The future SIDIS measurement on transversely polarized deuterons by the COMPASS Collaboration

Since 2005, measurements of Collins and Sivers asymmetries from the HERMES and COMPASS experiments have allowed to assess that the transversity and the Sivers PDFs are different from zero and measurable in semi-inclusive DIS on transversely polarised targets. Most of the data were collected on proton targets, only small event samples were collected in the early phase of the COMPASS experiment on a deuteron ($^6$LiD) target and more recently at JLab, on $^3$He, so that the $d$-quark and the sea-quarks PDFs are much more poorly known than the $u$-quark PDFs. This constitutes an important limitation to the knowledge of the transverse spin structure of the nucleon. For this reason the COMPASS Collaboration has proposed to measure semi-inclusive DIS on transversely polarised deuterons with good accuracy, comparable with that of the existing transverse spin asymmetry data on protons. The proposal has been accepted by CERN and the experiment will run in 2021, as soon as the Long Shut-down 2 is over, providing measurements which will stay unique for many years to come. Projections will be given for the extraction of the transversity PDFs, and for the evaluation of the isovector tensor charge of the nucleon.Comment: 9 pages, 5 figure and 2 table

Transverse spin and transverse momentum structure of the nucleon from the COMPASS experiment

A selection is presented of recent results from the COMPASS Collaboration on transverse spin and transverse momentum effects in semi-inclusive deeply inelastic scattering (SIDIS) of 160 GeV/c muons off proton and deuteron targets.Comment: 10 pages, 6 figures, proceedings of the invited talk at the XV Workshop on High Energy Spin Physics DSPIN-13, Dubna, Russia, October 8-12, 201

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

The spin structure of the nucleon: A phenomenological introduction

Abstract The investigation of the spin structure of the nucleon via semi-inclusive deep inelastic scattering on polarised nucleons is updated with the most recent results of the JLab, HERMES, and COMPASS experiments. A short description is given of these experiments, which are complementary in phase space and use sophisticated and different techniques to polarise the nucleon targets. The cases of target spin parallel or orthogonal to the direction of the incoming lepton require different experimental techniques, have a different phenomenology and need a different theoretical treatment. After reviewing these differences, the most recent transverse spin advances are presented, and evidence is given that the new data already allow for a rather precise extraction of the transversity and of the Sivers PDFs

Le Linee di campo : cardine per la comprensione del concetto di campo

This thesis deals with the concept of a field, in particular magnetic and gravitational ones at two school levels: primary and secondary ones.From the analysis of previous research and a deep content analysis, we focused this work on some specific hypothesis of research, based on two principal research questions: 1) can field lines representation facilitate a more global vision of the field (as opposed to the local one) and a differentiation of the different types of field by their maps; 2) can the differentiation of polar and dipolar fields allow students to identify the specific properties of the different types of field.The research hypothesis are presented in two groups, one for each school level, and they are specified in sub-hypotheses, and put to the test. They are mostly related to the distinction between the two effects of magnetic interaction (attraction and orientation), to the conception of magnetic field lines as “lines of orientation” (and not lines of force), to the distinction between unipolar and dipolar field.In two preliminary studies, at primary school, we identified some potentialities and difficulties of this approach at this school level. In particular: the source of magnetic field is more easily recognised by children than that of the gravitational field, in the magnetic interaction the attraction effect is dominant with respect to the rotation effect, and finally children are able to differentiate the shape of magnetic and gravitational fields, but they have some difficulties to pass from the difference between the shapes of field lines to the difference between the actions of the two sources.On the basis of these two preliminary studies at primary school, we designed two teaching-learning sequences about magnetic field, at primary (9-10 years old) and secondary (18-19 years old) school levels.At primary school level, field representation by field lines was accessible at a large part of the children. They where able to identify magnetic field lines with lines of orientation (and not of force) and to differentiate between the maps of the two fields (magnetic and gravitational), but we still observed the difficulty to pass from the difference between the maps to the difference between the actions of the two sources, whereas the obstacle “attraction is dominant”, found in the preliminary researches, seemed overcome.At secondary school level, students used the shape of field lines to differentiate polar and dipolar fields. Field lines were used also to identify the analogies between fields. In this school context, the results of the analysis of the sequence and of the post test show to which extent – in fact: large - the approach proposed helps students consistently progress toward an understanding of the concept of a field. They also suggest guidelines for future research.Ce travail de thèse se centre sur le concept de champ, en particulier sur les champs gravitationnel et magnétique et sur deux principales hypothèses de recherche : 1) la représentation des lignes de champ peut faciliter l'accès à une vision globale du champ (en rupture avec une vision locale dominante) et à une différenciation des divers champs par les formes des lignes; 2) la différenciation des champs polaires et dipolaires peut permettre d'identifier les propriétés spécifiques des divers types de champs. Deux enquêtes préliminaires au niveau de l'école primaire ont permis de développer des séquences d'enseignement concernant le champ magnétique à l'école primaire (9-10 ans) et secondaire (18-19 ans). A l'école primaire la représentation des deux champs à travers les lignes du champ est accessible à une bonne partie des enfants qui identifient les lignes de champ magnétique à des lignes d'orientation (et non "de force"), et différencient la forme des lignes de champ magnétique et gravitationnel mais ils ont des difficultés à retraduire cette différence de cartographie en terme de différence entre les actions des deux sources, tandis que l'obstacle "attraction dominante", relevé dans les études préliminaires, est largement surmonté. Au niveau de l'école secondaire, les élèves utilisent la forme des lignes des champs pour différentier les champs polaires et dipolaires. Les lignes de champ sont utilisées aussi pour identifier les analogies entre les champs. Les indications recueillies en cours de séquence comme lors d'un post test rendent crédible, dans ce contexte scolaire, l'adoption de l'approche proposée ici, et permettent d'orienter les recherches pour l'affiner

Radiative Corrections to High Energy Lepton Bremsstrahlung on Heavy Nuclei

One-loop radiative corrections to the leptonic tensor in high energy bremsstrahlung on heavy nuclei are calculated. Virtual and real photon radiation is taken into account. Double bremsstrahlung is simulated by means of Monte Carlo. Numerical results are presented for the case of muon bremsstrahlung in conditions of the COMPASS experiment at CERN.Comment: 7 pages, 1 figur

Two-Dimensional Hydrodynamic Models of Super Star Clusters with a Positive Star Formation Feedback

Using the hydrodynamic code ZEUS, we perform 2D simulations to determine the fate of the gas ejected by massive stars within super star clusters. It turns out that the outcome depends mainly on the mass and radius of the cluster. In the case of less massive clusters, a hot high velocity ($\sim 1000$ km s$^{-1}$) stationary wind develops and the metals injected by supernovae are dispersed to large distances from the cluster. On the other hand, the density of the thermalized ejecta within massive and compact clusters is sufficiently large as to immediately provoke the onset of thermal instabilities. These deplete, particularly in the central densest regions, the pressure and the pressure gradient required to establish a stationary wind, and instead the thermally unstable parcels of gas are rapidly compressed, by a plethora of re-pressurizing shocks, into compact high density condensations. Most of these are unable to leave the cluster volume and thus accumulate to eventually feed further generations of star formation. The simulations cover an important fraction of the parameter-space, which allows us to estimate the fraction of the reinserted gas which accumulates within the cluster and the fraction that leaves the cluster as a function of the cluster mechanical luminosity, the cluster size and heating efficiency.Comment: Accepted for publication in ApJ; 27 pages, 9 figures, 1 tabl

Effects of Quark Spin Flip on the Collins Fragmentation Function in a Toy Model

The recent extension of the NJL-jet model to hadronization of transversely polarized quarks allowed the study of the Collins fragmentation function. Both favored and unfavored Collins fragmentation functions were generated, the latter purely by multiple hadron emissions, with 1/2 moments of opposite sign in the region of the light-cone momentum fraction $z$ accessible in current experiments. Hints of such behavior has been seen in the measurements in several experiments. Also, in the transverse momentum dependent (TMD) hadron emission probabilities, modulations of up to fourth order in sine of the polar angle were observed, while the Collins effect describes just the linear modulations. A crucial part of the extended model was the calculation of the quark spin flip probability after each hadron emission in the jet. Here we study the effects of this probability on the resulting unfavored and favored Collins functions by setting it as a constant and use a toy model for the elementary single hadron emission probabilities. The results of the Monte Carlo simulations showed that preferential quark spin flip in the elementary hadron emission is needed to generate the favored and unfavored Collins functions with opposite sign 1/2 moments. For the TMD hadron emission modulations, we showed that the model quark spin flip probabilities are a partial source of the higher rode modulations, while the other source is the Collins modulation of the remnant quark from the hadron emission recoil.Comment: 7 pages, 6 figures. To appear in proceedings of HITES 2012, Conference in Honor of Jerry P. Draayer, Horizons of Innovative Theories, Experiments, and Supercomputing in Nuclear Physics, New Orleans, Louisiana, June 4-7, 201