exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

Relic astrophysical and cosmological neutrinos
and their discovery
IPNO Participation: C. Volpe, J. Kneller, S. Galais
Collaboration : R. Lazauskas (IPHC Strasbourg), C. Lunardini (University of Arizona), P. Vogel
(CALTECH)
Deux fonds de neutrinos n’ont jamais été observé: les neutrinos reliques de supernovae (à effondrement
gravitationnel) et les neutrino cosmologiques, provenant de l’Univers primordiale. Les premiers pourront
etre observés dans les prochains détécteurs de grande taille, selon les calculs actuels. Une étude de faisabilité
(LAGUNA, FP7, 2008-10) se déroule à l’heure actuelle. Nous réalisons des calculs très poussés de
propagation des neutrinos dans les étoiles massives et nous faisons des prédictions pour ces observatoires
de prochaine génération. Nous explorons aussi des voies alternatives. Par exemple nous avons étudié la
possibilité d’observer les neutrinos reliques provenant des explosions galactiques par la mesure du Technetium-97
dans la roche. En ce qui concerne les neutrinos cosmologiques, nous n’avons à présent que des
effets indirects, dans BBN et sur les grandes structures. Une stratégie interessante a été proposée récemment:
la capture sur noyaux radioactifs.
Two diffuse neutrino backgrounds have never
been observed : the one formed by past corecollapse
supernova explosions and the cosmological
background produced by the Early Universe.
The energy range of these two backgrounds are
very different, the first being in the several tens of
MeV energy range while the second has typical
energies of meV.
The diffuse supernova neutrino background
The observation of the relic supernova neutrino
background would bring key information on the
star formation rate, on the supernova dynamics
and on unknown neutrino properties. The current
best limits come from the Super-Kamiokande and
SNO observations. Present predictions show that
the use of large scale observatories, such as
MEMPHYS, GLACIER or LENA (LAGUNA DS,
FP7, 2008-2010), or of advanced technologies
(like adding Gadolinium to water) should bring to
the diffuse supernova neutrino background discovery.
We have performed the very first calculations
including the neutrino-neutrino interaction and
shock waves and shown the latter impact the predictions
at the level of 10-20%. Such variations are
important since they are of the same order as the
variations induced by the still unknown neutrino
parameters (third neutrino mixing angle and hierarchy).
Our calculations show that shock wave effects
should be included in future predictions. With
this aim we have proposed a schematic model.
Besides we have shown that the shock wave suppresses
the sensitivity on the neutrino-neutrino
interaction [1].
In [2] we have investigated the possibility to observe
relic galactic supernova neutrinos by the
measurement of Technetium-97 abundance in Molybdenum-98
ore, following a previous idea of Hax
ton and Jonhson [3]. Indeed electron neutrinos interact
with Mo-98 and depending on their energy
can eject one neutron leaving Tc-97. This specific
process is particularly interesting since the threshold
suppresses the huge solar neutrino background.
We have perfomed the most updated calculations
including the progress in neutrino physics and including
our understanding of neutrino propagation
in dense media. Our results show that the contribution
coming from relic supernova is at the level of
10% of the total contribution (solar plus supernovae).
We conclude that to make this strategy
clearly attractive one needs very precise solar neutrino
measurements and systematic measurements
of neutrino-nucleus cross sections. Note that the
experimental sensitivity reaches the level required
for this measurement.
[1] S. Galais, J. Kneller, C. Volpe, J. Gava, Phys.
Rev. D 81, 053002 (2010, arXiv: 0906.5294 .
[2] R. Lazauskas, C. Lunardini, C. Volpe, JCAP
0904, 029 (2009), arXiv: 0901.0581 .
[3] Haxton and Johson, Nature 333, 325 (1988).
The cosmological neutrino background
The interest the capture on radioactive nuclei for
cosmological neutrios was first pointed out by
Weinberg. In a recent paper Cocco, Mangano and
Messina have used it to show the interest for the
cosmological neutrino backgroiund observation [4].
In [5] we have analyzed the possibility and calculated
the number of events associated to the capture
on tritium. Since this process does not have
any threshold, the associated cross sections are
very large.
[4] Cocco, Mangano and Messina JCAP 0706, 015
(2007), arXiv: 0703075.
[5] R. Lazauskas, P. Vogel, C. Volpe, Jour. Phys. G
35, 025001 (2008), arXiv: 0710.5312.
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