897 research outputs found

    Search for decays of stopped exotic long-lived particles produced in proton-proton collisions at √s = 13 TeV

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    A search is presented for the decays of heavy exotic long-lived particles (LLPs) that are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC and come to rest in the CMS detector. Their decays would be visible during periods of time well separated from proton-proton collisions. Two decay scenarios of stopped LLPs are explored: a hadronic decay detected in the calorimeter and a decay into muons detected in the muon system. The calorimeter (muon) search covers a period of sensitivity totaling 721 (744) hours in 38.6 (39.0) fb^(−1) of data collected by the CMS detector in 2015 and 2016. The results are interpreted in several scenarios that predict LLPs. Production cross section limits are set as a function of the mean proper lifetime and the mass of the LLPs, for lifetimes between 100 ns and 10 days. These are the most stringent limits to date on the mass of hadronically decaying stopped LLPs, and this is the first search at the LHC for stopped LLPs that decay to muons

    Search for decays of stopped exotic long-lived particles produced in proton-proton collisions at s\sqrt s = 13 TeV

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    A search is presented for the decays of heavy exotic long-lived particles (LLPs) that are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC and come to rest in the CMS detector. Their decays would be visible during periods of time well separated from proton-proton collisions. Two decay scenarios of stopped LLPs are explored: a hadronic decay detected in the calorimeter and a decay into muons detected in the muon system. The calorimeter (muon) search covers a period of sensitivity totaling 721 (744) hours in 38.6 (39.0) fb1fb^{−1} of data collected by the CMS detector in 2015 and 2016. The results are interpreted in several scenarios that predict LLPs. Production cross section limits are set as a function of the mean proper lifetime and the mass of the LLPs, for lifetimes between 100 ns and 10 days. These are the most stringent limits to date on the mass of hadronically decaying stopped LLPs, and this is the first search at the LHC for stopped LLPs that decay to muons

    Collider Searches for Long-Lived Particles Beyond the Standard Model

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    Experimental tests of the Standard Model of particle physics (SM) find excellent agreement with its predictions. Since the original formation of the SM, experiments have provided little guidance regarding the explanations of phenomena outside the SM, such as the baryon asymmetry and dark matter. Nor have we understood the aesthetic and theoretical problems of the SM, despite years of searching for physics beyond the Standard Model (BSM) at particle colliders. Some BSM particles can be produced at colliders yet evade being discovered, if the reconstruction and analysis procedures not matched to characteristics of the particle. An example is particles with large lifetimes. As interest in searches for such long-lived particles (LLPs) grows rapidly, a review of the topic is presented in this article. The broad range of theoretical motivations for LLPs and the experimental strategies and methods employed to search for them are described. Results from decades of LLP searches are reviewed, as are opportunities for the next generation of searches at both existing and future experiments.Comment: 79 pages, 36 figures, submitted to Progress in Particle and Nuclear Physic

    Prospects for discovering supersymmetric long-lived particles with MoEDAL

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    We present a study on the possibility of searching for long-lived supersymmetric partners with the MoEDAL experiment at the LHC. MoEDAL is sensitive to highly ionising objects such as magnetic monopoles or massive (meta)stable electrically charged particles. We focus on prospects of directly detecting long-lived sleptons in a phenomenologically realistic model which involves an intermediate neutral long-lived particle in the decay chain. This scenario is not yet excluded by the current data from ATLAS or CMS, and is compatible with astrophysical constraints. Using Monte Carlo simulation, we compare the sensitivities of MoEDAL versus ATLAS in scenarios where MoEDAL could provide discovery reach complementary to ATLAS and CMS, thanks to looser selection criteria combined with the virtual absence of background. It is also interesting to point out that, in such scenarios, in which charged staus are the main long-lived candidates, the relevant mass range for MoEDAL is compatible with a potential role of Supersymmetry in providing an explanation for the anomalous events observed by the ANITA detector.Comment: 12 pages, 6 figures; preliminary results presented in arXiv:1903.11022; matches published version in EPJ

    The experimental status of direct searches for exotic physics beyond the standard model at the Large Hadron Collider

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    The standard model of particle physics is an extremely successful theory of fundamental interactions, but it has many known limitations. It is therefore widely believed to be an effective field theory that describes interactions near the TeV scale. A plethora of strategies exist to extend the standard model, many of which contain predictions of new particles or dynamics that could manifest in proton-proton collisions at the Large Hadron Collider (LHC). As of now, none have been observed, and much of the available phase space for natural solutions to outstanding problems is excluded. If new physics exists, it is therefore either heavy (i.e. slightly above the reach of current searches) or hidden (i.e. currently indistinguishable from standard model backgrounds). We summarize the existing searches, and discuss future directions at the LHC.Comment: 33 pages, 7 figure

    Exotic Phenomena Searches at Hadron Colliders

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    This review presents a selection of the final results of searches for various exotic physics phenomena in proton-proton collisions at sqrt(s)=7 and 8 TeV delivered by the LHC and collected with the ATLAS and CMS detectors in 2011 (5 fb-1) and in the first part of 2012 (4 fb-1). Searches for large extra dimensions, gravitons, microscopic black holes, long-lived particles, dark matter, and leptoquarks are presented in this report. No sign of new physics beyond the Standard Model has been observed so far. In the majority of the cases these searches set the most stringent limits to date on the aforementioned new physics phenomena.Comment: 10 pages, 4 figures, Proceedings of the PIC 2012, Strbske Pleso, Slovaki

    Getting Stuck: Using Monosignatures to Test Highly Ionizing Particles

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    In this paper we argue that monojet and monophoton searches can be a sensitive test of very highly ionizing particles such as particles with charges 150e\gtrsim 150e and more generally particles that do not reach the outer parts of the detector. 8 TeV monojet data from the CMS experiment excludes such objects with masses in the range 650 GeV\lesssim 650~{\text{GeV}} and charges 100e\gtrsim 100e. This nicely complements searches for highly ionizing objects at ALICE, ATLAS, CMS and LHCb. Expected improvements in these channels will extend the sensitivity range to m750 GeVm\lesssim 750~{\text{GeV}}. This search strategy can directly be generalized to other particles that strongly interact with the detector material, such as e.g. magnetic monopoles.Comment: 15 pages, 8 figures, version published in PL

    Physics reach of MoEDAL at LHC: magnetic monopoles, supersymmetry and beyond

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    MoEDAL is a pioneering experiment designed to search for highly ionising messengers of new physics such as magnetic monopoles or massive (pseudo-)stable charged particles, that are predicted to exist in a plethora of models beyond the Standard Model. Its ground-breaking physics program defines a number of scenarios that yield potentially revolutionary insights into such foundational questions as, are there extra dimensions or new symmetries, what is the mechanism for the generation of mass, does magnetic charge exist, what is the nature of dark matter, and, how did the big-bang develop at the earliest times. MoEDAL's purpose is to meet such far-reaching challenges at the frontier of the field. The physics reach of the existing MoEDAL detector is discussed, giving emphasis on searches for magnetic monopoles, supersymmetric (semi)stable partners, doubly charged Higgs bosons, and exotic structures such as black-hole remnants in models with large extra spatial dimensions and D-matter in some brane theories.Comment: 17 pages, 8 figures; combines two invited talks in 5th International Conference on New Frontiers in Physics (ICNFP 2016), 6-14 Jul 2016, Kolymbari, Greece; based on arXiv:1405.7662, arXiv:1411.7651, arXiv:1511.0174

    Long-lived charged particles and multi-lepton signatures from neutrino mass models

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    Lepton number violation (LNV) is usually searched for by the LHC collaborations using the same-sign di-lepton plus jet signature. In this paper we discuss multi-lepton 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, that leave highly ionizing tracks in the detectors. We focus on one particular 1-loop neutrino mass model in this class and discuss its LHC phenomenology in some detail.Comment: 14 pages, 9 figure
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