Search for the Photoexcitation of Exotic Mesons in theπ+π+π−System

Abstract

A search for exotic mesons in the pi;{+}pi;{+}pi;{-} system photoproduced by the charge exchange reaction gammap-->pi;{+}pi;{+}pi;{-}(n) was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic J;{PC}=1;{-+} resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the a_{2}(1320) and the pi_{2}(1670) mesons, but no evidence for the a_{1}(1260), nor the pi_{1}(1600) exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic pi_{1}(1600) cross section, less than 2% of the a_{2}(1320) production.

Decay properties of the1−+hybrid state

“…Some other recent experimental papers include Refs. [12][13][14][15]. We note here that the existence of 1 ð2015Þ is still questionable, and it is not included in the most recent Particle Data Group 2010 [16].…”

Prediction of possible exotic states in the system *

“…Later, strong evidence for π 1 (1600) in the ρπ channel [15] with mass π 1 (1600) = 1660 ± 10 +0 −64 MeV and a width of Γ π1(1600) = 269 ± 21 +42 −64 MeV was reported by the COMPASS Collaboration at CERN. However, the CLAS Collaboration at JLab did not find the evidence for π 1 (1600) state in the speculated 3π final state in the photoproduction reaction γp → π + π + π − (n) missing [16].…”

Unitary coupled-channels model for three-mesons decays of heavy mesons

“…À 0 0 p data from the E852 experiment [2][3][4], a 1 ð1260Þ, a 2 ð1320Þ, 2 ð1670Þ, and a 4 ð2020Þ resonances were identified, and the exotic J PC ¼ 1 Àþ meson near 1.6 GeV [ 1 ð1600Þ] proposed from an earlier analysis was ruled out. The CLAS analysis [6] of p ! þ þ À n data identified a 2 ð1320Þ and 2 ð1670Þ, but neither a 1 ð1260Þ nor exotic 1 ð1600Þ at the expected levels.…”