arXiv subjects

Ali N. Khorramian

Publications and source records attributed to Ali N. Khorramian.

At least 19 recordsLinked to original sources

arXiv2018

The impact of the LHCb $B^{\pm}$ production cross-section on parton distribution functions and determining the mass of heavy quarks

In this work, the impact of recent measurements of heavy-flavour production in $pp$ collisions on parton distribution functions (PDFs) and their uncertainties is studied. In this regard, the absolute and normalised cross sections of beauty hadron production measured by LHCb at center-of-mass energy of 7 TeV and 13 TeV are separately included in the next-to-leading order (NLO) global QCD analysis together with the measurements of the inclusive and heavy-flavour production cross sections at HERA. It is illustrated that the heavy-flavour data of the LHCb experiment impose additional constraints on the PDFs, especially on the gluon distribution at low partonic fractions $x$ of the proton momentum. One of the most important results of the present analysis is the significant reduction of the gluon uncertainties in the region less than $x=10^{-4}$ that can play a crucial rule in many areas of high energy physics investigations.

hep-ph↗

arXiv2014

Target mass corrections and higher twist effects in polarized deep-inelastic scattering

We perform a next-to-leading-order QCD analysis to world data on polarized structure functions $g_1$ and $g_2$ in a fixed-flavor number scheme. We include target mass corrections and higher twist effects in our fitting procedure and study their non-negligible effects on physically interesting quantities. Twist-3 contributions to both polarized structure functions are determined, and the accuracy of the extracted polarized parton distribution functions is improved. $^{3}\rm He$ and $^{3}\rm H$ polarized structure functions are described based on our fit result. Moreover, sum rules are derived and compared with available theoretical and experimental results.

hep-ph↗

arXiv2013

QCD analysis of polarized DIS and the SIDIS asymmetry world data and light sea-quark decomposition

The results of our new QCD analysis of helicity parton distributions of the nucleon at full next-to-leading order (NLO) accuracy in the fixed-flavor number scheme will be presented. Performing a combined QCD fit on the global sets of latest inclusive and the semi-inclusive polarized deep inelastic scattering data, we are able to extract new polarized parton distribution functions (PPDFs) at the input scale $Q_{0}^2=1$ GeV$^2$. Particulary, we have calculated PPDFs considering light sea-quark decomposition and the results are compared with the experimental data and the most precise theoretical models obtained by recent analyses. The latest COMPASS2010 SIDIS data, which were not available for the previous analyses, are employed in the current analysis and the effect of COMPASS SIDIS data is studied in detail. Also the uncertainties of PPDFs are determined using the standard Hessian technique.

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arXiv2012

New parton distributions in fixed flavour factorization scheme from recent deep-inelastic-scattering data

We present our QCD analysis of the proton structure function $F_2^p(x,Q^2)$ to determine the parton distributions at the next-to-leading order (NLO). The heavy quark contributions to $F_2^i(x,Q^2)$, with $i$ = $c$, $b$ have been included in the framework of the `fixed flavour number scheme' (FFNS). The results obtained in the FFNS are compared with available results such as the general-mass variable-flavour-number scheme (GM-VFNS) and other prescriptions used in global fits of PDFs. In the present QCD analysis, we use a wide range of the inclusive neutral-current deep-inelastic-scattering (NC DIS) data, including the most recent data for charm $F_2^c$, bottom $F_2^b$, longitudinal $F_L$ structure functions and also the reduced DIS cross sections $σ_{r,NC}^\pm$ from HERA experiments. The most recent HERMES data for proton and deuteron structure functions are also added. We take into account ZEUS neutral current $e^ \pm p$ DIS inclusive jet cross section data from HERA together with the recent Tevatron Run-II inclusive jet cross section data from CDF and DØ. The impact of these recent DIS data on the PDFs extracted from the global fits are studied. We present two families of PDFs, {\tt KKT12} and {\tt KKT12C}, without and with HERA `combined' data sets on $e^{\pm}p$ DIS. We find these are in good agreement with the available theoretical models.

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arXiv2012

A global analysis of diffractive events at HERA

We extract diffractive parton distribution functions (DPDFs) and diffractive structure functions from the most recent H1 and ZEUS diffractive DIS data obtained by various methods. We consider Pomeron as an object with parton distribution function, evolving according to the next-to-leading order (NLO) DGLAP equations within the framework of the `Fixed Flavour Number Scheme' (FFNS). Having performed a global fit analysis, we achieve a very good description of all available measurements by introducing a new set of quark distribution form for the Pomeron. We predict longitudinal and charm proton diffractive structure function as well. Our results are compared with other analysis from the literature.

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arXiv2011

Polarized Deeply Inelastic Scattering (DIS) Structure Functions for Nucleons and Nuclei

We extract parton distribution functions (PDFs) and structure functions from recent experimental data of polarized lepton-DIS on nucleons at next-to-leading order (NLO) Quantum Chromodynamics. We apply the Jacobi polynomial method to the DGLAP evolution as this is numerically efficient. Having determined the polarized proton and neutron spin structure, we extend this analysis to describe 3He and 3H polarized structure functions, as well as various sum rules. We compare our results with other analyses from the literature.

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arXiv2010

Nonsinglet parton distribution functions from the precise next-to-next-to-next-to leading order QCD fit

We present the results of our QCD analysis for non-singlet unpolarized quark distributions and structure function $F_2(x,Q^2)$ up to N$^3$LO. In this regards 4-loop anomalous dimension can be obtain from the Padé approximations. The analysis is based on the Jacobi polynomials expansion of the structure function. New parameterizations are derived for the non-singlet quark distributions for the kinematic wide range of $x$ and $Q^2$. Our calculations for non-singlet unpolarized quark distribution functions up to N$^3$LO are in good agreement with available theoretical models. The higher twist contributions of $F_2^{p,d}(x,Q^2)$ are extracted in the large $x$ region in N$^3$LO analysis. The values of $Λ_{QCD}$ and $α_s(M_z^2)$ are determined.

hep-ph↗

arXiv2008

NNLO QCD contributions to the flavor non-singlet sector of ${\bf {F_2(x,Q^2)}}$

We present the results of our QCD analysis for nonsinglet unpolarized quark distributions and structure function $F_2(x,Q^2)$. New parameterizations are derived for the nonsinglet quark distributions for the kinematic wide range of $x$ and $Q^2$. The analysis is based on the Jacobi polynomials expansion of the structure function. The higher twist contributions of proton and deuteron structure function are obtained in the large $x$ region. Our calculations for nonsinglet unpolarized quark distribution functions based on the Jacobi polynomials method are in good agreement with the other theoretical models. The values of $Λ_{QCD}$ and $α_s(M_z^2)$ are determined.

hep-ph↗

arXiv2008

QCD Analysis for Nuclear Parton Distributions in the Next to Leading Order

A QCD analysis of the nuclear parton distributions and structure functions in the NLO is performed by using the world data. By having bounded parton distributions for a nuclear with atomic number A, we can obtain the nuclear structure function in x space. Our results for nuclear structure function ratio $F^A_2 /F^D_2$ for some different values of A, are in good agreement with the experimental data. We compare our results for LO and NLO approximation.

hep-ph↗

arXiv2007

Simple model for QCD analysis of the proton helicity structure

In this paper we use the experimental data to obtain the polarized parton distribution functions (PPDFs) in the LO and NLO approximations. The analysis is based on the Jacobi polynomials expansion of the polarized structure function (PSF). Our calculations for polarized parton distribution functions based on the Jacobi polynomials method are in good agreement with the other theoretical models.

hep-ph↗

arXiv2007

The Jacobi Polynomials QCD analysis for the polarized structure function

We present the results of our QCD analysis for polarized quark distribution and structure function $xg_1 (x,Q^2)$. We use very recently experimental data to parameterize our model. New parameterizations are derived for the quark and gluon distributions for the kinematic range $x ε[10^{-8},1]$, $Q^2 ε[1,10^6]$ GeV^2. The analysis is based on the Jacobi polynomials expansion of the polarized structure functions. Our calculations for polarized parton distribution functions based on the Jacobi polynomials method are in good agreement with the other theoretical models. The values of $Λ_{QCD}$ and $α_s(M_z)$ are determined.

hep-ph↗

arXiv2007

The NNLO non-singlet QCD analysis of parton distributions based on Bernstein polynomials

A non-singlet QCD analysis of the structure function $xF_3$ up to NNLO is performed based on the Bernstein polynomials approach. We use recently calculated NNLO anomalous dimension coefficients for the moments of the $xF_3$ structure function in $νN$ scattering. In the fitting procedure, Bernstein polynomial method is used to construct experimental moments from the $xF_3$ data of the CCFR collaboration in the region of $x$ which is inaccessible experimentally. We also consider Bernstein averages to obtain some unknown parameters which exist in the valence quark densities in a wide range of $x$ and $Q^2$. The results of valence quark distributions up to NNLO are in good agreement with the available theoretical models. In the analysis we determined the QCD-scale $Λ^ {\bar{MS}}_{QCD, N_{f}=4}=211$ MeV (LO), 259 MeV (NLO) and 230 MeV (NNLO), corresponding to $α_s(M_Z^2)=0.1291$ LO, $α_s(M_Z^2)=0.1150$ NLO and $α_s(M_Z^2)=0.1142$ NNLO. We compare our results for the QCD scale and the $α_s(M_Z^2)$ with those obtained from deep inelastic scattering processes.

hep-ph↗

arXiv2007

An approach to NNLO QCD analysis of non-singlet structure function

We use the next-to-next-to-leading order (NNLO) contributions to anomalous dimension governing the evolution of non-singlet quark distributions. We use the xF3 data of the CCFR collaboration to obtain some unknown parameters which exist in the non-singlet quark distributions in the NNLO approximation. In the fitting procedure, Bernstein polynomial method is used. The results of valence quark distributions in the NNLO, are in good agreement with the available theoretical model.

hep-ph↗

arXiv2006

EMC effect and nuclear structure functions

We analyze experimental data of nuclear structure function ratios $F_2^A/F_2^D$ for obtaining optimum parton distribution functions (PDFs) in nuclei. Then, uncertainties of the nuclear PDFs are estimated by the Hessian method. Parametrization of nuclear parton distribution is investigated in the leading order of $α_s$. The parton distribution are provided at $Q^2=1 GeV^2$ with a number of parameters, which are determined by a $χ^2$ analysis of the data on nuclear structure function. From the analysis, we propose parton distributions at $Q^2=1 GeV^2$ for nuclei from deuteron to heavy ones with a mass number $A\sim 208$.

hep-ph↗

arXiv2006

The Role of Polarized Valons in the Flavor Symmetry Breaking of Nucleon Sea

Next-to-leading order approximation of the quark helicity distributions are used in the frame work of polarized valon model. The flavor-asymmetry in the light-quark sea of the nucleon can be obtained from the contributions of unbroken sea quark distributions. We employ the polarized valon model and extract the flavor-broken light sea distributions which are modeled with the help of a Pauli-blocking ansatz. Using this ansatz, we can obtain broken polarized valon distributions. From there and by employing convolution integral, broken sea quark distributions are obtainable in this frame work. 0ur results for $δu$, $δd$, $δ\bar u$, $δ\bar d$ and $δ\bar s$ are in good agreement with recent experimental data for polarized parton distribution from HERMES experimental group and also with GRSV model. Some information on orbital angular momentum as a main ingredient of total nucleon spin are given. The $Q^2$ evolution of this quantity, using the polarized valon model is investigated.

hep-ph↗

arXiv2004

Next-to-Leading order approximation of polarized valon and parton distributions

Polarized parton distributions and structure functions of the nucleon are analyzed in the improved valon model. The valon representation provides a model to represent hadrons in terms of quarks, providing a unified description of bound state and scattering properties of hadrons. Polarized valon distributions are seen to play an important role in describing the spin dependence of parton distributions in the leading order (LO) and next-to-leading order (NLO) approximations. In the polarized case, a convolution integral is derived in the framework of the valon model. The Polarized valon distribution in a proton and the polarized parton distributions inside the valon are necessary to obtain the polarized parton distributions in a proton. Bernstein polynomial averages are used to extract the unknown parameters of the polarized valon distributions by fitting to the available experimental data. The predictions for the NLO calculations of the polarized parton distributions and proton structure functions are compared with the LO approximation. It is shown that the results of the calculations for the proton structure function, $xg_1^p$, and its first moment, $Γ_{1}^p$, are in good agreement with the experimental data for a range of values of $Q^{2}$. Finally the spin contribution of the valons to the proton is calculated.

hep-ph↗

arXiv2004

Nuclear Parton Densities and Structure Functions

We calculate nuclear parton distribution functions (PDFs), using the constituent quark model. We find the bounded valon distributions in a nuclear to be related to free valon distributions in a nucleon. By using improved bounded valon distributions for a nuclear with atomic number $A$ and the partonic structure functions inside the valon, we can calculate the nuclear structure function in $x$ space. The results for nuclear structure-function ratio $F_2^A/F_2^D$ at some values of $A$ are in good agreement with the experimental data.

hep-ph↗

arXiv2003

Polarized parton distribution functions in the valon model framework, using QCD fits to Bernstein polynomials

In this paper polarized valon distribution is derived from unpolarized valon distribution. In driving polarized valon distribution some unknown parameters exist which must be determined by fitting to experimental data. Here we have used Bernstein polynomial method to fit QCD predictions for the moments of $g_1^p$ structure function, to suitably the constructed appropriate average quantities of the E143 and SMC experimental data. After calculating polarized valon distributions and all parton distributions in a valon, polarized parton density in a proton are available. The results are used to evaluate the spin components of proton. It turns out that the results of polarized structure function are in good agreement with all available experimental data on $g_{1}^p$ of proton.

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