New method for beyond the Standard Model invisible particle searches in tau lepton decays

E De La Cruz-Burelo,M Hernandez-Villanueva,A De Yta-Hernandez

doi:10.1103/physrevd.102.115001

Abstract

Motivated by models proposed to explain the Standard Model anomalies, and the unprecedented $\tau^{+}\tau^{-}$ data to be collected by the Belle~II experiment during the next years, we study the kinematics of tau pair decays and propose a new method to search for lepton flavor violating processes in tau lepton decays to invisible beyond Standard Model particles, such as $\tau \to \ell \alpha$, where $\ell$ is either an electron or a muon, and $\alpha$ is a massive particle that escapes undetected. The new method improves by one order of magnitude the expected upper limit on the $\tau \to \ell \alpha$ production in 3x1 prong tau decays and establishes the possibility of performing this search in 1x1 prong tau decays which has not been previously considered.

Highlights

The Standard Model of particle physics (SM) has been incredibly successful in explaining all observed data until today, with few remaining tensions between prediction and experiment, for instance, the longstanding 3.7 standard deviations discrepancy in the anomalous magnetic moment of the muon aμ 1⁄4 ðg − 2Þμ=2 [1,2,3,4,5,6,7]
One of these strategies involves searching for the extremely SM suppressed lepton flavor violating (LFV) processes, which observation will be a clear signal of beyond the SM (BSM) physics
We have studied the kinematics of the decay of a particle-antiparticle pair for known center-of-mass energy when in each decay, one of the produced particles escapes detection

Summary

INTRODUCTION

The Standard Model of particle physics (SM) has been incredibly successful in explaining all observed data until today, with few remaining tensions between prediction and experiment, for instance, the longstanding 3.7 standard deviations discrepancy in the anomalous magnetic moment of the muon aμ 1⁄4 ðg − 2Þμ=2 [1,2,3,4,5,6,7] Observed phenomena such as the predominance of matter over antimatter in the universe, the neutrino masses, or dark matter, among others, suggest physics beyond the SM (BSM). Z0 gauge bosons [12,13,14], and which aim to explain SM anomalies like the aμ discrepancy One possibility of such processes is τ → lα, where l is either an electron or a muon, and α is a massive particle that escapes detection. We propose a new two-dimensional method that, compared to the standard search technique, reduces an order of magnitude the expected upper limit on the production of this BSM decay, and opens the possibility of an additional search in 1 × 1 prong decays, which is most abundantly produced

KINEMATIC CONSTRAINTS

Simulated data selection

Production measurement

CONCLUSIONS