Effect of Systematic Uncertainty Estimation on the Muon g - 2 Anomaly

The statistical significance that characterizes a discrepancy between a measurement and theoretical prediction is usually calculated assuming that the statistical and systematic uncertainties are known. Many types of systematic uncertainties are, however, estimated on the basis of approximate procedures and thus the values of the assigned errors are themselves uncertain. Here the impact of the uncertainty on the assigned uncertainty is investigated in the context of the muon g - 2 anomaly. The significance of the observed discrepancy between the Standard Model prediction of the muon’s anomalous magnetic moment and measured values are shown to decrease substantially if the relative uncertainty in the uncertainty assigned to the Standard Model prediction exceeds around 30%. The reduction in sensitivity increases for higher significance, so that establishing a 5σ effect will require not only small uncertainties but the uncertainties themselves must be estimated accurately to correspond to one standard deviation.

Searching for heavy leptoquarks at a muon collider

The LHCb Collaboration recently gave an update on testing lepton flavour universality with B+→ K+ℓ+ℓ−, in which a 3.1 standard deviations from the standard model prediction was observed. The g-2 experiment also reports a 3.3 standard deviations from the standard model on muon anomalous magnetic moment measurement. These deviations could be explained by introducing new particles including leptoquarks. In this paper, we show the possibility to search for heavy spin-1 leptoquarks at a future TeV scale muon collider by performing studies from three channels: 1) same flavour final states with either two bottom or two light quarks, 2) different flavour quark final states, and 3) a so-called “VXS” process representing the scattering between a vector boson and a leptoquark to probe the coupling between leptoquark and tau lepton. We conclude that a 3 TeV muon collider with 3 ab−1 of integrated luminosity is already sufficient to cover the leptoquark parameter space in order to explain the LHCb lepton flavour universality anomaly.

Mixed modulus and anomaly mediation in light of the muon g − 2 anomaly

The new measurement of the anomalous magnetic moment of muon at the Fermilab Muon g− 2 experiment has strengthened the significance of the discrepancy between the standard model prediction and the experimental observation from the BNL measurement. If new physics responsible for the muon g− 2 anomaly is supersymmetric, one should consider how to obtain light electroweakinos and sleptons in a systematic way. The gauge coupling unification allows a robust prediction of the gaugino masses, indicating that the electroweakinos can be much lighter than the gluino if anomaly-mediated supersymmetry breaking is sizable. As naturally leading to mixed modulus-anomaly mediation, the KKLT scenario is of particular interest and is found capable of explaining the muon g− 2 anomaly in the parameter region where the lightest ordinary supersymmetric particle is a bino-like neutralino or slepton.

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

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.

The new $$(g-2)_\mu $$ result and the $$\mu \nu $$SSM

The $$\mu \nu \mathrm {SSM}$$ μ ν SSM is a highly predictive alternative model to the MSSM. In particular, the electroweak sector of the model can explain the longstanding discrepancy between the experimental result for the anomalous magnetic moment of the muon, $$(g-2)_\mu $$ ( g - 2 ) μ , and its Standard Model prediction, while being in agreement with all other theoretical and experimental constraints. The recently published MUON G-2 result is within $${0.8}\,\sigma $$ 0.8 σ in agreement with the older BNL result on $$(g-2)_\mu $$ ( g - 2 ) μ . The combined result was announced as $$a_\mu ^{\mathrm{exp}} = (11 659 {206.1}\pm {4.1}) \times 10^{-10}$$ a μ exp = ( 11659 206.1 ± 4.1 ) × 10 - 10 , yielding a new deviation from the Standard Model prediction of $$\Delta a_\mu = ({25.1}\pm {5.9}) \times 10^{-10}$$ Δ a μ = ( 25.1 ± 5.9 ) × 10 - 10 , corresponding to $${4.2}\,\sigma $$ 4.2 σ . Using this improved bound we update the analysis in the $$\mu \nu \mathrm {SSM}$$ μ ν SSM as presented in Kpatcha et al. (Eur Phys J C 81(2):154. arXiv:1912.04163 [hep-ph], 2021) and set new limits on the allowed parameters space of the electroweak sector of the model. We conclude that significant regions of the model can explain the new $$(g-2)_\mu $$ ( g - 2 ) μ data.

Muon (g − 2) in the B-LSSM

The difference between the updated experimental result on the muon anomalous magnetic dipole moment and the corresponding theoretical prediction of the standard model on that is about 4.2 standard deviations. In this work, we calculate the muon anomalous MDM at the two-loop level in the supersymmetric B − L extension of the standard model. Considering the experimental constraints on the lightest Higgs boson mass, Higgs boson decay modes h → γγ, WW, ZZ, $$ b\overline{b} $$ b b ¯ , $$ \tau \overline{\tau} $$ τ τ ¯ , B rare decay $$ \overline{B} $$ B ¯ → Xsγ, and the transition magnetic moments of Majorana neutrinos, we analyze the theoretical predictions of the muon anomalous magnetic dipole moment in the B − L supersymmetric model. The numerical analyses indicate that the tension between the experimental measurement and the standard model prediction is remedied in the B − L supersymmetric model.

On measurement of photon polarization in radiative penguin B decays to baryons

A measurement of the photon polarization in radiative penguin B decays provides a test of the Standard Model and a probe for New Physics, that can lead to a deviation from the Standard Model prediction of left-handed photons in $$b\rightarrow s \gamma $$ b → s γ . We propose a new method to measure the photon polarization using the baryonic decay $$B^- \rightarrow \Lambda \bar{p} \gamma $$ B - → Λ p ¯ γ . The P-violating $$\Lambda $$ Λ -hyperon decay allows a measurement of the $$\Lambda $$ Λ helicity to be performed, which can be uniquely related to the photon polarization in a model-independent way. The $$B^- \rightarrow \Lambda \bar{p} \gamma $$ B - → Λ p ¯ γ decay was recently measured to have a large branching fraction providing a possibility to get meaningful results with the data already available at LHC and B-factory experiments. An increase of the B-meson sample at high luminosity LHC experiments and Belle II should provide a really stringent test by using this method already in the near future.

Standard Model prediction of the Bc lifetime

Applying an operator product expansion approach we update the Standard Model prediction of the Bc lifetime from over 20 years ago. The non-perturbative velocity expansion is carried out up to third order in the relative velocity of the heavy quarks. The scheme dependence is studied using three different mass schemes for the $$ \overline{b} $$ b ¯ and c quarks, resulting in three different values consistent with each other and with experiment. Special focus has been laid on renormalon cancellation in the computation. Uncertainties resulting from scale dependence, neglecting the strange quark mass, non-perturbative matrix elements and parametric uncertainties are discussed in detail. The resulting uncertainties are still rather large compared to the experimental ones, and therefore do not allow for clear-cut conclusions concerning New Physics effects in the Bc decay.

MUSiC: a model-unspecific search for new physics in proton–proton collisions at $$\sqrt{s} = 13\,\text {TeV} $$

Results of the Model Unspecific Search in CMS (MUSiC), using proton–proton collision data recorded at the LHC at a centre-of-mass energy of 13$$\,\text {TeV}$$ TeV , corresponding to an integrated luminosity of 35.9$$\,\text {fb}^{-1}$$ fb - 1 , are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.