arXiv subjects

Alekhin Sergey

Publications and source records attributed to Alekhin Sergey.

10 recordsLinked to original sources

arXiv2002

Perturbative stability of the QCD analysis of DIS data

We perform pQCD analysis of the existing DIS data for charged leptons with account of corrections up to the NNLO. The parton distributions, value of strong coupling constant, and high-twist terms are extracted and their stability with respect to account of the NNLO corrections is analyzed. All the quantities are generally stable within their experimental errors. Obtained value of the strong coupling constant is $α_s^{\rm NNLO}(M_{\rm Z})=0.1143\pm 0.0014 ({\rm exp})$ with a guess $α_s^{\rm NNNLO}(M_{\rm Z})\sim 0.113$.

hep-ph↗

arXiv2001

Impact of the three-loop corrections on the QCD analysis of the deep-inelastic-scattering data

We perform the analysis of the existing inclusive deep inelastic scattering (DIS) data within NNLO QCD approximation. The parton distributions functions (PDFs) and the value of strong coupling constant $α_{s}(M_Z)=0.1143\pm0.0013 (exp)$ are obtained. The sensitivity of the PDFs to the uncertainty in the value of the NNLO corrections to the splitting functions is analyzed. It is shown that the PDFs errors due to this uncertainty is generally less than the experimental uncertainty in PDFs through the region of $x$ spanned by the existing DIS data.

hep-ph↗

arXiv2000

Global fit to the charged leptons DIS data: \boldmath{$α_{\rm s}$,} parton distributions, and high twists

We perform the NLO QCD analysis of the world data on inclusive deep inelastic scattering cross sections of charged leptons off the proton and the deuterium targets. The parton distributions, the value of strong coupling constant $α_{\rm s}$, and the twist 4 contributions to the structure functions $F_2$ and $F_{\rm L}$ are extracted with the complete account for the correlations of data points due to the systematic errors. Sensitivity of the $α_{\rm s}$ value and the high twist contribution to the procedures of accounting for the systematic errors is studied. The impact of theoretical uncertainties on the value of $α_{\rm s}$ and on the parton distributions is analysed. The obtained value of strong coupling constant with the account of these uncertainties is $α_{\rm s}(M_{\rm Z})=0.1165\pm0.0017({\rm stat+syst}) \pm^{0.0026}_{0.0034}({\rm theor})$. The uncertainties of parton-parton luminosities for the FNAL and LHC colliders are estimated.

hep-ph↗

arXiv2000

Statistical properties of the estimator using covariance matrix

The statistical properties of estimator using covariance matrix for the account of point-to-point correlations due to systematic errors are analyzed. It is shown that the covariance matrix estimator (CME) is consistent for the realistic cases (when systematic errors on the fitted parameters are not extremely large comparing with the statistical ones) and its dispersion is always smaller, than the dispersion of the simplified $χ^2$ estimator applied to the correlated data. The CME bias is negligible for the realistic cases if the covariance matrix is calculated during the fit iteratively using the parameter estimator itself. Analytical formula for the covariance matrix inversion allows to perform fast and precise calculations even for very large data sets. All this allows for efficient use of the CME in the global fits.

hep-ex↗

arXiv1999

The QCD renormalization scale stability of high twists and $α_s$ in deep inelastic scattering

A sensitivity of twist-4 and $α_s$ values extracted in the NLO QCD analysis of nonsinglet SLAC-BCDMS-NMC deep inelastic scattering data to the choice of QCD renormalization scale (RS) is analysed. It is obtained that the high twist (HT) contribution to structure function $F_2$, is retuned with the change of RS. This retuning depends on the choice of starting QCD evolution point $Q_0$ and x. At $Q_0 > 10 GeV^2$ the HT contribution to $F_2$ is retuned at small $x$ and almost not retuned at large $x$; at small $Q_0$ it exhibits approximate RS stability for all x in question. The HT contribution to $F_ L$ is RS stable for all $Q_0$ and x. The RS sensitivity of $α_s$ also depends on the choice of $Q_0$: at large $Q_0$ this sensitivity is weaker, than at small one. For $Q_0^2=9 GeV^2$ the value $α_s(M_Z)=0.1183\pm0.0021(stat+syst)\pm0.0013(RS)$ is obtained. Connection with the higher order QCD corrections is discussed.

hep-ph↗

arXiv1999

Value of $α_s$ and high twists from combined analysis $e-μ$ DIS data

We perform a NLO QCD analysis of the combined SLAC-BCDMS-NMC-E665-H1-ZEUS data on inclusive deep inelastic cross section. Particular attention was paid to the extraction of strong coupling constant $α_s$ and high twist (HT) contribution to the structure functions $F_2$ and $F_L$. It was shown that at small and moderate x there is a visible dependence of the extracted values of HT contribution to $F_2$ on the QCD renormalization scale, which indicates that in this region extracted HT can absorb NNLO QCD corrections. At larger x the dependence of HT on the renormalization scale is negligible and the influence of NNLO correction on their values should be less significant. The value of $α_s(M_Z)=0.1159\pm0.0031$ (total) is obtained, where the error includes statistical, systematical and theoretical uncertainties.

hep-ph↗

arXiv1999

Combined analysis of SLAC-BCDMS-NMC data at high x: α_s and high twists

We perform a NLO QCD analysis of the nonsinglet part of the combined SLAC-BCDMS-NMC data on inclusive deep inelastic cross section with the extraction of $α_s$. We show that the value of $α_s$ obtained in the analysis is sensitive to the statistical inference procedures dealing with systematic errors on the data. The fit with the complete account of point-to-point correlations of the data gives the value of $α_s(M_Z)=0.1183\pm0.0021(exp.)\pm0.0013(ren.scale)$ that is compatible with the LEP measurements and the world average. Model independent x-shape of high twist contributions to the structure functions $F_L$ and $F_2$ is extracted. Twist-4 contribution to $F_L$ is found to be in qualitative agreement with the predictions of infrared renormalon model. Twist-6 contribution to $F_L$ exhibit weak trend to negative values, and twist-6 contribution to $F_2$ - to positive values, although both are compatible with zero within errors.

hep-ph↗

arXiv1999

High twist contribution to the longitudinal structure function $F_L$ at high $x$

We performed NLO QCD fit of combined SLAC/BCDMS/NMC DIS data at high $x$. Model independent x-shape of high twist contribution to structure function $F_L$ is extracted. Twist-4 contribution is found to be in fair agreement with the predictions of infrared renormalon model. Twist-6 contribution exhibits weak tendency to negative values, although in the whole is compatible with zero within errors.

hep-ph↗

arXiv1999

The NLO DGLAP extraction of $α_s$ and higher twist terms from CCFR $xF_3$ and $F_2$ structure functions data for $νN$ DIS

We performed the detailed NLO analysis of the combined CCFR $xF_3$ and $F_2$ structure functions data and extracted the value of $α_s$, parameters of distributions and higher-twist (HT) terms using the direct solution of the DGLAP equation. The value of $α_s(M_Z)=0.1222\pm 0.0048 (exp)\pm 0.0040(theor)$ was obtained. The result has larger central value and errors, than the original result of the CCFR collaboration, in view of the incorporation into the fits of the HT terms as the free model independent parameters. The $x$-shapes of the HT contributions to $xF_3$ and $F_2$ are in agreement with the results of other model-independent extractions and are in qualitative agreement with the predictions of the infrared renormalon model. We also argue that the low $x$ CCFR data might have the defects, since their inclusion into the fits led to the following low $x$-behaviour of the gluon distribution $xG(x,9 GeV^2) \sim x^{0.092\pm 0.0073}$, in contradiction with the results of its extraction from low $x$ HERA data.

hep-ph↗

arXiv1998

On the value of $α_s$ from the analysis of the SLAC/BCDMS deep inelastic scattering data

We performed NLO QCD analysis of the nonsinglet part of the combined SLAC/BCDMS data on $F_2$ with the extraction of $α_s$ and high twist contribution. It was shown that the value of $α_s$ obtained in the analysis is sensitive to the statistical inference procedures dealing with systematic errors on the data. The fit with the complete account of point-to-point correlations of the data gave the value of $α_s(M_Z)=0.1180\pm0.0017 (68% C.L.)$, to be compared with the previously reported value of $α_s(M_Z)=0.113\pm0.003 (99% C.L.)$. This new value of $α_s$ is compatible with the LEP measurements and the world average. The high twist contribution being strongly anti-correlated with the value of $α_s$ became lower than it was previously reported.

hep-ph↗