Study of the $\eta $-Meson Production with Polarized Proton Beam

Abstract

and the WASA-at-COSY CollaborationThe pp → ppη reaction was investigated at excess energies of 15 MeV and 72 MeV using the azimuthally symmetric WASA detector and a polarized proton beam of the Cooler Synchrotron COSY. The aim of the studies is the determination of partial wave contributions to the production process of the η meson in nucleon-nucleon collisions. Here we present preliminary results of the extraction of the position of the interaction region with respect to the WASA detector and preliminary results on the degree of polarization of the COSY proton beam used in the experiment.

Determination of the COSY Proton Beam Polarization Using the WASA Detector

“…In the case of the control sample, the measured polarization is consistent with zero, within the statistical uncertainty. Figure 4 shows the results before and after the correction for shifts of the center of the beam-target interaction region from its nominal position [36,37]. The average polarization of all acquired data was calculated analyzing all events together.…”

Polarization determination for the studies of the eta meson production

“…To find the vertex coordinates, (v x ; v y ; v z ), two methods [8,9] were applied in the experiment. Results obtained from both methods are presented at Tab.…”

“…Table 1: Vertex position calculated for the experiment based on the two independent methods. Detailed descriptions of the methods are given in [8,9]. As a cross check we also calculated the polarization by adding all events together and determining the asymmetry for the whole data sample.…”

Unresolved Issues in the Search for Eta-mesic Nuclei

“…Conclusions about the existence of eta mesic states based on scattering length approaches for the final state should however be taken with some caution as will be discussed in the next section. Some hope of shedding light on the existence of these light nuclear states lies in the ongoing efforts made by the WASA collaboration at COSY [19,20,21,22,23].…”