arXiv subjects

A. Courtoy

Publications and source records attributed to A. Courtoy.

At least 37 records · Page 2Linked to original sources

arXiv2017

The Tensor and the Scalar Charges of the Nucleon from Hadron Phenomenology

We discuss the impact of the determination of the nucleon tensor charge on searches for physics Beyond the Standard Model. We also comment on the future extraction of the subleading-twist PDF $e(x)$ from Jefferson Lab soon-to-be-released Beam Spin Asymmetry data as well as from the expected data of CLAS12, as the latter is related to the scalar charge. These analyses are possible through the phenomenology of Dihadron Fragmentation Functions related processes, which we report on here as well.

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arXiv2016

Quark Orbital Angular Momentum in the MIT Bag Model

We present the results for the Generalized Transverse Momentum Distribution related to quark Orbital Angular Momentum, {\it i.e.} $F_{14}$, in the MIT bag model. This model has been modified to include the Peierls--Yoccoz projection to restore translational invariance. Such a modification allows to fulfill more satisfactorily basic sum rules, that would otherwise be less elegantly carried out with the original version. Using the same model, we have calculated the twist-$3$ GPD that corresponds to Orbital Angular Momentum à la Ji, through the Penttinen--Polyakov--Shuvaev--Strikman sum rule. Recently, a new relation between the two definitions of the quark Orbital Angular Momentum at the density level has been proposed, which we illustrate here within the model. The sum rule is fulfilled. Still within the framework of the MIT bag model, we analyze the Wandzura--Wilczek expression for the GPD of interest. The genuine quark-gluon contribution is evaluated directly thanks to the equation of motion of the bag, which allows for a direct control of the kinematical contributions to the twist-3 GPD.

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arXiv2016

Phenomenology of Dihadron Fragmentation Function

We report on the phenomenological results obtained through Dihadron Fragmentation Functions related processes. In 2015, an update on the fitting techniques for the Dihadron Fragmentation Functions has led to an improved extraction of the transversity PDF and, as a consequence, the nucleon tensor charge. We discuss the impact of the determination of the latter on search for physics Beyond the Standard Model, focusing on the error treatment. We also comment on the future of the extraction of the subleading-twist PDF $e(x)$ from JLab soon-to-be-released Beam Spin Asymmetry data.

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arXiv2015

Update on the phenomenology of collinear Dihadron FFs

We summarize recent results obtained thanks to the phenomenology of Dihadron Fragmentation Functions. The results include the update on the fitting techniques for both the Dihadron Fragmentation Functions themselves and the transversity PDF. The determination of the tensor charge of the nucleons as well as the impact of the latter on search for physics beyond the standard model are also discussed. So is the future extraction of the subleading-twist PDF $e(x)$ from JLab soon-to-be-released Beam Spin Asymmetry data.

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arXiv2015

Realistic estimate of valence transversity distributions from inclusive dihadron production

We present an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. The e+e- data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. Then, the transversity distribution has been extracted by using the most recent and more precise COMPASS data for deep-inelastic scattering off proton targets. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

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arXiv2014

Dihadron Fragmentation Functions and Transversity

We present preliminary results for an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets by HERMES and COMPASS allow for a flavor separation of the valence components of transversity, while di-hadron fragmentation functions are taken from the semi-inclusive production of two pion pairs in back-to-back jets in $e^+ e^-$ annihilation. The latter data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. After encoding this piece of information into the deep-inelastic scattering cross section, the transversity has been re-extracted by using the most recent and more precise COMPASS data for proton target. This picture represents the current most realistic estimate of the uncertainties on our knowledge of transversity. The preliminary results indicate that the valence up component seems smaller and with a narrower error band than in previous extraction.

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arXiv2014

Phenomenology of hadron structure --- why low energy physics matters

The description of the internal structure of hadrons is one of the main goal of QCD. At moderate energy scales, the hadronic representation succeeds to the partonic description, rendering challenging the description of the dynamics of scattering processes and hadronic structure. The information on the hadron structure is embodied in the long distance contributions which are defined as Parton Distribution Functions (PDFs). PDFs are a key framework for connecting the low and high-energy regimes, in that the knowledge on non- perturbative QCD carries important consequences at the high-energy level. We here review recent progress in the description of the proton, from complementary approaches such as fits of PDFs, phenomenological analyses and experimental predictions in view of the JeffersonLab upgrade and applications for high-energy colliders.

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arXiv2013

Phenomenology of $α_s$ at intermediate energy: the quark-hadron duality approach

In this contribution to the proceedings, we analyze the transition from perturbative and non- perturbative QCD embedded in the coupling constant. In the study of quark-hadron duality, we suggest that the realization of the latter is related to the inclusion of non-perturbative effects at the level of the coupling constant. The outcome of our analysis is a smooth transition from perturba- tive to non-pertuperturbative QCD physics, embodied in the running of the coupling constant at intermediate scales. While our approach is purely perturbative, we compare our result to various non-perturbative schemes.

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arXiv2013

Detecting correlated di-hadron pairs: about the extraction of transversity and beyond

We summarize the latest achievements about the extraction of the transversity parton distribution and proton tensor charge based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. Recently released data for proton and deuteron targets by HERMES and COMPASS allow for a flavor separation of the valence components of transversity. At variance with the Collins effect, this extraction is performed in the framework of collinear factorization and relies on di-hadron fragmentation functions. The latter have been taken from the first recent analysis of the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. We also comment on the possibility of isolating new azimuthally asymmetric correlations of opposite pion pairs, which could arise when a fragmenting quark crosses parity-odd domains localized in Minkowski space-time and induced by the topologically nontrivial QCD background (the so-called θ vacuum).

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arXiv2013

Analysis of $α_s$ from the realization of quark-hadron duality

We present an analysis of the role of the running coupling constant at the intersection of perturbative and nonperturbative QCD in the context of the quark-hadron duality à la Bloom-Gilman. Our framework will be the unpolarized structure function of the proton in the resonance region. We suggest that the realization of duality is related to the inclusion of nonperturbative effects at the level of the coupling constant. The outcome of our analysis is a smooth transition from perturbative to nonperturbative QCD physics, embodied in the running of the coupling constant at intermediate scales.

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arXiv2013

Valence transversities: the collinear extraction

In these proceedings, we propose an extraction of the valence transversity parton distributions. Based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets, this extraction of transversity is performed in the framework of collinear factorization. The recently released data for proton and deuteron targets at HERMES and COMPASS allow for a flavor separation of the valence transversities, for which we give a complete statistical study.

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arXiv2013

Extraction of $α_s$ from deep inelastic scattering at large $x$

We present an analysis of the role of the running coupling constant at the intersection of perturbative and nonperturbative QCD. Although the approaches that have been considered so far in these two regimes appear to be complementary to each other, a unified description might derive through the definition of the effective coupling, as they both provide ways of analyzing its freezing at low values of the scale. We extract the effective coupling from all available experimental data on the unpolarized structure function of the proton, $F_2^p$, at large values of Bjorken $x$, including the resonance region. We suggest that parton-hadron duality observed in this region can be explained if nonperturbative effects are included in the coupling constant. The outcome of our analysis is a smooth transition from perturbative to nonperturbative QCD physics, embodied in the running of the coupling constant at intermediate scales.

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arXiv2012

First extraction of valence transversities in a collinear framework

We present an extraction of the valence transversity parton distributions based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. Recently released data for proton and deuteron targets at HERMES and COMPASS permit a flavor separation of valence transversities. The present extraction is performed in the framework of collinear factorization, where dihadron fragmentation functions are involved. The latter are taken from a previous analysis of electron-positron annihilation measurements.

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arXiv2012

The Strong Coupling Constant from Hadron Structure Phenomenology

We present recent developments on the role of the running coupling constant at the intersection of perturbative and nonperturbative QCD. A number of experiments show a smooth transition from small to large scales given by the four-momentum transfer in the reactions. This is at variance with perturbative QCD where the running coupling constant becomes infinite when the scale equals $Λ_{\tiny QCD}$. Approaches using an effective coupling constant could help interpret the opposite trend of data as compared to standard perturbative QCD predictions. We give an overview of the role of the coupling constant in the procedure to match nonperturbative hadronic model to perturbative QCD and we propose an extraction of an effective coupling constant from inclusive electron proton scattering data at large Bjorken x.

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arXiv2012

Status on the transversity parton distribution: the dihadron fragmentation functions way

We report on the extraction of dihadron fragmentation functions (DiFF) from the semiinclusive production of two hadron pairs in back-to-back jets in e+e- annihilation. A nonzero asymmetry in the correlation of azimuthal orientations of opposite $π^+π^-$ pairs is related to the transverse polarization of fragmenting quarks through a significant polarized DiFF. A combined analysis of this asymmetry and the spin asymmetry in the SIDIS process $ep^{\uparrow}\to e'(π^+π^-)X$ has led to the first extraction of the u and d-flavor transversity parton distribution function in the framework of collinear factorization.

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arXiv2012

First extraction of Interference Fragmentation Functions from e+e- data

We report on the first extraction of interference fragmentation functions from the semi-inclusive production of two hadron pairs in back-to-back jets in e+e- annihilation. A nonzero asymmetry in the correlation of azimuthal orientations of opposite π+π- pairs is related to the transverse polarization of fragmenting quarks through a significant polarized dihadron fragmentation function. Extraction of the latter requires the knowledge of its unpolarized counterpart, the probability density for a quark to fragment in a π+π- pair. Since data for the unpolarized cross section are missing, we extract the unpolarized dihadron fragmentation function from a Monte Carlo simulation of the cross section.

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arXiv2011

The role of the running coupling constant in the unveiling of the hadronic structure

One of the main open questions in physics is the understanding of the internal structure of the strongly interacting particles, or hadrons. It is still a challenge to describe consistently the dynamics of scattering processes and hadronic structure at moderate energy scales. The study of Parton Distribution Functions (PDFs) sets a connection between the perturbative and non-perturbative worlds, through the following scheme: one builds models consistent with QCD in a moderate energy range, PDFs are evaluated in these models, and, finally, the scale dependence of these distributions is studied. In these proceedings, we revisit the standard procedure to match non-perturbative models to perturbative QCD, using experimental data. The strong coupling constant plays a central role in the QCD evolution of parton densities. We will extend this procedure with a non-perturbative generalization of the QCD running coupling and use this new development to understand why perturbative treatments are working reasonably well in the context of hadronic models. Vice versa, this new procedure broadens the ways of analyzing the freezing of the running coupling constant.

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arXiv2011

First glances at the transversity parton distribution through dihadron fragmentation functions

We present first observations of the transversity parton distribution based on an analysis of pion-pair production in deep inelastic scattering off transversely polarized targets. The extraction of transversity relies on the knowledge of dihadron fragmentation functions, which we take from electron-positron annihilation measurements. This is the first attempt to determine the transversity distribution in the framework of collinear factorization.

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