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The Kamiokande achieved much result in observation of astronomical
neutrino and inspection of Grand Unified Theories. But, as for observation
device of Kamiokande, small the ability reached a limit. So, compared with
Kamiokande, Super Kamiokande experimental device that has good performance
and scale of 20 times was built.
The first purpose of this experiment that has been taking data from
April 1996 is to examine the models of Grand Unified Theories. The secondary
purpose is to observe neutrinos flew from the sun and atmosphere. And furthermore,
by observing the neutorinos, further study of the astrophysics to approach
the mystery of the evolution of the universe is expected.
detector:
Super Kamiokande Detector
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size: 41.4 m (height)X 39.3 m (diameter) {cylinder form}
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weight : Pure water 50000 t
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optical sensor: Photomultiplier (a diameter of 50 cm of the largest area
in the world) 11200
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energy precision: 2.5% (for 1GeV) to 16% (for 10MeV)
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energy thereshold: 5MeV
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place: Mozumi mine, Kamioka, Japan
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construction cost: about 90 million dollars (10.4 billion yen) (for 6 years
1991-1996)
inside the tank:
Detection method
Detector used with Super Kamiokande is water Cherenkov type detector.
A principle of this detector is to detect the Cherenkov light that occurs
when the charged particle travels at velocity higher than the velocity
of light in the water.
When the speed of a charged particle in the water is larger than the
velocity of light in the water , in other words it is
1 > B >= (1/n), B = (v/c)
v : Speed of a charged particle
c: Velocity of light in a vacuum
n: refractive index of water (1.33).
This Cherenkov light occurs in conical direction of
cos(\theta) = (1/n* B )
to the direction of charged particle.
This Cherenkov light is observed with 11146 50cm diameter photomultiplier
tubes(PMT's) mounted uniformly on the inner surface wall of the tank. Since
this light is ring shaped, it is called Cherenkov ring. By the information
of time and charge from PMT's, it is possible to obtain the information
of vertex point, particle id, direction, and momentum, etc. From these,
events can be reconstructed to see phenomenon that occurred.
For sample events PRESS
HERE
A figure of image of observation of event
study contents:
-> Data analysis of atomospheric and solar neutorino
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Atmosphere neutrino:
Atmospheric neutorinos are the decay products of hadoronic showers
produced by primary cosmic ray interactions in the atmosphere. A characteristic
of this atmosphere neutrino is that relative flux of the atmospheric muon
and electron neutrino is in a ratio of 2 to 1. However, recent year, this
ratio is off the expectation largely and said to be around 1.2 to 1. This
could be explained by neutrino oscillations. Which one type of the neutrino
transforms into another type while traveling. This neutrino oscillation
indicates that neutrino has mass. Therefore, we're doing a detailed selection
and analysis of the events.
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Solar neutrino:
The Solar neutrinos are produced inside the sun in the process of pp-chain
reaction and CNO cycle of nuclear fusion.
There is a large disagreement between the theory calculation and the
observation of the solar neutorinos. This disagreement is left only with
possibility of neutrino oscillation. In other words, the neutrinos have
transformed to other types of neutrino while travelling down to the earth.
This is the same as atmospheric neutrino, indicating that there is non-zero
mass to neutrino. Since Super Kamiokande can observe 10000 events of solar
neutrino a year, we're also measuring the energy spectrum and the day/night
difference.
KAMIOKANDE