Low-energy neutrino physics with KamLAND Tadao Mitsui (Research Center for Neutrino Science, Tohoku U.) for the KamLAND collaboration Now2010, Grand Hotel Daniela, Conca Specchiulla, September 4-11, 2010

KamLAND is for NOW Neutrino workshop oscillation 2010

Outline Introduction Reactor neutrino Geoneutrino KamLAND-Zen (0  with 136 Xe)

KamLAND collaboration

March 2010, at UC Berkeley KamLAND collaboration

Nuclear reactors Continental crust (island arc) KamLAND location and sources of electron antineutrinos Oceanic crust Mantle “Peak” at ~180 km KamLAND

KamLAND detector 1.36 g/l PPO

Water tank Buffer oil Liquid scintillator Delayed signal Prompt signal 0.9~8MeV Kevlar ropes Balloon Phototubes Balloon 13m  2.2MeV time Nhit Kamioka Liquid Antineutrino Detector

Reactor neutrino

Data-2008 PRL100,  m 2 =  0.21  10  5 eV 2 All data (2002 – 2007 May) before scintillator purification  m 2 uncertainty: about 2/3 of data-2004 (PRL94,081801) (Solar + KamLAND) Reactor result (2008)

Spectral difference  m 2 uncertainty due to energy scale Energy scale uncertainty is the largest source of  m 2 uncertainty Energy scale difference of 1.37% (systematic uncertainty) 1  (statistical only) difference of  m 2

Energy scale: 1.9%, total: 2.77% Total  m 2 uncertainty (KamLAND+solar): 2.77 %

Energy scale determination in the organic scintillator Cherenkov-Birks model

KamLAND data contributing to  13 search G. L. Fogli, E. Lisi, A. Marrone, A. Palazzo, and A. M. Rotunno PRL 101, (2008)

JHEP04(2010)056 M.C. Gonzalez-Garcia,a;b Michele Maltonic and Jordi Salvado KamLAND data contributing to  13 search Our own analysis is also on going, with stimulated by those groups

Geoneutrino

Electron antineutrinos produced in the Earth’s interior (crust and mantle) by decays of 238 U, 232 Th, and 40 K Decays of 238 U, 232 Th, and 40 K : ~40% of Earth’s power Earth’s power:  plate tectonics, earthquakes, volcanoes, geomagnetism, … Origin and history of the Earth Pointed out since discovered (1950’s, G. Gamow, …) Geoneutrinos

T1/2= 4.47 billion y T1/2= billion y T1/2= 1.28 billion y Calculation of geo- energy spectrum

C The expected 238 U, 232 Th, and 40 K decay chain electron anti-neutino energy distribution. KamLAND can only detect electron antineutrinos to the right of the vertical dotted black line; hence it is insensitive to 40 K electron antineutrinos. Nature 436, 28 July 2005 KamLAND can detect Calculation of geo- energy spectrum

Data-2008: PRL100, (reactor + geo) Data-2005: Nature436, 499 Data-2010: Neutrino2010 (preliminary) Experimental investigation of geoneutrino (step by step: investigation → hint → …) Zero geonu disfavored at: ~2  > 4  Zero geonu “rejected?” at: ~2.7 

Nature 436, 28 July 2005 Data-set: days (Mar. 9, Oct. 30, 2004) Fiducial: 5 m radius 13 C( ,n) 16 O 42  11 reactor 80.4  7.2 Total BG  events observed “signal”  Th 238 U Systematic uncertainty (E =E prompt +0.8MeV) Data-2005

Data-2008 Events / MeV Reactor- geo - Data-2005: 7.09  proton yr Data-2008: 2.44  proton yr (  3.4)

Data-2008 geo- (U+Th, ratio fixed): 4.4  1.6  10 6 cm  2 s  1 (73  27 events) Finite signal: 2.7  (~2  for Data-2005) U+Th: 69.7 events expected in Reference model (Enomoto et al.) Georeactor at the center of the Earth < 6.2 TW (solar + KamLAND data)

Data-2010

BG reduction by purification and better estimation by direct calibration

Reactor BG: time variation analysis

Data-2008 v.s. Data-2010 Data-2008: PRL100, Data-2010: Neutrino2010 preliminary In data-2010, Th only is disfavored for the first time, due to higher-energy peak contribution

Full analysis (rate+shape+time)

KamLAND + Borexino v.s. model Multi-point observation is essentially important

Dilemma of near-field contribution At Kamioka, about one half of geonu is from Japanese island crust (continental crust) This contributes much for the “non-zero geonu significance”, but a background if we are interested in more deep mantle contribution To understand and “cancel” the near-field contribution, multi-point observation is more and more important (now Kamioka + Gran sasso!) “As many antineutrino detectors as seismograph.” (A. Suzuki 2002) Contour of percentage of the contribution to geonu flux at Kamioka

KamLAND-Zen (0  with 136 Xe) (Zero neutrino double beta decay)

Noble gas: can be dissolved into liquid scintillator up to ~ 3 wt%, with little effect (damage) on the scintillator character, such as light yield, transparency, and density. Slow 2  decay (T 1/2 2 > yr): modest requirement for energy resolution, suitable for liquid scintilltor experiment (KamLAND: 6.3%/√E[MeV]) Up to 90% enrichment has been established 136 Xe and liquid scintillator experiment PRL 72, 1411 (1994) R.S. Raghavan

Target sensitivity with 400-kg 136 Xe

Modification of KamLAND Develop “mini-balloon”: to reduce cosmogenic bg (mainly 10 C), bg from scintilltor ( 208 Tl etc), smaller balloon should be installed, in which Xe is loaded up to maximum concentration Develop Xe storage, and dissolve/extraction system (design almost fixed, to construct in a few month) Develop dead-time free electronics to tag 10 C by  -n- 10 C triple coincidence (installed, now running and trying to detect neutrons after a muon)

BG and mini-balloon design (by MC simulation) 214 Bi can be reduced by a factor ~10 by tagging, so 238 U, 232 Th < g/g is the requirement for the balloon film (now we searching for clean film)

Tagging 214 Bi and complicated battles 214 Bi- 214 Po tag: short coincidence time (   =164.3  s) is good, but  is easily stopped in the balloon film (15  m film: 90% tagged, 25  m: 80%, 50  m: 60%, according to MC) 214 Pb- 214 Bi tag: long coincidence time (   =19.9 min.), so reduction of bg of  +  from 214 Pb (0.5 ~ 1 MeV) is further challenge: 40 K in the film, 210 Bi in the scintillator (reduction by distillation?) and balloon film ( 222 Rn control during the balloon fabrication)

Test balloon of 15-  m thick Quarter-scale balloon was fabricated Very fragile, we gave up, then design thickness is now 25  m

Test balloon of 80-  m thick We understand this is too thick, but to perform installation test etc, this full-scale test balloon was fabricated (March 2010)

Balloon installation test Thanks to ATOX Co., Ltd. (Company for reactor maintenance)

Balloon installation test

Summary Reactor neutrino: continue precise measurement Geoneutrino: multi-point observation just started KamLAND-Zen: start in 2011 with 400-kg 136 Xe, aiming at the effective mass ~50 meV