SNOLAB WORKSHOP OCT. 4 2008 V. Zacek Université de Montréal

• Project overview

• Progress report

• Milestones and Schedule

• Infrastructure needs

• Personnel & HQP

• Outlook

Université de Montréal, Queen’s University, University of Alberta, Laurentian University, University of Indiana, South Bend, SNOLAB, CTU Prague, Bubble Technology Industries

AA

AFA C

MM

MMG

2

24

Enhancement factor

Neutralino interaction with matter:

Depending on the type of target nucleusand neutralino composition

Spin independent interaction (CA A2 )

Spin dependent interaction

CA = (8/)(ap<Sp>+ an<Sn>)2(J+1)/J

0.0147n3/2131Xe

0.0026p5/2127I

0.084n1/229Si

0.0026n9/273Ge

0.011p3/223Na

0.863p1/219F

0.11p3/27Li

2UnpairedSpinIsotope

Spin of the nucleus is approximately the spinof the unpaired proton or neutron

Active Target C4F10

Comparison SD and SI - searches

• no channel favoured

• largely uncorrelated

• destructive interference possible in SI sector

Need to explore both sectors!

Spin Dependent Sector (TAUP ’07)

KIMS: 3403 kgd

NAIAD: 12523 kgd

PICASSO: 22 kgd

SM predictions O(10-3 pb)

Superheated droplets at ambient T & P *

150m droplets of carbofluorides

dispersed in polymerised gel

Active liquid: C4F10 Tb= - 1.7 oC)

Radiation triggers phase transition

Events recorded by piezo-electric transducers

* Inspired by personal neutron dosimeters @ Bubble Technology Industries, ON

Main Features

- each droplet is an independent “clean” Bubble Chamber

- keV threshold for DM induced recoils - with full efficiency for nuclear recoils

- excellent gamma & MIP at Erec= 5 keV

- continuous operation 30h

- recompression recycles burst droplets

- low cost, with potential for a large DM experiment

- in house fabrication

1st generation: 10 mL

2nd generation : 1L

3rd generation : 4.5L

Detector Response

226Ra spike (200 m Ø)

Detector Response

226Ra spike (200 m Ø)

AcBe neutrons (data +MC)

Detector Response

226Ra spike (200 m Ø)

AcBe neutrons (data +MC)

Recoil nuclei from 50 GeV WIMP

Detector Response

Gamma & MIP rejection better 1010 above Erec= 10keV!

226Ra spike (200 m Ø)

AcBe neutrons (data +MC)

Reoil nuclei from 50 GeV WIMP

& MIP response

2.6 kg PHASE

Critical item at the moment: ADC boards!

• 20 / 32 installed

• 4 more ready; 8 to be debugged (soldering accident)

• 32 detectors 2.6 kg of C4F10

• 288 acoustic R/O channels

• 3D event localization

• 20 detectors running

• another 8 detectors u/g ; 4 ready @ UdeM to ship

• analysis in progress

• publication of intermediary results in prep.

Temperature & Pressure Control System (TPCS)

- TPCS units

- temp. precision: ± 0.10C

- 4 detectors /TPCS

- 40 h data taking

- 15 h recompression

Data Analysis

• filter events (high pass)

• Integrate Ampl.2

• time frequency analyis

• spike cuts

Compare to known backgrounds Limits @90%C.L.

Sensitivity (22 kgd )

PRELIMINARY

’07 ’08 ’09 ’10 ’11

2.6 kg 32 modules

Data taking 8 –16 modules

Data taking 20 modules

Preamps, DAQ boards

Installation + 12 modules

Data taking 32 modules

R&D backg. /100

2.6 kg* (backg./100)

Data taking 32 modules

R&D 30L mod. high ldg.

Phase II 25 kg

30L detector prod.

Data taking Ladder Lab ?

Timeline & Milestones

700 kgd

7000 kgd

* Present background of 0.003 cts g-1h-1

700 kgd

0.002 pb

0.006 pb

0.06 pb*

Scientific Reach

2.6 kg Phase (ongoing)700 kgdBckg 0.003 cts h-1g-1 2.6 kg*

700 kgdBckg: 3x10-5 cts h-1g-1

25 kg Phase 000 kgd 30L modulesBackg.: 3x10-5 cts h-1g-1

Spin Dependent Sector

MSSM

Infrastructure needs

• On site support extremely helpful (I. Lawson)

short interventions, change electronics, assistance before/ after power outages

• Access @ measuring time at HP(Ge)

regular assays of samples || to detector fabrication

• Office space / cubicles

with full installation c.o.g. shifting to SNOLAB

• Radiochemistry and low background expertise

SNOLAB (Laurentian) radio chemistry lab for spike work

• Electronics maintenance support from technician (Reg, Noël)

• Computing support for on-line servers and network

• Clean lab space for sample preparation

Discrimination of Nuclear Recoils from Alpha Particles

Average of peak amplitudes of nine transducers / detector

High pass filter with cut-off at 15 KHz

PICASSO discovered a significant difference between amplitudes of neutron and - particle induced events ! Accepted for pub. In New Journal of Physics arXive: 0807.1536

Signals carry information about first moment of bubble

formation

n-calibration - background

Discrimination of Nuclear Recoils from Alpha Particles

Are these really events?

PICASSO discovered a significant difference in amplitudes between neutron and

- particle induced events ! Accepted for pub. In New Journal of Physics arXive: 0807.1536

Signals carry information about first moment of bubble

formation

-like Temperature response!

Discrimination of Nuclear Recoils from Alpha Particles

PICASSO discovered a significant difference between amplitudes of neutron and - particle induced events ! Accepted for pub. In New Journal of Physics arXive: 0807.1536

Why not observed earlier?

Previous detector had smaller droplets!

• now 200 m compared to < 10 m

• range of nuclear recoils < Lc

• but range of alphas >> Lc

• many bubbles can form on track (depend on temperature)

Nuclear recoil: point like, strong ionisation

-particles: ionization on 35m track

# prim. bubbles Poisson distributed !

- n Discrimination: a tentative explanation

# of primary bubbles

<> = 1

<> = 4

<> = 8

# of bubbles created

T = 300C

T = 400C

T = 500C

Lc

Lc

Lc

(in MIP sensitive region: T = 600 C > 20 bubbles)

1

- n Discrimination: Temperature Dependence

Strong saturation of raw signals above 300C!

• From bubble chamber operation:

bubble density dE/dx

bubble density strongly increases with T

• Plesset-Zwick theory:

bubble growth

pressure amplitude acceleration & temperature

first 50s of signal preserve m resolution of prim. event

t

- n Discrimination: Discussion

Next: • increase discrimination by controlling gain new pulser

• increase resolution by using 3D info

• eliminate saturation effects by reducing gain

• run at one temperature only ! (450?)

Very exciting!

Ultra Pure Water system (18.2 MΩ ⇔ 0.2ppb)

Detector Fabrication

• Well organized, timed and rapid!

• Chain production of 3 –4 detectors / working day

• Large droplets ( 200 m Ø)

• CsCl loaded matrix replaced by hydrocarbon based version

intrinsically much cleaner in U/Th !!

performance issues under investigation

3.

Imaging the sample

Determination of Droplet Size (L.U.)

Tracing the droplets

Droplet size distribution (volume)

2400 droplets

gel sample: 0.7 mL

• Analyze gel from more detectors and compare

• Continue development of nondestructive method

Calibration with mono-energetic neutrons

neutron induced nuclear recoils similar to WIMPS

n-p reactions on 7Li and 51V targets at 6 MV UdeM-Tandem

threshold measurements in the sev. keV region

Progress in Test Beam Calibration

Detection efficiency (T) Neutralino response (T)

Lithium (7Li)

Vanadium (51V)528 keV

40 keV

Previous measurements: 7Li target

200 keV < En < 5000 keV.

New measurements: 51V target

5 keV < En < 90 KeV

Target selection

Check of resonance in V-target

Five 51V resonances:

97, 61, 50, 40 and 5 keV

Improved Calibration of the Detector Response

51V resonances

7Li data

Theory

Monte Carlo Simulations

• Response at threshold not a step function!

• - increases with neutron energy!

)1(exp1),(th

th EEEEP

Test beam

New!

AmBe source (u/g calib.)

COLLABORATION DEMOGRAPHY

Present compostion

• MSc students: 5

• PhD students: 1

• Ugrad. lab students 2 (IUSB)

• Postdocs: 3

• Researchers and faculty: 10 (4 FTE)

• Engineers (electr.) 1

• Technicians 4

Careers & Training:

• completed MSc theses: 11 (4 in ’08)

• completed PhD theses: 4 (2 in ’08)

• RA faculty: 2 U. Wichoski (UdeM L.U.) C. Krauss (Q.U. U.A.)

• > 30 summer students during the last six years

• > 6 “stage” students from France (région Rhône Alpes)

Distribution of Tasks

Montréal: - electronics, DAQ, analysis

- detector fabrication + R&D

- calibration, quality control

Queen’s: - slow control (T&P), u/g install. + coordination

- on-line monitoring, DAQ, analysis

- detector fabrication, purification +R&D

Alberta: - slow control, u/g install., electronics

- analysis + coordination

Laurentian: - det. characterization, purification, u/g install.

SNOLAB: - HP(Ge) assays, on-site support (I. Lawson)

Indiana: - piezo transducer fabrication, quality control

Prague: - detector container fabrication / Monte Carlo

PICASSO - COUPP - MOU

SD

SI

PICASSO/COUPP Joint Strategy for 100kg Detector?

PICASSO / COUPP eventually also SI interactions?

Summary

• 2.6 kg Phase with 32 detectors nearly completed

• 20 of 32 detectors installed; 28 u/g; 31 modules ready

• Upgrade gradually with cleaner detectors “saltless” detectors

• New discovery of n - discrimination

• Physics results to be published soon

• Complete Phase 1 with 700 kgd in 2009

• R&D on purification (1/100) and 30L detectors

• prepare 25 kg phase 7000 kgd

1952 Donald Glaser: “Some Effects of Ionizing Radiation on the

Formation of Bubbles in Liquids” (Phys. Rev. 87, 4, 1952)

1958 G. Brautti, M. Crescia and P. Bassi: “A Bubble Chamber Detector

for Weak Radioactivity” ( Il Nuovo Cimento, 10, 6, 1958)

1960 B. Hahn and S. Spadavecchia “Application of the Bubble

Chamber Technique to detect Fission Fragments” (Il Nuovo

Cimento 54B, 101, 1968)

1993 “Search for Dark Matter with Moderately

Superheated Liquids” (V.Z., Il Nuovo Cimento, 107, 2, 1994)

Superheated Liquids For Particle Detection

Superheated Liquids & Dark Matter: SIMPLE, COUPP, PICASSO

Detector Response

neutrons

WIMPS

MIPS

Detector Response

B. Hahn, Il Nuovo Cimento, 1961, Vol. 22, 650