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
Outline
Introduction
Reactor neutrino
Geoneutrino
KamLAND-Zen
136
(0nbb with Xe)
KamLAND collaboration
KamLAND collaboration
March 2010, at UC Berkeley
KamLAND location and sources of
electron antineutrinos
Continental crust
KamLAND
Continental crust
(island arc)
Nuclear reactors
“Peak” at
~180 km
Oceanic crust
Mantle
KamLAND detector
1.36 g/l PPO
Kamioka Liquid Antineutrino Detector
Kevlar ropes
Water tank
Buffer oil
Balloon
Liquid scintillator
Phototubes
Delayed signal
2.2MeV
Nhit
Prompt signal
0.9~8MeV
time
Balloon 13m
Reactor neutrino
Reactor result (2008)
Dm2=7.59+0.21-0.21×10-5 eV2
(Solar + KamLAND)
All data (2002 –
2007 May)
before scintillator
purification
Dm2 uncertainty:
about 2/3 of
data-2004
(PRL94,081801)
Data-2008 PRL100,221803
Spectral difference
Dm2 uncertainty due to energy scale
1 s (statistical only)
difference of Dm2
Energy scale
difference of 1.37%
(systematic
uncertainty)
Energy scale uncertainty is the largest source
of Dm2 uncertainty
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. Rotunno
PRL 101, 141801 (2008)
KamLAND data contributing to q13 search
M.C. Gonzalez-Garcia,a;b Michele Maltonic and Jordi Salvado
JHEP04(2010)056
Our own analysis
is also on going,
with stimulated
by those groups
Geoneutrino
Geoneutrinos
Electron antineutrinos produced in the
Earth’s interior (crust and mantle) by decays
of 238U, 232Th, and 40K
Decays of 238U, 232Th, and 40K :
~40% of Earth’s power
Earth’s power:  plate tectonics,
earthquakes, volcanoes, geomagnetism, …
Origin and history of the Earth
Pointed out since n discovered
(1950’s, G. Gamow, …)
Calculation of geo-n energy spectrum
T1/2=
4.47 billion y
T1/2=
14.05 billion y
T1/2=
1.28 billion y
Calculation of geo-n energy spectrum
Nature 436, 28 July 2005
C
KamLAND
can detect
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.
Experimental investigation of geoneutrino
(step by step: investigation → hint → …)
Data-2005: Nature436, 499
Zero geonu disfavored at: ~2 s
Data-2008: PRL100,221803 (reactor + geo)
Zero geonu “rejected?” at: ~2.7 s
Data-2010: Neutrino2010 (preliminary)
>4s
Data-2005
152 events observed
“signal” 25 +19 -18
Nature 436, 28 July 2005
Data-set:
749.1 days
(Mar. 9, 2002
-Oct. 30, 2004)
Systematic
uncertainty
232Th
Fiducial:
5 m radius
238U
(En=Eprompt+0.8MeV)
Events / 0.425 MeV
Data-2008
geo
-n
Reactor-n
Data-2005: 7.09×1031 proton yr
Data-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-2010
Data-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
Contour of
percentage of
the contribution
to geonu flux
at Kamioka
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)
KamLAND-Zen
136
(0nbb with Xe)
(Zero neutrino double beta decay)
136Xe
and liquid scintillator experiment
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 2n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
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 (T =19.9
1/2
214
min.), so reduction of bg of b+g from Pb (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 to
ATOX Co., Ltd.
(Company for reactor
maintenance)
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