arXiv subjects

Hamzeh Khanpour

Publications and source records attributed to Hamzeh Khanpour.

At least 19 recordsLinked to original sources

arXiv2026

Modern Determination of Pion and Kaon Fragmentation Functions from SIA and High-Precision COMPASS SIDIS Multiplicities

We present a combined determination of charged-pion and charged-kaon fragmentation functions (FFs), denoted HAPS-PiFF1.0 and HAPS-KaFF1.0, at next-to-leading order (NLO) and within a next-to-next-to-leading-order (NNLO) perturbative QCD setup. The analysis combines single-inclusive electron-positron annihilation (SIA) data with charge-separated semi-inclusive deep-inelastic-scattering (SIDIS) multiplicities from HERMES and COMPASS. A central goal of this work is to incorporate the modern COMPASS SIDIS input, namely the COMPASS 2025 proton-target multiplicities and the COMPASS 2026 revised isoscalar-target multiplicities, into a common charged-pion and charged-kaon FF analysis and to assess their role in the resulting flavor separation. The revised isoscalar data supersede the earlier COMPASS measurements used in previous global fits. The charge-separated pion multiplicities provide important constraints on favored and unfavored light-quark fragmentation, while the kaon measurements enhance the sensitivity to light-quark, unfavored, and strange-to-kaon fragmentation channels. In both analyses, the gluon FF remains indirectly constrained in the present SIA+SIDIS framework and should be interpreted with appropriate caution. The extractions are carried out using the publicly available MontBlanc framework, and the resulting HAPS-PiFF1.0 and HAPS-KaFF1.0 replica sets are provided in the standard LHAPDF format.

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arXiv2026

Toward Precision Helicity PDFs from Global DIS and SIDIS Fits with Projected EIC Measurements

We present a new global determination of the helicity-dependent parton distribution functions (PDFs) of the proton, based on inclusive deep-inelastic scattering (DIS) and semi-inclusive DIS (SIDIS) data within a consistent next-to-leading order (NLO) QCD framework. In addition to existing measurements, we incorporate simulated pseudodata for the future Electron-Ion Collider (EIC), considering two beam-energy configurations, $E_e \times E_p = 5 \times 41~\mathrm{GeV^2}$ and $18 \times 275~\mathrm{GeV^2}$, corresponding to an extended kinematic reach down to $x \sim 10^{-5}$. We focus on longitudinal double-spin asymmetries $A_1^h$ for charge-separated pion and kaon production in SIDIS off a longitudinally polarized proton target. These projected measurements significantly improve the flavor separation of sea-quark polarized PDFs ($Δ\bar{u}$, $Δ\bar{d}$, $Δs$) and reduce the uncertainties on both quark and gluon helicity distributions, with the largest impact at small $x$. Polarized PDFs are extracted using a neural-network parametrization and a Monte Carlo replica methodology to propagate experimental uncertainties, while theoretical constraints such as positivity are imposed during the fit. We demonstrate that the inclusion of EIC pseudodata leads to a substantially more precise determination of polarized PDFs, with the largest impact in the small-$x$ region. The resulting polarized PDF sets are provided in the LHAPDF format.

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arXiv2026

Revisiting Unidentified Charged-Hadron Fragmentation Functions with Modern COMPASS SIDIS Multiplicities

We present \texttt{HAPS-hFF1.0}, a new global QCD analysis of unidentified charged-hadron fragmentation functions (FFs) using single-inclusive electron-positron annihilation (SIA) data together with the modern COMPASS semi-inclusive deep-inelastic scattering (SIDIS) multiplicities. The COMPASS input consists of the 2025 proton-target measurement and the revised isoscalar-target multiplicities provided in the COMPASS addendum 2026. The extraction is performed at both next-to-leading order (NLO) and next-to-next-to-leading order (NNLO), allowing us to study the perturbative stability of the QCD fit and the impact of the updated SIDIS information on the flavor structure of the FFs. We find that the modern COMPASS multiplicities can be consistently described together with the SIA data and provide important charge-separated constraints on the light-quark and antiquark FFs. The comparison between the NLO and NNLO extractions indicates a stable quark-sector determination, while the gluon FF remains less directly constrained in the present SIA+SIDIS analysis. Our results highlight the importance of the modern COMPASS SIDIS multiplicities for precision studies of unidentified charged-hadron fragmentation and for future global FF determinations. The resulting \texttt{HAPS-hFF1.0} replicas are publicly available in standard LHAPDF format.

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arXiv2025

Improved Constraints on Pion Fragmentation Functions from Simulated Electron-Ion Collider Data

We present a quantitative assessment of the anticipated impact of future Electron-Ion Collider (EIC) measurements on the extraction of parton-to-pion fragmentation functions (FFs). Our analysis combines simulated semi-inclusive deep-inelastic scattering (SIDIS) pseudo-data at EIC energies of 45 GeV and 140 GeV with existing single-inclusive electron-positron annihilation (SIA) and SIDIS experimental data. The pion fragmentation functions are determined at next-to-leading-order (NLO) accuracy using a perturbative QCD framework and a neural network parametrization. Uncertainties are rigorously estimated through Monte Carlo sampling, accounting for both experimental errors and variations in input parton distribution functions. Our results demonstrate that incorporating EIC pseudo-data reduces their uncertainties, especially at medium to large momentum fractions ($z$). This improvement is particularly pronounced for the gluon and selected quark FFs, highlighting the substantial role that EIC measurements will play in achieving high-precision extractions of FFs and informing future experimental and theoretical developments in collider physics.

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arXiv2025

Bottom quark forward-backward asymmetry at the future electron-positron collider FCC-ee

The Standard Model (SM) prediction for the \PZ-boson pole $b$-quark forward-backward (FB) asymmetry is: $(A_{FB}^{0,b})_{th} = 0.1030 \pm 0.0002$. The LEP electron-positron collider measured instead $A_{FB}^{0,b} = 0.0992 \pm 0.0016$, value which presents the largest discrepancy with any of the SM predictions as of today. All the $A_{FB}^b$ measurements performed at LEP suffered however of an important statistical uncertainty and of different sources of systematic uncertainties. This study shows that the proposed high-luminosity electron-positron collider FCC-ee, collecting orders of magnitude more data at the \PZ-pole than LEP, will significantly reduce the statistical uncertainties on the measurement of $A_{FB}^{0,b}$, thus allowing us to shed further light on this tension.

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arXiv2024

Revisiting constraints on proton PDFs from HERA DIS, Drell-Yan, W/Z Boson production, and projected EIC measurements

We present new parton distribution functions (PDFs) at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) in perturbative QCD, derived from a comprehensive global QCD analysis of high-precision data sets from combined HERA deep-inelastic scattering (DIS), the Tevatron, and the Large Hadron Collider (LHC). To improve constraints on quark flavor separation, we incorporate Drell-Yan pair production data, which provides critical sensitivity to the quark distributions. In addition, we include the latest W and Z boson production data from the CDF, D0, ATLAS, and CMS collaborations, further refining both quark and gluon distributions. Our nominal global QCD fit integrates these datasets and examines the resulting impact on the PDFs and their associated uncertainties. Uncertainties in the PDFs are quantified using the Hessian method, ensuring robust error estimates. Furthermore, we explore the sensitivity of the strong coupling constant, $α_s(M_Z^2)$, and proton PDFs in light of the projected measurements from the Electron-Ion Collider (EIC), where improvements in precision are expected. The analysis also investigates the effects of inclusive jet and dijet production data, which provide enhanced constraints on the gluon PDF and $α_s(M_Z^2)$.

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arXiv2024

Study of nuclear corrections on the charged hadron fragmentation functions in a Neural Network global QCD analysis

In this work, we present a new global QCD analyses, referred to as PKHFF.23, for charged pion, kaon, and unidentified light hadrons. We utilize a Neural Network to fit the high-energy lepton-lepton and lepton-hadron scattering data, enabling us to determine parton-to-hadron fragmentation functions (FFs) at next-to-leading-order (NLO) accuracy. The analyses include all available single-inclusive $e^+e^-$ annihilation (SIA) and semi-inclusive deep-inelastic scattering (SIDIS) data from the COMPASS Collaboration for charged pions, kaons, and unidentified light hadrons. Taking into account the most recent nuclear parton distribution functions (nuclear PDFs) available in the literature, we evaluate the effect of nuclear corrections on the determination of light hadrons FFs. The Neural Network parametrization, enriched with the Monte Carlo methodology for uncertainty estimations, is employed for all sources of experimental uncertainties and the proton PDFs. Our results indicate that incorporating nuclear corrections has a marginal impact on the central values of FFs and their corresponding uncertainty bands. The inclusion of such corrections does not significantly affect the fit quality of the data as well. The study suggests that while nuclear corrections are a consideration, their impact in such QCD analysis is limited.

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arXiv2024

AAK24: Global QCD analysis on polarized parton distribution in the presence of $A_2$ asymmetry measurements

This article introduces {\tt AAK24}, a Next-to-Leading Order (NLO) QCD analysis of polarized data from both polarized Deep Inelastic Scattering (DIS) and Semi-Inclusive Deep Inelastic Scattering (SIDIS) experiments on the nucleon. The {\tt AAK24} QCD analysis incorporates SU(2) and SU(3) symmetry breaking, specifically $δ\bar{u} \neq δ\bar{d} \neq δ\bar{s}$, while assuming $δ\bar{s}$ and $δs$ are equal. Emphasizing the significance of the semi-inclusive data, the study explores the determination of polarized sea quark distributions. Recent experimental data from {\tt JLAB17}, {\tt COMPASS16}, and {\tt COMPASS17}, including the $A_2$ asymmetry measurements along with SIDIS observables, are thoroughly examined for their impact on the central values of polarized PDFs, their uncertainties, and overall fit quality. Additionally, we include the nonperturbative target mass corrections (TMC) as well as higher-twist terms (HT) which are particularly important. In this work, the uncertainties are quantified using the standard Hessian method. The main results and findings of the {\tt AAK24} QCD analysis show overall good agreement with the analyzed experimental data, aligning well with other polarized PDF determinations, particularly {\tt DSSV14}, {\tt LSS10}, {\tt JAM17}, and {\tt AKS14}, all considering SU(2) and SU(3) symmetry breaking.

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arXiv2024

Determination of $K^0_S$ Fragmentation Functions including BESIII Measurements and using Neural Networks

In this study, we revisit the extraction of parton-to-$K^0_S$ hadron fragmentation functions, named FF24-$K^0_S$, focusing on both next-to-leading-order and next-to-next-to-leading-order accuracy in perturbative QCD. Our approach involves the analysis of single inclusive electron-positron annihilation (SIA) data. The two key improvements are, on the one hand, the incorporation of the latest experimental data from the BESIII experiment and, on the other hand, the adoption of Neural Networks in the fitting procedure. To address experimental uncertainties, the Monte Carlo method is employed. Our investigation also explores the impact of hadron mass corrections on the description of SIA data, spanning a broad kinematic regime with a particular emphasis on the range of small $z$ values. The theory prediction for $K^0_S$ production at both NLO and NNLO accuracy exhibits good agreement with experimental data within their respective uncertainties.

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arXiv2024

Exploring non-standard $Hb\bar{b}$ interactions at future electron-proton colliders

In this paper, we use the charged-current Higgs boson production process at future electron-proton colliders, $e^-p \to H j ν_e$, with the subsequent decay of the Higgs boson into a $b\bar{b}$ pair, to probe the Standard Model effective field theory with dimension-six operators involving the Higgs boson and the bottom quark. The study is performed for two proposed future high-energy electron-proton colliders, the Large Hadron Electron Collider (LHeC) and the Future Circular Collider (FCC-he) at the center-of-mass energies of 1.3 TeV and 3.46 TeV, respectively. Constraints on the CP-even and CP-odd $Hb\bar{b}$ couplings are derived by analyzing the simulated signal and background samples. A realistic detector simulation is performed and a multivariate technique using the gradient Boosted Decision Trees algorithm is employed to discriminate the signal from background. Expected limits are obtained at $95\%$ Confidence Level for the LHeC and FCC-he assuming the integrated luminosities of 1, 2 and 10 ab$^{-1}$. We find that using 1 ab$^{-1}$ of data, the CP-even and CP-odd $Hb\bar{b}$ couplings can be constrained with accuracies of the order of $10^{-3}$ and $10^{-2}$, respectively, and a significant region of the unprobed parameter space becomes accessible.

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arXiv2023

Effect of symmetry breaking of polarized light sea quarks on the nucleon and nuclear structure functions, and sum rules

In this study, we performed calculations and analyses of the structure functions of polarized nucleons and light nuclei, specifically $^3$He and $^3$H, using second-order Feynman diagrams. Our investigation focused on two main aspects: Firstly, we examined the symmetry properties of polarized light sea quarks. Secondly, we conducted a detailed investigation into the impacts of symmetry breaking on the structure functions of both nucleons and nuclei. To achieve this, we utilized the existing polarized Parton Distribution Functions (polarized PDFs) available in the literature. These PDFs were used to calculate and compare the polarized structure functions $g_1$ and $g_2$ of the nuclei. Additionally, we examined and analyzed the Bjorken and Efremov-Leader-Teryaev sum rules by utilizing the moments of the polarized structure functions. The Lorentz color force components, namely $F_E^{y,n}$ and $F_B^{y,n}$, are determined using the twist-2, twist-3, and twist-4 matrix elements. When symmetry breaking is applied, it is observed that they have similar magnitudes but opposite signs. Our theoretical predictions for the polarized structure functions of nucleons and light nuclei, taking into account the symmetry breaking of light sea quarks, exhibit better agreement with experimental data.

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arXiv2023

Determination of diffractive PDFs from global QCD analysis of inclusive diffractive DIS and dijet cross-section measurements at HERA

We present an updated set of {\tt SKMHS} diffractive parton distribution functions (PDFs). In addition to the diffractive deep-inelastic scattering (diffractive DIS) data sets, the recent diffractive dijet cross sections measurements by the H1 experiment from the HERA collider are added to the data sample. The new set of diffractive PDFs, entitled {\tt SKMHS23} and {\tt SKMHS23-dijet}, are presented at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) accuracy in perturbative QCD. Since the gluons directly contribute to jet production through the boson-gluon fusion process, the data on diffractive dijet production in inclusive DIS help to constrain the gluon density, allowing for the determination of both the quark and gluon densities with better accuracy. The NLO and NNLO theory predictions calculated using both {\tt SKMHS23} and {\tt SKMHS23-dijet} are compared to the analyzed data showing excellent agreements. The effect arising from the inclusion of diffractive dijet data and higher order QCD corrections on the extracted diffractive PDFs and data/theory agreements are clearly examined and discussed.

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arXiv2022

Fragmentation Functions for $Ξ^-/\barΞ^+$ Using Neural Networks

We present a determination of fragmentation functions (FFs) for the octet baryon $Ξ^-/\barΞ^+$ from data for single inclusive electron-positron annihilation. Our parametrization in this QCD analysis is provided in terms of a Neural Network (NN). We determine fragmentation functions for $Ξ^-/\barΞ^+$ at next-to-leading order and for the first time at next-to-next-to-leading order in perturbative QCD. We discuss the improvement of higher-order QCD corrections, the quality of fit, and the comparison of our theoretical results with the fitted datasets. As an application of our new set of fragmentation functions, named SHKS22, we present predictions for $Ξ^- / \barΞ^+$ baryon production in proton-proton collisions at the LHC experiments.

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arXiv2022

Neural Network QCD analysis of charged hadron Fragmentation Functions in the presence of SIDIS data

In this paper, we present a QCD analysis to extract the Fragmentation Functions (FFs) of unidentified light charged hadron entitled as SHK22.h from high-energy lepton-lepton annihilation and lepton-hadron scattering data sets. This analysis includes the data from all available single inclusive electron-positron annihilation (SIA) processes and semi-inclusive deep-inelastic scattering (SIDIS) measurements for the unidentified light charged hadron productions. The SIDIS data which has been measured by the COMPASS experiment could allow the flavor dependence of the FFs to be well constrained. We exploit the analytic derivative of the Neural Network (NN) for fitting of FFs at next-to-leading-order (NLO) accuracy in the perturbative QCD (pQCD). The Monte Carlo method is implied for all sources of experimental uncertainties and the Parton distribution functions (PDFs) as well. Very good agreements are achieved between the SHK22.h FFs set and the most recent QCD fits available in literature, namely JAM20 and NNFF1.1h. In addition, we discuss the impact arising from the inclusion of SIDIS data on the extracted light-charged hadron FFs. The global QCD resulting at NLO for charged hadron FFs provides valuable insights for applications in present and future high-energy measurement of charged hadron final state processes.

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arXiv2022

A global QCD analysis of diffractive parton distribution function considering higher twist corrections within the xFitter framework

We present {\tt SKMHS22}, a new set of diffractive parton distribution functions (PDFs) and their uncertainties at next-to-leading-order accuracy in perturbative QCD within the {\tt xFitter} framework. We describe all available diffractive DIS data sets from HERA and the most recent high-precision H1/ZEUS combined measurements considering three different scenarios. First, we extract the diffractive PDFs considering the standard twist-2 contribution. Then, we include the twist-4 correction from the longitudinal virtual photons. Finally, the contribution of subleading Reggeon exchange to the structure-function $F_2^D$ is also examined. For the contribution of heavy flavors, we utilize the Thorne-Roberts general mass variable number scheme. We show that for those corrections, in particular, the twist-4 contribution allows to include the high-$β$ region and leads to a better description of the diffractive DIS data sets. We find that the inclusion of the subleading Reggeon exchange significantly improves the description of the diffractive DIS cross-section measurements. The resulting sets are in good agreement with all diffractive DIS data analyzed, which cover a wider kinematical range than in previous fits. The {\tt SKMHS22} diffractive PDFs sets presented in this work are available via the {\tt LHAPDF} interface. We also make suggestions for future research in this area.

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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.

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arXiv2021

QCD analysis of pion fragmentation functions in the xFitter framework

We present the first open-source analysis of fragmentation functions (FFs) of charged pions (entitled IPM-xFitter) computed at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) accuracy in perturbative QCD using the xFitter framework. This study incorporates a comprehensive and up-to-date set of pion production data from single-inclusive annihilation (SIA) processes, as well as the most recent measurements of inclusive cross-sections of single pion by the BELLE collaboration. The determination of pion FFs along with their theoretical uncertainties is performed in the Zero-Mass Variable-Flavor Number Scheme (ZM-VFNS). We also present comparisons of our FFs set with recent fits from the literature. The resulting NLO and NNLO pion FFs provide valuable insights for applications in present and future high-energy analysis of pion final state processes.

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arXiv2021

Probing four-fermion operators in the triple top production at future hadron colliders

In this paper, we study the triple top quark production at the future high-energy proton-proton colliders to probe the four-fermion interactions involving three top quarks. We employ the Standard Model Effective Field Theory (SMEFT) to find the upper limits at $95\%$ CL on the Wilson coefficients of these kinds of four-fermion operators. We consider a detailed analysis with a unique signal signature of two same-sign leptons. A full simulation chain includes all the relevant backgrounds, realistic detector simulations and a cut-based technique are taken into account. This study is presented for the HE-LHC working at the center of mass energy of 27 TeV with 15~ab$^{-1}$ and FCC-hh working at the center of mass energy of 100 TeV with 30~ab$^{-1}$. We show that the future high-energy proton-proton colliders could reach an impressive sensitivity to four-fermion contact interactions involving three top quarks.

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