https://doi.org/10.1140/epjc/s2005-02126-0
theoretical physics
Factorisation, parton entanglement and the Drell-Yan process
1
Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
2
Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22603, Hamburg, Germany
3
Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 16, 69120, Heidelberg, Germany
* e-mail: dboer@nat.vu.nl
We discuss the angular distribution of the lepton pair in the Drell-Yan process, 
. This process gives information on the spin-density matrix 
of the annihilating quark-antiquark pair in 
. There is strong experimental evidence that even for unpolarised initial hadrons is non-trivial, and therefore the quark-antiquark system is polarised. We discuss the possibilities of a general - which could be entangled - and a factorising . We argue that instantons may lead to a non-trivial of the type indicated by experiments.
© Springer-Verlag, 2005
