Non standard neutrino interactions at LEP2 and the LHC

TL;DR

This paper investigates the potential of LEP2 and LHC experiments to detect non-standard neutrino interactions (NSI) at high energies, providing bounds and sensitivity estimates for these interactions arising from new physics at dimension eight.

Contribution

It offers a comparative analysis of LEP2 and LHC sensitivities to NSI, utilizing contact interaction models and the Equivalence Theorem to estimate experimental bounds.

Findings

LEP2 constrains NSI coefficients to ^{-2} - 10^{-3}

LHC can probe NSI with  imes 10^{-3} sensitivity at 14 TeV

High- GeV particles with >400 GeV p_T are key signatures

Abstract

We consider Non-Standard neutrino Interactions (NSI) connecting two neutrinos with two first-generation fermions ($e, u$ or $d$), which we assume to arise at at dimension eight due to New Physics. The coefficient is normalised as $4 \epsilon G_F/\sqrt{2}$. We explore signatures of NSI-on-electrons at LEP2, and of NSI-on-quarks at the LHC, treating the NSI as contact interactions at both energies. In models where the coefficients of dangerous dimension six operators are suppressed by cancellations, LEP2 provides interesting bounds on NSI operators ($\epsilon \lsim 10^{-2} - 10^{-3}$), which arise because $\sqrt{s} \sim 200$ GeV, and the cancellation applied at zero momentum transfer. At the LHC, we use the Equivalence Theorem, which relates the longitudinal $W$ to the Higgs, to estimate the rate for $\bar{q} q W^+W^- e_\alpha^+ e_\beta^-$ induced by NSI. We find that the cross-section is small, but that the outgoing particles have very high $p_T > 400$ GeV, which reduces the issue of backgrounds. In a conservative scenario, we find that the LHC at 14 TeV and with 100 fb$^{-1}$ of data would have a sensitivity to $\epsilon \gsim 3 \times 10^{-3}$.