • 13 m length • Inner diameter : 5. 9 m
Magnetic field and Pt resolution (CMS) Integrated magnetic field as a function of Acceptance as a function of
Muon Chambers • ATLAS – – Monitored Drift Tube (Barrel, End-cap Precision) Resistive Plate Chamber (Barrel Trigger) Thin Gap Chamber (End-cap Trigger) Cathode Strip Chamber (Forward Precision) • CMS – Drift Tube (Barrel Precision) – Resistive Plate Chamber (Barrel + End-cap Trigger) – Cathode Strip Chamber (End-cap Precision) (Tracking chamber => Gas chamber!)
How to read the signal?
Energy loss of charged particle Bethe-Bloch formula (ionizing particle): (Max kinetic energy, which can transferred to electron) A: mass number [g/mol] of the material z: Charge of incident particle Z: Atomic number of material d: Density correction I : Mean excitation energy of material I=I 0 Z
Energy loss of charged particle • We should also consider bremsstrahlung for high energy muon (>100 Ge. V)
Ionization Incident particle interact with gas molecule, then producing electron and ion pairs (nprim). nprim has relationship with average Z of gas molecule This primary electrons are energetic enough to ionize other molecule (secondary : ns ~3)
d. E/dx (ke. V/cm) np (i. p. ) /cm) nt (i. p. ) /cm) Gas Z A δ(g/cm 3) Ei (e. V) I 0 (e. V) H 2 2 2 8. 38× 10− 5 15. 9 15 37 4. 03 0. 34 5. 2 9. 2 He 2 4 1. 66× 10− 4 24. 5 25 41 1. 94 0. 32 5. 9 7. 8 N 2 14 28 1. 17× 10− 3 16. 7 16 35 1. 68 1. 96 10 56 O 2 16 32 1. 33× 10− 3 12. 8 12 31 1. 69 2. 26 22 73 Ne 10 20. 2 8. 39× 10− 4 21. 5 22 36 1. 68 1. 41 12 39 Ar 18 39. 9 1. 66× 10− 3 15. 7 16 26 1. 47 2. 44 29. 4 94 Kr 36 83. 8 3. 49× 10− 3 13. 9 14 24 1. 32 4. 6 22 192 Xe 54 131. 3 5. 49× 10− 3 12. 1 12 22 1. 23 6. 76 44 307 CO 2 22 44 1. 86× 10− 3 13. 7 14 33 1. 62 3. 01 34 91 CH 4 10 16 6. 70× 10− 4 15. 2 13 28 2. 21 1. 48 16 53 C 4 H 10 34 58 2. 42× 10− 3 10. 6 11 23 1. 86 4. 5 46 195 Wi (Me. V cm 2/g) Properties of several gases used in proportional counters (from different sources, see the References section). Energy loss and ion pairs (i. p. ) per unit length are given at atmospheric pressure for minimum ionizing particles
Ionization • Total number of electron : ntot=nprim+ns=d. E/Wi – Wi [e. V/cm]: Effective energy to produce ion-electron pair Ex: Consider Ar(70)+Isobutane(30) ntot=2440/24 *0. 7 + 4500/23 * 0. 3 =124 pair/cm nprim= 29. 4 * 0. 7 + 46 * 0. 3 =34 pair/cm
Electron Drift In the absence of electric fields electron –ion pairs recombine and the net liberated charges disappear. MWPC In a uniform electric field the motion of electrons and ions alternate between acceleration and collision with the gas molecules. The resulting motion, in both cases, is a uniform velocity which depends on the intensity of the electric field and the properties of the gases. Cylindrical
Position measurement with Drift chamber Measure arrival time of electrons at sense wire relative to a time t 0.
Gas amplification Townsend avalanche: a: first townsend coefficient E/p > 10^4/cm If we neglect the space-charge effect and photoelectric effect by de-excitation of molecule, total charge (Q) = n 0 e. M M (gas amplification factor) is written as a function of a (a: radius of wire) Induced signal is written as
Choice of gas • In the avalanche process molecules of the gas can be brought to excited states. Solution: addition of polyatomic gas as a quencher Absorption of photons in a large energy Range. Energy dissipation by collisions or dissociation into smaller molecules. ⇔ penning effect
Operation mode M < 104 : Ionization mode (using DC mode for radiation monitor) M > 104 : Proportional mode (MWPC, DC) M > 106 : Limited Proportional mode M > 108 : G. M mode or Streamer mode (survey meter)
Difference between G. M and Streamer G. M mode Large output signal Long dead time Long term stability Streamer mode Large output signal Short dead time Large discharge sometime occur Limited mean free path of photon
HV dependence of Output charge (ex. RPC) Streamer Limited proportional Proportional
Monitored Drift Tube (ATLAS) • 6 / 8 drift tube layers, arranged in 2 multilayers glued to a spacer frame • length: 1 – 6 m, width: 1 – 2 m • optical system to monitor chamber deformations • gas: Ar: CO 2 (93: 7) to prevent aging, 3 bar • chamber resolution: 50 µm Æ single tube resolution: 100 µm Æ required wire position accuracy: 20 µm Barrel End Cap
MDT (Layout) BOL BOS BML BIS BMS Number of MDT : 1194 Number of Channels: 370000 Area: 5500 m 2
Monitored Drift Tube (ATLAS) Position resolution: 50 µm monitoring of high mechanical precision during production a= 25 μm b= 30 mm gas: Ar: CO 2 (93: 7) tube wall: 0. 4 mm Al 30 mm diameter endplug
MDT (Wire Positions with a X-Ray Method) X-tomograph at CERN measurement of the intensity as function of the motor position accuracy of wire position measurement: 3 µm mechanical precision measured with X-ray method selected chambers tested: 74 of 650 chambers produced at 13 sites scanned so far average wire positioning accuracy: 15 µm
MDT (Cosmic ray test) goals: e. g. Test Facility at the University of Munich • check functionality of all tubes and electronics channels • measurement of wire positions y z • deviations from nominal positions compared to X-ray results: rmsy = 25 µm, rmsz = 9 µm
MDT (Tracking efficiency) track-reconstruction efficiency total track-reconstruction efficiency: +0. 03 • ( 99. 97 )% without irradiation - 0. 9 +0. 23 • ( 99. 77 )% at highest ATLAS rate - 0. 8 (for 4 m long tubes) Æ even at highest expected irradiation no deterioration of track-reconstruction efficiency
Drift Tube (CMS) • Gas : Ar(85) + CO 2(15) • HV = 3. 6 k. V • Spatial Resolution: 100μm – (Single cell space resolution : < 250μm)
Drift Tube (Layout: CMS)
Drift Tube (CMS) HV=3600 V cm
Drift Tube (Tracking efficiency : CMS)
Cathode Strip Chamber (ATLAS, CMS) • 50 mm wire spaced by 3. 2 mm • gas : Ar(40%)+CO 2(50%) +CF 4(10%) • HV~3. 6 k. V • 9. 5 mm gas gap • Special resolution < 100μm
CSC (ATLAS, CMS)
CSC (ATLAS, CMS) S = d = 2. 54 mm W = 5. 6 mm 32 four-layer chambers 2. 0 < |h| < 2. 7 |Z| ~ 7 m, 1 < r < 2 m 4 gas gaps per chamber 31, 000 channels Gas Ar: CO 2: CF 4 (30: 50: 20) High voltage : 3. 2 k. V
• • • Multiwire proportional chambers determine muon position by interpolating the charge on 3 to 5 adjacent strips Precision (x-) strip pitch ~ 5 mm Spatial resolution s ~ 60 m. Second set of y-strips measure transverse coordinate to ~ 1 cm. Position accuracy unaffected by gas gain or drift time variations. Accurate intercalibration of adjacent channels essential.
Resistive Plate Chamber (ATLAS, CMS) • gas: C 2 H 2 F 4: iso. C 4 H 10 (97: 3) • 2 mm gas gap • HV=9 k. V
RPC (ATLAS, CMS) • Resistive Plate Chambers are gaseous, self-quenching parallel-plate detectors. • They are built from a pair of electrically transparent bakelite plates separated by small spacers. Signal are induced capacitively on external readout strips. - 420. 000 channels in 596 double gap chambers. Gas: C 2 H 2 F 4: iso. C 4 H 10 (97: 3). HV : 9 k. V. Performance: -efficiency: >99%. -space-time resolution of 1 cm 1 ns. -rate capability: ~1 k. Hz/cm².
Thin Gap Chamber (ATLAS) Requirements on ATLAS: ASD: Amp. Shaper Discriminator Wire potential 3. 0 k. V Gas mixture CO 2 + n-pentane (55%) (45%) Wire diameter 50 m – Fast signal response (<25 ns) – High efficiency (>99 %) – Radiation-proof (~0. 6 C/cm) – Rate capability (~k. Hz/cm 2) 1. 3 m 1. 4 m
TGC performance (ATLAS) Efficiency map (KOBE Univ. ) Incident angle dependence of drift time
TGC Production Procedure Checking quality Graphite spraying 80 boards/month 4 board /day FR 4 Frame Gluing 4 boards/day 3 persons Wire winding 2 boards /day 1 person Mounting Read-out boards 1 Unit/day 3 persons Making doublet (triplet) Singlet closing 2 TGCs /day 3 persons 1 Unit/day 2 persons Paper honeycomb
TGC Quality Control • TGC is fabricated by the gluing processes (we can no longer reopen it after closing TGC). • We have to control the surface distortion less than 200 m • We apply following tests: ü Measurement of the surface resistance of cathode after the graphite spraying, ü High voltage test before and after closinglet TGC, ü Pulse test after mounting adapter board and ü High voltage test after mounting adapter board. ü Pulse response check by b-ray radioactive source ü Cosmic ray test at KOBE Univ.
Graphite spraying and FR 4 frame Gluing • Graphite spraying by automatic sprayer – two-dimensional linear actuator – spray gun by the pneumatic control AT FR 4 Frame gluing : To control the quality of epoxy adhesive. Screen painting method for parts and Auto dispenser for button supports are adopted.
Wire winding Washing machine: Øto remove some dusts on the cathode plane by mist. ØWashing away the solder flux with ultrasonic cleaning Ø(water-soluble flux is used) Wire winding machine ü Consists of a linear actuator and a rotating table. Mist sprayer ü Total ~ 800, 000 wires Anode Wire: Gold plated Tungsten (A. L. M. T. co. Ltd. ) Solder: Sn(80)+Zn(20) • Flux: Water soluble flux Ultrasonic wave
TGC closing • In order to make flat plane, the combination of the vacuum-press and the suction plate technique have been adapted.
Physics impact using muon spectrometer
4 Muon final state • H→mmmm
2 Muon final state • For SUSY – H/A→mm • L-R symmetry – Z’ boson Due to bremsstrahlung of muon at calorimeter
Charge Identification • Important for – B physics – SUSY (same charge tag) – Extended Gauge model boson • Z’, W’ – Higgs (reconstruction)
Physics Impact of the Initial Detector The initial detector configuration for the first physics run consists of the following elements Magnet system A meaningful detector needs the full magnet system, Furthermore the construction of the barrel toroid is critical for the schedule, as it will condition the installation for all the other detector components Inner Detector The following components will be deferred (staging/upgrades): - Part of the Pixel system (3 rd point) - Part of the RODs - Potentially some TRT electronics - TRT end-cap wheels type C
Muon instrumentation The following components will be deferred (staging/upgrades) for the low luminosity phase: - EEL and EES MDT chambers, electronics and supports - Half of the CSC chamber layers (mechanics and electronics) The following component can appear as partially staged item: -Part of the end-wall MDT chambers High Level Trigger and DAQ The system needs to be designed to cost in a way that it can be easily upgraded Reduced processors from Common Projects Shielding A limited part of the high-luminosity shielding can be deferred by about one year
What we should know on analysis The main impact of the initial detector configuration is that the discovery potential for the Higgs signal in several final states will be degraded by about 10% (meaning that 20% more integrated luminosity is required to compensate) Possible penalties on the pattern recognition performance from the less robust tracking systems are not included in these results Staged items Main impact expected on tt. H ttbb Loss in significance Outermost TRT wheels + MDT H 4 ~ 7% Cryostat Gap scintillators MDT H 4 e ~ 8% A/H 2 ~ 10% for m ~ 300 Ge. V One pixel layer (The studies are documented in ATLAS RRB-D 2001 -118) ~ 8%
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