Moments of polarized parton distribution functions

We present novel results for the first moment of the spin-dependent structure function g ₁(x,Q ²) of the nucleon at small (Q ² < 0.3 GeV²) photon virtuality in the framework of a relativistic formulation of baryon chiral perturbation theory. We perform a next-to-leading order calculation and obtain significant differences to previously found results based on the heavy-baryon approach for the proton and neutron.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.39.Fe Chiral Lagrangians - 14.20.Dh Protons and neutrons     

Old and new parton distribution and fragmentation functions

A short review of problems with parton distribution functions in nucleons, non-polarized and polarized, is given. The main part is devoted to the transversity distribution its possible measurement and its first experimental probe via spin asymmetry in semi-inclusive DIS. It is argued that the proton transversity distribution could be successfully measured in future DIS experiments with longitudinally polarized target.     

Dynamical and thermal descriptions in parton distribution functions

We suggest a duality between the standard (dynamical) and statistical distributions of partons in the nucleons. The temperature parameter entering into the statistical form for the quark distributions is estimated. It is found that this effective temperature is practically the same for the dependence on longitudinal and transverse momenta and, in turn, it is close to the freeze-out temperature in high-energy heavy-ion collisions.     

Measurement of the polarized parton distribution functions at HERMES

The HERMES experiment at DESY has measured the inclusive and semi-inclusive double-spin asymmetries of polarized positrons scattering from polarized hydrogen and deuterium targets in the kinematic range of Bjørken-x 0.023 < x < 0.06 and 1 GeV ² < Q ² < 10 GeV². A RICH detector was installed for the deuterium running period and by providing the identification of charged pions and kaons has enabled the first measurement of charged kaon asymmetries. Based on the measured proton and deuterium asymmetries the polarized quark distributions have been extracted in leading-order pQCD.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Hb Total and inclusive cross-sections (including deep-inelastic processes) - 13.88. + e Polarization in interactions and scatteringJ. Stewart: For the HERMES Collaboration     

Statistical effect in the parton distribution functions of the nucleon

A new and simple statistical approach is performed to calculate the parton distribution functions (PDFs) of the nucleon in terms of light-front kinematic variables. We do not put in any extra arbitrary parameter or corrected term by hand, which guarantees the stringency of our approach. Analytic expressions of the x-dependent PDFs are obtained in the whole x   region [0,1]$[0,1]$, and some features, especially the low-x rise, are more agreeable with experimental data than those in some previous instant-form statistical models in the infinite-momentum frame (IMF). Discussions on heavy-flavored PDFs are also presented.     

Extent of sensitivity of single photon production to parton distribution functions

We have studied the production of single isolated prompt photons in high-energy proton–proton collisions at the RHIC ( \(\sqrt {s}\) = 200 GeV) and the LHC ( \(\sqrt {s}\) = 7 TeV) energies within the framework of perturbative QCD upto next-to leading order of strong coupling (α _s). We have used five different parametrizations of parton distribution function (PDF) starting from the old CTEQ4M to the new CT10 distributions and compared our results with the recent single-prompt photon data from the PHENIX and the CMS Collaborations. The prompt photon cross-section is found to be described equally well by all the PDFs within the experimental errors at the RHIC and the LHC energies. The deviation in the single-prompt photon yield for different PDF sets is within ±20% when compared to CTEQ4M, indicating the upper bound of uncertainty in determining the gluon density. The diphoton measurement could be a potential candidate to constrain the gluon distribution inside the proton.     

A model calculation of double parton distribution functions of the pion

Two-parton correlations in the pion are investigated in terms of double parton distribution functions. A Poincaré covariant light-front framework has been adopted. As non perturbative input, the pion wave function obtained within the so-called soft-wall AdS/QCD model has been used. Results show how novel dynamical information on the structure of the pion, not accessible through one-body quantities, are encoded in double parton distribution functions.     

The impact of target mass correction on polarized parton distribution functions

Considering the nonzero mass effect of the target in extracting polarized parton distribution functions (PPDFs) in preasymptotic region is not negligible. We extract PPDFs from available proton structure function data and study the numerical effects of target mass corrections (TMCs). PPDFs with and without this correction are compared.     

Single diffractive hadron-nucleus interactions within the dual parton model

Single diffractive hadron-nucleus interactions are studied within the framework of the dual parton model. Introducing a diffractive component into the Monte-Carlo event generator DTUNUC we investigate particle production and the dependence of the diffractive cross section on the atomic number of the target nucleus. A comparison of the numerical results with recent experimental data is presented. We furthermore introduce hadronic cross section fluctuations and discuss their influence on diffractive proton-nucleus cross sections.     

First glances at the transversity parton distribution through dihadron fragmentation functions

We present first observations of the transversity parton distribution based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. The extraction of transversity relies on the knowledge of dihadron fragmentation functions, which we take from electron-positron annihilation measurements. This is the first attempt to determine the transversity distribution in the framework of collinear factorization.     

Structure functions and parton distributions

We review recent developments in the determination of parton densities from deep inelastic and related data. We show how the asymmetries observed in theW ^± rapidity distributions and inpp/pn Drell-Yan production further constrain the partons at moderatex.