[Paper Review] Prospects for precision measurements in nuclear beta decay at the LHC era

Martín González‐Alonso, O. Naviliat-Cuncic|arXiv (Cornell University)|Apr 5, 2013

Particle physics theoretical and experimental studies4 references4 citations

TL;DR

This paper evaluates the role of precision nuclear and neutron beta decay experiments in probing new physics beyond the Standard Model, using an effective field theory framework to compare sensitivities with Large Hadron Collider (LHC) searches. It identifies the Fierz interference term as the dominant probe for exotic scalar and tensor couplings, showing that low-energy beta decay experiments provide competitive, complementary constraints to high-energy collider data.

ABSTRACT

Precision measurements in nuclear beta decay offer a sensitive window to search for new physics beyond the standard electroweak model and allow also the determination of the fundamental weak vector coupling in processes involving the lightest quarks. Searches for new physics are also a strong motivation for experiments carried out at the high energy frontier reached at the most powerful particle colliders. It is instructive to confront results from the low energy and the high energy frontiers in order to look for possible complementarities and orient new avenues for experiments at low energies. We review here the status of constraints on new physics obtained from nuclear and neutron decays and compare them to those from other semi-leptonic processes and from the LHC. We stress the requirements of new precision experiments in beta decay in order to impact the search for new physics at the light of current and projected LHC results. We describe recent experimental results and ongoing developments in nuclear and neutron beta decay, with emphasis on their planned goals to improve present limits on exotic weak couplings.

Motivation & Objective

• To assess the sensitivity of precision beta decay experiments to new physics beyond the Standard Model.
• To compare constraints on exotic weak couplings from low-energy beta decays with those from high-energy LHC searches.
• To identify the most sensitive observable in beta decay for probing scalar and tensor interactions.
• To guide future experimental goals by comparing projected LHC sensitivities with planned low-energy experiments.
• To emphasize the importance of the Fierz interference term in optimizing experimental design and sensitivity.

Proposed method

• Uses an effective field theory (EFT) framework to describe non-Standard Model (NP) interactions in semi-leptonic decays at low energies.
• Introduces a quark-level effective Lagrangian with six independent NP couplings: three CP-conserving and three CP-violating, including vector, scalar, tensor, and pseudoscalar interactions.
• Maps quark-level NP couplings to hadronic-level correlation coefficients, particularly focusing on the Fierz interference term.
• Compares constraints on NP couplings from beta decay measurements with those from other semi-leptonic processes and LHC data.
• Analyzes the sensitivity of current and projected experiments to exotic couplings, emphasizing the dominance of the Fierz term in correlation measurements.
• Projects required experimental precision (e.g., $10^{-3}$ or better on the Fierz term) to match or exceed future LHC reach.

Experimental results

Research questions

• RQ1 How do precision measurements in nuclear and neutron beta decay constrain exotic scalar and tensor couplings compared to LHC searches?
• RQ2 What is the dominant observable in beta decay for detecting new physics beyond the Standard Model?
• RQ3 To what extent do current and planned low-energy experiments complement high-energy collider results in probing new physics?
• RQ4 How do radiative corrections and nuclear structure effects limit the theoretical precision of beta decay observables?
• RQ5 What experimental precision is required in the Fierz term to match or surpass the sensitivity of future LHC results?

Key findings

• The Fierz interference term is the only relevant parameter for constraining exotic scalar and tensor couplings in precision beta decay experiments.
• For the most precise measurements, the Fierz term dominates sensitivity to exotic couplings due to its linear dependence on the NP parameters.
• Current constraints on CP-conserving exotic couplings from beta decay are competitive with those from other semi-leptonic processes and with LHC results.
• The sensitivity of future low-energy experiments to exotic couplings depends critically on achieving precision at the $10^{-3}$ level or better on the Fierz term.
• Projected LHC results will probe effective scales comparable to those accessible by next-generation beta decay experiments, creating a strong interplay between low- and high-energy frontiers.
• Theoretical uncertainties in radiative corrections and nuclear structure effects currently limit the sensitivity of beta decay measurements, leaving room for improvement through better calculations.