First measurement of the spin-transfer parameter K-n00n in the (p)over-bar-p->(n)over-bar-n reaction at 875MeV/c

The spin-transfer parameter K-n00n of the <(p)over bar p up arrow> --> <(n)over bar up arrow n> charge exchange reaction has been measured for the first time at the CERN Low Energy Antiproton Ring (LEAR), at 875 MeV/c (p) over bar momentum, in the centre-of-mass scattering-angle range from 45 degrees to 78 degrees. To measure the transverse polarisation of the (n) over bar's, a thick scintillator counter hodoscope was used as live target, and the elastic <(n)over bar p> scattering on the hydrogen of the scintillator was used as analysing reaction of the (n) over bar transverse polarisation. Its so far unmeasured analysing power is taken as linear in momentum transfer, A(<(n)over bar p>) = alpha . q, and results are given for alpha . K-n00n. The values one obtains for K-n00n, estimating alpha from <(N)over bar N> potential models, are less than 0.25, in agreement with the predictions.