Is there really a $W \to τν$ puzzle?

Abstract

According to the Particle Data Group, the measurements of ${\cal B}(W^+ \to τ^+ ν_τ)$ and ${\cal B}(W^+ \to \ell^+ ν_\ell)$ ($\ell = e,μ$) disagree with one another at the $2.3σ$ level. In this paper, we search for a new-physics (NP) explanation of this $W \to τν$ puzzle. We consider two NP scenarios: (i) the $W$ mixes with a $W'$ boson that couples preferentially to the third generation, (ii) $τ_{L,R}$ and $ν_{τL}$ mix with isospin-triplet leptons. Unfortunately, once other experimental constraints are taken into account, neither scenario can explain the above experimental result. Our conclusion is that the $W \to τν$ puzzle is almost certainly just a statistical fluctuation.

14 pages; references and discussion added; journal version