Constraining the SMEFT with Bayesian reweighting

We illustrate how Bayesian reweighting can be used to incorporate the constraints provided by new measurements into a global Monte Carlo analysis of the Standard Model Effective Field Theory (SMEFT). This method, extensively applied to study the impact of new data on the parton distribution functions of the proton, is here validated by means of our recent SMEFiT analysis of the top quark sector. We show how, under well-defined conditions and for the SMEFT operators directly sensitive to the new data, the reweighting procedure is equivalent to a corresponding new fit. We quantify the amount of information added to the SMEFT parameter space by means of the Shannon entropy and of the Kolmogorov-Smirnov statistic. We investigate the dependence of our results upon the choice of alternative expressions of the weights.

Download Full-text

$$ t\overline{t}b\overline{b} $$ at the LHC: on the size of corrections and b-jet definitions

Journal of High Energy Physics ◽

10.1007/jhep08(2021)008 ◽

2021 ◽

Vol 2021 (8) ◽

Author(s):

Giuseppe Bevilacqua ◽

Huan-Yu Bi ◽

Heribertus Bayu Hartanto ◽

Manfred Kraus ◽

Michele Lupattelli ◽

...

Keyword(s):

Cross Sections ◽

Top Quark ◽

Decay Channel ◽

Parton Density ◽

Accurate Estimate ◽

Distribution Functions ◽

Parton Distribution Functions ◽

Shell Effects ◽

Quark Decay ◽

The Impact

Abstract We report on the calculation of the next-to-leading order QCD corrections to the production of a $$ t\overline{t} $$ t t ¯ pair in association with two heavy-flavour jets. We concentrate on the di-lepton $$ t\overline{t} $$ t t ¯ decay channel at the LHC with $$ \sqrt{s} $$ s = 13 TeV. The computation is based on pp → e+νeμ−$$ \overline{\nu} $$ ν ¯ μ$$ b\overline{b}b\overline{b} $$ b b ¯ b b ¯ matrix elements and includes all resonant and non-resonant diagrams, interferences and off-shell effects of the top quark and the W gauge boson. As it is customary for such studies, results are presented in the form of inclusive and differential fiducial cross sections. We extensively investigate the dependence of our results upon variation of renormalisation and factorisation scales and parton distribution functions in the quest for an accurate estimate of the theoretical uncertainties. We additionally study the impact of the contributions induced by the bottom-quark parton density. Results presented here are particularly relevant for measurements of $$ t\overline{t}H $$ t t ¯ H (H → $$ b\overline{b} $$ b b ¯ ) and the determination of the Higgs coupling to the top quark. In addition, they might be used for precise measurements of the top-quark fiducial cross sections and to investigate top-quark decay modelling at the LHC.

Download Full-text

Parton distributions in the SMEFT from high-energy Drell-Yan tails

Journal of High Energy Physics ◽

10.1007/jhep07(2021)122 ◽

2021 ◽

Vol 2021 (7) ◽

Author(s):

Admir Greljo ◽

Shayan Iranipour ◽

Zahari Kassabov ◽

Maeve Madigan ◽

James Moore ◽

...

Keyword(s):

Cross Sections ◽

Neutral Current ◽

Light Quark ◽

High Energy ◽

New Physics ◽

Effective Field ◽

Distribution Functions ◽

High Mass ◽

Parton Distribution Functions ◽

The Impact

Abstract The high-energy tails of charged- and neutral-current Drell-Yan processes provide important constraints on the light quark and anti-quark parton distribution functions (PDFs) in the large-x region. At the same time, short-distance new physics effects such as those encoded by the Standard Model Effective Field Theory (SMEFT) would induce smooth distortions to the same high-energy Drell-Yan tails. In this work, we assess for the first time the interplay between PDFs and EFT effects for high-mass Drell-Yan processes at the LHC and quantify the impact that the consistent joint determination of PDFs and Wilson coefficients has on the bounds derived for the latter. We consider two well-motivated new physics scenarios: 1) electroweak oblique corrections ($$ \hat{W},\hat{Y} $$ W ̂ , Y ̂ ) and 2) four-fermion interactions potentially related to the LHCb anomalies in R(K(*)). We account for available Drell-Yan data, both from unfolded cross sections and from searches, and carry out dedicated projections for the High-Luminosity LHC. Our main finding is that, while the interplay between PDFs and EFT effects remains moderate for the current dataset, it will become a significant challenge for EFT analyses at the HL-LHC.

Download Full-text

Impact of the top quark cross-section data on parton distribution functions

International Journal of Modern Physics A ◽

10.1142/s0217751x18501427 ◽

2018 ◽

Vol 33 (24) ◽

pp. 1850142 ◽

Cited By ~ 2

Author(s):

M. Azizi ◽

A. Khorramian ◽

H. Abdolmaleki ◽

S. Paktinat Mehdiabadi

Keyword(s):

Cross Section ◽

Top Quark ◽

Parton Distribution ◽

Valence Quark ◽

Quark Distribution ◽

Distribution Functions ◽

Parton Distribution Functions ◽

Top Quark Production ◽

Quark Production ◽

The Impact

Recent measurements of top quark pair production cross-section, which is performed at the LHC and the Tevatron collider, are studied using Hessian profiling technique to obtain their impact on the parton distribution functions (PDFs). The top quark production data covers different center-of-mass energies [Formula: see text], 5.02, 7, 8 and 13 TeV in either [Formula: see text] or [Formula: see text] collisions. It is explained how the Hessian profiling method may be used to assess the impact of these new data on PDFs and consequently on their predictions. In this research, the impact of recent measurements of top quark pair cross-sections on different CT14, MMHT2014 and NNPDF3.0 PDF sets is investigated. The analysis results show that the recent top quark production at the LHC and Tevatron data provide significant constraints in particular on the central value, relative uncertainties or both for the [Formula: see text]-quark distribution and the gluon PDFs in both CT14 and MMHT2014 PDF sets and are insensitive to valence-quark PDFs. A small constraint on the [Formula: see text]-sea quark distribution for CT14 PDF is also observed. There is no impact on the NNPDF3.0 PDF set in presence of these data.

Download Full-text

Heavy-flavor hadro-production with heavy-quark masses renormalized in the $$ \overline{\mathrm{MS}} $$, MSR and on-shell schemes

Journal of High Energy Physics ◽

10.1007/jhep04(2021)043 ◽

2021 ◽

Vol 2021 (4) ◽

Author(s):

M. V. Garzelli ◽

L. Kemmler ◽

S. Moch ◽

O. Zenaiev

Keyword(s):

Heavy Quark ◽

Cross Sections ◽

Top Quark ◽

Quark Mass ◽

Production Cross ◽

Hadron Collider ◽

Distribution Functions ◽

Heavy Flavor ◽

Parton Distribution Functions ◽

Heavy Quark Mass

Abstract We present predictions for heavy-quark production at the Large Hadron Collider making use of the $$ \overline{\mathrm{MS}} $$ MS ¯ and MSR renormalization schemes for the heavy-quark mass as alternatives to the widely used on-shell renormalization scheme. We compute single and double differential distributions including QCD corrections at next-to-leading order and investigate the renormalization and factorization scale dependence as well as the perturbative convergence in these mass renormalization schemes. The implementation is based on publicly available programs, MCFM and xFitter, extending their capabilities. Our results are applied to extract the top-quark mass using measurements of the total and differential $$ t\overline{t} $$ t t ¯ production cross-sections and to investigate constraints on parton distribution functions, especially on the gluon distribution at low x values, from available LHC data on heavy-flavor hadro-production.

Download Full-text

Top-induced contributions to H → $$ b\overline{b} $$ and H → $$ c\overline{c} $$ at $$ \mathcal{O}\left({\alpha}_s^3\right) $$

Journal of High Energy Physics ◽

10.1007/jhep12(2020)058 ◽

2020 ◽

Vol 2020 (12) ◽

Author(s):

Roberto Mondini ◽

Ulrich Schubert ◽

Ciaran Williams

Keyword(s):

Top Quark ◽

Clustering Algorithm ◽

Percent Level ◽

Effective Field ◽

Total Width ◽

Monte Carlo Code ◽

Final State ◽

Fully Differential ◽

State Selection ◽

The Impact

Abstract In this paper we present a fully-differential calculation for the contributions to the partial widths H →$$ b\overline{b} $$ b b ¯ and H →$$ c\overline{c} $$ c c ¯ that are sensitive to the top quark Yukawa coupling yt to order $$ {\alpha}_s^3 $$ α s 3 . These contributions first enter at order $$ {\alpha}_s^2 $$ α s 2 through terms proportional to ytyq (q = b, c). At order $$ {\alpha}_s^3 $$ α s 3 corrections to the mixed terms are present as well as a new contribution proportional to $$ {y}_t^2 $$ y t 2 . Our results retain the mass of the final-state quarks throughout, while the top quark is integrated out resulting in an effective field theory (EFT). Our results are implemented into a Monte Carlo code allowing for the application of arbitrary final-state selection cuts. As an example we present differential distributions for observables in the Higgs boson rest frame using the Durham jet clustering algorithm. We find that the total impact of the top-induced (i.e. EFT) pieces is sensitive to the nature of the final-state cuts, particularly b-tagging and c-tagging requirements. For bottom quarks, the EFT pieces contribute to the total width (and differential distributions) at around the percent level. The impact is much bigger for the H →$$ c\overline{c} $$ c c ¯ channel, with effects as large as 15%. We show however that their impact can be significantly reduced by the application of jet-tagging selection cuts.

Download Full-text

Impact of scale, nuclear PDF and temperature variations on the interpretation of medium-modified jet production data from the LHC

Journal of High Energy Physics ◽

10.1007/jhep04(2021)006 ◽

2021 ◽

Vol 2021 (4) ◽

Author(s):

A. Andronic ◽

J. Honermann ◽

M. Klasen ◽

C. Klein-Bösing ◽

J. Salomon

Keyword(s):

Distribution Functions ◽

Production Data ◽

Crossover Temperature ◽

Parton Distribution Functions ◽

Temperature Variations ◽

Nuclear Modification Factor ◽

Nuclear Modification ◽

Modification Factor ◽

The Impact ◽

Jet Structure

Abstract In this paper we present a study of in-medium jet modifications performed with JEWEL and PYTHIA 6.4, focusing on the uncertainties related to variations of the perturbative scales and nuclear parton distribution functions (PDFs) and on the impact of the initial and crossover temperature variations of the medium. The simulations are compared to LHC data for the jet spectrum and the nuclear modification factor. We assess the interplay between the choice of nuclear PDFs and different medium parameters and study the impact of nuclear PDFs and the medium on the jet structure via the Lund plane.

Download Full-text

Delineating the Polarized and Unpolarized Parton Structure of the Nucleon

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194515600538 ◽

2015 ◽

Vol 37 ◽

pp. 1560053

Author(s):

Pedro Jimenez-Delgado

Keyword(s):

Parton Distribution ◽

Distribution Functions ◽

Distribution Analysis ◽

Coupling Constant ◽

Parton Distribution Functions ◽

Careful Treatment ◽

Future Data ◽

The Impact

Reports on our latest extractions of parton distribution functions of the nucleon are given. First an overview of the recent JR14 upgrade of our unpolarized PDFs, including NNLO determinations of the strong coupling constant and a discussion of the role of the input scale in parton distribution analysis. In the second part of the talk recent results on the determination of spin-dependent PDFs from the JAM collaboration are reported, including a careful treatment of hadronic and nuclear corrections, as well as reports on the impact of present and future data in our understanding of the spin of the nucleon.

Download Full-text

ON THE $\bar{d}/\bar{u}$ ASYMMETRY AND PARTON DISTRIBUTIONS

International Journal of Modern Physics A ◽

10.1142/s0217751x02005554 ◽

2002 ◽

Vol 17 (02) ◽

pp. 269-278

Author(s):

ALEJANDRO DALEO ◽

CARLOS A. GARCIA CANAL ◽

GABRIELA A. NAVARRO ◽

RODOLFO SASSOT

Keyword(s):

Parton Distribution ◽

Distribution Functions ◽

Parton Distribution Functions ◽

Parton Distributions ◽

The Impact

We discuss the impact of different measurements of the [Formula: see text] asymmetry in the extraction of parametrizations of parton distribution functions.

Download Full-text

Chiral perturbation theory and nucleon–pion-state contaminations in lattice QCD

International Journal of Modern Physics A ◽

10.1142/s0217751x17300113 ◽

2017 ◽

Vol 32 (15) ◽

pp. 1730011 ◽

Cited By ~ 12

Author(s):

Oliver Bär

Keyword(s):

Perturbation Theory ◽

Chiral Perturbation Theory ◽

Distribution Functions ◽

Leading Order ◽

Chiral Perturbation ◽

Parton Distribution Functions ◽

Physical Point ◽

Source Sink ◽

The Impact ◽

Quark Momentum

Multiparticle states with additional pions are expected to be a non-negligible source of excited-state contamination in lattice simulations at the physical point. It is shown that baryon chiral perturbation theory can be employed to calculate the contamination due to two-particle nucleon–pion-states in various nucleon observables. Leading order results are presented for the nucleon axial, tensor and scalar charge and three Mellin moments of parton distribution functions (quark momentum fraction, helicity and transversity moment). Taking into account phenomenological results for the charges and moments the impact of the nucleon–pion-states on lattice estimates for these observables can be estimated. The nucleon–pion-state contribution results in an overestimation of all charges and moments obtained with the plateau method. The overestimation is at the 5–10% level for source-sink separations of about 2 fm. The source-sink separations accessible in contemporary lattice simulations are found to be too small for chiral perturbation theory to be directly applicable.

Download Full-text