Anomalous Drell-yan Asymmetry from Hadronic or Qcd Vacuum Effects

where φ is the angle between the lepton and hadron planes in the lepton center of mass frame (see Fig. 3 of Ref.1). In the parton model (order αs) quark-antiquark annihilation yields λ = 1, μ = ν = 0. The leading order (LO) perturbative QCD corrections (order αs) lead to μ 6= 0, ν 6= 0 and λ 6= 1, such that the so-called Lam-Tung relation 1 − λ − 2ν = 0 holds. Beyond LO, small deviations from the Lam-Tung relation will arise. If one defines the quantity κ ≡ − 1 4 (1 − λ − 2ν) as a measure of the deviation from the Lam-Tung relation, it has been calculated2,3 that at order αs κ is small and negative: −κ∼ 0.01, for values of the muon pair’s transverse momentum QT of up to 3 GeV/c. Surprisingly, the data is incompatible with the Lam-Tung relation and with its small order-αs modification as well 3. These data from CERN’s NA10 Collaboration4,5 and Fermilab’s E615 Collaboration6 are for πN → μμX , with N = D and W . The π-beam energies range from 140 GeV