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R&D works on Liquid Xenon Photon Detector for μ g e γ experiment at PSI

R&D works on Liquid Xenon Photon Detector for μ g e γ experiment at PSI. Outline Introduction Prototype R&D works Summary. Satoshi Mihara ICEPP, Univ. of Tokyo. Introduction, μ g e γ at PSI. aims to achieve the sensitivity down to Br( μ g e γ ) ～ 10 -14.

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R&D works on Liquid Xenon Photon Detector for μ g e γ experiment at PSI

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  1. R&D works on Liquid Xenon Photon Detectorfor μgeγ experiment at PSI • Outline • Introduction • Prototype R&D works • Summary Satoshi Mihara ICEPP, Univ. of Tokyo

  2. Introduction,μgeγat PSI aims to achieve the sensitivity down toBr(μgeγ)～10-14 • Detecte+andγ, “back to back” and “in time” • 100% duty factor continuous beam of ～108μ/sec • Liquid Xe photon detector • Solenoidal magnetic spectrometer with a graded magnetic field R&D works on Liquid Xenon Photon Detector for μ→eγ http://meg.psi.ch STARTS IN 2003 and RUNS 1- 2 years

  3. Introduction,cont’d γ • μ beam stopped on the target 108/sec • Ee=52.8MeV Eγ=52.8MeV Back to back, in time • Sensitivity • Nm=1x108/sec, 2.2x107 sec running Ω/4π=0.09,εe=0.95,εγ=0.7,andεsel=0.8 aSingle Event sensitivity : 0.94x10-14 • Mainbackgroundsources • Radiativeμ+ decay • Accidental overlap NOT back to back, NOT in time • Reduced down to 10-15 level μ e R&D works on Liquid Xenon Photon Detector for μ→eγ μgeνν+”γ” μgeννγ ν γ ν ν γ e ν e ?

  4. Requirement on the Photon Detector • Good Energy Resolution • Good Position Resolution • Good time Resolution R&D works on Liquid Xenon Photon Detector for μ→eγ

  5. Liquid Xe Photon Detector • 800 liter liquid Xe • 800 PMTs inside liquid(HAMAMATSU R6041Q) • Detect scintillation light(λ=175nm) from Liq. Xe(-100℃) • Fast response, Good Energy, and Position resolutions • Wph = 24 eV (c.f. Wph(NaI) = 17eV) • τfast=45nsec • Mini-Kamiokande type R&D works on Liquid Xenon Photon Detector for μ→eγ NaI: too slow CsI, BGO: poor resolution at 52.8MeV Inhomoginity to cover large area !

  6. Strategy for the Detector Construction • PMT Development • Refrigerator Development • Purification System Development • Attenuation Length Measurement • Small Prototype • Large Prototype • Final Detector R&D works on Liquid Xenon Photon Detector for μ→eγ

  7. Small Prototype ofLiquid Xe Photon Detector • 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 R&D works on Liquid Xenon Photon Detector for μ→eγ • Metal channel dynodes • Possible to be operated at low -100o • Silica window to transmit UV light • Typical gain 106, Typical Q.E. 10% • Possible to sustain up to 3 atom

  8. Small PrototypeExperimental Procedure • Xenon liquified with a nitrogen cooling pipe • Kept in stable temp.(-100o) 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

  9. Small PrototypeSignal from PMTs • Typical PMT output for liq. Xe scintillation light • Triggering condition for γ ray events (ex. For g from Mn) • > 220 p.e. in R1 • > 50 p.e. in R2 • > 10 p.e. in R3 • > 100 p.e. in E1 • > 20 p.e. in E2 Loose enough to trigger Almost all events where γ interacted well inside the sensitive volume c R&D works on Liquid Xenon Photon Detector for μ→eγ

  10. Small PrototypeAnalysis • Position of γ interaction: Weighting the position of the PMTs with their individual pulse heights • For selecting the fully contained events: Requiring the γ int. position should lie within a central region of 2cmx1cmφ R&D works on Liquid Xenon Photon Detector for μ→eγ

  11. Small PrototypeResult, Energy Resolution • Fitting the spectrums with an asymmetric Gaussian function. • Results are compared with MC prediction. Simulation of γ int. and energy deposition : EGS4 Simulation of the propagation of scint. Light EGS cut off energy : 1keV Att. Length (absorption):29cm Wph = 24eV • 0.7% in σ is expected at 52.8MeV. R&D works on Liquid Xenon Photon Detector for μ→eγ

  12. Small PrototypeResult, Position Resolution • PMTs are divided into two groups by the y-z plane. • γ int. positions are calculated in each group and then compared with each other. • Position resolution is estimated as sz1-z2/√2 • Possible to achieve for 52.8MeV γ σ<3mm in position meas. R&D works on Liquid Xenon Photon Detector for μ→eγ

  13. Small PrototypeResult, Time Resolution • 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<50psec at 52.8 MeV. R&D works on Liquid Xenon Photon Detector for μ→eγ

  14. Short Summary on the Small Prototype Extrapolation to Higher Energy • Energy 0.7% • Position <3mm • Time <50psec R&D works on Liquid Xenon Photon Detector for μ→eγ in σ at 52.8MeV Excellent! Go to the next step Large Prototype

  15. Energy Deposit(arbitrary unit) Depth from Xe surface(cm) Large PrototypeHow Large? • To study the detector response to higher energy γrays, large volume is required to fully contain events. R&D works on Liquid Xenon Photon Detector for μ→eγ Depth ～40cm x 40cm x 50cm Active Volume 224 PMTs

  16. Large PrototypeVessel Design • 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. • Refrigerator • Feedthrough • PMT holder structure • Surface level meter etc, etc… R&D works on Liquid Xenon Photon Detector for μ→eγ

  17. Construction ofthe Large Prototype Vessel R&D works on Liquid Xenon Photon Detector for μ→eγ

  18. Construction of the Large Prototype Vessel • Pressure test up to 0.6MPa • Vacuum leak test • Cooling test with liquid nitrogen R&D works on Liquid Xenon Photon Detector for μ→eγ All OK. Ready to fill liquid xenon inside

  19. Assembling • Holder • Front: G10, Plastic • Side, Rear:Aluminum • 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

  20. Pulse Tube Refrigerator • Conventionally liq. Nitrogen has been used gwaste 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. R&D works on Liquid Xenon Photon Detector for μ→eγ Pressure Oscillation Mechanically moving 70W

  21. Liquefaction Test • Pre-cooling before liquefaction with 0.2MPa 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. R&D works on Liquid Xenon Photon Detector for μ→eγ • PMTs operated for 2.5 days stably. • Calibration with LED and α source signals done • Currently preparing γ beam test in June.

  22. γ beam at TERAS • Use inverse-compton scattered γbeam provided at TERAS in ETL AIST in Tsukuba, Japan. • Eγ:10,20,30,40MeV • γ beam intensity: 1kHz (typ.) • Analyze the edge of the Compton photon spectrum. • Test will start in the middle of June. R&D works on Liquid Xenon Photon Detector for μ→eγ 40MeV γ NaI Taken after acc. trouble. Better BG condition now!

  23. Plan for Attenuation Length Measurement Step1 PMT1:Absorption + Scattering Length meas. PMT2: used as a reference. Collimators to prevent scinti. light from hitting the wall. Mask in front of PMT1 to define the illuminated area on the photo cathode. Liq. Nitrogen R&D works on Liquid Xenon Photon Detector for μ→eγ PMT1 • Step2 • PMT2: Scatt. Length meas. • PMT1: reference at a fixed point. PMT2 dL/L ~ 5 x L(m) [%] X ray

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

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

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