Odd and Even Partial Waves of $etapi^-$ and $eta_s14pi^-$ in 191 GeV$/c pi^- p$

Abstract

In the year 2008 COMPASS recorded diffractive events of the signature p ( 191 GeV ) p ! X fast p . We present results of the analysis of the subsystems X = h ( 0 ) p . Besides the known resonances a 2 ( 1320 ) , a 4 ( 2040 ) , we study the properties of the spin-exotic P _s16 wave, and all other natural- parity exchange partial waves up to spin J = 6. We find a striking difference between the two final states: whereas the even partial waves 2, 4, 6 in the two systems are related by phase-space factors, the odd partial waves are relatively suppressed in the hp system. The relative phases between the even waves appear identical whereas the phase between the D and P waves behave quite differently, suggesting different resonant and non-resonant contributions in the two odd- angular-momentum systems. Branching ratios and parameters of the well-known resonances a 2 and a 4 are measured. We find m ( a 2 ) = 1315_s16-12 MeV _s19 G ( a 2 ) = 119_s16-14 MeV _s19 and m ( a 4 ) = 1900 _s16 80 - 20 MeV _s19 G ( a 4 ) = 300 _s16 80 - 100 MeV : (consistent with COMPASS’s 3 pi analyses.) The relative branchings we measure are BR ( a 2 ! h 0 p ) BR ( a 2 ! hp ) = ( 5 2 ) % _s19 BR ( a 4 ! h 0 p ) BR ( a 4 ! hp ) = ( 23 7 ) %