Searching for a squark LSP of the first two families at the LHC

TL;DR

This study examines collider signatures of a first-two-family squark LSP in the μνSSM with RPV, where right-handed neutrinos address the μ problem and generate neutrino masses via an EW seesaw. By scanning a minimal, neutrino- and Higgs-consistent parameter space, the authors characterize squark decays (predominantly ̃q → q ν, with subdominant ̃q → q H ν/ℓ) and confront predictions with ATLAS/CMS searches for prompt and displaced decays. They derive LHC bounds that depend on squark flavor: m̃_q ≳ 1.65–1.70 TeV for s̃_R and c̃_R, and m̃_q ≳ 1.36–1.80 TeV for other cases, with cτ limits ranging from mm to cm scales; the first-family squark LSPs are excluded unless the gluino is very heavy (∼7–27 TeV). Overall, the results constrain μνSSM parameter space and guide future LHC searches for RP-violating SUSY in the squark sector.

Abstract

We analyse relevant signals expected at the LHC for a squark of the first two families as the lightest supersymmetric particle (LSP). The discussion is established in the framework of the $μν$SSM, where the presence of $R$-parity violating couplings involving right-handed neutrinos solves simultaneously the $μ$-problem and the accommodation of neutrino masses and mixing angles. The squarks are pair produced and decay dominantly to a neutrino and a quark. They also have two sub-dominant three body decays to quark, Higgs and neutrino/charged lepton. The decays can be prompt or displaced, depending on the regions of the parameter space of the model. We focus the analyses on squarks of right up-type, right down-type, and left up-type; since squarks of left down-type cannot be the LSP because of D-term contributions. We compare the predictions of these scenarios with ATLAS and CMS searches for prompt and long-lived particles. To analyse the parameter space we sample the $μν$SSM for a squark LSP, paying special attention to reproduce the current experimental data on neutrino and Higgs physics, as well as flavour observables. Because of the contribution of squark-squark final states to the production cross section, the results depend on the squark family. In particular, for a right strange squark LSP, the lower limit on the mass is $1646$ GeV, corresponding to an upper limit on the decay length of $54.7$ mm, and for a right (left) scharm LSP, the limits are $1625$ ($1357$) GeV and $13.4$ ($1.9$) mm. However, the first family of squarks as LSP turns out to be excluded, unless the gluino is heavier than $7$ TeV, which produces a limit on the squark mass of $1800$ GeV.

Figures (8)

• Figure 1: Dominant decay channel in the $\mu\nu{\rm SSM}$ for a squark of the first two families as the LSP.
• Figure 2: Sub-dominant decay channels in the $\mu\nu{\rm SSM}$ for a squark of the first two families as the LSP. (left) Decay to quark, Higgs and neutrinos; (right) Decay to quark, Higgs and leptons.
• Figure 3: Proper decay length $c\tau$ for a right strange squark LSP versus the right strange physical squark mass. Dark (light) points are allowed (excluded) by LHC constraints.
• Figure 4: Branching ratios of a right strange squark LSP decaying to $s\nu$ (left plot) and $s h\nu$ (right plot). Dark (light) points are allowed (excluded) by LHC constraints.
• Figure 5: The same as in Fig. \ref{['fig:strange-ctau']} but for a right scharm LSP.