arXiv subjects

T. Stefaniak

Publications and source records attributed to T. Stefaniak.

10 recordsLinked to original sources

arXiv2020

HL-LHC and ILC sensitivities in the hunt for heavy Higgs bosons

The prediction of additional Higgs bosons is one of the key features of physics beyond the Standard Model (SM) that gives rise to an extended Higgs sector. We assess the sensitivity of the Large Hadron Collider (LHC) in the high luminosity (HL) run alone and in combination with a possible future International Linear Collider (ILC) to probe heavy neutral Higgs bosons. We employ the Minimal Supersymmetric Standard Model (MSSM) as a framework and assume the light CP-even MSSM Higgs boson to be the Higgs boson observed at 125 GeV. We discuss the constraints on the MSSM parameter space arising from the precision measurements of the rates of the detected signal at 125 GeV and from direct searches for new heavy Higgs bosons in the $τ^+τ^-$, $b\bar{b}$ and di-Higgs ($hh$) final states. A new benchmark scenario for heavy Higgs searches in the $b\bar{b}$ channel is proposed in this context. For the future Higgs rate measurements at the HL-LHC and ILC two different scenarios are investigated, namely the case where the future rate measurements agree with the SM prediction and the case where the rates agree with the predictions of possible realizations of the MSSM Higgs sector in nature.

hep-ph↗

arXiv2020

Higgs boson potential at colliders: status and perspectives

This document summarises the current theoretical and experimental status of the di-Higgs boson production searches, and of the direct and indirect constraints on the Higgs boson self-coupling, with the wish to serve as a useful guide for the next years. The document discusses the theoretical status, including state-of-the-art predictions for di-Higgs cross sections, developments on the effective field theory approach, and studies on specific new physics scenarios that can show up in the di-Higgs final state. The status of di-Higgs searches and the direct and indirect constraints on the Higgs self-coupling at the LHC are presented, with an overview of the relevant experimental techniques, and covering all the variety of relevant signatures. Finally, the capabilities of future colliders in determining the Higgs self-coupling are addressed, comparing the projected precision that can be obtained in such facilities. The work has started as the proceedings of the Di-Higgs workshop at Colliders, held at Fermilab from the 4th to the 9th of September 2018, but it went beyond the topics discussed at that workshop and included further developments.

hep-ph↗

arXiv2018

A Higgs Boson at 96 GeV?!

We briefly summarize some searches for Higgs bosons with a mass of m_phi <= 110 GeV at LEP and the LHC. We discuss a possible signal in the diphoton decay mode at m_phi = 96 GeV as reported by CMS, together with a 2 sigma hint in the bb final state at LEP. We briefly review possible interpretation of such a new particle in various BSM models. We focus on possible explanations as reported within the NMSSM and the munuSSM. Conclusions for future collider projects are briefly outlined.

hep-ph↗

arXiv2018

Status of the Charged Higgs Boson in Two Higgs Doublet Models

The existence of charged Higgs boson(s) is inevitable in models with two (or more) Higgs doublets. Hence, their discovery would constitute unambiguous evidence for new physics beyond the Standard Model (SM). Taking into account all relevant results from direct charged and neutral Higgs boson searches at LEP and the LHC, as well as the most recent constraints from flavour physics, we present a detailed analysis of the current phenomenological status of the charged Higgs sector in a variety of well-motivated Two Higgs Doublet Models (2HDMs). We find that charged Higgs bosons as light as 75 GeV can still be compatible with the combined data, although this implies severely suppressed charged Higgs couplings to all fermions. In more popular models, e.g. the 2HDM of Type II, we find that flavour physics observables impose a combined lower limit on the charged Higgs mass of M_H+ > 600 GeV - independent of tan(beta) - which increases to M_H+ > 650 GeV for tan(beta) < 1. We furthermore find that in certain scenarios, the signature of a charged Higgs boson decaying into a lighter neutral Higgs boson and a W boson provides a promising experimental avenue that would greatly complement the existing LHC search programme for charged Higgs boson(s).

hep-ph↗

arXiv2015

Physics at the e+ e- Linear Collider

A comprehensive review of physics at an e+e- Linear Collider in the energy range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC results, experiments from low energy as well as astroparticle physics.The report focuses in particular on Higgs boson, Top quark and electroweak precision physics, but also discusses several models of beyond the Standard Model physics such as Supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analyzed as well.

hep-ph↗

arXiv2014

Resurrecting light stops after the 125 GeV Higgs in the baryon number violating CMSSM

In order to accommodate the observed Higgs boson mass in the CMSSM, the stops must either be very heavy or the mixing in the stop sector must be very large. Lower stop masses, possibly more accessible at the LHC, still give the correct Higgs mass only if the trilinear stop mixing parameter $|A_t|$ is in the multi-TeV range. Recently it has been shown that such large stop mixing leads to an unstable electroweak vacuum which spontaneously breaks charge or colour. In this work we therefore go beyond the CMSSM and investigate the effects of including baryon number violating operators $λ'' \bar{\bf U} \bar{\bf D}\bar{\bf D}$ on the stop and Higgs sectors. We find that for $λ'' \simeq {\mathcal{O}}(0.3)$ light stop masses as low as 220 GeV are consistent with the observed Higgs mass as well as flavour constraints while allowing for a stable vacuum. The light stop in this scenario is often the lightest supersymmetric particle. We furthermore discuss the importance of the one-loop corrections involving R-parity violating couplings for a valid prediction of the light stop masses.

hep-ph↗

arXiv2012

MSSM Interpretations of the LHC Discovery: Light or Heavy Higgs?

A Higgs-like particle with a mass of about 126 GeV has been discovered at the LHC. Within the experimental uncertainties, the measured properties of this new state are compatible with those of the Higgs boson in the Standard Model (SM). While not statistically significant at present, the results show some interesting patterns of deviations from the SM predictions, in particular a higher rate in the γγ decay mode observed by ATLAS and CMS, and a somewhat smaller rate in the ττ mode. The LHC discovery is also compatible with the predictions of the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM), interpreting the new state as either the light or the heavy CP-even MSSM Higgs boson. Within the framework of the MSSM with seven free parameters (pMSSM-7), we fit the various rates of cross section times branching ratio as measured by the LHC and Tevatron experiments under the hypotheses of either the light or the heavy CP-even Higgs boson being the new state around 126 GeV, with and without the inclusion of further low-energy observables. We find an overall good quality of the fits, with the best fit points exhibiting an enhancement of the γγrate, as well as a small suppression of the bb and ττ channels with respect to their SM expectations, depending on the details of the fit. For the fits including the whole data set the light CP-even Higgs interpretation in the MSSM results in a higher relative fit probability than the SM fit. On the other hand, we find that the present data also permit the more exotic interpretation in terms of the heavy CP-even MSSM Higgs, which could give rise to experimental signatures of additional Higgs states in the near future.

hep-ph↗

arXiv2012

Bounds on R-parity Violation from Resonant Slepton Production at the LHC

We consider the ATLAS and CMS searches for dijet resonances, as well as the ATLAS search for like-sign dimuon pairs at the LHC with 7 TeV center of mass energy. We interpret their exclusions in terms of bounds on the supersymmetric R-parity violating parameter space. For this we focus on resonant slepton production followed by the corresponding decay.

hep-ph↗

arXiv2011

Constraining Selectron LSP Scenarios with Tevatron Trilepton Searches

The Tevatron collaborations have searched for associated production of charginos and neutralinos via trilepton final states. No events above the Standard Model prediction were observed. We employ these results to put stringent bounds on R-parity violating models with a right-handed scalar electron as the lightest supersymmetric particle. We work in the framework of lepton number violating minimal supergravity. We find that within these models the complete parameter space consistent with the anomalous magnetic moment of the muon can be excluded at 90% confidence level. We also give prospects for Tevatron trilepton searches assuming an integrated luminosity of 10 fb^{-1}. We find that Tevatron will be able to test selectron LSP masses up to 170 GeV.

hep-ph↗

arXiv2011

Discovery Potential of Selectron or Smuon as the Lightest Supersymmetric Particle at the LHC

We investigate the LHC discovery potential of R-parity violating supersymmetric models with a right-handed selectron or smuon as the lightest supersymmetric particle (LSP). These LSPs arise naturally in R-parity violating minimal supergravity models. We classify the hadron collider signatures and perform for the first time within these models a detailed signal over background analysis. We develop an inclusive three-lepton search and give prospects for a discovery at a center-of-mass energy of 7 TeV as well as 14 TeV. There are extensive parameter regions which the LHC can already test with 7 TeV and an integrated luminosity of 1 inverse femtobarn. We also propose a method for the mass reconstruction of the supersymmetric particles within our models at 14 TeV.

hep-ph↗