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The PicassoExperiment

Plans and Results

The PicassoExperiment

Plans and ResultsCarsten Krauss

Queen s UniversityCarsten Krauss

Queen s University

January 24, 2006University of Pennsylvania

January 24, 2006University of Pennsylvania

Overview

Dark Matter

Superheated Droplet Detector

Prototype run results

SNOLAB

PICASSO 32

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PICASSO

Project In CAnada to Search forSupersymmetric Objects

Detect recoils of spin-dependentinteractions with dark matter particles

Picasso Collaboration

Indiana University at South Bend

I. Levine, W. Feighery, J. Nuerenberg, E. Behnke, C. Muthusi

Université de Montréal

V. Zacek, L. Lessard, C. Leroy, G. Azuelos, J.-P. Martin, U. Wichoski, P. Doane, R. Gornea, M. Bernabe-Heider, M. H. Genest, R. Guenette, F. Aubin, Y. Landry, N. Starinski, G. Richard

Prague Technical University

S. Pospisil, I. Stekl, J. Sodomka, J. Bocan

Queen s University

A. J. Noble, C. B. Krauss, X. X. Dai, K. Clark, C. Storey, C. Hearns

University of Pisa

S. Shore

Yale University

F. d'Errico

Universita di Lisboa

T. Girard, F. Giuliani, T. Morlat, J. G. Marques, A. Fernandes, R. Martins, M. Da Costa

Paris VI, VII

G. Waysand, D. Limagne

Dark Matter

First hints aboutdiscrepancy incosmological observationsin 1933

Since then more data takenand more hints forexistence of dark matterhave been found

Dark Matter II

WMAP microwave background picture

suggests flatness of universe and thereforelarger matter density than seen

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Dark Matter III

Cosmological pictureis consistent andpoints towards amissing piece in theunderstanding of theworld

Hardly anyone islooking for anythingbut prove for theexistence of darkmatter

Dark Matter SearchAnnihilation Signal search

Alternative to direct observations isobservation of annihilation signal which ispredicted to occur mainly at galactic cores

Satellite based gamma ray telescopes likeEGRET have not seen conclusive signals

Promising new experiment GLAST mightchange the picture

Super-Symmetry and DarkMatter

Dark matter particle can very likely be the LSPor Neutralino

Interesting convergence between interests ofSUSY theorists and cosmological dark matter

Recoil Signal

WIMP only interacts by elastic nuclear recoils

For spin dependent interactions Fluorine is the mostfavourable target material because its nuclear matrixelement is the largest

Recoil energy in keV rangeExpect less than 1 count/day/kg active mass

Superheated Droplets

Freon droplets suspended in gelmatrix

Each droplet is like a mini-bubblechamber

Nuclear recoils trigger phase transition

Fluorine recoil track

Freon dropletNucleation cores

Detector PrincipleSDDs originally developed for neutron dosimetryand are in use at nuclear facilities

Active material is C4F10 in superheated form

Only fissions, alphas and nuclear recoils are detected

Insensitive to minimally ionizing particles andgammas

Seitz bubble chamber limit:

critical energy inside critical radius leads toformation of bubble in superheated medium

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Superheated DropletDetector

Bubble size is crucial for background rate andsensitivity

Average bubble size increased by factor of sixsince

Detector

Contains gel matrix to keepsuperheated bubblessuspendedUse CsCl to match density ofbubbles to gel

Started feasibility studies withcommercial 5ml detectors

inceased size and purity since

Signal Processing

acoustic shock-wave is picked up bypiezo

Typical bubble signal sampled with960kHz (4096 samples)

Filter & Event Selection

2 dimensional Fourier transformation used to distinguishbubbles from background noise

If enough power is concentrated in trigger window andfrequency range 20-90kHz, signal is identified as bubble

Filter Efficiency

Filter has been tested over fulltemperature range

Response is fairly high and uniform

includes trigger efficiency

Calibration

Tandem acceleratorin Montreal used tocalibrate detectorswith mono-energeticneutrons (7Li(p,n)reaction)

Beam-line upgradedto run with lowerenergy, narrowerenergy spread

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Neutron Calibration

Neutron cross-section well known,modeled and reproduced in detectorresponse

Temperature Dependence

Threshold and response changes withtemperature

Detection Threshold

Detector only becomes sensitive to background at hightemperatures

-particles are a problem over the entire range of operation

Alpha Response

Spiked detector gives alpha response

Identical results from Ac and Th spike

Extremely important input for understanding ofbackground

Gamma Response

Response curve modeled well

(This is the response for another type ofdetector with a different gas mixture)

Successful Purification

Development since the start ofpurification efforts

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Internal Background

This is the most difficult challengePICASSO faces for the next steps

Currently purifying detectoringredients with methods developedby SNO and refined for PICASSO

New and more efficient methods areneeded

Radiopurity

Most critical single problem:

Internal activity from CsCl has to be purified

Two possible ways: Replacing CsCl salt - breakthrough inpurification

Raw Salt Measured U

U CriteriaTh Criteria

Raw Salt Measured Th

As built detectors II, UPurifiedsalt. U

RadiopurityStatus: Improvement by

better handling(cleanroom,procedures)

larger size handlingsystem, cover gassystem

New method ofpurification

Problem: long turn-around times

Large scale purificationsystem for SDD ingredients

in Montreal

Spacial Reconstruction

Very promisingstudies toreconstruct thelocation of theexploded bubble tobe able to suppresshot-spots andsurface events

(Here only 4 piezos,final new detectorswill have up to 9)

Sudbury

Sudbury, Ontario

Installation At SNO

SNO kindly agreed tohost PICASSO in thewater area

We re in the fortunatesituation to use to onlyfree space at the lab

Still the guest statusrequires extra thoughtand effort

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Data Taking in 20040.27 µ/m2/day

6 1 liter detectors were operatedfor 7 months

2 independent temperaturecontrol systems

2 readout channels for eachdetector

1 foot water cubes for neutronshielding

4096 12bit samples for eachtrigger with a sampling rate of960kHz

Data taken remotely

60t tank area in the SNOwater utility area

SNO Phase Detector

1 liter containers

SNO developed polypropylen

Mineral oil between gel and pressureline

Droplet sizes between 10-100µm

Data-taking for 30h;re-pressureization for 10-15h

Two piezo-electric sensors on eachdetector

Data Analysis

Data with 3 detectors used for analysiswith an active mass of 7.45, 6.62 and5.35g

Total exposure was 1.98±0.19kg d

used local WIMP matter density of0.3GeV/c2/cm3, vrel=244km/s andvesc=600km/s (standard parameters)

Result

Count rate for 3 used detectors

Alpha rate of cleanest and older type ofdetector (with expected neutralino signalfor mWIMP=50GeV and =2pb, 5pb, 10pb)

Interpretation I

Exclusion plotfor spin-dependentneutralinos

lowest point inparameterspace

p=1.31pb andn=21.5pb for a

WIMP with29GeV mass

Interpretation II

Limits in spin-independent sector less stringent

Effective coupling strength an for neutrons and ap

for protons for a WIMP mass of 50GeV

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Papers - in PressPublished by Phys. Lett. B 624, 3-4 (2005), 186-194

PICASSO 32 System

32 detectors

8 temperature and pressure control systems

up to 288 readout channels

sampling at 2MHz with 15.000samples/trigger

temperature stability 1/16ºC

operating range between 15º and 50ºC

switchable neutron source for calibration

Temperature and PressureControl System

Developed atQueen s

Houses 4 detectors

Operates between20 and 55ºC

Stable at 1/16 of adegree Celsius

all 8 are currently inproduction

PICASSO 324 new detectors are readyfor installation (sinceNovember)

-contamination belowsensitivity of surface lab

Purification method (withHTiO) now stable andreproduceable

New method has beenfound and is tested now

Exclusion Limit forPICASSO 32

Projected

The Area

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Frame installation inFrame installation inJanuary at the sameJanuary at the samelocation as old setuplocation as old setup

Installation Schedule Data Taking

Future Plans SNOLAB

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SNOLAB Plan SNOLAB Hopefuls

SNO+

Majorana (Majorana/Gerda III)

GasEXO

DEAP

SuperCDMS

PICASSO

Scaling of Picasso

Sketch for the 100kg active mass phase

Plan to move the system to the rectangular hallof SNOLAB

All of the details still have to worked out

Pending success in PICASSO 32 phase

Pending success in PICASSO 32 phase

Summary

Data taken in 2004 has been analyzed

PICASSO principle works

To be competitive background has to bereduced and system has to be scaled up

PICASSO 32 will be installed in the nextmonths

New, improved results to be ready nextyear