The Spin Structure of the Nucleon

The present status of the nucleon's spin structure is reviewed with emphasis on new experimental results.Comment: Invited talk presented at the XIX International Symposium on Lepton and Photon Interactions, Stanford University, August 9-14, 1999, 16 pages, 15 figure

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

Why there is no crisis of the "spin crisis"

In a recent eprint [1] it is argued that the experimental determinations of the spin-dependent structure function g1 have been done incorrectly and that a reanalysis of those data suggests that the original motivation to argue fora "spin crisis", namely the small contribution of quark spins to the nucleon spin, is invalid. In a subsequent note [2] the theoretical understanding, as it has evolved from almost 30 years of theoretical and experimental scrutiny, has been shortly summarised. In this short note, arguments are presented that the line of reasoning in Ref. [1] does not apply, at least not for the Compass data.Comment: 2 pages, no figure

Nucleon longitudinal spin structure at COMPASS

The nucleon spin structure is studied at COMPASS via the measurement of the spin dependent properties of deep inelastic muon-deuteron scattering. Both inclusive and semi-inclusive observables are investigated, with the emphasis put on the latter. This allows to access, in particular, the gluon polarization ($\Delta G/G$) and the flavor decomposition of the quark helicity distributions. Results from measurements with longitudinal target polarization are presented, as well as uncertainties expected from the first 3 years of data taking.Comment: 4 pages, 2 figures. Prepared for 10th International Baryons Conference (Baryons 2004). To be published with the conference proceedings in Nuclear Physics

First measurements of Collins and Sivers asymmetries at COMPASS

COMPASS is a fixed-target experiment on the SPS M2 beamline at CERN. Its LiD target can be polarised both longitudinally and transversally with respect to the longitudinally polarised 160 GeV/c muon beam. Approximately 20% of the beam-time in 2002, 2003 and 2004 was spent in the transverse configuration, allowing the first measurement of both the Collins and Sivers asymmetries on a deuterium target. First results from the the transverse data of the COMPASS run in 2002 are reported here.Comment: 4 pages, 1 figure, contribution to parallel session of BARYONS04, Oct 25-29 2004, Palaiseau, France Removed typo, corrected erroneous referenc

Spin Physics with COMPASS

The recently proposed COMPASS experiment at CERN attempts a measurement of the gluon polarisation with a precision of delta(Delta g/g) = 0.1. The experiment uses open charm muoproduction to tag the photon-gluon fusion process

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