Coupling QCD-Scale Axionlike Particles to Gluons

First Constraints on Heavy QCD Axions with a Liquid Argon Time Projection Chamber Using the ArgoNeuT Experiment

We present the results of a search for heavy QCD axions performed by the ArgoNeuT experiment at Fermilab. We search for heavy axions produced in the NuMI neutrino beam target and absorber decaying into dimuon pairs, which can be identified using the unique capabilities of ArgoNeuT and the MINOS near detector. This decay channel is motivated by a broad class of heavy QCD axion models that address the strong CP and axion quality problems with axion masses above the dimuon threshold. We obtain new constraints at a 95% confidence level for heavy axions in the previously unexplored mass range of 0.2-0.9 GeV, for axion decay constants around tens of TeV.

New physics searches at kaon and hyperon factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

Prospects for Probing Axionlike Particles at a Future Hadron Collider through Top Quark Production

Axionlike particles (ALPs) emerge from spontaneously broken global symmetries in high energy extensions of the Standard Model (SM). This causes ALPs to be among the objectives of future experiments that intend to search for new physics beyond the SM. We discuss the reach of future pp collider FCC-hh in probing the ALP model parameters through top quark pair production associated with ALP (tt¯+ALP) in a model-independent approach. The search is performed in the semi-leptonic decay mode of tt¯ and the analysis is performed using a parametric simulation of the detector response for a projected integrated luminosity of 30ab−1. It is shown that tt¯+ALP production at the FCC-hh is a promising channel with significant sensitivity to probe the ALP coupling with gluons. The ALP coupling with gluons obtained from HL-LHC and other experiments is presented for comparison.

High Quality QCD Axion at Gravitational Wave Observatories

The axion solution to the strong CP problem is delicately sensitive to Peccei-Quinn breaking contributions that are misaligned with respect to QCD instantons. Heavy QCD axion models are appealing because they avoid this so-called quality problem. We show that generic realizations of this framework can be probed by the LIGO-Virgo-KAGRA interferometers, through the stochastic gravitational wave (GW) signal sourced by the long-lived axionic string-domain wall network and by upcoming measurements of the neutron and proton electric dipole moments. Additionally, we provide predictions for searches at future GW observatories, which will further explore the parameter space of heavy QCD axion models.

Search for an Axionlike Particle in B Meson Decays

Axionlike particles (ALPs) are predicted in many extensions of the standard model, and their masses can naturally be well below the electroweak scale. In the presence of couplings to electroweak bosons, these particles could be emitted in flavor-changing B meson decays. We report herein a search for an ALP, a, in the reaction B^{±}→K^{±}a, a→γγ using data collected by the BABAR experiment at SLAC. No significant signal is observed, and 90% confidence level upper limits on the ALP coupling to electroweak bosons are derived as a function of ALP mass, improving current constraints by several orders of magnitude in the range 0.175  GeV<m_{a}<4.78  GeV.

High Quality QCD Axion and the LHC

The QCD axion provides an elegant solution to the strong CP problem. While the minimal realization is vulnerable to the so-called "axion quality problem," we will consider a more robust realization in the presence of a mirror sector related to the standard model by a (softly broken) Z_{2} symmetry. We point out that the resulting "heavy" axion, while satisfying all theoretical and observational constraints, has a large and uncharted parameter space, which allows it to be probed at the LHC as a long-lived particle (LLP). The small defining axionic coupling to gluons results in a challenging hadronic decay signal which we argue can be distinguished against the background in such a long-lived regime, and yet, the same coupling allows for sufficient production at the hadron colliders thanks to the large gluon-parton luminosity. Our study opens up a new window towards accelerator observable axions and, more generally, singly produced LLPs.

New Physics Implications of Recent Search for K_{L}→π^{0}νν[over ¯] at KOTO

The KOTO experiment recently reported four candidate events in the signal region of K_{L}→π^{0}νν[over ¯] search, where the standard model only expects 0.10±0.02 events. If confirmed, this requires physics beyond the standard model to enhance the signal. We examine various new physics interpretations of the result including these: (1) heavy new physics boosting the standard model signal, (2) reinterpretation of "νν[over ¯]" as a new light long-lived particle, or (3) reinterpretation of the whole signal as the production of a new light long-lived particle at the fixed target. We study the above explanations in the context of a generalized new physics Grossman-Nir bound coming from the K^{+}→π^{+}νν[over ¯] decay, bounded by data from the E949 and the NA62 experiments.

Nonresonant Searches for Axionlike Particles at the LHC

We propose a new collider probe for axionlike particles (ALPs), and more generally for pseudo-Goldstone bosons: nonresonant searches that take advantage of the derivative nature of their interactions with Standard Model particles. ALPs can participate as off shell mediators in the s channel of 2→2 scattering processes at colliders like the LHC. We exemplify the power of this novel type of search by deriving new limits on ALP couplings to gauge bosons via the processes pp→ZZ, pp→γγ, and pp→jj using run 2 CMS public data, probing previously unexplored areas of the ALP parameter space. In addition, we propose future nonresonant searches involving the ALP coupling to other electroweak bosons and/or the Higgs particle.

Photoproduction of Axionlike Particles

We explore the sensitivity of photon-beam experiments to axionlike particles (ALPs) with QCD-scale masses whose dominant coupling to the standard model is either to photons or gluons. We introduce a novel data-driven method that eliminates the need for knowledge of nuclear form factors or the photon-beam flux when considering coherent Primakoff production off a nuclear target, and show that data collected by the PrimEx experiment in 2004 could improve the sensitivity to ALPs with 0.03≲m_{a}≲0.3  GeV by an order of magnitude. Furthermore, we explore the potential sensitivity of running the GlueX experiment with a nuclear target and its planned PrimEx -like calorimeter. For the case where the dominant coupling is to gluons, we study photoproduction for the first time, and predict the future sensitivity of the GlueX experiment using its nominal proton target. Finally, we set world-leading limits for both the ALP-gluon coupling and the ALP-photon coupling based on public mass plots.