Effective LFV couplings at the electron-proton collider

TL;DR

The paper addresses the sensitivity to lepton flavour violating (LFV) dimension-six operators mediating $e$-$\mu$ transitions at the LHeC. It employs both a cuts-based approach and an optimal observable method to estimate constraints on the Wilson coefficients $C_i/\Lambda^2$ at $\sqrt{s}=1.3$ TeV with integrated luminosity up to $\sim \text{ab}^{-1}$, also evaluating the impact of initial electron polarization. The results indicate reach at $\mathcal{O}(10^{-2}-10^{-1})\ \text{TeV}^{-2}$ for various operator structures, with beam polarization providing additional gains, notably for chiral operators. Overall, the study demonstrates that $ep$ colliders offer a powerful, complementary probe of LFV new physics in the high-energy frontier.

Abstract

We estimate the accuracy with which the coefficient of the lepton flavour-violating dimension-six operators can be measured at the proposed electron-proton collider. Cuts-based analysis is performed to compute the signal significance at the centre of mass energy of 1.3 TeV, with a total integrated luminosity upto $\sim$ab$^{-1}$. Using the optimal observables method for the kinematic distributions, we study the sensitivity of the effective couplings. We also study the impact of the initial electron beam polarisation.

Figures (3)

• Figure 1: 5$\sigma$ discovery contours in the planes of different Wilson coefficient pairs.
• Figure 2: Kinematic distributions used in the optimal observable analysis: transverse momentum $p_T$ (left) and scattering angle $\cos\theta$ (right) of the final state muon.
• Figure 3: $2\sigma$ exclusion contours obtained from the optimal observable analysis for different pairs of Wilson coefficients.