Abstract
The NA62 experiment reports an investigation of the \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) mode from a sample of K+ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0.389 ± 0.024) × 10−10, corresponding to 2.2 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. 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 1.78 × 10−10 for the \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of (\( {0.48}_{-0.48}^{+0.72} \)) × 10−10, 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.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
A.J. Buras, D. Buttazzo, J. Girrbach–Noe and R. Knegjens, \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) and \( {K}_L\to {\pi}^0\nu \overline{\nu} \) in the standard model: status and perspectives, JHEP 11 (2015) 033.
G. Buchalla and A.J. Buras, The rare decays \( K\to \pi \nu \overline{\nu},B\to X\nu \overline{\nu} \) and B → l+l−: an update, Nucl. Phys. B 548 (1999) 309 [hep-ph/9901288] [INSPIRE].
A.J. Buras, M. Gorbahn, U. Haisch and U. Nierste, Charm quark contribution to \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) at next-to-next-to-leading order, JHEP 11 (2006) 002 [Erratum ibid. 11 (2012) 167] [hep-ph/0603079] [INSPIRE].
J. Brod, M. Gorbahn and E. Stamou, Two-loop electroweak corrections for the \( K\to \pi \nu \overline{\nu} \) decays, Phys. Rev. D 83 (2011) 034030.
G. Isidori, F. Mescia and C. Smith, Light-quark loops in K → πνν, Nucl. Phys. B 718 (2005) 319 [hep-ph/0503107].
F. Mescia and C. Smith, Improved estimates of rare K decay matrix elements from Kℓ3 decays, Phys. Rev. D 76 (2007) 034017.
Particle Data Group collaboration, P.A. Zyla et al., Review of particle physics, Prog. Theor. Exp. Phys. 2020 (2020) 083C01.
M. Blanke, A.J. Buras and S. Recksiegel, Quark flavour observables in the Littlest Higgs model with T-parity after LHC Run 1, Eur. Phys. J. C 76 (2016) 182 [arXiv:1507.06316] [INSPIRE].
M. Blanke, A.J. Buras, B. Duling, K. Gemmler and S. Gori, Rare K and B decays in a warped extra dimension with custodial protection, JHEP 03 (2009) 108 [arXiv:0812.3803] [INSPIRE].
A.J. Buras, D. Buttazzo and R. Knegjens, \( K\to \pi \nu \overline{\nu} \) and ε′/ε in simplified new physics models, JHEP 11 (2015) 166 [arXiv:1507.08672] [INSPIRE].
J. Aebischer, A.J. Buras and J. Kumar, Another SMEFT story: Z′ facing new results on ε′/ε, ∆MK and \( K\to \pi \nu \overline{\nu} \), arXiv:2006.01138 [INSPIRE].
G. Isidori, F. Mescia, P. Paradisi, C. Smith and S. Trine, Exploring the flavour structure of the MSSM with rare K decays, JHEP 08 (2006) 064 [hep-ph/0604074] [INSPIRE].
M. Tanimoto and K. Yamamoto, Probing SUSY with 10 TeV stop mass in rare decays and CP violation of kaon, Prog. Theor. Exp. Phys. 2016 (2016) 123B02.
T. Blažek and P. Maták, Left-left squark mixing, \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) and minimal supersymmetry with large tan β, Int. J. Mod. Phys. A 29 (2014) 1450162 [arXiv:1410.0055] [INSPIRE].
M. Bordone, D. Buttazzo, G. Isidori and J. Monnard, Probing lepton flavour universality with \( K\to \pi \nu \overline{\nu} \) decays, Eur. Phys. J. C 77 (2017) 618 [arXiv:1705.10729] [INSPIRE].
C. Bobeth and A.J. Buras, Leptoquarks meet ε′/ε and rare Kaon processes, JHEP 02 (2018) 101 [arXiv:1712.01295] [INSPIRE].
S. Fajfer, N. Košnik and L. Vale Silva, Footprints of leptoquarks: from \( {R}_{K^{\left(\ast \right)}} \) to \( K\to \pi \nu \overline{\nu} \), Eur. Phys. J. C 78 (2018) 275 [arXiv:1802.00786] [INSPIRE].
E949 collaboration, New measurement of the \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) branching ratio, Phys. Rev. Lett. 101 (2008) 191802 [arXiv:0808.2459] [INSPIRE].
BNL-E949 collaboration, Study of the decay \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) in the momentum region 140 < Pπ < 199 MeV/c, Phys. Rev. D 79 (2009) 092004 [arXiv:0903.0030] [INSPIRE].
NA62 collaboration, First search for \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) using the decay-in-flight technique, Phys. Lett. B 791 (2019) 156 [arXiv:1811.08508] [INSPIRE].
E. Cortina Gil et al., The beam and detector of the NA62 experiment at CERN, 2017 JINST 12 P05025.
R. Ammendola et al., The integrated low-level trigger and readout system of the CERN NA62 experiment, Nucl. Instrum. Meth. A 929 (2019) 1 [arXiv:1903.10200] [INSPIRE].
J. Allison et al., Recent developments in Geant4, Nucl. Instrum. Meth. A 835 (2016) 186.
G. Anzivino et al., Precise mirror alignment and basic performance of the RICH detector of the NA62 experiment at CERN, 2018 JINST 13 P07012.
G. Aglieri Rinella et al., The NA62 GigaTracKer: a low mass high intensity beam 4D tracker with 65 ps time resolution on tracks, 2019 JINST 14 P07010.
C. Gatti, Monte Carlo simulation for radiative kaon decays, Eur. Phys. J. C 45 (2006) 417 [hep-ph/0507280] [INSPIRE].
K. Cranmer, Practical Statistics for the LHC, in 2011 European School of High-Energy Physics, pp. 267–308, 2014, DOI [arXiv:1503.07622] [INSPIRE].
R.D. Cousins et al., Evaluation of three methods for calculating statistical significance when incorporating a systematic uncertainty into a test of the background-only hypothesis for a Poisson process, Nucl. Instrum. Meth. A 595 (2008) 480.
A.L. Read, Presentation of search results: the CLs technique, J. Phys. G 28 (2002) 2693 [INSPIRE].
Y. Grossman and Y. Nir, \( K(L)\to {\pi}^0\nu \overline{\nu} \) beyond the standard model, Phys. Lett. B 398 (1997) 163 [hep-ph/9701313] [INSPIRE].
G.J. Feldman and R.D. Cousins, A Unified approach to the classical statistical analysis of small signals, Phys. Rev. D 57 (1998) 3873 [physics/9711021] [INSPIRE].
W.A. Rolke and A.M. López, Confidence intervals and upper bounds for small signals in the presence of background noise, Nucl. Instrum. Meth. A 458 (2001) 745 [hep-ph/0005187].
Author information
Authors and Affiliations
Consortia
Corresponding authors
Additional information
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
ArXiv ePrint: 2007.08218
Deceased (A. Zinchenko, A. Ostankov, V. Semenov, F. Hahn)
Rights and permissions
Open Access . This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.
About this article
Cite this article
The NA62 collaboration., Cortina Gil, E., Kleimenova, A. et al. An investigation of the very rare \( {K}^{+}\to {\pi}^{+}\nu \overline{\nu} \) decay. J. High Energ. Phys. 2020, 42 (2020). https://doi.org/10.1007/JHEP11(2020)042
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1007/JHEP11(2020)042