25
Neutrinos from Heavenly Sources
There are two kinds of natural neutrino sources in the universe: one coming
from the cosmic neutrinos, which were created during the early moments of
the universe from various collisions, such as e
+ e
− and μ
+ μ
− , and decays, such
as of the weak bosons and the Z bosons, etc. Those neutrinos have become
very cold and have very low energy due to the expansion of the universe. They
were discussed in Chap. 17. Their energies now are less than an eV.
There is another source where the neutrinos are produced at the current
era of the universe from violent collisions of energetic protons with protons
via the process pp → pn + (π
+ , K
+ ), followed by the decays of pion
and kaon e.g. (π
+ , K
+ ) → (μ
+
+ ν μ , e
+
+ ν e ) or via proton–proton
fusion as in the stellar cores. Those neutrinos produced in violent collisions of
protons typically have higher energy since they are not affected by the Hubble
expansion. For the stellar core emitted neutrinos, the energies are of the order
of one to 10 MeVs and for more energetic proton–proton collisions, they can
be of order GeVs. In the course of our discussion of neutrino oscillation, we
have considered two such heavenly sources of neutrinos: solar neutrinos with
MeV range energies emitted from the core of the Sun, and atmospheric sources
with GeV range energies originating from energetic protons in cosmic rays,
colliding with hydrogen and other atoms in the atmosphere. These are all in
some sense “natural–born” neutrinos, like the cosmic neutrinos. The question
then is, are there more sources of neutrinos from the sky, like the solar and
atmospheric neutrinos, and if so, what are their energies, and is it useful to
look for them? The answers to all these questions is “yes” and we will delve
into them briefly below.
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_25
189
Neutrinos from Heavenly Sources
There are two kinds of natural neutrino sources in the universe: one coming
from the cosmic neutrinos, which were created during the early moments of
the universe from various collisions, such as e
+ e
− and μ
+ μ
− , and decays, such
as of the weak bosons and the Z bosons, etc. Those neutrinos have become
very cold and have very low energy due to the expansion of the universe. They
were discussed in Chap. 17. Their energies now are less than an eV.
There is another source where the neutrinos are produced at the current
era of the universe from violent collisions of energetic protons with protons
via the process pp → pn + (π
+ , K
+ ), followed by the decays of pion
and kaon e.g. (π
+ , K
+ ) → (μ
+
+ ν μ , e
+
+ ν e ) or via proton–proton
fusion as in the stellar cores. Those neutrinos produced in violent collisions of
protons typically have higher energy since they are not affected by the Hubble
expansion. For the stellar core emitted neutrinos, the energies are of the order
of one to 10 MeVs and for more energetic proton–proton collisions, they can
be of order GeVs. In the course of our discussion of neutrino oscillation, we
have considered two such heavenly sources of neutrinos: solar neutrinos with
MeV range energies emitted from the core of the Sun, and atmospheric sources
with GeV range energies originating from energetic protons in cosmic rays,
colliding with hydrogen and other atoms in the atmosphere. These are all in
some sense “natural–born” neutrinos, like the cosmic neutrinos. The question
then is, are there more sources of neutrinos from the sky, like the solar and
atmospheric neutrinos, and if so, what are their energies, and is it useful to
look for them? The answers to all these questions is “yes” and we will delve
into them briefly below.
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_25
189