Search results for "distribution function"

EPPS16: Nuclear parton distributions with LHC data

2017

We introduce a global analysis of collinearly factorized nuclear parton distribution functions (PDFs) including, for the first time, data constraints from LHC proton-lead collisions. In comparison to our previous analysis, EPS09, where data only from charged-lepton-nucleus deep inelastic scattering (DIS), Drell-Yan (DY) dilepton production in proton-nucleus collisions and inclusive pion production in deuteron-nucleus collisions were the input, we now increase the variety of data constraints to cover also neutrino-nucleus DIS and low-mass DY production in pion-nucleus collisions. The new LHC data significantly extend the kinematic reach of the data constraints. We now allow much more freedom…

First global next-to-leading order determination of diffractive parton distribution functions and their uncertainties within the {\tt xFitter} framew…

2018

We present {\tt GKG18-DPDFs}, a next-to-leading order (NLO) QCD analysis of diffractive parton distribution functions (diffractive PDFs) and their uncertainties. This is the first global set of diffractive PDFs determined within the {\tt xFitter} framework. This analysis is motivated by all available and most up-to-date data on inclusive diffractive deep inelastic scattering (diffractive DIS). Heavy quark contributions are considered within the framework of the Thorne-Roberts (TR) general mass variable flavor number scheme (GM-VFNS). We form a mutually consistent set of diffractive PDFs due to the inclusion of high-precision data from H1/ZEUS combined inclusive diffractive cross sections me…

Production of exotic tetraquarks QQq¯q¯ in heavy-ion collisions at the LHC

2019

We investigate the production of exotic tetraquarks, $QQ\overline{q}\overline{q}\ensuremath{\equiv}{T}_{QQ}$ ($Q=c$ or $b$ and $q=u$ or $d$), in relativistic heavy-ion collisions using the quark coalescence model. The ${T}_{QQ}$ yield is given by the overlap of the density matrix of the constituents in the emission source with the Wigner function of the produced tetraquark. The tetraquark wave function is obtained from exact solutions of the four-body problem using realistic constituent models. The production yields are typically one order of magnitude smaller than previous estimations based on simplified wave functions for the tetraquarks. We also evaluate the consequences of the partial r…

Relativity and constituent quark structure in model calculations of parton distributions

2004

According to recent studies, Parton Distribution Functions (PDFs) and Generalized Parton Distributions (GPDs) can be evaluated in a Constituent Quark Model (CQM) scenario, considering the constituent quarks as composite objects. In here, a fully covariant model for a system of two particles, together with its non relativistic limit, are used to calculate PDFs and GPDs. The analysis permits to realize that by no means the effects of Relativity can be simulated taking into account the structure of the constituent particles, the two effects being independent and necessary for a proper description of available high energy data in terms of CQM.

2019

Abstract The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted with the hadron transverse momentum P T , allow for the extraction of important transverse-momentum-dependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information on the Sivers function, which is a leading-twist distribution that arises from a correlation between the transverse momentum of an unpolarised quark in a transversely polarised nucleon and the spin of the nucleon. Using the high-statistics data collected by the COMPASS Collaboration in 2010 with a transversely polarised proton target, we have evaluated two types of P T -weighted…

Double Parton Distributions in Light-Front Constituent Quark Models

2014

Double parton distribution functions (dPDF), accessible in high energy proton-proton and proton nucleus collisions, encode information on how partons inside a proton are correlated among each other and could represent a tool to explore the 3D proton structure. In recent papers, double parton correlations have been studied in the valence quark region, by means of constituent quark models. This framework allows to understand clearly the dynamical origin of the correlations and to establish which, among the features of the results, are model independent. Recent relevant results, obtained in a relativistic light-front scheme, able to overcome some drawbacks of previous calculations, such as the…

Double parton correlations in Light-Front constituent quark models

2014

Double parton distribution functions (dPDF) represent a tool to explore the 3D proton structure. They can be measured in high energy proton-proton and proton nucleus collisions and encode information on how partons inside a proton are correlated among each other. dPFDs are studied here in the valence quark region, by means of a constituent quark model, where two particle correlations are present without any additional prescription. This framework allows to understand the dynamical origin of the correlations and to clarify which, among the features of the results, are model independent. Use will be made of a relativistic light-front scheme, able to overcome some drawbacks of the previous cal…

Advanced trap spectroscopy using the glow rate technique based on bleaching of color centers

2001

Abstract The glow rate technique (GRT) is the extension of the known heating rate method to the full glow curve. The GRT like the fractional glow technique (FGT) offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated recombination kinetics at different heating rates. The extension of the GRT to the direct measurements of thermostimulated bleaching of the radiation-induced color centers is presented. The experimental procedure involves measurements of the deca…

Glow Rate Technique for Spectroscopy of Complex Thermostimulated Relaxation Processes

1996

The glow rate technique (GRT) developed for the analysis of complex trap spectra, is the extension of the known heating rate method to the full glow curve. It is shown that using two glow curves measured at different heating rate constants, a special mean activation energy of simultaneously emptied traps can be obtained as a function of temperature or emitted light sum to a good approximation. Expressions have been derived for the calculation of the mean activation energy function from data measured using a linear, logarithmic or a hyperbolic heating mode. Theoretical expressions for the mean activation energy function have been obtained and discussed for arbitrary trap distribution functio…

Trap Spectroscopy by the Glow Rate Technique using Bleaching of Colour Centres

2002

An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF 3 :Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F A and F…