Parton distribution functions at the lhc robert thorne february 15th, 20 university college london. Specialized minimimal parton distribution function scarrazzasmpdf. In this contribution we present a status report on the recent progress towards an analysis of nuclear parton distribution functions npdfs using the nnpdf methodology. The momentum distribution functions of the partons within the proton are simply called parton distribution functions pdfs. Oct 31, 2010 the article is a good consise outline of the state of parton distributions at present. Towards the determination of the photon parton distribution. Then, the valence d quark distribution can be expressed as moreover, we also fix a 2, a 3, and a 4 of xg, as the structure function f 2 is insensitive to the large x behavior of gluon distribution. In the framework of perturbative qcd the structure functions are directly related to the parton distribution functions, i. Neural network parton distribution function listed as nnpdf.
Accessing gluon parton distributions in large momentum. Each input parton distribution set is converted into a metaparametrization based on a common functional form. A determination of the charm content of the proton. Npdf nuclear parton distribution function acronymfinder.
In the nnpdf approach, the parton distribution functions or the fragmentation functions are parameterized at a low scale, around the boundary between the perturbative and nonperturbative regimes of qcd, namely gev the proton mass as opposed to other fitting approaches, where the pdf shape is parametrised in terms of relatively simple functional forms more or less. Parton distributions from highprecision collider data inspire. The lhapdf project maintains a repository of pdfs from various groups in a new standardized lhapdf6 format, additionally older formats such as. Parton distribution functions at the lhc robert thorne february 15th, 20 university college london ippp research associate with contributions from alan martin, james stirling, graeme watt and arnold mathijssen and ben watt ucl february 20. We present a first estimate of the impact of a fitted charm contribution in the fonll structure functions, and we discuss the development. We present a first determination of the nuclear parton distribution functions npdf based on the nnpdf methodology. Out of this data, and in combination with the constraints of promptphoton production. Neural network parton distribution function how is.
The analysis of lhc data is complicated by the fact that it is a protonproton collider. Nnpdf stands for neural network parton distribution function. We provide a discussion of the impact of a subset of drellyan data from lhc on the determination of the photon parton distribution function pdf, using the nnpdf methodology. Parton distribution functions and top quark differential cross section. Towards parton distributions with fitted charm sciencedirect.
Nuclear parton distributions from neural networks arxiv. Physics stack exchange is a question and answer site for active researchers, academics and students of physics. In perturbative qcd, parton distribution functions pdfs are used to. We discuss how the nnpdf fitting approach can be extended to account for the dependence on the atomic mass number a, and introduce novel algorithms to improve the training of the neural network parameters within the nnpdf. These pdfs are released by individual groups as discrete grids as a function of the bjorkenx and energy scale q. The inclusion of dimuon data in the analysis allows a determination of the strange content of the proton with faithful uncertainty estimation together with a precision determination of electroweak. Towards the determination of the photon pdf constrained by lhc data stefano carrazza 1.
Nnpdf is the acronym used to identify the parton distribution functions from the nnpdf collaboration. In this contribution, we discuss how the fonll generalmass variable flavour number scheme can be extended to allow for the possibility of a fitted charm pdf. This definition appears very rarely and is found in the following acronym finder categories. Ct18 parton distribution functions this page provides numerical table files for the computation of ct18 nexttoleading order nlo and nexttonexttoleading order nnlo parton distribution functions. The notation for a parton distribution function, fah 1 x1. The underlying hard processes which may produce new physics involve instead partonparton collisions, where a parton is a quark, antiquark or gluon.
The nnpdf collaboration determines the structure of the proton using contemporary methods of artificial intelligence. Parton distributions from highprecision collider data. Q where i labels the parton species depends on two variables. The width in each line is the uncertainty in the parton distribution function for that parton. In this contribution, we discuss how the fonll generalmass variable flavour number scheme can.
How is nuclear parton distribution function abbreviated. Parton distribution functions pdfs are essential nonperturbative inputs for calculation of any observable with hadronic initial states. Parton distribution functions school of physics and astronomy. Second, since the proton structure function is less sensitive to the d quark distribution, we fix the du ratio from the cj15 analysis.
Any continuous function can be approximated with neural network with one internal layer and nonlinear neuron activation function. The nnpdf approach neural networks neural networks are nonlinear statistical tools. Pdf towards the determination of the photon parton. A metaanalysis of parton distribution functions pdf paperity. Here the experimentally evaluated valence distribution from dy data 22 were used. Jul 03, 20 we provide a discussion of the impact of a subset of drellyan data from lhc on the determination of the photon parton distribution function pdf, using the nnpdf methodology.
Sep 05, 2018 the rise of the parton densities at low \x\ and high \q2\ values is a foundational prediction of qcd derujula et al. We present preliminary results for fits of parton distribution functions pdfs which include the resummation of smallx logarithms at nllx accuracy, performed in the nnpdf framework. Sq2, f qpx,q2 and f gpx,q2 to all mix and contribute in. They provide a parametrization which is redundant and robust. The article is a good consise outline of the state of parton distributions at present. Nnpdf parton densities are extracted from global fits to. Nuclear parton distributions from leptonnucleus scattering.
Abstract modern parton distribution function fits require an accurate treatment of heavy quark mass effects. Results and conclusion in this work, we use difftop package to study the predicted distributions of topquark transverse momentum generated by using different pdf sets such as ct10 2, mstw 3 and nnpdf. The nnpdf methodology uses machine learning techniques in. Npdf is defined as nuclear parton distribution function very rarely. Modern parton distribution function fits require an accurate treatment of heavy quark mass effects. Citeseerx document details isaac councill, lee giles, pradeep teregowda. A precise knowledge of the socalled parton distribution functions pdfs of. Andrea piccione, joan rojo for the nnpdf collaboration. The momentum distribution functions of the partons within the proton are. There is however not a unique set of parton distribution functions commonly accepted. This page provides numerical table files for the computation of ct18 nexttoleading order nlo and nexttonexttoleading order nnlo parton distribution functions.
Mstw, cteq, nnpdf, abkm, hera, jimenezdelgado et al etc all lhc crosssections rely on our. Furthermore, we determine the parton distribution function of the photon from deep inelastic scattering data using the nnpdf methodology. A metaanalysis of parton distribution functions pdf. Gluon parton distribution functions pdfs in the proton can be calculated directly on euclidean lattices using large momentum effective theory lamet. Neural network parton distribution function how is neural. Recently, the nnpdf global analysis based on an input distribution. I have made numerous small edits in the text, which either in my opinion make the english more clear, or add in a few words a little more information. We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function pdf is parametrized on the same footing as the light quarks and the gluon in a global pdf analysis. Nnpdf is listed in the worlds largest and most authoritative dictionary database of abbreviations and acronyms. Nnpdf parton densities are extracted from global fits to data based on a combination of a monte carlo method for uncertainty estimation and the use of neural networks as basic interpolating functions.
The nnpdf collaboration performs research in the field of highenergy physics. Neural networks, monte carlo techniques and parton distribution functions alberto guffanti albertludwigsuniversitat freiburg on behalf of the nnpdf collaboration. Sep 15, 2015 modern parton distribution function fits require an accurate treatment of heavy quark mass effects. Nnpdf use neural networks to extract the pdfs, and monte carlo methods to determine their statistical distribution. By analyzing parameters of the metaparametrizations from all input pdf ensembles. Dynamical parton distribution functions the dynamical approach to parton distributions the longitudinal structure function the dynamical determination of strange parton distributions the treatment of heavy quarks. Parton distributions from highprecision collider data springerlink. The neural network approach to parton distributions.
Q is the density of parton species i per unit of momentum fraction. By analyzing parameters of the metaparametrizations from all input pdf ensembles, a. Refined analysis on the parton distribution functions of. A metaanalysis is a method for comparison and combination of nonperturbative parton distribution functions pdfs in a nucleon obtained with heterogeneous procedures and assumptions. Sq2, f qpx,q2 and f gpx,q2 to all mix and contribute in the theoretical formulae for all processes. Neural networks, monte carlo techniques and parton.
A metaanalysis of parton distribution functions springerlink. Introduction one of the main sources of systematic errors in hadron colliders such as lhc is the uncertainty that aiects the parton distribution functions pdfs, which limit the accuracy of our knowledge of proton structure. To realize this goal, one has to find renormalized gluon quasipdfs in which power divergences and operator mixing are thoroughly understood. A parton distribution function pdf within so called collinear factorization is defined as the probability density for finding a particle with a certain longitudinal momentum fraction x at resolution scale q 2. This analysis is based on neutralcurrent deepinelastic structure function data and is performed up to nnlo in qcd calculations with heavy quark mass effects. Nnpdf is defined as neural network parton distribution function somewhat frequently. A precise knowledge of the socalled parton distribution functions pdfs of the proton, which describe their structure in terms of their quark and gluon. A precise knowledge of the socalled parton distribution functions pdfs of the proton, which describe their structure in terms of their quark and gluon constituents, is a crucial ingredient of the physics program of the large hadron collider of cern. Parton distributions for the lhc run ii inspire inspire hep. Towards a new generation of parton densities with deep learning. Parton distribution functions and top quark differential. These hard processes may be computed using perturbative qcd. New parton distribution functions from a global analysis of quantum.
Parton distribution functions school of physics and. Introduction to parton distribution functions scholarpedia. Towards parton distributions with fitted charm nasaads. We observe an improvement in the description of dis data at small values of bjorken x when resummation effects are included. In previous work we have shown that the photon pdf determined from deepinelastic scattering dis data only has large uncertainties, suggesting the need for more data from other processes such as drellyan, which. Large experimental uncertainties in parton distribution functions pdfs precise pdfs at large x are needed, e.
1353 1484 126 784 861 835 546 587 824 1494 1265 839 313 871 1312 1164 900 1544 1353 1337 586 1289 31 874 857 982 319 685 372 793 1310 312 1469 914 524 1365