KamLAND Update
June 17, 2005
LEPP Journal Club
Lauren Hsu
Lawrence Berkeley National Laboratory
Outline
I.
Introduction
II.
Role of Reactor Experiments in Neutrino
Oscillations
II.
KamLAND Overview and Results on 2nd
Reactor Analysis
III.
The Future of KamLAND Reactor
Measurements
IV.
Other Future Measurements: Geoneutrinos and Be7
KamLAND Update - Lauren Hsu
KamLAND
KAMioka Liquid scintillator
Anti-Neutrino Detector
Detecting reactor anti-neutrinos 1 km
beneath Mt. Ikeyama
Inside the
Kamioka Mine
Surrounded by 53 Japanese Nuclear Reactors
Physics Reach of KamLAND
KamLAND Update - Lauren Hsu
The KamLAND Collaboration
Tohoku U.
LBNL
Stanford
CalTech
KS State U.
U. of TN
U. of AL
TUNL
Drexel
U. of NM
U. of HI
IHEP
CENBG
KamLAND Update - Lauren Hsu
•
Role of Reactor Experiments in Neutrino
Oscillations
KamLAND Update - Lauren Hsu
Neutrino Oscillations Review
Like quarks, neutrino flavor and mass eigenstates are not the same:
UMNSP =
cos12 sin12 0
-sin12 cos12 0
0
0
1


0
0
cos23 sin23
-sin23 cos23

cos13 0 e-isin13
0
1
0
-e-isin13 0 cos13
Atmospheric
Solar and KamLAND
1
0
0
1
0
0
0
0
e-i/2 0
0
e-i(/2+)
Future reactor or
accelerator
Majorana phases
Simplified expression for two flavor oscillations in a vacuum:
22 sin2(1.27 m2(eV2)L(m)/E (MeV))
P( l
)
=
sin
l’

 


oscillations imply neutrinos have mass!
KamLAND Update - Lauren Hsu
Sampling of -Oscillation
Experiments
By no means comprehensive!
Reactor
(KamLAND)
2
m23
& sin223
v (?)
disappearance
Energy: ~ GeV
Baseline: 15 13,000 km
tan12 & m 212
2
m23
& sin223
e disappearance
+ appearance
vu (?)
disappearance
Energy: ~5-15 MeV
Energy: ~ GeV
Baseline:
1.5108
km
Baseline: 250 km
KamLAND Update - Lauren Hsu
2
m12 & sin212
-e disappearance
Energy: few MeV
Baseline: 180 km
Neutrino Mass Heirarchy
m2
Normal
or
Inverted?
e


m2 3
2
m23 = (1-3)10-3 eV2
m2 2
m2
atmospheric
2 = (7.90.06)10-5 eV2
m12
1
?
0.0
KamLAND Update - Lauren Hsu
Solar and KamLAND
Reactor Anti-Neutrino
Experiments
Basics
•
•
•
•
•
Disappearance Experiment
Detect anti neutrino via inverse beta-decay
Energy range ~few MeV
Reactor anti-neutrino experiments performed since 1950’s
Detector relatively simple and basic design unchanged
Why a Reactor Neutrino Experiment?
No matter effects
Man-made source
Opportunity to study anti-neutrino vs neutrino oscillations
KamLAND Update - Lauren Hsu
Anti-Neutrino Production in
Reactors
235U
+ n  X1 + X2 + 2n
• Anti-neutrinos produced in beta decay of daughter isotopes resulting from
fission
• Production of anti-neutrinos well understood theoretically and fission yields
precisely monitored by power companies (to 2% uncertainty)
No need for a near detector to monitor flux!
Averaged Relative Fission Yields:
235U:238U:239Pu:241Pu
= 0.563: 0.079: 0.301:0.057
Net thermal power output by all Japanese
Nuclear Reactors is 200 GW.
KamLAND Update - Lauren Hsu
Un-Oscillated Reactor Neutrino
Spectrum
Verified to 2% accuracy by earlier generation of reactor anti-neutrino experiments
KamLAND Update - Lauren Hsu
Why KamLAND?
KamLAND Optimizations:
More Overburden: Avoids
Cosmogenic Backgrounds
Long Baseline – optimizes
sensitivity to oscillations
Large (1 kTon!) – combats
1/R2 drop-off in intensity
KamLAND sees ~1 anti-neutrino
event/day at an effective
baseline of 180 km.
The First KamLAND Result
PRLBefore
90 (2003)
KamLAND
021802
- e disappearance!
KamLAND is the first reactor experiment to observe
KamLAND Update - Lauren Hsu
Physics Implications for the
First Result
KamLAND Update - Lauren Hsu
III.
KamLAND Overview and Results on 2nd
Reactor Analysis
KamLAND Update - Lauren Hsu
The KamLAND Detector
(1879)
KamLAND Update - Lauren Hsu
The Target Volume
Liquid Scintillator:
• Serves as both the target and the
detector, > 1031 protons
• 20% Pseudocume + 80% Mineral Oil
+ 1.5 g/l PPO
• Optimal light yield while maintaining
long attenuation length (~20 m).
Welding the Balloon
Balloon:
• Separates target LS volume from
buffer oil
• 135 m Nylon/EVOH
(ethylene vinyl alcohol copolymer)
• Supported by kevlar ropes
KamLAND Update - Lauren Hsu
KamLAND Photo-Multipliers
PMT and acrylic panel installation
• 1325 17” tubes
• 554 20” tubes (since
2/03)
• Transit time spread
< 3 ns
• Separated from inner
buffer by acrylic
panels
• 200 17” hits for 1 MeV
energy deposit
KamLAND Update - Lauren Hsu
The Outer Detector
• 3.2 kT water Cerenkov detector (~200
PMT’s)
• Detects 92% of muons passing through
inner detector
• Buffers inner detector from spallation
products and radioactivity in rock.
KamLAND Update - Lauren Hsu
Anti-Neutrino Signal Detection
Coincident energy deposits are a distinct signature of inverse beta-decay:
e + p  e+ + n
Prompt Energy:
positron energy deposit
(K.E. + annihilation ’s)
Delayed Energy:
n-capture releases 2.2
MeV , ~200 s later
KamLAND Update - Lauren Hsu
Selecting Candidate Events
Apply Time and Spacial Cuts to Obtain Candidate Coincidence Events
Candidate Coincidence
Events: t = [0.5, 1000]s
-e energy obtained from
E = Eprompt + 0.8 MeV
KamLAND Update - Lauren Hsu
Basic KamLAND Data
Reconstruction
How much energy deposited and where?
Energy Reconstruction:
• Energy  Number of Hit PMT’s
• Correction for Vertex Position
• Corrections for Quenching and
Cerenkov
Vertex Reconstruction
• Determined by Very Precise Timing of Hits (~ few ns):
• Inherent Detector Resolution ~15cm.
• Based on push-pull minimization algorithm.
Energy and Vertex fitter Calibrated w/ Co60, Ge68, Zn65, and AmBe deployed
along the z-axis.
KamLAND Update - Lauren Hsu
Energy Calibration
KamLAND Update - Lauren Hsu
Energy Estimation
Correcting for
Nonlinearity of
Energy Scale
Only observe -e above 3.4 MeV
(Eprompt = 2.6 MeV)
KamLAND Update - Lauren Hsu
Muon Tracking
Rate of Muons hitting
KamLAND is ~1 Hz
Reconstruction of Tracks:
• Pattern recognition based on
expected timing of inner
detector hits
• Good agreement with
simulation of muons passing
through detailed mountain
topography
Uncorrelated Backgrounds
Lots of steel in the
chimney region!
Uncorrelated backgrounds:
• From radioactive isotopes
in detector and surrounding
material.
• Activity concentrated near
balloon
• Fiducial volume cut defined
at r = 5.5m
KamLAND Update - Lauren Hsu
Correlated Cosmogenic
Backgrounds
Spallation Products
Muons interacting with material
produce neutrons and delayed
neutron  - emitters
He8 thought to be a negligeable contribution
KamLAND Update - Lauren Hsu
13C(,n)16O
Background
low energy
~6 MeV
4.4 MeV
Background Prompt E (MeV)
KamLAND Update - Lauren Hsu
KamLAND Reactors
Total reactor
power
uncertainty
in analysis is 2%
(conservative
estimate)
KamLAND Update - Lauren Hsu
Dip in Nuclear Power Output
no-osc rate e events/day
KamLAND
Falsified saftey records prompted shutdown of several nuclear power plants
KamLAND Update - Lauren Hsu
Looking for Correlations in
Un-Oscillated Rate Changes
KamLAND Update - Lauren Hsu
What Were Improvements?
• More Statistics: 515.1 live days compared to 145.1 live days.
•
13C(,n)16O
background discovered and included in analysis
• Better Optimized Cuts (fiducial volume increased from 5m
to 5.5m)
• Addition of 20” tubes (improved energy resolution from
7%/E(MeV) to 6%/E(MeV))
• Reactor off-time allowed for study of correlation of signal
with reactor flux.
Second results includes re-analysis of same data-sample used in first
KamLAND Update - Lauren Hsu
Observation of Spectral Distortion from
Neutrino Oscillations
Measurement of Energy Spectral Distortion Due to Oscillation: PRL 94 081802 (2005)
258 events observed
365 expected
KamLAND Update - Lauren Hsu
Looking for Oscillatory Behavior
0.7% goodness of fit
1.8% goodness of fit
Simplified expression for two flavor oscillations in a vacuum:
P(ll’) = sin22 sin2(1.27m2(eV2)L(m)/E (MeV))
KamLAND Update - Lauren Hsu
2
Unparalled Sensitivity to m12
Extract Oscillation Parameters and Combine with Solar Data
PRL 94 081802 (2005)
PRL 94 081802 (2005)
+0.6
-5 eV2, tan2
Solar + KamLAND: m
=7.9

10
KamLAND
Update
Lauren
Hsu
-0.5
12
12 =0.4
2
+0.10
-0.07
IV.
The Future of KamLAND Reactor
Measurements
KamLAND Update - Lauren Hsu
Future Improvements: Reactor
Analysis
Further Improvements Require Reducing Systematic Uncertainty!
Systematic Unc. on Rate
%
Fiducial Volume
4.7
un-oscillated e spectrum (theor.)
2.5
Energy Threshold
2.3
Reactor Power
2.1
Cut Efficiency
1.6
Fuel Composition
1.0
Cross Section
0.2
Livetime
0.06
Total
7.1
Compare to statistical uncertainty: 6.7%
Better understanding of 13C(,n)16O will also improve shape analysis
KamLAND Update - Lauren Hsu
Full Volume Calibration
• A new full-volume calibration device
• Off-axis calibration to improve energy and vertex estimation
• Reduce fiducial volume uncertainty
Testing 4 at LBNL
Source placement uncertainty of 2 cm will
measure fiducial volume to 2-3% uncertainty
KamLAND Update - Lauren Hsu
A Muon Tracker
• Gold-plated muon events will
cross-check the muon trackreconstruction.
• Three layer tracking chamber
prop tubes
• ~200 events per day in
coincidence with inner detector
• x-y resolution of 2-3 cm.
• assembled by graduate
student(s) at LBNL.
KamLAND Update - Lauren Hsu
A Full-Detector Simulation
Geant4 visualization of
KamLAND
Goal: A Tuned Full-Detector Simulation
Helps to reduce systematic uncertainty
for next analysis and increase understanding of detector
KamLAND Update - Lauren Hsu
A Change in Effective
Baseline?
Shika upgrade will be complete in 2006.
Impact on baseline will depend on the oscillation parameters!
2)
(sin212, m12
KamLAND Update - Lauren Hsu
Projected Future Sensitivity
KamLAND will continue
to make the most sensitive
measurements on m212for the
forseeable future
KamLAND Update - Lauren Hsu
V.
Other Future Measurements: Geo-neutrinos
and Be7
KamLAND Update - Lauren Hsu
Geo-Anti-Neutrinos
First search for geologically produced - e!
surface heat flux measurements
16 TW of Heat predicted from decay of
238U and 232Th concentrated in earth’s crust
Total Heat radiated by Earth is ~44 TW
KamLAND Update - Lauren Hsu
A Measurable Spectrum Below
2.6 MeV
Geo-neutrino analysis is
very sensitive to quenched neutrons
from 13C(,n)16O background
Th + U signal
reactor - -e
background
KamLAND Update - Lauren Hsu
Be7 Phase: 2nd KamLAND
Phase
KamLAND Update - Lauren Hsu
An Ambitious Purification Project
Detecting e
Via elastic Scattering
(no coincidence to
suppress radioactive
backgrounds)
KamLAND Update - Lauren Hsu
Purification R&D
Current R&D shows promising results.
Kr removal is
through He
bubbling and Kr
trap
~10-4 achieved
• $10 million must be spent this year
• Construction of Purification Hall already begun
• 3 Distillation towers will be installed.
KamLAND Update - Lauren Hsu
Post Purification Goal
KamLAND Update - Lauren Hsu
Timeline for KamLAND
Excavation of new purification chamber
started in April and nearly finished.
KamLAND Update - Lauren Hsu
Summary
• KamLAND is the first experiment to observe disappearance of reactor
anti-neutrinos (99.998% significance).
• Latest results (summer 2004) show evidence for spectral distortion.
combined solar-experiment and KamLAND results give:
m212= 7.9
+0.6
-0.5
10-5eV2 and tan212= 0.40
+0.10
-0.07
• Future reactor measurements will benefit from full-volume calibration, a
muon tracker, full-detector Monte Carlo, and purification.
• Expect results soon on geo-neutrinos – the first limit ever for
observation of anti-neutrinos produced from the earth.
• Phase II of KamLAND: 7Be neutrinos from the sun. Purification stage
is already beginning, and measurements to start in 2007.
KamLAND Update - Lauren Hsu
Acknowledgements
Almost all pieces of this talk borrowed liberally from
my KamLAND colleagues
Reference:
http://www.ba.infn.it/~now2004/talks/12_09_04/plen/KamLAND.pdf
KamLAND Update - Lauren Hsu
Mozumi 4/05
KL Control Room
to Kamioka Mine
KamLAND Update - Lauren Hsu