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Liquid Xenon Photon Detector Satoshi MIHARA ICEPP, Univ. of Tokyo

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Presentation on theme: "Liquid Xenon Photon Detector Satoshi MIHARA ICEPP, Univ. of Tokyo"— Presentation transcript:

1 Liquid Xenon Photon Detector Satoshi MIHARA ICEPP, Univ. of Tokyo
MEG Experiment at PSI Satoshi MIHARA, U Zuerich Seminar Liquid Xenon Photon Detector Satoshi MIHARA ICEPP, Univ. of Tokyo

2 Satoshi MIHARA, U Zuerich Seminar
Contents MEG Experiment Physics Motivation MEG Detector Liquid Xenon Photon Detector Liquid Xenon Detector Components Performance Studies using Prototypes Status of the Detector Construction Satoshi MIHARA, U Zuerich Seminar

3 Satoshi MIHARA, U Zuerich Seminar
Lepton Flavor Violation (LFV) is strictly forbidden in SM. Neutrino oscillation LF is not conserved Contribute ∝ (mn/mW)4 Supersymmetry Off-diagonal terms in the slepton mass matrix μ e g μ e W g nm ne Satoshi MIHARA, U Zuerich Seminar Just below the current limit Br(μ→eγ) = 1.2 x 10-11 (MEGA, PRL 83(1999)83)

4 Satoshi MIHARA, U Zuerich Seminar
MEG Experiment at PSI Proposal submitted and approved in 1999 Situation at that time Neutrino oscillation discovery in 1998 4 possible solutions SUSY seesaw model tanb Satoshi MIHARA, U Zuerich Seminar Small tanb region was being excluded by LEP Higgs searches.

5 Satoshi MIHARA, U Zuerich Seminar
Current Situation KamLAND 766 ton-year data, 2004 SNO NaCl+D2O data, 2005 g-2 result K.Hagiwara, A.D. Martin, D.Nomura, and T.Teubner Satoshi MIHARA, U Zuerich Seminar

6 Satoshi MIHARA, U Zuerich Seminar
Signal and Background Signal Eg = mm/2 = 52.8MeV Ee = mm/2 = 52.8MeV q = 180o Time coincidence Background Radiative m decay Accidental overlap m g e g n m Satoshi MIHARA, U Zuerich Seminar n e n g m n ? e

7 Satoshi MIHARA, U Zuerich Seminar
Basic Concept Intense DC m beam Reduce pile-up Photon Detector Good resolution A few % for Energy A few mm for position ~100psec for timing Fast response Uniform Positron Detector Reduce BG Michel positron Minimum amount of material PSI Liquid Xenon Photon Detector COBRA Spectrometer Satoshi MIHARA, U Zuerich Seminar

8 Satoshi MIHARA, U Zuerich Seminar
MEG Detector Satoshi MIHARA, U Zuerich Seminar

9 COBRA Spectrometer (COnstant Bending Radius)
Sweep out curling positrons rapidly. Constant bending radius independent of the emission angles. COBRA Satoshi MIHARA, U Zuerich Seminar

10 Satoshi MIHARA, U Zuerich Seminar
COBRA Magnet Gradient magnetic field, 1.27 T at z=0 Small magnetic field around the photon detector. 0.197X0 around the center Cooling by using two GM-type refrigerators  No need of liquid He for operation Satoshi MIHARA, U Zuerich Seminar CERN Courier 44 number

11 Satoshi MIHARA, U Zuerich Seminar
Drift Chamber Position resolutions (~300mm) for both r and z. Vernier pad readout for z measurement Low material Satoshi MIHARA, U Zuerich Seminar

12 Satoshi MIHARA, U Zuerich Seminar
Timing Counter Plastic scintillator + Fine-mesh PMTs SciFi+APD to measure the impact point along the z-direction Satoshi MIHARA, U Zuerich Seminar

13 Satoshi MIHARA, U Zuerich Seminar
Xenon Detector Satoshi MIHARA, U Zuerich Seminar

14 Satoshi MIHARA, U Zuerich Seminar
Liquid Xenon Detector Why liquid xenon? How the detector works? Components Performance Study using prototypes Status of the detector construction Satoshi MIHARA, U Zuerich Seminar

15 Satoshi MIHARA, U Zuerich Seminar
Why liquid xenon? Good resolutions Large light output yield Wph(1MeV e) = 22.4eV Pile-up event rejection Fast response and short decay time ts = 4.2nsec, tT=45nsec (for electron, no E) Uniform A.Hitachi PRB 27 (1983)5279 Satoshi MIHARA, U Zuerich Seminar NaI BGO GSO LSO LXe Effective Atomic number 50 73 58 65 54 Density (g/cm3) 3.7 7.1 6.7 7.4 3.0 Relative light output (%) 100 15 20-40 45-70 80 Decay time (nsec) 230 300 60 40 4.2,22,45

16 Liquid Xenon and Sci light
Density 3.0 g/cm3 Triple point 161K, 0.082MPa Normal operation at T~167K P~0.12MPa Narrow temperature range between liquid and solid phases Stable and reliable temperature control is necessary Scintillation light emission mechanism Liquid Solid Pressure [MPa] Satoshi MIHARA, U Zuerich Seminar 0.1 0.082 Gas Excitation Triple point Recombination 161 165 Temperature [K]

17 Satoshi MIHARA, U Zuerich Seminar
MEG Xenon Detector Active volume ~800l is surrounded PMTs on all faces ~850PMTs in the liquid No segmentation Energy All PMT outputs Position PMTs on the inner face Timing Averaging of signal arrival time of selected PMTs Satoshi MIHARA, U Zuerich Seminar

18 Reconstruction of the event depth
Using event broadness on the inner face Necessary to achieve good timing resolution Satoshi MIHARA, U Zuerich Seminar g

19 Satoshi MIHARA, U Zuerich Seminar
Detector Components Photomultiplier Operational in liquid xenon, Compact UV light sensitive Refrigerator Stable temperature control Sufficient power to liquefy xenon Low noise, maintenance free Xenon Purifier Purification during detector operation Satoshi MIHARA, U Zuerich Seminar

20 Satoshi MIHARA, U Zuerich Seminar
Photomultiplier R&D Ichige et al. NIM A327(1993)144 Photocathode Bialkali :K-Cs-Sb, Rb-Cs-Sb Rb-Cs-Sb has less steep increase of sheet resistance at low temperature K-Cs-Sb has better sensitivity than Rb-Cs-Sb Multialkali :+Na Sheet resistance of Multialkali dose not change so much. Difficult to make the photocathod, noisy Dynode Structure Compact Possible to be used in magnetic field up to 100G Metal channel  Uniformity is not excellent Satoshi MIHARA, U Zuerich Seminar

21 PMT Development Summary
1st generation R6041Q 2nd generation R9288TB 3rd generation R9869 228 in the LP (2003 CEX and TERAS) 127 in the LP (2004 CEX) 111 In the LP (2004 CEX) Not used yet in the LP Rb-Sc-Sb Mn layer to keep surface resistance at low temp. K-Sc-Sb Al strip to fit with the dynode pattern to keep surface resistance at low temp. Al strip density is doubled. 4% loss of the effective area. 1st compact version QE~4-6% Under high rate background, PMT output reduced by 10 -20% with a time constant of order of 10min. Higher QE ~12-14% Good performance in high rate BG Still slight reduction of output in very high BG Higher QE~12-14% Much better performance in very high BG Satoshi MIHARA, U Zuerich Seminar

22 PMT Base Circuit Necessary to reduce heat load from the circuit
Heat load in the cryostat ↔ Refrigerator cooling power ~150W Reduce base current 800V 55microA  44mW/PMT 40-50W heat load from 850PMTs Zener diodes at last 2 stages for high rate background Zener diode is very noisy at low temperature  filtering on the base Satoshi MIHARA, U Zuerich Seminar Reference PMT = no Zener PMT with Zener

23 Pulse Tube Refrigerator
No mechanically moving part in the cold part Quiet Maintenance free Crucial for the MEG xenon detector Satoshi MIHARA, U Zuerich Seminar

24 Satoshi MIHARA, U Zuerich Seminar
Refrigerator R&D MEG 1st spin-off Technology transferred to a manufacturer, Iwatani Co. Ltd Performance obtained at Iwatani 189 6.7 kW compressor 4 Hz operation Satoshi MIHARA, U Zuerich Seminar

25 Satoshi MIHARA, U Zuerich Seminar
Xenon Purifier Attenuation of Sci light Scintillation light emission from an excited molecule Xe+Xe*Xe2*2Xe + hn Attenuation Rayleigh scattering lRay~30-45cm Absorption by impurity Satoshi MIHARA, U Zuerich Seminar

26 Possible Contaminants
Remaining Gas Analysis (RGA) for investigating what causes short absorption length. Remaining gas in the chamber was sampled to the analyzing section. Vacuum level LP Chamber 2.0x10-2Pa Analyzing section 2.0x10-3Pa He Satoshi MIHARA, U Zuerich Seminar H2O CO/N2 O2 Xe CO2

27 Satoshi MIHARA, U Zuerich Seminar
Water Contamination Usually water can be removed by heating the cryostat during evacuation. MEG liq. Xenon detector cannot be heated because of the PMTs inside. Water molecule is usually trapped on cold surface in the cryostat. However when the cryostat is filled with fluid, water molecules seem to dissolve in the fluid. Circulation/Purification after filling with fluid. Satoshi MIHARA, U Zuerich Seminar

28 Satoshi MIHARA, U Zuerich Seminar
Large Prototype 70 liter active volume (120 liter LXe in use) Development of purification system for xenon Total system check in a realistic operating condition: Monitoring/controlling systems Sensors, liquid N2 flow control, refrigerator operation, etc. Components such as Feedthrough,support structure for the PMTs, HV/signal connectors etc. PMT long term operation at low temperature Performance test using 10, 20, 40MeV Compton g beam 60MeV Electron beam g from p0 decay Satoshi MIHARA, U Zuerich Seminar

29 Satoshi MIHARA, U Zuerich Seminar
Purification System Xenon extracted from the chamber is purified by passing through the getter. Purified xenon is returned to the chamber and liquefied again. Circulation speed 5-6cc/minute Gas return To purifier Circulation pump Satoshi MIHARA, U Zuerich Seminar

30 Heated Metal Getter Purifier
Metal getter technology based on zirconium metals form irreversible chemical bonds to remove all oxide, carbide and nitride impurities Getter Material (GM) such as Zr GM + O2  GMO GM + N2   GMN GM + CO2  CO + GMO  GMC + GMO GM + CO  GMC + GMO GM + H2O  H + GMO  GMO + H (bulk) GM + H2  GM + H (bulk) GM + Hydrocarbons, CxHx, etc.  GMC + H (bulk) GM + He, Ne, Ar, Kr, Xe (inert gases)  No reaction These chemical reactions occur on the surface of the metal, and the reaction products then diffuse into the bulk structure. Longer life time than catalyst media Need temperature control of the metal Satoshi MIHARA, U Zuerich Seminar Heat allows bulk diffusion of impurities

31 Purification Performance
Xenon Detector Large Prototype 3 sets of Cosmic-ray trigger counters 241Am alpha sources on the PMT holder Stable detector operation for more than 1200 hours Satoshi MIHARA, U Zuerich Seminar Cosmic-ray events a events

32 Satoshi MIHARA, U Zuerich Seminar
Absorption Length Fit the data with a function : A exp(-x/ labs) labs >100cm (95% C.L) from comparison with MC. CR data indicate that labs > 100cm has been achieved after purification. Satoshi MIHARA, U Zuerich Seminar

33 Satoshi MIHARA, U Zuerich Seminar
Upgrade of the system Purification in Gas phase Evaporate and liquefy Slow Cooling power consumption We know that water is the main impurity to be removed. Purification system dedicated to remove water Not in gas phase but in liquid phase Satoshi MIHARA, U Zuerich Seminar

34 Liquid-phase Purification System
Xenon circulation in liquid phase. Impurity (water) is removed by a purifier cartridge filled with molecular sieves. 100 l/hour circulation. Satoshi MIHARA, U Zuerich Seminar

35 Liquid-phase Purifier Prototype
Temperature Sensor PMT’s Purifier Cartridge Molecular sieves, 13X 25g water Freq. Inverter OMRON PT Satoshi MIHARA, U Zuerich Seminar

36 Liquid-phase Purification Performance
In ~10 hours, λabs ~ 5m Satoshi MIHARA, U Zuerich Seminar

37 Satoshi MIHARA, U Zuerich Seminar
Performance Studies Small Prototype Test of the detector principle Large Prototype Inverse-Compton g beam p0  g g produced via charge exchange process p-pp0n Satoshi MIHARA, U Zuerich Seminar

38 Satoshi MIHARA, U Zuerich Seminar
TERAS g Beam Compton Spectrum (Eg-Ec/2)2+(Ec/2)2 Satoshi MIHARA, U Zuerich Seminar Collimator size Electron beam (TERAS, Tsukuba in Japan) Energy: 764MeV Energy spread: 0.48%(sigma) Divergence: <0.1mrad(sigma) Beam size: 1.6mm(sigma) Laser photon Energy: 1.17e-6x4 eV (for 40MeV) Energy spread: 2x10-5 (FWHM) Divergence: unknown Beam size: unknown 10MeV 20MeV 40MeV

39 Energy Spectrum Fitting
Suppose Compton Spectrum around the edge (E-Ec/2)2+Ec2/4 Detector Response Function Gaussian with Exponential tail f(x) = N*exp{t/s2(t/2-(x-x0)}, x<x0+t N*exp{-1/2((x-x0)/s)2}, x>x0+t Convolution Integration +/- 5s Principle… Eg Satoshi MIHARA, U Zuerich Seminar Npe Convolution of Compton Spectrum Response Function sE~1.9%

40 Measurement with half the front PMT switched off
g To simulate the convex front geometry of the cryostat Switch off half of the PMTs in the front face Use 4x4 PMTs out of 6x6 PMTs Switch off PMTs on the side walls Satoshi MIHARA, U Zuerich Seminar

41 Satoshi MIHARA, U Zuerich Seminar
TERAS Data Only 4x4 PMTs on the front face Switching off half the front PMTs Compton Edge shifts by 6.2% Resolutions are almost same (1.84 to 1.85% in s) before and after switching off. Switching off PMTs on the side wall(s) 1 plane off  2.05% in s 2 planes off  2.22% in s 3, 4 planes off  > 3% in s Number of Photoelectrons 4 planes off 3 planes off 2 planes off 1 plane off 1/Npe 1/sqrt(Npe) Satoshi MIHARA, U Zuerich Seminar

42 Switching off PMTs on side walls
Deterioration of the energy resolution when switching off PMTs is not mainly caused by loss of Npe. PMTs on the side walls compensate 1st conversion point dependence. 1 plane off Satoshi MIHARA, U Zuerich Seminar Number of Photoelectrons D 3 planes off Number of Photoelectrons

43 Effect of a “faulty” PMT
All PMTs on: s=1.8% Switching off one PMT on the front wall. the nearest PMT s=2.3% 2nd nearest PMT s=1.9% 3rd nearest PMT s=1.9% 300 PMTs on the front face in the final detector ~4/300 = 1.3% loss of acceptance F30 off s=2.3% Satoshi MIHARA, U Zuerich Seminar F22 off s=1.9% F28 off s=1.9%

44 Satoshi MIHARA, U Zuerich Seminar
CEX beam test Charge Exchange elementary process p-pp0n p0(28MeV/c)  g g 54.9 MeV < E(g) < 82.9 MeV Requiring q>170o FWHM = 1.3 MeV Requiring q > 175o FWHM = 0.3 MeV p0 Eg q q Eg 170o 175o Eg 54.9MeV 82.9MeV 1.3MeV for q>170o 0.3MeV for q>175o Satoshi MIHARA, U Zuerich Seminar

45 Satoshi MIHARA, U Zuerich Seminar
Beam Test Setup H2 target+degrader LYSO Eff ~14% Satoshi MIHARA, U Zuerich Seminar NaI LP S1 Eff(S1xLP)~88% beam

46 Satoshi MIHARA, U Zuerich Seminar
Energy Resolutions CEX 2004 55 MeV 83 MeV to Xe = 1.23 ±0.09 % FWHM=4.8 % Satoshi MIHARA, U Zuerich Seminar 55 MeV to Xe Exenon[nph] 83 MeV σ = 1.00±0.08 % FWHM=5.2%

47 Energy Resolution vs Energy
PSI 2003 TERAS 2003 alpha Satoshi MIHARA, U Zuerich Seminar Right  is a nice function of gamma energy

48 Position Reconstruction
Localized Weight Method Satoshi MIHARA, U Zuerich Seminar Projection to x and y directions. Peak point and distribution spread Position reconstruction using the selected PMT

49 Examples of Reconstruction
Satoshi MIHARA, U Zuerich Seminar (40 MeV gamma beam w/ 1 mm collimator)

50 Satoshi MIHARA, U Zuerich Seminar
Timing/Z Resolution p- Improving Z resolution is essential to improve timing resolution. Intrinsic timing resolution can be evaluated by comparing left and right parts of the detector. <T> = (TLTR)/2 NaI g S1 g Xenon LYSO tLP - tLYSO Satoshi MIHARA, U Zuerich Seminar TL Left Right TR g

51 Absolute timing, Xe-LYSO analysis
normal gain high gain 110 psec 103 psec 55 MeV Satoshi MIHARA, U Zuerich Seminar s LYSO Beam L-R depth reso. = = psec = = psec Normal gain High gain A few cm in Z

52 Status of Xenon Detector Construction
PMT 850 PMTs being tested in PSI and Pisa Cryostat Under construction Delivery to PSI early in 2006 Gas system Getting ready in pE5 area in PSI Satoshi MIHARA, U Zuerich Seminar

53 Satoshi MIHARA, U Zuerich Seminar
Summary MEG at PSI Search for μ→eγ with better sensitivity than previous experiments Xenon detector COBRA spectrometer PSI m beam Detector preparation will finish in several months DAQ in 2006 Satoshi MIHARA, U Zuerich Seminar

54 Further Information Please visit http://meg.psi.ch Beam
Drift Chamber system Timing Counter Electronics Software Waveform analysis Etc. Please visit Satoshi MIHARA, U Zuerich Seminar


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