RD works on Liquid Xenon Photon Detector for

R&D works on Liquid Xenon Photon Detector for μgeγ experiment at PSI Outline l　Introduction l　Prototype R&D works l　Summary Satoshi Mihara ICEPP, Univ. of Tokyo 20/10/2000 R&D works on Liquid Xenon Photon Detector for μ→eγ

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 2 Introduction, 　μgeγ at PSI aims to achieve the sensitivity down to Br(μgeγ)～ 10 -14 n Detect e+ and γ, “back to n back” and “in time” 100% duty factor continuous beam of ～ 108μ/sec n n Liquid Xe photon detector Solenoidal magnetic spectrometer with a graded magnetic field http: //meg. psi. ch

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 3 Introduction, cont’d n μ beam stopped on the target 108/sec u Ee=52. 8 Me. V Eγ=52. 8 Me. V μ Back to back, in time n Sensitivity u γ e Nm=1 x 108/sec, 2. 2 x 107 sec running Ω/4π=0. 09, εe=0. 95, εγ=0. 7, and εsel=0. 8 a. Single Event sensitivity : 0. 94 x 10 -14 n Main background sources u Radiative μ+ decay γ ν Accidental overlap NOT back to back, NOT in time e a Reduced down to 10 -15 level u μgeνν+”γ” μgeννγ ν ν γ ν e ?

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 4 Requirement on the Photon Detector n Good Energy Resolution n Good Position Resolution n Good time Resolution

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan Liquid Xe Photon Detector 5 n n Detect scintillation light(λ=175 nm) from Liq. Xe(-100℃) Fast response, Good Energy, and Position resolutions u • 800 liter liquid Xe • 800 PMTs inside liquid(HAMAMATSU R 6041 Q) Wph = 24 e. V (c. f. Wph(Na. I) = 17 e. V) u u ! τfast =45 nsec Mini-Kamiokande type Na. I: too slow Cs. I, BGO: poor resolution at 52. 8 Me. V Inhomoginity to cover large area

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 6 Strategy for the Detector Construction n Small Prototype n n Large Prototype Final Detector n n PMT Development Refrigerator Development Purification System Development Attenuation Length Measurement

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 7 Small Prototype of Liquid Xe Photon Detector n n n 32 2 -inch PMTs surround the active volume of 2. 34 liter γ-ray sources of Cr, Cs, Mn, and Y α source for PMT calibration Metal channel dynodes n Possible to be operated at low -100 o n Silica window to transmit UV light n Typical gain 106, Typical Q. E. 10% n Possible to sustain up to 3 atom n

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan Small Prototype 8 Experimental Procedure n n n Xenon liquified with a nitrogen cooling pipe Kept in stable temp. (-100 o) and pressure (1. 2 atom) by controlling the flow of liquid nitrogen PMT operation in liquid xenon has been successful for more than one month

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan Small Prototype 9 Signal from PMTs n n Typical PMT output for liq. Xe scintillation light c Triggering condition for γ ray events (ex. For g from Mn) u u u > > > 220 p. e. in R 1 50 p. e. in R 2 10 p. e. in R 3 100 p. e. in E 1 20 p. e. in E 2 Loose enough to trigger Almost all events where γ interacted well inside the sensitive volume

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 10 Small Prototype Analysis n Position of γ interaction: Weighting the position of the PMTs with their individual pulse heights n For selecting the fully contained events: Requiring the γ int. position should lie within a central region of 2 cmx 1 cmφ

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 11 Small Prototype Result, Energy Resolution n n Fitting the spectrums with an asymmetric Gaussian function. Results are compared with MC prediction. Simulation of γ int. and energy deposition : EGS 4 Simulation of the propagation of scint. Light EGS cut off energy : 1 ke. V Att. Length (absorption): 29 cm Wph = 24 e. V n 0. 7% in σ is expected at 52. 8 Me. V.

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 12 Small Prototype Result, Position Resolution n PMTs are divided into two groups by the y-z plane. u u n γ int. positions are calculated in each group and then compared with each other. Position resolution is estimated as 　　　　sz 1 -z 2/√ 2 Possible to achieve for 52. 8 Me. V γ σ<3 mm in position meas.

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 13 Small Prototype Result, Time Resolution n n PMTs are divided again into two groups by the y-z plane. In each group the average of the time measured by TDC is calculated after slewing correction for each PMT. The time resolution is estimated by taking the difference between two groups. Resolution improves as ～ 1/√Npe σ<50 psec at 52. 8 Me. V.

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 14 Short Summary on the Small Prototype Extrapolation to Higher Energy n n n Energy 0. 7% Position <3 mm Time <50 psec in σ at 52. 8 Me. V Excellent! Go to the next step Large Prototype

How Large? n To study the detector response to higher energy γ rays, large volume is required to fully contain events. Energy Deposit(arbitrary unit) R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan Large Prototype Depth ～ 40 cm x 50 cm Active Volume 224 PMTs Depth from Xe surface(cm) 15

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 16 Large Prototype Vessel Design n n Vessel should be large enough to install the detector. Possibility to reuse for future PMT calibration. Thinner entrance window thickness. Thermal insulation. Most of all components used in the final detector should be tested in Large Prototype. u Refrigerator u Feedthrough u PMT holder structure u Surface level meter etc, etc…

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan Construction of the Large Prototype Vessel 17

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan Construction of the Large Prototype Vessel 18 n n n Pressure test up to 0. 6 MPa Vacuum leak test Cooling test with liquid nitrogen All OK. Ready to fill liquid xenon inside

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 19 Assembling n Holder Front: G 10, Plastic u Side, Rear: Aluminum u n n Blue LEDs for PMT gain adjustment α sources for calibration Temperature sensors Surface Level meter

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 20 Pulse Tube Refrigerator n n Conventionally liq. Nitrogen has been used g waste of nitrogen, not suitable for long term physics experiment. Purse tube refrigerator is the best for this purpose since there is no moving part in the low temperature stage. Mechanically moving Pressure Oscillation 70 W

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 21 Liquefaction Test n n n n Pre-cooling before liquefaction with 0. 2 MPa gas xenon inside. Liquefaction of xenon 100 liter liquid for ~ 2 day (2. 0 liter/hour). Recondensation using the refrigerator was successfully done. Several basic measurements done. PMTs operated for 2. 5 days stably. Calibration with LED and α source signals done Currently preparing γ beam test in June.

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 22 γ beam at TERAS n Use inverse-compton scattered γ beam provided at TERAS in ETL AIST in Tsukuba, Japan. u u n n Eγ: 10, 20, 30, 40 Me. V γ beam intensity: 1 k. Hz (typ. ) Analyze the edge of the Compton photon spectrum. Test will start in the middle of June. Na. I 40 Me. V γ Taken after acc. trouble. Better BG condition now!

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan Plan for Attenuation Length Measurement 23 Step 1 PMT 1: Absorption + Scattering Length meas. PMT 2: used as a reference. Collimators to prevent scinti. light from hitting the wall. Mask in front of PMT 1 to define the illuminated area on the photo cathode. Liq. Nitrogen PMT 1 Step 2 PMT 2: Scatt. Length meas. PMT 1: reference at a fixed point. d. L/L ~ 5 x L(m) [%] PMT 2 X ray

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 24 Summary n Small Prototype u u u n Small prototype of liquid Xe photon detector was successfully constructed and tested with γ -ray sources of 320 ke. V-1836 ke. V. Scintillation light from xenon is directly observed with PMTs located inside the liquid. Excellent Energy, Position, Time resolutions. Large Prototype u u 100 liter liquefaction test was successfully done. Currently preparing for a large prototype test using inverse-compton scattered beam of higher energy γ rays < 40 Me. V.

R&D works on Liquid Xenon Photon Detector for μ→eγ Nu. FACT’ 01 29/05/2001 Tsukuba, Japan 25 Summary cont’d n Refrigerator u u n Attenuation Length Measurement u u n Recondensation of 100 liter of liq. Xenon was successful. Studying other coolants for obtaining better cooling efficiency. Setup construction is going on. Measurements will start in this autumn at Novosibirsk. Final Detector u u Design work just started. Xenon, γ window, PMT mass-production.