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Arbelaez, C., Cottin, G., Helo, J. C., & Hirsch, M. (2020). Long-lived charged particles and multilepton signatures from neutrino mass models. Phys. Rev. D, 101(9), 095033–13pp.
Abstract: Lepton number violation (LNV) is usually searched for by the LHC collaborations using the same-sign dilepton plus jet signature. In this paper, we discuss multilepton signals of LNV that can arise with experimentally interesting rates in certain loop models of neutrino mass generation. Interestingly, in such models, the observed smallness of the active neutrino masses, together with the high multiplicity of the final states, leads in large parts of the viable parameter space of such models to the prediction of long-lived charged particles, which leave highly ionizing tracks in the detectors. We focus on one particular one-loop neutrino mass model in this class and discuss its LHC phenomenology in some detail.
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Beltran, R., Cottin, G., Helo, J. C., Hirsch, M., Titov, A., & Wang, Z. S. (2023). Long-lived heavy neutral leptons from mesons in effective field theory. J. High Energy Phys., 01(1), 015–38pp.
Abstract: 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.
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Beltran, R., Cottin, G., Helo, J. C., Hirsch, M., Titov, A., & Wang, Z. S. (2022). Long-lived heavy neutral leptons at the LHC: four-fermion single-N-R operators. J. High Energy Phys., 01(1), 044–18pp.
Abstract: 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.
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Beltran, R., Cottin, G., Hirsch, M., Titov, A., & Wang, Z. S. (2023). Reinterpretation of searches for long-lived particles from meson decays. J. High Energy Phys., 05(5), 031–31pp.
Abstract: 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.
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Candia, P., Cottin, G., Mendez, A., & Muñoz, V. (2021). Searching for light long lived neutralinos at Super-Kamiokande. Phys. Rev. D, 104(5), 055024–11pp.
Abstract: 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 article, 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.
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