Selected low energy probes for new physics

Abstract

In this work we select two interesting methods in the intensity frontier of particle physics, as low energy probes of New Physics. First, we address a crucial unknown property of the neutrino, its Majorana or Dirac nature. The Majorana nature of the neutrino can be established via the observation of lepton number violating processes. We propose a new strategy for detecting the Charge and Parity (CP) violating phases and the effective mass of muon Majorana neutrinos by measuring observables associated with neutrino-antineutrino oscillations in π± decays. Within the generic framework of quantum field theory, we compute the non-factorizable probability for producing a pair of same-charged muons in π± decays as a distinctive signature of νμ — —νμ oscillations. We show that an intense neutrino beam through a long baseline experiment is favored for probing the Majorana phases. Using the neutrino-antineutrino oscillation probability reported by MINOS collaboration, a new stringent bound on the effective muon-neutrino mass is derived. Secondly, we aim to constrain New Physics with allowed processes within the Standard Model (SM) but measured with very good precision, enough to test for its accuracy. We choose an interesting set of observables, not yet exploited, and within the range of charm physics, the D meson leptonic and semileptonic decays. Latest Lattice results on D form factors evaluation from first principles show that the standard model (SM) branching ratios prediction for the leptonic Ds —> ℓνℓ decays and the semileptonic SM branching ratios of the D0 and D+ meson decays are in good agreement with the world average experimental measurements. It is possible to disprove New Physics hypothesis or find bounds over several models beyond the SM. Using the observed leptonic and semileptonic branching ratios for the D meson decays, we performed a combined analysis to constrain non standard interactions.