scholarly journals Photon and leptons induced processes at the LHC

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Luca Buonocore ◽  
Paolo Nason ◽  
Francesco Tramontano ◽  
Giulia Zanderighi
Keyword(s):  
Cross Sections ◽  
Parton Shower ◽  
Search Strategy ◽  
Scalar Particle ◽  
Leading Order ◽  
Hadronic Tensor ◽  
Factorization Approach ◽  
Exotic Particles ◽  
Initial States ◽  
Standard Model Process

Abstract We study a few basic photon- and lepton-initiated processes at the LHC which can be computed using the recently developed photon and lepton parton densities. First, we consider the production of a massive scalar particle initiated by lepton-antilepton annihilation and photon-photon fusion as representative examples of searches of exotic particles. Then we study lepton-lepton scattering, since this Standard-Model process may be observable at the LHC. We examine these processes at leading and next-to-leading order and, using the POWHEG method, we match our calculations to parton shower programs that implement the required lepton or photon initial-states. We assess the typical size of cross-sections and their uncertainties and discuss the preferred choices for the factorization scale. These processes can also be computed starting directly from the lepto-production hadronic tensor, leading to a result where some collinear-enhanced QED corrections are missing, but all strong corrections are included. Thus, we are in the unique position to perform a comparison of results obtained via the factorization approach to a calculation that does not have strong corrections. This is particularly relevant in the case of lepton-scattering, that is more abundant at lower energies where it is affected by larger strong corrections. We thus compute this process also with the hadronic-tensor method, and compare the results with those obtained with POWHEG. Finally, for some lepton-lepton scattering processes, we compare the size of the signal to the main quark-induced background, which is double Drell-Yan production, and outline a preliminary search strategy to enhance the signal to background ratio.

scholarly journals Production of prompt photons associated with jets at LHC in kT-factorization

2019 ◽  
Vol 222 ◽  
pp. 03015
Author(s):  
Maxim Malyshev ◽  
Artem Lipatov ◽  
Hannes Jung
Keyword(s):  
Monte Carlo ◽  
Cross Sections ◽  
Parton Shower ◽  
Gluon Fusion ◽  
Monte Carlo Generator ◽  
Hadronic Jets ◽  
Factorization Approach ◽  
Associated Production ◽  
Parton Showering ◽  
Collinear Limit

We use the kT–factorization approach to calculate total and differential cross sections of associated production of prompt photons and hadronic jets at the LHC energies. Our consideration relies on the pegasus Monte-Carlo generator with implemented ℴ(αα2s) off-shell gluon–gluon fusion subprocess g*g* → γqq− and several subleading quark-initiated contributions from ℴ(ααs) and ℴ(αα2s) subprocesses, taken into account in the collinear limit. Using Monte-Carlo generators CASCADE and PYTHIA, we investigate parton showering effects and compare our predictions with the data, taken by CMS and ATLAS collaborations at the LHC. We demostrate reasonabledescription of the data and the importance of parton shower effects in the kT–factorization.

scholarly journals Fixed-order and merged parton-shower predictions for WW and WWj production at the LHC including NLO QCD and EW corrections

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Stephan Bräuer ◽  
Ansgar Denner ◽  
Mathieu Pellen ◽  
Marek Schönherr ◽  
Steffen Schumann
Keyword(s):  
Cross Sections ◽  
Parton Shower ◽  
Higher Order ◽  
Order Effects ◽  
Leading Order ◽  
Combined Analysis ◽  
Fixed Order ◽  
Higher Order Effects ◽  
Inclusive Sample ◽  
Electroweak Corrections

Abstract First, we present a combined analysis of pp $$ \to {\mu}^{+}{v}_{\mu }{\mathrm{e}}^{-}{\overline{v}}_{\mathrm{e}} $$ → μ + v μ e − v ¯ e and pp $$ \to {\mu}^{+}{v}_{\mu }{\mathrm{e}}^{-}{\overline{v}}_{\mathrm{e}}\mathrm{j} $$ → μ + v μ e − v ¯ e j at next-to-leading order, including both QCD and electroweak corrections. Second, we provide all-order predictions for pp $$ \to {\mu}^{+}{v}_{\mu }{\mathrm{e}}^{-}{\overline{v}}_{\mathrm{e}}+ $$ → μ + v μ e − v ¯ e + jets using merged parton-shower simulations that also include approximate EW effects. A fully inclusive sample for WW production is compared to the fixed-order computations for exclusive zero- and one-jet selections. The various higher-order effects are studied in detail at the level of cross sections and differential distributions for realistic experimental set-ups. Our study confirms that merged predictions are significantly more stable than the fixed-order ones in particular regarding ratios between the two processes.

scholarly journals PARTON SHOWERS BEYOND THE LEADING ORDER: A FACTORIZATION APPROACH

2001 ◽  
Vol 16 (supp01a) ◽  
pp. 238-241 ◽  
Author(s):  
F. HAUTMANN
Keyword(s):  
Recent Work ◽  
Parton Shower ◽  
Leading Order ◽  
Factorization Approach

We discuss recent work on methods for incorporating nonleading QCD corrections in parton shower algorithms.

scholarly journals Dependence of inclusive jet production on the anti-kT distance parameter in pp collisions at $$ \sqrt{\mathrm{s}} $$ = 13 TeV

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
A. M. Sirunyan ◽  
◽  
A. Tumasyan ◽  
W. Adam ◽  
F. Ambrogi ◽  
...  
Keyword(s):  
Nonperturbative Effects ◽  
Cross Sections ◽  
Parton Shower ◽  
Center Of Mass ◽  
Leading Order ◽  
Jet Production ◽  
Center Of Mass Energy ◽  
Inclusive Jet ◽  
Inclusive Jet Production ◽  
Distance Parameter

Abstract The dependence of inclusive jet production in proton-proton collisions with a center-of-mass energy of 13 TeV on the distance parameter R of the anti-kT algorithm is studied using data corresponding to integrated luminosities up to 35.9 fb−1 collected by the CMS experiment in 2016. The ratios of the inclusive cross sections as functions of transverse momentum pT and rapidity y, for R in the range 0.1 to 1.2 to those using R = 0.4 are presented in the region 84 < pT< 1588 GeV and |y|< 2.0. The results are compared to calculations at leading and next-to-leading order in the strong coupling constant using different parton shower models. The variation of the ratio of cross sections with R is well described by calculations including a parton shower model, but not by a leading-order quantum chromodynamics calculation including nonperturbative effects. The agreement between the data and the theoretical predictions for the ratios of cross sections is significantly improved when next-to-leading order calculations with nonperturbative effects are used.

scholarly journals Matching in $$ pp\to t\overline{t}W/Z/h+ $$ jet SMEFT studies

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Reza Goldouzian ◽  
Jeong Han Kim ◽  
Kevin Lannon ◽  
Adam Martin ◽  
Kelci Mohrman ◽  
...  
Keyword(s):  
Standard Model ◽  
Cross Section ◽  
Cross Sections ◽  
Parton Shower ◽  
Inclusive Cross Section ◽  
Relative Impact ◽  
Matrix Elements ◽  
Leading Order ◽  
Relative Cross Section ◽  
The Impact

Abstract In this paper, we explore the impact of extra radiation on predictions of $$ pp\to \mathrm{t}\overline{\mathrm{t}}\mathrm{X},\mathrm{X}=\mathrm{h}/{\mathrm{W}}^{\pm }/\mathrm{Z} $$ pp → t t ¯ X , X = h / W ± / Z processes within the dimension-6 SMEFT framework. While full next-to-leading order calculations are of course preferred, they are not always practical, and so it is useful to be able to capture the impacts of extra radiation using leading-order matrix elements matched to the parton shower and merged. While a matched/merged leading-order calculation for $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{X} $$ t t ¯ X is not expected to reproduce the next-to-leading order inclusive cross section precisely, we show that it does capture the relative impact of the EFT effects by considering the ratio of matched SMEFT inclusive cross sections to Standard Model values, $$ {\sigma}_{\mathrm{SM}\mathrm{EFT}}\left(\mathrm{t}\overline{\mathrm{t}}\mathrm{X}+\mathrm{j}\right)/{\sigma}_{\mathrm{SM}}\left(\mathrm{t}\overline{\mathrm{t}}\mathrm{X}+\mathrm{j}\right)\equiv \mu $$ σ SMEFT t t ¯ X + j / σ SM t t ¯ X + j ≡ μ . Furthermore, we compare leading order calculations with and without extra radiation and find several cases, such as the effect of the operator $$ \left({\varphi}^{\dagger }i{\overleftrightarrow{D}}_{\mu}\varphi \right)\left(\overline{t}{\gamma}^{\mu }t\right) $$ φ † i D ↔ μ φ t ¯ γ μ t on $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{h} $$ t t ¯ h and $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{W} $$ t t ¯ W , for which the relative cross section prediction increases by more than 10% — significantly larger than the uncertainty derived by varying the input scales in the calculation, including the additional scales required for matching and merging. Being leading order at heart, matching and merging can be applied to all operators and processes relevant to $$ pp\to \mathrm{t}\overline{\mathrm{t}}\mathrm{X},\mathrm{X}=\mathrm{h}/{\mathrm{W}}^{\pm }/\mathrm{Z}+\mathrm{jet} $$ pp → t t ¯ X , X = h / W ± / Z + jet , is computationally fast and not susceptible to negative weights. Therefore, it is a useful approach in $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{X} $$ t t ¯ X + jet studies where complete next-to-leading order results are currently unavailable or unwieldy.

scholarly journals IR-improved DGLAP parton shower effects for associated production of a W boson and jets in pp collisions at s = 8 and 13 TeV

2020 ◽  
Vol 35 (32) ◽  
pp. 2050197
Author(s):  
B. Shakerin ◽  
B. F. L. Ward
Keyword(s):  
Matrix Element ◽  
Energy Dependence ◽  
Cross Sections ◽  
Parton Shower ◽  
W Boson ◽  
Exact Formula ◽  
Leading Order ◽  
Angular Correlations ◽  
Associated Production ◽  
Theoretical Predictions

In a previous paper, hereafter referred to as I, we have analyzed the 7 TeV LHC data on [Formula: see text] events from the standpoint of IR-improved DGLAP parton shower effects, using the IR-improved Herwiri1.031 parton shower MC in comparison with the Herwig6.5 parton shower MC in the context of the exact [Formula: see text] matrix element matched parton shower framework provided by MG5_aMC@NLO. In this paper, we extend this analysis to the LHC 8 and 13 TeV data to investigate the energy dependence of the results obtained in I. Specifically, [Formula: see text] events are generated in the MADGRAPH5_aMC@NLO framework and showered by HERWIG6.521 and HERWIRI1.031 with [Formula: see text] and 0 GeV, respectively. The differential cross sections are reported as functions of jet multiplicity, transverse linear momenta [Formula: see text], the jet pseudorapidity [Formula: see text] and the scalar sum of jet transverse momenta [Formula: see text] for different jet multiplicities 1–3. The dijet cross sections as functions of transverse linear momenta, invariant mass of the dijet and the jet separation are shown as well. Distributions of angular correlations between the jets and the muon are examined as well and the corresponding cross sections are presented. The respective measured cross sections are compared with the exact next-to-leading-order (NLO) matrix element matched parton shower theoretical predictions provided by MADGRAPH5_aMC@NLO/HERWIRI1.031 [Formula: see text] and MADGRAPH5_aMC@NLO/HERWIG6.521 [Formula: see text] and the phenomenological consequences are discussed with an eye toward their energy dependence.

scholarly journals Charged current Drell-Yan production at N3LO

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Claude Duhr ◽  
Falko Dulat ◽  
Bernhard Mistlberger
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Production Cross Section ◽  
Production Cross ◽  
Hadron Collider ◽  
Charge Asymmetry ◽  
Charged Current ◽  
Leading Order ◽  
Neutrino Pair ◽  
The Impact

Abstract We present the production cross section for a lepton-neutrino pair at the Large Hadron Collider computed at next-to-next-to-next-to-leading order (N3LO) in QCD perturbation theory. We compute the partonic coefficient functions of a virtual W± boson at this order. We then use these analytic functions to study the progression of the perturbative series in different observables. In particular, we investigate the impact of the newly obtained corrections on the inclusive production cross section of W± bosons, as well as on the ratios of the production cross sections for W+, W− and/or a virtual photon. Finally, we present N3LO predictions for the charge asymmetry at the LHC.

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 VUV and Soft X-ray Spectroscopy of Actinides

2003 ◽  
Vol 802 ◽  
Author(s):  
Clifford G. Olson ◽  
John J. Joyce ◽  
Tomasz Durakiewicz ◽  
Elzbieta Guziewicz ◽  
Martin Butterfield
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Spectral Characteristics ◽  
Electronic States ◽  
Momentum Dependence ◽  
Auger Electrons ◽  
X Ray ◽  
Relative Cross Section ◽  
Initial States ◽  
Valence Bands

ABSTRACTOptical and photoelectron spectroscopies using VUV and Soft X-ray photons are powerful tools for studies of elemental and compound actinides. Large changes in the relative atomic cross sections of the 5f, 6d and sp electrons allow decomposition of the character of the valence bands using photoemission. Resonant enhancement of photoelectrons and Auger electrons at the 5d core threshold further aids the decomposition and gives a measure of elemental specificity. Angle-resolved photoemission can be used to map the momentum dependence of the electronic states. The large changes in relative cross section with photon energy yields further details when the mapping is done at equivalent points in multiple zones. Spectra for well understood rare earth materials will be presented to establish spectral characteristics for known atomic character initial states. These signatures will be applied to the case of USb to investigate f-d hybridization near the Fermi level.

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