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

1000 ton Liquid Scintillator

Balloon made of transparentnylon/EVOH composite film,supported by cargo net structure.

Stainless steel tank filled withparaffin oil (0.04% lighter than LS).

1325 17-inch + 554 20-inch PMT’sPhotosensitive coverage ~ 34%

3mm thick acrylic wall: Rn barrier

Water Cherenkov outer detector225 – 20inch PMT’s

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

Detecting anti-neutrinos at KamLAND

1.804MeVEt

0.8MeVmΔmEE enpnΔ

dpe+

0.5 MeV 2.2 MeV

np

0.5 MeV

e

e-

• Inverse beta decay

• The positron loses its energy, then annihilates with an electron.

(it’s 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.

PromptDelayed

Δpν

EEEe

_

)2.2(

_

MeVdpn

nepe

Event Reconstruction-- Sort out waveforms coming from various ATWD’s at various times and bundle theminto events – performed by “event builder”( putting together waveforms that come fromthe same detector trigger )

ATWD – Analog Transient Waveform Digitizer

-- Convert the waveforms intopulses and extract arrival timesand collected charge (numberof photoelectrons collected by PMT)

-- Area under each pulse is integrated,which corresponds to collected chargeof the pulse.The pulse with the largest friction of the total charge (at least 15%) is chosen as thetrue PMT pulse within the waveform. Time is determined from the pulse shape.

-- Raw waveforms collected from ATWD’s present a list of voltages

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.

Determining event energies• Estimation of particle’s 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 Birks’s law.

Cherenkov light is emitted whenever particle moves through theMedium with speed grater than speed of light in that medium.

Estimation of the fraction of energy lost is based on Monte Carlo calculations.

Selecting electron anti-neutrinos

• Veto after muons

• Rp, Rd < 5.5m

• Δr < 1.6m• 0.5μs < ΔT < 500μs

• 1.8MeV < Ed< 2.6MeV

• 2.6MeV < Ep< 8.5MeV

e+

0.5 MeV 2.2 MeV

0.5 MeV

PromptDelayed

Modes of s1/2 neutron disappearance from 12C :

Search of the neutron decay into invisible channels,

e.g. neutrinos.

( branches predicted by nuclear model )

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 hydrogenin the scintillator ( lifetime ~200 s )

3. The third hit will be due to delayed + decay of10Cgs with lifetime of 27.8s and detectable

energy in the range 1.74 – 3.65 MeV