arXiv subjects

Krisztian Peters

Publications and source records attributed to Krisztian Peters.

At least 19 recordsLinked to original sources

arXiv2026

Cryogenic RF characterization of the MAGO cavity for high-frequency gravitational-wave detection

Superconducting radio-frequency (SRF) cavities are promising resonant sensors for gravitational-wave detection in the kHz-MHz frequency range. We report the cryogenic RF characterization of a prototype superconducting niobium cavity with an unconventional geometry designed for narrow electromagnetic mode separation. Following an adapted surface preparation procedure, cryogenic tests were performed at Fermilab and DESY at temperatures down to 2\,K. Mechanical tuning at room temperature achieved a mode splitting of approximately 11\,kHz at cryogenic temperature. High electromagnetic quality factors consistent with previous prototype cavities were measured. The measurements further revealed phase transfer characteristics relevant for stable low-level RF control as well as indications of mode coupling potentially caused by one-point multipacting. In addition, first cryogenic measurements of the mechanical eigenmodes yielded mechanical quality factors significantly below commonly assumed theoretical values. These results demonstrate the successful application of established SRF preparation and characterization techniques to a non-standard resonator geometry and provide important experimental input for the development of future SRF-based gravitational-wave detectors.

physics.ins-det↗

arXiv2026

Complementarity of di-top and four-top searches in interpreting possible signals of new physics

Final states comprising two or more top quarks are important search channels at the Large Hadron Collider for scalar particles predicted in models of physics beyond the Standard Model. While the di-top final state profits from a higher signal cross section, it can be subject to intricate interference patterns. Besides the interference with the large QCD background, in case of the presence of more than one high-mass scalar also large signal--signal interference contributions can occur. We show that in such scenarios it is crucial to account for loop-level mixing for obtaining accurate exclusion bounds. We demonstrate how the interference patterns can obscure the interpretation of possible deviations from the Standard Model expectations. We show that the four-top final state, while giving rise to a smaller signal cross section, provides important complementary information due to its much smaller signal--background interference contributions. Thus, the results obtained from the four-top final state can be instrumental for pinpointing the underlying new physics scenario.

hep-ph↗

arXiv2026

Challenges and Opportunities of Gravitational Wave Searches above 10 kHz

The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band. The scarcity of possible astrophysical sources in most of this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising of these sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of a series of workshops on the topic of high-frequency gravitational wave detection, held in 2019 (ICTP, Trieste, Italy), 2021 (online) and 2023 (CERN, Geneva, Switzerland).

gr-qc↗

arXiv2025

First characterisation of the MAGO cavity, a superconducting RF detector for kHz-MHz gravitational waves

Heterodyne detection using microwave cavities is a promising method for detecting high-frequency gravitational waves or ultralight axion dark matter. In this work, we report on studies conducted on a spherical 2-cell cavity developed by the MAGO collaboration for high-frequency gravitational waves detection. Although fabricated around 20 years ago, the cavity had not been used since. Due to deviations from the nominal geometry, we conducted a mechanical survey and performed room-temperature plastic tuning. Measurements and simulations of the mechanical resonances and electromagnetic properties were carried out, as these are critical for estimating the cavity's gravitational wave coupling potential. Based on these results, we plan further studies in a cryogenic environment. The cavity characterisation does not only provide valuable experience for a planned physics run but also informs the future development of improved cavity designs.

gr-qc↗

arXiv2022

Constraining the CP structure of Higgs-fermion couplings with a global LHC fit, the electron EDM and baryogenesis

CP violation in the Higgs couplings to fermions is an intriguing, but not yet extensively explored possibility. We use inclusive and differential LHC Higgs boson measurements to fit the CP structure of the Higgs Yukawa couplings. Starting with simple effective models featuring CP violation in a single Higgs-fermion coupling, we probe well-motivated models with up to nine free parameters. We also investigate the complementarity of LHC constraints with the electron electric dipole moment bound, taking into account the possibility of a modified electron Yukawa coupling, and assess to which extent CP violation in the Higgs-fermion couplings can contribute to the observed baryon asymmetry of the universe. Even after including the recent analysis of angular correlations in $H\toτ^+τ^-$ decays, we find that a complex tau Yukawa coupling alone may be able to account for the observed baryon asymmetry, but with large uncertainties in the baryogenesis calculation. A combination of complex top and bottom quark Yukawa couplings yields a result four times larger than the sum of their separate contributions, but remains insufficient to account for the observed baryon asymmetry.

hep-ph↗

arXiv2021

Indirect $\mathcal{CP}$ probes of the Higgs-top-quark interaction: current LHC constraints and future opportunities

The $\mathcal{CP}$ structure of the Higgs boson in its coupling to the particles of the Standard Model is amongst the most important Higgs boson properties which have not yet been constrained with high precision. In this study, all relevant inclusive and differential Higgs boson measurements from the ATLAS and CMS experiments are used to constrain the $\mathcal{CP}$-nature of the top-Yukawa interaction. The model dependence of the constraints is studied by successively allowing for new physics contributions to the couplings of the Higgs boson to massive vector bosons, to photons, and to gluons. In the most general case, we find that the current data still permits a significant $\mathcal{CP}$-odd component in the top-Yukawa coupling. Furthermore, we explore the prospects to further constrain the $\mathcal{CP}$ properties of this coupling with future LHC data by determining $tH$ production rates independently from possible accompanying variations of the $t\bar t H$ rate. This is achieved via a careful selection of discriminating observables. At the HL-LHC, we find that evidence for $tH$ production at the Standard Model rate can be achieved in the Higgs to diphoton decay channel alone.

hep-ph↗

arXiv2021

Probing the Weinberg Operator at Colliders

Motivated by searches for $0νββ$ decay in nuclear experiments and collider probes of lepton number violation at dimension $d\geq7$, we investigate the sensitivity to the $d=5$ Weinberg operator using the non-resonant signature $pp\to \ell^\pm \ell'^{\pm} j j$ at the LHC. We develop a prescription for the operator that is applicable in collisions and decays, and focus on the $\ell\ell'=μμ$ channel, which is beyond the reach of nuclear decays. For a Wilson coefficient $C^{μμ}_5=1$, scales as heavy as $Λ\sim 8.3~(11)$~TeV can be probed with $\mathcal{L}=300~{\rm fb}^{-1}~(3~{\rm ab}^{-1})$. This translates to an effective $μμ$ Majorana mass of $\vert m_{μμ}\vert\sim7.3~(5.4)$~GeV, and establishes a road map for testing the Weinberg operator at accelerators.

hep-ph↗

arXiv2021

Majorana Neutrinos in Same-Sign $W^\pm W^\pm$ Scattering at the LHC: Breaking the TeV Barrier

We revisit the sensitivity to non-resonant, heavy Majorana neutrinos $N$ in same-sign $W^\pm W^\pm$ scattering at the $\sqrt{s}=13$ TeV LHC and its high-luminosity upgrade. As a benchmark scenario, we work in the context of the Phenomenological Type I Seesaw model, relying on a simulation up to next-to-leading order in QCD with parton shower matching. After extensively studying the phenomenology of the $pp\toμ^\pmμ^\pm j j$ process at the amplitude and differential levels, we design a simple collider analysis with remarkable signal-background separation power. At 95\% confidence level we find that the squared muon-heavy neutrino mixing element $\vert V_{μN} \vert^{2}$ can be probed down to about $0.06-0.3 ~ (0.03-0.1)$ for $m_N = 1-10~{\rm TeV}$ with $\mathcal{L}=300$ fb$^{-1}~(3$ ab$^{-1})$. For heavier masses of $m_N = 20~{\rm TeV}$, we report sensitivity for $\vert V_{μN} \vert^{2}\gtrsim 0.5~(0.3)$. The $W^\pm W^\pm$ scattering channel can greatly extend the mass range covered by current LHC searches for heavy Majorana neutrinos and particularly adds invaluable sensitivity above a few hundred GeV. We comment on areas where the analysis can be improved as well as on the applicability to other tests of neutrino mass models.

hep-ph↗

arXiv2017

Prospects for beyond Standard Model Higgs boson searches at future LHC runs and other machines

The discovery of the Higgs boson at the LHC opened up a new possibility to obtain a precise understanding of the origin of mass and the structure of the vacuum. Several theories beyond the Standard Model predict an extended Higgs sector, with additional scalar particles. We outline the complementary search possibilities for these beyond Standard Model Higgs bosons at the LHC and at possible future high-energy collider facilities.

hep-ex↗

arXiv2010

Search for the Higgs boson in the gamma gamma final state at the Tevatron

We present searches for Higgs bosons decaying to the di-photon final state using up to 5.4/fb of data at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. Whilst the branching ratio to the di-photon final state is small in the Standard Model, this channel contributes appreciably to the overall Higgs sensitivity at the Tevatron. In parallel, the limit is re-interpreted in fermiophobic models where the di-photon branching ratio is considerably larger. This decay channel will be of major importance in the light mass Standard Model Higgs search at the LHC.

hep-ex↗

arXiv2009

Higgs Searches

We present the status and prospects of Higgs searches at the Tevatron and the LHC. Results from the Tevatron are using up to 5/fb of data collected with the CDF and D0 detectors. The major contributing processes include associated production with vector bosons and gluon fusion. Improvements across the full mass range resulting from the larger data sets, improved analyses techniques and increased signal acceptance are discussed. Recent results exclude the SM Higgs boson in a mass range of 160 < mH < 170 GeV. Searches for the neutral MSSM Higgs boson in the region 90 < mA < 200 GeV exclude tanB values down to 30 for several benchmark scenarios.

hep-ex↗

arXiv2008

Searches for squarks and gluinos at D0

Recent results obtained by the D0 Collaboration on searches for squarks and gluinos in proton-antiproton collisions at sqrt(s) =1.96 TeV at the Fermilab Tevatron collider are discussed. For the inclusive searches, events with multiple jets of hadrons and large missing transverse energy in the final state are studied within the framework of minimal supergravity and assuming R-parity conservation. Searches for the scalar top quark are studied in two final state topologies: with events of two charm jets and large missing transverse energy or leptons, jets and missing transverse energy. The data, corresponding to integrated luminosities of up to 2.1/fb, show no excess of a signal above the expected background in any of the decay channels examined. Instead, upper limits at 95% Confidence Level on the squarks and gluino masses are derived.

hep-ex↗

arXiv2007

Higgs Searches at the Tevatron

Recent preliminary results obtained by the CDF and D0 Collaborations on searches for the Higgs boson in proton anti-proton collisions at Sqrt(s)=1.96 TeV at the Fermilab Tevatron collider are discussed. The data, corresponding to integrated luminosities of about 1 fb-1, show no excess of a signal above the expected background in any of the decay channels examined. Instead, upper limits at 95% Confidence Level on the cross section are established. Further, a combined Standard Model Tevatron cross section limit is presented.

hep-ex↗

arXiv2006

The Pomeranchuk Singularity and Vector Boson Reggeization in Electroweak Theory

We investigate the high energy behaviour of vector boson scattering in the electroweak sector of the standard model. In analogy with the BFKL analysis in QCD we compute production amplitudes in the multi-Regge limit and derive, for the vacuum exchange channel, the integral equation for vector particle scattering. We also derive and solve the bootstrap equations for the isospin-1 exchange channel, both for the reggeizing charged and non-reggeizing neutral vector bosons.

hep-ph↗

arXiv2006

Precision Calibration of the D0 HCAL in Run II

Most of the physics analyses at a hadron collider rely on a precise measurement of the energy of jets in the final state. This requires a precise in situ calibration of the calorimeter with the final detector setup. We present the basic procedure and results of the in situ gain calibration of the D0 HCAL in Run II. The gain calibration works on top of the pulser-based calibration of the readout electronics and is based entirely on collision data.

physics.ins-det↗

arXiv2006

Heavy quark production and non-linear gluon evolution at the LHC

We investigate the importance of unitarity corrections to parton evolution in heavy flavor production at the LHC. The gluon distribution is determined with a fit to HERA data applying a unified BFKL-DGLAP approach, in which the non-linear evolution is described by the Balitsky-Kovchegov equation. First we estimate b anti-b production at CDF and D0. Then, cross sections for heavy quark production at various LHC experiments are estimated, tracing the impact of the unitarity corrections.

hep-ph↗

arXiv2006

Hard Diffractive Results and Prospects at the Tevatron

We review hard diffractive results and prospects at the Tevatron with an emphasis on factorization breaking in diffractive processes. Upper limits on the exclusive di-jet and chi_c^0 production cross sections at CDF and the status of the D0 Forward Proton Detectors are discussed.

hep-ex↗

arXiv2003

QCD Corrections to $γγ\to ZZ$ at Small Scattering Angles

QCD corrections to the electroweak cross section of $γγ\to ZZ$ at high energies and small scattering angles have been calculated. The dominant contributions are due to $t$-channel gluon exchange, i.e. photons dissociate into quark-antiquark pairs giving rise to two colour dipoles which interact through gluons. Corrections resulting from the leading log BFKL amplitude are of the order of a few percent close to the forward region already at the 1 TeV energy range and are rising with the scattering energy. We also considered the helicity non-conserving cases in which the QCD corrections in comparison to the electroweak part of the amplitude strongly grow with energy. The helicity non-conserving scattering process is of particular interest since it is sensitive to the Higgs sector.

hep-ph↗