Abstract

Searches for new light bosons can offer insights into the nature of the Higgs boson and dark matter. These particles are introduced in many extensions of the standard model, such as supersymmetry and models with hidden sectors. In this seminar I present a search for pair production of new light bosons with the CMS detector at the LHC. The search is uniquely sensitive to signatures with multi-muon final states and is designed to be model independent. The results of the analysis using 13 TeV collision data set are interpreted in the context of two relevant benchmark models. I will also discuss the phase-2 upgrade of the CMS detector and how it can improve the sensitivity in these searches.

Abstract

As the experiments at the LHC accumulate larger and larger data sets with dozens of searches showing no signs of physics beyond the standard model, it becomes imperative to examine the assumptions made in these searches. One of the most ubiquitous assumptions is that new particles will have short lifetimes and leave decay products that originate from the proton-proton interaction point. If the new particles are instead long-lived, they may produce experimental signatures that are completely missed by these more conventional searches. One particularly challenging signature of long-lived particles is the so-called “disappearing track,” where a new long-lived charged particle decays in the middle of the tracker of a collider detector to invisible decay products. In this talk, I will discuss the search for disappearing tracks in the 13 TeV data collected by the CMS detector, and how this search fits into the broader search for new physics at the LHC.

Abstract: While the gravitational evidence for the existence of Dark Matter (DM) is overwhelming, there is no good DM candidate among the particles of the Standard Model, and there is no evidence yet for non-gravitational interactions between DM and Standard Model particles. A search is described for evidence of particle DM production with a signature containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 fb-1 of proton-proton collisions at the LHC at a center-of-mass energy of 8 TeV. The results are interpreted in terms of limits on the DM-nucleon scattering cross section, as a function of the DM particle mass, for both spin-dependent and spin-independent scenarios.

A related study searches for invisible decays of Higgs bosons in associated ZH production, using the same final state with a Z boson and missing transverse mometum. The study uses the full 2011 and 2012 data samples at 7 TeV and 8 TeV, respectively. The search is sensitive to non-Standard-Model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. By assuming Standard Model Higgs boson cross sections and acceptances, an upper limit is obtained on the invisible branching fraction of the Higgs boson. The limit is also interpreted in terms of a Higgs-portal model of DM interactions.