Collider probes of axion-like particles

By M. Bauer, M. Neubert, A. Thamm. 2017

417 citations recorded by the source corpus.

A bstractAxion-like particles (ALPs), which are gauge-singlets under the Standard Model (SM), appear in many well-motivated extensions of the SM. Describing the interactions of ALPs with SM fields by means of an effective Lagrangian, we discuss ALP decays into SM particles at one-loop order, including for the first time a calculation of the a → πππ decay rates for ALP masses below a few GeV. We argue that, if the ALP couples to at least some SM particles with couplings of order (0.01 − 1) TeV−1, its mass must be above 1 MeV. Taking into account the possibility of a macroscopic ALP decay length, we show that large regions of so far unconstrained parameter space can be explored by searches for the exotic, on-shell Higgs and Z decays h → Za, h → aa and Z → γa in Run-2 of the LHC with an integrated luminosity of 300 fb−1. This includes the parameter space in which ALPs can explain the anomalous magnetic moment of the muon. Considering subsequent ALP decays into photons and charged leptons, we show that the LHC provides unprecedented sensitivity to the ALP-photon and ALP-lepton couplings in the mass region above a few MeV, even if the relevant ALP couplings are loop suppressed and the a → γγ and a → ℓ+ℓ− branching ratios are significantly less than 1. We also discuss constraints on the ALP parameter space from electroweak precision tests.

Subfields: Artificial Intelligence, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/9e0179959d1804a474b5a99837a65d455ba9667e

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Citations in the corpus

The landscape of QCD axion models (2020, background): “These bounds are nicely complemented by constraints from beam dump and reactor experiments which exclude axion (and ALP) masses from MeV up to several GeVs [282–293].”
Dark matter, millicharges, axion and scalar particles, gauge bosons, and other new physics with LDMX (2018, background): “55 can lead to exotic Higgs decays to Za and aa, and Z boson decays to γa [165].”
Muonic Boson Limits: Supernova Redux (2021, neutral): “Assuming x < 1 so that the bosons cannot decay into a muon pair, the loop factors are [42, 43]”
Physics beyond colliders at CERN: beyond the Standard Model working group report (2019, methodology): “[334].”
Expression of interest for the CODEX-b detector (2019, background): “The Lagrangian for an ALP, a, can be parameterized as [61]”
Hot axions and the H0 tension (2018, background): “Finally, a derivative coupling to leptons also induces a Cγγ ≈ c`m(2)a/m(2)` [55], and this is always negligible (Cγγ 10−16) for ma O(eV).”
Higgs Physics at the HL-LHC and HE-LHC (2019, background): “We require 100 signal events, since this is what is typically needed to suppress backgrounds in new-physics searches with prompt Higgs decays [144, 219, 849] (see also [844] for further discussion).”
FASER’s physics reach for long-lived particles (2018, methodology): “Decays into 3-body final states are phase-space suppressed, and, in fact, the decay to the lightest allowed hadronic final state, a → πππ, vanishes in the case of gauu = gadd [92].”
TASI Lectures on the Strong CP Problem and Axions (2018, background): “Even if these couplings are zero at tree level, they are still generated by RG evolution [37].”