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Register a new userTransverse pion structure beyond leading twist in constituent models
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The understanding of the pion structure as described in terms of transverse-momentum dependent parton distribution functions (TMDs) is of importance for the interpretation of currently ongoing Drell-Yan experiments with pion beams. In this work we discuss the description of pion TMDs beyond leading twist in a pion model formulated in the light-front constituent framework. For comparison, we also review and derive new results for pion TMDs in the bag and spectator models.
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We present and discuss the theory and phenomenology of the leading twist theory of nuclear shadowing which is based on the combination of the generalization of the Gribov-Glauber theory, QCD factorization theorems, and the HERA QCD analysis of diffraction in lepton-proton deep inelastic scattering (DIS). We apply this technique for the analysis of a wide range of hard processes with nuclei---inclusive DIS on deuterons, medium-range and heavy nuclei, coherent and incoherent diffractive DIS with nuclei, and hard diffraction in proton-nucleus scattering---and make predictions for the effect of nuclear shadowing in the corresponding sea quark and gluon parton distributions. We also analyze the role of the leading twist nuclear shadowing in generalized parton distributions in nuclei and in certain characteristics of final states in nuclear DIS. We discuss the limits of applicability of the leading twist approximation for small x scattering off nuclei and the onset of the black disk regime and methods of detecting it. It will be possible to check many of our predictions in the near future in the studies of the ultraperipheral collisions at the Large Hadron Collider (LHC). Further checks will be possible in pA collisions at the LHC and forward hadron production at the Relativistic Heavy Ion Collider (RHIC). Detailed tests will be possible at an Electron-Ion Collider (EIC) in the USA and at the Large Hadron-Electron Collider (LHeC) at CERN.
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J. P. B. C. de Melo (Laboratorio de Fisica Teorica en Computacional
, Universidade Cruzeiro do Sul
, SP
2014
Using the light-front pion wave function based on a Bethe-Salpeter amplitude model, we study the properties of the pion in symmetric nuclear matter. The pion model we adopt is well constrained by previous studies to explain the pion properties in vacuum. In order to consistently incorporate the constituent up and down quarks of the pion immersed in symmetric nuclear matter, we use the quark-meson coupling model, which has been widely applied to various hadronic and nuclear phenomena in a nuclear medium with success. We predict the in-medium modifications of the pion lectromagnetic form factor, charge radius and weak decay constant in symmetric nuclear matter.
We analyze the CLAS data on the photoproduction of hyperon resonances, as well as the available data for the ground state $Lambda$ and $Sigma ^{0}$ of the CLAS and SLAC-E84 collaborations, by considering constituent-counting rule suggested by perturbative QCD. The counting rule emerges as a scaling behavior of cross sections in hard exclusive reactions with large scattering angles, and it enables us to determine the number of elementary constituents inside hadrons. Therefore, it could be used as a new method for identifying internal constituents of exotic-hadron candidates. From the analyses of the $gamma , p to K^{+} Lambda$ and $K^{+} Sigma ^{0}$ reactions, we find that the number of the elementary constituents is consistent with $n_{gamma} = 1$, $n_{p} = 3$, $n_{K^{+}} = 2$, and $n_{Lambda} = n_{Sigma ^{0}} = 3$. Then, the analysis is made for the photoproductions of the hyperon resonances $Lambda (1405)$, $Sigma (1385)^{0}$, and $Lambda (1520)$, where $Lambda (1405)$ is considered to be a $bar K N$ molecule and hence its constituent number could be five. However, we find that the current data are not enough to conclude the numbers of their constituent. It is necessary to investigate the higher-energy region at $sqrt{s} > 2.8$ GeV experimentally beyond the energy of the available CLAS data for counting the number of constituents clearly. We also mention that our results indicate energy dependence in the constituent number, especially for $Lambda (1405)$. If an excited hyperon is a mixture of three-quark and five-quark states, the energy dependence of the scaling behavior could be valuable for finding its composition and mixture.
We compute the contribution of twist-2 and twist-3 parton distribution functions to the small-$b$ expansion for transverse momentum dependent (TMD) distributions at all powers of $b$. The computation is done by the twist-decomposition method based on the spinor formalism for all eight quark TMD distributions. The newly computed terms are accompanied by the prefactor $(M^2b^2)^n$ and represent the target-mass corrections to the resummed cross-section. For the first time, a non-trivial expression for the pretzelosity distribution is derived.
A simple model of nonfemtoscopic particle correlations in proton-proton collisions is proposed. The model takes into account correlations induced by the conservation laws as well as correlations induced by minijets. It reproduces well the two-pion nonfemtoscopic correlations of like-sign and unlike-sign pions in proton-proton collision events at $sqrt{s} = 900$ GeV analyzed by the ALICE Collaboration. We also argue that similar nonfemtoscopic correlations can appear in the hydrodynamic picture with event-by-event fluctuating nonsymmetric initial conditions that are typically associated with nonzero higher-order flow harmonics.
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