SNO Liquid Scintillator Project

NOW 200417 September 2004

Mark Chen

Queen’s University &The Canadian Institute forAdvanced Research

• Fall 04 to Dec 06: SNO Phase III– 3He proportional counter array now in place

• dedicated Neutral Current Detectors (NCD’s)

– nominal end date: 31 Dec 2006• bring total uncertainty on 8B solar NC signal

below 5%

– physics with heavy water will be complete

what should be done with the detector after?

Introduction

• SNO plus liquid scintillator → physics program– pep and CNO solar neutrinos– geo-neutrinos– 240 km baseline reactor oscillation

confirmation– supernova neutrinos

• working name: SNO+

Fill with Liquid Scintillator

• test solar models: 7Be, pep, CNO

• precision survival probability measurement: pep

• observe rise in survival probability at lower energies: lower energy 8B, 7Be, pep

Low Energy Solar Neutrinos

from Peña-Garay

SSM pep flux:predicted to ±1-2%allows precision test

Survival Probability Rise

pep

SNO CC/NC

m2 = 7.9 × 10−5 eV2

tan2 = 0.4

3000 pep/year/600 tons >0.8 MeV

3900 CNO/year/600 tons >0.8 MeV

7Be solar neutrinos

using BPB2001 and best-fit LMA

Event Rates (Oscillated)

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

11C Cosmogenic Background

Real KamLAND Backgrounds

external

pep window

• 11C cosmogenic production– t1/2 = 20 min makes this difficult to veto at shallower depths– positron decay guarantees >1 MeV energy deposited, right in the

pep e− recoil window– but at SNO depths, muon rate is small enough to allow easy

tagging (or even tolerate this background without veto)

• CNO neutrinos are a “background”– good energy resolution desired to see clear “recoil edge” for

monoenergetic pep – clearly interesting, for astrophysics, first observation of CNO

• radiopurity requirements challenging– 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 can achieve KamLAND-level purity

pep Solar Backgrounds

from J. Bahcall and C. Peña-Garay

“Our global analyses show that a measurement of the -e scattering rate by pep solar neutrinos would yield essentially equivalent information about neutrino oscillation parameters and solar neutrino fluxes as a measurement of the -e scattering rate by pp solar neutrinos.”

• which is to say that a pep solar neutrino experiment would be an alternative to a pp solar neutrino experiment, in some regards…

More on pep Solar Neutrinos

• can we detect antineutrinos from decay of U and Th in the Earth’s mantle and crust?

• knowing Earth’s total radioactivity would be very important for geophysics– understanding thermal history of

the Earth– thought to account for ~40%

total heat generation– dominant heat source driving

mantle convection• how much in the mantle and the

crust?

Antineutrino Geophysics

• detecting geo-neutrinos from natural radioactivity in the Earth (U, Th) helps to determine the radiogenic portion of Earth’s total heat flow

• by doing so, it also tests theories of Earth’s origin based upon the “Bulk Silicate Earth”…e.g. see Rothschild, Chen, Calaprice, Geophys. Res. Lett., 25, 1083 (1998)

• e.g. see NOW 2004 talk by G. Fiorentini…

More on Geo-Neutrinos

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

KamLAND will soon make first detection…

terrestrial antineutrino event rates:• Borexino: 10 events per year (280 tons of C9H12) / 29 events reactor• KamLAND: 29 events per year (1000 tons CH2)• Sudbury: 64 events per year (1000 tons CH2) / 87 events reactor

Rothschild, Chen, Calaprice(1998)

Geo-Neutrino Signal

from G. Fiorentini

“SNO is considering move to liquid scintillator after physics with heavy water is completed. With very low reactor background, well in the middle of Canadian shield (an “easy” geological situation) it will have have excellent opportunitiesexcellent opportunities.”

• which is to say that fundamental models are tested by experimental values…if those model calculations and measurements (for Sudbury) have smaller uncertainties (than for Kamioka), what we learn from the experimental measurements (at Sudbury) has potentially greater value

SNO+ Geo-Neutrinos

• SNO+ can try to confirm reactor neutrino oscillations

• move KamLAND’s spectral distortion to higher energies by going to a longer baseline

• this moves KamLAND spectral distortion features away from the geo-neutrinos– improves geo-neutrino detection– spectral shape confirmation

Reactor Antineutrinos

• table from Suekane’s NOON2003 talk

Top Ten List

BruceBruce

Location, Location, Location

• 240 km baseline – places 2nd oscillation maximum in the middle of the reactor neutrino positron spectrum

• 51 events per year (no oscillation expectation) from 6 reactors at full power 14 GWth

• there are 2 more reactors at Bruce that may be restarted

• not a precision test, will not further constrain oscillation parameters…just a confirmation, with statistics like K2K (e.g. in 3 years, expectation of ~150 events, observation of ~100 events…)

Bruce-SNO+

KamLAND Spectral Distortion

T. Araki et al., hep-ex/0406035 (2004)

SNO+ Spectral Distortion

• for relatively little cost, there is an opportunity to use existing equipment (i.e. most of the SNO detector) to enable new measurements

• costs are:– liquid scintillator procurement– mechanics of new configuration– fluid handling and safety systems– scintillator purification

3 Measurements for Low Cost

• 1 kton organic liquid scintillator would maintain excellent supernova neutrino capability– e + p [large rate]– e + 12C (CC)– e + 12C (CC)– x NC excitation of 12C (NC)– x + p elastic scattering (NC) [large

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

Supernova Neutrinos

• letter of interest submitted on 12 April 2004• SNO+ option “study group”

M. Chen*, A. Hallin, C. Kraus, J.R. Leslie, J. Maneira, R. MacLellan, A.B. McDonald, A. Wright Queen’sM. Boulay Los AlamosD. Hahn, M. Yeh BrookhavenX. Dai CarletonB. Cleveland, R. Ford SNOLABD. Hallman, C. Virtue LaurentianR.G.H. Robertson U of Washington

• potential collaborators from outside SNO have indicated some interest

SNOLAB LOI

• fully funded expansion of SNO underground site into an international facility for underground experiments– double beta decay– dark matter– solar neutrinos– supernova neutrinos

• excavation expected to begin late 2004, completed by 2006• space ready for experiments in 2007

• liquid scintillator cocktail design– optimize optical properties (attenuation length, light yield, pulse-

shape discrimination, scattering)– chemical compatibility with acrylic– high density preferred ( = 1 g/cm3) to use with existing H2O

buffer outside the acrylic vessel• mechanical “hold-down” system• cover gas improvements (lower radon)• safety, fluid handling underground• scintillator purification• SNO detector state (surviving PMT’s, acrylic vessel

certification)• calibrations and operations

Technical Aspects of R&D

• SNO+ R&D: one year– complete technical description– full cost estimates– completed feasibility studies– fully-developed science goals

• if above okay, full proposal(s) to be submitted 11/2005

• call for new collaborators in parallel with above• when above approved, 2 years to first fill

(04/2008)

Schedule

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

• add isotopes to liquid scintillator– dissolved Xe gas (2%)– chemical loading (Nd, Se, Te)

– dispersion of nanoparticles (Nd2O3, TeO2)

• enormous quantities (high statistics) and low backgrounds trade off for poor energy resolution of liquid scintillator

Double Beta Decay: SNO++

Candidate Selection

2 Background

• 0: 1057 events per year with 1% Nd- loaded liquid scintillator (natural Nd)

• S/B: 0/2 (upper half peak) = 2.3

• crude illustration below:

Test <m> = 0.150 eV

statistical test of the shape to extract 0 and 2 components!

• R&D to develop SNO+ underway• staged approach envisioned:

– deployment of pure scintillator for antineutrinos– next stage: go for purification to try for low energy

solar neutrinos– next stage: deploy double beta (e.g. nanoparticles),

would jump to this stage ASAP– long-term program provides steady and “early”

science output for SNOLAB

• new collaborators are welcome

Summary