EXPERIMENTAL RESULTS ABOUT NEUTRINO
A scientific result is always temporary.
It navigates between "certitudes" until a new result come
to replace or improve it. This even more true about the neutrino.
If you want to look at more complete neutrino physics
results, I advise you to look at two Web sites that were
among my best references:
Last results (31 march 2006):
MINOS experiment has observed 92 events of neutrino-mu interactions, where
it was expecting 177+-11. MINOS has thus observed a disappearance effect at 5 sigmas
and provide the following value for the square neutrinos masses difference:
Dm2 = 3.1 +- 0.6 +- 0.1 10-3 eV2
Have a look at:
In 1998, the main results were the following:
||Cross section on nucleon at 1 GeV
|| < 2.8 eV
|| < 5.8 10-20 MeV/T
|| around 10-38 cm2
|| < 16=70 keV
|| < 4.3 10-20 MeV/T
|| environ 10-38 cm2
|| < 18.2 MeV
|| < 3.1 10-17 MeV/T
|| around 10-38 cm2
| There are 3 families
of light neutrinos.
| The neutrinos have all left helicity
and anti-neutrinos have all right helicity
(but the term "all" can be discussed!)
|Neutrinos may be have a non zero mass
Two recent results seem to
indicate neutrinos oscillation:
LSND (Usa) and
|Other experiments like Chooz,
Chorus or Nomad did not find any evidence for
but they push further the limits
on the two factors that control neutrinos oscillations:
The result of an experiment searching for neutrinos oscillation is often
represented on a two dimensional graphics
where is displayed
The first parameter is the difference of the squared masses oif the two types
of neutrinos that oscillate in each other (simplified case of a two types neutrino
oscillation). The second parameter is the maximal probability that a neutrino
is an experiment near Los Alamos, at a particle accelerator that delivers
and anti whose energy is about 40
MeV. The LSND detector, which receives
those neutrinos detected 22 anti-electrons which could come from
anti interactionss and
40 electrons that could come from
In the first case, only 22 anti-electrons were expected;
in the second case only 5 electrons were expected.
There is clearly more type than predicted.
can be interpreted by
oscillation to . The final result
is a area where should be located
the values of the two oscillation parameters
et in order to
to interpret as a neutrino oscillation this unexpected result of LSND.
is located under a mountain in Kamioka mine, in Japan.
It is a huge water tank (a cylinder 41 m by 39 m which contains
about 50000 tons of pure water!) whose internal surface is covered with 11200
photomultipliers which detect the Cerenkov light of the particles
coming for instance from a
interaction with the water.
Super-Kamiokande detects solar or atmospheric neutrinos whose energy is above 5 MeV.
For what concerns solar neutrinos, Super-Kamiokande has already detected 44000
neutrinos, and this number is 37% of the expected number, confirming the results
of Homestake, Gallex, etc...
Below 1 GeV, 1158 events of type "interaction of a
" were detected in 1997, but
1573 were expected. During the same period, 1231 events of type "interaction
of a " were detected,
and 1049 were expected.
This seemed to indicate
a lack of .
One more time, the " neutrinos oscillation" interpretation
could be made, if the oscillation parameters were in a precisely defined
CHOOZ is a detector located near the Chooz nuclear plant,
in France. The number of anti
coming out the reactor and detected was about
the expected number. This result allowed to establish a limit on neutrinos
oscillations, that is an area
in which oscillation between anti
and anti does not exist.
You can remark that the results of Kamiokande (the previous experiment before
Super-Kamiokande) were not compatible with this exclusion area.
NOMAD and CHORUS
NOMAD and CHORUS
are detectors located at CERN, near Geneva, under a
neutrino beam of about
30 GeV. The two experiments are still analysing their data
but the first results seems to indicate the absence
oscillation, for values above 4.2 10-3.
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Last update: 26/06/1999 : http://wwwlapp.in2p3.fr/neutrinos/anresult.html