12 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
No full textTransverse 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
No full textWe 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
The 3-dimensional distribution of quarks in momentum space
No full textWe present the distribution of unpolarized quarks in a transversely polarized proton in three-dimensional momentum space. Our results are based on the extractions of the unpolarized and Sivers transverse momentum dependent parton distributions (TMDs) in a fully consistent TMD framework
Global extraction of partonic transverse momentum distributions from semi-inclusive deep inelastic scattering and Drell-Yan data
No full textWe 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
A first determination of the unpolarized quark TMDs from a global analysis
No full textTransverse 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
Global fit of unpolarized Transverse Momentum Distributions
No full textIn 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
Flavor dependence of unpolarized quark transverse momentum distributions from a global fit
No full textFlavor dependence of unpolarized quark Transverse Momentum Distributions from a global fit
No full textInternational audienceWe present an extraction of the unpolarized transverse-momentum-dependent parton distribution and fragmentation functions that takes into account possible differences between quark flavors and final-state hadrons. The extraction is based on experimental measurements from Drell-Yan processes and semi-inclusive deep-inelastic scattering, whose combination is essential to distinguish flavor differences. The analysis is carried out at NLL accuracy. The extracted flavor-dependent distributions give a very good description of the data (). The resulting uncertainties take fully into account also the uncertainties in the determination of the corresponding collinear distributions
Transverse-spin-dependent azimuthal asymmetries of pion and kaon pairs produced in muon-proton and muon-deuteron semi-inclusive deep inelastic scattering
No full textA set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised <sup>6</sup>LiD (deuteron) and NH3 (proton) targets is presented. All available data collected in the years 2003–2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of 160GeV/c at the CERN SPS were analysed. The asymmetries provide access to the transversity distribution functions via a fragmentation function that in principle may be independently obtained from e+e− annihilation data. Results are presented, discussed and compared to existing measurements as well as to model predictions. Asymmetries of π+π− pairs measured with the proton target as a function of the Bjorken scaling variable are sizeable in the range x>0.032, indicating non-vanishing transversity distribution and di-hadron interference fragmentation functions. As already pointed out by several authors, the small asymmetries of π+π− measured on the <sup>6</sup>LiD target can be interpreted as indication for a cancellation of u and d-quark transversity distributions
