Virginia Tech® home

Hadronic Physics Reactions

DIS diagram

DIS diagram
Deep Inelastic Scattering diagram. A lepton "l" is scattered off a proton "P", and a high virtuality photon "gamma" interacts with a quark. The unknown final state is indicated by "X". The quark parton distribution function (pdf) q(x) reflects the probability of interacting with a quark q carrying a momentum fraction x of the proton's momentum.

Deep Inelastic Scattering corresponds to the scattering of a lepton (electron) off the proton, with the exchange of a virtual photon. Thanks to the photon's high virtuality (its 4-momentum squared), it interacts with a quark, which allow to probe the partonic structure of the proton. The proton remnants are undetected. The knowledge of the lepton scattering angle tells us about the longitudinal momentum fraction of the proton's momentum carried by the struck quark. The partonic structure of the proton can be parametrized by "Parton Distribution Functions" (pdf), which can be seen as probabilities of interacting with quarks (or gluons) carrying a certain longitudinal momentum. 

Handbag Diagram
Generic Handbag Diagram for Compton-like Scattering processes off a quark. A real or virtual photon is scattered off a quark of the nucleon, and a real or virtual photon is emitted. We indicate the separation between the "hard" calculable part and the "soft" part which can be parametrized by Generalized Parton Distributions.

Spacelike and Timelike Deeply Virtual Compton Scattering and Double Deeply Virtual Compton Scattering are reactions involving the scattering of real or virtual photons off quarks of the nucleon. As for DIS, the virtuality of at least one of the photon allows to probe the partonic content of the nucleon. These reactions which are sensitive to the longitudinal momentum of the quarks and their transverse position. The partonic structure of the nucleon can be parametrized by Generalized Parton Distributions (GPDs).