Thesis

Study of the Strange Quark Polarisation Puzzle in the COMPASS Experiment at CERN

• Call:

  IDPASC Portugal - PHD Programme 2014

• Academic Year:

  2014 /2015

• Domain:

  Experimental Particle Physics

• Supervisor:

  Paula Bordalo

• Co-Supervisor:

  Marcin Stolarski

• Institution:

  Instituto Superior Técnico

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  COMPASS is a high-energy physics experiment at CERN. Its purpose is the study of hadron structure, namely a better understanding of the spin structure of the nucleon. In that view, data already collected by COMPASS in previous years of deep inelastic scattering of a muon beam off a polarized target offer a very interesting framework to the deep understanding of nucleon structure, addressing subjects like the gluon polarisation in the nucleon and the polarized parton distribution functions. In particular, the strange quark polarisation puzzle is an interesting open topic. The extraction of strange asymmetries, s↑↑(x) and s↑↓(x), coming from the two experimental spin configurations, parallel and anti-parallel, allows the measurement of both the spin independent and the spin dependent strange parton distributions, s(x) and Δs(x). So far, the results on the measurement of Δs(x) are inconsistent because they are depending on the observed final state. As strange quarks are building blocks of kaons, one expects that the strange quarks polarization should be precisely measured in events where a kaon is detected. These studies are based on very reliable kaon identification, from the RICH detector of COMPASS. Also the gluon polarisation will be addressed and it should use the more advanced tools like artificial Neural Networks or developing other techniques as genetic algorithms.