arXiv subjects

Roman Kogler

Publications and source records attributed to Roman Kogler.

At least 19 recordsLinked to original sources

arXiv2026

Electroweak and Single Top-Quark Conspiracy in Current LHC Data

Recent LHC measurements of electroweak single top-quark and top-quark associated Higgs boson production show a number of rate shifts, while related multiboson channels remain close to their Standard Model predictions. Gauge symmetry relates these processes such that deviations can be organised as the low-energy imprint of a common ultraviolet origin. A Standard Model Effective Field Theory (SMEFT) analysis of these rates together with $Z$-pole observables identifies the pattern: a weak top dipole and a triple-gauge deformation carry the largest pulls, accompanied by a positive left-handed top-quark current. An acceptable fit is also obtained with the pure triple-gauge coefficient set to zero. We then ask whether a gauge-invariant model can produce this set of operators and still pass the numerous constraints from experimental data. Within weakly coupled renormalisable matching, no single scalar, vector or vector-like-quark multiplet is sufficient to reproduce the full pattern. A minimal possibility is a multi-threshold vector-like-quark sector (a singlet, a doublet and two triplets) whose currents arise at tree level, while the dipole requires additional loop dynamics that the current sector does not fix. A representative realisation, confronted with direct, indirect and flavour constraints, points to correlated measurements of electroweak single top-quark production, improved $tH$ and $t \bar t H$ sensitivity, and updated searches for vector-like quarks.

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arXiv2026

The Higgs boson through the lens of electroweak precision data

The global electroweak fit tests the quantum structure of the Standard Model by confronting precision measurements with high-order theoretical predictions. This paper presents an updated Gfitter analysis using the latest experimental inputs, notably the new world average of the $W$-boson mass, and state-of-the-art theoretical calculations. The fit yields indirect determinations of precision observables, including the $W$ and Higgs-boson masses, the top-quark mass, and the effective leptonic weak mixing angle, confirming the remarkable internal consistency of the Standard Model. The analysis is further extended to the Higgs sector by combining ATLAS and CMS signal-strength measurements with electroweak precision data in the $\kappa$ framework. The resulting electroweak constraints on the Higgs couplings to vector bosons allow a determination of the total Higgs-boson width with a precision of about 10\% or better within a leading-logarithmic oblique interpretation, and provide bounds on invisible and undetected Higgs-boson branching fractions without using direct searches for invisible Higgs decays. The paper also presents bounds on Wilson coefficients in the Standard Model Effective Field Theory together with projections for the precision of the global electroweak fit achievable at the FCC-ee.

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arXiv2025

How to Unfold Top Decays

Using unfolded top-quark decay data we can measure the top quark mass, as well as search for unexpected kinematic effects. We present a new generative unfolding method for the two tasks and show how they both benefit from unbinned, high-dimensional unfolding. Unlike weight-based or iterative generative methods we include a targeted unbiasing with respect to the training data. This shows significant advantages over standard, iterative methods, in terms of applicability, flexibility and accuracy.

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arXiv2024

Dispelling the $\sqrt{L}$ myth for the High-Luminosity LHC

Extrapolations of sensitivity to new interactions and standard model parameters critically inform the programme at the Large Hadron Collider (LHC) and potential future collider cases. To this end, statistical considerations based on inclusive quantities and established analysis strategies typically give rise to a sensitivity scaling with the square root of the luminosity, $\sqrt{L}$. This suggests only a mild sensitivity improvement for LHC's high-luminosity phase, compared to the collected data up to the year 2025. We discuss representative analyses in top quark, Higgs boson and electroweak gauge boson phenomenology and provide clear evidence that the assumption that the sensitivity in searches and measurement scales only with $\sqrt{L}$ at the High-Luminosity LHC is overly conservative at best, and unrealistic in practice. As kinematic coverage enables more targeted search strategies with sufficient statistical sensitivity, employing a multitude of features in data dispels the scaling based on more inclusive selections.

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arXiv2024

Higgs boson off-shell measurements probe non-linearities

The measurements of off-shell Higgs boson contributions in massive gauge boson pair production are known to probe its electroweak interactions across different energy scales. Often employed as an estimator of the Higgs boson width in restricted theories of beyond the Standard Model physics, we revisit this measurement and re-advertise its potential to constrain aspects of Higgs boson non-linearity. We show that this so-called off-shell measurement complements related analyses of multi-Higgs final states.

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arXiv2022

Status of the global electroweak fit with Gfitter in the light of new precision measurements

We present results from the global electroweak fit to precision measurements in the Standard Model (SM). The fit uses the latest theoretical calculations for observables on the $Z$ pole and the $W$ boson mass, yielding precise SM predictions for the effective weak mixing angle and the masses of the $W$ and Higgs bosons, as well as the top quark. We study the impact of the latest measurements on the fit and provide comparisons of the resulting predictions for individual observables with recent measurements.

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arXiv2022

QFitter -- A Quantum Fitting Framework Applied to Effective Field Theories

The use of experimental data to constrain the values of the Wilson coefficients of an Effective Field Theory (EFT) involves minimising a $χ^2$ function that may contain local minima. Classical optimisation algorithms can become trapped in these minima, preventing the determination of the global minimum. The quantum annealing framework has the potential to overcome this limitation and reliably find the global minimum of non-convex functions. We present QFitter, a quantum annealing method to perform EFT fits. Using a state-of-the-art quantum annealer, we show with concrete examples that QFitter can be used to fit sets of at least eight coefficients, including their quadratic contributions. An arbitrary number of observables can be included without changing the required number of qubits. We provide an example in which $χ^2$ is non-convex and show that QFitter can find the global minimum more accurately than its classical alternatives.

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arXiv2022

Jets and Jet Substructure at Future Colliders

Even though jet substructure was not an original design consideration for the Large Hadron Collider (LHC) experiments, it has emerged as an essential tool for the current physics program. We examine the role of jet substructure on the motivation for and design of future energy frontier colliders. In particular, we discuss the need for a vibrant theory and experimental research and development program to extend jet substructure physics into the new regimes probed by future colliders. Jet substructure has organically evolved with a close connection between theorists and experimentalists and has catalyzed exciting innovations in both communities. We expect such developments will play an important role in the future energy frontier physics program.

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arXiv2019

Jet Substructure at the Large Hadron Collider: Experimental Review

Jet substructure has emerged to play a central role at the Large Hadron Collider, where it has provided numerous innovative ways to search for new physics and to probe the Standard Model, particularly in extreme regions of phase space. In this article we focus on a review of the development and use of state-of-the-art jet substructure techniques by the ATLAS and CMS experiments.

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arXiv2018

Update of the global electroweak fit and constraints on two-Higgs-doublet models

We present an update of the global fit of the Standard Model electroweak sector to latest experimental results. We include new kinematic top quark and $W$ boson mass measurements from the LHC, a $\sin^2θ^{\ell}_{\mathrm{eff}}$ result from the Tevatron, and a new evaluation of the hadronic contribution to $α(M_Z^2)$. We present tests of the internal consistency of the electroweak Standard Model and updated numerical predictions of key observables. The electroweak data combined with measurements of the Higgs boson coupling strengths and flavour physics observables are used to constrain parameters of two-Higgs-doublet models.

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arXiv2017

Higgs characterisation in the presence of theoretical uncertainties and invisible decays

While the Higgs characterisation programme is well underway, direct signs for new physics beyond the Standard Model remain elusive. Performing a fit of fully differential Higgs production cross sections at the LHC to a subset of Higgs-relevant effective operators, we discuss the extent to which theoretical uncertainties can limit the sensitivity in such a new physics search programme. Extending the dimension-6 Higgs Effective Field Theory framework by introducing new light degrees of freedom that can contribute to an invisible (or undetectable) Higgs decay width $h \to ϕϕ$, we show how differential coupling fits can disentangle effects from non-Standard Model couplings and an invisible decay width, as present in many new physics scenarios, such as Higgs-portal dark matter. Including the so-called off-shell measurement that has been advocated as a sensitive determination of the Higgs width in the $κ$ framework, we show explicitly that this method does not provide complementary sensitivity for scale-separated new physics $Λ\gg m_h \gg m_ϕ$, which is favoured in beyond the Standard Model scenarios that relate astrophysics and collider phenomenology in light of non-observation of new physics during run 1 of the LHC.

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arXiv2016

A new tagger for hadronically decaying heavy particles at the LHC

A new algorithm for the identification of boosted, hadronically decaying, heavy particles at the LHC is presented. The algorithm is based on the known procedure of jet clustering with variable distance parameter $R$ and adapts the jet size to its transverse momentum $p_T$. Subjets are found using a mass jump condition. The resulting algorithm - called Heavy Object Tagger with Variable $R$ (HOTVR) - features little algorithmic complexity and combines jet clustering, subjet finding and rejection of soft clusters in one sequence. While the HOTVR algorithm can be used for the identification of any heavy object decaying hadronically, e.g. W, Z, H, t, or possible new heavy resonances, this paper targets specifically the tagging of boosted top quarks. The studies presented here demonstrate a stable performance of the HOTVR algorithm in a wide range of top quark $p_T$, from low $p_T$, where the decay products can be resolved, to the region of boosted decays at high $p_T$.

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arXiv2016

Higgs coupling measurements at the LHC

Due to the absence of tantalising hints for new physics during the LHC's run 1, the extension of the Higgs sector by dimension six operators will provide the new phenomenological standard for searches of non-resonant extensions of the Standard Model. Using all dominant and subdominant Higgs production mechanisms at the LHC, we compute the constraints on Higgs physics-relevant dimension six operators in a global and correlated fit. We show in how far these constraints can be improved by new Higgs channels becoming accessible at higher energy and luminosity, both through inclusive cross sections as well as through highly sensitive differential distributions. This allows us to discuss the sensitivity to new effects in the Higgs sector that can be reached at the LHC if direct hints for physics beyond the SM remain elusive and the impact of these constraints on well-motivated BSM scenarios.

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arXiv2013

Search for heavy resonances decaying to top quarks

In many models of physics beyond the Standard Model the coupling of new states to third generation quarks is enhanced. A review is presented of searches by the CMS collaboration for heavy particles decaying to final states involving top quarks. This includes searches for heavy gauge bosons and excited states. Several final states originating from the top quark decays are considered and the event reconstruction is optimised accordingly. The analyses presented use data collected with the CMS experiment during the year 2012 at the LHC, in proton-proton collisions at a centre-of-mass energy of 8 TeV.

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arXiv2013

The global electroweak Standard Model fit after the Higgs discovery

We present an update of the global Standard Model (SM) fit to electroweak precision data under the assumption that the new particle discovered at the LHC is the SM Higgs boson. In this scenario all parameters entering the calculations of electroweak precision observalbes are known, allowing, for the first time, to over-constrain the SM at the electroweak scale and assert its validity. Within the SM the W boson mass and the effective weak mixing angle can be accurately predicted from the global fit. The results are compatible with, and exceed in precision, the direct measurements. An updated determination of the S, T and U parameters, which parametrize the oblique vacuum corrections, is given. The obtained values show good consistency with the SM expectation and no direct signs of new physics are seen. We conclude with an outlook to the global electroweak fit for a future e+e- collider.

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arXiv2012

Precision jet measurements at HERA and determination of α_s

The status is reviewed of recent high precision measurements of inclusive-jet, dijet and trijet production in deep-inelastic scattering and photoproduction by the HERA experiments H1 and ZEUS. The measurements are in good agreement with perturbative QCD calculations at next-to-leading order and are used for the extraction of the value of the strong coupling at the mass of the Z boson, α_s(M_Z). The methods and results of the QCD analyses are presented and a summary of the values of α_s(M_Z) from recent jet measurements at HERA is given.

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arXiv2011

Data Preservation in High Energy Physics

Data from high-energy physics experiments are collected with significant financial and human effort and are mostly unique. However, until recently no coherent strategy existed for data preservation and re-use, and many important and complex data sets have simply been lost. While the current focus is on the LHC at CERN, in the current period several important and unique experimental programs at other facilities are coming to an end, including those at HERA, b-factories and the Tevatron. To address this issue, an inter-experimental study group on HEP data preservation and long-term analysis (DPHEP) was convened at the end of 2008. The group now aims to publish a full and detailed review of the present status of data preservation in high energy physics. This contribution summarises the results of the DPHEP study group, describing the challenges of data preservation in high energy physics and the group's first conclusions and recommendations. The physics motivation for data preservation, generic computing and preservation models, technological expectations and governance aspects at local and international levels are examined.

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arXiv2011

Measurement of Multijet Production in DIS and Determination of the Strong Coupling Constant

Inclusive jet, dijet and trijet differential cross sections have been measured in neutral current deep-inelastic scattering for exchanged boson virtualities $150 < Q^2 < 15000$ GeV$^2$ with the H1 detector at HERA using an integrated luminosity of 351 pb$^{-1}}$. The multijet cross sections are presented as a function of $Q^2$, the transverse momentum of the jet $P_T$ (the mean transverse momentum for dijets and trijets) and the proton's longitudinal momentum fraction of the parton participating in the hard interaction $ξ$. The cross sections are compared to perturbative QCD calculations at next-to-leading order and the value of the strong coupling $α_s(M_Z)$ is determined.

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