arXiv subjects

D. B. Stamenov

Publications and source records attributed to D. B. Stamenov.

13 recordsLinked to original sources

arXiv2004

The Role of Higher Twist in Determining Polarized Parton Densities from DIS data

Different methods to extract the polarized parton densities from the world polarized DIS data are considered. The higher twist corrections $h^N(x)/Q^2$ to the spin dependent proton and neutron $g_1$ structure functions are found to be non-negligible and important in the QCD analysis of the present experimental data. Their role in determining the polarized parton densities in the framework of the different approaches is discussed.

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arXiv2003

Importance of Higher Twist Corrections in Polarized DIS

The higher twist corrections $h^N(x)/Q^2$ to the spin dependent proton and neutron $g_1$ structure functions are extracted from the world data on $g_1(x,Q^2)$ in a model independent way and found to be non-negligible. Their role in determining the polarized parton densities in the nucleon is discussed. It is also considered how the results are influenced by the recent JLab and HERMES/d inclusive DIS data.

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arXiv2003

On the Role of Higher Twist in Polarized Deep Inelastic Scattering

The higher twist corrections $h^N(x)/Q^2$ to the spin dependent proton and neutron structure functions $g_1^N(x, Q^2)$ are extracted in a model independent way from experimental data on $g_1^N$ and found to be non-negligible. It is shown that the NLO QCD polarized parton densities determined from the data on g1, including higher twist effects, are in good agreement with those found earlier from our analysis of the data on g1/F1 and A1 where higher twist effects are negligible. On the contrary, the LO QCD polarized parton densities obtained from the data on g1, including higher twist, differ significantly from our previous results.

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arXiv2002

Can the polarization of the strange quarks in the proton be positive ?

Recently, the HERMES Collaboration at DESY, using a leading order QCD analysis of their data on semi-inclusive deep inelastic production of charged hadrons, reported a marginally positive polarization for the strange quarks in the proton. We argue that a non-negative polarization is almost impossible.

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arXiv2002

A New Evaluation of Polarized Parton Densities in the Nucleon

We present a new leading and next-to-leading QCD analysis of the world data on inclusive polarized deep inelastic scattering. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to the newly incorporated SLAC/E155 proton data is discussed.

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arXiv2000

On the Sensitivity of the Polarized Parton Densities to Flavour SU(3) Symmetry Breaking

Motivated by the possibility that it may be misleading to assume SU(3) symmetry in the analysis of hyperon β-decays, we study the sensitivity of the polarized parton densities, derived from the world data on inclusive polarized deep inelastic lepton-nucleon scattering, to variation of the value of the nonsinglet axial charge a_8 from its SU(3) value of 3F-D.

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arXiv1998

Scheme Dependence in Polarized Deep Inelastic Scattering

We study the effect of scheme dependence upon the NLO QCD analysis of the world data on polarized DIS. The reliability of an analysis at NLO is demonstrated by the consistency of our polarized densities with the NLO transformation rules relating them to each other. We stress the importance of the chiral JET scheme in which all the hard effects are consistently absorbed in the Wilson coefficient functions.

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arXiv1998

Polarized Parton Densities in the Nucleon

We present a critical assessment of what can be learnt from the present data on inclusive polarized DIS. We examine critically some of the simplifying assumptions made in recent analyses and study in detail the question of the determination of the gluon, strange sea and valence quark polarized densities. We have also carried out a new NLO QCD analysis of the world data. We find an excellent fit to the data and present our results for the polarized parton densities.

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arXiv1997

NLO QCD Analysis of Polarized Deep Inelastic Scattering

We have carried out a NLO analysis of the world data on polarized DIS in the MS/bare scheme. We have studied two models of the parametrizations of the input parton densities, the first due to Brodsky, Burkhardt and Schmidt (BBS) which gives a simultaneous parametrization for both the polarized and unpolarized densities and in which the counting rules are strictly imposed, the second in which the input polarized densities are written in terms of the unpolarized ones in the generic form Deltaq(x)=f(x)q(x) with f(x) some simple smooth function. In both cases a good fit to the polarized data is achieved. As expected the polarized data do not allow a precise determination of the polarized gluon density. Concerning the polarized sea-quark densities, these are fairly well determined in the BBS model because of the interplay of polarized and unpolarized data, whereas in the second model, where only the polarized data are relevant, the polarized sea-quark densities are largely undetermined.

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arXiv1996

A Possible Explanation of the Excess Jet Production at Large E_T

We demonstrate that the significant discrepancy between the previous predictions of the conventional QCD and the CDF inclusive jet production data could be an indication that the behaviour of the Callan-Symanzik βfunction in QCD corresponds to it having an ultraviolet finite fixed point.

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arXiv1996

Constraints on "Second Order Fixed Point" QCD from the CCFR Data on Deep Inelastic Neutrino-Nucleon Scattering

The results of LO {\it Fixed point} QCD (FP-QCD) analysis of the CCFR data for the nucleon structure function $~xF_3(x,Q^2)~$ are presented. The predictions of FP-QCD, in which the Callan-Symanzik $~β~$ function admits a {\it second order} ultraviolet zero at $~α= α_0~$ are in good agreement with the data. Constraints for the possible values of the $~β~$ function parameter $~b~$ regulating how fast $~α_ s(Q^2)~$ tends to its asymptotic value $~α_{0}\ne 0~$ are found from the data. The corresponding values of $~α_{0}~$ are also determined. Having in mind our recent " First order fixed point" QCD fit to the same data we conclude that in spite of the high precision and the large $~(x,Q^2)~$ kinematic range of the CCFR data they cannot discriminate between QCD and FP-QCD predictions for $~xF_3(x,Q^2)~$.

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arXiv1995

"Fixed point" QCD Analysis of the CCFR Data on Deep Inelastic Neutrino- Nucleon Scattering

The results of LO \it {Fixed Point} QCD (FP - QCD) analysis of the CCFR data for the nucleon structure function $~xF_3(x,Q^2)~$ are presented. The predic- tions of FP - QCD, in which $~α_s(Q^2)~$ tends to a nonzero coupling constant $~α_0~$ as $~Q^2\to \infty~$, are in good agreement with the data. The description of the data is even better than that in the case of LO QCD. The FP-QCD parameter $~α_0~$ is determined with a good accuracy: $~α_0 = 0.198\pm 0.009~$. Having in mind the recent QCD fits to the same data we conclude that unlike the high precision and large $~(x,Q^2)~$ kinematic range of the CCFR data they cannot discriminate between QCD and FP - QCD predictions for $~xF_3(x,Q^2)~$.

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arXiv1994

Once More on the Radiative Corrections to the Nucleon Structure Functions in QCD

A new representation of the next to leading QCD corrections to the nucleon structure functions is given in terms of parton distributions. All $~α_{s}~$ corrections to the leading logarithmic approximation (LLA) are included. In contrast to the similar representations in the literature terms of order $~O(α_{s}^{2})~$ do not attend in our expressions for the nucleon structure functions taken in the next to leading logarithmic approximation. This result is generelized for any order in $~α_{s}~$ beyond the LLA. Terms of order $~O(α^{n}_{s})~$ which belong only to the approximation in consideration are present in such a representation for the structure functions.

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