Measurement of exclusive ρ+ρ− production in mid-virtuality two-photon interactions and study of the γγ∗→ρρ process at LEP

Exclusive ρ+ρ− production in two-photon collisions between a quasi-real photon, γ, and a mid-virtuality photon, γ∗, is studied with data collected at LEP at centre-of-mass energies 183GeV⩽s⩽209GeV with a total integrated luminosity of 684.8pb−1. The cross section of the γγ∗→ρ+ρ− process is determined as a function of the photon virtuality, Q2, and the two-photon centre-of-mass energy, Wγγ, in the kinematic region: 0.2GeV2⩽Q2⩽0.85GeV2 and 1.1GeV⩽Wγγ⩽3GeV. These results, together with previous L3 measurements of ρ0ρ0 and ρ+ρ− production, allow a study of the γγ∗→ρρ process over the Q2-region 0.2GeV2⩽Q2⩽30GeV2.