The QCD Spin Structure of Nucleons (Summary of Parallel Session 2)

This paper attempts to summarise the highlights of the talks presented in Parallel Session II of the SPIN 2004 Symposium dedicated to the QCD spin structure of nucleons. Emphasis is put on new data and theoretical developments.Comment: 10 pages, 14 Figures, Part of Spin 2004 Proceeding

Future Programme of COMPASS at CERN

COMPASS at CERN is preparing for a new series of measurements on the nucleon structure comprising deep virtual Compton scattering and hard exclusive meson production using muon beams, as well as Drell-Yan reactions using a polarised proton target and a negative pion beam. The former will mainly constrain the generalised parton distribution H and determine the transverse size of the nucleon, while the latter measurements will provide information on transverse-momentum dependent parton distribution functions. The projected results of the programme and the necessary hardware upgrades are discussed.Comment: 4 Pages, 5 figures, Proceedings of DIS2012, Bon

Deep inelastic scattering from unpolarised targets

In this paper the experimental status of unpolarised structure functions is reviewed. In particular the latest results from the NMC, E665, CCFR, and HERA experiments are discussed. Emphasis is put on the fixed-target experiments, which cover with high precision the x region relevant for the present polarised DIS experiments.Comment: 25 pages, LaTeX, Invited Talk given at the International School of Nucleon Structure, 1st Course: The Spin Structure of the Nucleon, Erice, Italy, 3--10 August 1995, to be published by World Scientifi

The Spin Structure of the Nucleon

This article reviews our present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon. We discuss present experimental investigations of the nucleon's internal spin structure, the theoretical interpretation of the different measurements and the open questions and challenges for future investigation.Comment: Review, 43 pages, 23 figures, to appear in Reviews of Modern Physic

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise. © 2015

The COMPASS spectrometer at CERN

The COMPASS spectrometer was designed for the NA58 fixed-target experiment at the CERN SPS. The physics aim is the study of the spin structure of the nucleon and the spectroscopy of hadrons with muon and hadron beams. Several novel techniques like Micromegas, GEMs and straw tracking detectors were deployed as well as large area CsI- based photo detectors for the RICH. A powerful DAQ and custom front- end electronics allow very high data rates. The paper focuses on the performance of the spectrometer during the first physics run in 2002 in which 5 billion events corresponding to 260 TByte of data were collected with a 160 GeV muon beam and polarised deuteron target

Nucleon polarised parton distribution functions

An introduction to the present status of spin-dependent parton distribution functions is given. Both, results from lepton scattering experiments and from polarised proton-proton collisions with longitudinal polarisation are included. Particular emphasis is put on recent results for the gluon polarisation, which is a key element in the nucleon spin structure. Very large gluon polarisation scenarios, put forward to explain the small quark spin contribution to the nucleon spin, are now strongly disfavoured