Abstract
The Parton Distributions Functions (PDFs) and the spin structure of the nucleon are studied by the COMPASS experiment at CERN. The transverse momentum dependent (TMD) PDFs of the proton will be accessed via Drell-Yan (DY) dimuon production in negative pion collisions on a NH 3 transversely polarised target. From this measurement the dimuon azimuthal asymmetries will be extracted, that can be related to 4 TMDs known as transversity, pretzelosity, Sivers and Boer-Mulders. The latter 2 TMDs are time-reversal odd distributions and are expected to change their sign when compared with the ones obtained from Semi-Inclusive Deep Inelastic Scattering, also studied in COMPASS. We aim at performing the first polarised DY measurement starting in 2014.
Highlights
The Drell-Yan process, which consists in the quark-antiquark annihilation into a virtual photon giving a lepton pair in the final state, is an excellent tool to study the transverse momentum dependent (TMD) Parton Distributions Functions (PDFs)
The transverse momentum dependent (TMD) PDFs of the proton will be accessed via Drell-Yan (DY) dimuon production in negative pion collisions on a NH3 transversely polarised target
The TMD PDFs are expected to be sizeable in the valence quark region, which is probed by pion induced DrellYan off a fixed target
Summary
The Drell-Yan process, which consists in the quark-antiquark annihilation into a virtual photon giving a lepton pair in the final state, is an excellent tool to study the TMD PDFs. The TMD PDFs are expected to be sizeable in the valence quark region, which is probed by pion induced DrellYan off a fixed target. The DY process is well calculable, the cross-section consists in a sum of terms, each of which contains a convolution of two PDFs. The DY cross-section in LO QCD considering an unpolarised beam and a transversely polarised target can be written as:. The DY cross-section in LO QCD considering an unpolarised beam and a transversely polarised target can be written as: In the COMPASS DY programme four of them will be accessed, namely BoerMulders, Sivers, transversity and pretzelosity, by the measurement of the transverse spin azimuthal asymmetries
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