17 research outputs found
The Recoil Proton Polarization: a new discriminative DVCS observable
Generalized parton distributions describe the correlations between the
longitudinal momentum and the transverse position of quarks and gluons in a
nucleon. They can be constrained by measuring photon leptoproduction
observables, arising from the interference between Bethe-Heitler and Deeply
virtual Compton scattering processes. At leading-twist/leading-order, the
amplitude of the latter is parameterized by complex integrals of the GPDs {H,
E, \~H, \~E} . As data collected on an unpolarized or longitudinally polarized
target constrains H and \~H, E is poorly known as it requires data collected
with a transversely polarized target, which is very challenging to implement in
fixed target experiments. The only alternative considered so far has been DVCS
on a neutron with a deuterium target, while assuming isospin symmetry and
absence of final-state interactions. Today, we introduce the polarization of
the recoil proton as a new DVCS observable, highly sensitive to E, which
appears feasible for an experimental study at a high-luminosity facility such
as Jefferson Lab
Consistent Feature Construction with Constrained Genetic Programming for Experimental Physics
A good feature representation is a determinant factor to achieve high
performance for many machine learning algorithms in terms of classification.
This is especially true for techniques that do not build complex internal
representations of data (e.g. decision trees, in contrast to deep neural
networks). To transform the feature space, feature construction techniques
build new high-level features from the original ones. Among these techniques,
Genetic Programming is a good candidate to provide interpretable features
required for data analysis in high energy physics. Classically, original
features or higher-level features based on physics first principles are used as
inputs for training. However, physicists would benefit from an automatic and
interpretable feature construction for the classification of particle collision
events.
Our main contribution consists in combining different aspects of Genetic
Programming and applying them to feature construction for experimental physics.
In particular, to be applicable to physics, dimensional consistency is enforced
using grammars.
Results of experiments on three physics datasets show that the constructed
features can bring a significant gain to the classification accuracy. To the
best of our knowledge, it is the first time a method is proposed for
interpretable feature construction with units of measurement, and that experts
in high-energy physics validate the overall approach as well as the
interpretability of the built features.Comment: Accepted in this version to CEC 201
Accessing pion GPDs through the Sullivan process: is it feasible?
Describing hadronic structure is one of the most intriguing problems in physics. In this respect, generalized parton distributions (GPDs) constitute an outstanding tool, allowing to draw âthree dimensional picturesâ of hadronâs inside. Starting from contemporary models for pionâs GPDs fulfilling all constraints imposed by QCD, we compute Compton form factors of pions subjected to deeply virtual Compton scattering. We show CFFâs behaviour to be gluon-dominated at EICâs kinematics. Finally we evaluate lepton-beam-spin asymmetries in the Sullivan process, demonstrating the existence of such and thus triggering optimism about the possibility of probing pionâs 3D structure at electron-ion colliders
Electroproduction de photon et de Ïâ° au laboratoire Jefferson-Hall A
Defined in the mid 90's, the generelized parton distributions (GPDs) represent a higher level of information than the form factors and parton distribution fuctions: indeed they encapsulate the correlation between the fraction of longitudinal momentum and the transverse position of the partons inside the nucleon. Consequently we can access the distribution of the partons in the transverse plane according to their longitudinal momentum. Moreover we can derive the total angular orbital momentum of quarks thanks to Ji's sum rule. Experimentally, we access the GPDs through the study of deep exclusive processes (asymmetries, cross sections,...). A worldwide experimental program started in the early 2000's. This thesis presents two data analyses carried on two data sets from experiments running at Jefferson laboratory - Hall A in 2004 and 2010. From the 2004 data set, we have extracted unpolarized and polarized photon electroproduction cross sections. A careful study of the systematic errors has greatly improved the quality of the results. They seem to indicate the necessity to take into account target-mass and finite-t corrections up to twist-4. From the 2010 data set, we have performed the first separation of the longitudinal and transverse responses of neutral pion electroproduction. The results confirm the assumption of a significant contribution of the transverse response although kinematically suppressed with respect to the longitudinal response. These results of high precision validate the GPD approach and will allow to improve the existing models.Définies aux milieux des années 1990, les distributions de partons généralisées (GPDs) représentent un degré d'information supérieur aux facteurs de formes et fonctions de distributions de partons: en effet elles conservent la corrélation entre fraction d'impulsion longitudinale et position transverse des partons dans le nucléon. Par conséquent les GPDs permettent d'accéder à la distributions des partons dans le plan transverse en fonction de leur impulsion longitudinale. De plus il est possible de calculer le moment orbital angulaire total des quarks par le biais de la rÚgle de somme de Ji. Nous accédons expérimentalement aux GPDs par des observables liées à des processus exclusifs (asymmétries, sections efficaces,...). Un programme expérimental mondial a commencé au début des années 2000 afin de caractériser les GPDs. Ce document décrit l'analyse de données de deux expériences réalisées en 2004 et 2010 dans le Hall A au laboratoire Jefferson en Virginie. A partir des données de 2004, nous avons extrait les sections efficaces d'électroproduction de photon polarisées et non polarisées. Une étude approfondie des erreurs systématiques a significativement améliorée la qualité des résultats. Ces derniers semblent indiquer la nécessité de prendre en compte les corrections de cible massive et de transfert d'impulsion fini jusqu'au twist-4. A partir des données 2010, nous avons réalisé pour la premiÚre fois une séparation des réponses longitudinale et transverse de l'électroproduction de pions neutres. Les résultats ont confirmé l'hypothÚse d'une contribution transverse significative bien qu'étant de twist supérieur par rapport à la contribution longitudinale. Ces données de haute précision, que ce soit pour le photon ou le pion neutre, valident le formalisme des GPDs et permettront d'affiner les modÚles afin de réaliser la tomographie 3D du nucléon
New JLab/Hall A Deeply Virtual Compton Scattering results
New data points for unpolarized Deeply Virtual Compton Scattering cross sections have been extracted from the E00-110 experiment at Q=1.9~GeV effectively doubling the statistics available in the valence region. A careful study of systematic uncertainties has been performed