k T factorization is violated in production of high-transverse-momentum particles in hadron-hadron collisions

By J. Collins, J. Qiu. 2007

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We show that hard-scattering factorization is violated in the production of high-p{sub T} hadrons in hadron-hadron collisions, in the case that the hadrons are back-to-back, so that k{sub T} factorization is to be used. The explicit counterexample that we construct is for the single-spin asymmetry with one beam transversely polarized. The Sivers function needed here has particular sensitivity to the Wilson lines in the parton densities. We use a greatly simplified model theory to make the breakdown of factorization easy to check explicitly. But the counterexample implies that standard arguments for factorization fail not just for the single-spin asymmetry but for the unpolarized cross section for back-to-back hadron production in QCD in hadron-hadron collisions. This is unlike corresponding cases in e{sup +}e{sup -} annihilation, Drell-Yan, and deeply inelastic scattering. Moreover, the result endangers factorization for more general hadroproduction processes.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/69ed87eddba424a9cc51c85f169d8cb199346f54