SNO+: SNO with Liquid Scintillator

SNOLAB Workshop IV

August 15, 2005

Mark ChenQueen’s University

Outline

• brief review of the science

• technical progress

• project issues– SNOLAB infrastructure– funding– collaboration– schedule

• SNO plus liquid scintillator → physics program– pep and CNO low energy solar neutrinos

• tests the neutrino-matter interaction, sensitive to new physics

– geo-neutrinos– 240 km baseline reactor oscillation confirmation– supernova neutrinos– double beta decay?

Fill with Liquid Scintillator

• complete our understanding of neutrinos from the Sun

pep, CNO, 7Be

• explore the neutrino-matter interaction which is sensitive to new physics

• 3rd recommendation of the APS Neutrino Study

Low Energy Solar Neutrinos

pep

SNO CC/NC

m2 = 8.0 × 10−5 eV2

tan2 = 0.45

SSM pep flux:uncertainty ±1.5%

known source → precision test

Survival Probability Rise

transition from matter to vacuumdominance…tests the neutrino-matter interaction

sensitive to new physics:• non-standard interactions• solar density perturbations• mass-varying neutrinos• CPT violation• large 13

• sterile neutrino admixture

improves precision on 12

observing the rise confirms MSW and that we know what’s going on

stat + syst + SSM errors estimated

• non-standard interactions

• MSW is linear in GF and limits from -scattering experiments g2 aren’t that restrictive

• mass-varying neutrinos

Friedland, Lunardini, Peña-Garay, hep-ph/0402266

Barger, Huber, Marfatia, hep-ph/0502196

pep solar neutrinos are at the “sweet spot” to test for new physics

New Physics25.0

NC non-standard Lagrangian

CHARM limit

Miranda, Tórtola, Valle, hep-ph/0406280

Guzzo, Reggiani, de Holanda, hep-ph/0302303see also Burgess et al., hep-ph/0310366

3600 pep/year/kton >0.8 MeV

2300 CNO/year/kton >0.8 MeV

7Be solar neutrinos

using BS05(OP)and best-fit LMA

Event Rates (Oscillated)

resolution with 450 photoelectrons/MeV

these plots from the KamLAND proposal muon rate in KamLAND: 26,000 d−1 compared with SNO: 70 d−1

11C Cosmogenic Background

SNO+ pep

SNOLAB is the only deep site that exists where the pep solar neutrinos could be measured with precision.

pep solar neutrinos are a known source – enables a precision measurement (this is not the case with 7Be).

pp solar neutrinos are more difficult and may not reveal as much as pep (pp survival probability set by the average vacuum Pee).

First observation of the CNO solar neutrino would be important for astrophysics.

Real KamLAND Backgrounds

external

pep window

• radiopurity requirements– 40K, 210Bi (Rn daughter)– 85Kr, 210Po (seen in KamLAND) not a problem

since pep signal is at higher energy than 7Be– U, Th not a problem if one can repeat

KamLAND scintillator purity– 14C not a problem since pep signal is at higher

energy

pep Solar Backgrounds

Geo-NeutrinosGeo-Neutrinos

can we detect the antineutrinos produced can we detect the antineutrinos produced by natural radioactivity in the Earth?by natural radioactivity in the Earth?

Image by: Colin Rose, Dorling Kindersley

radioactive decay of heavy elements (uranium, thorium) produces antineutrinos

assay the entire Earth by looking at its “neutrino glow”

e

Earth’s Heat FlowEarth’s Heat Flow

models of Earth’s heat sources suggest models of Earth’s heat sources suggest that radioactivity contributes 40-100% that radioactivity contributes 40-100% towards Earth’s total heat flowtowards Earth’s total heat flow

the radiogenic portion is not that well known!

geophysicists want to understand Earth’s thermal history

H.N. Pollack, S.J. Hurter and J.R. Johnson, Reviews of Geophysics 31(3), 267-280, 1993

Geo-Neutrino SignalGeo-Neutrino Signalterrestrial antineutrino event rates:

• Borexino: 10 events per year (280 tons of C9H12) / 29 events reactor• KamLAND: 29 events per year (1000 tons CH2) / 480 events reactor• SNO+: 64 events per year (1000 tons CH2) / 87 events reactor

the above plot is for Borexino…geo/reactor ratio at Sudbury would be twice as high

KamLAND geo-neutrino detection…great start!

Rothschild, Chen, Calaprice(1998)

Fundamental GeophysicsFundamental Geophysics

SNO+ geo-neutrinos: a good follow-up to SNO+ geo-neutrinos: a good follow-up to KamLAND’s first detectionKamLAND’s first detection potential to really constrain the radiogenic potential to really constrain the radiogenic

heat flowheat flow potential for geochemistry (U and Th potential for geochemistry (U and Th

separation)separation) tests models of Earth’s chemical origintests models of Earth’s chemical origin

• 1 kton organic liquid scintillator would maintain excellent supernova neutrino capability– e + p [large rate]

– e + 12C (CC)

– e + 12C (CC)

– e + 13C (CC) [2.2 MeV threshold, 1.1% abundance]

– x NC excitation of 12C (NC)

– x + p elastic scattering (NC) [large rate]

see Beacom et al., PRD 66, 033001(2002)

Supernova Neutrinos

• SNO plus liquid scintillator plus double beta isotopes: SNO++

• add isotopes to liquid scintillator– dissolved Xe gas (2%)– organometallic chemical loading (Nd, Se, Te) – dispersion of nanoparticles (Nd2O3, TeO2)

• enormous quantities (high statistics) and low backgrounds help compensate for the poor energy resolution of liquid scintillator

• possibly source in–source out capability

Double Beta Decay: SNO++

150Nd

• 3.37 MeV endpoint• (9.7 ± 0.7 ± 1.0) × 1018 yr

2half-life

measured by NEMO-III• isotopic abundance 5.6%

1% natural Nd-loaded liquid scintillator in SNO++ has 560 kg of 150Nd compared to 37 g in NEMO-III

• cost: $1/g for metallic Nd; cheaper as Nd salt…on the web NdCl3 sold in lot sizes of 100 kg, 1 ton, 10 tons

table from F. Avignone Neutrino 2004

2 Background

• good energy resolution needed

• but whopping statistics

helps compensate for poor

resolution and…

turns this into an endpoint

shape distortion measure

rather than a peak search

0: 1000 events peryear with 1% naturalNd-loaded liquidscintillator in SNO++

Test <m> = 0.150 eV

maximum likelihood statistical test of the shape to extract 0 and 2 components…~240 units of 2 significance after only 1 year!

Klapdor-Kleingrothaus et al., Phys. Lett. B 586, 198, (2004)

simulation:one year of data

by Alex Wright

Nd-carboxylate in PseudocumeneNd-carboxylate in Pseudocumenemade by Yeh, Garnov, Hahn at BNL

window with >6 m light attenuation length

{

external 241Am

Compton edge 137Cs207Bi conversionelectrons

Nd Scintillator Works!

• new physics for relatively low cost• lower energy solar neutrinos: the best (and only) game in

town to test the neutrino-matter interaction• SNO+ is uniquely positioned to make these

measurements (depth, geology, appropriate distance to reactors, low backgrounds)

• costs are:– liquid scintillator procurement– mechanics of new configuration, AV certification– fluid handling and safety systems– scintillator purification– electronics/DAQ spares or upgrades?

Extending SNO Science

SNO+ TechnicalSNO+ Technical

liquid scintillator selection and designliquid scintillator selection and design AV engineeringAV engineering

cover gas, fluid handling, safetycover gas, fluid handling, safety scintillator purificationscintillator purification electronics/DAQ (spares, upgrade…)electronics/DAQ (spares, upgrade…)

to be tackled next year

AV Hold-downAV Hold-down

Bob Brewer working on designBob Brewer working on design SNO had rope basket support for the AV in an SNO had rope basket support for the AV in an

old design (+10% density difference Dold design (+10% density difference D22O-HO-H22O)O) believes optimization of above design can believes optimization of above design can

hold down 15% buoyancy (scintillator density hold down 15% buoyancy (scintillator density = 0.85) = 0.85)

Scintillator DesignScintillator Design

high density (>0.85 g/cmhigh density (>0.85 g/cm33)) chemical compatibility with acrylicchemical compatibility with acrylic high light yield, long attenuation and high light yield, long attenuation and

scattering lengthsscattering lengths

high flash pointhigh flash point low toxicitylow toxicity low costlow cost

LAB Advantages

• compatible with acrylic (e.g. Bicron BC-531 )– “BC-531 is particularly suited for intermediate sized

detectors in which the containers are fabricated with common plastic materials such as PVC and acrylics. The scintillator provides over twice the light output of mineral oil based liquids having similar plastic compatibility.”

• high flash point 130 °C• low toxicity (pseudocumene 2 4 0)

• cheap, (common feedstock for LAS detergent)• plant in Quebec makes 120 kton/year, supplier

has been very accommodating• high purity

110

LAB Process

Petresa Plant – Bécancour, QC

Scintillating SNO Monte Carlo

• Alex Wright’s implementation and calculations

PC+1.5 g/L PPO with KamLAND yield

629 ± 25 pe/MeV

above no acrylic 711 ± 27 pe/MeV

PC+1.5 g/L PPO and 50 mg/L bisMSB

826 ± 24 pe/MeV

above no acrylic 878 ± 29 pe/MeV

KamLAND (20% PC in dodecane, 1.52 g/L PPO)

~300 pe/MeV for 22% photocathode coverage SNO+ has 54% PMT

coverage; acrylic vessel only diminishes light ouput by ~10%

Light Yield

“safe” scintillators

high density

LAB has 75% greater light yield than KamLAND scintillator

Vladimir Novikov’s studies and results

Light Attenuation Length

Petresa LABas received

~10 m

preliminary measurement

Default Scintillator Identified

• LAB has the smallest scattering of all scintillating solvents investigated

• LAB has the best acrylic compatibility of all solvents investigated

• density = 0.86 acceptable• …default is Petresa LAB with 4 g/L PPO,

wavelength shifter 10-50 mg/L bisMSB• for unloaded scintillator physics…light output

(photoelectrons/MeV) more than 3× KamLAND

Still Need to Check for LAB

• compatibility with stressed acrylic

• long term stability

• accurately measure long attenuation lengths – for Monte Carlo input

• accurately measure mean scattering length – for Monte Carlo input

• fluorescence timing, quantum yields

• alpha-beta PSD (not critical, but useful)

Answers to LOI Questions

• what are the ultimate sensitivity limits for a neutrinoless double beta decay search?– this is important to investigate and we are

eager to explore the potential; as the double beta decay option is a lower priority “bonus”, we have focused on developing other aspects of the project first

More LOI Questions

• existing SNO utility drift adequate for scintillator purification?

• power requirements?– above two questions: scintillator purification being

examined and no anomalously large demands foreseen for the above items, though not yet known

• estimate access needs during installation?– in progress (AV mechanics, process fluids and cover

gas)• space and power demands change for double

beta?– not foreseen to be different

LOI Questions cont’d

• what are the main challenges for scintillator purification (beyond KamLAND and Borexino)?– SNO+ pep has fewer backgrounds than Borexino and

KamLAND due to higher energy (85Kr, 210Po, alphas no longer problems)

– 210Bi and 40K stand out as “new” backgrounds more critical for SNO+ than for the others

• 210Bi benefits from KamLAND 210Pb reduction investigations• 40K will be targeted in 2006 SNO+ scintillator purification

research

• need space for these activities?– above ground…spike tests at Laurentian or Queen’s

LOI Questions: Safety

• plans to ensure safe handling and containment– being developed…“safe” scintillator candidate

LAB is favourable in this regard

LOI Questions: Funding and Establish Collaboration

• possible funding sources: NSERC, CFI, US DOE, new European collaborators

• actively trying to recruit collaborators• current numbers:

– Queen’s 15– Laurentian 2– SNOLAB 4– BNL 3– LANL 1+– LIP Lisbon 1+– TU Munich 5 potential– potential interest from collaborators in Italy, Russia

• SNO+ is an NSERC-funded R&D project• goal is proof of principle by Fall 2005

– AV hold-down engineering solution demonstrated– liquid scintillator mixture selected/designed with

demonstrated compatibility with acrylic and suitable optical properties

– fluid handling and safety underground discussed– scientific motivation fully developed for proposal– ballpark project cost estimates

• inclusion in Canada’s IPP-NSERC long range plan

Near Term Project Schedule

SNO+ in 2006

• need more collaborators• project management• scintillator purification R&D• electronics/DAQ plans…• full TDR by Fall 2006

– including process engineering and AV mechanics

• proposals to funding agencies by Fall 2006

SNO+ in 2007

• start of capital funding

• construction of hold-down net

• access detector after D2O removed

• scintillator procurement contracts

• …and on to converting SNO into an operating, multi-purpose, liquid scintillator detector with unique physics capabilities