arXiv subjects

Francesco Hautmann

Publications and source records attributed to Francesco Hautmann.

At least 19 recordsLinked to original sources

arXiv2026

Transverse momentum correlations and QED effects in TMD determinations

Extractions of the non-perturbative, transverse momentum dependent (TMD) hadron's structure from experimental measurements of vector-boson spectra at hadron colliders are strongly influenced by correlations across boson's transverse momentum bins and by Quantum Electrodynamics (QED) effects, both from photon emission and from the photon-photon collision background. We present a Monte Carlo framework to take this into account, and illustrate the results with a comparison of theoretical predictions with the high-precision LHCb measurements of $Z$-boson production in the forward rapidity region. We discuss the relationship with the CMS data set at central rapidities.

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arXiv2026

Resummation-scale uncertainties in PDF determinations

We investigate the impact of resummation-scale variations on parton distribution function (PDF) determinations. These variations introduce an additional source of theoretical uncertainty related to the evolution of PDFs and strong coupling $α_s$ that has never previously been accounted for in PDF fits. Using the open-source xFitter framework, we quantify this uncertainty in fits to HERA deep-inelastic scattering data and examine its implications for predictions of top-quark pair production at the LHC. We show that the resulting resummation-scale uncertainties have a sizable impact on LHC observables, highlighting the importance of including this source of uncertainty in precision QCD analyses.

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arXiv2026

Bin-to-bin correlations in the extraction of proton's transverse structure

We investigate the determination of non-perturbative QCD contributions, associated with proton's transverse structure, from high-precision experimental data for electroweak boson production at the LHC. We demonstrate that these determinations are strongly affected by correlated uncertainties across transverse-momentum bins in the region of low boson's transverse momenta. We illustrate our results through a detailed analysis of LHCb measurements of $Z$-boson spectra at forward rapidities, and a comparison with CMS measurements at central rapidities. We further examine the influence on the extraction of the non-perturbative parameters from final-state electromagnetic radiation, photon-induced background, large-$x$ contributions to parton distributions in the forward region, matching to perturbative next-to-leading order. We comment on the comparison of our results with those from the underlying-event tuning of parton-shower Monte Carlo event generators.

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arXiv2025

Intrinsic $k_T$ and soft gluons in Monte Carlo event generators

Experimental measurements of the transverse momentum of Drell-Yan lepton pairs are sensitive to non-perturbative physics associated with the intrinsic parton transverse momentum $k_T$. We discuss recent determinations of intrinsic $k_T$ in the context of transverse momentum dependent (TMD) parton branching calculations and collinear parton-shower Monte Carlo generators. We illustrate the influence of the soft-gluon resolution scale and the non-perturbative Sudakov region on the intrinsic $k_T$ extraction. We emphasize the relevance of the correct treatment of correlated uncertainties between different transverse momentum bins in TMD fits and present an application to the determination of the intrinsic $k_T$ in the forward rapidity region.

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arXiv2025

Perturbative RGE systematics in precision observables

QCD calculations for collider physics make use of perturbative solutions of renormalisation group equations (RGEs). Ambiguities related to these solutions can contribute significantly to systematic uncertainties of theoretical predictions for physical observables. We propose a general method to estimate these systematic effects using techniques inspired by soft-gluon and transverse-momentum resummation approaches. We first discuss the cases of the evolution of strong coupling $α_s$, collinear parton-distribution functions (PDFs), and transverse-momentum-dependent distributions (TMDs). We then study the implications for precision observables in hadron-collider processes, such as the deep-inelastic scattering structure functions and the transverse-momentum distribution of the lepton pair in Drell-Yan production.

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arXiv2025

A $p_T$-ratio observable for studies of intrinsic transverse momentum of partons from Drell-Yan $p_T$ spectra

The determination of the intrinsic transverse momentum distribution of partons is central both for applications of parton shower Monte Carlo generators and for QCD studies of transverse momentum dependent (TMD) parton densities. Valuable information on this distribution is provided by experimental measurements of Drell-Yan transverse momentum $p_T$, in the region of low transverse momenta, with fine binning in $p_T$. However, such fine-binning measurements are challenging, as they require an extremely delicate control of systematic uncertainties. We suggest a $p_T$ observable based on measuring ratios between cross sections of suitably defined low-$p_T$ and high-$p_T$ regions. This observable does not rely on any dedicated partition of bins and has lower systematic uncertainties, and is shown to provide a good sensitivity to the intrinsic transverse momentum.

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arXiv2024

Coarse-grained binning in Drell-Yan transverse momentum spectra

We report a study of the determination of the intrinsic transverse momentum of partons, the intrinsic $k_T$, from the dilepton transverse momentum $p_T$ in Drell-Yan (DY) production at hadron colliders. The result shows that a good sensitivity to the intrinsic $k_T$ distribution is achieved by measuring relative ratios between the cross sections of suitably defined low-$p_T$ and high-$p_T$ regions. The study is performed through both a pseudo-data test and an extraction from measurements of the DY process by the CMS collaboration. Since the methodology does not rely on any dedicated partition of bins, this $p_T$-ratio observable requires less special treatment in very low $p_T$ regions, and propagates lower systematic uncertainties induced from unfolding or momentum migration, in contrast with previous proposals of using a fine-binning measurement of the differential cross section.

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arXiv2024

Exploring SMEFT Couplings Using the Forward-Backward Asymmetry in Neutral Current Drell-Yan Production at the LHC

Neutral current Drell-Yan (DY) lepton-pair production is considered in the framework of the Standard Model Effective Field Theory (SMEFT). Using the open-source fit platform xFitter, we investigate the impact of high-statistics measurements of the neutral current DY (NCDY) forward-backward asymmetry $A_{\rm{FB}}$ near the weak boson mass scale in the present and forthcoming stages of the Large Hadron Collider (LHC). Besides recovering earlier results on the $A_{\rm{FB}}$ sensitivity to parton distribution functions, we analyze the precision determination of $Z$-boson couplings to left-handed and right-handed $u$-quarks and $d$-quarks, and explore Beyond-Standard-Model contributions using the SMEFT framework. We perform a sensitivity study and comment on the role of the $A_{\rm{FB}}$ asymmetry for the electroweak SMEFT fit and precision $Z$-boson physics at the LHC and high-luminosity HL-LHC.

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arXiv2022

PDF bias and flavor dependence in TMD distributions

Transverse momentum dependent (TMD) distributions match collinear parton density functions (PDF) in the limit of small transverse distances, which is accounted for by global extractions of TMD distributions. We study the influence of the collinear PDF value and uncertainties on the determination of unpolarized TMD distributions and the description of Drell-Yan (DY) and Z-boson production measurements at low transverse momenta. We take into account, for the first time, flavor-dependent non-perturbative TMD profiles. We carry out a Bayesian analysis to incorporate the propagation of PDF uncertainties into TMD extractions. We find that collinear PDF uncertainties and non-perturbative TMD flavor dependence are both essential to obtain reliable TMD determinations, and should be included in future global analyses.

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arXiv2022

Enhancing the Large Hadron Collider Sensitivity to Charged and Neutral Broad Resonances of New Gauge Sectors

In scenarios beyond the Standard Model (BSM) characterized by charged ($W^\prime$) or neutral ($Z^\prime$) massive gauge bosons with large width, resonant mass searches are not very effective, so that one has to exploit the tails of the mass distributions measured at the Large Hadron Collider (LHC). In this case, the LHC sensitivity to new physics signals is influenced significantly by systematic uncertainties associated with the Parton Distribution Functions (PDF), particularly in the valence quark sector relevant for the multi-TeV mass region. As a BSM framework featuring such conditions, we consider the 4-Dimensional Composite Higgs Model (4DCHM), in which multiple $W^\prime$ and $Z^\prime$ broad resonances are present, with strongly correlated properties. By using the QCD tool xFitter, we study the implications on $W^\prime$ and $Z^\prime$ searches in Drell-Yan (DY) lepton decay channels that follow from the reduction of PDF uncertainties obtained through combining high-statistics precision measurements of DY lepton-charge and forward-backward asymmetries. We find that the sensitivity to the BSM states is greatly increased with respect to the case of base PDF sets, thereby enabling one to set more stringent limits on (or indeed discover) such new particles, both independently and in correlated searches.

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arXiv2021

Complementarity of Lepton-Charge and Forward-Backward Drell-Yan Asymmetries for Precision Electroweak Measurements and Quark Density Determinations

We address the impact of future measurements of charged and neutral current Drell-Yan (DY) asymmetries and their combination on Parton Distribution Functions (PDFs) uncertainties. We quantify the reduction of PDF uncertainties using the QCD tool xFitter. We examine the effects of such reduced PDF errors on both Standard Model (SM) and Beyond SM (BSM) observables.

hep-ph↗

arXiv2021

Lepton-Charge and Forward-Backward Asymmetries in Drell-Yan Processes for Precision Electroweak Measurements and New Physics Searches

Precision determinations of Standard Model (SM) Electro-Weak (EW) parameters at the Large Hadron Collider (LHC) are dominated by uncertainties due to Parton Distribution Functions (PDFs). Reweighting and profiling techniques are routinely employed to treat this. We explore approaches based on combining measurements of charged current and neutral current Drell-Yan (DY) asymmetries to improve PDF uncertainties. We present the results of a numerical analysis performed with the open-source platform xFitter. PDF uncertainties are examined for lepton-charge and forward-backward asymmetries in regions of transverse and invariant masses near the vector-boson peak, based on LHC Run III and HL-LHC luminosity scenarios. We discuss the complementarity of the asymmetries in reducing PDF uncertainties in observables relevant to both SM and Beyond the SM (BSM) physics.

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arXiv2020

Probing Nucleons and Nuclei in High Energy Collisions

This volume is a collection of contributions for the 7-week program "Probing Nucleons and Nuclei in High Energy Collisions" that was held at the Institute for Nuclear Theory in Seattle, WA, USA, from October 1 until November 16, 2018. The program was dedicated to the physics of the Electron Ion Collider (EIC), the world's first polarized electron-nucleon (ep) and electron-nucleus (eA) collider to be constructed in the USA. These proceedings are organized by chapters, corresponding to the weeks of the program: Week I, Generalized parton distributions; Week II, Transverse spin and TMDs; Week III, Longitudinal spin; Week IV, Symposium week; Weeks V & VI, eA collisions; Week VII, pA and AA collisions. We hope these proceedings will be useful to readers as a compilation of EIC-related science at the end of the second decade of the XXI century.

hep-ph↗

arXiv2020

Non-perturbative contributions to vector-boson transverse momentum spectra in hadronic collisions

Experimental measurements of Drell-Yan (DY) vector-boson production are available from the Large Hadron Collider (LHC) and from lower-energy collider and fixed-target experiments. In the region of low vector-boson transverse momenta $q_T$, which is important for the extraction of the $W$-boson mass at the LHC, QCD contributions from non-perturbative Sudakov form factors and intrinsic transverse momentum distributions become relevant. We study the potential for determining such contributions from fits to LHC and lower-energy experimental data, using the framework of low-$q_T$ factorization for DY differential cross sections in terms of transverse momentum dependent (TMD) distribution functions. We investigate correlations between different sources of TMD non-perturbative effects, and correlations with collinear parton distributions. We stress the relevance of accurate DY measurements at low masses and with fine binning in transverse momentum for improved determinations of long-distance contributions to Sudakov evolution processes and TMDs.

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arXiv2019

PDF Profiling Using the Forward-Backward Asymmetry in Neutral Current Drell-Yan Production

Non-perturbative QCD effects from Parton Distribution Functions (PDFs) may be constrained by using high-statistics Large Hadron Collider (LHC) data. Drell-Yan (DY) measurements in the Charged Current (CC) case provide one of the primary means to do this, in the form of the lepton charge asymmetry. We investigate here the impact of measurements in Neutral Current (NC) DY data mapped onto the Forward-Backward Asymmetry ($A_{\rm FB}$) on PDF determinations, by using the open source fit platform {\tt{xFitter}}. We demonstrate the potential impact of $A_{\rm FB}$ data on PDF determinations and perform a thorough analysis of related uncertainties.

hep-ph↗

arXiv2019

Extending parton branching TMDs to small $x$

We explore the possibility to include small-$x$ dynamics effects in the parton branching (PB) approach to transverse momentum dependent (TMD) parton distribution functions. To this end, we first revisit the PB method at leading order, presenting a new fit to inclusive-DIS precision data, and performing a numerical study of the dynamic soft-gluon resolution scale. Next we investigate the effects of modified CCFM kernels, including both Sudakov and non-Sudakov form factors.

hep-ph↗

arXiv2019

TMD parton distributions from parton showers

We present the determination of Transverse Momentum Dependent (TMD) parton distributions from Monte Carlo parton showers. We investigate the effective TMD distributions obtained from the PYTHIA8 and HERWIG6 parton showers and compare them to the TMD distributions determined within the Parton Branching method.

hep-ph↗

arXiv2019

Using Forward-Backward Drell-Yan Asymmetry in PDF Determinations

We study the impact of the inclusion of Neutral Current (NC) DY data from LHC mapped in the Forward-Backward Asymmetry ($A_{\rm FB}$) observable on PDF uncertainties, using the open source platform \texttt{xFitter}. We find that $A_{\rm FB}$ enables new PDF sensitivity at current and future luminosity stages of LHC.

hep-ph↗