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Innovative Liquid Xenon Photon Detector for μ→eγ Experiment at PSI

This research and development project focuses on creating a cutting-edge Liquid Xenon Photon Detector for the μ→eγ experiment at PSI, aiming for superior energy, position, and time resolutions to achieve a single-event sensitivity of 0.94x10-14. The prototype works include designing a detector with 800 liters of liquid Xenon, 800 PMTs, and a fast response time for detecting scintillation light. Different strategies such as PMT development and purification system development are being explored. Experimental procedures and results from the Small Prototype show promising energy resolution and position and time resolutions below 3mm and 50psec, respectively.

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Innovative Liquid Xenon Photon Detector for μ→eγ 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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