arXiv subjects

Johannes Haller

Publications and source records attributed to Johannes Haller.

14 recordsLinked to original sources

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 $κ$ 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.

hep-ph↗

arXiv2024

Ultrafast jet classification on FPGAs for the HL-LHC

Three machine learning models are used to perform jet origin classification. These models are optimized for deployment on a field-programmable gate array device. In this context, we demonstrate how latency and resource consumption scale with the input size and choice of algorithm. Moreover, the models proposed here are designed to work on the type of data and under the foreseen conditions at the CERN LHC during its high-luminosity phase. Through quantization-aware training and efficient synthetization for a specific field programmable gate array, we show that $O(100)$ ns inference of complex architectures such as Deep Sets and Interaction Networks is feasible at a relatively low computational resource cost.

hep-ex↗

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.

hep-ph↗

arXiv2018

Searches for LFV with CMS: leptoquarks with couplings to quarks of the 3rd generation

Leptoquarks (LQ) with couplings to the third generation of Standard Model (SM) quarks have been proposed as possible explanations of the flavour anomalies indicating the violation of lepton flavour universality (LFV). The CMS collaboration has initiated an extensive search programme for these new states in the LHC run-2 data recorded at $\sqrt{s}=13$ TeV. In this article, the CMS search results in the LQ pair-production final states $τb\,τb$, $νt\,νt$, $νb\,νb$, $τt\,τt$, and $μt\,μt$, as well as in the LQ single-production final state $τ\,τb$ are discussed. No significant deviation from the SM is observed in any of these channels. For a broad range of LQ decay modes, exclusion limits on the LQ masses are determined at 95% confidence level reaching from 1.0 TeV to 1.8 TeV.

hep-ex↗

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.

hep-ph↗

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 $p_T$.

hep-ph↗

arXiv2011

Revisiting the Global Electroweak Fit of the Standard Model and Beyond with Gfitter

The global fit of the Standard Model to electroweak precision data, routinely performed by the LEP electroweak working group and others, demonstrated impressively the predictive power of electroweak unification and quantum loop corrections. We have revisited this fit in view of (i) the development of the new generic fitting package Gfitter, (ii) the insertion of constraints from direct Higgs searches at LEP and the Tevatron, and (iii) a more thorough statistical interpretation of the results. Gfitter is a modular fitting toolkit, which features predictive theoretical models as independent plugins, and a statistical analysis of the fit results using toy Monte Carlo techniques. The state-of-the-art electroweak Standard Model is fully implemented, as well as generic extensions to it. This paper introduces the Gfitter project, and presents state-of-the-art results for the global electroweak fit in the Standard Model, and for a model with an extended Higgs sector (2HDM). Numerical and graphical results for fits with and without including the constraints from the direct Higgs searches at LEP and Tevatron are given. Perspectives for future colliders are analysed and discussed. Including the direct Higgs searches, we find M_H=(116.4 +18.3 -1.3) GeV, and the 2sigma and 3sigma allowed regions [114,145] GeV and [[113,168] and [180,225]] GeV, respectively. For the strong coupling strength at fourth perturbative order we obtain alpha_S(M_Z)=0.1193 +0.0028 -0.0027(exp) +- 0.0001(theo). Finally, for the mass of the top quark, excluding the direct measurements, we find m_t=(178.2 +9.8 -4.2) GeV. In the 2HDM we exclude a charged-Higgs mass below 240 GeV at 95% confidence level. This limit increases towards larger tan(beta), where e.g., M_H+-<780 GeV is excluded for tan(beta)=70.

hep-ph↗

arXiv2010

The electroweak fit and constraints on new physics

The global electroweak fit of the Standard Model (SM) with Gfitter can be used to constrain yet unknown SM parameters, such as the Higgs mass, but also physics beyond the SM (BSM) via the formalism of oblique parameters. This paper presents updated results of the Gfitter SM fit using the latest available electroweak precision measurements and the recent combination of direct Higgs searches at the Tevatron. In addition, newly obtained constraints on BSM models, such as models with extra dimensions, little Higgs and a fourth fermion generation, are presented. While a light Higgs mass is preferred by the fit in the SM, significantly larger Higgs masses are allowed in these new physics models.

hep-ph↗

arXiv2009

Combining Triggers in HEP Data Analysis

Modern high-energy physics experiments collect data using dedicated complex multi-level trigger systems which perform an online selection of potentially interesting events. In general, this selection suffers from inefficiencies. A further loss of statistics occurs when the rate of accepted events is artificially scaled down in order to meet bandwidth constraints. An offline analysis of the recorded data must correct for the resulting losses in order to determine the original statistics of the analysed data sample. This is particularly challenging when data samples recorded by several triggers are combined. In this paper we present methods for the calculation of the offline corrections and study their statistical performance. Implications on building and operating trigger systems are discussed.

hep-ex↗

arXiv2008

Fits of the Electroweak Standard Model and Beyond using Gfitter

The global fit of the Standard Model to electroweak precision data, routinely performed by the LEP electroweak working groups and others, has been revisited in view of (i) the development of the new generic fitting package, Gfitter, (ii) the insertion of constraints from direct Higgs searches at LEP and Tevatron, and (iii) a more thorough statistical interpretation of the results. This paper describes the Gfitter project, and presents state-of-the-art results for the global electroweak fit in the Standard Model, and for a model with an extended Higgs sector. Example results are an estimation of the mass of the Higgs boson (M_H = 116.4^{+18.3}_{-1.3} GeV) and a forth-order result for the strong coupling strength (alpha_S(M_Z^2) = 0.1193^{+0.0028}_{-0.0027}(exp)+/-0.0001(theo)). Using toy Monte Carlo techniques the p-value of the SM has been determined (p=0.22). As an example of a New Physics model constraints are derived for the Two Higgs Doublet Model of Type-II using observables from the B and K physics sectors.

hep-ph↗

arXiv2005

The first-level trigger of ATLAS

Due to the huge interaction rates and the tough experimental environment of pp collisions at a centre-of-mass energy sqrt(s)=14TeV and luminosities of up to 10^34 cm^-2 s^-1, one of the experimental challenges at the LHC is the triggering of interesting events. In the ATLAS experiment a three-level trigger system is foreseen for this purpose. The first-level trigger is implemented in custom hardware and has been designed to reduce the data rate from the initial bunch-crossing rate of 40 MHz to around 75 kHz. Its event selection is based on information from the calorimeters and dedicated muon detectors. This article gives an overview over the full first-level trigger system including the Calorimeter Trigger, the Muon Trigger and the Central Trigger Processor. In addition, recent results are reported that have been obtained from test-beam studies performed at CERN where the full first-level trigger chain was established successfully for the first time and used to trigger the read-out of up to nine ATLAS sub-detector systems.

physics.ins-det↗

arXiv2005

Discovery Potential of MSSM Higgs Bosons with ATLAS

In this article the potential of the ATLAS experiment to discover MSSM Higgs bosons is discussed. Various Monte-Carlo studies for SM Higgs boson production and dedicated MSSM Higgs boson analyses are taken into account to investigate the discovery potential in four different CP-conserving MSSM benchmark scenarios, the Mh-max scenario, the no mixing scenario, the gluophobic scenario and the small alpha scenario. The most recent theoretical calculations are used for the prediction of Higgs masses and couplings. The results are shown for integrated luminosities of 30 and 300 inverse fb. With 300 inverse fb, a five sigma discovery of at least one Higgs boson state is possible in all scenarios for all values of tan beta and MA. The heavy neutral and charged Higgs states can only be discovered in parts of the parameter space.

hep-ex↗

arXiv2004

Searches for SUSY and Exotics at HERA

The HERA collaborations, H1 and ZEUS, have searched for physics beyond the Standard Model in ep collisions at centre-of-mass energies of up to 319 GeV. In this article the experimental results coming from the HERA I phase are summarised and the constraints on theories of new physics including Contact Interactions, Large Extra Dimensions, Leptoquarks, FCNC and various scenarios in R-parity violating supersymmetry are discussed. In addition the first results on searches for new physics coming from the upgraded HERA II collider are presented.

hep-ex↗

arXiv2003

Results on searches for new physics at HERA

The H1 and ZEUS collaborations have searched for signals of physics beyond the Standard Model in ep collisions at a center-of-mass energy of 301-319 GeV. During the HERA I phase each experiment accumulated an integrated luminosity of about 110 pb^{-1} for e^+p and about 15 pb^{-1} for e^-p collisions. The data have been analysed searching for contact interaction effects, leptoquarks, lepton flavor violation, squarks in R-parity violating supersymmetric models, excited fermions and FCNC single top production. In this article a summary of the results is given.

hep-ex↗