Production of Δ0 resonances in the target and projectile fragmentation regions in p+12C and d+12C collisions at 4.2 GeV/c per nucleon

The Δ0(1232) production has been investigated with 4π acceptance separately in the target and projectile fragmentation regions in p+12C and d+12C collisions at an incident momentum of 4.2 GeV/c per nucleon. The masses and widths (Г) of the Δ0 resonances originating from the target and projectile regions have been extracted from their reconstructed invariant mass distributions, obtained with the help of an angular criterion. The width of the mass distribution of Δ0 coming from the target 12C fragmentation region in both p+12C and d+12C collisions has been about 2.3 times smaller than that of Δ0 produced in free nucleons collisions. The Monte Carlo model calculations, which simulate the point of entrance of an incident particle into target 12C, its mean free path inside 12C, and point of Δ0 production (excitation) inside 12C as well as its point of exit from the target nucleus, have been implemented to estimate the lifetime of Δ0 resonances originating from the target fragmentation region in p+12C and d+12C collisions. It is assumed that the lifetime of Δ0, excited inside a 12C nucleus, can be modelled as the sum of two lifetimes: time of Δ0 flight through the nucleus and time of decay of the free Δ0 resonance outside the nucleus. The obtained model lifetime of Δ0 resonances has agreed very well with the experimental lifetime of Δ0 originating from the target fragmentation region in both p+12C and d+12C collisions, determined from the experimental width (Г) of Δ0. The widths of Δ0 resonances, coming from the projectile fragmentation region in p+12C and d+12C collisions, have coincided within the uncertainties with the width of Δ0 produced in collisions of free nucleons.