Diffractive production of Drell-Yan pairs and heavy flavors

Partonic interpretation of high-energy reactions is known to depend on a reference frame. Particularly, in the rest frame of the target Drell-Yan process looks like a freeing of the projectile ll̄ fluctuation, rather than qq̄ → ll̄ annihilation. The lightcone representation for Drell-Yan reaction is very similar to that in DIS and exposes a substantial contamination of soft interactions which turns out to be dominant in diffractive production of lepton pairs and in nuclear shadowing. We estimate the fraction of diffractive events in the total Drell-Yan cross section, which scales in M, and find a substantial deviation from factorization. An analogous approach is developed for diffractive production of heavy flavors. Light-cone representation for Drell-Yan reaction Drell-Yan mechanism of lepton pair production in hadronic collisions at small x2 ≪ 1 has much in common with deep-inelastic lepton scattering at small Bjorken xBj [1]-[3] (we use the standard notations [4] x1 − x2 = xF and x1x2 = M /s, where xF and M are the Feynman variable and the effective mass of the lepton pair). Actually, the factorization theorem is a reflection of such a similarity. However, for our purpose (diffraction, nuclear shadowing) it is convenient to use the light-cone representation for Drell-Yan process [1]-[3]. In the rest frame of the target proton the projectile beam hadron is surrounded by a parton cloud which contains with a small probability a lepton pair. The freeing of the leptons by means of interaction between the projectile partons and the target is equivalent to the Drell-Yan mechanism [4] of lepton pair production. The cross section of lepton pair production can be represented in a factorized form [1]-[3]