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First World Measurements in the COMPASS Experiment at CERN

Details

  • Call:

    IDPASC Portugal - PHD Programme 2015

  • Academic Year:

    2015 / 2016

  • Domain:

    Experimental Particle Physics

  • Supervisor:

    Sergio Ramos

  • Co-Supervisor:

    Catarina Quintans

  • Institution:

    Instituto Superior Técnico

  • Host Institution:

    Laboratório de Instrumentação e Física Experimental de Partículas

  • Abstract:

    In the COMPASS experiment collisions of polarised muons with polarised targets (6LiD, NH3) allow the study of the nucleon spin dependent structure functions. One of the main goals has been the extraction, via the Semi-Inclusive Deep Inelastic Scattering (SIDIS), of the contributions of the different quark flavours and of the gluon to the nucleon total spin. The COMPASS International Collaboration has about 220 members from 22 institutes. In the framework of the approved COMPASS programme, in which the LIP group has, together with the Torino group, the leadership, important studies are being addressed leading to the first world measurement of the polarised Drell-Yan (DY) process via its muon pair decay. The COMPASS setup was redesigned in order to perform a dimuon experiment with the use a high intensity pion beam of 190 GeV/c colliding with a NH3 polarised target, in view of the first world measurement of the transversely polarised DY process. Following the pilot run in the fall of 2014, the data taking will start shortly. The aim is the study of azimuthal asymmetries, which allow the extraction of correlations between the parton transverse momentum and the nucleon spin, from which some of the Transverse Momentum Dependent Parton Distribution Functions (TMD PDFs) will be extracted, namely Sivers, Boer-Mulders and pretzelosity functions. Another goal is the comparison of these results with previous COMPASS ones coming from SIDIS. A first objective is to check the QCD prediction that these functions, although universal, change sign between SIDIS and DY. Also addressed will be the study of Psi asymmetries in view of a better understanding of its production mechanism, namely the duality between the Psi and the Drell-Yan productions.