An investigation of the very rare <mml:msup>K+</mml:msup>→<mml:msup>π+</mml:msup>νν<mml:mo stretchy="true"><overbar></mml:mover> decay



Gil, E Cortina, Kleimenova, A, Minucci, E, Padolski, S, Petrov, P, Shaikhiev, A, Volpe, R, Numao, T, Velghe, B, Bryman, D
et al (show 190 more authors) (2020) An investigation of the very rare <mml:msup>K+</mml:msup>→<mml:msup>π+</mml:msup>νν<mml:mo stretchy="true"><overbar></mml:mover> decay. JOURNAL OF HIGH ENERGY PHYSICS, 2020 (11). 42-.

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Abstract

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>The NA62 experiment reports an investigation of the <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math></jats:alternatives></jats:inline-formula> mode from a sample of <jats:italic>K</jats:italic><jats:sup>+</jats:sup> decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0<jats:italic>.</jats:italic>389 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>024) <jats:italic>×</jats:italic> 10<jats:sup><jats:italic>−</jats:italic>10</jats:sup>, corresponding to 2.2 events assuming the Standard Model branching ratio of (8<jats:italic>.</jats:italic>4 <jats:italic>±</jats:italic> 1<jats:italic>.</jats:italic>0) <jats:italic>×</jats:italic> 10<jats:sup><jats:italic>−</jats:italic>11</jats:sup>. Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1<jats:italic>.</jats:italic>78 <jats:italic>×</jats:italic> 10<jats:sup><jats:italic>−</jats:italic>10</jats:sup> for the <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math></jats:alternatives></jats:inline-formula> branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of (<jats:inline-formula><jats:alternatives><jats:tex-math>$$ {0.48}_{-0.48}^{+0.72} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mn>0.48</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.48</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.72</mml:mn> </mml:mrow> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula>) <jats:italic>×</jats:italic> 10<jats:sup><jats:italic>−</jats:italic>10</jats:sup>, are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.</jats:p>

Item Type: Article
Uncontrolled Keywords: Fixed target experiments, Flavor physics, Flavour Changing Neutral Currents, Rare decay
Depositing User: Symplectic Admin
Date Deposited: 18 Nov 2020 11:50
Last Modified: 14 Mar 2024 23:05
DOI: 10.1007/JHEP11(2020)042
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3107381