Browsing by Author "Quaresma, Márcia"
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- Measurement of the Polarised Drell-Yan process at COMPASSPublication . Quaresma, MárciaThe COMPASS experiment at CERN has been playing an important role in the studies of the spin content of the nucleon. The Semi-Inclusive Deep Inelastic Scattering (SIDIS) process gives access to the transverse momentum dependent parton distribution functions (TMDs) by the measurement of azimuthal asymmetries that have been studied in COMPASS and published in recent years. TMDs are also accessible by the transversely polarised Drell-Yan (DY) process which will be measured in COMPASS. This will be the first ever polarised DY measurement. The valence quarks region will be dominant due to the use of a negative pion beam at 190 GeV/c momentum impinging on a transversely polarised ammonia target. The QCD prediction that Sivers TMD change sign when accessed by SIDIS or by DY will be checked by the COMPASS measurement. The data taking is scheduled to start in the fall of this year. After one year of data collection, a statistical error below 2% in the azimuthal asymmetry related to the u quark Sivers function is expected. Details of the final experimental setup will be presented.
- Polarised Drell-Yan measurement in the COMPASS experiment at CERNPublication . Quaresma, MárciaThe COMPASS experiment at CERN has been contributing to the description of the nucleon spin structure, namely the transverse momentum dependent parton distribution functions (TMDs), through the Semi-Inclusive Deep Inelastic Scattering (SIDIS) using a muon beam impinging on polarised targets. These TMD functions are also accessible via the transversely polarised Drell-Yan (DY) process, which will be studied in the next COMPASS data taking, starting this Autumn. This process, in which the proton valence region will be explored, will be studied in collisions of a 190 GeV$/c$ negative pion beam with a transversely polarised ammonia target. The QCD prediction that Sivers TMD change sign when accessed through SIDIS or via DY will be checked by the new COMPASS measurement. Considering one year of data taking, the Sivers azimuthal asymmetry statistical error is expected to be less than 2\%. In addition to the polarised target, other nuclear targets will give the possibility to study unpolarised DY subjects. The experimental setup will be presented, and predictions and expectations will be discussed.
- Study of transverse momentum dependent distributions from polarised Drell-Yan at COMPASSPublication . Quaresma, MárciaThe 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.