Measuring the tth coupling from SSDL+2b measurements

48 citations (47 excluding self-citations).

The Problem

After the Higgs discovery, measuring the top Yukawa coupling became a high priority. But the existing approaches all had indirect contamination: the h→γγ rate depends on the top Yukawa through a loop, so any BSM contribution to the loop is degenerate with the coupling itself. Similarly, the dominant tth search channels at the time relied on h→bb, where large uncertainties in the bottom Yukawa and QCD backgrounds degraded sensitivity. A cleaner, more direct measurement was needed.

The Key Idea

The same-sign dilepton plus two b-jets (SSDL+2b) channel in tth production provides direct access to the top Yukawa without passing through loop-level couplings. Both tops decay leptonically and the Higgs decays via h→WW*, so the measurement relies on the well-measured WW* branching ratio rather than the uncertain bb channel. Taking a ratio with the Wh→WWW* rate further cancels Higgs width uncertainties. The dominant background is fake leptons, for which we developed a new data-driven estimation method. This approach exemplified the search strategies philosophy of finding the right observable to isolate a specific coupling, complementing work like the CMSSM mapping that characterized what the LHC could probe.

Recollections

[To be added.]

• DOI
• arXiv:1306.5695
• INSPIRE