S-storage operators

In 1990, J.L. Krivine introduced the notion of storage operator to simulate, for Church integers, the "call by value" in a context of a "call by name" strategy. In this present paper, we define, for every $\lambda$-term S which realizes the successor function on Church integers, the notion of S-storage operator. We prove that every storage operator is a $S-storage operator. But the converse is not always true

Nucleon Transverse Structure at COMPASS

COMPASS is a fixed target experiment at CERN. Part of its physics programme is dedicated to study the transverse spin and the transverse momentum structure of the nucleon using SIDIS. For these measurements, data have been collected using transversely polarised proton and deuteron targets. A selection of recent measurements of azimuthal asymmetries using data collected with transversely polarised protons is presented.Comment: 4 pages, 3 figures, PANIC 201

Review of COMPASS results on transverse-spin effects in SIDIS

The transversity parton distribution remains a poorly known cornerstone in the nucleon spin structure. While the Collins effect in spin asymmetries in Semi-Inclusive DIS (SIDIS) is one crucial tool to address the transversity function, the most promising alternative is the azimuthal asymmetry in SIDIS when a hadron pair is detected in the final state. In this case, the chiral-odd transversity function is coupled to another chiral-odd function, i.e. the hadron-pair interference fragmentation function (IFF). The measurement of azimuthal asymmetries in hadron-pair production on a transversely polarised nucleon target has been performed at COMPASS using a 160 GeV/c muon beam of CERN's M2 beam line. Results from the 2007 and 2010 recent measurements will be presented and compared to model predictions.Comment: 8 pages, 6 figures, The European Physical Society Conference on High Energy Physics, EPS-HEP2013, 18-24 July, 2013, Stockholm, Swede

Study of the hadronisation process from single hadron and hadron-pair production in SIDIS at COMPASS

Hadron production in hard scattering reactions is described by the hadronization mechanism which combines quarks into final-state hadrons. Within the theoretical framework of leading-twist collinear QCD, the cross section for hadron production in semi-inclusive deep-inelastic scattering can be factorized into a hard scattering cross section describing the hard interaction at the quark level calculable in perturbative QED, and non-perturbative universal functions: parton distribution functions which reflect the quark structure of initial-state hadrons and collinear fragmentation functions which encode details on the hadronization process. In the last decades, a major effort has been achieved on theoretical and experimental levels and allowed to constraint, with very high precision, parton distribution functions except strange quark distribution, which still carries large uncertainties. Fragmentation functions, however, remain at a very preliminary stage of study with a growing interest in a more accurate and precise knowledge. Nowadays, while pion fragmentation functions are known with a limited precision and kaon fragmentation functions are poorly known, the situation for dihadron fragmentation functions turns out to be behind the schedule and no studies or measurements have been yet performed.Measuring both single hadron and hadron pair multiplicities in semi-inclusive deep inelastic scattering at COMPASS represent a fundamental contribution towards a better understanding of the hadronization process and a first measurement for hadron pair multiplicities in SIDIS. These measurements will be presented and discussed.Comment: 4 pages, 5 figures, contribution given at the 20th International Symposium on Spin Physics (SPIN2012) JINR, Dubna, Russia, September 17 - 22, 2012. To be published in "Physics of Elementary Particles and Atomic Nuclei" review journa