october 8th, 2009 sujeewa kumaratunga 1/27 recent progress in picasso sujeewa kumaratunga for the...

Recent Progress in

PICASSO

Sujeewa Kumaratunga

for

the PICASSO collaboration

October 8th, 2009 Sujeewa Kumaratunga 2/22

Outline

PICASSO Introduction Neutron Beam Calibration Data Analysis Results


PICASSO

Project In CAnada to Search for Supersymmetric Objects

or in French

Projet d'Identification de CAndidats Supersymétriques

SOmbres

Université de Montréal - Queen’s University, Kingston - Laurentian

University, Sudbury - University of Alberta - Saha Institute Kolkata, India – SNOLAB - University of Indiana, South Bend - Czech

Technical University in Prague – Bubble Technology Industry, Chalk

River.SNOLAB


CASD : Spin dependent interaction <Sp,n>2

F(q2) : nucl. form facor important for large q2 and large A

Neutralino Nucleon Interaction Crosssections

)(4 2

2

2 qFCMM

MMG A

A

AFA

Enhancement factor General form of cross sections:

CASI : Spin independent – coherent interaction A2

Spin-dependent Spin-independent

How does PICASSO detect Neutralinos (WIMPs)?


How to detect Neutralinos

Weakly Interacting particles Use bubble chamber principal

Minimize background Go underground: shield from Cosmic Rays

(SNOLAB) Use water boxes to shield radioactivity from rock


A bubble forms if:

• particle creates a heat spike

• with enough energy Emin

• deposited within Rmin

The Seitz Theory of Bubble Chambers

Rmin

Pext Pvap

« proto-bubble » minmin ERdx

dEEdep

)(

)(2min TP

TR

2

3

min ))((

)(

3

16

TP

TE

P(T) = superheat (T) = Surface tension = critical length factor = energy convers. efficiency

F. Seitz, Phys. Fluids I (1) (1958) 2

Top

Pvap

Liquid

Tb

Pext Vaporp = Superheat


PICASSO detectors Super heated C4F10 droplets

200μm, held in matrix in polymerized gel act as individual bubble

chambers When neutron interactions

cause 19F recoils or ionizing particle deposits energy Superheated liquid vaporizes

forming small bubbles Bubbles grow explosively (50μs) Turns entire C4F10 droplet to

vapour that resonates Resulting acoustic signal

registered by piezo electric sensors


PICASSO Detector Status

Now Complete 32 detectors, 9 piezos each total active mass of 2248.6g 1795.1g of Freon mass Temperature & Pressure

control system 40 hr data taking 15hr recompression

Neutron Beam Calibration


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 several keV region

Test Beam Calibration

5 keV

40 keV

50 keV

61 keV

97 keVPro

ba

bili

ty o

f d

ete

ctio

n

Temperature (C)

Theory => detector efficiency


Test Beam Calibration

Detection efficiency (T) Neutralino response (T)


PICASSO detector responses

226Ra spike (200 μm Ø)

AmBe neutrons( data + Monte Carlo)

Recoil nuclei from 50 GeV/c2 WIMP

γ MIP &response

226 Raspike 200)μ mØ(

AmBe neutrons( data + Monte Carlo)

Recoil nuclei from 50 GeV/c2 WIMP

γ MIP &response

PICASSO Data Analysis


PICASSO events

raw signalhigh pass filtered signal

neutrons

noise

different amplitude scales

Take power of signal and integrate to get energy : PVar


PVar Distributions for Calibration Runs

Distributions are temperature dependant


PVar Distributions for neutron and alpha

background

neutronsalphas

Neutrons and alphas well separated

signal


FVar Distributions for neutron and background

Noise

Neutrons (WIMPs) & alphas

Fracture

Blast


Null HypothesisAlpha Rate Fitted: Detectors 71,72

• Rates have been normalized to 19F

72

71

15.171

2

ndf

25.172

2

ndf

PICASSO New Results


PICASSO New Results

σp = - 0.0051pb ± 0.124pb ± 0.007pb (1σ)

90%C.L. limit of σp = 0.16 pb for a WIMP mass of 24 GeV/c2.

13.75±0.48 kg.days


PICASSO Future

PICASSO set up now complete Analysis of the other detectors underway New detector fabrication methods used in some

of the detectors show significant alpha background rejection

Exploit fully our new discrimination techniques to separate signal from noise and background

Scale up to larger detectors 25-100kg

32 det expected sensitivty 0.05 pb

backup


- CDM ?

DIRECT SEARCHES• lab detectors interact with galactic WIMPS• fast WIMPS produce measurable recoils• probe - halo density / structure at solar system

• no signal limits on X-section

• constraints on MSSM parameter space

ACCELERATOR SEARCHES

• no signal limits on mass range

• cannot tell if WIMP is stable

• constraints on MSSM parameter space

Complementarity !!!

• Discovery of cosmol. WIMP does not prove yet SUSY accelerator searches

• LHC signal does not yet prove CDM discovery (in) direct searches

INDIRECT SEARCHES• gravitational trapping (sun, galactic centre etc)• annihilating of slow WIMPS • detection of annihil. products: pairs of , , , Z’s• probe abundance elsewhere• no signal limits on X-section

• constraints on parameter space


Dark Matter - Introduction

What is visible matter? Baryons and radiation

(things that interact electromagnetically)

Only 5% of matter is “visible”

22% of “invisible” universe=> Dark Matter

• What is dark matter?• Discrepancies between

– Temperature and distribution of hot gasses in galaxies and galaxy clusters

and– Rotational speeds of galaxies and

orbital speeds of galaxies in clusters

• Gravitational Lensing


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 - timeline

Superheated Liquids & Dark Matter: SIMPLE, COUPP, PICASSO


PICASSO Results

σp = - 0.0051pb ± 0.124pb ± 0.007pb (1σ)

limit of σp = 0.16 pb (90%C.L.) for a WIMP mass of 24 GeV/c2.

13.75±0.48 kg.days (Previous exposure

1.98 kg days)


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


Alpha Neutron Separation

Average of peak amplitudes of 9 transducers (after HP filter)

Signals carry information of the first moments of bubble formation

Why are neutron and alpha signals different in energy? Alphas create multiple nucleation

sites along tracks from ionization; also 1 nucleation at the beginning from recoiling parent nucleus and 1 at end from Bragg peak

Neutron create only 1 nucleation site from the highly localized energy deposition

Is this separation a pseudo effect? No! Neutrons from source are not

symmetrical like alphas – does this have an effect? No!

Could signal from neutrons attenuate over time due to increased vapor bubble formation? No!

neutrons alphas


Some numbers…

6321721Total Number of Events selected with Pvar ,Fvar

7.146.60Exposure (kg.d)

68.97 ±3.565.06±3.2Active Mass F19 per detetctor (g)

103.5101.5Run length (days)

Detector 72Detector 71


Systematics

0.1CTemperature

20%Energy resolution

2%Hydrostatic pressure gradient inside detector

3%Pressure variation

3%Neutron Threshold Energy

5%Active mass (C4F

10)

UncertaintySystematic


PCut= μ− 1 . 64 σ o f G au s sian

What next with PVar?

Use neutron calibration runs to get PVar distributions for neutrons.

Fit a Gaussian and select 95% : this will be our signal

If PVar>PCut => we got particle induced event!!


PICASSO New Results

σp = - 0.0051pb ± 0.124pb ± 0.007pb (1σ)

90%C.L. limit of σp = 0.16 pb for a WIMP mass of 24 GeV/c2.

13.75±0.48 kg.days

october 8th, 2009 sujeewa kumaratunga 1/27 recent progress in picasso sujeewa kumaratunga for the...

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