Abstract
The precise measurement of the branching ratio of an ultrarare decay K+ → π+vv¯ (~10-10 according to the calculation within the Standard Model) allows to probe New Physics via indirect effects at mass scales higher than those accessible at the LHC. The NA62 experiment at the CERN SPS is aimed at measuring this branching ratio with the 10% precision. To achieve such level of precision, a novel decay-in-flight technique is used. The statistics collected during the first NA62 physics run in 2016 allowed to demonstrate the proof of the experimental method and obtain O(10-10) single event sensitivity. The preliminary results based on the 2016 data set are described.
Highlights
The ultra rare decay K+ → π+ννproceeds via flavor changing neutral currents and is highly suppressed in the Standard Model (SM) due to the GIM mechanism
The NA62 experiment at the CERN SPS is a new generation fixed target experiment which aims at measuring the branching ratio (BR) of the K+ → π+ννdecay with the decay–in–flight technique
The selection acceptance Aπνν is calculated from the Monte Carlo (MC), the efficiency RV induced by the random activity in veto detectors is measured from the control data, as well as the PNN trigger efficiency trig
Summary
The ultra rare decay K+ → π+ννproceeds via flavor changing neutral currents and is highly suppressed in the Standard Model (SM) due to the GIM mechanism. Within the SM, the main contribution to the branching ratio (BR) comes from box and penguin diagrams, which contain CKM matrix elements as external inputs. These elements give the largest uncertainty to the BR. Models with new sources of flavour violation give the largest deviations from SM [3, 4] due to weaker constraints from B physics.
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