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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