Abstract
The production of eta ^{(prime )}pi pairs constitutes one of the golden channels to search for hybrid exotics, with explicit gluonic degrees of freedom. Understanding the dynamics and backgrounds associated to eta ^{(prime )}pi production above the resonance region is required to impose additional constraints to the resonance extraction. We consider the reaction pi ^-prightarrow eta ^{(prime )} pi ^- ,p measured by COMPASS. We show that the data in 2.4< m_{eta ^{(prime )}pi } < 3.0{mathrm {,GeV}} can be described by amplitudes based on double-Regge exchanges. The angular distribution of the meson pairs, in particular in the eta ' pi channel, can be attributed to flavor singlet exchanges, suggesting the presence of a large gluon content that couples strongly to the produced mesons.
Highlights
Thorough partial wave analysis to disentangle resonance from nonresonant background can be a challenging endeavor
The reaction is expected to be dominated by cross-channel Regge exchanges, which is consistent with the cross section peaking in the forward and backward directions, with the peaks shrinking with increasing η( )π mass cf
Since a forward–backward asymmetry arises from the interference between even and odd waves, the larger exotic P-wave in η π is consistent with the observed larger asymmetry
Summary
The reaction is expected to be dominated by cross-channel Regge exchanges, which is consistent with the cross section peaking in the forward and backward directions, with the peaks shrinking with increasing η( )π mass cf. Fig. 2 of Ref. [9]. Since a forward–backward asymmetry arises from the interference between even and odd waves, the larger exotic P-wave in η π is consistent with the observed larger asymmetry This connection between resonances and Regge exchanges can be formalized via dispersion relations, e.g. in the form of finite energy sum rules [13,14,15]. A necessary step in this procedure is to fit the high mass region with analytical amplitudes that respect Regge asymptotic behavior. This is the main purpose of this work. The kinematical description of the η( )π reactions, statistical analysis, error propagation from the COMPASS partial waves to the intensity distribution, and other details and complementary information are left to the Appendices
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