Abstract
The NA62 experiment at CERN Super Proton Synchrotron (SPS) is currently taking data to measure the ultra-rare decay K + → π + ν ν ¯ . This decay, whose Branching Ratio (BR) is predicted with high precision within the Standard Model (SM), is one of the best candidates to reveal the indirect effects of New Physics (NP) at the highest mass scales. The NA62 experiment is designed to measure BR ( K + → π + ν ν ¯ ) with a decay-in-flight technique, novel for this channel. NA62 took data in 2016, 2017 and 2018; statistics collected in 2016 allows NA62 to reach the SM sensitivity for this decay, reaching the single event sensitivity (SES) and showing the proof of principle of the experiment. The preliminary result on BR ( K + → π + ν ν ¯ ) from the analysis of the 2016 data set is described.
Highlights
The K + → π + ννprocess is a flavor-changing neutral current (FCNC) decay proceeding through box and electroweak penguin diagrams
After unblinding the signal regions, one event is found in SR2, as shown in Figure 4; the corresponding pion has a momentum of 15.3 GeV/c, with the RICH clearly indicating that it is a pion (Figure 5)
The first search for the decay K + → π + ννwith an in-flight kaon-decay technique is reported by the NA62 collaboration
Summary
The K + → π + ννprocess is a flavor-changing neutral current (FCNC) decay proceeding through box and electroweak penguin diagrams. A quadratic GIM mechanism and the transition of the quark top into the quark down make this process extremely rare. The K + → π + ννdecay is extremely sensitive to New Physics (NP), probing the highest mass scales among the rare meson decays. The largest deviations from the SM are expected in models with new sources of flavor violation due to weaker constraints from B physics [5,6]. K + → π + ννdecay using a kaon-decay-at-rest technique. The result of their measure was [7,8]: BRmeas (K + → π + νν) = (17.3 ± 11.5) · 10−11. The NA62 experiment at CERN aims to precisely measure BR(K + → π + νν) with a novel decay-in-flight technique. The first result of NA62 from the analysis of data collected in 2016 is reported, corresponding to about 5% fraction of the statistics collected by NA62 during a full-year data-taking period
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