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  1. Abstract

    Lepton universality (LU) typically refers to the lepton coupling, which is considered to be the same fore,μ, andτleptons, if the interaction is electroweak according to the Standard Model, and it is hence a compelling probe for New Physics. The same principle of universal electroweak lepton interaction leads to the expectation that lepton scattering yields are equal foreandμbeams under the same kinematic condition. The mere mass difference betweeneandμaffects kinematic quantities (such as the relation between scattering angle andQ2), and the lepton mass dependence of elastic cross sections for leptons scattered from structured and pointlike objects are taken into account. By comparinge+,e,μ+, andμscattering yields, two-photon exchange (TPE) effects, universal or not, can be separated from the general LU test of thee/μyield ratio. With its separable mixed beams ofe+/μ+ande/μ, respectively, the MUSE experiment at PSI is not only designed to measure the proton charge radius with four lepton species, but is also uniquely suited to probe TPE and LU, while benefitting from partial cancellations of certain shared systematics. An overview will be given of the MUSE experiment, the sensitivity, and the present status.

     
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  6. Abstract The search for a dark photon holds considerable interest in the physics community. Such a force carrier would begin to illuminate the dark sector. Many experiments have searched for such a particle, but so far it has proven elusive. In recent years the concept of a low mass dark photon has gained popularity in the physics community. Of particular recent interest is the 8 Be and 4 He anomaly, which could be explained by a new fifth force carrier with a mass of 17 MeV/ c 2 . The proposed Darklight experiment would search for this potential low mass force carrier at ARIEL in the 10-20 MeV/ c 2 e + e − invariant mass range. This proceeding will focus on the experimental design and physics case of the Darklight experiment. 
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