Abstract
The EMC effect or a modification of parton distributions in bound nucleons as compared to free ones, has been extensively studied during the last 30 years but its full understanding is still lacking. The COMPASS experiment at CERN will provide new results on the EMC effect, originating from the Drell-Yan process and studied in the 190 GeV=c π- beam scattering on the ammonia and tungsten targets. The present understanding of the EMC effect and experimental possibilities of COMPASS in this context are discussed.
Highlights
The momentum distribution functions of the partons within the hadron (q(x, Q2), q(x, Q2), g(x, Q2)), called Parton Distribution Functions (PDFs) describe the internal structure of hadrons in the quarkparton model
At the leading order in QCD the PDFs are related to the structure function F2(x, Q2) which is directly accessible in deep-inelastic charged lepton-nucleon scattering experiments: F2(x, Q2) =
It was found to be different from unity and at least for x 0.7 not following expectations from Fermi-motion calculations. This result demonstrated for the first time that the structure function F2 is modified, when nucleons are embedded in a nucleus
Summary
The momentum distribution functions of the partons within the hadron (q(x, Q2), q(x, Q2), g(x, Q2)), called Parton Distribution Functions (PDFs) describe the internal structure of hadrons in the quarkparton model. They represent the probability densities to find a parton carrying a proton momentum fraction x at a negative four-momentum transfer squared Q2. At the leading order in QCD the PDFs are related to the structure function F2(x, Q2) which is directly accessible in deep-inelastic charged lepton-nucleon scattering experiments: F2(x, Q2) =. Where eq is the quark charge (in units of elementary charge |e|)
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