Towards a solution of the charmonium production controversy:   k_t-factorization versus color octet mechanism
  The cross section of \chi_{cJ} hadroproduction is calculated in the k_t-factorization approach. We find a significant contribution of the \chi_{c1} state due to non-applicability of the Landau-Yang theorem because of off-shell gluons. The results are in agreement with data and, in contrast to the collinear factorization, show a dominance of the color singlet part and a strong suppression of the color octet contribution. Our results could therefore lead to a solution of the longstanding controversy between the color singlet model and the color octet mechanism. 
Ph. Hagler, R. Kirschner, A. Schafer, L. Szymanowski, O.V. Teryaev