arXiv subjects

S. Rezaie

Publications and source records attributed to S. Rezaie.

7 recordsLinked to original sources

arXiv2026

Numerical Study of MRW-Type Unintegrated Double Parton Distribution Functions from Non-Factorized DPDFs

Double parton scattering provides a sensitive probe of multiparton correlations inside hadrons. In this work we present a numerical study of unintegrated double parton distribution functions constructed from non-factorized collinear DPDFs. As input we use the \texttt{GS09} DPDFs and evolve them to unequal scales with a numerical double DGLAP evolution framework, which is validated through the corresponding momentum and valence-number sum rules. We investigate MRW-inspired prescriptions for generating transverse momentum dependence in the double parton case. In particular, we study the double LO-MRW approach (DLO-MRW) in the perturbative region, the double modified KMRW approach (DMKMRW), the double virtuality ordered MRW (DVO-MRW) model, and a normalization-matched version of the latter. The DMKMRW, DVO-MRW, and matched DVO-MRW prescriptions can be applied directly to the full collinear DPDF, including its nonhomogeneous component, and avoid the piecewise treatment required in the conventional LO-MRW construction. We analyze the normalization, transverse momentum dependence, flavor dependence, and sensitivity to longitudinal DPDF correlations of the resulting distributions. The DMKMRW model is normalization preserving by construction, while the DVO-MRW model shows nontrivial normalization deviations that are removed in the matched version. Non-factorized effects are strongly channel-dependent. In DMKMRW, they enter mainly through longitudinal DPDF correlations, whereas in the LO-MRW and virtuality-ordered models, they also modify the transverse momentum shape. The largest deviations occur near the double parton kinematic boundary and in channels affected by valence-number and quark-antiquark correlations.

hep-ph↗

arXiv2025

Prompt diphoton production compared to measurements at 13 TeV in $k_t$-factorization: A comparative analysis of unintegrated PDF models

We perform an in-depth comparative analysis of unintegrated parton distribution function (UPDF) models for isolated prompt diphoton production in proton-proton collisions at $\sqrt{s}=13$~TeV within the $k_t$-factorization framework. Predictions are obtained with three UPDF approaches: Parton Branching (PB), NLO-MRW, and Modified KMRW (MKMRW). Tree-level $q + \bar q\!\to\!\gamma +\gamma$, $q + \bar q\!\to\!\gamma + \gamma + g$, and $q + g\!\to\!\gamma +\gamma + q$ subprocesses are generated with \textsc{KaTie} using off-shell initial states; the loop-induced $g + g\!\to\!\gamma + \gamma$ channel is evaluated independently. We compare differential cross sections with ATLAS measurements across a broad set of observables, including the photon transverse momenta, diphoton invariant mass and transverse momentum, the Collins-Soper angle, acoplanarity, $\phi^*_\eta$, and a transverse thrust-related variable. This comparative study quantifies the impact of the UPDF choice on the diphoton spectra. We find that the PB model provides the most consistent agreement over all distributions, whereas NLO-MRW tends to overshoot in regions correlated with larger factorization scales and MKMRW generally undershoots due to stronger Sudakov suppression. With standard scale variations, our results indicate that $k_t$-factorization with PB UPDFs can accurately describe diphoton production, while fixed-order collinear predictions typically require higher-order corrections together with parton-shower effects to achieve a comparable description.

hep-ph↗

arXiv2025

Z boson production in proton-lead collisions: A study utilizing MRW nuclear TMDs

This paper investigates the production of Z bosons in proton-lead collisions at a center of mass energy of $\sqrt{s} = 8.16$ TeV, utilizing various transverse momentum dependent parton distribution functions (TMDs), including the leading order Martin-Ryskin-Watt (LO-MRW), next-to-leading order MRW (NLO-MRW), and parton branching (PB) approaches. By comparing theoretical predictions with experimental data from the CMS collaboration, we assess the performance of these TMD models across different kinematic regions. Our analysis reveals that while both LO-MRW and NLO-MRW models generally align well with experimental data, the LO-MRW model tends to overestimate in certain kinematic regions. The NLO-MRW model, with its strong ordering constraint, provides better agreement in these areas. This study highlights the impact of different impositions of angular and strong ordering constraints in the LO-MRW and NLO-MRW approaches in describing Z boson production.

hep-ph↗

arXiv2024

PDFxTMDLib: A High-Performance C++ Library for Collinear and Transverse Momentum Dependent Parton Distribution Functions

Collinear parton distribution functions (cPDFs) and transverse momentum dependent distributions (TMDs) are essential for calculating cross sections in high-energy physics, particularly within collinear and kt-factorization frameworks. Currently, there exists two libraries, such as LHAPDF and TMDLib, to obtain these physical objects. However, there are limitations in both libraries, especially for TMDs, such as restricted customization and extensibility. Users are limited to the implementations provided by these libraries and cannot easily support unconventional PDFs. Moreover, no standard TMD library currently provides a consistent framework for QCD coupling evaluation or for studying uncertainties at the distribution level--features that are important for diagnostic and comparative analyses in phenomenological research. To address these shortcomings, we introduce PDFxTMDLib, a modern C++ library designed to offer a robust and flexible solution. This library supports both collinear PDFs and TMDs while allowing greater customization. It also opens the way to support higher-order distributions. In this article, we describe the structure of PDFxTMDLib. We also demonstrate its validity and performance by integrating it into the PYTHIA Monte Carlo event generator to compute Drell-Yan cross sections. Additionally, comparisons of PDFs obtained from PDFxTMDLib with those from LHAPDF and TMDLib confirm the reliability of PDFxTMDLib's results.

hep-ph↗

arXiv2021

Inclusive jet and dijet productions using $k_t$ and $(z,k_t)\textrm{-factorizations}$ versus ZEUS collaboration data

In this paper, we investigate the differential cross sections of the inclusive jet and dijet productions of the ZEUS collaboration data at the center of mass energies of $\sim 300\;GeV$ and $ 319\;GeV$ using the $k_t$ and $(z,k_t)\textrm{-factorizations}$ with the different unintegrated and double unintegrated parton distribution functions, i.e., UPDFs and DUPDFs, respectively. The \textsc{KaTie} event generator is used to calculate the differential cross section with the UPDFs, while for the input DUPDFs the calculations are directly performed by evaluating the corresponding matrix elements. We check the effect of choosing the different implementation of angular or strong ordering constraints using the UPDFs and the corresponding DUPDFs of Kimber-Martin-Ryskin (KMR) and the leading-order (LO) and next-to-leading-order (NLO) Martin-Ryskin-Watt (MRW) approaches. The impacts of choosing virtualities $k^2 = k_t^2$ or $k^2 = {k_t^2\over {(1-z)}}$ in the differential cross section predictions for the ZEUS experimental data are also investigated. It is observed that, as one should expect, the applications of $(z,k_t)\textrm{-factorization}$ is better than the $k_t\textrm{-factorization}$ framework for the predictions of high virtuality $Q^2$ with respect to the ZEUS collaboration data, and also the results of the KMR and LO-MRW UPDFs and DUPDFs are reasonably close to each other and in general can describe the data. It is also observed that only in the case of $k_t$-factorization, the inclusion of Born level makes our results to overshoot the inclusive jet experimental data.

hep-ph↗

arXiv2021

A validity check of the KATIE parton level event generator in the $k_t$-factorization and collinear frameworks

In the present paper, we check and study the validity of the \textsc{KaTie} parton level event generator, by calculating the inclusive electron-proton (ep) dijet and the Proton-proton (p-p) Drell-Yan electron-pair productions differential cross sections in the $k_t$- and collinear factorization frameworks. The Martin-Ryskin-Watt (MRW) unintegrated parton distribution functions (UPDFs) are used as the input UPDFs. The results are compared with those of ZEUS ep inclusive dijet and ATLAS p-p Drell-Yan electron-pair productions, experimental data. The \textsc{KaTie} parton level event generator can directly calculate the cross sections in the $k_t$-factorization framework. It is noticed that the lab to the Breit transformation in this generator is not correctly implemented by its author, so the produced output does not cover the ep ZEUS experimental data in which the mentioned transformation is applied. By fixing the above transformation in the \textsc{KaTie} generator code, we could appropriately produce the ep inclusive dijet differential cross section, in comparison with those of ZEUS data. It is also shown that the MRW at the NLO level, with the angular ordering constraint can successfully predict the ATLAS p-p Drell-Yan data. Finally, as it is expected, we conclude that the $k_t$-factorization is an appropriate tool for the small longitudinal parton momenta and high center of mass energies, with respect to the collinear one.

hep-ph↗

arXiv2021

Three-photon productions within the $k_t$-factorization for the ATLAS-LHC data

Recently, the ATLAS data of isolated three-photon production showed that the next-to-leading order (NLO) collinear factorization is not enough to describe experimental data. Therefore, one needs to calculate the cross section beyond the NLO, and as showed later, these data can be well described by the NNLO calculation within the collinear factorization framework. However, it is shown that the $k_t$-factorization can be quite successful in describing exclusive and high energy collision processes, henceforth we decided to calculate isolated three-photon production within this framework. In this work we use the Martin, Ryskin, and Watt unintegrated parton distribution functions (MRW UPDFs) at LO and NLO levels, in addition to parton branching (PB) UPDFs in order to calculate cross section which we utilize the KATIE parton level event generator. It will be shown that in contrast to collinear factorization, the $k_t$-factorization can describe quiet well the three-photon production ATLAS data. Interestingly our results using the NLO-MRW and PB UPDFs can cover the data within their uncertainty bands, similar to the NNLO collinear results.

hep-ph↗