Antineutrino induced Lambda(1405) production off the proton

TL;DR

This paper investigates antineutrino-induced Lambda(1405) production off protons using a chiral unitary approach, revealing two poles and predicting observable differences in invariant mass distributions that can inform baryonic state properties.

Contribution

It introduces a detailed chiral unitary model for antineutrino reactions producing Lambda(1405), highlighting the two-pole structure and its experimental signatures.

Findings

Two Lambda(1405) poles generate a single peak in pi Sigma distributions.

Backward angles favor the higher-mass Lambda(1405) state at ~1420 MeV.

Predicted event rates suggest experimental observability at MINERvA.

Abstract

We have studied the strangeness changing antineutrino induced reactions $\bar{\nu}_{l} p \rightarrow l^+ \phi B $, with $\phi B = K^-p$, $\bar{K}^0n$, $\pi^0\Lambda$, $\pi^0\Sigma^0$, $\eta\Lambda$, $\eta\Sigma^0$, $\pi^+\Sigma^-$, $\pi^-\Sigma^+$, $K^+\Xi^-$ and $K^0\Xi^0$, using a chiral unitary approach. These ten coupled channels are allowed to interact strongly, using a kernel derived from the chiral Lagrangians. This interaction generates two $\Lambda(1405)$ poles, leading to a clear single peak in the $\pi \Sigma$ invariant mass distributions. At backward scattering angles in the center of mass frame, $\bar{\nu}_{\mu} p \rightarrow \mu^+ \pi^0 \Sigma^0$ is dominated by the $\Lambda(1405)$ state at around 1420~MeV while the lighter state becomes relevant as the angle decreases, leading to an asymmetric line shape. In addition, there are substantial differences in the shape of $\pi \Sigma$ invariant mass distributions for the three charge channels. If observed, these differences would provide valuable information on a claimed isospin I=1, strangeness S=-1 baryonic state around 1400 MeV. Integrated cross sections have been obtained for the $\pi \Sigma$ and $\bar K N$ channels, investigating the impact of unitarization in the results. The number of events with $\Lambda(1405)$ excitation in $\bar\nu_\mu p$ collisions in the recent antineutrino run at the MINERvA experiment has also been obtained. We find that this reaction channel is relevant enough to be investigated experimentally and to be taken into account in the simulation models of future experiments with antineutrino beams.