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 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.

scholarly journals Transverse momentum dependent PDFs at N3LO

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Markus A. Ebert ◽  
Bernhard Mistlberger ◽  
Gherardo Vita
Keyword(s):  
Transverse Momentum ◽  
Cross Sections ◽  
Production Cross ◽  
Gluon Fusion ◽  
Building Blocks ◽  
Distribution Functions ◽  
Leading Order ◽  
Parton Distribution Functions ◽  
Transverse Momentum Dependent ◽  
Collinear Limit

Abstract We compute the quark and gluon transverse momentum dependent parton distribution functions at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. Our calculation is based on an expansion of the differential Drell-Yan and gluon fusion Higgs production cross sections about their collinear limit. This method allows us to employ cutting edge multiloop techniques for the computation of cross sections to extract these universal building blocks of the collinear limit of QCD. The corresponding perturbative matching kernels for all channels are expressed in terms of simple harmonic polylogarithms up to weight five. As a byproduct, we confirm a previous computation of the soft function for transverse momentum factorization at N3LO. Our results are the last missing ingredient to extend the qT subtraction methods to N3LO and to obtain resummed qT spectra at N3LL′ accuracy both for gluon as well as for quark initiated processes.

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 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.

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.

Parton Distribution Functions

2018 ◽  
Author(s):  
John Campbell ◽  
Joey Huston ◽  
Frank Krauss
Keyword(s):  
Cross Sections ◽  
Parton Distribution ◽  
Distribution Functions ◽  
Data Sets ◽  
Hard Scattering ◽  
Leading Order ◽  
Parton Distribution Functions ◽  
Global Fitting

Parton Distribution Functions (PDFs) are a necessary ingredient in the calculation of cross sections at collider experiments with hadron beams. This chapter explores the techniques of determining the PDFs and their uncertainties, based on global analyses of data sets arising from a variety of hard-scattering processes. PDFs are determined at leading order, next-to-leading order, and next-to-next-to-leading order, with the corresponding orders of hard coefficients and evolution. Differences in the PDFs of different orders, and in their uncertainties, are described. Combinations of PDFs from different global fitting groups are discussed, and several useful tools for comparisons of PDFs are described.

scholarly journals Jet cross sections at the LHC and the quest for higher precision

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
Johannes Bellm ◽  
Andy Buckley ◽  
Xuan Chen ◽  
Aude Gehrmann-De Ridder ◽  
Thomas Gehrmann ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Phenomenological Study ◽  
Hadron Collider ◽  
Scale Dependence ◽  
Leading Order ◽  
Theoretical Predictions ◽  
Fixed Order ◽  
Jet Cross Sections ◽  
Perturbative Corrections

Abstract We perform a phenomenological study of Z plus jet, Higgs plus jet and di-jet production at the Large Hadron Collider. We investigate in particular the dependence of the leading jet cross section on the jet radius as a function of the jet transverse momentum. Theoretical predictions are obtained using perturbative QCD calculations at the next-to and next-to-next-to-leading order, using a range of renormalization and factorization scales. The fixed order predictions are compared to results obtained from matching next-to-leading order calculations to parton showers. A study of the scale dependence as a function of the jet radius is used to provide a better estimate of the scale uncertainty for small jet sizes. The non-perturbative corrections as a function of jet radius are estimated from different generators.

scholarly journals Measurements of event properties and multi-differential jet cross sections and impact of CMS measurements on Proton Structure and QCD parameters

2018 ◽  
Vol 172 ◽  
pp. 02001
Author(s):  
Anterpreet Kaur
Keyword(s):  
Cross Sections ◽  
Top Quark ◽  
Center Of Mass ◽  
Distribution Functions ◽  
Parton Distribution Functions ◽  
Mass Distributions ◽  
Inclusive Jets ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Jet Cross Sections

We present results on the measurements of characteristics of events with jets including jet-charge, investigations of shapes and jet mass distributions. The measurements are compared to theoretical predictions including those matched to parton shower and hadronization. Multi-differential jet cross sections are also presented over a wide range in transverse momenta from inclusive jets to multi-jet final states. These measurements have an impact on the determination of the strong coupling constant as well as on parton distribution functions (PDFs) and are helpful in the treatment of heavy flavours in QCD analyses. We also show angular correlations in multi-jet events at highest center-of-mass energies and compare the measurements to theoretical predictions including higher order parton radiation and coherence effects. Measurements of cross sections of jet and top-quark pair production are in particular sensitive to the gluon distribution in the proton, while the electroweak boson production - inclusive or associated with charm or beauty quarks - gives insight into the flavour separation of the proton sea and to the treatment of heavy quarks in PDF-related studies.

scholarly journals Production of cc¯ and bb¯ Quark Pairs in pp Collisions at Energies of Experiments at the Large Hadron Collider

2019 ◽  
Keyword(s):  
Large Hadron Collider ◽  
Heavy Quark ◽  
Cross Sections ◽  
Hadron Collider ◽  
Distribution Functions ◽  
Tree Level ◽  
Event Generator ◽  
Final States ◽  
Leading Order ◽  
Parton Distribution Functions

Production of charm and beauty quark–antiquark pairs in proton–proton collisions is simulated with the codes generated in the framework of MadGraph5_aMC@NLO. The tree–level partonic processes are taken into account in first three orders of the perturbative quantum chromodynamics. The considered hard processes have two, three, and four partons in the final states. These final states contain one or two heavy quark–antiquark pairs. The calculations are performed with parton distribution functions (PDF) obtained with neural network methods by NNPDF collaboration. Influence of the multiple partonic interactions (MPI), initial– and final–state showers on the cross sections (CSs) is studied consistently taking advantage of Pythia 8 event generator. The CSs are computed in central and forward rapidity regions under conditions of the ALICE and LHCb experiments at the Large Hadron Collider at CERN. The studied transverse momentum interval of the heavy quarks spreads up to 30 GeV/c. The CSs calculated at the leading order (LO) with Pythia 8, in the tree approximation with MadGraph5, and within Fixed Order plus Next–to–Leading Logarithms (FONLL) approach agree with each other within bands of the uncertainties inherent to underlying theory and methods. Inclusion of next–to–leading order (NLO) and N2LO partonic processes into calculations in addition to LO ones results in growth of the CSs. This increase reduces to some extent discrepancies with the CSs measured by ALICE and LHCb. Variations of the CSs due to renormalization– and factorization–scale dependence are much larger than the increase of the CSs in NLO and N2LO, than the uncertainties springing in the NNPDF model, and then the accuracy achieved in the ALICE and LHCb cross section measurements. Effects of the MPI, the space– and time–like partonic showers on the heavy quark CSs are found to be not very essential.

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