An investigation of the very rare K+→ π+νν¯ decay

, NA62 Collaboration (2020) An investigation of the very rare K+→ π+νν¯ decay. Journal of High Energy Physics, 2020 (11). ISSN 1029-8479

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The NA62 experiment reports an investigation of the K+→ π+νν¯ 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+→ π+νν¯ 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.

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Journal Article
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Journal of High Energy Physics
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Export Date: 18 November 2020 Correspondence Address: Marchevski, R.; Institut für Physik and PRISMA Cluster of excellence, Universität Mainz, University of LancasterGermany; email: References: Buras, A.J., Buttazzo, D., Girrbach, J., –Noeknegjens, R., K + → π + ν ν ¯ and K L → π 0 ν ν ¯ in the standard model: Status and perspectives JHEP, 11 (2015), p. 033; Buchalla, G., Buras, A.J., The rare decays K → πν ν ¯, B → Xν ν ¯ and B → l+ l− An Update, Nucl. Phys. B, 548 (1999), p. 309. , [hep-ph/9901288] [INSPIRE]; Buras, A.J., Gorbahn, M., Haisch, U., Nierste, U., Charm quark contribution to K+→ π+νν¯ at next-to-next-to-leading order (2006) JHEP, 11, p. 2. , [INSPIRE]; Brod, J., Gorbahn, M., Stamou, E., Two-loop electroweak corrections for the K → πν ν ¯ decays (2011) Phys. Rev. D, 83; Isidori, G., Mescia, F., Smith, C., Light-Quark Loops in K → πνν, Nucl. Phys. B, 718 (2005), p. 319. , [hep-ph/0503107]; Mescia, F., Smith, C., Improved estimates of rare K decay matrix elements from K ℓ3 decays Phys. Rev. D, 76 (2007); Zyla, P.A., Review of particle physics (2020) Prog. Theor. Exp. Phys, , (2020); Blanke, M., Buras, A.J., Recksiegel, S., Quark flavour observables in the Littlest Higgs model with T-parity after LHC Run 1 (2016) Eur. Phys. J. C, 76, p. 182. , [] [INSPIRE]; Blanke, M., Buras, A.J., Duling, B., Gemmler, K., Gori, S., Rare K and B decays in a warped extra dimension with custodial protection (2009) JHEP, (3), p. 108. , (,), [arXiv:, 0812.3803,] [, INSPIRE,]; Buras, A.J., Buttazzo, D., Knegjens, R., K → πν ν ¯ and ε′/ε in simplified new physics models (2015) JHEP, 11, p. 166. , [arXiv:1507.08672] [INSPIRE]; Aebischer, J., Buras, A.J., Kumar, J., Another SMEFT Story: Z′ Facing New Results on ε′/ε, ∆M K and K → πν ν ¯, , INSPIRE]; Isidori, G., Mescia, F., Paradisi, P., Smith, C., Trine, S., Exploring the flavour structure of the MSSM with rare K decays (2006) JHEP, 8, p. 64. , [INSPIRE]; Tanimoto, M., Yamamoto, K., Probing SUSY with 10 TeV stop mass in rare decays and CP violation of kaon (2016) Prog. Theor. Exp. Phys., 2016, p. 123B02; Blažek, T., Maták, P., Left-left squark mixing, K+→ π+νν¯ and minimal supersymmetry with large tan β (2014) Int. J. Mod. Phys. A, 29, p. 1450162. , [] [INSPIRE]; Bordone, M., Buttazzo, D., Isidori, G., Monnard, J., Probing lepton flavour universality with K→ πνν¯ decays (2017) Eur. Phys. J. C, 77, p. 618. , [] [INSPIRE]; Bobeth, C., Buras, A.J., Leptoquarks meet ε′/ε and rare Kaon processes (2018) JHEP, 2, p. 101. , [] [INSPIRE]; Fajfer, S., Košnik, N., Vale Silva, L., Footprints of leptoquarks: from RK(∗) to K→ πνν¯ (2018) Eur. Phys. J. C, 78, p. 275. , [] [INSPIRE]; New measurement of the K + → π + ν ν ¯ branching ratio Phys. Rev. Lett., 101 (2008). , 0808.2459, INSPIRE; Study of the decay K + → π + ν ν ¯ in the momentum region 140 < P π < 199 MeV/c (2009) Phys. Rev. D, 79. , 0903.0030, INSPIRE; First search for K + → π + ν ν ¯ using the decay-in-flight technique (2019) Phys. Lett. B, 791, p. 156. , 1811.08508, INSPIRE; Cortina Gil, E., The beam and detector of the NA62 experiment at CERN (2017) JINST, 12; Ammendola, R., The integrated low-level trigger and readout system of the CERN NA62 experiment (2019) Nucl. Instrum. Meth. A, 929, p. 1. , (,), [arXiv:, 1903.10200,] [, INSPIRE,]; Allison, J., Recent developments in Geant4 (2016) Nucl. Instrum. Meth. A, 835, p. 186; Anzivino, G., Precise mirror alignment and basic performance of the RICH detector of the NA62 experiment at CERN (2018) JINST, 13; Aglieri Rinella, G., The NA62 GigaTracKer: A low mass high intensity beam 4D tracker with 65 ps time resolution on tracks (2019) JINST, 14; Gatti, C., Monte Carlo simulation for radiative kaon decays (2006) Eur. Phys. J. C, 45, p. 417. , [INSPIRE]; Cranmer, K., Practical Statistics for the LHC (2014) 2011 European School of High-Energy Physics, pp. 267-308; Cousins, R.D., 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 (2008) Nucl. Instrum. Meth. A, 595, p. 480; Read, A.L., Presentation of search results: the CLs technique (2002) J. Phys. G, 28, p. 2693. , [INSPIRE]; Grossman, Y., Nir, Y., K (L) → π 0 ν ν ¯ beyond the standard model (1997) Phys. Lett. B, 398, p. 163; Feldman, G.J., Cousins, R.D., A Unified approach to the classical statistical analysis of small signals (1998) Phys. Rev. D, 57, p. 3873. , physics/9711021] [INSPIRE; Rolke, W.A., López, A.M., Confidence intervals and upper bounds for small signals in the presence of background noise (2001) Nucl. Instrum. Meth., 458, p. 745
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19 Nov 2020 12:15
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24 Nov 2020 08:59