Measurements of Angular Distributions of Muons From Upsilon Meson Decays   in p p-bar Collisions at sqrt(s)=1.96 TeV
  The angular distributions of muons from Upsilon(1S,2S,3S) to mu+mu- decays are measured using data from proton anti-proton collisions at sqrt(s)=1.96 TeV corresponding to an integrated luminosity of 6.7 /fb and collected with the CDF II detector at the Fermilab Tevatron. This analysis is the first to report the full angular distributions as functions of transverse momentum pT for the Upsilon mesons in both the Collins-Soper and s-channel helicity frames. This is also the first measurement of spin alignment of Upsilon(3S) mesons. Within the kinematic range of Upsilon rapidity |y|<0.6 and pT up to 40 GeV/c, the angular distributions are found to be nearly isotropic. 
T. Aaltonen, B. \'Alvarez Gonz\'alezz, S. Amerio, D. Amidei, A.   Anastassovx, A. Annovi, J. Antos, G. Apollinari, J.A. Appe...
hep-ex