CERN Accelerating science

Article
Report number	arXiv:1512.04249
Title	The $2\pi$ Subsystem in Diffractively Produced $\pi^-\pi^+\pi^-$ at COMPASS
Related title	The $2\pi$ Subsystem in Diffractively Produced $\pi^-\pi^+\pi^-$ at COMPASS
Author(s)	Krinner, Fabian (Munich, Tech. U.)
Collaboration	for the COMPASS collaboration
Publication	2016-05-25
Imprint	14 Dec 2015
Number of pages	6
In:	AIP Conf. Proc. 1735 (2016) 030013
In:	16th International Conference on Hadron Spectroscopy, Newport News, VI, USA, 13 - 18 Sep 2015, pp.030013
DOI	10.1063/1.4949396
Subject category	Particle Physics - Experiment ; Particle Physics - Phenomenology ; Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN SPS ; COMPASS NA58
Abstract	The COMPASS experiment at CERN has collected a large dataset of $50$ million $\pi^-\pi^+\pi^-$ events produced diffractively from a proton target using a $190\,\mathrm{GeV}/c$ pion beam. The partial-wave analysis (PWA) of these high-precision data reveals previously unseen details but is limited in parts by systematic effects. The PWA is based on the isobar model, in which multi-particle decays are described as a chain of subsequent two-body decays. Here, fixed mass distributions for the appearing intermediate resonances, the so-called isobars, are assumed. These shapes, which e.g. may be parametrized by Breit-Wigner amplitudes, represent prior knowledge that has to be put into the analysis model and may therefore introduce a model dependence, thus increasing systematic uncertainties. We present a novel method, which allows to extract isobar amplitudes directly from the data in a more model-independent way. As a first application, diffractively produced $\pi^-\pi^+\pi^-$ events are analyzed. Here, the focus lies in particular on the scalar $\pi^+\pi^-$ subsystem, where in a previous analysis a signal for a new axial-vector state $a_1(1420)$ was found in the $f_0(980)\pi$ decay mode.
Copyright/License	arXiv nonexclusive-distrib. 1.0

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