The ALPs from the Top: Searching for long lived axion-like particles from exotic top decays

Abstract

We propose a search for long lived axion-like particles (ALPs) in exotic top decays. Flavour-violating ALPs appear as low energy effective theories for various new physics scenarios such as t-channel dark sectors or Froggatt-Nielsen models. In this case the top quark may decay to an ALP and an up-or charm-quark. For masses in the few GeV range, the ALP is long lived across most of the viable parameter space, suggesting a dedicated search. We propose to search for these long lived ALPs in t t events, using one top quark as a trigger. We focus on ALPs decaying in the hadronic calorimeter, and show that the ratio of energy deposits in the electromagnetic and hadronic calorimeters as well as track vetoes can efficiently suppress Standard Model backgrounds. Our proposed search can probe exotic top branching ratios smaller than 10 −4 with a conservative strategy at the upcoming LHC run, and potentially below the 10 −7 level with more advanced methods. Finally we also show that measurements of single top production probe these branching ratios in the very short and very long lifetime limit at the 10 −3 level.

ALP Production in Weak Mesonic Decays

“…Flavor physics experiments have received more and more attention from the phenomenological community. [22,[24][25][26][47][48][49][50] Strong limits on the ALP couplings in Equation ( 1) can be derived, for example, through the study of the K → 𝜋a decay. In large part of the literature a flavor universal ALP-fermion coupling, often dubbed c aΦ , is assumed.…”

New Higgs decays to axion-like particles

“…Many of those couplings are constrained by data collected at low-energy and flavour facilities [21][22][23][24][25][26][27][28][29][30][31][32][33] colliders including LEP [34][35][36][37] and the LHC [36][37][38][39][40][41][42][43][44][45][46][47][48] or in astrophysical events [49][50][51][52][53][54][55]. Some couplings have been shown to be only testable in Higgs physics, particularly through yet unexplored decays of the Higgs boson.…”