2004/11/30 by Daniël Boer, D. Boer, A. Brandenburg +4
Physics and Astronomy · #Bar (unit) #Drell–Yan process #Electron #Factorization #Hadron #High-Energy Particle Collisions Research #Instanton #Lepton #Nuclear physics #Pair production #Particle physics #Particle physics theoretical and experimental studies #Parton #Physics #Quantum Chromodynamics and Particle Interactions #Quantum entanglement #Quantum mechanics #Quark #Spin (aerodynamics) #hep-ph
paper · pdf · doi:10.1140/epjc/s2005-02126-0
published as Eur.Phys.J. C40 (2005) 55-61 · 14 pages, 2 figures, comments and references added; to appear in EPJC
arxiv created 2005/01/18 · openalex publication_date 2005/02/09 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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.