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HK: Fachverband Physik der Hadronen und Kerne

HK 74: Poster

HK 74.33: Poster

Donnerstag, 23. März 2023, 17:30–19:00, HSZ EG

Study of the π⁻π⁺ subsystem with J^PC = 1^– in the diffractively produced π⁻π⁻π⁺ final state at COMPASS * — •Martin Bartl for the COMPASS collaboration — Physik-Department E18, Technische Universität München

The COMPASS experiment is a fixed-target experiment at CERN fed by the SPS beam. The flagship spectroscopy analysis is based on the diffractive process π⁻p→π⁻π⁻π⁺p, for which a large data sample of 46 × 10⁶ events has been collected.

This large data sample allows us to apply the so-called freed-isobar partial-wave analysis method, which extracts the amplitudes of the decay process with well-defined J^PC quantum numbers for the π⁻π⁺ subsystem, as well as for the 3π system. The π⁻π⁺ amplitudes are extracted in a quasi-model-independent way as a function of 2π mass, 3π mass, and squared four-momentum transfer. This highly detailed information allows us not only to test the assumptions of the isobar model, but also to perform in-depth studies of the 2π resonances that appear in the 3π system.

We study the 2π amplitudes with J^PC = 1^–. These 2π amplitudes are dominated by the well-known ρ(770) resonance, but may also contain signals from excited ρ states, which are still elusive. The employed approach allows us to extract the pole positions, i.e. masses and widths, of these resonances and study their systematics.

*funded by the DFG under Germany’s Excellence Strategy - EXC2094 - 390783311 and BMBF Verbundforschung 05P21WOCC1 COMPASS.