1,720,964 research outputs found
Phenomenological analysis of unpolarized partonic Transverse Momentum Distributions and Sivers Function
No full textParton distribution functions describe the internal structure of the nucleon in terms of its elementary constituents (quarks and gluons). They cannot be easily computed from first principles, because they require the ability to carry out Quantum Chromodynamics (QCD) calculations in its nonperturbative regime. Many experimental observables in hard scattering experiments involving hadrons are related to parton distribution functions (PDFs) and fragmentation functions (FFs), in a way that is specified by factorization theorems. Collinear PDFs describe the distribution of partons integrated over all components of partonic momentum except the one collinear to the parent hadron, while TMD PDFs include also the dependence on the transverse momentum k⊥. They can be interpreted as three-dimensional generalizations of collinear PDFs.
Availability of measurements of different processes in different experiments makes it possible to extract PDFs and FFs through so-called global fits. In this thesis we present a first attempt at the extraction of unpolarized TMDs parton distribution and fragmentation functions from a wide set of data, covering a large kinematic region and including measurements taken from semi-inclusive deep-inelastic scattering, Drell-Yan and Z boson production. In the second part of the thesis we analyze a polarized TMDs, the so-called Sivers distribution function, which describes the density of unpolarized partons inside a polarized nucleons. The extraction of the Sivers function is directly connected with the first part of our study, as it requires the knowledge of the unpolarized TMDs.
The work is organized in the following way. In Ch. 2, the theory for transverse momentum dependent parton distribution and fragmentation function is shown, focusing on the unpolarized and on the Sivers distribution. We discuss the relation between the experimental observables and the TMDs and how the latter evolve with respect to their characteristic scales.
In Ch. 3 the general formalism for TMDs in SIDIS, DY processes, and Z production is briefly outlined, including a description of the assumptions and approximations in the phenomenological implementation of TMD evolution equations. We present the data included in the global fit and the criteria for selecting the data analyzed. In the last part we show the results of our analysis and discuss their stability in relation to different choices for the parametrization of our functional form.
In Ch. 4 we discuss our extraction of the Sivers function from SIDIS data on the Sivers asymmetry, coming from Hermes Compass and JLab experiments. In the first part the parametrization and choices for the parametrization and evolution of the Sivers are discussed.
Subsequently, the criteria for selecting the data analysed in the fit are summarized and commented. Finally, the results of our global fit are presented and the agreement between our theoretical prediction and the experimental measurements for the Sivers asymmetry is discussed.
In the final section, we summarize the results and present an outlook for future improvements
Extraction of Transverse Momentum Distributions from semi-inclusive DIS and Drell-Yan data
Full text linkTransverse momentum dependent distribution and fragmentation functions of unpolarized quarks inside unpolarized protons are extracted, for the first time, through a simultaneous analysis of semi-inclusive deep-inelastic scattering, Drell-Yan and Z boson hadroproduction processes. This study is performed at leading order in perturbative QCD, with energy scale evolution at the next-to-leading logarithmic accuracy. Moreover, some specific choices are made to deal with low scale evolution around 1 GeV2. Since only data in the low transverse momentum region are considered, no matching to fixed-order calculations at high transverse momentum is needed
Extraction of partonic transverse momentum distributions from semi-inclusive deep-inelastic scattering, Drell-Yan and Z-boson production
Full text linkWe present an extraction of unpolarized partonic transverse momentum distributions (TMDs) from a simultaneous fit of available data measured in semi-inclusive deep-inelastic scattering, Drell-Yan and Z boson production. To connect data at different scales, we use TMD evolution at next-to-leading logarithmic accuracy. The analysis is restricted to the low-transverse-momentum region, with no matching to fixed-order calculations at high transverse momentum. We introduce specific choices to deal with TMD evolution at low scales, of the order of 1 GeV2. This could be considered as a first attempt at a global fit of TMDs
Global extraction of partonic transverse momentum distributions from semi-inclusive deep inelastic scattering and Drell-Yan data
Full text linkWe discuss a first attempt at a global extraction of unpolarized partonic transverse momentum dependent (TMD) distributions and fragmentation functions from a simultaneous fit of data measured in semi-inclusive deep-inelastic scattering, Drell–Yan and Z boson production. This analysis is performed in the low transverse momentum region, at leading order in perturbative QCD. To connect data at different scales, we use TMD evolution at next-to-leading logarithmic accuracy
Global fit of unpolarized Transverse Momentum Distributions
Full text linkIn this talk we present the latest results by the MAP Collaboration about the extraction of unpolarized quark Transverse-Momentum-Dependent Distributions (TMD PDFs) and Fragmentation Functions (TMD FFs) from global fits of Drell-Yan and Semi-Inclusive Deep-Inelastic Scattering (SIDIS) data sets
A first determination of the unpolarized quark TMDs from a global analysis
Full text linkTransverse momentum dependent distribution and fragmentation functions of unpolarized quarks inside unpolarized protons are extracted, for the first time, through a simultaneous analysis of semi-inclusive deep-inelastic scattering, Drell-Yan and Z boson hadroproduction processes. This study is performed at leading order in perturbative QCD, with energy scale evolution at the next-to-leading logarithmic accuracy. Moreover, some specific choices are made to deal with low scale evolution around 1 GeV2. Since only data in the low transverse momentum region are considered, no matching to fixed-order calculations at high transverse momentum is needed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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