Abstract
A search for the K+ → π+X decay, where X is a long-lived feebly interacting particle, is performed through an interpretation of the K+ → {pi}^{+}nu overline{nu} analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of X masses, 0–110 MeV/c2 and 154–260 MeV/c2, and lifetimes above 100 ps are considered. The limits set on the branching ratio, BR(K+ → π+X), are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.
Highlights
Signal selectionAdditional momentum-dependent constraints supplement the definition of the signal regions using alternative squared missing mass variables, constructed either by replacing the GTK measurement of the beam 3-momentum with the average beam momentum and direction, or the STRAW 3-momentum measurement with one measured by the ring imaging Cherenkov counter (RICH) under the π+ mass hypothesis
The K+ → π+X decay is presented here
The experiment is designed to study K+ decays occurring in the 60 m fiducial volume (FV) starting 2.6 m downstream of GTK3 and housed inside a 117 m long vacuum tank, containing a magnetic spectrometer, and ending at the ring imaging Cherenkov counter (RICH)
Summary
Additional momentum-dependent constraints supplement the definition of the signal regions using alternative squared missing mass variables, constructed either by replacing the GTK measurement of the beam 3-momentum with the average beam momentum and direction, or the STRAW 3-momentum measurement with one measured by the RICH under the π+ mass hypothesis. Events with incorrect reconstruction of m2miss due to momenta mismeasurements and improve background rejection, but decrease acceptance at the boundaries of the signal regions
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