Speaker
Caroline Riedl
(University of Illinois at Urbana-Champaign)
Description
An overview of pion-induced Drell-Yan (DY) scattering at COMPASS is given. In 2015, COMPASS was scattering a 190 GeV pion beam off a transversely polarized proton target and unpolarized nuclear targets. The Sivers asymmetry, and other spin-dependent azimuthal asymmetry amplitudes, were extracted from these data. The Sivers asymmetry is of particular interest since it is expected to change sign between DY and semi-inclusive deep-inelastic (SIDIS) scattering. By averaging the target spins, COMPASS has also access to the spin-independent azimuthal modulation arising from the Boer-Mulders TMD, which allows to study the violation of the so-called Lam-Tun relation. The comparison of cross sections off different nuclear targets provides the pathway to investigating a flavor-dependent EMC effect. A second data set of spin-dependent Drell-Yan data is being taken in the 2018 run and is expected to supersede the precision of the 2015 data by at least 50%. For this DY analysis, COMPASS currently uses the supercomputer Blue Waters (BW) for production of both experimental data (tracking) and simulated Monte Carlo (MC) data. Due to the massive parallel computing resources of BW, experimental data can be processed significantly faster than at CERN, detector efficiency maps can be produced in much greater detail, and MC data can be generated at larger amount, including CPU-intensive tasks such as pile-up.
Primary author
Caroline Riedl
(University of Illinois at Urbana-Champaign)
