BGU Physics Department logo

Interplay between measurements in particle colliders and theories beyond the Standard Model

Yevgeny Kats

The most powerful particle physics experiment ever built, the Large Hadron Collider (LHC) at CERN, holds great promise. In 2012, it discovered the Higgs boson, and the significantly higher energy and collision rate that it provides today may allow discovering new types of particles, some of which could explain the various open questions in fundamental physics (the origin of the electroweak scale, dark matter, the matter-antimatter asymmetry in the Universe, and others).

While waiting for discoveries, the results of measurements and new-physics searches from the LHC can be re-used for examining the viability of new physics scenarios other than those for which they were originally designed. Determining the status of those scenarios involves simulating the relevant physical process, the resulting signatures in the detectors, and the analysis done in the experimental studies. As a welcome by-product, we identify general gaps in the experimental coverage of potential new physics signatures.

In one such project, our goal was to clarify the experimental status of supersymmetry as a natural explanation for the electroweak symmetry breaking scale. Besides requiring the existence of a light superpartner (as at least the higgsino is expected to be light), and a gluino within the kinematic range of the 8 TeV LHC, we have kept our analysis quite general, allowing for arbitrary departures from any minimal model of supersymmetry. We were able to argue that gluino decays always give rise to either a significant amount of missing energy and/or frequently produce top quarks and/or large jet multiplicity, to the extent that they are covered by a certain class of LHC searches in each case. We have found that gluinos are almost always excluded up to masses above 1 TeV. We have also identified several classes of scenarios in which the limits were weaker, and proposed strategies for addressing these gaps.

Further reading: Toward Full LHC Coverage of Natural Supersymmetry, J. A. Evans, Y. Kats, D. Shih, M. J. Strassler, JHEP 1407, 101 (2014) [pdf]

In an earlier work, motivated by the lack of any signals in supersymmetry searches based on missing energy, we have addressed the status of more general models of supersymmetry, those that do not assume R-parity. As a compromise between minimizing the fine-tuning of the electroweak symmetry breaking scale, and the apparent absence of significant production of colored superpartners, we considered scenarios in which the only light colored superpartners are the third-generation squarks (and in particular, one of the stops). We constructed a set of simplified models that span the parameter space of the R-parity violating couplings and the mediators through which the stop may decay. We derived limits on these models using a complete set of potentially relevant recent LHC searches. We then looked into the least constrained scenarios in more detail and suggested several ideas for search methods that may allow addressing many of them.

Further reading: LHC Coverage of RPV MSSM with Light Stops, J. A. Evans and Y. Kats, JHEP 1304, 028 (2013) [pdf]

Currently we are analyzing certain novel LHC signatures predicted by the Clockwork Theory. Stay tuned!

CMS search
One of the LHC searches motivated by our models
[CMS collaboration, Phys. Lett. B 739 (2014) 229]

Apart from providing feedback to the experimental community, this type of studies make us prepared to interpret any hints of new particles that the LHC might report in the future. One hint, near the mass of 750 GeV, was reported at the end of 2015. The hint has disappeared since then, by it made us think about various theoretical ideas that may still turn out useful in other contexts.

Further reading: