Paths to Discovery at the LHC: Dark Matter and Track Triggering

We know amazingly little about the substance that contributes more than 80% of the matter content of the universe. The unknown nature of this "Dark Matter" (DM) has motivated a broad and primarily US-led direct detection program. Despite their strong limits on spin-independent DM interactions, direct detection experiments are unable to effectively constrain all regions of Dark Matter production phase-space. For example, the lack of coherence enhancement in spin-dependent axial-vector and tensor interactions leads to production cross section bounds that are weaker than those of spin-independent interactions by several orders of magnitude. The Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) provides powerful and complementary Dark Matter discovery channels. The canonical approach to Dark Matter detection in CMS, pioneered in analyses at the Fermilab Tevatron, involves the "mono-jet" topology. When produced, neutral, stable DM particles escape the detector without interaction, giving rise to a significant "transverse missing energy" (6ET ) signal. As per its namesake, the mono-jet search also requires a high transverse momentum (pT) hadronic jet, against which the DM particles recoil. This search strategy is largely model independent; it is only assumed that Dark Matter couples to quarks/gluons and that particle Dark Matter is neutral and stable. The broader class of LHC \mono-object" searches (mono-photon, mono-W and mono-Z) improves sensitivity to Dark Matter production by including additional final-states. A related tt+DM search is sensitive to couplings to heavy avor, and can be understood within the same theoretical framework as the mono-object analyses. A mono-top search is instead sensitive to a class of models that include avor-changing and baryon number violating interactions. Depending on the choice of model, any one of the signatures described can function as the primary Dark Matter discovery channel at the LHC. All must be explored in order to maximize the potential for discovery in Run-2 of the LHC. My group will lead the exploration of Dark Matter in Run-2 by searching for the associated production of Dark Matter and heavy standard model particles W bosons and top quarks. The recent P5 report and the updated European Strategy for Particle Physics both identify the high-luminosity LHC (HL-LHC) as the highest near/medium-term priority for the particle physics community. The HL-LHC will deliver 3000 fb-1, or 10 times the luminosity integrated by the end of 2021. More than 1:7x10^8 Higgs bosons will be produced during the 10 years of HL-LHC operation, enabling precision measurements of Higgs properties, the study of its self-interactions, and the observation of its rare decay modes. When observed, deviations in the properties of known particles from standard model predictions will hint at the mass scale of the new physics that contributes. Direct searches for new particle production in CMS will gain sensitivity to multi-TeV masses and to sub-femtobarn production cross section. Sensitivity to these scales could be crucial for the detection of Dark Matter, which might only interact with known particles weakly via a heavy mediator. The key enabler of HL-LHC physics goals will be a real-time \Level-1" (L1) tracking trigger. L1 trigger systems implement the first stage of data refinement in hadron collider experiments. These systems examine data from every beam crossing and have just microseconds to decide if collision data should be retained or discarded. This is a "hard" real-time requirement. Th