scholarly journals A first determination of parton distributions with theoretical uncertainties

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Rabah Abdul Khalek ◽  
Richard D. Ball ◽  
Stefano Carrazza ◽  
Stefano Forte ◽  
Tommaso Giani ◽  
...  
Keyword(s):  
Covariance Matrix ◽  
Hadron Collider ◽  
Distribution Functions ◽  
Leading Order ◽  
Parton Distribution Functions ◽  
Parton Distributions ◽  
Central Values ◽  
Sources Of Uncertainty ◽  
Fixed Order

Abstract The parton distribution functions (PDFs) which characterize the structure of the proton are currently one of the dominant sources of uncertainty in the predictions for most processes measured at the Large Hadron Collider (LHC). Here we present the first extraction of the proton PDFs that accounts for the missing higher order uncertainty (MHOU) in the fixed-order QCD calculations used in PDF determinations. We demonstrate that the MHOU can be included as a contribution to the covariance matrix used for the PDF fit, and then introduce prescriptions for the computation of this covariance matrix using scale variations. We validate our results at next-to-leading order (NLO) by comparison to the known next order (NNLO) corrections. We then construct variants of the NNPDF3.1 NLO PDF set that include the effect of the MHOU, and assess their impact on the central values and uncertainties of the resulting PDFs.

scholarly journals HIGGS PRODUCTION IN ASSOCIATION WITH BOTTOM QUARKS AT HADRON COLLIDERS

2006 ◽  
Vol 21 (02) ◽  
pp. 89-109 ◽  
Author(s):  
S. DAWSON ◽  
C. B. JACKSON ◽  
L. REINA ◽  
D. WACKEROTH
Keyword(s):  
Standard Model ◽  
Cross Sections ◽  
Hadron Collider ◽  
Distribution Functions ◽  
Bottom Quarks ◽  
Final States ◽  
Leading Order ◽  
Hadron Colliders ◽  
Parton Distribution Functions ◽  
Model Case

We review the present status of the QCD corrected cross-sections and kinematic distributions for the production of a Higgs boson in association with bottom quarks at the Fermilab Tevatron and CERN Large Hadron Collider. Results are presented for the Minimal Supersymmetric Standard Model where, for large tan β, these production modes can be greatly enhanced compared to the Standard Model case. The next-to-leading order QCD results are much less sensitive to the renormalization and factorization scales than the lowest order results, but have a significant dependence on the choice of the renormalization scheme for the bottom quark Yukawa coupling. We also investigate the uncertainties coming from the Parton Distribution Functions and find that these uncertainties can be comparable to the uncertainties from the remaining scale dependence of the next-to-leading order results. We present results separately for the different final states depending on the number of bottom quarks identified.

H1 INCLUSIVE CROSS-SECTION MEASUREMENTS AND AN EXTRACTION OF PARTON DISTRIBUTION FUNCTIONS

2005 ◽  
Vol 20 (21) ◽  
pp. 1557-1571
Author(s):  
BURKARD REISERT
Keyword(s):  
Cross Section ◽  
Parton Distribution ◽  
Inclusive Cross Section ◽  
Distribution Functions ◽  
Parton Distribution Functions ◽  
Single Experiment ◽  
Parton Distributions ◽  
The Standard Model ◽  
Qcd Analysis

An extraction of the parton distributions of the proton by a next-to-leading order QCD fit in the framework of the Standard Model is presented. The fit implements a novel decomposition of the quark species into up- and down-type quark distributions, which is the key to enable a determination of flavor separated parton distributions from a single experiment. The fit is performed on the inclusive unpolarized neutral and charged current cross-section measurements by the H1 collaboration at HERA. The discussion of uncertainties of parton distribution functions is based upon but extends the QCD analysis published together with the H1 data.

scholarly journals Unpolarized quark and gluon TMD PDFs and FFs at N3LO

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Ming-xing Luo ◽  
Tong-Zhi Yang ◽  
Hua Xing Zhu ◽  
Yu Jiao Zhu
Keyword(s):  
Distribution Functions ◽  
Leading Order ◽  
Momentum Fraction ◽  
Parton Distribution Functions ◽  
Third Order ◽  
Probability Interpretation ◽  
Transverse Momentum Dependent ◽  
Precision Determination ◽  
Fragmentation Functions

Abstract In this paper we calculate analytically the perturbative matching coefficients for unpolarized quark and gluon Transverse-Momentum-Dependent (TMD) Parton Distribution Functions (PDFs) and Fragmentation Functions (FFs) through Next-to-Next-to-Next-to-Leading Order (N3LO) in QCD. The N3LO TMD PDFs are calculated by solving a system of differential equation of Feynman and phase space integrals. The TMD FFs are obtained by analytic continuation from space-like quantities to time-like quantities, taking into account the probability interpretation of TMD PDFs and FFs properly. The coefficient functions for TMD FFs exhibit double logarithmic enhancement at small momentum fraction z. We resum such logarithmic terms to the third order in the expansion of αs. Our results constitute important ingredients for precision determination of TMD PDFs and FFs in current and future experiments.

scholarly journals EXTRACTIONS OF POLARIZED AND UNPOLARIZED PARTON DISTRIBUTION FUNCTIONS

2014 ◽  
Vol 25 ◽  
pp. 1460038
Author(s):  
P. JIMENEZ-DELGADO
Keyword(s):  
Parton Distribution ◽  
Distribution Functions ◽  
Short Report ◽  
Parton Distribution Functions ◽  
Parton Distributions ◽  
Target Mass ◽  
Pdf Analysis ◽  
The Status ◽  
Polarized Deep Inelastic Scattering

An overview of our ongoing extractions of parton distribution functions of the nucleon is given. First JAM results on the determination of spin-dependent parton distribution functions from world data on polarized deep-inelastic scattering are presented first, and followed by a short report on the status of the JR unpolarized parton distributions. Different aspects of PDF analysis are briefly discussed, including effects of the nuclear structure of targets, target-mass corrections and higher twist contributions to the structure functions.

scholarly journals Can $$ \overline{\mathrm{MS}} $$ parton distributions be negative?

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Alessandro Candido ◽  
Stefano Forte ◽  
Felix Hekhorn
Keyword(s):  
Strong Coupling ◽  
Cross Sections ◽  
Parton Distribution ◽  
Distribution Functions ◽  
Leading Order ◽  
Parton Distribution Functions ◽  
Parton Distributions ◽  
Factorization Scheme ◽  
Perturbative Regime

Abstract It is common lore that Parton Distribution Functions (PDFs) in the $$ \overline{\mathrm{MS}} $$ MS ¯ factorization scheme can become negative beyond leading order due to the collinear subtraction which is needed in order to define partonic cross sections. We show that this is in fact not the case and next-to-leading order (NLO) $$ \overline{\mathrm{MS}} $$ MS ¯ PDFs are actually positive in the perturbative regime. In order to prove this, we modify the subtraction prescription, and perform the collinear subtraction in such a way that partonic cross sections remain positive. This defines a factorization scheme in which PDFs are positive. We then show that positivity of the PDFs is preserved when transforming from this scheme to $$ \overline{\mathrm{MS}} $$ MS ¯ , provided only the strong coupling is in the perturbative regime, such that the NLO scheme change is smaller than the LO term.

scholarly journals PineAPPL: combining EW and QCD corrections for fast evaluation of LHC processes

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
S. Carrazza ◽  
E. R. Nocera ◽  
C. Schwan ◽  
M. Zaro
Keyword(s):  
Cross Sections ◽  
General Purpose ◽  
Distribution Functions ◽  
Monte Carlo Generator ◽  
Leading Order ◽  
Parton Distribution Functions ◽  
Fast Evaluation ◽  
Theoretical Predictions ◽  
Fixed Order ◽  
Unique Ability

Abstract We introduce PineAPPL, a library that produces fast-interpolation grids of physical cross sections, computed with a general-purpose Monte Carlo generator, accurate to fixed order in the strong, electroweak, and combined strong-electroweak couplings. We demonstrate this unique ability, that distinguishes PineAPPL from similar software available in the literature, by interfacing it to MadGraph5_aMC@NLO. We compute fast-interpolation grids, accurate to next-to-leading order in the strong and electroweak couplings, for a representative set of LHC processes for which EW corrections may have a sizeable effect on the accuracy of the corresponding theoretical predictions. We formulate a recommendation on the format of the experimental deliverables in order to consistently compare them with computations that incorporate EW corrections, and specifically to determine parton distribution functions to the same accuracy.

scholarly journals COMPARISON OF LEADING AND NEXT-TO-LEADING LOGARITHMIC ELECTROWEAK CORRECTIONS TO HIGGS PRODUCTION

2013 ◽  
Vol 28 (20) ◽  
pp. 1350098 ◽  
Author(s):  
FABIO SIRINGO
Keyword(s):  
Vector Boson ◽  
Hadron Collider ◽  
Analytical Form ◽  
Distribution Functions ◽  
Higgs Production ◽  
Effective Theory ◽  
Parton Distribution Functions ◽  
Soft Collinear Effective Theory ◽  
Fixed Order ◽  
Electroweak Corrections

Using soft-collinear effective theory, the leading-log radiative electroweak corrections are written in a closed and analytical form for the hadronic cross-section of Higgs production through vector boson fusion, qq → qqH, one of the most promising channels for studying the Higgs boson at Large Hadron Collider (LHC). The simple leading-log resummation is compared with a full next-to-leading-log calculation, and its accuracy is found to be of order 1% up to 10 TeV, i.e. better than the accuracy of parton distribution functions. Corrections are found to be larger than predicted by one-loop fixed-order approximations at LHC energies. The method provides a simple way of incorporating the electroweak corrections in software packages, improving the accuracy of simulations.

scholarly journals DeepXS: fast approximation of MSSM electroweak cross sections at NLO

2020 ◽  
Vol 80 (1) ◽  
Author(s):  
Sydney Otten ◽  
Krzysztof Rolbiecki ◽  
Sascha Caron ◽  
Jong-Soo Kim ◽  
Roberto Ruiz de Austri ◽  
...  
Keyword(s):  
Cross Sections ◽  
Particle Production ◽  
Production Cross ◽  
Hadron Collider ◽  
Distribution Functions ◽  
Monte Carlo Integration ◽  
Leading Order ◽  
Parton Distribution Functions ◽  
Dimensional Parameter ◽  
O 10

AbstractWe present a deep learning solution to the prediction of particle production cross sections over a complicated, high-dimensional parameter space. We demonstrate the applicability by providing state-of-the-art predictions for the production of charginos and neutralinos at the Large Hadron Collider (LHC) at the next-to-leading order in the phenomenological MSSM-19 and explicitly demonstrate the performance for $$pp\rightarrow \tilde{\chi }^+_1\tilde{\chi }^-_1,$$pp→χ~1+χ~1-,$$\tilde{\chi }^0_2\tilde{\chi }^0_2$$χ~20χ~20 and $$\tilde{\chi }^0_2\tilde{\chi }^\pm _1$$χ~20χ~1± as a proof of concept which will be extended to all SUSY electroweak pairs. We obtain errors that are lower than the uncertainty from scale and parton distribution functions with mean absolute percentage errors of well below $$0.5\,\%$$0.5% allowing a safe inference at the next-to-leading order with inference times that improve the Monte Carlo integration procedures that have been available so far by a factor of $$\mathscr {O}(10^7)$$O(107) from $$\mathscr {O}(\mathrm{min})$$O(min) to $$\mathscr {O}(\mu \mathrm{s})$$O(μs) per evaluation.

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