4
Seen as bump in $\mathit I = 1$ state. See also COOPER 1968 . PEASLEE 1975 confirm ${{\overline{\mathit p}}}{{\mathit p}}$ results of ABRAMS 1970 , no narrow structure.
References:
ANISOVICH
2002
PL B542 8
Combined Analysis of Meson Channels with $\mathit I$ = 1, $\mathit C$ = -1 from 1940 to 2410-MeV
COUPLAND
1977
PL 71B 460
Antiproton Proton Total Elastic Cross Sections in the ${{\mathit T}}$ and ${{\mathit U}}$ Regions (0.69 to 2.43 ${\mathrm {GeV/}}\mathit c$)
ALSPECTOR
1973
PRL 30 511
High Statistics Investigation of the Broad ${{\mathit T}}$ and ${{\mathit U}}$ Peaks in Antiproton Interactions
ABRAMS
1970
PR D1 1917
Total Cross Sections of ${{\mathit K}^{\pm}}$ Mesons and Antiprotons on Nucleons up to 3.3 ${\mathrm {GeV/}}\mathit c$