München 2019 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 54: Poster

HK 54.9: Poster

Thursday, March 21, 2019, 16:30–19:00, Foyer Theresanium

Extracting the Chiral Anomaly from Primakoff Reactions in COMPASS Data — •Dominik Steffen for the COMPASS collaboration — Physik-Department E18, Technische Universität München

The COMPASS collaboration at CERN has measured pion-photon scattering reactions via the Primakoff effect. In these reactions, high-energetic pions scatter off quasi-real photons stemming from the Coulomb field of nuclei with high atomic number. The single-π⁰ production π⁻ γ^(*) → π⁻π⁰ shows a strong contribution of the ρ(770) resonance in the invariant-mass spectrum of the π⁻π⁰ system. On the low-mass side of the ρ(770) contribution, close to the kinematic threshold, a tail is present in the spectrum which is not driven by a resonance but by the chiral anomaly: the non-resonant production of a π⁰ is only possible by the point-like coupling of the photon to three pions defined by the respective coupling constant F_3π called chiral anomaly. Previous extractions of the chiral anomaly date back to the Serpukhov experiment in 1987, are restricted to the kinematic threshold region, and extracted the chiral anomaly to a 10%-level. COMPASS measured the invariant mass spectrum including the ρ(770)-resonance which allows for more precise extraction of F_3π. The contribution will present the status of the analysis.

This work was supported by the BMBF, the DFG Cluster of Excellence "Origin and Structure of the Universe" (Exc 153), the Maier-Leibnitz-Laboratorium der Universität und der Technischen Universität München.