arXiv subjects

Giovanna Cottin

Publications and source records attributed to Giovanna Cottin.

At least 19 recordsLinked to original sources

arXiv2026

Can LLP detectors probe the reheating temperature? A case study of vector dark matter

We study an extension of the singlet-scalar Higgs portal featuring a dark vector $V_μ$ and a real scalar $ϕ$. The vector is a dark matter (DM) candidate, while $ϕ$ is long-lived and decays via higher-dimensional operators. We explore the DM production via freeze-in at low and high reheating temperatures. At colliders, the decay $ϕ\to Z+V$ yields distinctive long-lived particle (LLP) signatures. We explore the interplay between cosmological constraints and LLP searches at the LHC and FCC-hh, showing that far detectors can probe otherwise inaccessible parameter space and place novel bounds on the reheating temperature.

hep-ph↗

arXiv2026

Reheating the FCC: Probing Early Matter Domination with Long-Lived Particles

We study a GeV-scale Higgs-portal scalar $ϕ$ that can dominate the early Universe and later decay into Standard Model states, ending an early matter-dominated era. Ordinary cosmic reheating is the minimal example of this scenario. The small Higgs mixing makes $ϕ$ a long-lived particle (LLP), linking the reheating temperature $T_\text{rh}$ to displaced-decay signatures at colliders. Including finite-temperature suppression of the decay width, we map FCC-hh LLP sensitivity onto the $[m_ϕ, T_\text{rh}]$ plane. We find that FCC-hh displaced searches could probe GeV-scale transition temperatures, up to the electroweak scale within the broken-phase Higgs-portal description.

hep-ph↗

arXiv2026

"Niñas Atómicas" (Atomic Girls): An initiative that generates opportunities for young girls in STEM

We report on an initiative that seeks to encourage high school girls to develop critical thinking and transferable skills widely used in scientific work, as well as to generate a concrete space of opportunities for girls to experience how real science is done. Our "Niñas Atómicas" workshop combines the teaching of particle physics, electronics, programming and scientific methodology through building and operating a dedicated experiment: a muon counter. Girls from all over Chile can apply to this workshop, where every year they are guided by female scientists for two weeks. We report on the contents and methodology of our workshop and provide details on how to build the muon detector. We report results on muon flux and proper lifetime, two muon properties which can be extracted from the data collected by the girls with the muon detectors they built themselves. Insights into the girl's experiences during the 2024 and 2025 editions of the workshop are also detailed, with the aim to contribute to the wider physics education research and outreach communities.

physics.ed-ph↗

arXiv2025

Testing frozen-in pNGB dark matter with a long-lived dark Higgs

We consider a simple Higgs portal dark matter (DM) model, where the Standard Model is extended with a complex singlet scalar. The imaginary part of the scalar becomes a massive and stable pseudo-Nambu-Goldstone boson, serving as the DM candidate, while the real part gives rise to a second (dark) Higgs boson. We focus on the freeze-in production of the DM, paying particular attention to low-reheating temperature scenarios, where the dark Higgs can be a long-lived particle (LLP). We also explore the phenomenology of this dark Higgs at the LHC and the Future Circular Collider in hadron-hadron mode, discussing its discovery prospects in regions of parameter space consistent with current DM constraints. Our results emphasize the impact of the cosmic reheating dynamics on the DM freeze-in production and their critical role in interpreting collider signatures. Furthermore, our findings suggest that LLP searches may provide insights into the fundamental dynamics of reheating.

hep-ph↗

arXiv2025

Heavy neutral leptons and top quarks in effective field theory

We study the phenomenology of heavy neutral leptons (HNLs) at the LHC in effective field theory, concentrating on $d=6$ operators with top quarks. Depending on the operator choice and HNL mass, the HNLs will be produced either from proton-proton collisions in association with a single top, or via non-standard decays of top quarks. For long-lived HNLs we estimate the sensitivity reach of different detectors to various operators with top quarks and the HNLs for the high-luminosity phase of the LHC. For certain operators, ATLAS and some far detectors (MATHUSLA and ANUBIS) will be able to probe the associated new-physics scale as large as 12 TeV and 4.5 TeV, respectively, covering complementary HNL-mass ranges.

hep-ph↗

arXiv2025

Probing light neutralinos from pair-produced sleptons with displaced vertices at the high-luminosity LHC

We study light neutralinos ($\tilde χ_1^0$) with masses ranging from 10 GeV to several hundred GeV within the framework of R-parity-violating (RPV) supersymmetry. These light neutralinos can be long-lived, decaying with a macroscopic displacement (order cm) inside the LHC main detectors. Complementing previous works on the subject, here we focus on their production through the electroweak pair production of left-chiral sleptons ($\tilde e_{L}$), with the signal process $pp\to \tilde e^+_{L} \tilde e^-_{L} \to e^+ \tilde χ_1^0 e^- \tilde χ_1^0$. In contrast to the previous study with a singly produced slepton, where the RPV coupling $λ'_{111}$ induces both the production and decay of the light neutralino, in our scenario the production proceeds through Drell-Yan-like processes that are essentially independent of RPV couplings. Correspondingly, we implement a displaced-vertex search strategy for which our numerical analysis shows that the high-luminosity LHC can probe $λ'_{111}$ values up to three orders of magnitude smaller, and neutralino masses up to about four times larger than those accesible in the previously studied single-slepton production scenario.

hep-ph↗

arXiv2025

Long-lived particle phenomenology in one-loop neutrino mass models with dark matter

Neutrino masses and dark matter (DM) might have a common origin. The scotogenic model can be considered the proto-type model realizing this idea, but many other variants exist. In this paper we explore the phenomemology of a particular DM neutrino mass model, containing a triplet scalar. We calculate the relic density and check for constraints from direct detection experiments. The parameter space of the model, allowed by these constraints, contains typically a long-lived or quasi-stable doubly charged scalar, that can be searched for at the LHC. We reinterpret existing searches to derive limits on the masses of the scalars of the model and estimate future sensitivities in the high-luminosity phase of the LHC. The searches we discuss can serve to constrain also many other 1-loop neutrino mass models.

hep-ph↗

arXiv2025

Reinterpretation and preservation of data and analyses in HEP

Data from particle physics experiments are unique and are often the result of a very large investment of resources. Given the potential scientific impact of these data, which goes far beyond the immediate priorities of the experimental collaborations that obtain them, it is imperative that the collaborations and the wider particle physics community publish and preserve sufficient information to ensure that this impact can be realised, now and into the future. The information to be published and preserved includes the algorithms, statistical information, simulations and the recorded data. This publication and preservation requires significant resources, and should be a strategic priority with commensurate planning and resource allocation from the earliest stages of future facilities and experiments.

hep-ph↗

arXiv2024

Quark flavor violation and axion-like particles from top-quark decays at the LHC

We study axion-like particles (ALPs) with quark-flavor-violating couplings at the LHC. Specifically, we focus on the theoretical scenario with ALP-top-up and ALP-top-charm interactions, in addition to the more common quark-flavor-diagonal couplings. The ALPs can thus originate from decays of top quarks which are pair produced in large numbers at the LHC, and then decay to jets. If these couplings to the quarks are tiny and the ALPs have $\mathcal{O}(10)$ GeV masses, they are long-lived, leading to signatures of displaced vertex plus multiple jets, which have the advantage of suppression of background events at the LHC. We recast a recent ATLAS search for the same signature and reinterpret the results in terms of bounds on the long-lived ALP in our theoretical scenario. We find that the LHC with the full Run 2 dataset can place stringent limits, while at the future high-luminosity LHC with 3 ab$^{-1}$ integrated luminosity stronger sensitivities are expected.

hep-ph↗

arXiv2024

Searching for light neutralinos with a displaced vertex at the LHC

We study a bino-like light neutralino ($\tilde χ_1^0$) produced at the LHC from the decay of a scalar lepton ($\tilde e_L$) through the process $pp\to \tilde e_{L} \to e\tilde χ_1^0$ in the context of R-parity-violating (RPV) supersymmetry where $\tilde χ_1^0$ is the lightest supersymmetric particle. For small masses and RPV couplings, the neutralino is naturally long-lived and its decay products can be identified as displaced tracks. Following existing searches, we propose a displaced-vertex search strategy for such a light neutralino with a single RPV coupling switched on, $λ'_{111}$, in the mass range $10\,\mbox{GeV} \lesssim m_{\tilde χ_1^0}\lesssim 230\,\mbox{GeV}$. We perform Monte Carlo simulations and conclude that at the high-luminosity LHC, the proposed search can probe values of $λ'_{111}$ down to two orders of magnitude smaller than current bounds and up to 40 times stronger than projected limits from monolepton searches.

hep-ph↗

arXiv2023

Reinterpretation of searches for long-lived particles from meson decays

Many models beyond the Standard Model predict light and feebly interacting particles that are often long-lived. These long-lived particles (LLPs) in many cases can be produced from meson decays. In this work, we propose a simple and quick reinterpretation method for models predicting LLPs produced from meson decays. With the method, we are not required to run Monte-Carlo simulation, implement detector geometries and efficiencies, or apply experimental cuts in an event analysis, as typically done in recasting and reinterpretation works. The main ingredients our method requires are only the theoretical input, allowing for computation of the production and decay rates of the LLPs. There are two conditions for the method to work: firstly, the LLPs in the models considered should be produced from a set of mesons with similar mass and lifetime (or the same meson) and second, the LLPs should, in general, have a lab-frame decay length much larger than the distance between the interaction point and the detector. As an example, we use this method to reinterpret exclusion bounds on heavy neutral leptons (HNLs) in the minimal ``3+1'' scenario, into those for HNLs in the general effective-field-theory framework as well as for axion-like particles. We are able to reproduce existing results, and obtain new bounds via reinterpretation of past experimental results, in particular, from CHARM and Belle.

hep-ph↗

arXiv2023

Long-lived heavy neutral leptons with a displaced shower signature at CMS

We study the LHC discovery potential in the search for heavy neutral leptons (HNL) with a new signature: a displaced shower in the CMS muon detector, giving rise to a large cluster of hits forming a displaced shower. A new Delphes module is used to model the CMS detector response for such displaced decays. We reinterpret a dedicated CMS search for neutral long-lived particles decaying in the CMS muon endcap detectors for the minimal HNL scenario. We demonstrate that this new strategy is particularly sensitive to active-sterile mixings with $τ$ leptons, due to hadronic $τ$ decays. HNL masses between $\sim 1 - 6$ GeV can be accessed for mixings as low as $|V_{τN}|^{2}\sim 10^{-7}$, probing unique regions of parameter space in the $τ$ sector.

hep-ph↗

arXiv2022

Long-lived heavy neutral leptons from mesons in effective field theory

In the framework of the low-energy effective field theory of the Standard Model extended with heavy neutral leptons (HNLs), we calculate the production rates of HNLs from meson decays triggered by dimension-six operators. We consider both lepton-number-conserving and lepton-number-violating four-fermion operators involving either a pair of HNLs or a single HNL. Assuming that HNLs are long-lived, we perform simulations and investigate the reach of the proposed far detectors at the high-luminosity LHC to (i) active-heavy neutrino mixing and (ii) the Wilson coefficients associated with the effective operators, for HNL masses below the mass of the $B$-meson. We further convert the latter to the associated new-physics scales. Our results show that scales in excess of hundreds of TeV and the active-heavy mixing squared as small as $10^{-15}$ can be probed by these experiments.

hep-ph↗

arXiv2022

Revisiting the scotogenic model with scalar dark matter

The scotogenic model is a well motivated scenario that provides both an explanation for neutrino masses and for dark matter. We focus on a real scalar dark matter candidate in this model, produced through standard thermal freeze-out. We analyze the parameter space of the model compatible with the observed dark matter relic abundance, direct and indirect detection searches, limits from lepton flavour violating decays and constraints from the neutrino sector. As the mass differences of the dark matter with the neutral and charged states are found to be small, the new scalars and fermions of the theory will have macroscopic lifetimes, and could thus be potentially detected with long-lived particle signatures at colliders. We find regions in the parameter space to be - partially or fully - consistent with the dark matter relic abundance, and the prediction of a long-lived charged scalar or lightest neutral fermion in the scotogenic scenario, for dark matter masses below 500 GeV. We discuss on the collider phenomenology in some detail.

hep-ph↗

arXiv2022

Long-lived heavy neutral leptons at the LHC: four-fermion single-$N_R$ operators

Interest in searches for heavy neutral leptons (HNLs) at the LHC has increased considerably in the past few years. In the minimal scenario, HNLs are produced and decay via their mixing with active neutrinos in the Standard Model (SM) spectrum. However, many SM extensions with HNLs have been discussed in the literature, which sometimes change expectations for LHC sensitivities drastically. In the $N_R$SMEFT, one extends the SM effective field theory with operators including SM singlet fermions, which allows to study HNL phenomenology in a "model independent" way. In this paper, we study the sensitivity of ATLAS to HNLs in the $N_R$SMEFT for four-fermion operators with a single HNL. These operators might dominate both production and decay of HNLs, and we find that new physics scales in excess of 20 TeV could be probed at the high-luminosity LHC.

hep-ph↗

arXiv2021

Searching for light long-lived neutralinos at Super-Kamiokande

Light neutralinos could be copiously produced from the decays of mesons generated in cosmic-ray air showers. These neutralinos can be long-lived particles in the context of R-parity violating (RPV) supersymmetric models, implying that they could be capable of reaching the surface of the earth and decay within the instrumental volume of large neutrino detectors. In this letter, we use atmospheric neutrino data from the Super-Kamiokande experiment to derive novel constraints for the RPV couplings involved in the production of long-lived light neutralinos from the decays of charged $D$-mesons and kaons. Our results highlight the potential of neutrino detectors to search for long-lived particles, by demonstrating that it is possible to explore regions of parameter space that are not yet constrained by any fixed-target nor collider experiments.

hep-ph↗

arXiv2021

Heavy neutral leptons in effective field theory and the high-luminosity LHC

Heavy neutral leptons (HNLs) with masses around the electroweak scale are expected to be rather long-lived particles, as a result of the observed smallness of the active neutrino masses. In this work, we study long-lived HNLs in $N_R$SMEFT, a Standard Model (SM) extension with singlet fermions to which we add non-renormalizable operators up to dimension-6. Operators which contain two HNLs can lead to a sizable enhancement of the production cross sections, compared to the minimal case where HNLs are produced only via their mixing with the SM neutrinos. We calculate the expected sensitivities for the ATLAS detector and the future far-detector experiments: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA, and MoEDAL-MAPP in this setup. The sensitive ranges of the HNL mass and of the active-heavy mixing angle are much larger than those in the minimal case. We study both, Dirac and Majorana, HNLs and discuss how the two cases actually differ phenomenologically, for HNL masses above roughly 100 GeV.

hep-ph↗

arXiv2021

Displaced Neutrino Jets at the LHeC

Extending the Standard Model with right-handed neutrinos (RHNs) is well motivated by the observation of neutrino oscillations. In the type-I seesaw model, the RHNs interact with the SM particles via tiny mixings with the active neutrinos, which makes their discovery in the laboratory, and in particular at collider experiments in general challenging. In this work we instead consider an extension of the type-I seesaw model with the addition of a leptoquark (LQ), and employ a non-minimal production mechanism of the RHN via LQ decay, which is unsuppressed by neutrino mixing. We focus on relatively light RHN with mass $\mathcal{O}(10)$ GeV and LQ with mass 1.0 TeV, and explore the discovery prospect of the RHN at the proposed Large Hadron electron Collider. In the considered mass range and with the given interaction strength, the RHN is long lived and, due to it stemming from the LQ decay, it is also heavily boosted, resulting in collimated decay products. The unique signature under investigation is thus a displaced fat jet. We use kinematic variables to separate signal from background, and demonstrate that the ratio variables with respect to energy/number of displaced and prompt tracks are useful handles in the identification of displaced decays of the RHN. We also show that employing a positron beam provides order of magnitude enhancement in the detection prospect of this signature.

hep-ph↗