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A bstract By working in QED, we obtain the electron, positron, and photon Parton Distribution Functions (PDFs) of the unpolarised electron at the next-to-leading logarithmic accuracy. The PDFs account for all of the universal effects of initial-state collinear origin, and are key ingredients in the calculations of cross sections in the so-called structure- function approach. We present both numerical and analytical results, and show that they agree extremely well with each other. The analytical predictions are defined by means of an additive formula that matches a large- z solution that includes all orders in the QED coupling constant α , with a small- and intermediate- z solution that includes terms up to O ( α 3 ).

A bstract We illustrate how electron Parton Distribution Functions (PDFs) with next-to-leading collinear logarithmic accuracy must be employed in the context of perturbative predictions for high-energy e + e − -collision processes. In particular, we discuss how the renormalisation group equation evolution of such PDFs is affected by the presence of multiple fermion families and their respective mass thresholds, and by the dependences on the choices of the factorisation and renormalisation schemes. We study the impact of the uncertainties associated with the PDFs on physical cross sections, in order to arrive at realistic precision estimates for observables computed with collinear-factorisation formulae. We do so by presenting results for the production of a heavy neutral object as well as for t t ¯ and W + W − pairs, including next-to-leading-order effects of electroweak origin.

A common library, TMDlib2, for Transverse-Momentum-Dependent distributions (TMDs) and unintegrated parton distributions (uPDFs) is described, which allows for easy access of commonly used TMDs and uPDFs, providing a three-dimensional (3D) picture of the partonic structure of hadrons. The tool TMDplotter allows for web-based plotting of distributions implemented in TMDlib2, together with collinear pdfs as available in LHAPDF.

We present NNFF1.1h, a new determination of unidentified charged-hadron fragmentation functions (FFs) and their uncertainties. Experimental measurements of transverse-momentum distributions for charged-hadron production in proton-(anti)proton collisions at the Tevatron and at the LHC are used to constrain a set of FFs originally determined from electron–positron annihilation data. Our analysis is performed at next-to-leading order in perturbative quantum chromodynamics. We find that the hadron-collider data is consistent with the electron–positron data and that it significantly constrains the gluon FF. We verify the reliability of our results upon our choice of the kinematic cut in the hadron transverse momentum applied to the hadron-collider data and their consistency with NNFF1.0, our previous determination of the FFs of charged pions, kaons, and protons/antiprotons.

We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale μ m determines at which energy scale μ the QCD theory transitions from N F to N F + 1 in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling α S ( μ ) . We study the variation of the matching scales, and their impact on a global PDF fit of the combined HERA data. As the choice of the matching scale μ m effectively is a choice of scheme, this represents a theoretical uncertainty; ideally, we would like to see minimal dependence on this parameter. For the transition across the charm quark (from N F = 3 to 4), we find a large μ m = μ c dependence of the global fit χ 2 at NLO, but this is significantly reduced at NNLO. For the transition across the bottom quark (from N F = 4 to 5), we have a reduced μ m = μ b dependence of the χ 2 at both NLO and NNLO as compared to the charm. This feature is now implemented in xFitter 2.0.0, an open source QCD fit framework.

Achieving the highest precision for theoretical predictions at the LHC requires the calculation of hard-scattering cross sections that include perturbative QCD corrections up to (N)NNLO and electroweak (EW) corrections up to NLO. Parton distribution functions (PDFs) need to be provided with matching accuracy, which in the case of QED effects involves introducing the photon parton distribution of the proton, x γ ( x , Q 2 ) . In this work a determination of the photon PDF from fits to recent ATLAS measurements of high-mass Drell–Yan dilepton production at s = 8  TeV is presented. This analysis is based on the xFitter framework, and has required improvements both in the APFEL program, to account for NLO QED effects, and in the aMCfast interface to account for the photon-initiated contributions in the EW calculations within MadGraph5_aMC@NLO. The results are compared with other recent QED fits and determinations of the photon PDF, consistent results are found.

We analyze deeply virtual Compton scattering on pions projected for a future electron-ion collider and conveyed in the Sullivan process. The relevant amplitude is known to be parametrized by generalized parton distributions. Hence taking advantage of state-of-the-art models for them, supplemented with effective leading-order scale evolution, we evaluate the amplitude for the process to occur and examine the pion’s structure from the perspective of electron-ion colliders. We estimate the expected event-rates for the Sullivan process showing: first, that deeply virtual Compton scattering on pions may be measurable at forthcoming experimental facilities. Second, that gluons may be decisive in the description of pions, driving the behavior of the relevant amplitudes and modulating the expected event-rates.

The nucleolus is a nuclear body where different important molecular processes occurs. Beyond ribosomal biogenesis, other relevant functions were recently assigned to this nuclear region, which are related to cell proliferation control and apoptosis, involvement in telomere formation, transfer RNA modifications and stress sensing. Morphologically it is organized in three main areas: roundish electron-light regions, known as Fibrillar Centers (FCs), surrounded by the Dense Fibrillar Component (DFC). These fibrillary structures lie inside the Granular Component (GC), which constitutes most of the nucleolus. Moreover patches of heterochromatin delimitate the nucleolar periphery, interspaced by euchromatin, with thin strands of condensed chromatin enter the nucleolar body. Some aspects of nucleolar morphology have been correlated to their corresponding molecular activity. It is established that rDNA is present within the FC, DFC, in the perinucleolar heterochromatin and in its intranucleolar strands, whereas ribosomal RNA was localized to DFC and GC. rRNA transcription occurs in the FC/DFC complex, while outside the nucleolus reside transcriptionally inactive rDNA repeats. However we still have little knowledge about the condensed regions of perinucleolar heterochromatin. In order to characterize the molecular activity of this area, we decided to investigate its epigenetics status. We hypothesized that, being a condensed region, it would show the classical markers of repression find in the other nuclear regions characterized by compact chromatin. Indeed we analysed at ultrastructural level the distribution of the histone markers H3K27me3 and H3K9me3, which are known to be involved in chromatin condensation and gene silencing. This study was carried out by immunocytochemistry of these histone marker distributions at electron microscopy. Moreover quantifications and statistics of the marker distributions using bioinformatics tools were carried out. We were able to highlight that not only in all compact regions of the nuclear and nucleolar heterochromatin these two repressive histone markers were present, but also that they were specifically confined to the heterochromatin. From our analysis no significant difference in their density or distributions were found between the nucleolar associated and nuclear heterochromatin. Considering these results, we hypothesize that the general mechanisms of chromatin condensation which involve H3K27me3 and H3K9me3 could be similar in different nuclear domains.