Low Energy Neutrinost in SuperKamiokande TAUP 2015 Torino

Low Energy Neutrinost in Super-Kamiokande TAUP 2015 @Torino September 7 2015 Hiroyuki Sekiya ICRR, University of Tokyo for the Super-K Collaboration Hiroyuki Sekiya TAUP 2015 Torino September 7 2015

Super-Kamiokande 50 kton pure water Cherenkov detector 1 km (2. 7 km w. e) underground in Kamioka 11129 50 cm PMTs in Inner Detector 1885 20 cm PMTs in Outer Detector Physics targets of Super-Kamiokande This talk ν r la So N S lic e R ~3. 5 Me. V ~20 Hiroyuki Sekiya ay c e ν ~100 d n o ot Pr WI Atmospheric ν Te. V ~1 Ge. V TAUP 2015 s P M Torino September 7 2015 2

Super-K n + e- Solar neutrinos observation Hiroyuki Sekiya TAUP 2015 ne Torino September 3 7 2015

SK 8 B Solar neutrino observation SK has observed solar neutrino ◦ ~77000 solar n interactions for 18 years(~ 1. 5 solar cycle) SK I-IV combined flux 2. 341± 0. 044(stat. +syst. ) − 1 x 106 cm− 2�� �� �� Phase Energy threshold Me. V(kin. ) Live time (say) 8 B Flux × 106/cm 2/sec SK-I 4. 5 1496 2. 38± 0. 02± 0. 08 SK-II 6. 5 791 2. 41± 0. 05+0. 16 -0. 15 SK-III 4. 0 548 2. 40± 0. 04± 0. 05 SK-IV 3. 5 2034 2. 31± 0. 02± 0. 04 y ar n i lim e pr Hiroyuki Sekiya TAUP 2015 DATA/MC = 0. 4459± 0. 0084(stat. +syst. ) Torino September 7 2015 4

Time variation of 8 B solar neutrino flux No correlation with the 11 years solar activity is observed. Super-K solar rate measurements are fully consistent with a constant solar neutrino flux emitted by the Sun. c 2 = 13. 10/18(dof) Preliminary SK-II SK-IV SK-III Sun spot number was obtained by the web page of NASA http: //solarscience. msfc. nasa. gov/greenwch/spot_num. tx t Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 5

Oscillation analysis: Solar global fit This SK update and other latest results are combined. Without reactor θ 13 constraint Combined solar fit with Kam. LAND preliminary sin 2θ 13=0. 0242± 0. 0026 Solar Kam. LAND Solar+Kam. LAND Solar Reactor Non-zero q 13 at 2 s from solar+Kam. LAND Good agreement with Daya Bay, RENO & DC ~2σ tension in Δm 221 between solar and Kam. LAND Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 6

Search for the direct MSW signal Current main motivation of SK 8 B n observation Energy spectrum distortion Flux day-night asymmetry “Nighttime regeneration” of ne by earth matter effect Neutrino survival probability Vacuum oscillation dominant Solar+Kam. LAND sin 2θ 12=0. 308 Δm 221=7. 50 x 10 -5 e. V 2 up -t ur Solar sin 2θ 12=0. 311 Δm 221=4. 85 x 10 -5 e. V 2 n! Matter oscillation dominant JHEP 0311: 004(2003) Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 7

SK I-IV combined recoil spectrum Test of “spectrum upturn” ◦ MSW is slightly disfavored by ~1. 7 σ using the Solar + Kam. LAND best fit parameters ~1. 0 σ using the Solar Global best fit parameters. Total # of bins of SK I-IV is 83 χ2 Solar + Kam. LAND 70. 13 Solar global 68. 14 Quadratic fit 67. 67 Exponential 67. 54 Hiroyuki Sekiya Preliminary All SK phases are combined without regard to energy resolution or systematics in this figure. Statistic error only 8 BMC: 5. 25× 106/cm 2/sec Neutrino energy spectrum is convoluted in the electron recoil spectrum. For de-convolution, generic functions are used as a survival probability; TAUP 2015 Torino September 7 2015 8

Solar best fit sin 2θ 12=0. 311 Δm 221=4. 85 x 10 -5 e. V 2 Day-Night flux asymmetry preliminary Solar+Kam. LAND sin 2θ 12=0. 308 Δm 221=7. 50 x 10 -5 e. V 2 preliminary θz Earth Sun Δm 221=4. 84 x 10 -5 e. V 2 sin 2θ 12=0. 311 sin 2θ 13=0. 025 Fitted asymmetry amplitude Δm 221=4. 84 x 10 -5 e. V 2 Δm 221=7. 50 x 10 -5 e. V 2 SK-I -2. 0± 1. 8± 1. 0% -1. 9± 1. 7± 1. 0% SK-II -4. 4± 3. 8± 1. 0% -4. 4± 3. 6± 1. 0% SK-III -4. 2± 2. 7± 0. 7% -3. 8± 2. 6± 0. 7% SK-IV -3. 6± 1. 6± 0. 6% -3. 3± 1. 5± 0. 6% combined -3. 3± 1. 0± 0. 5% -3. 1± 1. 0± 0. 5% non-zero significance 3. 0σ 2. 8σ Hiroyuki Sekiya SK-I - IV combined TAUP 2015 (Eth=4. 5 Me. V for SK-I, III, IV 6. 5 Me. V for SK-II) This is the “direct” indication for matter enhanced neutrino oscillation Torino September 7 2015 9

DSNB (SRN) 1010 stellar/galaxy × 1010 galaxies × 0. 3%(become SNe) ~O(1017)SNe ar. Xiv: 1307. 5458, 1004. 3311 NOW Neutrinos from past SNe 8 B hep １ billion years ago DSNB ne DSNB nc atm nm ne 10 billion years ago Beginning of the universe Hiroyuki Sekiya Theoretical flux prediction : 0. 3~1. 5 /cm 2/s (17. 3 Me. V threshold) Super-K should be most sensitive to ne TAUP 2015 Torino September 7 2015 10

Status of DSNB search Search window for SRN at SK : From ~10 Me. V to ~30 Me. V Limited by BG. More than 1 order reduction is needed. Comparison with Expected ne spectra ◦ n tagging efficiency (by proton) is low… PRD 79 08013(2009) BG subtracted 11 Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 11

SK-Gd project Beacom and Vagins PRL 93, 171101 (2004) Identify nep events by Large cross section Captures on Gd neutron tagging with Gadolinium. for thermal neutron (48. 89 kb) Neutron captured Gd emits 3 -4 gs in total 8 Me. V Gd 2(SO 4)3 was selected to dissolve. 100 % 0. 1% Gd (0. 2% in Gd 2(SO 4)3) gives ~90% efficiency for n capture 80 % 60 % 40 % In Super-K this requires dissolving ~100 tons of Gd 2(SO 4)3 20 % 0% 0. 0001 0. 001% % 0. 01 % 0. 1% 1% Gd in Water Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 12

Expected signal with SK-Gd 10 years SRN flux from Horiuchi et al. PRD, 79, 083013 (2009) Assumption n capture efficiency: 90% Gd g detection efficiency: 74%. 35% of the SK-IV invisible muon BG ◦ By n-tagging Min/nominal/Max are due to uncertainties in astronomy. Expect number of events in 10 years in Etotal =10 -30 Me. V Teff 6 Me. V case: 26 -34 events Teff 4 Me. V case: 13 -16 events Background: ~18 events Aiming at “discovery” of SRN Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 13

EGADS 200 m 3 tank with 240 PMTs Evaluating Gadolinium’s Action on Detector Systems To study the Gd water quality with actual detector materials. The detector fully mimic Super-K detector. : SUS frame, PMT and PMT case, black sheets, etc. EGADS 2014 Gd water circulation system (purify water with keeping Gd) 15 m 3 tank to dissolve Gd Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 14

Water transparency during adding Gd had been dissolved from Nov. 2014 to May. 2015 Hiroyuki Sekiya TAUP 2015 Torino September 23 7 2015 15

Water transparency after Gd conc. got 0. 2% SK-III and SK-IV value Top Middle Bottom The light left at 15 m in the 200 m 3 tank was very stable and ~75% for 0. 2% Gd 2(SO 4)3 , which corresponds to ~92% of SK-IV pure water average Effect on the vertex resolution Hiroyuki Sekiya TAUP 2015 Effect on the energy resolution Torino 23 September 7 2015 16

Neutron capture signal in EGADS Using Delayed signal spectrum Am/Be + BGO Data MC Time to delayed signal Data MC Gd concentration dependence was confirmed. [μsec] Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 17

Official statement from SK collaboration Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 18

Summary Solar n observation • • • SK has observed ~77000 8 B n interactions over 18 years, by far the largest sample of solar neutrino events in the world. – No correlation with the solar activity cycle. SK recoil electron energy spectrum slightly disfavors “MSW upturn” SK data provide the first indication (at 2. 8~3. 0 s) of terrestrial matter effects on 8 B solar n oscillation. For DSNB detection Gd project in SK (was known as GADZOOKS!) started in 2002. • EGADS started in 2009 to evaluate Gd effect to SK. • In 2015, 0. 2% of Gd sulfate was dissolved in EGADS and it was confirmed that there is no showstopper for putting Gd into SK. SK-Gd was accepted by Super-K in June 2015. • Stay tuned for low energy SK neutrino Hiroyuki Sekiya TAUP 2015 Torino September 7 2015 19