Results

The models that have been considered so far are described, and the derived limits are displayed. For each model, the results from the latest dataset that has been studied are shown by default, but sometimes an archive of the limits from previously studied datasets is also provided, so that the progression can be observed as more data are added.

Simplified Dark Matter Models

Searches for new physics at the LHC are often interpreted in terms of simplified models. Simplified models provide a generic framework for analysing experimental signatures using a small number of parameters, such as masses and couplings of new fields, without reference to specific UV-complete models. Such an approach is particularly well-suited for interpreting the search for dark matter in a more model-independent way, and can be used to connect results from the LHC with dark matter searches in direct detection and from the observation of cosmic rays.

Vector-like Quarks

Vector-Like quarks (VLQ) are hypothetical coloured, non-chiral, spin-1/2 particles. While fourth-generation quarks with chiral couplings are in general excluded by measurements at the LHC and elsewhere [63], vector-like quarks are not, and remain the simplest example of coloured fermions not yet excluded by data [26]. VLQs occur in several non-supersymmetric theories beyond-the-standard model that propose solutions to the hierarchy problem, offering mechanisms by which the Higgs mass is stabilised [26]. New sources of CP violation can also be introduced by these new particles [51]. VLQs are produced in SU(2) singlets, doublets or triplets of flavours X, T, B or Y, where T and B have the same charge as the SM top and bottom quarks (t and b), whilst Y and X have charges −4/3 and +5/3, respectively. VLQs can be produced in pairs via QCD or singly in association with SM quarks via electroweak interactions. They decay into to Z, W or Higgs bosons in association with SM quarks. Direct experimental searches for VLQ contributions set lower limits on their mass with various values depending in detail upon the production mechanism, flavour or branching ratio assumptions considered, but generally between 700 GeV and nearly 2 TeV [45][22][81][18]. The eventual sensitivity of the LHC and its upgrades is projected to approach 4 TeV [31].

R-Parity-Violating Supersymmetry

Supersymmetric extensions of the SM typically conserve a quantum number known as R-Parity, written as \(R_p = (−1)^{3B+L+2S}\). This has the effect of suppressing proton decay, excluding the single production of supersymmetric particles, and ensuring the stability of the lightest SUSY particle (LSP). However, the most general SUSY lagrangian allows R-Parity violating (RPV) terms; subsets of these terms can be included in a model without inducing unacceptably high rates of proton decay. RPV superymmetric models retain many of the theoretical motivations of supersymmetry (and may in some cases even retain a viable Dark Matter candidate). However, R-Parity violation in general can change the collider phenomenology significantly. For example in many cases the LSP decay removes the typical missing momentum signatures upon which many collider searches rely. For this reason the phenomenology of RPV models has been studied at past colliders (see for example [27][43][69]) and is currently a topic of interest at the LHC [62], perhaps especially as more conventional SUSY searches continue to draw blanks.