Kaon physics at the CERN-SPS

The NA48/2 and NA62 collaborations report on recent results, current status, and prospects of kaon physics at the CERN-SPS. The NA62 collaborations aims to measure the decay K±→ π±νν̄ with an uncertainty of 10% or better. The NA62 detector and preliminary results from a pilot run in 2014 are presented. In addition, recent results of the NA48/2 collaboration are reported. A search for Dark Photons has been performed in π0 decays via the kaon decays K±→ π±π0 and K±π0μ±ν. No dark photon signal was observed and new upper limits on the mixing parameter ϵ2 and the dark photon mass were computed. We also report the first observation of the kaon decay K±→ π±π0e+e−

Measurement of the Branching Fractions of Semileptonic Kaon Decays and Extraction of the CKM Parameter ∣Vus∣\lvert V_{us} \rvert

Semileptonic kaon decays $(K_{l3} = K^+ → π^0 l^+ \nu$ with $l = e, \mu)$ provide a clean way to extract the parameter $\lvert V_{us} \rvert$ of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. It is one of the fundamental parameters of the Standard Model and is only accessible via experimental measurement. The NA62 collaboration collected $K^+$ decay data in 2007 which are analyzed in the presented work. In total $28 \cdot 10^6 K_{\mu 3}$ , $37 \cdot 10^6 K_{e3}$ , and $2\cdot 10^6 K_{2 \pi}$ candidates were extracted from the data set and used to compute the ratios of branching fractions $\frac{Br(K_{\mu 3})}{Br(K_{2 \pi})} = 0.16066(12) \text{stat.} (66) \text{syst.} = 0.1607(7)$, $\frac{Br(K_{e3})}{Br(K_{2 \pi})} = 0.24320(17) \text{stat.} (41) \text{syst.} = 0.2432(4)$, and $\frac{Br(K_{\mu 3})}{Br(K_{e3})} = 0.66061(17) \text{stat.} (245) \text{syst.} = 0.6606(25)$ which represent the most precise measurements available. The semileptonic branching fractions $Br(K_{\mu 3}) = 3.321(19) \%$ and $Br(K_{e3}) = 5.027(22) \%$ follow from the world average of $Br(K_{2 \pi})$ measurements. They are used to extract the CKM parameter $\lvert V_{us} \rvert = 0.2219(10)$. The new $\lvert V_{us} \rvert$ result leads to the unitarity relation $\lvert V_{ud} \rvert ^2 + \lvert V_{us} \rvert ^2 + \lvert V_{ub} \rvert ^2 = 0.9983(6)$ which disagrees by 2.8 standard deviations with the CKM unitarity prediction. The $e − \mu$ lepton universality is tested with the ratio of the semileptonic branching fractions $\frac{Br(K_{\mu 3})}{Br(K_{e3})}$ and agrees with the Standard Model prediction

Measurement of the branching fractions of semileptonic kaon decays and extraction of the CKM parameter |Vus|

Semileptonic kaon decays (Kl3 = K^+ → π^0 l^+ ν with l = e, μ) provide a clean way to extract the parameter |Vus| of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. It is one of the fundamental parameters of the Standard Model and is only accessible via experimental measurement. The NA62 collaboration collected K^+ decay data in 2007 which are analyzed in the presented work. In total 28·10^6 Kμ337·10^6 Ke3and 2·10^6 K2π candidates were extracted from the data set and used to compute the ratios of branching fractions Br(Kμ3)/Br(K2π) = 0.16066(12)stat. (66)syst. = 0.1607(7), Br(Ke3)/Br(K2π) = 0.24320(17)stat. (41)syst. = 0.2432(4), and Br(Kμ3)/Br(Ke3) = 0.66061(17)stat. (245)syst. = 0.6606(25) which represent the most precise measurements available. The semileptonic branching fractions Br(Kμ3) = 3.321(19)% and Br(Ke3) = 5.027(22)% follow from the world average of Br(K2π) measurements. They are used to extract the CKM parameter |Vus| = 0.2219(10) . The new |Vus| result leads to the unitarity relation |Vud|^2 +|Vus|^2 +|Vub|^2 = 0.9983(6) which disagrees by 2.8 standard deviations with the CKM unitarity prediction. The e − μ lepton universality is tested with the ratio of the semileptonic branching fractions and agrees with the Standard Model prediction.Semileptonische Kaonzerfälle (Kl3 = K^+ → π^0 l^+ ν with l = e, μ) ermöglichen eine besonders sauberere Extraktion des Parameters |Vus| der Cabibbo-Kobayashi-Maskawa (CKM) Quark-Mischungsmatrix. Dieser ist ein fundamentaler Parameter des Standardmodells und ist nur durch experimentelle Messungen bestimmbar. Die NA62-Kollaboration hat im Jahr 2007 K^+-Zerfallsdaten aufgenommen, die in der präsentierten Arbeit untersucht wurden. Insgesamt wurden 28·10^6 Kμ3 -, 37·10^6 Ke3 - und 2·10^6 K2π -Kandidaten selektiert. Diese werden genutzt, um die Verhältnisse Br(Kμ3)/Br(K2π) = 0.16066(12)stat. (66)syst. = 0.1607(7), Br(Ke3)/Br(K2π) = 0.24320(17)stat. (41)syst. = 0.2432(4), and Br(Kμ3)/Br(Ke3) = 0.66061(17)stat. (245)syst. = 0.6606(25) zu bestimmen. Diese repräsentieren die derzeit genauesten verfügbaren Messungen. Die semileptonischen Verzweigungsverhältnisse Br(Kμ3) = 3.321(19)% und Br(Ke3) = 5.027(22)% werden unter Nutzung des globalen Mittelwerts von Br(K2π) bestimmt. Diese dienen als Grundlage für die Bestimmung des CKM-Parameters |Vus| = 0.2219(10). Der neue |Vus|-Wert führt zur Unitaritätsbeziehung |Vud|^2 +|Vus|^2 +|Vub|^2 = 0.9983(6)die um 2.8 Standardabweichungen verschieden ist von der Standardmodell-Vorhersage für die CKM-Unitarität. Die e − μ Leptonuniversalität wird mit dem Verhältnis Br(Kμ3) überprüft und das Ergebnis stimmt mit der Standardmodell-Vorhersage überein

Viral manipulation of functionally distinct interneurons in mice, non-human primates and humans

© 2020, The Author(s), under exclusive licence to Springer Nature America, Inc. Recent success in identifying gene-regulatory elements in the context of recombinant adeno-associated virus vectors has enabled cell-type-restricted gene expression. However, within the cerebral cortex these tools are largely limited to broad classes of neurons. To overcome this limitation, we developed a strategy that led to the identification of multiple new enhancers to target functionally distinct neuronal subtypes. By investigating the regulatory landscape of the disease gene Scn1a, we discovered enhancers selective for parvalbumin (PV) and vasoactive intestinal peptide-expressing interneurons. Demonstrating the functional utility of these elements, we show that the PV-specific enhancer allowed for the selective targeting and manipulation of these neurons across vertebrate species, including humans. Finally, we demonstrate that our selection method is generalizable and characterizes additional PV-specific enhancers with exquisite specificity within distinct brain regions. Altogether, these viral tools can be used for cell-type-specific circuit manipulation and hold considerable promise for use in therapeutic interventions

Search for heavy neutral lepton production in K+K^+ decays

A search for heavy neutral lepton production in $K^+$ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the $10^{-7}$ to $10^{-6}$ level are established on the elements of the extended neutrino mixing matrix $|U_{\ell 4}|^2$ ($\ell=e,\mu$) for heavy neutral lepton mass in the range $170-448~{\rm MeV}/c^2$. This improves on the results from previous production searches in $K^+$ decays, setting more stringent limits and extending the mass range.A search for heavy neutral lepton production in K+ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the 10−7 to 10−6 level are established on the elements of the extended neutrino mixing matrix |Ue4|2 and |Uμ4|2 for heavy neutral lepton mass in the ranges 170–448 MeV/ c2 and 250–373 MeV/ c2 , respectively. This improves on the previous limits from HNL production searches over the whole mass range considered for |Ue4|2 , and above 300 MeV/ c2 for |Uμ4|2

First search for K+→π+ννˉK^+\rightarrow\pi^+\nu\bar{\nu} using the decay-in-flight technique

International audienceThe NA62 experiment at the CERN SPS reports the first search for K+→π+νν¯ using the decay-in-flight technique, based on a sample of 1.21×1011 K+ decays collected in 2016. The single event sensitivity is 3.15×10−10 , corresponding to 0.267 Standard Model events. One signal candidate is observed while the expected background is 0.152 events. This leads to an upper limit of 14×10−10 on the K+→π+νν¯ branching ratio at 95% CL

A search for the K+→μ−νe+e+K^+\to\mu^-\nu e^+e^+ decay

A search for the $K^+\to\mu^-\nu e^+e^+$ decay, forbidden within the Standard Model by either lepton number or lepton flavour conservation depending on the flavour of the emitted neutrino, has been performed using the dataset collected by the NA62 experiment at CERN in 2016--2018. An upper limit of $8.1\times 10^{-11}$ is obtained for the decay branching fraction at 90% CL, improving by a factor of 250 over the previous search

Search for K+K^+ decays to a muon and invisible particles

The NA62 experiment at CERN reports searches for $K^+\to\mu^+N$ and $K^+\to\mu^+\nu X$ decays, where $N$ and $X$ are massive invisible particles, using the 2016-2018 data set. The $N$ particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of ${\cal O}(10^{-8})$ of the neutrino mixing parameter $|U_{\mu4}|^2$ for $N$ masses in the range 200-384 MeV/$c^2$ and lifetime exceeding 50 ns. The $X$ particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for $X$ masses in the range 10-370 MeV/$c^2$ are reported for the first time, ranging from ${\cal O}(10^{-5})$ to ${\cal O}(10^{-7})$. An improved upper limit of $1.0\times 10^{-6}$ is established at 90% CL on the $K^+\to\mu^+\nu\nu\bar\nu$ branching fraction.The NA62 experiment at CERN reports searches for K+→μ+N and K+→μ+νX decays, where N and X are massive invisible particles, using the 2016–2018 data set. The N particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of O(10−8) of the neutrino mixing parameter |Uμ4|2 for N masses in the range 200–384 MeV/ c2 and lifetime exceeding 50 ns. The X particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for X masses in the range 10–370 MeV/ c2 are reported for the first time, ranging from O(10−5) to O(10−7) . An improved upper limit of 1.0×10−6 is established at 90% CL on the K+→μ+ννν¯ branching fraction.The NA62 experiment at CERN reports searches for $K^+\to\mu^+N$ and $K^+\to\mu^+\nu X$ decays, where $N$ and $X$ are massive invisible particles, using the 2016-2018 data set. The $N$ particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of ${\cal O}(10^{-8})$ of the neutrino mixing parameter $|U_{\mu4}|^2$ for $N$ masses in the range 200-384 MeV/$c^2$ and lifetime exceeding 50 ns. The $X$ particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for $X$ masses in the range 10-370 MeV/$c^2$ are reported for the first time, ranging from ${\cal O}(10^{-5})$ to ${\cal O}(10^{-7})$. An improved upper limit of $1.0\times 10^{-6}$ is established at 90% CL on the $K^+\to\mu^+\nu\nu\bar\nu$ branching fraction

Searches for lepton number violating K+→π−(π0)e+e+K^+\to\pi^-(\pi^0)e^+e^+ decays

Searches for lepton number violating $K^+\to\pi^-e^+e^+$ and $K^+\to\pi^-\pi^0e^+e^+$ decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of $5.3\times 10^{-11}$ and $8.5\times 10^{-10}$ are obtained on the decay branching fractions at 90% confidence level. The former result improves the limit by a factor of four over the previous best limit, while the latter result represents the first limit on the $K^+\to\pi^-\pi^0e^+e^+$ decay rate.Searches for lepton number violating K+→π−e+e+ and K+→π−π0e+e+ decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016–2018. Upper limits of 5.3×10−11 and 8.5×10−10 are obtained on the decay branching fractions at 90% confidence level. The former result improves by a factor of four over the previous best limit, while the latter result represents the first limit on the K+→π−π0e+e+ decay rate.Searches for lepton number violating $K^+\to\pi^-e^+e^+$ and $K^+\to\pi^-\pi^0e^+e^+$ decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of $5.3\times 10^{-11}$ and $8.5\times 10^{-10}$ are obtained on the decay branching fractions at 90% confidence level. The former result improves by a factor of four over the previous best limit, while the latter result represents the first limit on the $K^+\to\pi^-\pi^0e^+e^+$ decay rate

Measurement of the very rare K+→π+ννˉK^+\rightarrow\pi^+\nu\bar{\nu} decay

The NA62 experiment reports the branching ratio measurement BR$(K^+ \rightarrow \pi^+ \nu\bar{\nu}) = (10.6^{+4.0}_{-3.4} |_{\rm stat} \pm 0.9_{\rm syst}) \times 10 ^{-11}$ at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare $K^+ \rightarrow \pi^+ \nu\bar{\nu}$ decay, observed with a significance of 3.4$\sigma$. The experiment achieves a single event sensitivity of $(0.839\pm 0.054)\times 10^{-11}$, corresponding to 10.0 events assuming the Standard Model branching ratio of $(8.4\pm1.0)\times10^{-11}$. This measurement is also used to set limits on BR($K^+ \to \pi^+ X$), where $X$ is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample