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

Neu

trino

works

hoposcillation

2010

Outline

Introduction

Reactor neutrino

Geoneutrino

KamLAND-Zen

(0nbb with 136Xe)

KamLAND collaboration

March 2010, at UC Berkeley

KamLAND collaboration

Nuclear reactors

Continental crust

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 signalPrompt signal 0.9~8MeV

Kevlar ropes

Balloon

Phototubes

Balloon 13m

2.2MeV

time

Nhi

t

Kamioka Liquid Antineutrino Detector

Reactor neutrino

Data-2008 PRL100,221803

Dm2=7.59+0.21-0.21×10-5 eV2

All data (2002 – 2007 May)

before scintillator

purification

Dm2 uncertainty:

about 2/3 of

data-2004

(PRL94,081801)

(Solar + KamLAND)

Reactor result (2008)

Spe

ctra

l diff

eren

ceDm2 uncertainty due to energy scale

Energy scale uncertainty is the largest source

of Dm2 uncertainty

Energy scaledifference of 1.37%(systematic uncertainty)

1 s (statistical only)difference of Dm2

Energy scale: 1.9%, total: 2.77%

Total Dm2 uncertainty (KamLAND+solar): 2.77 %

Energy scale determination in the organic scintillator

Cherenkov-Birks model

KamLAND data contributing to q13 search

G. L. Fogli, E. Lisi, A. Marrone, A. Palazzo, and A. M. RotunnoPRL 101, 141801 (2008)

JHEP04(2010)056

M.C. Gonzalez-Garcia,a;b Michele Maltonic and Jordi Salvado

KamLAND data contributing to q13 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 238U, 232Th, and 40KDecays of 238U, 232Th, and 40K :

~40% of Earth’s powerEarth’s power: plate tectonics, earthquakes, volcanoes, geomagnetism, …Origin and history of the EarthPointed out since discovered

(1950’s, G. Gamow, …)

Geoneutrinos

T1/2=4.47 billion y

T1/2=14.05 billion y

T1/2=1.28 billion y

Calculation of geo-n energy spectrum

C

The expected 238U, 232Th, and 40K 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 40K electron antineutrinos.

Nature 436, 28 July 2005

KamLANDcan detect

Calculation of geo-n energy spectrum

Data-2008: PRL100,221803 (reactor + geo)

Data-2005: Nature436, 499

Data-2010: Neutrino2010 (preliminary)

Experimental investigation of geoneutrino(step by step: investigation → hint → …)

Zero geonu disfavored at: ~2 s

> 4 s

Zero geonu “rejected?” at: ~2.7 s

Nature 436, 28 July 2005

Data-set:749.1 days(Mar. 9, 2002-Oct. 30, 2004)Fiducial:5 m radius

13C(,n)16O4211 rea

ctor 8

0.4

7.2

Total BG 1

27.0

13.1

152 events observed“signal” 25 +19 18

232Th238U

Systematicuncertainty

(E=Eprompt+0.8MeV)

Data-2005

Data-2008E

ven

ts /

0.42

5 M

eV

Reactor-n

geo-n

Data-2005: 7.09×1031 proton yrData-2008: 2.44×1032 proton yr (×3.4)

Data-2008

geo-n (U+Th, ratio fixed):

4.4±1.6×106 cm-2 s-1 (73±27 events)

Finite signal: 2.7s (~2s 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-2010Data-2008: PRL100,221803 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 ofpercentage ofthe contributionto geonu fluxat Kamioka

KamLAND-Zen(0nbb with 136Xe)

(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 n decay (T1/22n > 1022 yr): modest requirement

for energy resolution, suitable for liquid scintilltor experiment (KamLAND: 6.3%/√E[MeV])

Up to 90% enrichment has been established

136Xe and liquid scintillator experiment

PRL 72, 1411 (1994) R.S. Raghavan

Target sensitivity with 400-kg 136Xe

Target sensitivity with 400-kg 136Xe

Modification of KamLAND

Develop “mini-balloon”: to reduce cosmogenic bg (mainly 10C), bg from scintilltor (208Tl 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 10C by m-n-10C triple coincidence (installed, now running and trying to detect neutrons after a muon)

BG and mini-balloon design(by MC simulation)

214Bi can be reduced by a factor ~10 by tagging, so 238U, 232Th < 10-12 g/g is the requirement for the balloon film (now we searching for clean film)

Tagging 214Bi and complicated battles

214Bi-214Po tag: short coincidence time (T1/2=164.3 ms) is good, but a is easily stopped in the balloon film (15 mm film: 90% tagged, 25 mm: 80%, 50 mm: 60%, according to MC)214Pb-214Bi tag: long coincidence time (T1/2=19.9 min.), so reduction of bg of b+g from 214Pb (0.5 ~ 1 MeV) is further challenge: 40K in the film, 210Bi in the scintillator (reduction by distillation?) and balloon film (222Rn control during the balloon fabrication)

Test balloon of 15-mm thick

Quarter-scale balloon was fabricated

Very fragile, we gave up, then design thickness is now 25 mm

Test balloon of 80-mm 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 toATOX Co., Ltd.(Company for reactormaintenance)

Balloon installation test

Balloon installation test

Summary

Reactor neutrino: continue precise measurement

Geoneutrino: multi-point observation just started

KamLAND-Zen: start in 2011 with 400-kg 136Xe, aiming at the effective mass ~50 meV