arXiv subjects

S. Atashbar Tehrani

Publications and source records attributed to S. Atashbar Tehrani.

At least 19 recordsLinked to original sources

arXiv2026

Integrating Heisenberg uncertainty and maximum entropy principles verses statistical approach to nucleon structure

There are many methods to calculate the parton distributions. In this work, we are trying to determine the unknown parameters of valence quark and gluon densities, taking into account some constraints simultaneously. For this purpose, we consider two different approaches. At first approach, a parameterized form for the valence densities are assumed. Using the constraints imposed by the Heisenberg uncertainty and maximum entropy principles and also considering the quark number and momentum sum rules, the unknown parameters of the parton distributions are determined. In second approach, we attribute a statistical distributions to quark, anti-quarks and gluon densities which are including temperature T, volume V and chemical potential, $\mu$, as thermodynamic parameters. In this case, using only the maximum entropy principle and the quark number together with momentum sum rules, the parton distributions in terms of thermodynamic parameters are extracted. The results for valence quark densities in both approaches and additionally the gluon density in second approach are in {satisfactory match} with results from some parametrization models. By evolving these densities to the desired energy scales, we are able to calculate the nucleon $xF_3$ structure function and also the ratio of valence quark densities.

hep-ph↗

arXiv2025

Fragmentation functions of the pion, kaon, and proton in the NLO approximation: Laplace transform approach

Using repeated Laplace transform, We find an analytical solution for DGLAP evolution equations for extracting the pion, kaon and proton Fragmentation Functions (FFs) at NLO approximation. We also study the symmetry breaking of the sea quarks Fragmentation Functions, $D_{\bar q}^h (z,Q^2)$ and simply separated them according to their mass ratio. Finally, we calculate the total Fragmentation Functions of these hadrons and compare them with experimental data and those from global fits. Our results show a good agreement with the FFs obtained from global parameterizations as well as with the experimental data.

hep-ph↗

arXiv2025

Fragmentation Functions of neutral mesons $π^0$ and $k ^0$ with Laplace transform approach

With an analytical solutions of DGLAP evolution equations based on the Laplace transform method , we find the fragmentation functions (FFs) of neutral mesons, $π^0$ and $k ^0$ at NLO approximation. We also calculated the total fragmentation functions of these mesons and compared them with experimental data and those from global fits. The results show a good agreements between our solutions and other models and also are compatible with experimental data.

hep-ph↗

arXiv2021

Analytical perturbation theory and Nucleon structure function in infrared region

We employ analytic QCD (anQCD) approach to analyze the unpolarized nucleon structure function (NSF) in deep inelastic scattering ( DIS ) processes at the next-to-leading order (NLO) accuracy. Considering the unreliable results of underlying perturbative QCD (pQCD) at energy scale $Q^2\simΛ^2$ and even less we modify the calculations at these scales using anQCD approach and compare them with results from underlying pQCD and also with the available experimental data. In these progresses the massive perturbation theory (MPT) model is also used where an effective mass is attributed to gluons. We finally use the Jacobi polynomials formalism to transfer the calculations from Mellin moment space to Bjorken-$x$ space. To confirm the validity of anQCD approach the Gottfired sum rule is also investigated. The achieved numerical results at low energy scales are compatible with what is expected and corresponding to an admissible behaviour of parton densities.

hep-ph↗

arXiv2021

Nuclear parton distribution functions with uncertainties in a general mass variable flavor number scheme

In this article we obtain a new set of nuclear parton distribution functions (nuclear PDFs) at next-to-leading order and next-to-next-to-leading order accuracy in perturbative QCD. The common nuclear deep-inelastic scattering (DIS) data analyzed in our study are complemented by the available charged-current neutrino DIS data with nuclear targets and data from Drell-Yan cross-section measurements for several nuclear targets. In addition, the most recent DIS data from the Jefferson Lab CLAS and Hall C experiments are also added to our data sample. For these specific datasets, we consider the impact of target mass corrections and higher twist effects which are expected to be important in the region of large $x$ and intermediate-to-low $Q^2$. Our analysis is based on a publicly available open-source tool {\tt APFEL}, which has been modified to be applicable for our analysis of nuclear PDFs. Heavy quark contributions to nuclear DIS are considered within the framework of the {\tt FONLL} general-mass variable-flavor-number scheme. The most recent {\tt CT18} PDFs are used as baseline proton PDFs. The uncertainties of nuclear PDFs are determined using the standard Hessian approach. The results of our global QCD analysis are compared with existing nuclear PDF sets and with the fitted cross-sections, for which our set of nuclear PDFs provides a very good description.

hep-ph↗

arXiv2021

Charm-quark pole mass from HERA Combined and LHCb charm production data

One of the most popular definition for the charm-quark mass is the charm-quark pole mass $m_c^{\rm pole}$. In this contribution, we extract the charm-quark pole mass through perturbative Quantum Chromo Dynamics (pQCD) analysis up to the next-to-next-to-leading order (NNLO) corrections from HERA Combined and LHCb charm production recent data sets. Then, we investigate for the first time the charm-quark pole mass $m_c^{\rm pole}$ pure impact, as an extra pQCD parameter on the proton Parton Distribution Functions (PDFs) at the NNLO corrections.

hep-ph↗

arXiv2021

Improved determination of strange distribution function from the global analysis using BHPS model

We study the impact of intrinsic strange (IS) component of nucleon sea on the global analysis of parton distribution functions (PDFs) considering a wide range of experimental data. To this aim, we consider two scenarios on the basis of BHPS model results for the IS distribution. In the first scenario, we apply the results presented through the BHPS model and in the second scenario we use its evolved distributions. For each scenarios, we present the limit of the IS probability $ {\cal P}_5^{s\bar{s}} $ for the standard tolerance criteria $ Δχ^2=1 $ and $ 18.112 $ at $ 1σ$ and $ 4σ$ levels. Our results show that the experimental data can tolerate an IS component with a greater probability $ {\cal P}_5^{s\bar{s}} $ if one employs the second scenario. We obtain $ {\cal P}_5^{s\bar{s}}\approx 0.01 $ and $ {\cal P}_5^{s\bar{s}}\approx 0.025 $ for $ Δχ^2=1 $ and $18.112$, respectively, at the $ 4σ$ level. We also calculate the ratio of strange-to-light sea-quark densities $r_s$ in the proton both including and excluding the IS component. Our results show that one can obtain a higher value for the ratio $r_s$ if the IS component is included.

hep-ph↗

arXiv2020

QCD analysis of non-singlet structure functions at NNLO accuracy, based on the Laplace transform

In this work, using the Laplace transformation technique we present our results for non-singlet quark distributions as well as nucleon structure function $F_2(x,Q^2)$ in unpolarized case at next-to-next-to-leading order (NNLO) QCD accuracy. We shall particularly compare our results for the sets of valence-quark parton distribution functions with the contemporary collaborations like CT14, CT18, MMHT14, MKAM16 and NNPDF. To construct the nucleon structure function we employ the expansion of Jacobi polynomials which is a suitable transform to convert the results of non-singlet structure function from the Laplace $s$-space to Bjorken $x$-space. We shall also consider the contributions of target mass correction as well as the higher twist effects at large-$x$ region for the proton and deuteron structure functions. Our results for the unpolarized quark distribution functions and nucleon structure functions are in good agreement with recent theoretical models and available experimental data.

hep-ph↗

arXiv2020

Structure and tidal deformability of a hybrid star within the framework of the field correlator method

The structure of hybrid stars within the nonperturbative framework of the field correlator method, extended to zero-temperature limit as a quark model, has been studied. For the hadronic sector, we have used the lowest-order constraint variational method by employing AV18 two-body nucleon-nucleon interaction supplemented by the phenomenological Urbana-type three-body force. For an adapted value of the gluon condensate, G2 = 0:006 GeV4, which gives the critical temperature of about Tc ? 170 MeV, stable hybrid stars with a maximum mass of 2:04M? are predicted. The stability of hybrid star has been investigated for a wide range of gluon condensate value, G2, and quark-antiquark potential, V1. A hybrid equation of state fulfills the constraints on tidal deformability and hence on the radii of the stars, extracted from the binary GW170817. Moreover, tidal deformability for different chirp masses and different binary mass ratios of hybrid stars have been studied. The mass-radius relation satisfies the new constraint obtained from the neutron star interior composition explorer (NICER). A comprehensive analysis on the structure of a hybrid star and also its compactness, tidal Love number, and tidal deformability has been conducted for several parameter sets of the quark equation of state. The influence of different crustal equations of state on the mentioned quantities has been studied. Our calculations suggest the value of quark-antiquark potential, V1, to be around 0.08 GeV. The results achieved in this study are in strong concurrence with the other calculations reported on this subject.

hep-ph↗

arXiv2020

Hybrid star within the framework of a lowest-order constraint variational method

The hadron-quark phase transition in the core of heavy neutron star (NS) has been studied. For the hadronic sector, we have used the lowest-order constraint variational method by employing $ AV_{18} $, $ AV_{14}$, $ UV_{14}$, and Reid $ 68 $ two-body nucleon-nucleon forces supplemented by the phenomenological Urbana-type three-body force. We have adopted the MIT bag model as well as three-flavor version of the Nambu- Jona-Lasinio (NJL) model to describe the quark phase. The equation of state (EOS) of a hybrid star (HS) is presented by combining two EOS of the hadronic sector and quark sector of a star, which are derived from independent models or theories. The hadron-quark transition is constructed by considering a sharp phase transition, i.e., Maxwell construction. The structure of the HS is calculated and reported by solving Tolman-Oppenheimer-Volkoff equations. Finally the radii and tidal deformability of purely NS and HS for the mass of $ 1.4M_{\odot} $ is computed and new constraints on these quantities are checked. The maximum mass of HS is found more than $ 2 M_{\odot} $ for both the NJL and MIT bag models. However, the maximum mass of $ 1.796 M_{\odot} $ ($ 1.896 M_{\odot} $) was the best result that would be calculated for a stable HS with the pure quark core within the MIT (NJL) model. All the hybrid EOS fulfill the constraints on radii and tidal deformability extracted from the binary GW170817 for HSs. A comprehensive analysis on the structure of purely NS and HS and also compactness, tidal Love number, and tidal deformability for the star with the mass of 1.4 $ M_{\odot} $ has been conducted for various EOS of the hadron sector and several parameter sets of the quark EOS. The results achieved in this study are in good concurrence with the other calculations reported on this subject.

nucl-th↗

arXiv2019

Nonsinglet polarized nucleon structure function in infrared-safe QCD

The polarized nucleon structure function in the nonsinglet case is investigated here by a new insight rather than conventional perturbative QCD (pQCD). For this purpose we note that the solution of the evolution equations in moment space involves noninteger powers of the coupling constant. Therefore it is possible to employ a new approach which is called fractional analytical perturbation theory Consequently, it is possible to remove the Landau singularities of the renormalized coupling, i.e., at the scales $Q \sim Λ$, using this approach. This provides an opportunity to continue the desired calculations toward small values of energy scales even less than the $Λ$ scale. To modify the analytical perturbation theory, a newer approach is introduced, called 2$δ$anQCD, in which the spectral function of the holomorphic coupling is parameterized in the low-energy region by two delta functions. This model gives us more reliable results for the considered QCD observables, even in the deep infrared region. We calculate the nonsinglet part of the polarized nucleon structure function, using the 2$δ$anQCD model, and compare it with the result from the underlying pQCD where both are in a new defined scheme, called the Lambert scheme. For this purpose we employ the anQCD package in the \textit{Mathematica} environment to establish the analytic (holomorphic) coupling constant. The results at various energy scales are also compared with the available experimental data, and it turns out that there is a good consistency between them. The results show that the obtained nucleon structure function at small energy scales has smoother behavior when using the 2$δ$anQCD model than the underlying pQCD. In fact the coupling constant in analytic QCD behaves moderately and it makes the result approach the available data in a better way.

hep-ph↗

arXiv2019

NNLO charmed-meson fragmentation functions and their uncertainties in the presence of meson mass corrections

The main aim of this paper is to present new sets of non-perturbative fragmentation functions (FFs) for $D^0$ and $D^+$ mesons at next-to-leading (NLO) and, for the first time, at next-to-next-to-leading order (NNLO) in the $\overline{\mathrm{MS}}$ factorization scheme with five massless quark flavors. This new determination of FFs is based on the QCD fit to the {\tt OPAL} experimental data for hadron production in the electron-positron single-inclusive annihilation (SIA). We discuss in detail the novel aspects of the methodology used in our analysis and the validity of obtained FFs by comparing with previous works in literature which have been carried out up to NLO accuracy. We will also incorporate the effect of charmed meson mass corrections into our QCD analysis and discuss the improvements upon inclusion of these effects. The uncertainties in the extracted FFs as well as in the corresponding observables are estimated using the "Hessian" approach. For a typical application, we use our new FFs to make theoretical predictions for the energy distributions of charmed mesons inclusively produced through the decay of unpolarized top quarks, to be measured at the CERN LHC. As a result of this analysis, suggestions are discussed for possible future studies on the current topic to consider any theory improvements and other available experimental observables.

hep-ph↗

arXiv2018

EMC effect in the next-to-leading order approximation based on the Laplace transformation

In this article, using Laplace transformation , an analytical solution is obtained for the DGLAP evolution equation at the next-to-leading order of perturbative QCD. The technique is also employed to extract, in the Laplace $s$-space, an analytical solution for the nuclear structure function, $F_2^A(x, Q^2)$. Firstly, the results for separate nuclear parton distributions for all parton types are presented which include valence quark densities, the anti-quark and strange sea PDFs and finally the gluon distribution. Based on the Laplace transformation, the obtained parton distribution functions and the nuclear structure function in the $x$-space are compared with the results from the [Phys.\ Rev.\ C series 86, 064301 (2012)] model. Our calculations are in good agreement with the available DIS experimental data as well as theoretical models which contain both small and large values of $x$-Bjorken variable. We compare our nuclear PDFs sets with those from other recent collaborations, in particular with the [ nCTEQ15 ] and [ HKN07] sets. The comparison between our results and those from the literature indicates a good agreement .

hep-ph↗

arXiv2018

Analytical approaches to the determination of spin-dependent parton distribution functions at NNLO approximation

In this paper, we present {\tt SMKA18} analysis which is a first attempt to extract the set of next-to-next-leading-order (NNLO) spin-dependent parton distribution functions (spin-dependent PDFs) and their uncertainties determined through the Laplace transform technique and Jacobi polynomial approach. Using the Laplace transformations, we present an analytical solution for the spin-dependent Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations at NNLO approximation. The results are extracted using a wide range of proton $g_1^{p}(x, Q^2)$, neutron $g_1^{n}(x, Q^2)$ and deuteron $g_1^{d}(x, Q^2)$ spin-dependent structure functions dataset including the most recent high-precision measurements from {\tt COMPASS16} experiments at CERN which are playing an increasingly important role in global spin-dependent fits. The careful estimations of uncertainties have been done using the standard 'Hessian error' propagation. We will compare our results with the available spin-dependent inclusive deep inelastic scattering dataset and other results for the spin-dependent PDFs in literature. The results obtained for the spin-dependent PDFs as well as spin-dependent structure functions are clearly explained both in the small and large values of $x$.

hep-ph↗

arXiv2017

Nuclear parton distribution functions (nPDFs) and their uncertainties in the LHC Era

We have presented the results of our next-to-next-to-leading order (NNLO) QCD analysis of nuclear parton distribution functions (nuclear PDFs) [Phys. Rev. D 93 (2016) 014026, arXiv:1601.00939 [hep-ph]] using all available neutral current charged-lepton ($\ell ^\pm$ + nucleus) deeply inelastic scattering (DIS) data as well as Drell-Yan (DY) cross-section ratios $σ_{\rm DY}^{A}/σ_{\rm DY}^{A^\prime}$ for a variety of nuclear targets. We have studied in detail the parametrizations and the atomic mass (A) dependence of the nuclear PDFs at NNLO at the input scale, $Q_0^2 = 2 \, {\rm GeV^2}$. Our {\tt KA15} nuclear PDFs provides a complete set of nuclear PDFs, $f_i^{(A, Z)}(x, Q^2)$, with a full functional dependence on $x$, A, $Q^2$. The uncertainties of the obtained nuclear modification factors for each parton flavour as well as the corresponding observables are estimated using the well-known Hessian method. The nuclear heavy quark contributions are also included into the analysis in the framework of zero-mass variable flavour number scheme (ZM-VFNS). We compare the results of our parametrization with all available nuclear DIS data and the results of other nuclear PDFs groups. We have found that our nuclear PDFs to be in reasonably good agreement with results in the literature. The estimates of errors provided by our global analysis ({\tt KA15}) are rather smaller than those of other groups. We have briefly reviewed different aspects of recent LHC heavy-ion collisions data including the first experimental data from the LHC proton+lead ($p-pb$) and lead+lead ($pb-pb$) run which can be used in the global fits of nuclear PDFs.

hep-ph↗

arXiv2017

Study of spin-dependent structure functions of $^3{\rm He}$ and $^3{\rm H}$ at NNLO approximation and corresponding nuclear corrections

We determine polarized parton distribution functions (PPDFs) and structure functions from recent experimental data of polarized deep inelastic scattering (DIS) on nuleons at next-to-next-to-leading order (NNLO) approximation in perturbative quantum chromodynamic (pQCD). The nucleon polarized structure functions are computed using the Jacobi polynomial approach while target mass corrections (TMCs) are included in our fitting procedure. Having extracted the polarized spin structure functions, we extend our study to describe $^3{\mathrm He}$ and $^3{\mathrm H}$ polarized structure functions, as well as the Bjorken sum rule. We also explore the importance of the nuclear corrections on the polarized nuclear structure functions at small and large values of $x$. Our results are compared with the recent available and high precision polarized $^3{\mathrm He}$ and $^3{\mathrm H}$ experimental data.

hep-ph↗

arXiv2017

Nucleon spin structure functions at NNLO in the presence of target mass corrections and higher twist effects

We extract polarized parton distribution functions (PPDFs), referred to as "KTA17," together with the highly correlated strong coupling $α_s$ from recent and up-to-date $g_1$ and $g_2$ polarized structure functions world data at next-to-next-to-leading order in perturbative QCD. The stability and reliability of the results are ensured by including nonperturbative target mass corrections as well as higher-twist terms which are particularly important at the large-$x$ region at low Q$^2$. Their role in extracting the PPDFs in the nucleon is studied. Sum rules are discussed and compared with other results from the literature. This analysis is made by means of the Jacobi polynomials expansion technique to the DGLAP evolution. The uncertainties on the observables and on the PPDFs throughout this paper are computed using standard Hessian error propagation which served to provide a more realistic estimate of the PPDFs uncertainties.

hep-ph↗

arXiv2017

Analytic derivation of the next-to-leading order proton structure function $F_2^p(x, Q^2)$ based on the Laplace transformation

An analytical solution based on the Laplace transformation technique for the DGLAP evolution equations is presented at next-to-leading order accuracy in perturbative QCD. This technique is also applied to extract the analytical solution for the proton structure function, $F_2^p(x, Q^2)$, in the Laplace $s$-space. We present the results for the separate parton distributions for all parton species, including valence quark densities, the anti-quark and strange sea parton distribution functions (PDFs), and the gluon distribution. We successfully compare the obtained parton distribution functions and the proton structure function with the results from {\tt GJR08} and {\tt KKT12} parametrization models as well as the $x$-space results using {\tt QCDnum} code. Our calculations show a very good agreement with the available theoretical models as well as the deep inelastic scattering (DIS) experimental data throughout the small and large values of $x$. The use of our analytical solution to extract the parton densities and the proton structure function is discussed in detail to justify the analysis method considering the accuracy and speed of calculations. Overall, the accuracy we obtain from the analytical solution using the inverse Laplace transform technique is found to be better than 1 part in 10$^{4}$ to 10$^{5}$. We also present a detailed QCD analysis of non-singlet structure functions using all available DIS data to perform global QCD fits. In this regard we employ the Jacobi polynomial approach to convert the results from Laplace $s$ space to Bjorken $x$ space. The extracted valence quark densities are also presented and compared to the {\tt JR14}, {\tt MMHT14}, {\tt NNPDF} and {\tt CJ15} PDFs sets. We evaluate the numerical effects of target mass corrections (TMCs) and higher twist (HT) terms on various structure functions, and compare fits to data with and without these corrections.

hep-ph↗