Production and decay of baryonic resonances in pion induced reactions

Abstract

Abstract. Pion induced reactions give unique opportunities for an unambiguous description of baryonic resonances and their coupling channels. A systematic energy scan and high precision data, in conjunction with a partial wave analysis, allow for the study of the excitation function of the various contributions. A review of available world data unravels strong need for modern facilities delivering measurements with a pion beam. Recently, HADES collaboration collected data in pion-induced reactions on light ( 12 C) and heavy ( 74 W) nuclei at a beam momentum of 1.7 GeV/c dedicated to strangeness production. Probing baryon resonancesOne of the key issues in the research of nature over the years was the investigation of baryon resonances, i.e. short-lived excited states of nucleons. From experimental point of view a resonance manifests as a peak located around a certain energy in differential cross section. Its composite nature is probed in scattering experiments and is characterized not only by the complex pole position of the scattering amplitude but also by the couplings to the various channels and hence decay branching ratios. Particularly the important region of 1-2 GeV is occupied by light-flavoured baryons. Such baryons are built out of three quarks (u, d, s) with possible spin either 1/2 or 3/2. Accounting for orbital motion, a supermutiplet SU (6) ) lies in the fact that missing states can couple weakly to the Nπ channel, which is a predominant source of knowledge about baryon properties. Additional difficulty stems from the fact that resonance spectral functions are usually quite broad and various resonances overlap. This challenge triggered great experimental effort resulting in collection of high precision and quality data in meson photo-and electroproduction [6]. In contrary

Δ(1232) Dalitz decay in proton-proton collisions at T=1.25 GeV measured with HADES at GSI

“…It paves the way to the study of higher resonances, where larger four-momentum transfer can be reached and, therefore, a larger sensitivity to electromagnetic form factors could be observed. This can be achieved with HADES and the pion beam at GSI [47]. Such studies constitute an indispensable complement to measurements of space-like transitions using meson electro-production experiments.…”

“…Thanks to its high acceptance, powerful particle (p/K/π/e) identification and very good mass resolution (2 − 3% for dielectrons in the light-vector meson mass range) it allows the study of both hadron and rare dielectron production in N + N [34,35,40,41], p + A [42], A + A [43][44][45], π + p [46,47], π + A collisions in the beam energy range of a few (A)GeV. Nucleon-nucleon reactions play a special role in this context, providing an important reference for p + A and A + A collisions.…”

Partial Wave Analysis of HADES Data for Two-Pion Production in Pion-Nucleon Reactions

“…HADES has proposed an experimental program [1,2] focused on combined measurements of hadron and dielectron production in pion induced reactions [3][4][5][6][7]. It offers a great opportunity to unambiguously fix the description of baryonic resonances and their coupling to the light vector mesons ρ and ω.…”

Partial wave analysis of HADES data for two-pion production in pion-nucleon reactions

“…The π − p elastic scattering has been reconstructed for all four pion beam momenta (for details, see [3]), and normalized in the θ CM π − range of 60 • − 110 • to the known world data (SAID database [8]), see Fig. 1, left panel.…”

“…A systematic energy scan and high precision data are needed [2]. In 2014, a large statistics of π − p scattering were collected by HADES at four pion beam momenta 0.656, 0.69, 0.748, and 0.8 GeV/c [3]. The data have been included into the multichannel partial wave analysis (PWA), developed by the Bonn-Gatchina group [4].…”