Speaker
Description
The $K^+\to\pi^+\nu\bar{\nu}$ decay is a golden channel in flavor physics. It’s highly suppressed in the Standard Model and sensitive to various indirect effects of new physics. The branching ratio of the K+ → pi+ nu nubar decay has been recently observed with 5 sigma significance by the NA62 experiment at the CERN SPS. To further improve the sensitivity to this channel at NA62, the contribution of background originating upstream of the decay region needs to be studied in detail. Contributions to this background are predicted to arise from interactions between the charged particle beam and the silicon beam spectrometer, GTK3, as well as the residual gas in the vacuum tank. The study of this component with combined 2018–2024 data is presented. The result shows beam-GTK3 interaction contributes $\sim 5\%$ of the upstream background while no clear evidence of beam-gas interaction is found.