Münster 2017 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 19: Hadron Structure and Spectroscopy III

HK 19.6: Talk

Tuesday, March 28, 2017, 15:45–16:00, F 5

Study of chiral dynamics in π⁻π⁰π⁰ production in Primakoff reactions at COMPASS — •Markus Krämer — Technische Universität München, Garching, Germany

COMPASS is a multipurpose fixed-target experiment at the CERN SPS, which addresses a wide variety of physic topics, in particular the structure and spectroscopy of hadrons. Diffractive dissociation of pions on nuclear targets allows for a clean access to the light-meson spectrum. * In addition, meson production is studied in pion-photon reactions via the Primakoff effect, where high-energetic pions scatter off the quasi-real photons surrounding the target nuclei. At low pion-photon center-of-mass energies, these reactions are governed by chiral dynamics and can be calculated using chiral perturbation theory. At higher energies, resonances are produced and their radiative coupling is investigated.

Using a 191 GeV/c negatively charged hadron beam (consisting mostly of pions) and a Ni target, 1.2 Million exclusive π⁻π⁰π⁰ events have been recorded in the region of small squared four-momentum transfer, i.e. t′<0.026 GeV²/c². At very low t′ < 0.002 GeV²/c², the contribution from electromagnetic interactions become visible in the t′ spectrum. This is used to determine the differential cross-section σ(π⁻γ→π⁻π⁰π⁰) near the three-pion threshold, where this reaction is dominated by chiral dynamics. In an alternative approach, this cross-section is determined by applying a partial-wave decomposition. Both methods and the obtained results will be presented.