The Search for Exotic Mesons in gamma p -> pi+pi+pi-n with CLAS at Jefferson Lab

TL;DR

This study used CLAS at Jefferson Lab to search for the exotic meson $ ext{pi}_1(1600)$ in photon-proton collisions, finding no evidence for its production despite observing known meson states.

Contribution

First partial-wave analysis of photoproduction data searching for the $ ext{pi}_1(1600)$ meson, providing experimental constraints on its production in photon-induced reactions.

Findings

No evidence for $ ext{pi}_1(1600)$ production in the dataset.

Confirmed presence of known mesons like $a_1(1260)$, $a_2(1320)$, and $ ext{pi}_2(1670)$.

Large dataset of 502,000 events analyzed.

Abstract

The $\pi_1(1600)$, a $J^{PC} = 1^{-+}$ exotic meson has been observed by experiments using pion beams. Theorists predict that photon beams could produce gluonic hybrid mesons, of which the $\pi_1(1600)$ is a candidate, at enhanced levels relative to pion beams. The g12 rungroup at Jefferson Lab's CEBAF Large Acceptance Spectrometer (CLAS) has recently acquired a large photoproduction dataset, using a liquid hydrogen target and tagged photons from a 5.71 GeV electron beam. A partial-wave analysis of 502K $\gamma p \to \pi^+\pi^+\pi^-n$ events selected from the g12 dataset has been performed, and preliminary fit results show strong evidence for well-known states such as the $a_1(1260)$, $a_2(1320)$, and $\pi_2(1670)$. However, we observe no evidence for the production of the $\pi_1(1600)$ in either the partial-wave intensities or the relative complex phase between the $1^{-+}$ and the $2^{-+}$ (corresponding to the $\pi_2$) partial waves.