Beta Decays and Non-Standard Interactions in the LHC Era (1303.6953v1)

Abstract: We consider the role of precision measurements of beta decays and light meson semi-leptonic decays in probing physics beyond the Standard Model in the LHC era. We describe all low-energy charged-current processes within and beyond the Standard Model using an effective field theory framework. We first discuss the theoretical hadronic input which in these precision tests plays a crucial role in setting the baseline for new physics searches. We then review the current and upcoming constraints on the various non-standard operators from the study of decay rates, spectra, and correlations in a broad array of light-quark systems. We finally discuss the interplay with LHC searches, both within models and in an effective theory approach. Our discussion illustrates the independent yet complementary nature of precision beta decay measurements as probes of new physics, showing them to be of continuing importance throughout the LHC era.

An Overview of Beta Decays and Non-Standard Interactions in the LHC Era

The paper "Beta Decays and Non-Standard Interactions in the LHC Era" explores the capabilities of precision measurements of beta decays and light meson semi-leptonic decays in investigating physics beyond the Standard Model (BSM) during the LHC period. It emphasizes the utility of an effective field theory (EFT) framework in capturing low-energy charged-current processes, both standard and non-standard, by constructing operators with SM fields and identifying non-standard interactions through precision tests.

The introduction of the paper contextualizes the historical significance of beta decays in establishing the $V-A$ structure of weak interactions, highlighting their role in the Standard Model's formulation. It discusses charged-current processes mediated by tree-level W exchange and presents the EFT approach as essential in analyzing potential deviations from the SM.

Effective Field Theory Framework

The authors argue that high-energy BSM dynamics can be probed using an effective Lagrangian, which includes dimension-six operators that augment the SM Lagrangian. This theoretical framework considers low-energy predictions and experimental constraints from various decay channels. A comprehensive list of the effective operators is presented, classified into four-fermion interactions and vertex corrections, complemented by detailed considerations of their implications for gauge-invariant processes.

The discussion leverages the EFT approach to derive constraints on non-standard operators induced by BSM physics, integrating theoretical inputs like hadronic and nuclear matrix elements crucial for precision predictions. The importance of precision in determining matrix elements up to the level of $10^{-3}$ is underscored, to match anticipated BSM effects at TeV energy scales.

Probing Non-Standard Interactions

Several key observables sensitive to BSM effects are scrutinized: decay total rates, leading to universality tests, and differential distributions, sensitive to Lorentz structures beyond the $V-A$ paradigm. Cabibbo and lepton universality tests reveal stringent constraints on non-standard couplings through precision determinations of CKM matrix elements and lepton decay ratios, respectively. The interplay with experimental measurements, such as pion decay ratios and neutron correlation coefficients, serves to test theoretical predictions.

The authors articulate constraints on scalar and tensor interactions from existing beta decay measurements, proposing future improvements from upcoming experiments to achieve higher sensitivities. They also discuss recoil effects in decay dynamics, capable of providing benchmarks for SM predictions and indicating potential BSM influences.

LHC Constraints

Crucially, the paper examines the capacity of collider experiments at the LHC to probe these non-standard charged-current interactions, drawing comparisons with low-energy observables. The LHC data are analyzed in terms of EFT, with bounds placed on several BSM couplings through $pp \to e \nu + X$ processes. The symmetry with low-energy probes is maintained, and the results are discussed in relation to both complementary and independent searches.

Model Examples

Illustrative examples of BSM models, such as the Left-Right Symmetric Model and the MSSM, are considered. The authors detail how these models introduce specific patterns of non-standard interactions, which can be constrained or explored in concert with beta decay and LHC results, highlighting the potential to explore particular regions of parameter space effectively.

Conclusion

The paper concludes by emphasizing the continued relevance of beta decays as viable probes of BSM physics, augmented by collaboration with LHC findings. This approach implements a unified examination of new physics, demonstrating that high-sensitivity measurements across varied systems offer immense potential in defining the boundaries of TeV-scale physics, making beta decay studies integral to the future of particle physics research.