Interpretation of Λ spin polarization measurements

The physics interpretation of the recent measurements of the spin polarization of hyperons produced in relativistic heavy-ion collisions is discussed. We suggest that the polarization measured in the rest frame should be projected along the direction of the total angular momentum that is first transformed to the same frame, and only then averaged over 's with different momenta in the center-of-mass frame. While this procedure does not affect the current measurements done in a broad transverse-momentum range, it may become important (representing a correction of about 10%) for the most energetic hyperons under study (with transverse momenta reaching 4--50. 28em{0ex}GeV/c). The proposed treatment is generally more appropriate for relativistic 's. Throughout the paper, we deliver explicit expressions for various boosts, rotations, and transformations of angular distributions, which may help to compare model predictions with the experimental results.