Berlin 2005 – scientific programme

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T: Teilchenphysik

T 707: QCD III

T 707.5: Talk

Wednesday, March 9, 2005, 15:00–15:15, TU H2037

Factorisation, Parton Entanglement and the Drell-Yan Process — •Andre Utermann¹, Daniel Boer², Arnd Brandenburg³, and Otto Nachtmann¹ — ¹Institut für Theoretische Physik, Universität Heidelberg — ²Department of Physics and Astronomy, Vrije Universiteit Amsterdam — ³DESY Hamburg

We discuss the angular distribution of the lepton pair in the Drell-Yan process, hadron+hadron→γ^∗+X→ l⁺+l⁻+X. This process gives information on the spin-density matrix ρ^(q,q) of the annihilating quark-antiquark pair in q+q→ l⁺+l⁻. There is strong experimental evidence that even for unpolarised initial hadrons ρ^(q,q) is nontrivial, and therefore the quark-antiquark system is polarised. We discuss the possibilities of a general ρ^(q,q) –which could be entangled– and a factorising ρ^(q,q). We argue that instantons may lead to a nontrivial ρ^(q,q) of the type indicated by experiments.