The exotic eta'pi- Wave in 190 GeV pi-p --> pi-eta'p at COMPASS

TL;DR

This paper reports a partial-wave analysis of eta'pi- production at 190 GeV, revealing a broad P_+ structure, phase motion, and the a_4(2040), contributing to understanding exotic meson states.

Contribution

It presents the first detailed partial-wave analysis of eta'pi- at high energy, identifying new structures and phase behaviors not previously observed.

Findings

Identification of a broad P_+ structure in eta'pi-

Observation of phase motion near the a_2(1320) mass

Detection of the a_4(2040) resonance

Abstract

A sample of 35,000 events of the type pi-p --> eta'pi-p_slow (eta' --> eta pi-pi+, eta --> gamma gamma) with -t>0.1 GeV^2/c^2 was selected from COMPASS 2008 data for a partial-wave analysis. We study the broad P_+ structure known from previous experiments at lower energies, in particular its phase motion relative to the D_+-wave near the a_2(1320) mass and relative to a broad D_+-wave structure at higher mass. We also find the a_4(2040). We compare kinematic plots for the eta'pi^- and eta pi- final states.