Abstract

We study lepton number violating and lepton number conserving semi-leptonic decays of heavy baryons $\Lambda_b^0$ to three charged leptons and a neutrino. The decays occur through two intermediate quasi-degenerate GeV-scale sterile neutrinos of either Majorana or Dirac type that can be on-shell. Interference between the intermediate heavy neutrinos leads to CP violation in the final states. Effect of neutrino oscillations between the heavy states are also considered in observables of interests, \emph{i.e.,} branching ratio, and the CP-asymmetry. Given the present constraints on the heavy-to-light mixing elements $|V_{eN}|$ and $|V_{\mu N}|$, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)\mu\mu e\nu$ with intermediate Majorana neutrinos is almost two orders of magnitude larger than for the same with Dirac neutrinos, whereas, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)ee\mu\nu$ is of the same order of magnitude for both Majorana and Dirac neutrino induced decays. CP-violation is found to be appreciable when the neutrino mass difference is comparable with the average decay widths.

Highlights

  • It is confirmed from neutrino oscillation experiments that active light neutrinos have mass [1,2,3], albeit very tiny

  • Interference between the intermediate heavy neutrinos leads to CP violation in the final states

  • In this paper we have studied Λ0b → ðΛþc ; pþÞl−1 l−2 lþ3 ν and its conjugate decays mediated by two quasi-degenerate GeV-scale sterile neutrinos

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Summary

INTRODUCTION

It is confirmed from neutrino oscillation experiments that active light neutrinos have mass [1,2,3], albeit very tiny. Low energy seesaw mechanism has been proposed where NR have a mass of the order few hundreds of MeV to a few GeV [11,12,13,14,15,16,17,18]. When the decays occur through intermediate Majorana neutrinos, branching ratio of Λ0b → ðΛc; pÞeeμν is at least two orders of magnitude suppressed compared to Λ0b → ðΛc; pÞμμeν due to present experimental upper bounds on the heavy to light mixing elements jVμNj2 < 10−5, jVeNj2 < 10−7. On the other hand, when the decays occur through intermediate Dirac neutrinos, the CP average branching ratios of Λ0b → ðΛc; pÞμμeν and Λ0b → ðΛc; pÞeeμν are of the same order of magnitude. Some details of our derivations are given in the Appendixes

FORMALISM
Neutrino oscillation
NUMERICAL ANALYSIS
SUMMARY
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