Status of AMoRE-Pilot · 2019. 12. 11. · 1/ 2 AMoRE project towards “zero”-background conditions: Reduction of the background α-background rejection with particle discrimination

Status of AMoRE-Pilot

Hyon-Suk Jo

Center for Underground Physics

Institute for Basic Science

KPS 2017 Spring Meeting – DCC, Daejeon – April 21, 2017

The goal of the AMoRE (Advanced Mo-based Rare process Experiment)

project is to search for neutrinoless double beta decay (0) of 100Mo using

Mo-based scintillating crystals and low-temperature sensors.

2n decay- 2nd order beta decay

- Rare nuclear decay

- (>1018 years of half life)

0n decay- Massive neutrino

- Majorana particle

- Beyond the SM model

- >1025 years of half-life

Neutrinoless double beta decay

(Z, A) → (Z+2, A) + 2e- + 2anti-ne (DL = 0, conserved)

(Z, A) → (Z+2, A) + 2e- (DL = 2, violated)

Hyon-Suk Jo KPS 2017 Spring Meeting - DCC April 21, 2017

Detector concept for the AMoRE experiment

Simultaneous measurement of heat and light

Particle discrimination for rejection of α-induced

background

Choice of 100Mo

- High Q-value (3034 keV)

- High natural abundance (9.6 %)

- Relatively short theoretically predicted half-life (0n)

21

40Ca100MoO4 used as source and detector

+ Metallic Magnetic Calorimeter (MMC, low temperature sensor)

“Source = detector” approach

High detection efficiency

High energy resolution

MMCs

Fast response, high energy resolution,

wide operating temperatures


AMoRE sensitivity to 0νββ

Sensitivity to

half-life of 0νββ

Isotopic

Abundance

Atomic mass Background rate

Energy

Resolution

Measurement

time

Detector MassDetection

Efficiency “Zero” background case

Sizeable background case

MtA

aNT A n )2(ln(exp)0

2/1

AMoRE project towards “zero”-background conditions:

Reduction of the background

α-background rejection with particle discrimination (heat and light measurement)

less than 0.001% of depleted 48Ca (natural abundance: 0.157%, Qββ=4.271 MeV)

low levels of internal and external backgrounds

High energy resolution with MMCs

High detection efficiency with “source = detector” approach

Detector mass

enrichment of 100Mo above 96%

Eb

Mt

A

aNT A

D n )2(ln(exp)0

2/1


separated two main labs

LTD lab, GeCOSINE,

AMoRE experiment at Y2L

Yangyang pumped storage Power Plant

Minimum vertical depth : 700 m

Access to the lab by car : around 2 km

Experiments

▪ COSINE (KIMS NaI) : dark matter search experiment

▪ AMoRE : neutrinoless double beta decay search experiment

Yangyang underground laboratory (Y2L, South Korea)

SeoulY2L


AMoRE-Pilot runs

• AMoRE-Pilot consists of several runs (a new run being started after an experimental

setup upgrade)

• Measurements performed at temperatures from 10 mK to 40 mK: background and

calibration measurements

• Main goals:

Reduction of the vibration noise (coming mostly from the pulse tube refrigerator

of the CF-DR)

Reduction of the background coming from external sources (detector setup, cryostat…)

The level of noise observed when using a CF-DR

is significantly higher than when using a wet DR

due to the pulse tube refrigerator of the CF-DR

inducing a large amount of vibration noise

Underground measurement (AMoRE-Pilot) with CF-DR

Above-ground measurement (prototype) with wet-DR


5 crystals (from 0.2kg to 0.4kg each, for a total mass of 1.5kg)

Each crystal module has a heat detector and a light detector

AMoRE-Pilot detector configuration: five 40Ca100MoO4 crystals

Heat detector

Light detector

Operating temperatures as low as 8 mK reached

using a Cryogen Free Dilution Refrigerator (CFDR)

23Hyon-Suk Jo KPS 2017 Spring Meeting - DCC April 21, 2017

5 crystals: SB28, S35, SS68, SE01, SB29

5 heat detectors + 5 light detectors

AMoRE-Pilot detector configuration

SB28 Heat detector

S35 Heat detector

SS68 Heat detector

SE01 Heat detector

SB29 Heat detector

SB28 Light detector

S35 Light detector

SS68 Light detector

SE01 Light detector

SB29 Light detector


• Main changes between run-1 and run-2 setups:

- Screws holding the crystals (heat detectors) and screws

holding the Ge wafers (light detectors) were redesigned

and replaced to reduce the level of vibration noise

• Main changes between run-2 and run-4 setups:

- Addition of mass spring damper

- Aluminium IVC replaced with a new OFE copper IVC

- Tightening of screws holding the crystals (heat detector)

and Ge wafers (photon detector)

- SE01 and SB29 positions swapped (SE01 at the bottom)

Setup changes between the AMoRE-Pilot runs


• From run-1 to run-2, the energy resolution of

phonon channels have been improved through

vibration reduction

• Photon channels still need more improvements

Pilot run-2 (SB29 not available)

Crystals MassAMoRE-Pilot

run-1

AMoRE-Pilot

run-2

SB28 0.20 kg 36.8 keV 25.0 keV

S35 0.25 kg N/A 16.3 keV

SS68 0.35 kg 52.6 keV 22.5 keV

SE01 0.35 kg 39.7 keV 24.6 keV

SB29 0.40 kg 42.6 keV N/A

FWHM energy resolution @ 2.6 MeV, at 20 mK

Energy resolution from run-2

FWHM energy resolution

as a function of temperature (run-2)


Particle discrimination from run-2

/

/

/

Me

an

tim

e (

ms)

Ris

e tim

e (

ms)

Lig

ht/

he

at

Energy (keV)

Phonon pulse height (V)

Energy (keV)

α2

β/γ2

αβ/γ x-x DP

(20 mK) (20 mK)

(20 mK)


Run-2: Discrimination Power (DP) as a function of temperature

• Performances of each particle discrimination

method vary from one crystal to another

• Overall, rise time provides the highest

Discrimination Power (DP)

α2

β/γ2

αβ/γ x-x DP

DP rise time

DP light/heat

DP mean time


Vibration from the pulse tube refrigerator

MC

4K

50K

Crystals &

MMCs

Pulse tube

refrigerator

LEAD

The pulse tube refrigerator (PTR) of the cryostat

generates mechanical vibration which turns into heat

noise and disturbs the baseline


Mass-spring damper

- Use of four phosphorus copper springs

- ~2 Hz natural frequency

- Thermal anchoring via copper tapes


Run-4: Averaged pulses


The different detectors produce different phonon and photon pulse heights

Average photon pulse of SB29

is very small due to MMC

current having leaked out

Comparison of light/heat ratio between run-2 and run-4

Run-2

Run-4

Large improvement of the light/heat ratio thanks to the

reduction of vibration noise in the photon channels


Comparison of DPLH between run-2 and run-4

Crystals DP(L/H) at 10 mK in Run-2 DP(L/H) at 10 mK in Run-4

SB28 0.4 4.8

S35 2.1 14.0

SS68 2.6 7.1

SE01 1.4 N/A

SB29 N/A 0.7


Run-4: energy resolution

FWHM at 2.6 MeV:

10.9 – 13.6 keV

(after optimal filtering)


Run-4: 2.6 MeV 208Tl rate from 20mK background data


Reduction of background from 2.6 MeV 208Tl from run-2 to run-4

Large reduction of the background after the

aluminium IVC was replaced with a new

one made of low-background copper

After the removal of the mu-metal

shield, the background seems to

slightly decrease


Run1 Run2 Run4

SB28 37.0 25.0 13.6

S35 - 16.3 10.9

SS68 53.0 22.5 13.5

SE01 40.0 24.6 -

SB29 43.0 - 13.0

FWHM Energy resolution (keV@ 2.6MeV) Background rate (counts/kg/day for 2.6MeV events)

Run1 Run2 Run4-

1

Run4-

2

SB28 72 49 14 7

S35 - 84 15 19

SS68 104 100 18 13

SE01 122 112 - -

SB29 95 - 25 16

Run1 Run2 Run4

MT L/H MT L/H MT L/H

SB28 2.0 - 3.9 0.4 9.6 4.8

S35 - - 4.7 2.1 9.3 14.0

SS68 1.4 7.3 1.5 2.6 3.4 7.1

SE01 2.7 2.2 3.9 1.3 - -

SB29 1.5 1.5 - - 7.6 0.7

Discrimination power (σ)

Run-4 summary


AMoRE-Pilot Run-5 setup


• Addition of a new vibration damper: spring suspended still (SSS)

- It does not take additional experimental space

- Vibration damping at refrigerator level is ideal, and necessary for

large-scale experiments

- Damping at mixing chamber level is limited by low

radioactivity/magnetism requirements

• Addition of a 6th detector module:

- Crystal mass: 340 g

- Total of 12 detector channels (6 heat detectors + 6 light detectors)

Spring suspended still (SSS)


Spring suspended still (SSS) is an Eddy current damper using magnets

Designed by Leiden Spin Imaging (Netherlands)

4K

StillEddy currents

Vibration reduction with SSS damper


SSS damper has a natural frequency of ~3 Hz

It provides a significant vibration reduction

Addition of a 6th detector module


6th crystal: 340 g

Total of 12 detector channels: 6 phonon sensors + 6 photon sensors

6 detector

modules

Overview

Thank you

• Through the different AMoRE-Pilot runs, several setup

upgrades allowed to reduce the vibration noise, which

improved the energy resolution and particle discrimination

powers (mean-time, rise-time, light/heat ratio)

• Background level has been significantly reduced after a

change of material in the setup and further improvements

are being investigated

• Run-5 setup was cooled down to 10 mK last night and

data taking should begin within the next few days! We will

be taking data for several months


Documents

Status of AMoRE-Pilot · 2019. 12. 11. · 1/ 2 AMoRE project towards “zero”-background conditions: Reduction of the background α-background rejection with particle discrimination