Displaced Neutrino Jets at the LHeC

TL;DR

This paper proposes a novel method to detect light right-handed neutrinos at the LHeC by leveraging leptoquark decay, resulting in a distinctive displaced fat jet signature, and demonstrates enhanced detection prospects with a positron beam.

Contribution

It introduces a new production mechanism for right-handed neutrinos via leptoquark decay, enabling detection independent of neutrino mixing suppression.

Findings

Displaced fat jet signature can be effectively identified using energy and track ratio variables.

Positron beam significantly improves the detection prospects of the RHN signature.

Long-lived, boosted RHNs produce collimated decay products distinguishable from background.

Abstract

Extending the Standard Model with right-handed neutrinos (RHNs) is well motivated by the observation of neutrino oscillations. In the type-I seesaw model, the RHNs interact with the SM particles via tiny mixings with the active neutrinos, which makes their discovery in the laboratory, and in particular at collider experiments in general challenging. In this work we instead consider an extension of the type-I seesaw model with the addition of a leptoquark (LQ), and employ a non-minimal production mechanism of the RHN via LQ decay, which is unsuppressed by neutrino mixing. We focus on relatively light RHN with mass $\mathcal{O}(10)$ GeV and LQ with mass 1.0 TeV, and explore the discovery prospect of the RHN at the proposed Large Hadron electron Collider. In the considered mass range and with the given interaction strength, the RHN is long lived and, due to it stemming from the LQ decay, it is also heavily boosted, resulting in collimated decay products. The unique signature under investigation is thus a displaced fat jet. We use kinematic variables to separate signal from background, and demonstrate that the ratio variables with respect to energy/number of displaced and prompt tracks are useful handles in the identification of displaced decays of the RHN. We also show that employing a positron beam provides order of magnitude enhancement in the detection prospect of this signature.