Study of the D0 ---> pi- pi+ pi- pi+ decay

Using data from the FOCUS (E831) experiment at Fermilab, they present new measurements for the Cabbibo-suppressed decay mode D{sup 0} {yields} {pi}{sup -}{pi}{sup +}{pi}{sup -}{pi}{sup +}. They measure the branching ratio {Lambda}(D{sup 0} {yields} {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -})/{Lambda}(D{sup 0} {yields} K{sup -} {pi}{sup +}{pi}{sup -}{pi}{sup +}) = 0.0914 {+-} 0.0018 {+-} 0.0022. An amplitude analysis has been performed, a first for this channel, in order to determine the resonant substructure of this decay mode. The dominant component is the decay D{sup 0} {yields} a{sub 1}(1260){sup +}{pi}{sup -}, accounting for 60% of the decay rate. The second most dominant contribution comes from the decay D{sup 0} {yields} {rho}(770){sup 0}{rho}(770){sup 0}, with a fraction of 25%. They also study the a{sub 1}(1260) line shape and resonant substructure. Using the helicity formalism for the angular distribution of the decay D{sup 0} {yields} {rho}(770){sup 0}{rho}(770){sup 0}, they measure a longitudinal polarization of P{sub L} = (71 {+-} 4 {+-} 2)%.