KamLAND Experiment

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KamLAND Experiment
Kamioka Liquid scintillator Anti-Neutrino Detector
- Largest low-energy anti-neutrino detector built
so far - Located at the site of former Kamiokande
experiment - High concentration of nuclear
reactors at the right distance
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1000 ton Liquid Scintillator Balloon made of
transparent nylon/EVOH composite film, supported
by cargo net structure. Stainless steel tank
filled with paraffin oil (0.04 lighter than
LS). 1325 17-inch 554 20-inch
PMTs Photosensitive coverage 34 3mm thick
acrylic wall Rn barrier Water Cherenkov outer
detector 225 20inch PMTs
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KamLAND Experiment
Designed to detect - anti-neutrino interactions
via inverse beta decay of electron scattering -
neutrinos from the Sun - terrestrial
anti-neutrinos - anti-neutrinos from the past
Supernova - exotic nucleon decay modes
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Detecting anti-neutrinos at KamLAND
Delayed
Prompt
2.2 MeV g
0.5 MeV ?

• Inverse beta decay

e-
e
0.5 MeV ?
n
p
p
d

• The positron loses its energy, then annihilates
  with an electron.
• (its a very fast event ns, seen as a
  unique flash by detector, brightness proportional
  to the kinetic energy of the positron plus 2
  annihilation gammas)

• The neutron first thermalizes then is captured by
  a proton with a mean capture time of 200ms.

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Event Reconstruction
-- Sort out waveforms coming from various ATWDs
at various times and bundle them into events
performed by event builder( putting together
waveforms that come from the same detector
trigger )
-- Raw waveforms collected from ATWDs present a
list of voltages
-- Convert the waveforms into pulses and extract
arrival times and collected charge (number of
photoelectrons collected by PMT)
-- Area under each pulse is integrated, which
corresponds to collected charge of the pulse. The
pulse with the largest friction of the total
charge (at least 15) is chosen as the true PMT
pulse within the waveform. Time is determined
from the pulse shape.
ATWD Analog Transient Waveform Digitizer
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Determining event vertices

• Assumed that interactions are point like events
  and that light is emitted isotropically from the
  interaction point
• Vertex determined using the pulse arrival times.

• Calibrated using sources deployed down
• the center of the detector.

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Determining event energies

• Estimation of particles energy is based on the
  hit pattern and the amount of light collected in
  the event and depends both on the particle
  position and particle type.
• The visible energy is calculated from the
  number of photo-electrons correcting for
  position.
• The real energy is calculated from the visible
  energy correcting for Cherenkov photons and
  scintillation light quenching.

Quenching is defined as saturation of the
scintillation emission for highly ionizing
particles. Described by Birkss law. Cherenkov
light is emitted whenever particle moves through
the Medium with speed grater than speed of light
in that medium. Estimation of the fraction of
energy lost is based on Monte Carlo calculations.
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Selecting electron anti-neutrinos
Delayed
Prompt
2.2 MeV g
0.5 MeV ?

• Veto after muons
• Rp, Rd lt 5.5m
• ?r lt 1.6m
• 0.5µs lt ?T lt 500µs
• 1.8MeV lt Edlt 2.6MeV
• 2.6MeV lt Eplt 8.5MeV

e
0.5 MeV ?
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Search of the neutron decay into invisible
channels, e.g. neutrinos.
Modes of s1/2 neutron disappearance from 12C
( branches predicted by nuclear model )
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3-hit event in the KamLAND detector
1. The first hit produced by monoenergetic ?s
with an energy of 3.35 MeV corresponding to the
de-excitation of a 2 level of 10C and by slow
down interactions of neutrons in the
scintillator 2. Second hit is due to the neutron
capture by hydrogen in the scintillator (
lifetime 200 ?s ) 3. The third hit will be due
to delayed ? decay of 10Cgs with lifetime of
27.8s and detectable energy in the range 1.74
3.65 MeV