Narrow Results

Charm production data from HERA may be used to determine the charm quark mass and jet production data from HERA may be used to determine α_s(M_Z). Recent results are summarised.

This contribution attempts to determine the $b$-quark pole mass $M_b$ and $\overline{\mathrm{\text{MS}}}$ running mass ${\bar{m}}_b$ with two different approaches at the next-to-next-to-leading order (NNLO) corrections. At the first approach, we derive a relation between the $b$-quark pole mass $M_b$ and its $\overline{\mathrm{\text{MS}}}$ running mass ${\bar{m}}_b$ at the NNLO corrections based on the perturbative Quantum Chromo Dynamics (pQCD) predictions. At the second approach, we extract numerical values of the $b$-quark pole and $\overline{\mathrm{\text{MS}}}$ running masses based on the NNLO phenomenology of H1 and ZEUS Collaborations combined beauty vertex production experimental data. Then we discuss about the compatibility between the pQCD theory results and phenomenology approach in determination of the $b$-quark pole and $\overline{\mathrm{\text{MS}}}$ running masses at the NNLO corrections. Also, we investigate the role and influence of the $b$-quark mass as an extra degree of freedom added to the input parameters of the Standard Model Lagrangian, on the improvement of the uncertainty band of the proton parton distribution functions (PDFs) and particularly on the gluon distribution.

Quantum chromodynamics is a fundamental non-Abelian gauge theory of strong interactions. The physical quantum chromodynamics vacuum state is a linear superposition of the $n$-vacua states with different topological numbers. Because of the configuration of the gauge fields, the tunneling events can induce the local parity-odd domains. Those interactions that occur in these domains can be affected by these effects. Considering the hadron (nucleon) system, we introduce the parity-odd parton distribution functions in order to describe the parity-odd structures inside the hadron in this paper. We obtain 8 parity-odd parton distribution functions at leading twist for spin-1/2 hadrons and present their properties. By introducing the parity-odd quark–quark correlator, we find the parity-odd effects vanish from the macroscopic point of view. In this paper, we consider the high energy semi-inclusive deeply inelastic scattering process to investigate parity-odd effects by calculating the spin asymmetries.

This paper presents a method for extracting the parton distribution functions (PDFs) at small momentum fractions $x$ and at the next-to-leading order (NLO) accuracy in perturbative quantum chromodynamics. It turns out that the PDFs can be described by the “Fractal” or self-similar distributions at low $x$ below $x<0.01$. To this end, a simple parametrization for the unintegrated PDFs based on the “Fractal” approach is considered. These functions have self-similar behavior at low $x$ and $k_t^2$ for sea quarks and have self-similar behavior at low $x$ for gluon distribution. By integration from these transverse momentum distributions (TMDs), the initial input densities are obtained and the model’s free parameters are then calculated using the experimental data released by the HERA experiment. The small-$x$ experimental datasets on electron–proton ($e^{-}p$) and positron–proton ($e^{+}p$) for natural current (NC) interactions in deep inelastic scattering (DIS) processes at HERA for the range of $1.2<Q^2<500$ (GeV²) and $x<0.01$ are included in this analysis. The uncertainty estimations in this analysis are carried out using the standard “Hessian” method. Considering the overall value of ${\chi }^2∕\mathrm{\text{dof}}$ and theory-to-data comparisons, the results indicate good agreements between the experimental datasets and the theoretical predictions. A detailed comparison is also presented between the model’s predictions for the relevant small-$x$ observable and recent parametrizations for the PDFs.

Charged hadron production in the $e^{+}{e}^{-}$ annihilations at 91 to 206GeV in full phase space and in $\overline{p}p$ collisions at 200 to 900GeV collision energies are studied using nonextensive Tsallis and stochastic Weibull probability distributions. The Tsallis distribution shows better description of the data than the Weibull distribution. The 2-jet modification of the statistical distribution is applied to describe $e^{+}{e}^{-}$ data. The main features of these distributions can be described by a two-component model with soft, collective interactions at low transverse energy and hard, constituent interactions dominating at high transverse energy. This modification is found to give much better description than a full-sample fit, and again Tsallis function is found to better describe the data than the Weibull one pointing at the nonextensive character of the multiparticle production process.

We analyze the charged-particle multiplicity distributions measured by the ALICE experiment, over a wide pseudorapidity range, for $pp$ collisions at $\sqrt{s}=8$, 7 and 2.76 TeV at the LHC. The analysis offers an understanding of particle production in high energy collisions in the purview of a new distribution, the shifted Gompertz distribution. Data are compared with the distribution and moments of the distributions are calculated. A modified version of the distribution is also proposed and used to improve the description of the data consisting of two different event classes: the inelastic and the nonsingle diffractive and their subsets in different windows of pseudorapidity, $\eta$. The distribution used to analyze the data has a wide range of applicability to processes in different fields and complements the analysis done by the ALICE collaboration in terms of various LHC event generators and IP-Glasma calculations.

Measurements of the Drell-Yan production of $W$ and $Z/{\gamma }^{\ast }$ bosons at the LHC provide a benchmark of our understanding of perturbative QCD and probe the proton structure in a unique way. The ATLAS collaboration has performed new measurements for $W^{+}$, $W^{-}$ and $Z/{\gamma }^{\ast }$ boson production, reaching unprecedented precision and strong constraints on parton distribution functions, in particular the strange quark density. Studying jet production in association with a vector boson, perturbative QCD predictions can be tested in a multi-scale environment. Once the QCD aspects of the vector boson production are understood, high precision measurements aim at the tests of the electroweak sector, such as measuring the $W$ boson mass.

Here, a selection of recent ATLAS measurements, as presented at the 21st Particles and Nuclei International Conference, in September 2017 in Beijing, China, is discussed.

We employ an effective Hamiltonian that includes the transverse and longitudinal confinement and the one-gluon exchange interaction with fixed coupling constant. By solving the eigenvalue equation in basis light-front quantization (BLFQ), we generate the light-front wavefunctions (LFWFs) for the nucleon in the valence quark Fock space. Fitting the model parameters, we obtain high quality descriptions of electromagnetic form factors and radius for proton while the results deviate somewhat from experimental data for neutron.

Recent results on the determination of the proton's parton distribution functions by the H1 and ZEUS collaborations at HERA are reviewed. A new set of inclusive and jet cross section measurements are also presented that have the potential to further reduce the present uncertainties of the PDFs.