Measurement of the Polarization of the Upsilon(1S) and Upsilon(2S) States in pp Collisions at s=1.96 TeV
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We present a study of the polarization of the Upsilon(1S) and Upsilon(2S) states using a 1.3 fb(-1) data sample collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron Collider. We measure the polarization parameter alpha=(sigma(T)-2 sigma(L))/(sigma(T)+2 sigma(L)), where sigma(T) and sigma(L) are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum (p(T)(Upsilon)) for the Upsilon(1S) and Upsilon(2S). Significant p(T)(Upsilon)-dependent longitudinal polarization is observed for the Upsilon(1S). A comparison with theoretical models is presented.