176
R. N. Mohapatra
called DUNE, which will use 40 kilotons of liquid argon as the detector fluid
and the second experiment is called Hyper-Kamiokande, which will use almost
500 kilotons of water.
The second kind of baryon number violation process mentioned above is the
neutron–anti-neutron oscillation. In this experiment, a free neutron in flight
transforms into its own anti-particle, as is predicted by certain theories [77].
This process probes physics near the energies where the present colliders are
searching for new physics. If this process is discovered, there is a possibility
that the related physics can also be searched for in new higher energy colliders
that are being planned. This is an exciting possibility.
Neutron–anti-neutron oscillation can be searched for in reactors where
many neutrons are emitted. Typically, about ten billion or more neutrons
are emitted per cm
2 per second. These neutrons in flight can convert to
anti-neutrons, and when the anti-neutron hits the detector, it will give a
spectacular annihilation signal that can be detected without any trouble (with
no background to confuse). There has been one experiment to search for
the oscillation of free neutrons in a reactor, at the Institute Laue-Langevin
(ILL) in Grenoble, France. In these experiments, one must suppress the Earth’s
magnetic field which has the effect of suppressing the n → ¯
n transition. This
is because how strongly the n and ¯
n mix depends on how little the magnetic
field is. This kind of technology, which can be used to shield magnetic fields
in a region of space, already exists and has been used in the ILL search
for neutron–anti-neutron oscillation. The technique uses a nickel–iron alloy,
called mu-metal. A more sensitive experiment to search for this oscillation will
require a longer baseline to allow more chances for the oscillation to happen.
One such experiment is being planned at the European Spallation Facility
(ESS) at Lund, Sweden, where a very high intensity neutron source will be
available soon.
Neutron oscillation can also occur inside a nucleus, though suppressed by
the nuclear energy difference between a neutron and anti-neutron, as they
“swim” inside it. This can give signals in a proton decay search experiment.
Instead of a positron, as in the case of proton decay, in this case, one gets a burst
of about four to five pions in the final state after the anti-neutron produced
in the oscillation annihilates with another proton or neutron in the nucleus.
The limits on this decay are similar to that for proton decay [2], leading to a
lower limit on the neutron–anti-neutron transition time of about a few years.
This limit is of the same order as was obtained in the ILL experiment.
R. N. Mohapatra
called DUNE, which will use 40 kilotons of liquid argon as the detector fluid
and the second experiment is called Hyper-Kamiokande, which will use almost
500 kilotons of water.
The second kind of baryon number violation process mentioned above is the
neutron–anti-neutron oscillation. In this experiment, a free neutron in flight
transforms into its own anti-particle, as is predicted by certain theories [77].
This process probes physics near the energies where the present colliders are
searching for new physics. If this process is discovered, there is a possibility
that the related physics can also be searched for in new higher energy colliders
that are being planned. This is an exciting possibility.
Neutron–anti-neutron oscillation can be searched for in reactors where
many neutrons are emitted. Typically, about ten billion or more neutrons
are emitted per cm
2 per second. These neutrons in flight can convert to
anti-neutrons, and when the anti-neutron hits the detector, it will give a
spectacular annihilation signal that can be detected without any trouble (with
no background to confuse). There has been one experiment to search for
the oscillation of free neutrons in a reactor, at the Institute Laue-Langevin
(ILL) in Grenoble, France. In these experiments, one must suppress the Earth’s
magnetic field which has the effect of suppressing the n → ¯
n transition. This
is because how strongly the n and ¯
n mix depends on how little the magnetic
field is. This kind of technology, which can be used to shield magnetic fields
in a region of space, already exists and has been used in the ILL search
for neutron–anti-neutron oscillation. The technique uses a nickel–iron alloy,
called mu-metal. A more sensitive experiment to search for this oscillation will
require a longer baseline to allow more chances for the oscillation to happen.
One such experiment is being planned at the European Spallation Facility
(ESS) at Lund, Sweden, where a very high intensity neutron source will be
available soon.
Neutron oscillation can also occur inside a nucleus, though suppressed by
the nuclear energy difference between a neutron and anti-neutron, as they
“swim” inside it. This can give signals in a proton decay search experiment.
Instead of a positron, as in the case of proton decay, in this case, one gets a burst
of about four to five pions in the final state after the anti-neutron produced
in the oscillation annihilates with another proton or neutron in the nucleus.
The limits on this decay are similar to that for proton decay [2], leading to a
lower limit on the neutron–anti-neutron transition time of about a few years.
This limit is of the same order as was obtained in the ILL experiment.