Solar Neutrinos Perspectives and Objectives Mark Chen Queen’s University and Canadian Institute for Advanced Research (CIFAR)

Outline This is a short talk reviewing where we are with respect to two aspects of solar neutrinos: solar neutrino spectrum – astrophysics neutrino oscillations: survival probability versus neutrino energy – particle physics

Solar Neutrino Energy Spectrum

Survival Probability – P ee (E  ) Borexino, Nature, 512, 383 (2014) SNO, PRC, 88, (2013) P ee EE LMA day-night asymmetry Night – blue Day – red

Have Been Detected pp [Borexino, radiochemical Ga experiments] confirmed the Sun shines by pp fusion 7 Be [Borexino, radiochemical Cl experiment] confirmed neutrino oscillations pep [Borexino] has potential for probing vacuum-matter transition 8 B [SNO, Super-Kamiokande, Borexino, KamLAND] observed neutrino flavour conversion measures θ 12 Still to be Detected CNO hep SNO upper limit < 2.3 × 10 4 cm –2 s –1

CNO Electron Capture Lines often forgotten not all that significant 13 N line MeV 15 O line MeV 17 F line MeV was an insignificant background for SNO NC line sources – opportunity for CNO detection? Stonehill, Formaggio, Robertson

pp solar neutrinos large liquid scintillators with low 14 C can detect, like Borexino did liquid xenon has the potential to detect pp solar neutrinos LZ, XENON1T, PANDAX, XMASS ~1 pp event/(day-tonne) with 50 keV threshold LZ detector diagram Borexino, Nature, 512, 383 (2014)

analysis tags used to reject 11 C by factor ~10, keeping 50% of the signal 98% CL detection or 2.05σ 98%CL pep Borexino

Borexino pep Δ  2 Details LMA oscillated rate SSM rate A. Wright

Borexino CNO Upper Limit upper limit at 99%CL is 2 × High-Z 3 × Low-Z

Deep Site Needed for CNO Solar Neutrino Detection deep underground site (e.g. SNOLAB, Jinping) reduces cosmogenic 11 C background Borexino at Gran Sasso 3800 m.w.e SNO+ at SNOLAB 6000 m.w.e

Pb-210/Bi-210 Backgrounds SNO+ signal extraction study

How to Improve pep and CNO? Borexino: nice work to suppress 11 C background, though some remains and the 210 Bi-CNO separation remains difficult suppressing further by factors ~100 or more (depth), and also tagging, will open up the window for improved spectral fitting 210 Bi-CNO solar can be separated, in principle lowest 210 Bi backgrounds possible helps to facilitate CNO and pep signals have covariances, as shown; thus, improving CNO signal extraction improves pep (plus lower backgrounds help directly improve pep signal extraction)

SNO+ CNO and SNO 8 B use the SNO 8 B measurement to constrain “environmental variables” in the solar core which also affects CNO  measure CNO flux (to ±10%) and compare with solar models to differentiate high-Z / low-Z core metallicity à la Haxton and Serenelli where will the SNO+ CNO measurement point to?

What Still to Learn from 8 B? “map out” the solar neutrino survival probability P ee as a function of E  can give us a handle on new physics ideal to use pep or lower energy 8 B for this observation of the day-night effect by Super-K at 2.7σ; is there a need to improve? figure from H. Sekiya’s talk at LRT 2015

Entire Slide for M. Nakahata’s Talk at NeuTel 2015

New Physics at the Vacuum-Matter Transition? Friedland, Lunardini, Peña-Garay P ee curve with non-standard interactions de Holanda and Smirnov Sterile Neutrinos Mass-Varying Neutrinos Gonzalez-Garcia, Maltoni

Entire Slide from H. Sekiya’s Talk

Low Energy 8 B Solar Neutrinos in SNO+ SNO+ 1 yr

CC Reactions on 13 C tagged interaction 1.1% natural abundance log ft = 3.67, threshold 2.2 MeV followed by 13 N  + decay with 10.0 min half-life use energy window, time and spatial coincidence to reject backgrounds CC offers potentially better spectral shape determination (than ES from SNO+ lower energy 8 B or Super-K) from Ianni, Montanino, Villante

13 C Low Energy 8 B Solar  rate of ~20 events/kton/yr including detection efficiency (cuts) observe the reaction and then observe 13 N decay at the same position, with energy between MeV, within ~30 min potentially very little background (cosmogenic or radioactive) need a 10 kton-sized detector (or larger, like JUNO or LENA) to get an appreciable signal