scholarly journals A Machine Learning approach to the EFT re-interpretation of the WZjj fully leptonic electroweak production

2021 ◽  
Vol 2105 (1) ◽  
pp. 012011
Author(s):  
Konstantinos Bachas ◽  
Ioannis Karkanias ◽  
Eirini Kasimi ◽  
Christos Leonidis ◽  
Chara Petridou ◽  
...  
Keyword(s):  
Machine Learning ◽  
Standard Model ◽  
Vector Boson ◽  
New Physics ◽  
Effective Field ◽  
Machine Learning Techniques ◽  
Atlas Collaboration ◽  
The Standard Model ◽  
Two Jets ◽  
Integrated Luminosity

Abstract In this paper we study the use of Machine Learning techniques to set constraints on indirect signatures of physics beyond the Standard Model in Vector Boson Scattering (VBS), in the electroweak (EWK) production of self-interacting W ± Z bosons in association with two jets. The WZ fully leptonic channel has been extensively studied by the ATLAS Collaboration at the LHC and we are about to provide results using the full Run 2 data corresponding to an integrated luminosity of 139fb −1. The EWK production of the WZ in association with two jets has been already observed at 36fb −1 with an observed significance of 5.3 standard deviations. A factor of four increase in the integrated luminosity provides an opportunity to check for deviations from the Standard Model (SM) predictions, in particular for model independent, indirect searches for New Physics. Such searches can be realized in the context of an extension of the SM in terms of an Effective Field Theory (EFT) formalism, providing a way to quantify possible deviations from the Standard Model. The EFT Lagrangian besides the Standard Model terms comprises contributions from higher dimension operators, their effect being determined by the strength of their corresponding parameters (Wilson coefficients scaled to the appropriate power of Λ, indicating the scale of the appearance of New Physics). In this paper an attempt is made to search for New Physics effects in the WZjj production, using state-of-the-art machine learning models where diverse network architectures are effectively combined into ensembles trained on the outcomes of base learners maximizing performance. The base learners are trained to identify pure WZjj signal events originating from the effect of EFT operators, from WZjj background events originating from strong (QCD) or EWK WZjj processes. We investigate the utilization of the ensemble model response in estimating the sensitivity of WZjj events in some of the dimension-8 EFT operators and compare the results to sensitive kinematic variables traditionally used to constrain the EFT operator effects.

scholarly journals A Heavy Scalar at the LHC from Vector-Boson Fusion

2018 ◽  
Vol 2018 ◽  
pp. 1-6
Author(s):  
Qiurong Mou ◽  
Sibo Zheng
Keyword(s):  
Standard Model ◽  
Vector Boson ◽  
Mass Range ◽  
New Physics ◽  
Vector Boson Fusion ◽  
Mixing Angle ◽  
The Standard Model ◽  
Scalar Mass ◽  
Event Simulations ◽  
Integrated Luminosity

A hypothetical scalar mixed with the standard model Higgs appears in few contexts of new physics. This study addresses the question what mass range is in the reach of 14 TeV LHC given different magnitudes of mixing angle α, where event simulations are based on production from vector-boson fusion channel and decays into SM leptons through WW or ZZ. It indicates that heavy scalar mass up to 539 GeV and 937 GeV can be excluded by integrated luminosity of 300 fb-1 and 3000 fb-1, respectively, for sin2α larger than 0.04.

On the model dependence of fiducial cross-section measurements

2019 ◽  
Vol 34 (38) ◽  
pp. 2050065
Author(s):  
Gabriel Facini ◽  
Kyrylo Merkotan ◽  
Matthias Schott ◽  
Alexander Sydorenko
Keyword(s):  
Standard Model ◽  
Cross Section ◽  
Production Cross ◽  
Hadron Collider ◽  
New Physics ◽  
Effective Field ◽  
Model Bias ◽  
Systematic Uncertainties ◽  
Standard Model Cross Section ◽  
The Standard Model

Fiducial production cross-section measurements of Standard Model processes, in principle, provide constraints on new physics scenarios via a comparison of the predicted Standard Model cross-section and the observed cross-section. This approach received significant attention in recent years, both from direct constraints on specific models and the interpretation of measurements in the view of effective field theories. A generic problem in the reinterpretation of Standard Model measurements is the corrections application of to data to account for detector effects. These corrections inherently assume the Standard Model to be valid, thus implying a model bias of the final result. In this work, we study the size of this bias by studying several new physics models and fiducial phase–space regions. The studies are based on fast detector simulations of a generic multi-purpose detector at the Large Hadron Collider. We conclude that the model bias in the associated reinterpretations is negligible only in specific cases, however, typically on the same level as systematic uncertainties of the available measurements.

scholarly journals Long-lived heavy neutral leptons at the LHC: four-fermion single-NR operators

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
Rebeca Beltrán ◽  
Giovanna Cottin ◽  
Juan Carlos Helo ◽  
Martin Hirsch ◽  
Arsenii Titov ◽  
...  
Keyword(s):  
Field Theory ◽  
Standard Model ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
High Luminosity ◽  
The Past ◽  
The Standard Model ◽  
Model Independent

Abstract Interest in searches for heavy neutral leptons (HNLs) at the LHC has increased considerably in the past few years. In the minimal scenario, HNLs are produced and decay via their mixing with active neutrinos in the Standard Model (SM) spectrum. However, many SM extensions with HNLs have been discussed in the literature, which sometimes change expectations for LHC sensitivities drastically. In the NRSMEFT, one extends the SM effective field theory with operators including SM singlet fermions, which allows to study HNL phenomenology in a “model independent” way. In this paper, we study the sensitivity of ATLAS to HNLs in the NRSMEFT for four-fermion operators with a single HNL. These operators might dominate both production and decay of HNLs, and we find that new physics scales in excess of 20 TeV could be probed at the high-luminosity LHC.

scholarly journals Search for single production of vectorlike top partners through th channel at the HE-LHC and FCC-hh

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Xi-Yan Tian ◽  
Liu-Feng Du ◽  
Yao-Bei Liu
Keyword(s):  
Standard Model ◽  
Production Cross ◽  
Branching Fraction ◽  
Hadron Collider ◽  
High Energy ◽  
New Physics ◽  
Beyond The Standard Model ◽  
The Standard Model ◽  
Single Production ◽  
Integrated Luminosity

AbstractThe vectorlike top partners are potential signature of some new physics beyond the Standard Model at the TeV scale. In this paper, we propose to search for the vectorlike T quark with charge 2/3 in the framework of a simplified model where the top partners only couples with the third generation of Standard Model quarks. We investigate the observability for electroweak production of a vectorlike T quark in association with a standard model bottom quark through the process $$pp \rightarrow T\bar{b}j$$ p p → T b ¯ j with the subsequent decay mode of $$T\rightarrow t(\rightarrow b W^+\rightarrow b \ell ^{+} \nu _{\ell })h( \rightarrow \gamma \gamma )$$ T → t ( → b W + → b ℓ + ν ℓ ) h ( → γ γ ) , at the proposed High Energy Large Hadron Collider (HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh) including the realistic detector effects. The 95% confidence level excluded regions and the $$5\sigma $$ 5 σ discovery reach in the parameter plane of $$\kappa _{T}-m_T$$ κ T - m T , are respectively obtained at the HE-LHC with the integrated luminosity of 15 ab$$^{-1}$$ - 1 and the FCC-hh with the integrated luminosity of 30 ab$$^{-1}$$ - 1 . We also analyze the projected sensitivity in terms of the production cross section times branching fraction at the HE-LHC and FCC-hh.

scholarly journals Precision SMEFT bounds from the VBF Higgs at high transverse momentum

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Jack Y. Araz ◽  
Shankha Banerjee ◽  
Rick S. Gupta ◽  
Michael Spannowsky
Keyword(s):  
Standard Model ◽  
Vector Boson ◽  
High Energy ◽  
Effective Field ◽  
Higgs Bosons ◽  
Quadratic Growth ◽  
Final States ◽  
High Transverse Momentum ◽  
The Standard Model ◽  
Independent Operator

Abstract We study the production of Higgs bosons at high transverse momenta via vector-boson fusion (VBF) in the Standard Model Effective Field Theory (SMEFT). We find that contributions from four independent operator combinations dominate in this limit. These are the same ‘high energy primaries’ that control high energy diboson processes, including Higgs-strahlung. We perform detailed collider simulations for the diphoton decay mode of the Higgs boson as well as the three final states arising from the ditau channel. Using the quadratic growth of the SMEFT contributions relative to the Standard Model (SM) contribution, we project very stringent bounds on these operators that far surpass the corresponding bounds from the LEP experiment.

scholarly journals Probing the nonunitarity of the leptonic mixing matrix at the CEPC

2016 ◽  
Vol 31 (33) ◽  
pp. 1644006 ◽  
Author(s):  
Stefan Antusch ◽  
Oliver Fischer
Keyword(s):  
Field Theory ◽  
Standard Model ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Neutrino Masses ◽  
Performance Parameters ◽  
The Standard Model ◽  
Mixing Matrix ◽  
Theory Framework

The nonunitarity of the leptonic mixing matrix is a generic signal of new physics aiming at the generation of the observed neutrino masses. We discuss the Minimal Unitarity Violation (MUV) scheme, an effective field theory framework which represents the class of extensions of the Standard Model (SM) by heavy neutral leptons, and discuss the present bounds on the nonunitarity parameters as well as estimates for the sensitivity of the CEPC, based on the performance parameters from the preCDR.

scholarly journals Is SMEFT enough?

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Timothy Cohen ◽  
Nathaniel Craig ◽  
Xiaochuan Lu ◽  
Dave Sutherland
Keyword(s):  
Standard Model ◽  
Symmetry Breaking ◽  
Independent Set ◽  
Higgs Doublet ◽  
New Physics ◽  
Effective Field ◽  
Electroweak Symmetry Breaking ◽  
Electroweak Symmetry ◽  
Goldstone Bosons ◽  
The Standard Model

Abstract There are two canonical approaches to treating the Standard Model as an Effective Field Theory (EFT): Standard Model EFT (SMEFT), expressed in the electroweak symmetric phase utilizing the Higgs doublet, and Higgs EFT (HEFT), expressed in the broken phase utilizing the physical Higgs boson and an independent set of Goldstone bosons. HEFT encompasses SMEFT, so understanding whether SMEFT is sufficient motivates identifying UV theories that require HEFT as their low energy limit. This distinction is complicated by field redefinitions that obscure the naive differences between the two EFTs. By reformulating the question in a geometric language, we derive concrete criteria that can be used to distinguish SMEFT from HEFT independent of the chosen field basis. We highlight two cases where perturbative new physics must be matched onto HEFT: (i) the new particles derive all of their mass from electroweak symmetry breaking, and (ii) there are additional sources of electroweak symmetry breaking. Additionally, HEFT has a broader practical application: it can provide a more convergent parametrization when new physics lies near the weak scale. The ubiquity of models requiring HEFT suggests that SMEFT is not enough.

scholarly journals Flavor-dependent radiative corrections in coherent elastic neutrino-nucleus scattering

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Oleksandr Tomalak ◽  
Pedro Machado ◽  
Vishvas Pandey ◽  
Ryan Plestid
Keyword(s):  
Standard Model ◽  
Cross Section ◽  
Cross Sections ◽  
Nuclear Physics ◽  
Heavy Particle ◽  
New Physics ◽  
Effective Field ◽  
Radiative Corrections ◽  
The Standard Model ◽  
Nucleus Scattering

Abstract We calculate coherent elastic neutrino-nucleus scattering cross sections on spin-0 nuclei (e.g. 40Ar and 28Si) at energies below 100 MeV within the Standard Model and account for all effects of permille size. We provide a complete error budget including uncertainties at nuclear, nucleon, hadronic, and quark levels separately as well as perturbative error. Our calculation starts from the four-fermion effective field theory to explicitly separate heavy-particle mediated corrections (which are absorbed by Wilson coefficients) from light-particle contributions. Electrons and muons running in loops introduce a non- trivial dependence on the momentum transfer due to their relatively light masses. These same loops, and those mediated by tau leptons, break the flavor universality because of mass-dependent electromagnetic radiative corrections. Nuclear physics uncertainties significantly cancel in flavor asymmetries resulting in subpercent relative errors. We find that for low neutrino energies, the cross section can be predicted with a relative precision that is competitive with neutrino-electron scattering. We highlight potentially useful applications of such a precise cross section prediction ranging from precision tests of the Standard Model, to searches for new physics and to the monitoring of nuclear reactors.

scholarly journals A FB in the SMEFT: precision Z physics at the LHC

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Víctor Bresó-Pla ◽  
Adam Falkowski ◽  
Martín González-Alonso
Keyword(s):  
Field Theory ◽  
Standard Model ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Precision Measurements ◽  
Vertex Corrections ◽  
The Standard Model ◽  
Electroweak Precision

Abstract We study the forward-backward asymmetry AFB in pp → ℓ+ℓ− at the Z peak within the Standard Model Effective Field Theory (SMEFT). We find that this observable provides per mille level constraints on the vertex corrections of the Z boson to quarks, which close a flat direction in the electroweak precision SMEFT fit. Moreover, we show that current AFB data is precise enough so that its inclusion in the fit improves significantly LEP bounds even in simple New Physics setups. This demonstrates that the LHC can compete with and complement LEP when it comes to precision measurements of the Z boson properties.

scholarly journals Exact SMEFT formulation and expansion to $$ \mathcal{O} $$(v4/Λ4)

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Chris Hays ◽  
Andreas Helset ◽  
Adam Martin ◽  
Michael Trott
Keyword(s):  
Standard Model ◽  
Particle Physics ◽  
Input Parameter ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
New Physics ◽  
Specific Model ◽  
Effective Field ◽  
The Standard Model ◽  
Mass Dimension

Abstract The Standard Model Effective Field Theory (SMEFT) theoretical framework is increasingly used to interpret particle physics measurements and constrain physics beyond the Standard Model. We investigate the truncation of the effective-operator expansion using the geometric formulation of the SMEFT, which allows exact solutions, up to mass-dimension eight. Using this construction, we compare the exact solution to the expansion at $$ \mathcal{O} $$ O (v2/Λ2), partial $$ \mathcal{O} $$ O (v4/Λ4) using a subset of terms with dimension-6 operators, and full $$ \mathcal{O} $$ O (v4/Λ4), where v is the vacuum expectation value and Λ is the scale of new physics. This comparison is performed for general values of the coefficients, and for the specific model of a heavy U(1) gauge field kinetically mixed with the Standard Model. We additionally determine the input-parameter scheme dependence at all orders in v/Λ, and show that this dependence increases at higher orders in v/Λ.

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