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Francesco Giuli

Publications and source records attributed to Francesco Giuli.

At least 37 records · Page 2Linked to original sources

The Forward Physics Facility: Sites, Experiments, and Physics Potential

The Forward Physics Facility (FPF) is a proposal to create a cavern with the space and infrastructure to support a suite of far-forward experiments at the Large Hadron Collider during the High Luminosity era. Located along the beam collision axis and shielded from the interaction point by at least 100 m of concrete and rock, the FPF will house experiments that will detect particles outside the acceptance of the existing large LHC experiments and will observe rare and exotic processes in an extremely low-background environment. In this work, we summarize the current status of plans for the FPF, including recent progress in civil engineering in identifying promising sites for the FPF and the experiments currently envisioned to realize the FPF's physics potential. We then review the many Standard Model and new physics topics that will be advanced by the FPF, including searches for long-lived particles, probes of dark matter and dark sectors, high-statistics studies of TeV neutrinos of all three flavors, aspects of perturbative and non-perturbative QCD, and high-energy astroparticle physics.

hep-ph↗

Precision measurements of the Lepton-Charge and Forward-Backward Drell-Yan Asymmetries to Enhance the Sensitivity to Broad Resonances of New Gauge Sectors

We study the impact of future measurements of lepton-charge and forward-backward asymmetries in Drell-Yan processes in regions of transverse and invariant masses near the Standard Model gauge bosons peaks to improve the Parton Distribution Functions uncertainties. We study the implications on $W^{'}$ and $Z^{'}$ searches following the reduction of these uncertainties. We find that the sensitivity to the Beyond the Standard Model states is greatly increased with respect to the case of base Parton Distribution Functions sets, thereby enabling one to set more stringent limits on (or indeed discover) such new particles.

hep-ph↗

The PDF4LHC21 combination of global PDF fits for the LHC Run III

A precise knowledge of the quark and gluon structure of the proton, encoded by the parton distribution functions (PDFs), is of paramount importance for the interpretation of high-energy processes at present and future lepton-hadron and hadron-hadron colliders. Motivated by recent progress in the PDF determinations carried out by the CT, MSHT, and NNPDF groups, we present an updated combination of global PDF fits: PDF4LHC21. It is based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either its Hessian reduction or its replica compression. Extensive benchmark studies are carried out in order to disentangle the origin of the differences between the three global PDF sets. In particular, dedicated fits based on almost identical theory settings and input datasets are performed by the three groups, highlighting the role played by the respective fitting methodologies. We compare the new PDF4LHC21 combination with its predecessor, PDF4LHC15, demonstrating their good overall consistency and a modest reduction of PDF uncertainties for key LHC processes such as electroweak gauge boson production and Higgs boson production in gluon fusion. We study the phenomenological implications of PDF4LHC21 for a representative selection of inclusive, fiducial, and differential cross sections at the LHC. The PDF4LHC21 combination is made available via the LHAPDF library and provides a robust, user-friendly, and efficient method to estimate the PDF uncertainties associated to theoretical calculations for the upcoming Run III of the LHC and beyond.

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↗

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.

hep-ph↗

Precision measurements of jet production at the ATLAS experiment

Measurements of jet production are sensitive to the strong coupling constant, high order perturbative calculations and parton distribution functions. In this talk we present the most recent ATLAS measurements in this area at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV. We present measurements of variables probing the properties of the multijet energy flow and of the Lund Plane using charged particles. We will also present new measurements sensitive to the strong coupling constant. For jet fragmentation, we present a measurement of the fragmentation properties of $b$-quark initiated jets, studied using charged B mesons. This analysis provides key measurements with which to better understand the fragmentation functions of heavy quarks. All results are corrected for detector effects and compared to several Monte Carlo predictions with different parton shower and hadronisation models.

hep-ex↗

Impact of charged and neutral Drell-Yan Asymmetries on precision measurements

We study the impact of future measurements of lepton-charge and forward-backward asymmetries on PDF determination. These results have been obtained employing standard profiling procedures and the open-source platform xFitter. The potential of the combination of charged-current and neutral-current Drell-Yan asymmetries in regions of transverse and invariant masses near the W/Z bosons peaks to improve the PDF uncertainties has also been explored.

hep-ph↗

HL-LHC Computing Review Stage-2, Common Software Projects: Event Generators

This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group (WG), as an input to the second phase of the LHCC review of High-Luminosity LHC (HL-LHC) computing, which is due to take place in November 2021. It complements previous documents prepared by the WG in the context of the first phase of the LHCC review in 2020, including in particular the WG paper on the specific challenges in Monte Carlo event generator software for HL-LHC, which has since been updated and published, and which we are also submitting to the November 2021 review as an integral part of our contribution.

hep-ph↗

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↗

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.

hep-ph↗

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.

hep-ph↗

Impact of A0 data on the Higgs boson production cross section at the LHC

In this talk, we present a way to improve the accuracy of theoretical predictions for Higgs boson production cross sections at the LHC using the measurements of lepton angular distributions. In this regards, we exploit the sensitivity of the lepton angular coefficient associated with the longitudinal Z-boson polarization to the parton density function (PDF) for gluons resolved from the incoming protons, in order to constrain the Higgs boson cross section from gluon fusion processes. We find that high-statistics determinations of the longitudinally polarized angular coefficient at the LHC Run 3 and high-luminosity HL-LHC improve the PDF systematics of the Higgs boson cross section predictions by 50% over a broad range of Higgs boson rapidities. This study has been conducted using the open-source fitting framework xFitter. This talk refers to the following paper: arXiv:2012.10298[hep-ph]

hep-ph↗

Challenges in Monte Carlo event generator software for High-Luminosity LHC

We review the main software and computing challenges for the Monte Carlo physics event generators used by the LHC experiments, in view of the High-Luminosity LHC (HL-LHC) physics programme. This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group as an input to the LHCC review of HL-LHC computing, which has started in May 2020.

hep-ph↗

Impact of ATLAS $V$ + jets data on PDF fits

This proceeding presents a new set of proton parton distribution functions, ATLASepWZVjet20, produced in an analysis at next-to-next-to-leading-order in QCD. The new datasets considered are the ATLAS measurements of $W^{\pm}$ and $Z$ boson production in association with jets in $pp$ collisions at $\sqrt{s}$ = 8 TeV at the LHC with integrated luminosities of 20.2 fb$^{-1}$ and 19.9 fb$^{-1}$ respectively. The analysis also considers the ATLAS measurements of differential $W^{\pm}$ and $Z$ boson production at $\sqrt{s}$ = 7 TeV with an integrated luminosity of 4.6 fb$^{-1}$ and deep-inelastic scattering data from $e^{\pm}p$ collisions at the HERA accelerator. An improved determination of the sea-quark densities at high Bjorken $x$ is shown, while confirming a strange-quark density of similar size as the up-and down-sea quark densities in the range $x\sim$ 0.02 found by previous ATLAS analyses.

hep-ex↗

New opportunities at the photon energy frontier

Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the energy frontier for photon-mediated interactions. UPC photons can be used for many purposes, including probing low-$x$ gluons via photoproduction of dijets and vector mesons, probes of beyond-standard-model processes, such as those enabled by light-by-light scattering, and studies of two-photon production of the Higgs.

hep-ph↗

HL-LHC Computing Review: Common Tools and Community Software

Common and community software packages, such as ROOT, Geant4 and event generators have been a key part of the LHC's success so far and continued development and optimisation will be critical in the future. The challenges are driven by an ambitious physics programme, notably the LHC accelerator upgrade to high-luminosity, HL-LHC, and the corresponding detector upgrades of ATLAS and CMS. In this document we address the issues for software that is used in multiple experiments (usually even more widely than ATLAS and CMS) and maintained by teams of developers who are either not linked to a particular experiment or who contribute to common software within the context of their experiment activity. We also give space to general considerations for future software and projects that tackle upcoming challenges, no matter who writes it, which is an area where community convergence on best practice is extremely useful.

physics.comp-ph↗

Parton Distribution Functions of the Charged Pion Within The xFitter Framework

We present the first open-source analysis of parton distribution functions (PDFs) of charged pions using xFitter, an open-source QCD fit framework to facilitate PDF extraction and analyses. Our calculations are implemented at next-to-leading order (NLO) using APPLgrids generated by MCFM generator. Using currently available Drell-Yan and photon production data, we find the valence distribution is well constrained; however, the considered data are not sensitive enough to unambiguously determine sea and gluon distributions. Fractions of momentum carried by the valence, sea and gluon components are discussed, and we compare with the results of JAM collaboration and the GRV group.

hep-ph↗

A new simple PDF parametrization: improved description of the HERA data

We introduce a new parametrization for the parton distribution functions (PDFs) designed to be flexible in the small-x region. We implement it in the xFitter open-source PDF fitting tool, and compare it to the default xFitter parametrization, widely used for many PDF studies, and notably for the HERAPDF determination. We find that we can describe the combined inclusive HERA I+II data using NNLO theory with a significantly higher quality than HERAPDF2.0: the $χ^2$ is reduced by more than 60 units, having used only four more parameters. Our result highlights a significant parametrization bias in the default xFitter parametrization at small x, which would lead to even more dramatic effects when used for higher energy colliders, where the small-x region is more relevant. We also find that the inclusion of small-x resummation, that was shown in previous studies to lead to similar improvements in the fit quality, further reduces the $χ^2$ by approximately 30 extra units.

hep-ph↗