Sensitivity of lepton number violating meson decays in different experiments

Abstract

We study the discovery prospect of different three body lepton number violating (LNV) meson decays M − 1 → − 1 − 2 M + 2 in the framework of right handed (RH) neutrino extended Standard Model (SM). We consider a number of ongoing experiments, such as, NA62 and LHCb at CERN, Belle II at SuperKEK, as well as at the proposed future experiments, SHiP, MATHUSLA and FCCee. The RH Majorana neutrino N mediating these meson decays provides a resonant enhancement of the rates, if the mass of N lies in the range (100 MeV − 6 GeV). We consider the effect of parent mesons velocity, as well as, the effect of finite detector size. Using the expected upper limits on the number of events for the LNV decay modes, M − 1 → − 1 − 2 π + (M 1 = B, B c , D, D s and K), we analyze the sensitivity reach of the mixing angles |V eN | 2 , |V µN | 2 , |V τ N | 2 , |V eN V µN |, |V eN V τ N | and |V µN V τ N | as a function of heavy neutrino mass M N . We show that, inclusion of parent meson velocity can account to a large difference for active-sterile mixing, specially for D, D s meson decay at SHiP and K meson decay at NA62. Taking into account the velocity of the D s meson, the future beam dump experiment SHiP can probe |V eN | 2 ∼ 10 −9 . For RH neutrino mass in between 2 -5 GeV, MATHUSLA can provide best sensitivity reach of active-sterile mixings. 1 − 2 π + [ [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63]. For RH neutrino search, this process has an advantage as compared to the LNV 0νββ-decay due to the lesser uncertainties in the meson decay constant.In the later process, the nuclear matrix elements (NME) uncertainty can make difference in the prediction of active-sterile mixing. We consider a number of three body ∆L = 2 mesonD, D s and K) and derive sensitivity reach of the activesterile mixing parameter in a number of ongoing and future experiments, such as, NA62, LHCb at CERN, Belle II, SHiP, MATHUSLA and FCC-ee. Note that, the light neutrino contribution to these meson decays are extremely suppressed. However, for RH neutrinos in the mass range of 0.140 GeV < M N < 6 GeV, the intermediate Majorana neutrinos can be produced on-shell. This results in resonant enhancement of these decay rates. In addition, large number of decaying mesons in these experiments, in-particular at SHiP will facilitateto improve the sensitivity reach significantly. In deriving these results, we consider parent meson velocity, that affects the probability of RH neutrino decay inside the detector. We show, that inclusion of parent meson velocity can give one or two orders of magnitude shift O(10 1 − 10 2 ) in the results obtained.The paper is organized as follows. In sec. 2, we very briefly review the basic features of the three RH neutrino framework, following which in sec. 3, we discuss in detail the contributions of the RH neutrino in meson decays. In sec. 4, we then compute the total decay width of RH neutrino N in the mass range 0.140 GeV ≤ M N ≤ 6 GeV. In sec. 5, we study the effects of parent meson velocity in the RH neutrino decay probabi...

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