Theoretical analysis of Lambda(1405) --> (Sigma pi)^0 mass spectra produced in p+p --> p + Lambda(1405) + K^+ reactions

TL;DR

This paper provides a theoretical analysis of the Lambda(1405) resonance production in proton-proton reactions, comparing spectral shapes with experimental data to determine its mass and width, and discusses the production mechanism.

Contribution

It introduces a realistic formulation of the Lambda(1405) invariant-mass spectra considering interference effects and compares various models with recent experimental data.

Findings

Lambda(1405) mass estimated at 1405 -9 +11 MeV/c^2

Width of Lambda(1405) determined as 62 +- 10 MeV

Spectral shapes are asymmetric and skewed, matching experimental observations

Abstract

We formulated the Lambda(1405) (abbreviated as Lambda^*) --> (Sigma pi)^0 invariant-mass spectra produced in p+p --> p + Lambda^* + K^+ reactions, in which both the incident channel for a quasi-bound K^-p state and its decay process to (Sigma pi)^0 were taken into account realistically. We calculated M(Sigma pi) spectral shapes for various theoretical models for Lambda^*. They are asymmetric and skewed, and were compared with recent experimental data of HADES, yielding M(Lambda^*) = 1405 -9 +11 MeV/c^2 and Gamma = 62 +- 10 MeV, where the interference effects of the Kbar N-Sigma pi resonance with I= 0 and 1 Sigma pi continuum are considered. The nearly isotropic proton distribution observed in DISTO and HADES is ascribed to a short collision length in the production of Lambda^*, which justifies the high sticking mechanism of Lambda^* and the participating proton into K^-pp.