Search for Axionlike Particles Produced in e + e − Collisions at Belle II

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This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses 2.2 nb−1 of integrated luminosity collected in 2015 and 2018 at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy $$ {E}_{\mathrm{T}}^{\gamma } $$ E T γ > 2.5 GeV, pseudorapidity |ηγ| < 2.37, diphoton invariant mass mγγ> 5 GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6–100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.

Section: Search For Alp Productionmentioning

confidence: 99%

Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb−1 of Pb+Pb data with the ATLAS detector

Collaboration¹,

Aad

Abbott

et al. 2021

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“…For ALPs in the mass range between 10 MeV and 10 GeV, and assuming that the ALPphoton coupling arises only from the ALP coupling to SU(2) L gauge bosons (i.e. that C BB = 0), one finds that this bound is of the same order of magnitude as the strongest constraints on the ALP-photon coupling obtained from LEP-2 [18,70] and Belle-II data [71] (see also [21]). With a future high-luminosity lepton collider such as the FCC-ee, the bound (5.15) could be improved significantly [24].…”

Section: Jhep06(2021)135mentioning

confidence: 85%

ALP — SMEFT interference

Galda

Neubert

Renner

2021

The Standard Model Effective Field Theory (SMEFT) offers a powerful theoretical framework for parameterizing the low-energy effects of heavy new particles with masses far above the scale of electroweak symmetry breaking. Additional light degrees of freedom extend the effective theory. We show that light new particles that are weakly coupled to the SM via non-renormalizable interactions induce non-zero Wilson coefficients in the SMEFT Lagrangian via renormalization-group evolution. For the well-motivated example of axions and axion-like particles (ALPs) interacting with the SM via classically shift-invariant dimension-5 interactions, we calculate how these interactions contribute to the one-loop renormalization of the dimension-6 SMEFT operators, and how this running sources additional contributions to the Wilson coefficients on top of those expected from heavy new states. As an application, we study the ALP contributions to the magnetic dipole moment of the top quark and comment on implications of electroweak precision constraints on ALP couplings.

“…In this section, we will argue that the models that generate a large coupling between the axion and SM leptons always contain light charged particles with masses around or below 100 GeV, and additional scalars that can both affect the value of g − 2 itself and potentially mix with the Higgs boson. , as well as the recent bounds from PRIMEX [40] and Belle II [41].…”

Section: Large Axion-fermion Couplingsmentioning

confidence: 97%

Challenges for an axion explanation of the muon g − 2 measurement

Buen-Abad

Fan

Reece

et al. 2021

The discrepancy between the muon g − 2 measurement and the Standard Model prediction points to new physics around or below the weak scale. It is tantalizing to consider the loop effects of a heavy axion (in the general sense, also known as an axion-like particle) coupling to leptons and photons as an explanation for this discrepancy. We provide an updated analysis of the necessary couplings, including two-loop contributions, and find that the new physics operators point to an axion decay constant on the order of 10s of GeV. This poses major problems for such an explanation, as the axion couplings to leptons and photons must be generated at low scales. We outline some possibilities for how such couplings can arise, and find that these scenarios predict new charged matter at or below the weak scale and new scalars can mix with the Higgs boson, raising numerous phenomenological challenges. These scenarios also all predict additional contributions to the muon g−2 itself, calling the initial application of the axion effective theory into question. We conclude that there is little reason to favor an axion explanation of the muon g – 2 measurement relative to other models postulating new weak-scale matter.