An investigation of the very rare $${K}^{+}\to {\pi}^{+}\nu \overline{\nu}$$ decay
A bstract The NA62 experiment reports an investigation of the $${K}^{+}\to {\pi}^{+}\nu \overline{\nu}$$ K + → π + ν ν ¯ 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 $${K}^{+}\to {\pi}^{+}\nu \overline{\nu}$$ K + → π + ν ν ¯ branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of ( $${0.48}_{-0.48}^{+0.72}$$ 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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Award ID(s):
Publication Date:
NSF-PAR ID:
10272505
Journal Name:
Journal of High Energy Physics
Volume:
2020
Issue:
11
ISSN:
1029-8479
1. A bstract 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 + → $${\pi}^{+}\nu \overline{\nu}$$ π + ν ν ¯ analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of X masses, 0–110 MeV /c 2 and 154–260 MeV /c 2 , 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,more »
3. A bstract Using a data sample of 980 fb − 1 collected with the Belle detector at the KEKB asymmetric-energy e + e − collider, we study the processes of $${\Xi}_c^0\to \Lambda {\overline{K}}^{\ast 0}$$ Ξ c 0 → Λ K ¯ ∗ 0 , $${\Xi}_c^0\to {\Sigma}^0{\overline{K}}^{\ast 0}$$ Ξ c 0 → Σ 0 K ¯ ∗ 0 , and $${\Xi}_c^0\to {\Sigma}^{+}{K}^{\ast -}$$ Ξ c 0 → Σ + K ∗ − for the first time. The relative branching ratios to the normalization mode of $${\Xi}_c^0\to {\Xi}^{-}{\pi}^{+}$$ Ξ c 0 → Ξ −more »
4. A bstract We present measurements of the branching fractions for the decays B → Kμ + μ − and B → Ke + e − , and their ratio ( R K ), using a data sample of 711 fb − 1 that contains 772 × 10 6 $$B\overline{B}$$ B B ¯ events. The data were collected at the ϒ(4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. The ratio R K is measured in five bins of dilepton invariant-mass-squared ( q 2 ): q 2 ∈ (0 . 1more »
5. A bstract We measure the branching fractions and CP asymmetries for the singly Cabibbo-suppressed decays D 0 → π + π − η , D 0 → K + K − η , and D 0 → ϕη , using 980 fb − 1 of data from the Belle experiment at the KEKB e + e − collider. We obtain $${\displaystyle \begin{array}{c}\mathcal{B}\left({D}^0\to {\pi}^{+}{\pi}^{-}\eta \right)=\left[1.22\pm 0.02\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right)\pm 0.03\left({\mathcal{B}}_{\mathrm{ref}}\right)\right]\times {10}^{-3},\\ {}\mathcal{B}\left({D}^0\to {K}^{+}{K}^{-}\eta \right)=\left[{1.80}_{-0.06}^{+0.07}\left(\mathrm{stat}\right)\pm 0.04\left(\mathrm{syst}\right)\pm 0.05\left({\mathcal{B}}_{\mathrm{ref}}\right)\right]\times {10}^{-4},\\ {}\mathcal{B}\left({D}^0\to \phi \eta \right)=\left[1.84\pm 0.09\left(\mathrm{stat}\right)\pm 0.06\left(\mathrm{syst}\right)\pm 0.05\left({\mathcal{B}}_{\mathrm{ref}}\right)\right]\times {10}^{-4},\end{array}}$$ B D 0 → π + π − η = 1.22 ± 0.02 stat ± 0.02more »