Solar Neutrino Results from SNO Kevin Graham Carleton University

Ray Davis and John Bahcall

Solar Neutrino Measurements understanding how the sun works - solar neutrino problem - solar neutrino flux measurements - temporal/consistency evaluations neutrino physics - flavour change/oscillation - MNSP parameters - new physics? 2n oscillation probability (modified by MSW for solar)

Solar Neutrino Spectra 8B Standard Solar Model (5.69 ± 0.91)x106 cm2 s-1 18.77 MeV hep SSM (7.97 ± 1.24)x103 cm2 s-1

The SNO Detector 9438 Inward- Looking PMTs 2039 m to surface 91 Outward Looking PMTs (Veto) 12 m diameter Acrylic vessel Norite Rock PMT Support Structure (PSUP) 5300 tonnes light water ~1000 tonnes heavy water 1700 tonnes light water

cosq = 1/(index of refraction) ~420 What We Measure Cherenkov Light cosq = 1/(index of refraction) ~420 PMT Measurements position charge time Reconstructed Event -event vertex -event direction -energy -isotropy

Neutrino Reactions in SNO CC n + d  p + p + e− e Q = 1.445 MeV good measurement of ne energy spectrum some directional info  (1 – 1/3 cosq) ne only NC x n +  p d Q = 2.22 MeV measures total 8B n flux from the Sun equal cross section for all n types ES n + e−  n + e− x x low statistics mainly sensitive to ne, some n and n strong directional sensitivity

SNO Data Taking Phases Phase I (pure D2O): 306.4 live days Te > 5 MeV R < 550 cm 2928 events n capture on D Single 6.25 MeV g High CC-NC corr. Te constrained Phase II (salty D2O): 391 live days Te > 5.5 MeV R < 550 cm 4722 events n capture on Cl Multiple g’s 8.6 MeV High CC-NC corr. Te unconstrained Phase III (3He n counters): n capture on 3He n + 3He g p + t Channels indep. gno correlation Reduced NC systematics counters in and collecting data Initial Results Recent Results Now Running

Signal Extraction maximum likelihood fit of model PDF’s to data event variables R (radial position) b14(isotropy) cosqsun and E(energy) b14 CC-NC separation cosqsun CC NC ES ES separation don’t use E g “energy-unconstrained” g fit out CC spectrum!

Results from Complete Phase II CC 2176+/-78 ES 279+/-26 NC 2010+/-85 #EVENTS 4722 candidate events 391 live days a Flux Results CC Energy Spectrum Neutrino Flavour Change! no significant sterile or NSI effects Day/Night Asymmetry

Global analysis of solar and reactor data “LMA I” only allowed region Maximal mixing rejected at ~5 s Solar + KamLAND

SNO Periodicity Analysis search for sinusoidal periodicity in Phase I and Phase II data used both a Lomb-Scargle periodogram and an unbinned maximum likelihood fit. (see PRD 72 2005, 052010) event arrival times are fit to: (t) = N [1 + A cos(2pft+d)] largest peak in combined data set occurs at a period of 2.4 days, with a significance statistic of S=8.8 Monte Carlo shows that 35% of simulated data sets give a peak at least this large. No evidence for modulation in any of SNO's data.

hep < 2.3 x 104 cm-2 s-1 (90% C.L.) <2.9 SSM Preliminary Phase I hep and Diffuse Supernova Neutrino Background Observed: 2 events Expected: 3.13 ± 0.60 background 0.99 ± 0.09 signal look in ‘high’ energy windows for hep and DSNB signals 8B hep atm DSNB DSNB for 22.9 < En/MeV < 36.9 : flux limit: <70 cm-2s-1 (90%CL) predicted flux: 0.2→1.5 cm-2s-1 hep < 2.3 x 104 cm-2 s-1 (90% C.L.) <2.9 SSM

NCD Phase Data 3He + n  p + 3H + 0.76 MeV event-by-event separation (pulse shape) different systematic uncertainties precision NC measurement

Characteristic 3He(n,p)t Spectrum from Calibration Data from 3He NCD-Strings Alpha Background Next adding Pulse Shape Discrimination Fit Characteristic 3He(n,p)t Spectrum from Calibration

Summary So far: What is next: 8B neutrino results from first two phases including fluxes, spectrum, D/N asymmetry search for periodicity in data hep and diffuse SN neutrino results What is next: first results from NCD phase muon and atmospheric analysis combined phase I and II results with lower energy threshold supernova watch other results to come! flavour change MSW effect q12 and Dm2 solar physics

Solar Neutrinos 8B only tiny fraction of solar neutrinos chlorine and gallium experiments integrate over different chains no real low energy spectrum 7Be interesting but large model uncertainty pep has small uncertainty and at ‘right’ energy can provide most physics

2n oscillation probability <Ynm|Yne> Neutrino Mixing for two neutrino mixing flavour eigenstates different from mass eigenstates (like quark CKM) e,m,t 1,2,3 2n oscillation probability <Ynm|Yne> Experimental Parameters L = distance to experiment E = neutrino energy Physics Parameters Dm2=m12-m22 sin22q appearance/disappearance

3 Neutrinos + Matter Effect 3 neutrinos (at least) a4 model parameters matter enhancement modifies oscillation amplitude (MSW effect) ne e W

Vacuum vs Matter Enhanced Survival Probability start with ne in sun transition region matter enhanced oscillation vacuum oscillation ne solar pp pep 8B

What do 8B n Measurements Tell Us? Fluxes - CC/NC ratio Day/Night - asymmetry CC Energy Spectrum -shape distortion Increasing Δm2 Decreasing q No. of CC events 6 MeV 13 MeV hep-ph/0406328 July 21 2004 Bandyopadhyay, Choubey, Goswami, Petcov, and Roy

Flux Results from Complete Phase II CC 2176+/-78 ES 279+/-26 NC 2010+/-85 #EVENTS 4722 candidate events 391 live days a energy-unconstrained results Unconstrained Fit Key Systematics CC NC Energy scale -0.9% +1.0% -3.3% +3.8% β14 mean -4.0% +3.7% -3.6% +4.5% Radial scale -2.6% +2.5% -3.0% +3.3% n capture -2.3% +2.1% Total -5.4% +4.8% -6.9% +7.7% Neutrino Flavour Change!

Measured Total Flux and SSM Predictions 8B Flux experimental uncertainty smaller than theoretical for this sector of solar neutrinos

Day-Night Asymmetries ACC= -0.056 ± 0.074 (stat.) ± 0.051 (syst.) ANC= 0.042 ± 0.086(stat.) ± 0.067 (syst.) AES= 0.146 ± 0.198(stat.) ± 0.032 (syst.) Constraining ANC to be zero: ACC= -0.037 ± 0.063(stat.) ±0.032(sys.) AES= 0.153 ± 0.198(stat.) ±0.030(sys.) Combined Pure D2O and Salt No evidence for asymmetries from matter effects in the earth

2-n oscillation region defined by SNO Allowed regions

Muon and atmospheric neutrino analysis