Solar Neutrinos Perspectives and Objectives Mark Chen Queens

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 – Pee(Eν ) Borexino, Nature, 512, 383 (2014) Pee SNO, PRC, 88, 025501 (2013) LMA day-night asymmetry Night – blue Day – red Eν

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, Kam. LAND] • observed neutrino flavour conversion • measures θ 12 Still to be Detected • CNO – 2 s–�� 1 • hep SNO upper limit < 2. 3 × 104 cm��

CNO Electron Capture Lines • often forgotten • not all that significant N line 2. 220 Me. V 15 O line 2. 754 Me. V 17 F line 2. 761 Me. V • 13 • • • 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, XENON 1 T, PANDAX, XMASS • ~1 pp event/(day-tonne) with 50 ke. V threshold Borexino, Nature, 512, 383 (2014) LZ detector diagram

pep Borexino • analysis tags used to reject 11 C factor ~10, keeping 50% of the signal • 98% CL detection or 2. 05σ 98%CL by

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

What Still to Learn from 8 B? • “map out” the solar neutrino survival probability Pee as a function of Eν • 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 Neu. Tel 2015

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

Entire Slide from H. Sekiya’s Talk

Low Energy 8 B Solar Neutrinos in SNO+ 1 yr

CC Reactions on 13 C • tagged interaction • 1. 1% natural abundance • log ft = 3. 67, threshold 2. 2 Me. V β + decay with 10. 0 min half-life • use energy window, time and spatial coincidence to reject backgrounds • followed by 13 N • 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 ν • 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 1. 0 -2. 2 Me. V, 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