Search

Assuming that the sbottom is the lightest supersymmetric particle (LSP), we carry out an analysis of the relevant signals expected at the LHC. The discussion is established in the framework of the $\mu\nu$SSM, where the presence of $R$-parity violating couplings involving right-handed neutrinos solves simultaneously the $\mu$-problem and the accommodation of neutrino masses and mixing angles. The sbottoms are pair produced at the LHC, decaying to a lepton and a top quark or a neutrino and a bottom quark. The decays can be prompt or displaced, depending on the regions of the parameter space of the model. We focus the analysis on the right sbottom LSP, since the left sbottom is typically heavier than the left stop because of the D-term contribution. We compare the predictions of this scenario with ATLAS and CMS searches for prompt and long-lived particles. To analyze the parameter space we sample the $\mu\nu$SSM for a right sbottom LSP, paying special attention to reproduce the current experimental data on neutrino and Higgs physics, as well as flavor observables. For displaced (prompt) decays, our results translate into lower limits on the mass of the right sbottom LSP of about $1041$ GeV ($1070$ GeV). The largest possible value found for the decay length is about $3.5$ mm., Comment: Version published in EPJC. Discussion expanded, references added. 28 pages, 4 figures, 3 tables, 1 appendix. Analysis of the stop LSP at the LHC carried out in arXiv:2111.13212

We revisit LHC searches for heavy invisible particles by exploiting QCD initial state radiation. We recast a dijet signal region in a general multijet plus MET search by ATLAS. We find that non-trivial mass limit can be obtained for various models of the electroweakino sector with the present data in hadronic channels. The winos are bound to be heavier than $m_{\tilde W} \gtrsim {160}$ GeV and higgsinos $m_{\tilde h} \gtrsim {100}$ GeV, depending on the chargino-neutralino mass splitting. The expected exclusion limits at the LHC Run 3 with $\mathcal{L} = 300$ fb$^{-1}$ increase to $m_{\tilde W} \gtrsim {200}$ GeV and $m_{\tilde h} \gtrsim {130}$ GeV for winos and higgsino, respectively. This is the first LHC limit for promptly decaying nearly mass-degenerate winos., Comment: 8 pages, 5 figures; updated references, expectations for LHC Run 3 added; to appear in PRD

We study the monojet and dijet channels at the LHC as a tool for searching for squarks and gluinos. We consider two separate R-parity conserving supersymmetric scenarios. In the first scenario we postulate a large mass hierarchy between squarks ($\tilde q$) and winos ($\widetilde W$), and wino-like neutralino is assumed to be the lightest supersymmetric particle (LSP). The associated squark-wino production, $pp \to \tilde q \widetilde W$, then leads to a monojet-like signature, where the high $p_T$ jet is originated from the squark decay, $\tilde q \to q + \widetilde W$. We demonstrate that this associated production, as well as the $pp \to \widetilde W \widetilde W + {\rm jets}$ production, have a significant impact on the exclusion limit in the squark-neutralino mass plane. The second scenario postulates that the lighter of the squark and gluino is only a few GeV heavier than the LSP neutralino. The associated squark-gluino production, $pp \to \tilde q \tilde g$, then leads to a distinctive monojet signature, where the high $p_T$ jet is produced from the decay of the heavier coloured particle into the lighter one ($\tilde q \to q + \tilde g$ for $m_{\tilde q} > m_{\tilde g}$ and $\tilde g \to q + \tilde q$ for $m_{\tilde g} > m_{\tilde q}$). The lighter coloured particle is effectively regarded as an invisible particle since the decay products are soft due to the approximate mass degeneracy. We recast existing monojet and dijet analyses and find a non-trivial exclusion limit in the squark-gluino mass plane in this scenario., Comment: 20 pages, 10 figures. Version published in JHEP

We analyze relevant signals expected at the LHC for a stop as the lightest supersymmetric particle (LSP). The discussion is carried out in the framework of the $\mu\nu$SSM, where the presence of $R$-parity violating couplings involving right-handed neutrinos solves the $\mu$-problem and reproduces neutrino data. The stops are pair produced at the LHC, decaying with displaced vertices to a lepton and a bottom quark or a neutrino and a top quark. We compare the predictions of this scenario with ATLAS and CMS searches for long-lived particles. To analyze the parameter space we sample the $\mu\nu$SSM for a stop LSP using a likelihood data-driven method, and paying special attention to reproduce the current experimental data on neutrino and Higgs physics, as well as flavor observables. Our results translate into a lower limit on the mass of the left (right) stop LSP of 1068 GeV (1341 GeV), corresponding to a decay length of 1.86 mm (6.61 mm)., Comment: Version published in EPJC. Discussion expanded, references added. 26 pages, 5 figures, 2 tables, 1 appendix. arXiv admin note: text overlap with arXiv:2104.03294

The $\mu\nu$SSM is a highly predictive alternative model to the MSSM. In particular, the electroweak sector of the model can explain the longstanding discrepancy between the experimental result for the anomalous magnetic moment of the muon, $(g-2)_\mu$, and its Standard Model prediction, while being in agreement with all other theoretical and experimental constraints. The recently published MUON G-2 result is within $0.8\,\sigma$ in agreement with the older BNL result on $(g-2)_\mu$. The combined result was announced as $a_\mu^{\rm exp} = (11659206.1 \pm 4.1) \times 10^{-10}$, yielding a new deviation from the Standard Model prediction of $\Delta a_\mu = (25.1 \pm 5.9) \times 10^{-10}$, corresponding to $4.2\,\sigma$. Using this improved bound we update the analysis in the $\mu\nu$SSM as presented in Ref. [1] and set new limits on the allowed parameters space of the electroweak sector of the model. We conclude that significant regions of the model can explain the new $(g-2)_\mu$ data., Comment: Version published in EPJC. Discussion expanded, references added. 34 pages, 10 figures, 1 table. Follow-up of arXiv:1912.04163

We analyze the anomalous magnetic moment of the muon $g-2$ in the $\mu\nu$SSM. This $R$-parity violating model solves the $\mu$ problem reproducing simultaneously neutrino data, only with the addition of right-handed neutrinos. In the framework of the $\mu\nu$SSM, light left muon-sneutrino and wino masses can be naturally obtained driven by neutrino physics. This produces an increase of the dominant chargino-sneutrino loop contribution to muon $g-2$, solving the gap between the theoretical computation and the experimental data. To analyze the parameter space, we sample the $\mu\nu$SSM using a likelihood data-driven method, paying special attention to reproduce the current experimental data on neutrino and Higgs physics, as well as flavor observables such as $B$ and $\mu$ decays. We then apply the constraints from LHC searches for events with multi-leptons + MET on the viable regions found. They can probe these regions through chargino-chargino, chargino-neutralino and neutralino-neutralino pair production. We conclude that significant regions of the parameter space of the $\mu\nu$SSM can explain muon $g-2$ data., Comment: Version published in EPJC. A compiling issue has been resolved in Fig. 11. 39 pages, 14 figures, 3 tables. Analyses of the scalar sector of the {\mu}{\nu}SSM in arXiv:1907.02092 and arXiv:1910.08062 are used

Within the framework of the $\mu\nu$SSM, a displaced dilepton signal is expected at the LHC from the decay of a tau left sneutrino as the lightest supersymmetric particle (LSP) with a mass in the range $45 - 100$ GeV. We compare the predictions of this scenario with the ATLAS search for long-lived particles using displaced lepton pairs in $pp$ collisions, considering an optimization of the trigger requirements by means of a high level trigger that exploits tracker information. The analysis is carried out in the general case of three families of right-handed neutrino superfields, where all the neutrinos get contributions to their masses at tree level. To analyze the parameter space, we sample the $\mu\nu$SSM for a tau left sneutrino LSP with proper decay length $c\tau > 0.1$ mm using a likelihood data-driven method, and paying special attention to reproduce the current experimental data on neutrino and Higgs physics, as well as flavor observables. The sneutrino is special in the $\mu\nu$SSM since its couplings have to be chosen so that the neutrino oscillation data are reproduced. We find that important regions of the parameter space can be probed at the LHC run 3., Comment: Version published in EPJC, 32 pages, 7 figures

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.

We analyze a multi-lepton signal plus missing transverse energy from neutrinos expected at the LHC for a Bino-like neutralino as the lightest supersymmetric particle (LSP), when the left sneutrino is the next-to-LSP and hence a suitable source of Binos. The discussion is carried out in the framework of the $\mu \nu$SSM, where the presence of $R$-parity violating (RPV) couplings involving right-handed neutrinos solves the $\mu$ problem and can reproduce simultaneously the neutrino data. Left sneutrinos/sleptons are pair produced at $pp$ collisions decaying to Binos, with the latter decaying via RPV to $W\ell$ or $Z\nu$. This signal can be compared with LHC searches for electroweak superpartners through chargino-neutralino production. The reduced cross section of the sneutrino/slepton production in comparison with the one of the latter process, limits the sensitivity of the searches to small sneutrino/slepton masses. Although the resulting compressed spectrum typically evades the aforementioned searches, we show that analyses using recursive jigsaw reconstruction are sensitive to these scenarios. As a by-product, we find that the region of Bino masses $110-120$ GeV and sneutrino masses $120-140$ GeV can give rise to a tri-lepton signal compatible with the local excess recently reported by ATLAS., Comment: Discussions expanded, one figure and references added, version published in Phys. Lett. B. 18 pages, 3 figures, 3 tables

We analyze a displaced dilepton signal expected at the LHC for a tau left sneutrino as the lightest supersymmetric particle with a mass in the range $45$-$100$ GeV. The sneutrinos are pair produced via a virtual $W$, $Z$ or $\gamma$ in the $s$ channel and, given the large value of the tau Yukawa coupling, their decays into two dileptons or a dilepton plus missing transverse energy from neutrinos can be significant. The discussion is carried out in the $\mu \nu$SSM, where the presence of $R$-parity violating couplings involving right-handed neutrinos solves the $\mu$ problem and can reproduce the neutrino data. To probe the tau left sneutrinos we compare the predictions of the $\mu \nu$SSM with the ATLAS search for long-lived particles using displaced lepton pairs in $pp$ collisions at $\sqrt s= 8$ TeV, allowing us to constrain the parameter space of the model. We also consider an optimization of the trigger requirements used in existing displaced-vertex searches by means of a High Level Trigger that exploits tracker information. This optimization is generically useful for a light metastable particle decaying into soft charged leptons. The constraints on the sneutrino turn out to be more stringent. We finally discuss the prospects for the $13$ TeV LHC searches as well as further potential optimizations., Comment: Version published in PRD, discussions expanded, references added, LEP and LHC constraints discussed in more detail, 29 pages, 9 figures, 9 tables

We analyze relevant signals expected at the LHC for a left sneutrino as the lightest supersymmetric particle (LSP). The discussion is carried out in the `$\mu$ from $\nu$' supersymmetric standard model ($\mu \nu$SSM), where the presence of $R$-parity breaking couplings involving right-handed neutrinos solves the $\mu$ problem and reproduces neutrino data. The sneutrinos are pair produced via a virtual $W$, $Z$ or $\gamma$ in the $s$ channel. From the prompt decay of a pair of left sneutrinos LSPs of any family, a significant diphoton signal plus missing transverse energy (MET) from neutrinos can be present in the mass range 118-132 GeV, with 13 TeV center-of-mass energy and an integrated luminosity of 100 fb$^{-1}$. In addition, in the case of a pair of tau left sneutrinos LSPs, given the large value of the tau Yukawa coupling diphoton plus leptons and/or multileptons can appear. We find that the number of expected events for the multilepton signal, together with properly adopted search strategies, is sufficient to give a significant evidence for a sneutrino of mass in the range 130-310 GeV, even with the integrated luminosity of 20 fb$^{-1}$. In the case of the signal producing diphoton plus leptons, an integrated luminosity of 100 fb$^{-1}$ is needed to give a significant evidence in the mass range 95-145 GeV. Finally, we discuss briefly the presence of displaced vertices and the associated range of masses., Comment: Version published in IJMPA. 54 pages, 8 figures, 14 tables