arXiv subjects

Alexander V. Sidorov

Publications and source records attributed to Alexander V. Sidorov.

10 recordsLinked to original sources

arXiv2016

Determination of the fragmentation functions from an NLO QCD analysis of the HERMES data on pion multiplicities

An NLO QCD analysis of the final HERMES data on pion multiplicities is presented and a new set of pion fragmentation functions is extracted from the best fit to the data. We have studied the so-called [x,z] and [Q^2,z] presentations of their data, as given by HERMES, which, in principle, should simply be two different ways of presenting the experimental data. We have based our extraction on an excellent fit to the [Q^2,z] presentation of the data. We also draw attention to what appears to be a problem with the [x,z] presentation of the HERMES data.

hep-ph↗

arXiv2015

New analysis concerning the strange quark polarization puzzle

The fact that analyses of semi-inclusive deep inelastic scattering suggest that the polarized strange quark density $Δs(x) + Δ\bar{s}(x)$ is positive in the measured region of Bjorken x, whereas all analyses of inclusive deep inelastic scattering yield significantly negative values of this quantity, is known as the "strange quark polarization puzzle". We have analyzed the world data on inclusive deep inelastic scattering, including the COMPASS 2010 proton data on the spin asymmetries, and for the first time, the new extremely precise JLab CLAS data on the proton and deuteron spin structure functions. Despite allowing in our parametrization, for a possible sign change, our results confirm that the inclusive data yield significantly negative values for the polarized strange quark density.

hep-ph↗

arXiv2014

Problems with the perturbative QCD interpretation of HERMES data on semi-inclusive lepto-production of pions

A theoretical analysis has been performed of the HERMES semi-inclusive deep inelastic data on the difference between $π^{+}$ and $π^{-}$ multiplicities. It turns out that the application of a standard perturbative QCD analysis, using, as usual, isospin symmetry for the fragmentation functions, leads to a poor description of the deuteron data at small z values. If one allows a breaking of isospin invariance, a good fit to both proton and deuteron data can be achieved for all measured z, but the level of isospin violation, especially at small values of z, is simply not credible. We suspect that the problem is a consequence of using the factorized QCD treatment in a kinematic region where it is unjustified.

hep-ph↗

arXiv2014

Importance of Semi Inclusive DIS Processes in Determining Fragmentation Functions

A NLO QCD analysis of the HERMES and COMPASS data on pion multiplicities is presented. Sets of pion fragmentation functions are extracted from fits to the data and compared with those obtained from other groups before these data were available. The consistency between HERMES and COMPASS data is discussed. We point out a possible inconsistency between the HERMES [x, z] and [Q^2, z] presentations of their data.

hep-ph↗

arXiv2012

Importance of Fragmentation Functions in Determining Polarized Parton Densities

New fragmentation functions (FFs) are extracted from a NLO QCD fit to the preliminary COMPASS data on pion and kaon multiplicities. It is shown that the new kaon FFs are very different from those of De Florian at al. (DSS) and Hirai et al. (HKNS). The sensitivity of the extracted polarized PDFs to the new FFs is discussed.

hep-ph↗

arXiv2011

A Possible Resolution of the Strange Quark Polarization Puzzle ?

The strange quark polarization puzzle, i.e. the contradiction between the negative polarized strange quark density obtained from analyses of inclusive DIS data and the positive values obtained from combined analyses of inclusive and semi-inclusive SIDIS data using de Florian et. al. (DSS) fragmentation functions, is discussed. To this end the results of a new combined NLO QCD analysis of the polarized inclusive and semi-inclusive DIS data, using the Hirai et. al. (HKNS) fragmentation functions, are presented. It is demonstrated that the polarized strange quark density is very sensitive to the kaon fragmentation functions, and if the set of HKNS fragmentation functions is used, the polarized strange quark density obtained from the combined analysis turns out to be negative and well consistent with values obtained from the pure DIS analyses.

hep-ph↗

arXiv2010

QCD Analysis of Polarized Inclusive and Semi-inclusive DIS Data

A new combined NLO QCD analysis of the polarized inclusive and semi-inclusive DIS data is presented. In contrast to previous combined analyses, the 1/Q^2 terms (kinematic - target mass corrections, and dynamic - higher twist corrections) in the expression for the nucleon spin structure function g1 are taken into account. The new COMPASS data are included in the analysis. The impact of the semi-inclusive (SIDIS) data on the polarized parton densities (PDFs) and on the higher twist corrections is demonstrated. The controversial behavior of the polarized strange quark density obtained from the fit to the DIS data alone, and a combined analysis of DIS and SIDIS data is discussed.

hep-ph↗

arXiv2009

Status of Longitudinal Polarized Parton Densities and Higher Twist

The present status of the longitudinal polarized parton densities (PDFs) and the contribution of their first moments to the nucleon spin is discussed. Special attention is paid to the role of higher twist effects in determining the PDFs and to the polarized strange quark and gluon densities, which are still not well determined from the present data.

hep-ph↗

arXiv2007

Progress in the Determination of Polarized PDFs and Higher Twist

The impact of the recent very precise CLAS and COMPASS g1/F1 data on polarized parton densities and higher twist effects is discussed. It is demonstrated that the low Q^2 CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function g1, while the large Q^2 COMPASS data influence mainly the strange quark and gluon polarizations. It is also shown that the uncertainties in the determination of the polarized parton densities are significantly reduced. We find also that the present inclusive DIS data cannot rule out a negative polarized and changing in sign gluon densities. The present status of the proton spin sum rule is discussed.

hep-ph↗

arXiv2005

Higher Twist Effects in Polarized DIS

The size of higher twist corrections to the spin proton and neutron g1 structure functions and their role in determining the polarized parton densities in the nucleon is discussed.

hep-ph↗