The Majorana nature of neutrinos can be experimentally verified only via lepton-number violating processes involving charged leptons. We study 36 lepton-number violating (LV ) processes from the decays of tau leptons and pseudoscalar mesons. These decays are absent in the Standard Model but, in presence of Majorana neutrinos in the mass range ∼ 100 MeV to 5 GeV, the rates for these processes would be enhanced due to their resonant contribution. We calculate the transition rates and branching fractions and compare them to the current bounds from direct experimental searches forL = 2 tau and rare meson decays. The experimental non-observation of such LV processes places stringent bounds on the Majorana neutrino mass and mixing and we summarize the existing limits. We also extend the search to hadron collider experiments. We find that, at the Tevatron with 8 fb −1 integrated luminosity, there could be 2σ (5σ) sensitivity for resonant production of a Majorana neutrino in the � ± � ± modes in the mass range of ∼ 10 − 180 GeV (10 − 120 GeV). This reach can be extended to ∼ 10 − 375 GeV (10 − 250 GeV) at the LHC of 14TeV with 100 fb −1 . The production cross section at the LHC of 10TeV is also presented for comparison. We study the � ± e ± modes as well and find that the signal could be large enough even taking into account the current bound from neutrinoless double-beta decay. The signal from the gauge boson fusion channel W + W + → l + l + at the LHC is found to be very weak given the rather small mixing parameters. We comment on the search strategy when a τ lepton is involved in the final state.

https://iopscience.iop.org/article/10.1088/1126-6708/2009/05/030/pdf

The Search for Heavy Majorana Neutrinos

https://cds.cern.ch/record/225868/files/cer-000138734.pdf

Searches for new particles in $Z$ decays using the ALEPH detector

Observational neutrino astrophysics

The top quark is the heaviest elementary particle observed to date. Its large mass makes the top quark an ideal laboratory to test predictions of perturbation theory concerning heavy quark production at hadron colliders. The top quark is also a powerful probe for new phenomena beyond the Standard Model (SM) of particle physics. In addition, the top quark mass is a crucial parameter for scrutinizing the SM in electroweak precision tests and for predicting the mass of the yet unobserved Higgs boson. Ten years after the discovery of the top quark at the Fermilab Tevatron, top quark physics has entered an era where detailed measurements of top quark properties are undertaken. In this paper an introduction to the phenomenology of top quark production in hadron collisions is given, the lessons learned in Tevatron Run I are summarized and the first Run II results are discussed. A brief outlook of the possibilities of top quark research at the Large Hadron Collider, currently under construction at CERN, is included.

/pdf/top-quark-physics-in-hadron-collisions-1tkfdpidnl.pdf

Top quark physics in hadron collisions

Neutral current flavor changing decays for the Z boson and the top quark in two-Higgs doublet models

http://vsharma.ucsd.edu/mypapers/alephpapers/newquark-lepton90.pdf

Y. Saadi

Papers

A search for new quarks and leptons from Z0 decay at LEP