Excited Hyperons Produced in Proton-Proton Collisions with Anke@COSY

TL;DR

This paper reports the observation of an excited neutral hyperon resonance in proton-proton collisions at COSY, measuring its mass, width, and production cross section, and investigates its nature and decay modes.

Contribution

It provides new experimental data on a neutral hyperon resonance around 1480 MeV/c2, including its mass, width, and production cross section, using multiple decay channels and mass techniques.

Findings

Indications of a neutral hyperon resonance at 1480 MeV/c2 with a width of 60 MeV/c2.

Production cross section of the hyperon resonance is a few hundred nanobarns.

Lambda(1405) resonance observed with a cross section of 4.5 microbarns, shape consistent with previous data.

Abstract

Excited neutral hyperons Y0* produced in the pp -> p K+ Y0* reaction with a COSY beam momentum of 3.65 MeV/c have masses below 1540 MeV/c2. The ANKE spectrometer allows the simultaneous observation of different decay modes: Y0* -> pion0Sigma0, pion+-Sigma-+, pion0Lambda, K-p by measuring kaons and pions of either charge in coincidence with protons. We have found indications for a neutral excited hyperon resonance Y0* with a mass of (1480 +- 15) MeV/c2 and a width of (60 +- 15) MeV/c2. The cross section for Y0* is of the order of few hundred nanobarns. It can be either a Sigma0 or a Lambda hyperon and on the basis of existing data no conclusion could be made whether it is a three-quark baryon or an exotic state. Missing- and invariant-mass techniques have been used to identify the Lambda(1405) resonance decaying via Sigma0pion0. The cross section for Lambda(1405) production is equal to (4.5 +- 0.9(stat) +- 1.8(syst)) microbarn. The shape and position of the Lambda(1405) distribution are similar to those found from other decay modes, so no support is given to the two-pole model.