Neutrino electromagnetic properties and new bounds on neutrino magnetic moments

We give a brief outline of possible neutrino electromagnetic characteristics, which can indicate new physics beyond the Standard Model. Special emphasis is put on recent theoretical development in searches for neutrino magnetic moments.Comment: 4 pages, to appear in J. Phys.: Conf. Ser. (2012), based on the talk presented at the XII International Conference on Topics in Astroparticle and Underground Physics (TAUP 2011), Munich 5-9 September 201

An interplay between momentum distortion and electronic correlation in symmetric (e, 3−1e) reactions

Abstract A theory is proposed for the treatment of the effects of distortion in electronimpact double ionization of atoms at large momentum transfer. The eikonal wave impulse approximation and the semiclassical post-collision interaction model are used to analyse the momentum distortion in symmetric (e, 3−1e) reactions at intermediate energies. The effect of a strong interplay between electron-electron spatial correlation and momentum distortion is determined. The results of the analysis provide a guide for symmetric (e, 3−1e) experiments which are being carried out or are underway. Due to recent progress in the studies of multiple ionization by electron impact [1] it has become possible to perform coincident double ionization experiments in the regime of large momentum transfer with good accuracy. In particular, the group in Rome has carried out a symmetric (e, 3−1e) experiment on the He atom 3 . To the best of our knowledge, this is the first such study of double ionization at large momentum transfer. In this experiment the energy of the projectile electron is 580 eV, the energies of the fast final electrons are 250 eV and the energy of the slow ejected electron is fixed by the energy conservation law at about 1 eV (see The predictions by Popov et a

Potentialities of a low-energy detector based on 4^4He evaporation to observe atomic effects in coherent neutrino scattering and physics perspectives

We propose an experimental setup to observe coherent elastic neutrino-atom scattering (CE$\nu$AS) using electron antineutrinos from tritium decay and a liquid helium target. In this scattering process with the whole atom, that has not beeen observed so far, the electrons tend to screen the weak charge of the nucleus as seen by the electron antineutrino probe. The interference between the nucleus and the electron cloud produces a sharp dip in the recoil spectrum at atomic recoil energies of about 9 meV, reducing sizeably the number of expected events with respect to the coherent elastic neutrino-nucleus scattering case. We estimate that with a 60 g tritium source surrounded by 500 kg of liquid helium in a cylindrical tank, one could observe the existence of CE$\nu$AS processes at 3$\sigma$ in 5 years of data taking. Keeping the same amount of helium and the same data-taking period, we test the sensitivity to the Weinberg angle and a possible neutrino magnetic moment for three different scenarios: 60 g, 160 g, and 500 g of tritium. In the latter scenario, the Standard Model (SM) value of the Weinberg angle can be measured with a statistical uncertainty of $\sin^2{\vartheta_W^{\mathrm{SM}}}^{+0.015}_{-0.016}$. This would represent the lowest-energy measurement of $\sin^2{\vartheta_W}$, with the advantage of being not affected by the uncertainties on the neutron form factor of the nucleus as the current lowest-energy determination. Finally, we study the sensitivity of this apparatus to a possible electron neutrino magnetic moment and we find that using 60 g of tritium it is possible to set an upper limit of about $7\times10^{-13}\,\mu_B$ at 90% C.L., that is more than one order of magnitude smaller than the current experimental limit.Comment: 9 pages, 7 figures, Fig. 3 corrected, improved discussion on electron form factor (Fig. 1 added) and detector layou

Testing neutrino magnetic moment in ionization of atoms by neutrino impact

The atomic ionization processes induced by scattering of neutrinos play key roles in the experimental searches for a neutrino magnetic moment. Current experiments with reactor (anti)neutrinos employ germanium detectors having energy threshold comparable to typical binding energies of atomic electrons, which fact must be taken into account in the interpretation of the data. Our theoretical analysis shows that the so-called stepping approximation to the neutrino-impact ionization is well applicable for the lowest bound Coulomb states, and it becomes exact in the semiclassical limit. Numerical evidence is presented using the Thomas-Fermi model for the germanium atom.Comment: 5 pages, 1 figur