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Marco Guzzi

Publications and source records attributed to Marco Guzzi.

At least 19 recordsLinked to original sources

Candia-v2: Logarithmic expansions for DGLAP evolution in $x$-space

We present Candia-v2, an open-source software package that generalizes the $x$-space Candia algorithm to next-to-next-to-next-to-leading order (N$^{3}$LO) accuracy in Quantum Chromodynamics (QCD). The code solves the DGLAP evolution equations for unpolarized nucleon parton densities using a highly efficient logarithmic expansion technique that can be systematically extended to all orders in QCD. Candia-v2 supersedes the previous original C implementation of the algorithm with significantly increased efficiency and improved API. The software is publicly available on GitHub under the GPLv3 license.

hep-ph

Strong Coupling Constant Determination from the new CTEQ-TEA Global QCD Analysis

We present a new determination of the strong coupling constant $\alpha_s$ from a global QCD analysis CT25 of parton distribution functions (PDFs) that incorporates high-precision experimental measurements from the Run-2 of the Large Hadron Collider together with a large sample of other measurements over a wide interval of energies. This work addresses two objectives: providing an up-to-date determination of $\alpha_s$ using NNLO calculations and a sensitive nucleon data set within a self-consistent framework, and critically assessing the robustness of the $\alpha_s(M_Z)$ extraction in light of systematic uncertainties as well as correlations of $\alpha_s(M_Z)$ with the functional forms of PDFs and other model parameters. In regard to the uncertainty assessment, we demonstrate that some commonly used criteria, including the dynamical tolerance and Bayesian hierarchical models, may produce significantly different or even unstable estimates for the net $\alpha_s$ uncertainty, and we introduce a concept of \textit{data-clustering safety} that the replicable uncertainty estimates must satisfy. Based on this in-depth examination of the CT25 global hadronic data set using a combination of analysis methods, and after demonstrating a weak correlation between $\alpha_s$ and the functional forms of CT25 PDF parametrizations, we find $\alpha_s(M_Z)=0.1183^{+0.0023}_{-0.0020}$ at the 68\% credibility level.

hep-ph

DGLAP evolution at N$^3$LO with the $\texttt{Candia}$ algorithm

We present a generalization of the $x$-space $\texttt{Candia}$ algorithm to next-to-next-to-next-to-leading order (N$^3$LO) accuracy in Quantum Chromodynamics (QCD) for solving the DGLAP evolution equations for unpolarized parton densities in the nucleon. The algorithm is based on logarithmic expansions of the solution and can be extended to all orders in QCD. An expansion equivalent to the exact solution of the DGLAP equation at N$^3$LO is presented in the non-singlet sector. Results for approximate N$^3$LO PDFs, evolved using the most recent approximations to the N$^3$LO DGLAP splitting functions, are provided for benchmarking. The new version of the code, $\texttt{Candia-v2}$, is publicly available at https://github.com/champso1/candia-v2.

hep-ph

Experimental Particle Physics Priorities 2025: A String Phenomenology Perspective

With the SNOWMASS 2021 process in the US and the on--going European Strategy Report 2025, the field of elementary particle physics is undergoing detailed community evaluation, and the experimental particle physics program, which requires substantial public investment, is under scrutiny. We offer an assessment of the current experimental particle physics priorities from a string phenomenology point of view. String theory provides a perturbatively consistent framework for quantum gravity. String phenomenology aims to connect between string theory and observational data. String theory is a consistent theory of quantum gravity that contains the other fundamental constituents of matter and interactions. As all forms of energy couple to gravity, string theory provides a framework that reproduces the structures of the Standard Model of particle physics and gives rise to detailed physics scenarios beyond the Standard Model, {\it e.g.} dark matter candidates, axions, additional gauge symmetries, etc. Given this breadth, we propose that from a string phenomenology perspective, the experimental particle physics priority is the nature of the Higgs boson and the electroweak symmetry breaking mechanism. An ideal facility in the near future to study this sector is a hadron collider at 50--60 TeV that utilises contemporary magnet technology and can be built in 10--15 years from decision.

hep-ph

Progress in top-quark pair production cross section calculations and impact on parton distribution functions of the proton

We discuss the impact of eligible top-quark pair production differential cross-section measurements at the LHC with a collision energy of 13 TeV on the parton distribution functions (PDFs) of the proton as well as the impact of approximate next-to-next-to-next-to-leading order (aN$^3$LO) QCD corrections combined with next-to-leading order (NLO) electroweak (EW) corrections on $t\bar t$ observables. We illustrate the effects on the gluon PDF at large $x$ from an optimal baseline selection of data in NNLO global fits, and show comparisons between the theory prediction for $t\bar t$ total and differential cross sections at aN$^3$LO QCD combined with NLO EW and recent measurements from the ATLAS and CMS collaborations at the LHC.

hep-ph

General Mass treatment for Z boson production in association with a heavy quark at hadron colliders

We present the application of the ACOT and S-ACOT general mass variable flavor number schemes to proton-proton collisions with particular attention to the production of final states with at least one heavy quark. Subtraction and residual heavy-quark parton distribution functions are introduced to facilitate the implementation of this scheme at higher orders in perturbative QCD. The calculation of Z-boson hadronic production with at least one $b$ jet beyond the lowest order in QCD is considered for illustration purposes.

hep-ph

General mass variable flavor number scheme for $Z$ boson production in association with a heavy quark at hadron colliders

We present a methodology to streamline implementation of massive-quark radiative contributions in calculations with a variable number of active partons in proton-proton collisions. The methodology introduces \textit{subtraction} and \textit{residual} heavy-quark parton distribution functions (PDFs) to implement calculations in the Aivazis-Collins-Olness-Tung (ACOT) factorization scheme and its simplified realization in various processes up to the next-to-the-next-to-leading order in the QCD coupling strength. Interpolation tables for bottom-quark subtraction and residual distributions for CT18 NLO and NNLO PDF ensembles are provided in the common LHAPDF6 format. A numerical calculation of $Z$-boson production with at least one $b$ jet at the Large Hadron Collider beyond the lowest order in QCD is considered for illustration purposes.

hep-ph

String Derived Z$^\prime$ Model at an Upgraded Superconducting Super Collider

The future of collider physics is under investigation. With the High Luminosity LHC program lasting until the late 2030s, the next machine in the energy frontier is envisioned to appear in 30--40 years, which may be too far into the future to sustain the field. In this paper we explore the physics potential of an Upgraded Superconducting Super Collider (USSC). The Original Superconducting Super Collider (OSSC) was planned to operate at 20TeV beam energy, and with improved magnet technology and/or longer tunnel, one may envision that it can be extended to 25--30TeV beam energy. Given that the decision on the OSSC construction took place in Autumn 1988 and it was planned to start operation in the 1996-1999 period, an USSC can be constructed 10--15 years from decision and fill the gap between the end of HL--LHC and the future envisioned machines. While the main mission of the USSC will be to test the Standard Model and its electroweak and strongly interacting sectors, as a specific example we illustrate the invariant mass distribution at NNLO in QCD for a 5 TeV $Z^\prime$ in the string derived $Z^\prime$ model.

hep-ph

Exploring the impact of high-precision top-quark pair production data on the structure of the proton at the LHC

The impact of recent LHC top-quark pair production single differential cross section measurements at 13 TeV collision energy on the structure of the proton is explored. In particular, the impact of these high-precision data on the gluon and other parton distribution functions (PDFs) of the proton at intermediate and large partonic momentum fraction $x$ is analyzed. This study extends the CT18 global analysis framework to include these new data. The interplay between top-quark pair and inclusive jet production as well as other processes at the LHC, is studied. In addition, a study of the impact of scale choice on the theory description of the new 13 TeV $t\bar t$ measurements is performed.

hep-ph

Top-quark cross sections and distributions at aN$^3$LO

We present theoretical predictions for top-quark total cross sections and for differential distributions in top-quark transverse momentum and rapidity. Third-order soft gluon corrections are added to the complete NNLO quantities to provide approximate N$^3$LO (aN$^3$LO) results, and electroweak corrections at NLO are also included. We calculate the theoretical uncertainties from scale dependence and from parton distribution functions in the proton, and estimate their impact on the total and differential cross sections. The higher-order corrections are large and they reduce the scale uncertainties. The results presented in this work include the best current theoretical input and are in good agreement with recent data from the LHC.

hep-ph

Precision studies for string derived $Z'$ dynamics at the LHC

We consider $Z'$s in heterotic string derived models and study $Z'$ resonant production at the TeV scale at the Large Hadron Collider (LHC). We use various kinematic differential distributions for the Drell-Yan process at NNLO in QCD to explore the parameter space of such models and investigate $Z'$ couplings. In particular, we study the impact of $Z$-$Z'$ kinetic-mixing interactions on forward-backward asymmetry ($A_{FB}$) and other distributions at the LHC.

hep-ph

The persistent nonperturbative charm enigma

The question of the existence and possible magnitude of nonperturbative (often called "intrinsic") charm in the proton has long confounded attempts to cleanly isolate such a contribution in global analyses of high-energy experiments. In this letter, we show that the available (non)perturbative QCD theory and hadronic data have still not developed to a sufficient level to clearly resolve this problem. We highlight a number of challenging aspects that must be confronted in extracting nonperturbative charm in PDF fits, and in so doing, present an updated next-to-next-to-leading order CT analysis of fitted charm, CT18 FC, which we also compare to recent studies. We outline the theory developments and future data needed to make progress on this subject.

hep-ph

Report of the Topical Group on Top quark physics and heavy flavor production for Snowmass 2021

This report summarizes the work of the Energy Frontier Topical Group on EW Physics: Heavy flavor and top quark physics (EF03) of the 2021 Community Summer Study (Snowmass). It aims to highlight the physics potential of top-quark studies and heavy-flavor production processes (bottom and charm) at the HL-LHC and possible future hadron and lepton colliders and running scenarios.

hep-ph

Heavy-flavor impact on CTEQ-TEA global QCD analyses

We discuss heavy-flavor production at hadron colliders in recent global QCD analyses to determine parton distribution functions (PDFs) in the proton. We discuss heavy-flavor treatments in precision theory predictions at the LHC. In particular, we discuss factorization schemes in presence of heavy flavors in proton-proton collisions, as well as the impact of heavy-flavor production at the LHC on PDFs. We show results of recent updates beyond CT18, the latest global QCD analysis from the CTEQ-TEA group.

hep-ph

Probing heavy-flavor parton distribution functions at hadron colliders

Precision measurements of heavy-flavor hadroproduction at the Large Hadron Collider (LHC) have the ability to probe heavy-flavor parton distribution functions (PDFs) in the proton. Sensitivity of inclusive $B^\pm$ meson production cross section measurements at LHCb 13 TeV to the bottom-quark PDF is illustrated by using theory predictions obtained with a the S-ACOT-MPS general mass variable flavor number (GMVFN) scheme within the QCD factorization formula. This approach can easily be extended to other heavy-flavor production processes, such as $Z$ boson production in association with a bottom- or a charm-jet. The inclusion of such measurements will represent an important improvement for future global QCD analyses that aim at reducing uncertainties of heavy-flavor PDFs, provided that a consistent general mass treatment in $pp$ collisions is used. This work is related to the activities of the Snowmass topic groups EF03, and EF06.

hep-ph

The Forward Physics Facility at the High-Luminosity LHC

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential.

hep-ex

CTEQ-TEA group updates: Photon PDF and Impact from heavy flavors in the CT18 global analysis

We discuss recent CTEQ-TEA group activities after the publication of the CT18 global analysis of parton distribution functions (PDFs) in the proton. In particular, we discuss a new calculation for the photon content in the proton, termed as CT18lux and CT18qed PDFs, and the impact of novel charm- and bottom-quark production cross section measurements at HERA on the CT18 global analysis.

hep-ph