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R&D work on a Liquid Xenon Detector for the m  e g Experiment at PSI on behalf of the MEG Collaboration University of Tokyo, Japan Presented by S. Mihara http://meg.psi.ch. MEG Experiment at PSI R&D of Liquid Xenon Photon Detector. m  e g Search as Frontier Physics. m e g in…

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Meg experiment at psi r d of liquid xenon photon detector

R&D work on a Liquid XenonDetector for the meg Experiment at PSIon behalf of the MEG Collaboration University of Tokyo, Japan Presented by S. Miharahttp://meg.psi.ch

MEG Experiment at PSI

R&D of Liquid Xenon Photon Detector


M e g search as frontier physics
me g Search asFrontier Physics

  • meg in…

    • SM+Neutrino Oscillation

      • Suppressed as ∝(mn/mW)4

    • SUSY

      • Large top Yukawa coupling

Current limit

by MEGA

  • Neutrino Oscillation + SUSY

    • Hisano and Nomura 1998

10-10

tanb

nm

ne

10-11

e

m

W

10-12

g

Br(meg)

10-13

Solar Neutrino

10-14

g

10-15

~

~

m

e

MnR(GeV)

SK+SNO etc.=Large Mixing Solution

~

c

m

e


Meg experiment overview
MEG Experiment Overview

  • Detect e+and g, “back to back” and “in time”

  • 100% duty factor continuous beam of ~ 108m/sec

    • better than pulsed beam to reduce pile-up events

  • Two characteristic components

    • Liquid Xe photon detector

    • Solenoidal magnetic spectrometer with a graded magnetic field (COBRA)


Signal and background

menn+”g”

n

n

g

e

?

Signal and Background

Signal

qeg= 180°

m

g

e

  • Signal

  • Main background sources

    • Radiative m+ decay

      • If neutrinos carry small amount of energy, the positron and gamma can mimic the signal.

    • Accidental overlap

      • A positron from usual Michel decay with energy of half of mm

      • Gamma from

        • Radiative muon decay or

        • Annihilation in flight of positron

          NOT back to back, NOT in time

Ee = 52.8 MeV

Eg = 52.8 MeV

menng

g

n

n

e


Requirement on the photon detector
Requirement onthe Photon Detector

  • Good resolutions

    • Energy

    • Position

    • Time

  • Large acceptance with good uniformity

  • Fast decay time to reduce pile-up events


Properties of xenon

Property

Unit

Saturated temperature

T(K)

164.78

Saturated pressure

P(MPa)

0.100

Latent heat (for liquid)

r(J/kg)X103

95.8

Latent heat (for solid)

r'(J/kg)X103

1.2

Specific heat

Cp(J/kgK)X103

0.3484

Density

r(kg/m3)X103

2.947

Thermal conductivity

k(W/mK)

0.108

Viscosity

m(Pa-s)X10-4

5.08

Surface tension

s(N/m)X10-3

18.46

Expansion coefficient

b(1/K)X10-3

2.43

Temperature/Pressure at triple point

Tt(K)/PT(MPa)

161.36/

0.0815

Properties of Xenon

  • Fast response, Good Energy, and Position resolutions

    • Wph = 24 eV

      (c.f. Wph(NaI) = 17eV)

    • tfast=4.2nsec tslow=22nsec

  • Narrow temperature range between liquid and solid phases

    • Stable temperature control with a pulse-tube refrigerator


Liquid xenon photon detector
Liquid XenonPhoton Detector

Shallow event

800 liter LXe viewed

by ~ 800PMTs

Deep event


Absorption of scintillation light
Absorption of Scintillation Light

Simulation

For Large Prototype

labs=7cm

  • Scintillation light emission from an excited molecule

    • Xe+Xe*Xe2*2Xe + hn

  • Water contamination absorbs scintillation light more strongly than oxygen.

Depth parameter

labs=500cm

Depth parameter

Depth


R d strategy
R&D Strategy

  • Small Prototype done

    • Proof-of-Principle Experiment

    • 2.3liter active volume

  • Large Prototype in progress

    • Establish operation technique

    • 70 liter active volume

  • Final Detector starting

    • ~800 liter


  • Small prototype
    Small Prototype

    • 32 2-inch PMTs surround the active volume of 2.34 liter

    • g-ray sources of Cr,Cs,Mn, and Y

    • asource for PMT calibration

    • Operating conditions

      • Cooling & liquefaction using liquid nitrogen

      • Pressure controlled

      • PMT operation of 1.0x106 gain

    • Proof-of-Principle Experiment

      • PMT works in liquid xenon?

      • Light yield estimation is correct?

      • Simple setup to simulate and easy to understand.

    S.Mihara et al. IEEE TNS 49:588-591, 2002


    Small prototype energy resolution
    Small PrototypeEnergy resolution

    • Results are compared with MC prediction.

      • Simulation of g int. and energy deposition : EGS4

      • Simulation of the propagation of scint. Light

        EGS cut off energy : 1keV

        Rayleigh Scattering Length: 29cm

        Wph = 24eV


    Small prototype position and timing resolutions
    Small PrototypePosition and Timing resolutions

    • PMTs are divided into two groups by the y-z plane

      • gint. positions are calculated in each group and then compared with each other.

      • Position resolution is estimated as

        sz1-z2/√2

    • The time resolution

      is estimated by

      taking the difference

      between two groups.

    • Resolution improves

      as ~1/√Npe


    Large prototype
    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


    Purification system

    Gas return

    To purifier

    Circulation pump

    Purification System

    • Enomoto Micro Pump MX-808ST-S

      • 25 liter/m

      • Teflon, SUS

    • Xenon extracted from the chamber ispurified by passing through the getter.

    • Purified xenon is returned to the chamber and liquefied again.

    • Circulation speed 5-6cc/minute


    Purification performance
    Purification Performance

    • 3 sets of Cosmic-ray trigger counters

    • 241Am alpha sources on the PMT holder

    • Stable detector operation for more than 1200 hours

    Cosmic-ray events

    a events


    Absorption length
    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.


    Response to gamma beam
    Response to Gamma Beam

    • Electron storage ring,

      TERAS, in AIST,

      Tsukuba Japan

    • Electron Energy, Current:

      762MeV, 200mA

    • 266nm laser to induce inverse-Compston scattering.

    • 40 MeV (20MeV, and 10MeV) Compton g provided.

    • The Compton edge is used to evaluate the resolution.

    • Data taking

      • Feb. 2002 (w/o purification)

      • Apr. 2003 (w/ purification)

    10MeV

    20MeV

    40MeV


    Energy spectrum
    Energy Spectrum

    • s2 :depth parameter:

    40MeV Compton gamma data

    w/o xenon purification

    40MeV Compton gamma data

    w/ xenon purification

    Depth parameter

    Depth parameter

    Total Number of Photoelectrons

    Total Number of Photoelectrons


    Energy resolution
    Energy Resolution

    Simulation

    52.8MeV g

    • Shallow events have dependence on the depth of the 1st int. point.

    • Discard these shallow events (~34%) for quick analysis.

    • Calibration not completed

    • Very Preliminary: sE < 2%

    Depth parameter

    Very Preliminary


    Position reconstruction
    Position Reconstruction

    • 2-step reconstruction

      • 1st step: Pre-determination of the peak

      • 2nd step: Precise determination with an iteration process

    • Data 40MeV Compton g

    (a)

    (b)

    (c)

    (d)


    Timing resolution
    Timing Resolution

    • Estimated using Electron Beam (60MeV) data

    • Resolution improves in proportion to 1/sqrt(Npe).

    • For 52.8 MeV g, s~60 psec + depth resolution.

    • QE improvement and wave-form analysis will help to achieve better resolution.

      (Visit “The DRS chip” by S.Ritt)

    s=75.6+/-2.0ps

    45 MeV Energy deposit by 60 MeV electron injection

    s Timing Resolution (psec)

    52.8MeV g

    (nsec)

    104

    4x104

    Number of Photoelectron


    Summary
    Summary

    • New experiment to search for meg at Paul Scherrer Institut

    • Two characteristic components (and many others)

      • Liquid Xenon Photon Detector

      • Solenoidal magnetic spectrometer with a graded magnetic field (COBRA)

    • R&D of liquid xenon photon detector using the large prototype

      • Long term stable operation using a pulse tube refrigerator

      • Purification of liquid xenon

      • Very preliminary result from the last g beam test

        • sE<2% for 40MeV Compton g


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