Constraints from the CHARM experiment on Heavy Neutral Leptons with tau mixing

Abstract

We re-analyze the results of the searches for Heavy Neutral Leptons (HNLs) by the CHARM experiment. We study HNL decay channel N → e + e − ν/µ + µ − ν and show that, in addition to the constraints on the HNL's mixings with νe or νµ, the same data also implies limits on the HNLs that mix only with ντ and have masses in the range 380 MeV < mN 1.6 GeV -the region in the parameter space that was considered in the literature as a target for HNLs searches.

Heavy neutral leptons below the kaon mass at hodoscopic detectors

“…with the understanding that N is the heavy mass eigenstate, which may be a Majorana or (pseudo-)Dirac particle, while α denotes any of the three SM flavors. Although mixing with all three SM flavors is expected, it is worth simplifying our discussion to the case where mixing [11] and NOMAD [12], see also [13]. The weak decays of N are straightforward to calculate, and we use the expressions in Ref.…”

Um candidato à matéria escura no contexto da física além do modelo padrão

“…7 of Ref. [31]). Next, we fix log 10 𝑓 = −15.6 to match the original limit, giving the number of events 𝑁 𝐸 = 𝑁 𝐷 × 𝑓 = 2.24 < 2.3 at 90% C.L..…”

“…Although the original CHARM analysis did not include 𝑈 𝜏 constraints, Ref. [31] extended the published results to do so by including neutral current contributions to the decays of the HNL, and we have done likewise.…”

“…The CHARM Collaboration searched for HNLs in the mass range 0.5 − 1.8 GeV produced in the decays of 𝐷 ± and 𝐷 0 [29]. In subsequent analyses [30,31], this range was expanded up to ∼2 GeV by considering also the production of 𝐷 𝑠 , which we emulate in this work.…”