arXiv subjects

Agnieszka Luszczak

Publications and source records attributed to Agnieszka Luszczak.

At least 19 recordsLinked to original sources

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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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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arXiv2020

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.

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arXiv2020

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.

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arXiv2019

Investigation of High Energy Behaviour of HERA Data

We analyse the high precision HERA $F_2$ data in the low-$x$ regions, $x<0,01$ and the very-low-$x$, $x<0.001$, regions using $λ$-Fits. $λ$ is a measure of the rate of rise of $F_2$ defined by $F_2 \propto (1/x)^λ$. We show that $λ$ determined in these two regions, at various $Q^2$ values, is systematically smaller in the very-low-$x$ region as compared to the low-$x$ region. We discuss some possible physical interpretations of this effect.

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arXiv2019

Dipole model analysis of high precision HERA data

We analyse, within a dipole model, the inclusive DIS cross section data, obtained from the combination of the H1 and ZEUS HERA measurements. We show that these high precision data are very well described within the dipole model framework, which is complemented with a valence quark structure functions. We discuss the properties of the gluon density obtained in this way.

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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.

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arXiv2019

Probing the strange content of the proton with charm production in charged current at LHeC

We study charm production in charged-current deep-inelastic scattering (DIS) using the xFitter framework. Recent results from the LHC have focused renewed attention on the determination of the strange-quark parton distribution function (PDF) and the DIS charm process provides important complementary constraints on this quantity. We examine the current PDF uncertainty, and use LHeC pseudodata to estimate the potential improvement from this proposed facility. As xFitter implements both fixed-flavor- and variable-flavor-number schemes, we can compare the impact of these different theoretical choices; this highlights some interesting aspects of multi-scale calculations. We find that the high-statistics LHeC data covering a wide kinematic range could substantially reduce the strange PDF uncertainty.

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arXiv2019

Recent QCD results from the xFitter project: Probing the strange content of the proton with charm production in charged current at LHeC

We investigate charm production in charged-current deep-inelastic scattering (DIS) using the xFitter program. xFitter is an open-source software framework for the determination of PDFs and the analysis of QCD physics, and has been used for a variety of LHC studies. The study of charged current DIS charm production provides an important perspective on the strange quark PDF, s(x). We make use of the xFitter tools to study the present s(x) constraints, and then use LHeC pseudodata to infer how these might improve. Furthermore, as xFitter implements both Fixed Flavor and Variable Flavor number schemes, we can examine the impact of these different theoretical choices; this highlights some interesting aspects of multi-scale calculations. This study provides a practical illustration of the many features of xFitter.

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arXiv2018

Impact of low-$x$ resummation on QCD analysis of HERA data

Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low $x$ and low $Q^2$. A resolution of this tension incorporating $\ln(1/x)$-resummation terms into the HERAPDF fits is investigated using the xFitter program. The kinematic region where this resummation is important is delineated. Such high-energy resummation not only gives a better description of the data, particularly of the longitudinal structure function $F_L$, it also results in a gluon PDF which is steeply rising at low $x$ for low scales, $Q^2 \simeq 2.5$ GeV$^2$, contrary to the fixed-order NLO and NNLO gluon PDF.

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arXiv2017

Dipole model analysis of highest precision HERA data, including very low $Q^2$'s

We analyse, within a dipole model, the final, inclusive HERA DIS cross section data in the low $x$ region, using fully correlated errors. We show, that these highest precision data are very well described within the dipole model framework starting from $Q^2$ values of 3.5 GeV$^2$ to the highest values of $Q^2 =$ 250 GeV$^2$.

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arXiv2016

Dipole model analysis of the new HERA I+II data

We use the dipole model to analyze the inclusive DIS cross section data, obtained from the HERA I+II measurements \cite{Abramowicz:2015mha}. We show that these combined data are very well described within the dipole model framework, which is complemented with a valence quark structure functions. Our motivation is to investigate the gluon density with the BGK dipole model \cite{BGK} as an alternative to the PDF approach. BGK dipole model uses for evolution the DGLAP mechanism in the $kt$ factorization scheme (in contrast to the collinear factorization for PDFs). We confirm our results from the previous paper \cite{Luszczak:2013rxa} with old HERA data \cite{HERA2010}. In addition we also performed a first, preliminary investigation of saturation. The analysis was done in the xFitter framework \cite{xFitter,xFitter2,xFitter3,xFitter4,xFitter5}.}

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arXiv2016

A determination of mc(mc) from HERA data using a matched heavy-flavor scheme

The charm quark mass is one of the fundamental parameters of the Standard Model Lagrangian. In this work we present a determination of the MSbar charm mass from a fit to the inclusive and charm HERA deep-inelastic structure function data. The analysis is performed within the xFitter framework, with structure functions computed in the FONLL general-mass scheme as implemented in APFEL. In the case of the FONLL-C scheme, we obtain mc(mc) = 1.335 +- 0.043(exp) +0.019 -0.000(param) +0.011 -0.008(mod) +0.033 -0.008(th) GeV. We also perform an analogous determination in the fixed-flavor-number scheme at next-to-leading order, finding mc(mc) = 1.318 +- 0.054(exp) +0.011 -0.010(param) +0.015 -0.019(mod) +0.045 -0.004(th) GeV, compatible with the FONLL-C value. Our results are consistent with previous determinations from DIS data as well as with the PDG world average.

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arXiv2009

Diffractive asymmetry of electroweak vector bosons at the LHC

We analyse diffractive weak boson production in $pp$ collisions. We show that the measurement of $W$ boson production asymmetry in the diffractive $pp$ collisions is a valuable method to test the concept of the flavour symmetric pomeron parton distributions.

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arXiv2009

Diffractive production of electroweak vector bosons at the LHC

We analyse diffractive electroweak vector boson production in hadronic collisions and show that the single diffractive W boson production asymmetry in rapidity is a particularly good observable at the LHC to test the concept of the flavour symmetric pomeron parton distributions. It may also provide an additional constraint for the parton distribution functions in the proton.

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arXiv2009

Precise dipole model analysis of diffractive DIS

We analyse the newest diffractive deep inelastic scattering data from HERA using the dipole model approach. We find a reasonable good agreement between the predictions and the data although the region of small values of a kinematic variable $β$ needs refinement. A way to do this is to consider an approach with diffractive parton distributions evolved with the DGLAP evolution equations.

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arXiv2009

Diffractive open charm production from the dipole model analysis

We present a precise comparison of the results of the dipole models with the newest data from HERA on the diffractive open charm production. We found good agreement with the data on the diffractive open charm production both for the the gluon distributions from the considered dipole models and the DGLAP fits to HERA data from our earlier analysis for diffractive parton distributions with higher twist. We also show that exclusive diffractive charm production can practically be neglected

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arXiv2008

Diffractive Parton Distributions from Fits with Higher Twist

We determine diffractive parton distributions of the proton from DGLAP based fits to HERA data including the twist--4 contribution from longitudinal polarized virtual photons, which is known to be important in the region of large beta. The biggest impact of this contribution is on the diffractive gluon distribution and on the diffractive longitudinal structure function to be determined from HERA data.

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