Abstract
B.1 is one of the experimental projects within the CRC16. It aims at the systematic investigation of the photoproduction of mesons off nucleons in order to understand reaction mechanisms and the relevant degrees of freedom in resonance formation. Of particular interest is the photoproduction of mesons heavier than the pion and resonances involving hidden or open strangeness. Essential hardware contributions have been made to the experimental programme of the CRC16 through tagging systems, and photon-beam polarisation and polarimetry. A new experiment has been set up within the framework of the BGO-OD collaboration. This combines a forward magnetic spectrometer with a central BGO calorimeter with charged particle recognition and identification. The BGO-OD experiment enables reconstruction of complex final states composed of both charged and neutral particles, complementary to the existing CBELSA/TAPS calorimeter which is optimised for multi-photon final states. Selected results of the 12-year CRC period are presented from both experiments.
Highlights
The goal of CRC 16 project B.1 is the systematic investigation of the photoproduction of mesons off nucleons
The most basic one is the beam asymmetry, Σ, which is accessible through linearly polarised photon beams, and provides seed for a whole class of double polarisation observables which are sensitive to aspects of spin-orbit interactions involved [39]
The new BGO-open dipole” (OD) detector opens a window to more complex final states of mixed neutral and charged particles
Summary
The goal of CRC 16 project B.1 is the systematic investigation of the photoproduction of mesons off nucleons. A dip in the cross section can be reproduced in a model based on vector meson-baryon interactions [29] It appears associated with the formation of a N∗(2030) vectormesonbaryon resonance, possibly in combination with a closeby N∗(2080), and it is predicted to be complemented by a peak structure in Ks0Σ0 photoproduction off the neutron. The photon tagging system is an essential feature of the CBELSA/TAPS experiment This includes the positioning system to align a diamond crystal to produce linearly polarised coherent bremsstrahlung, and a Møller polarimeter for in-situ measurements of the longitudinal electron beam polarisation. For the CBELSA/TAPS experiment, which is run in combination with the Bonn Frozen Spin polarised target, linearly polarised tagged photon beams and the necessary electron polarimetry for circularly polarised beam were provided Methods and results are described in Ref. [33]
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