A Search for Excited Neutrinos in e-p Collisions at HERA

TL;DR

This study searched for excited neutrinos in electron-proton collisions at HERA, setting new limits on their production and coupling parameters, but found no evidence of their existence.

Contribution

It provides the first comprehensive search for excited neutrinos at HERA with full data, establishing higher mass exclusion limits than previous experiments.

Findings

No evidence for excited neutrino production was observed.

New mass-dependent exclusion limits on production cross sections and couplings were set.

Limits extend the excluded mass range beyond previous searches.

Abstract

A search for excited neutrinos is performed using the full $e^{-}p$ data sample collected by the H1 experiment at HERA at a centre-of-mass energy of 319 GeV, corresponding to a total luminosity of 184 pb$^{-1}$.The electroweak decays of excited neutrinos ${\nu}^{*}{\to}{\nu}{\gamma}$, ${\nu}^{*}{\to}{\nu}Z$ and ${\nu}^{*}{\to}eW$ with subsequent hadronic or leptonic decays of the $W$ and $Z$ bosons are considered. No evidence for excited neutrino production is found. Mass dependent exclusion limits on $\nu^*$ production cross sections and on the ratio of the coupling to the compositeness scale $f/{\Lambda}$ are derived within gauge mediated models. A limit on $f/{\Lambda}$, independent of the relative couplings to the SU(2) and U(1) gauge bosons, is also determined. These limits extend the excluded region to higher masses than has been possible in previous excited neutrino searches.