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Helo, J. C., Kovalenko, S. G., Hirsch, M., & Pas, H. (2013). Short-range mechanisms of neutrinoless double beta decay at the LHC. Phys. Rev. D, 88(7), 073011–19pp.
Abstract: Lepton number violation (LNV) mediated by short- range operators can manifest itself in both neutrinoless double beta decay (0 nu beta beta) and in processes with same- sign dilepton final states at the LHC. We derive limits from existing LHC data at root s = 8 TeV and compare the discovery potential of the forthcoming root s = 14 TeV phase of the LHC with the sensitivity of current and future 0 nu beta beta decay experiments, assuming the short-range part of the 0 nu beta beta decay amplitude dominates. We focus on the first of two possible topologies triggered by one fermion and two bosons in the intermediate state. In all cases, except for the pure leptoquark mechanism, the LHC will be more sensitive than 0 nu beta beta decay in the future. In addition, we propose to search for a charge asymmetry in the final state leptons and to use different invariant mass peaks as a possible tool to discriminate the various possible mechanisms for LNV signals at the LHC.
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Helo, J. C., Kovalenko, S. G., & Hirsch, M. (2014). Heavy neutrino searches at the LHC with displaced vertices. Phys. Rev. D, 89(7), 073005–7pp.
Abstract: Sterile neutrinos with masses in the range of 1-100 GeV have been searched for in a variety of experiments. Here, we discuss the prospects of searching for sterile neutrinos at the LHC using displaced vertices. Two different cases are discussed: (i) the standard model extended with sterile neutrinos, and (ii) right-handed neutrinos in a left-right symmetric extension of the standard model. A dedicated displaced vertex search will allow us to probe parts of the parameter space not accessible to other searches, but both cases will require a large luminosity.
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Helo, J. C., & Hirsch, M. (2015). LHC dijet constraints on double beta decay. Phys. Rev. D, 92(7), 073017–7pp.
Abstract: We use LHC dijet data to derive constraints on neutrinoless double beta decay. Upper limits on cross sections for the production of “exotic” resonances, such as a right-handed W boson or a diquark, can be converted into lower limits on the double beta decay half-life for fixed choices of other parameters. Constraints derived from run-I data are already surprisingly strong and complementary to results from searches using same-sign dileptons plus jets. For the case of the left-right symmetric model, in case no new resonance is found in future runs of the LHC and assuming g(L) = g(R), we estimate a lower limit on the double beta decay half-life larger than 10(27) yr can be derived from future dijet data, except in the window of relatively light right-handed neutrino masses in the range 0.5 MeV to 50 GeV. Part of this mass window will be tested in the upcoming SHiP experiment. We also discuss current and future limits on possible scalar diquark contributions to double beta decay that can be derived from dijet data.
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Cottin, G., Helo, J. C., & Hirsch, M. (2018). Searches for light sterile neutrinos with multitrack displaced vertices. Phys. Rev. D, 97(5), 055025–6pp.
Abstract: We study discovery prospects for long-lived sterile neutrinos at the LHC with multitrack displaced vertices, with masses below the electroweak scale. We reinterpret current displaced vertex searches making use of publicly available, parametrized selection efficiencies for modeling the detector response to displaced vertices. We focus on the production of right-handed WR bosons and neutrinos N in a left-right symmetric model, and find poor sensitivity. After proposing a different trigger strategy ( considering the prompt lepton accompanying the neutrino displaced vertex) and optimized cuts in the invariant mass and track multiplicity of the vertex, we find that the LHC with root s = 13 TeV and 300 fb(-1) is able to probe sterile neutrino masses between 10 GeV < m(N) < 20 GeV ( for a right-handed gauge boson mass of 2 TeV < m(WR) < 3.5 TeV). To probe higher masses up to m(N) similar to 30 GeV and m(WR) < 5 TeV, 3000 fb(-1) will be needed. This work joins other efforts in motivating dedicated experimental searches to target this low sterile neutrino mass region.
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Cottin, G., Helo, J. C., & Hirsch, M. (2018). Displaced vertices as probes of sterile neutrino mixing at the LHC. Phys. Rev. D, 98(3), 035012–6pp.
Abstract: We investigate the reach at the LHC to probe light sterile neutrinos with displaced vertices. We focus on sterile neutrinos N with masses m(N) similar to (5-30) GeV that are produced in rare decays of the standard model gauge bosons and decay inside the inner trackers of the LHC detectors. With a strategy that triggers on the prompt lepton accompanying the N displaced vertex and considers charged tracks associated with it, we show that the 13 TeV LHC with 3000/fb is able to probe active-sterile neutrino mixings down to vertical bar V-lN vertical bar(2) approximate to 10(-9), with l = e, mu, which is an improvement of up to 4 orders of magnitude when comparing with current experimental limits from trileptons and proposed lepton-jets searches. In the case when tau mixing is present, mixing angles as low as vertical bar V-tau N vertical bar(2) approximate to 10(-8) can be accessed.
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