Evidence for exotic meson production in the reaction pi- p ---> eta pi- p at 18-GeV/c

The {eta}{pi}{sup {minus}} system has been studied in the reaction {pi}{sup {minus}}p{r_arrow}{eta}{pi}{sup {minus}}p at 18 GeV/c. A large asymmetry in the angular distribution is observed indicating interference between L-even and L-odd partial waves. The a{sub 2}(1320) is observed in the J{sup PC}=2{sup ++} wave, as is a broad enhancement between 1.2 and 1.6 GeV/c{sup 2} in the 1{sup {minus}+} wave. The observed phase difference between these waves shows that there is phase motion in addition to that due to a{sub 2}(1320) decay. The data can be fitted by interference between the a{sub 2}(1320) and an exotic 1{sup {minus}+} resonance with M=(1370{plus_minus}16{sup +50}{sub {minus}30}) MeV/c{sup 2} and {Gamma}=(385{plus_minus}40 {sup +65}{sub {minus}105}) MeV/c{sup 2} . {copyright} {ital 1997} {ital The American Physical Society}