T h e m ystery of th e solar n eu trin os

Novel Heavy-Water Detector Unreveils the Missing Solar Neutrinos(08.2001- Phys. Today)
The beta-decay route to a high-flux neutrino source (07.2004- Cern Courier)
Neutrinos provide new route to heavy elements in supernovae (2006- Phys. Rev.Lett)
Disappearing Atmospheric Neutrinos Don´t Seem to be Turning Sterile (2000-Phys.Rev.Letts.85)
Sterile neutrinos unravel astrophysics (2006 Phys. Rev. Letts. 96)
• https://www.institucional.us.es/foros/read.php?126,115924,115938
•http://www.aragoninvestiga.org/investigacion/temas_todo.asp?id
tema=31&intPagActual=1&categoria=Ciencias+Experimentales&id_categoria=290
• http://gesalerico.ft.uam.es/paginaspersonales/bellido/gravitacion/exp/NU.html
Some cientific articles
• http://hep.bu.edu/~superk/atmnu/
References:
The fussion reactions in solar core exclusively produces νe. Only 1/3 of them
are detected so it is suppossed that the remaining 2/3 oscillate into νµ and ντ.
The total flux of all these three flavors is in agreement with νe flux predicted
by SSM (Standard Solar Model).
FINDING THE MISSING NEUTRINOS
Something similar happens with solar neutrinos νe. A fraction of them suffer a
flavor change somewhere on their journey to the detector.
Oscillation between νµ and ντ is enough to explain all the results in hand. νµ is
oscillating with a putative “sterile” neutrino species that is impervious to the
normal weak interaction.
Superkamiokande (water detector in Japan) have made a strong case: the
missing neutrinos νµ´s are being transformed by “neutrino oscillation” into
another kind of neutrinos.
WHAT IS HAPPENING?
In the last years, physicits discovered that νµ produced by decays in cosmic-ray
showers in the upper athmosphere are, somehow, dissappearing before they can
reach an underground neutrino detector.
Neutrino Oscillation
Davis' experiment confirmed that the Sun produces neutrinos, but only about
one-third of the number of neutrinos predicted by theory could be detected.
That is because neutrinos change flavor while passing through the Sun in their
way to Earth.
The chlorine target was located underground, to protect it from cosmic rays.
The target had to be big because the probability of chlorine's capturing a
neutrino is very small.
In 1968, Ray Davis developed an experiment based on the idea that a solar
neutrino, generated in the fusion of the hydrogen in the solar core, produces
radioactive argon when it interacts with chlorine. He placed a tank of
perchloroethylene and a good source of chlorine, in the Homestake Gold Mine
in South Dakota.
The mystery of the solar neutrinos
• One last flavour was proposed in 1975 when the third lepton, the tauon, is
discovered at the Stanford Linear Accelerator. The existence of the tauon-neutrino
was confirmed in the same way as the electron-neutrino was, studing the tauon
decay.
• In 1962 it was discovered a new type (flavor) of neutrino. Leon M. Lederman,
Melvin Schwartz and Jack Steinberger prove that the neutrino produced in a pion
decay to generate a muon was different than the electron-neutrino. They call this
new kind of neutrino “muon-neutrino” or “muonic netrino”.
• In 1956 its existence was confirmed by Frederick Reines and Clyde Lorrain Cowan
using a huge water detector, in which the electron-antineutrinos could interact
with hydrogen nuclei (protons) to produce a neutron and a positron, which were,
afterwards, detected.
• The neutrino was first postulated in 1930
by Wolfgang Pauli in order to explain
conservation of momentum in the beta
decay.
History of the neutrino
(1)
(4)
Left and right images: dark
matter distribution in the
Universe
• During supernovae explosions, atomic nuclei capture protons and
become unstable. Antineutrinos are captured by free protons,
changing them into neutrons, so that they can be capture by these
highly charge nuclei, stabilizing them, and enabling the synthesis of
heavier elements. This is called the νp-process.
• Neutrino oscillations introduce the posibility of differentiate between matter
and antimatter versions of neutrinos. This charge-parity violation could help
to explain the disparity of the amounts of matter and antimatter observed in
the universe
Did you Know…?
(5)
Some of the most important neutrino detectors in the world
(7)
• Supernova explosions: the intense flux of
neutrinos that is expelled from the supernova is
supposed to be one of the main ways the
energy has to be released.
−
→ ν + e
−
ν + D →ν + p + n
Neutral-current reaction (NCR):
n with matter
ν τ interactio


→τ decays
→ detection
n with matter


→ µ decays
→ detection
ν µ interactio
Charge-current reactions (CCR):
ν e + n → p + e−
ν e + p → n + e+
n + ZAX N → A+Z1X N* +1 → A+Z1X N +1 + γ
⇒ + −
e + e → γ + γ
Proton interaction:
Nuclear and Particle Physics
Authors: J. Bartolomé, M. J. Milla, G. Sáez
IF THERE WAS A FOURTH NEUTRINO, HOW COULD IT BE DISTINGUISH
FROM THE OTHER? Two possible ways:
o νµ can interact with nuclei in two distint ways
o Exchanging charge νµ change into a charged muon, which can be detected.
o Neutral current reaction (NCR) dissapeared νµ´s swich into νs´s which do not scatter at all (cannot be
detected). The NCR shows the asymmetry of νµ´s oscillation.
o Passage through the matter would affect neutrino oscillation length.
o νµ
ντ oscillation is not affected while they are passing through the Earth, because both neutrinos
have identical forward elastic-scattering amplitudes.
o But, if for the νµ
νs oscillation, given that νs has no scattering amplitude, passage through matter
would modify the oscillation parameters.
Neutrino oscillation imply unequal masses. However it must be satisfied the following relation
2
ντ implies ∆ m µ2 e ≈ 1eV 2 bigger than the mass
∆ m 122 + ∆ m 23
+ ∆ m 312 = 0 The problem is that νµ
squared. So it is impossible to satisfy this formula.
There are two possibilities.
1. A fourth neutrino: νs
2. A way out might be to suggest that the data are actually describing a messy three-way
oscillation, rather than a simple pairwise one.
There are three neutrino flavors to play with, but they are not sufficient. They cannot explain
oscillations in solar, atmospheric and accelerated neutrinos.
Sterile Neutrino
Other interactions
Figure: chlorine detector at Homestake
Mine, were first detected the lack of solar
neutrinos.
ν + e
Electron scattering:
Despite neutrinos interact very weakly with matter, there are some reactions that
can be detected if we have a suitable detector:
How to detect an undetectable particle?
nuclear
• Artificial
sources:
reactors are the most commons, but
there are others, like man-made
neutrino beams from laboratories
(CNGS, KEK, etc.)
Figure: Proton – proton chain reaction in the solar core
• Geoneutrinos: these are the neutrinos
produced in the beta decays of the radioactive
elements inside the Earth.
• Atmospheric showers: when the primary
cosmic rays (typically protons) collide with
nuclei in the upper atmosphere, it is created a
shower of hadrons. The decay of these hadrons
produce the neutrinos (mainly muon- and
electron-neutrinos, approximately in a 2:1
ratio).
• The Sun: solar neutrinos are produced during the nuclear processes that take place
mainly in the core, in the proton - proton fusion chain. The study of these neutrinos has
become very important in the last few decades, not only because they can help to
understand nuclear processes that occurs in the stars, but their study has opened new
fundamental problems in nuclear physics, such as the “flavor oscillation”.
Neutrino sources
There are three different kinds of neutrinos (flavors) asociated with the three leptonic: electronic neutrino (ν e ), muonic neutrino ν µ and tauonic neutrino (ν τ ). There also exist their respectives antiparticles: ν e , ν µ , ν τ .
( )
Neutrinos are not affected by electromagnetic and strong nuclear forces, but they are affected by the weak nuclear and the gravitational forces.
The neutrino is a subatomic fermionic particle, chargeless and with half-integer spin. Recent studies have confirmed that neutrinos have mass, although its value is not exactly known. Nevertheless it has to be extremely small (at most 200,000 times smaller than the
electron mass) . Furthermore, their interaction with other particles is minimal; that is why neutrinos pass through ordinary matter without hardly perturbing it.
NEUTRINOS