Abstract
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.
Highlights
Clarifying whether or not low-energy supersymmetry (SUSY) exists in nature is one of the main goals of the LHC
By using the method described in the previous section, we evaluate the current and potential limits on the parameter space of our scenario from the displaced-vertex searches with the 8-TeVATLAS result [10], and discuss the prospects for the 13-TeV searches
We have analyzed the sensitivity of the displaced dilepton searches at the LHC to a tau left sneutrino lightest supersymmetric particle (LSP) with a mass in the range 45–100 GeV in the framework of the μνSSM
Summary
Clarifying whether or not low-energy supersymmetry (SUSY) exists in nature is one of the main goals of the LHC. It is worth noticing here that whereas vR ∼ TeV, vi ≲ 10−4 GeV because of the small contributions Yνi ≲ 10−6 whose size is determined by the electroweak-scale seesaw of the μνSSM [1,2] This is a generalized seesaw since the left-handed neutrinos mix with the right-handed one, and with the neutralinos. Yνi vu 2vi pffiffi vR − 2Aνi κvR λvR tan β ð1:5Þ where Aνi are the trilinear parameters in the soft Lagrangian, −εabTνi HbuLaiLνÃR, defining Tνi ≡ Aνi Yνi and with the summation convention not applied in this case Taking all this into account, scalar and pseudoscalar sneutrinos are dominantly pair produced via a Drell-Yan process mediated by a virtual W, Z or γ.
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