Abstract
We discuss dark shower signals at the LHC from a dark QCD sector, containing GeV-scale dark pions. The portal with the Standard Model is given by the mixing of the Z boson with a dark Z′ coupled to the dark quarks. Both mass and kinetic mixings are included, but the mass mixing is the essential ingredient, as it is the one mediating visible decays of the long-lived dark pions. We focus especially on the possibility that the dark Z′ is lighter than the Z. Indirect constraints are dominated by electroweak precision tests, which we thoroughly discuss, showing that both Z-pole and low-energy observables are important. We then recast CMS and LHCb searches for displaced dimuon resonances to dark shower signals initiated by the production of on-shell Z or Z′, where the visible signature is left by a dark pion decaying to μ+μ−. We demonstrate how dark shower topologies have already tested new parameter space in Run 2, reaching better sensitivity on a light dark Z′ compared to the flavor-changing decays of B mesons, which can produce a single dark pion at a time, and the electroweak precision tests.
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Acknowledgments
We thank Cristiano Alpigiani, Elias Bernreuther, Roberto Contino, Marco Ferla, Yee Bob Hsiung, Simon Knapen, Suchita Kulkarni, Jessie Shelton, Matthew Strassler, Indara Suarez, and Mia Tosi for useful discussions. We are also grateful to the authors of refs. [62, 68] for an exchange about DarkCast predictions. H.C. was supported by the Department of Energy under grant DE-SC0009999 and acknowledges the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-2210452, where part of this work was performed. X.J. was supported in part by the National Natural Science Foundation of China under grant 12342502. L.L. was supported by NASA under grant 80NSSC22K081 and the Department of Energy under grant DE-SC0010010. E.S. was supported in part by the Science and Technology Facilities Council under the Ernest Rutherford Fellowship ST/X003612/1.
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Cheng, HC., Jiang, XH., Li, L. et al. Dark showers from Z-dark Z′ mixing. J. High Energ. Phys. 2024, 81 (2024). https://doi.org/10.1007/JHEP04(2024)081
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DOI: https://doi.org/10.1007/JHEP04(2024)081