meg experiment at psi r&d of liquid xenon photon detector

Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003

R&D work on a Liquid XenonDetector for the e Experiment at PSI

on behalf of the MEG Collaboration

University of Tokyo, Japan Presented by S. Mihara

http://meg.psi.ch

I. MEG Experiment at PSI

II. R&D of Liquid Xenon Photon Detector


• Neutrino Oscillation + SUSY– Hisano and Nomura 1998

e e Search as Search asFrontier PhysicsFrontier Physics

Solar Neutrino

tan

SK+SNO etc.=Large Mixing SolutionSK+SNO etc.=Large Mixing Solution

Current limitby MEGA

• e in…– SM+Neutrino Oscillation

• Suppressed as (∝ m/mW)4

– SUSY• Large top Yukawa coupling

e

e~ ~

~

W e

e

MR(GeV)

Br(

e)

10-10

10-11

10-12

10-13

10-14

10-15


MEG Experiment OverviewMEG Experiment Overview

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

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

– better than pulsed beam to reduce pile-up events

• Two characteristic components

1. Liquid Xe photon detector

2. Solenoidal magnetic spectrometer with a graded magnetic field (COBRA)


Signal and BackgroundSignal and Background

• Signal• Main background sources

– Radiative + 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 m

• Gamma from– Radiative muon decay or– Annihilation in flight of positron

NOT back to back, NOT in time e

e+””

?

enn

e

Ee = 52.8 MeV

Signal e= 180°

Eg = 52.8 MeV

e


Requirement onRequirement onthe Photon Detectorthe Photon Detector

• Good resolutions– Energy– Position– Time

• Large acceptance with good uniformity

• Fast decay time to reduce pile-up events


Properties of XenonProperties 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

Property Unit

Saturated temperature T(K) 164.78

Saturated pressure P(MPa) 0.100

Latent heat (for liquid) (J/kg)X103 95.8

Latent heat (for solid) '(J/kg)X103 1.2

Specific heat Cp(J/kgK)X103 0.3484

Density (kg/m3)X103 2.947

Thermal conductivity (W/mK) 0.108

Viscosity (Pa-s)X10-4 5.08

Surface tension (N/m)X10-3 18.46

Expansion coefficient (1/K)X10-3 2.43

Temperature/Pressure at triple point Tt(K)/PT(MPa) 161.36/0.0815


Liquid XenonLiquid XenonPhoton DetectorPhoton Detector

3 cm

Liq. Xe

Liq. Xe

14 cm

(a)

(b)

05 10 15

2025

3035

0

10

20

30

40

50

0

2000

4000

6000

8000

10000

05

1015 20 25

3035

0

10

20

30

40

50

0

200

400

600

800

1000

1200

1400

1600

1800

52.8 MeV

52.8 MeV

800 liter LXe viewedby ~ 800PMTs

800 liter LXe viewedby ~ 800PMTs

Shallow event

Deep event


Absorption of Scintillation LightAbsorption of Scintillation Light• Scintillation light emission from an excited molecule

– Xe+Xe*Xe2*2Xe + h

• Water contamination absorbs scintillation light more strongly than oxygen. abs=7cm

abs=500cm

Depth

Dep

th p

aram

eter

Dep

th p

aram

eter

SimulationFor Large Prototype


• 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

R&D StrategyR&D Strategy


Small PrototypeSmall Prototype• 32 2-inch PMTs surround the

active volume of 2.34 liter

• -ray sources of Cr,Cs,Mn, and Y

• source 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.

•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

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


Small PrototypeSmall PrototypeEnergy resolutionEnergy resolution

• Results are compared with MC prediction.1. Simulation of int. and energy

deposition : EGS4

2. Simulation of the propagation of scint. Light

EGS cut off energy : 1keV

Rayleigh Scattering Length: 29cm

Wph = 24eV


Small PrototypeSmall PrototypePosition and Timing resolutionsPosition and Timing resolutions

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

– g int. positions are calculated in each group and then compared with each other.

– Position resolution is estimated as

sz1-z2/√2

• The time resolutionis estimated bytaking the difference

between two groups. • Resolution improves

as ～ 1/√Npe

•


Large PrototypeLarge 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 beam– 60MeV Electron beam


Purification SystemPurification System• Xenon extracted from the

chamber is purified by passing through the getter.

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

• Circulation speed 5-6cc/minute

• Enomoto Micro Pump MX-808ST-S– 25 liter/m

– Teflon, SUS

Gas return

To purifier

Circulation pump


Purification PerformancePurification 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 events


Absorption LengthAbsorption Length

• Fit the data with a function :

A exp(-x/ abs)

• abs >100cm (95% C.L) from comparison with MC.

• CR data indicate that abs > 100cm has been achieved after purification.


Response to Gamma Beam Response to Gamma Beam

10MeV

20MeV40MeV

• 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 provided.

• The Compton edge is used to evaluate the resolution.

• Data taking– Feb. 2002 (w/o purification)

– Apr. 2003 (w/ purification)


Energy SpectrumEnergy Spectrum• 2 :depth parameter:

40MeV Compton gamma dataw/ xenon purification

40MeV Compton gamma dataw/o xenon purification

Dep

th p

aram

eter

Dep

th p

aram

eter

Total Number of Photoelectrons Total Number of Photoelectrons


Energy ResolutionEnergy Resolution• 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: E < 2%

Dep

th p

aram

eter

Very Prel

iminary

Simulation

52.8MeV

Simulation

52.8MeV


Position ReconstructionPosition Reconstruction• 2-step reconstruction

– 1st step: Pre-determination of the peak

– 2nd step: Precise determination with an iteration process

• Data 40MeV Compton

(a) (b)

(c) (d)


Timing ResolutionTiming Resolution• Estimated using Electron Beam

(60MeV) data

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

• For 52.8 MeV ~ psec + depth resolution.

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

(Visit “The DRS chip” by S.Ritt)

T

imin

g R

esol

utio

n (p

sec)

104 4x104

45 MeV Energy deposit by 60 MeV electron injection

52.8MeV

(nsec)

=75.62.0ps=75.62.0ps

Number of Photoelectron


SummarySummary

• New experiment to search for e 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 beam test

• E<2% for 40MeV Compton

meg experiment at psi r&d of liquid xenon photon detector

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