Charmonium Production via Fragmentation at Higher Orders in alphas
Abstract
Quarkonium production at a given large pT is dominated by parton fragmentation: a parton which is produced with transverse momentum pT/z fragments into a quarkonium state which carries a fraction z of the parton momentum. Since parton production cross sections fall steeply with pT, high z fragmentation is favored. However, quantum number constraints may require the emission of gluons in the fragmentation process, and this softens the z dependence of the fragmentation function. We discuss the possibility that higher- order processes may enhance the large z part of fragmentation functions and thus contribute significantly to the quarkonium cross section. An explicit calculation of light quark fragmentation into etac shows that the higher-order process q -> q etac in fact dominates the lowest-order process q -> qg etac.
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