Exotic lepton flavour violating processes in the field of nucleus (Doctoral thesis)

Παπούλιας, Δημήτριος Κ.

The main objective of the present Thesis is to explore the exotic neutralcurrent (NC) neutrino processes, predicted by theories beyond the Standard Model (SM) of the electroweak interactions to take place in the field of nucleons and nuclei. The subject of neutrino non-standard interactions (NSI) plays a leading role in recent studies of lepton flavour violating (LFV) processes, now that the three oscillation in propagation paradigm is put in rather solid grounds. In particular, we concentrate on the vector NSI of neutrino scattering off nuclear systems, detectors of ongoing and designed extremely sensitive experiments searching for LFV. It is, furthermore, shown that within the framework of tensorial neutrino NSI, electromagnetic (EM) neutrino properties are also predicted, which are complementary to distinguish the Dirac or Majorana nature of neutrinos. For the case of neutrino EM interactions a thorough investigation is devoted demonstrating that neutrino-nucleus scattering is a promising probe to search for physics beyond the SM. The first stage of our research involves the development of the mathematical formalism where the relevant NSI operators are parametrised assuming typical phenomenological four-fermion contact interaction Lagrangians. The impact of the nuclear structure properties is studied through the appropriate transformation of the quark-level Lagrangians to the nuclear-level one. The corresponding neutrino-nucleus cross sections are evaluated by employing the nuclear method of the multipole decomposition of the hadronic current, established by Donnelly- Walecka. In addition, the various flavour preserving and flavour changing interaction channels, predicted to occur within NSI, are taken into consideration through the evaluation of the respective matrix elements entering the relevant cross sections. The nuclear physics aspects of these processes are systematically studied in the context of the state-of-the-art quasi-particle random phase approximation (QRPA). Specifically, for the case of coherent elastic neutrino-nucleus scattering (CENNS), the nuclear ground state is constructed by solving iteratively the Bardeen-Cooper-Schrieffer (BCS) equations. This way, realistic strong twonucleon pairing forces are taken into account maximising the reliability of the obtained results. Such nuclear structure corrections improve previous CENNS calculations ignoring the nuclear form factor, by even one order of magnitude. From the experimental physics perspective, for the case of both conventional and exotic neutrino processes, the accuracy of the obtained cross sections is exploited in order to compute with high significance the corresponding convoluted cross sections that represent the signal expected to be recorded by terrestrial nuclear detectors. Furthermore, we evaluate reliably other important experimental observables such as the differential event rates and the number of neutrino scattering events expected to be measured in Supernova (SN), Spallation Neutron Source (SNS) and reactor neutrino experiments. We illustrate that, such measurements may be very sensitive to neutrino-quark NSI or neutrino EM interactions (magnetic moment, mean charge-radius, milli-charge) and could provide more severe constraints as compared to those expected in future neutrino factory experiments. To this end, our study involves extensive calculations for a set of promising target materials throughout the periodic table of nuclides. Focusing on astrophysical (SN) and laboratory (SNS and reactor) neutrino sources as well as dark matter and multipurpose experiments, our results refer to the 20Ne, 40Ar, 76Ge and 132Xe isotopes, i.e. the target nuclei of ongoing and future experiments including the COHERENT, TEXONO, GEMMA and the direct detection of Cold Dark Matter (CDM) experiments. Therefore, this type of calculations is of primary importance for experiments searching forWIMP-nucleus scattering, since CENNS events constitutes an irreducible background. In view of the operation of extremely intense laboratory neutrino fluxes (at the SNS, J-PARC, Fermilab, PSI, etc.), the sensitivity to search for new physics will be largely increased, and, therefore, through CENNS measurements, several open questions (involving neutrino NSI, neutrino magnetic moment, sterile neutrino searches and others) may be answered. Our present results, in conjunction with those expected from sensitive muon-to-electron conversion experiments (Mu2e at Fermilab, COMET at J-PARC), may offer significant contribution to understand the fundamental nature of electroweak interactions in the leptonic sector and to constrain the parameters of beyond the SM Lagrangians.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Φυσικής
Subject classification: Nuclear structure
Keywords: Neutral current,Neutrino processes,Standard model
URI: http://olympias.lib.uoi.gr/jspui/handle/123456789/27765
Appears in Collections:Διδακτορικές Διατριβές

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