arXiv subjects

Babette Döbrich

Publications and source records attributed to Babette Döbrich.

At least 19 recordsLinked to original sources

arXiv2026

Hadronic heavy neutral lepton decays to the limit

Heavy Neutral Leptons are a class of hypothetical particle, motivated by simultaneously solving multiple of the standing issues of the Standard Model. In this work we investigate the decay structure of this type of particle in the hadronic picture for multi-body final states. We propose to link the resulting hadronic description to a partonic description in a seamless transition based on the hadron system's invariant mass. Beyond the impact on the total HNL lifetime, we will show that the multi-hadron channels emerging in this description can constitute interesting experimental signatures.

hep-ph↗

arXiv2026

The VORTEX cavity for the RADES axion haloscope

One of the major challenges in axion dark matter haloscope searches is a loss-less tuning mechanism that is able to cover a significant frequency range around the haloscope's central frequency. In this article, we report on the implementation and performance of an axion haloscope dubbed Vertical-cut Optimised Resonant Tunable cavity for dark matter EXploration (VORTEX) centred at $8.5$ GHz with a tuning range of around $800$ MHz. The performance of this setup is measured at temperatures in the mK range and compared to simulation. In addition, we test the cavity-mode structure of this cavity type directly via the `bead-pull method' and observe satisfactory agreement with expectations. The arrangement is poised to be used in an upcoming RADES (Relic Axion Detection Exploratory Setup) data-taking campaign employing a $12$ T solenoid magnet.

physics.ins-det↗

arXiv2026

Oscillating Imprints of Dark Matter in Mesons Decays

We study scenarios in which ultralight dark matter (ULDM) causes oscillations of the Cabibbo--Kobayashi--Maskawa (CKM) matrix elements, considering two frameworks. The first, previously proposed in the literature, employs the Nelson--Barr mechanism to solve the strong CP problem and the CKM phase is identified with a pseudo-Nambu--Goldstone boson. The second, inspired by Froggatt--Nielsen flavor models, relies on quadratic couplings of the ULDM to the Standard Model while naturally suppressing linear couplings. On the experimental side, we outline a strategy to search for such oscillations at flavor factories using meson decays, focusing on the NA62 experiment as the most promising candidate for discovery thanks to its large kaon statistics. We show that the sensitivity of lifetime-based observables is parametrically degraded when the total particle flux is not known exactly, leading to a substantial loss of sensitivity compared to naive estimates. We therefore advocate alternative observables based on direct counting of events, which retain the expected $1/\sqrt{N}$ scaling and provide a robust probe of oscillating CKM elements. Our results highlight flavor experiments as a novel probe of ULDM through time-dependent signatures.

hep-ph↗

arXiv2026

NO LESS: Novel Opportunities for Light Exotic Searches at the SPS

A powerful way to test models with feebly interacting particles in the MeV to GeV mass range is through proton beam-dump experiments. In this paper, we compare the current sensitivity of CERN's NA62 experiment running in beam-dump mode with that of a hypothetical experiment using the same detectors in a future CERN ECN3 beam-dump facility. When optimising such an experiment, the geometric setup is particularly relevant for the specific new-physics scenario under study, since different production mechanisms can generate different angular distributions of new particles. We show that even the most minimalistic reconfiguration of the existing NA62 experiment's detectors can already provide a very competitive sensitivity and collect data immediately after the beam is available.

hep-ex↗

arXiv2026

Particle Physics and Gravitational Waves as complementary windows on the Universe

Particle physics and gravitational waves provide complementary probes of the deep structure of the Universe. Gravitational waves from the mergers of neutron stars and black holes are sensitive to the structure of dense quark matter and to different dark matter scenarios. Measurements of stochastic gravitational waves backgrounds can teach us about possible first order phase transitions in the early Universe, including providing sensitivity to the TeV scale which is of key interest to future particle collider experiments. Gravitational waves measurements will also give new probes of the evolution and expansion of the Universe, complementary to measurements with electromagnetic radiation. This Perspectives article explores the physics synergies between the science opportunities provided by next generation gravitational waves measurements and particle physics experiments. Gravitational waves can also probe deep into the early Universe reaching physics much above possible collider energies if the signals can be detected.

astro-ph.CO↗

arXiv2026

The COSMIC WISPers White Paper: The physics case for Weakly Interacting Slim Particles

Axions and other very weakly interacting slim particles (WISPs), with masses below 1 GeV, arise naturally in many extensions of the Standard Model of particle physics. In particular, they could offer a new framework to explain the nature of dark matter and may help address a range of puzzling observations in astrophysics and particle physics. This review provides an overview of ongoing WISP searches and outlines the prospects for the next decade, spanning their theoretical motivation, indirect signatures in astrophysical observations, and dedicated laboratory experiments. It is based on the work carried on by the EU-funded COST Action ``Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments'' (CA21106, https://www.cost.eu/actions/CA21106). This network plays a key role in coordinating and supporting WISP searches across Europe, while also contributing to the development of a roadmap aimed at securing European leadership in this research area. It is emphasized that Europe is currently pursuing a rich, diverse, and cost-effective experimental program, with the potential to deliver one or more transformative discoveries.

hep-ph↗

arXiv2025

Experiments to test the hypothesis for solar and dark matter axions

We present a pedagogical introduction to the direct search of axions as dark matter, as well as to searches for solar axions. The plethora of experimental searches exploit the axion's coupling to two photons: They attempt to convert the axion dark matter to photons in a resonator placed in an external magnetic field or convert solar axions into X-rays in a magnet pointing towards the sun. We give a basic introduction to this concept, its many variants and to searches that exploit the axion's other couplings. We also speculate about potentially transformative developments for such searches in the near-term future.

hep-ph↗

arXiv2025

Kaon Physics: A Cornerstone for Future Discoveries

The kaon physics programme, long heralded as a cutting-edge frontier by the European Strategy for Particle Physics, continues to stand at the intersection of discovery and innovation in high-energy physics (HEP). With its unparalleled capacity to explore new physics at the multi-TeV scale, kaon research is poised to unveil phenomena that could reshape our understanding of the Universe. This document highlights the compelling physics case, with emphasis on exciting new opportunities for advancing kaon physics not only in Europe but also on a global stage. As an important player in the future of HEP, the kaon programme promises to drive transformative breakthroughs, inviting exploration at the forefront of scientific discovery.

hep-ph↗

arXiv2025

Split-cavity tuning of a rectangular axion haloscope operating around 8.4 GHz

The axion haloscope is the currently most sensitive method to probe the vanishingly small coupling of this prominent Dark Matter candidate to photons. To scan a sizeable axion Dark Matter parameter space, the cavities that make up the haloscope need to be tuned efficiently. In this article, we describe a novel technique to tune axion haloscopes around $8.4$~GHz in a purely mechanical manner without the use of dielectrics. We achieve tuning by introducing a gap along the cavity geometry. A quality factor reduction of less than 20\% is achieved experimentally for a tuning range of around 600~MHz at room temperature and at cryogenic temperatures for around 300~MHz. A larger tuning range would require an improved alignments mechanism. We present the results of a corresponding prototype and outline prospects to further develop this technique.

physics.ins-det↗

arXiv2024

On the impact of heavy meson production spectra on searches for heavy neutral leptons

Feebly Interacting Particles are a commonly considered extension to the Standard Model of Particle Physics. In many theoretical frameworks these particles can explain observed physical phenomena which are in tension with the current model. \textsc{ALPiNIST} is a simplified Monte Carlo framework aimed at evaluating past, present, and future, short and long baseline experiments for their sensitivities to different models of Axion-Like Particles. We present the extension of this framework to accommodate new classes of Feebly Interacting Particles with emphasis on Heavy Neutral Leptons. This extension is especially well motivated, solving multiple of the standing issues with the Standard Model at the same time. The fundamental importance of inputs on the resulting parameter sensitivity, and thus the need for a unified simulation set-up, is highlighted.

hep-ph↗

arXiv2024

Searching for Muonphilic Dark Sectors with Proton Beams

Proton beam-dump experiments are a high-intensity source of secondary muons and provide an opportunity to probe muon-specific dark sectors. We adopt a simplified-models framework for an exotic light scalar particle coupling predominantly or exclusively to muons. Equipped with state-of-the-art muon simulations, we compute the sensitivity reach in the parameter space $(m_S, \, g_μ)$ of the dark mediator, examining in detail the examples of the experiment NA62 in beam-dump mode and the proposed experiment SHiP. We find a significant yield of such exotics in the sub-GeV mass range. Our projections are competitive with those of primary muon-beam experiments and complementary to current constraints, spanning uncharted parameter space and accessing new physics potentially responsible for the $(g-2)_μ$ anomaly.

hep-ph↗

arXiv2023

Probing long-lived axions at the KOTO experiment

While the main goal of the J-PARC KOTO experiment is to measure the rare decay $K_L \to π^0 ν\bar ν$, the unique setup of KOTO raises the possibility to search for physics beyond the Standard Model, in an attempt to probe parts of the parameter space which are not covered by other experiments. In this paper, we test the possibility of using KOTO to search for heavy QCD axions, or axion-like particles, a well-motivated extension of the Standard Model emerging in a variety of models. In particular, we estimate the sensitivity of the current KOTO setup as well as the KOTO Step-2 for various benchmark scenarios of axion coupling to the Standard Model. We find that KOTO Step-2 can probe new regions in the parameter space, while KOTO with its current form can only reaffirm the existing bounds. The obtained axion datasets are available as an update of the public code of the ALPINIST framework, including implementation of KOTO setups in the simulation, allowing for interpretation of various analyses as searches for axions in custom models.

hep-ph↗

arXiv2023

The future search for low-frequency axions and new physics with the FLASH resonant cavity experiment at Frascati National Laboratories

We present a proposal for a new experiment, the FINUDA magnet for Light Axion SearcH (FLASH), a large resonant-cavity haloscope in a high static magnetic field which is planned to probe new physics in the form of dark matter (DM) axions, scalar fields, chameleons, hidden photons, as well as high frequency gravitational waves (GWs). Concerning the QCD axion, FLASH will search for these particles as the DM in the mass range (0.49-1.49) ueV, thus filling the mass gap between the ranges covered by other planned searches. A dedicated Microstrip SQUID operating at ultra-cryogenic temperatures will amplify the signal. The frequency range accessible overlaps with the Very High Frequency (VHF) range of the radio wave spectrum and allows for a search in GWs in the frequency range (100-300) MHz. The experiment will make use of the cryogenic plant and magnet of the FINUDA experiment at INFN Frascati National Laboratories near Rome (Italy); the operations needed to restore the functionalities of the apparatus are currently underway. We present the setup of the experiment and the sensitivity forecasts for the detection of axions, scalar fields, chameleons, hidden photons, and GWs.

physics.ins-det↗

arXiv2022

ALPINIST: Axion-Like Particles In Numerous Interactions Simulated and Tabulated

Proton beam dump experiments are among the most promising strategies to search for light and feebly interacting states such as axion-like particles (ALPs). The interpretation of these experiments is however complicated by the wide range of ALP models and the multitude of different production and decay channels that can induce observable signals. Here we propose a new approach to this problem by separating the calculation of constraints and projected sensitivities into model-independent and model-dependent parts. The former rely on extensive Monte Carlo simulations of ALP production and decays, as well as estimates of the detection efficiencies based on simplified detector geometries. Once these simulations have been performed and tabulated, the latter parts only require simple analytical rescalings that can be performed using the public code ALPINIST released together with this work. We illustrate this approach by considering several ALP models with couplings to Standard Model gauge bosons. For the case of ALPs coupled to gluons we show that the sensitivity of proton beam dump experiments can be extended significantly by considering hadronic ALP decays into three-body final states.

hep-ph↗

arXiv2021

A biased MC for muon production for beam-dump experiments

The search for feebly-interacting new-physics particles in the MeV-GeV mass range often involves high-intensity beams dumped into thick heavy targets. The challenge of evaluating the expected backgrounds for these searches from first principles is limited by the CPU time needed to generate the shower induced by the primary beam. We present a Monte Carlo biasing method allowing a three orders of magnitude increase in the efficiency for the simulation of the muon production in a 400 GeV$/c$ proton beam-dump setup. At the same time, this biasing method is maintaining nearly every feature of a simulation from first principles.

hep-ex↗

arXiv2020

Light in the beam dump -- ALP production from decay photons in proton beam-dumps

The exploration of long-lived particles in the MeV-GeV region is a formidable task but it may provide us a unique access to dark sectors. Fixed-target facilities with sufficiently energetic and intense proton beams are an ideal tool for this challenge. In this work we show that the production rate of Axion-Like-Particles (ALPs) coupled pre-dominantly to photons receives a significant contribution from daughter-photons of secondary $π^0$ and $η$ mesons created in the proton shower. We carefully compare the PYTHIA simulated spectra of such secondaries to experimental literature, compute the ALP flux from the Primakoff conversion of these photons, and finally revisit existing limits on ALPs and update the prospects for a set of existing and future searches. Our results show that taking this production mechanism into account significantly enhances the sensitivity compared to previous studies based on coherent ALP production in primary proton-nucleus interactions.

hep-ph↗

arXiv2020

Constraints on the coupling with photons of heavy axion-like-particles from Globular Clusters

We update the globular cluster bound on massive ($m_a$ up to a few 100 keV) axion-like particles (ALP) interacting with photons. The production of such particles in the stellar core is dominated by the Primakoff $γ+ Ze\to Ze +a$ and by the photon coalescence process $γ+γ\to a$. The latter, which is predominant at high masses, was not included in previous estimations. Furthermore, we account for the possibility that axions decay inside the stellar core, a non-negligible effect at the masses and couplings we are considering here. Consequently, our result modifies considerably the previous constraint, especially for $m_a \gtrsim 50$ keV. The combined constraints from Globular Cluster stars, SN 1987A, and beam-dump experiments leave a small triangularly shaped region open in the parameter space around $m_a \sim 0.5-1\,$ MeV and $g_{aγ} \sim 10^{-5}$ GeV$^{-1}$. This is informally known as the ALP "cosmological triangle" since it can be excluded only using standard cosmological arguments. As we shall mention, however, there are viable cosmological models that are compatible with axion-like particles with parameters in such region. We also discuss possibilities to explore the cosmological triangle experimentally in upcoming accelerator experiments.

hep-ph↗

arXiv2019

Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider

Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments --- as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER --- to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the High-Luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity "dark showers", highlighting opportunities for expanding the LHC reach for these signals.

hep-ex↗