Searches for lepton flavour and lepton number violation in kaon decays by the NA48/2 and NA62 experiments at CERN are presented. A precision measurement of the helicity-suppressed ratio RK of the K --> e nu and K --> mu nu decay rates has been performed using the full data set collected by the NA62 collaboration in 2007. The data sample amounted to 145,958 reconstructed K --> e nu candidates with 11.0% background contamination. The result is RK = (2.488 +- 0.010) X 10^{-5}, which is in agreement with the Standard Model expectation. An improved upper limit on the lepton number violating K+- --> pi-+ mu+- mu+- decay rate is also presented.
The Kaon physics program at CERN will be shortly presented, addressing the most recent results from the NA48/2 and NA62 experiments at the CERN SPS and future prospects.
Some Kaons and Hyperons rare decays branching ratios and form factors were measured by the NA48 experiment at CERN. The details of the measurements and their importance for the understanding of the CKM quark mixing matrix are discussed.
The NA48/2 experiment at the CERN SPS carried out data taking in 2003 and 2004. Analysis of the selected data samples of 7,146 $K^\pm\toπ^\pm e^+e^-$ decay candidates with 0.6% background, 1,164 $K^\pm\toπ^\pmγγ$ candidates with 3.3% background, and 120 $K^\pm\toπ^\pmγe^+e^-$ candidates with 6.1% background allowed precise measurements of branching fractions and other characteristics of these rare kaon decays.
The NA62 experiment at the CERN SPS aims to measure the branching ratio of the rare decay $K^+\toπ^+ν\barν$ with a relative precision of $\sim10%$. To achieve that goal, it is designed to be exposed to $1.2\times 10^{13}$ $K^+$ decays in its fiducial volume. The unprecedented $K^+$ flux will lead to record sensitivities to rare and forbidden decays of $K^+$ and $π^0$, including those that violate lepton flavour or lepton number conservation. The expected NA62 performances for lepton flavour conservation and lepton universality tests are discussed. Relevant on-going or recently completed measur…
Searches for violation of lepton flavour universality and lepton number conservation in kaon decays by the NA62 and NA48/2 experiments at CERN, status and future plans of the CERN kaon programme are presented. A precision measurement of the helicity-suppressed ratio $R_K$ of the $K^\pm\to e^\pmν$ and $K^\pm\toμ^\pmν$ decay rates has been performed using the full data set collected by the NA62 experiment in 2007--2008. The result is $R_K=(2.488\pm0.010)\times10^{-5}$, in agreement with the Standard Model expectation. An improved upper limit on the rate of the lepton number violating $K^\pm\toπ^…
The NA48/2 and NA62-$R_K$ experiments at CERN collected large samples of charged kaon decays in 2003--2004 and 2007, respectively. These samples, collected with different trigger conditions, allow to search for both short and long-living heavy neutrinos produced in $K^{\pm}\toμ^{\pm}N_4$ decays. The results of these complementary searches are presented in this letter. In the absence of observed signal, the limits obtained on $\mathcal{B}(K^{\pm}\toπ^{\mp}μ^{\pm}μ^{\pm})$, $\mathcal{B}(K^{\pm}\to μ^{\pm} N_4)\mathcal{B}(N_4\to πμ)$, $\mathcal{B}(K^{+}\toμ^{+}N_4)$ and on the mixing matrix eleme…
Recent results from the NA48/2 and NA62 kaon decay-in-flight experiments at CERN are presented. A precision measurement of the helicity-suppressed ratio RK of the K+- to e+- nu and K+- to mu+- nu decay rates has been performed using the full dedicated data set collected by the NA62 experiment (RK phase); the result is in agreement with the Standard Model expectation. New measurements of the K+- to pi+- gamma gamma decay at the NA48/2 and NA62 experiments provide further tests of the Chiral Perturbation Theory. A planned measurement of the branching ratio of the ultra-rare K+ to pi+ nu anti-nu …
The ratio $R_K = Γ(K^{\pm}\to e^{\pm}ν(γ)) / Γ(K^{\pm}\toμ^{\pm}ν(γ))$ provides a powerful probe of the structure of weak interactions. It is calculated with very high precision within the Standard Model, but corrections due to the presence of New Physics could be in a few percent range. Development of NA48/NA62 method based on test data samples of 2003-04, and the status of analysis based on a dedicated 2007 run are discussed. In addition, a proposal to measure the ultra rare decay $K^+\toπ^+ν\barν$ at the CERN SPS is presented.
The NA62 experiment at CERN SPS aims to measure the branching ratio of the ultra-rare kaon decay $K^+\toπ^+ν\barν$ with 10\% precision, collecting $\sim 100$ events, assuming the Standard Model~(SM) branching ratio of $8.4 \times 10^{-11}$, starting in 2016. The NA62 experiment uses a kaon decay-in-flight technique and is exposed to a 750~MHz high-energy unseparated charged hadron beam, in which kaons are a minor component (6\%). Kaon identification is therefore mandatory to reduce the interference of the dominant non-kaon component with the experimental measurements. The NA62 kaon identificat…
Searches for heavy neutrinos can be successfully performed by fixed target experiments at the CERN SPS. New results obtained by the NA62 and NA48/2 kaon experiments are summarized in this paper. The physics potential of future projects exploiting SPS protons with beam dump facilities to enlarge the sensitivity to heavy neutrinos above the kaon mass limit are also outlined.
NA62 is a fixed target kaon experiment at the CERN SPS which aims at measuring the branching ratio of the $K^+\toπ^+ν\barν$ decay with 10% precision. This ultra-rare kaon decay is theoretically extremely clean and an ideal place to look for physics beyond the Standard Model. The NA62 experiment has been running in 2016-2018 and has accumulated a large amount of kaon decays. The final result of the $K^+\toπ^+ν\barν$ analysis using the 2016 dataset is discussed as well as prospects for the analysis of the 2017 dataset. NA62 also has sensitivity to various other rare and forbidden kaon decays, as…
The availability of high intensity kaon beams at the CERN SPS North Area gives rise to unique possibilities for sensitive tests of the Standard Model in the quark flavor sector. Precise measurements of the branching ratios for the flavor-changing neutral current decays $K\toπν\barν$ can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. Building on the success of the NA62 experiment, plans are taking shape at CERN for a comprehensive program that will include experimental phases to measure the branching ratio for $K^+\toπ^+ν\barν$ to ~5% and to $K_L\toπ^0ν\…
Precision measurements of the branching ratios (BRs) for rare kaon decays can provide unique constraints on CKM unitarity and may reveal the existence of new physics. The BRs for two of these decays, $K^+\toπ^+ν\barν$ and $K_L\toπ^0ν\barν$, are strongly suppressed in the Standard Model, while their rates can be calculated with very small theoretical uncertainties.These decays are potentially sensitive to high mass scales, and several models of new physics predict large deviations from the Standard Model. Much progress has been made recently in the measurement of the $K\toπν\barν$ BRs. Followin…
The electric alpha and magnetic beta pion Compton polarizabilities characterize the pion's deformation in the electromagnetic field of the gamma during gamma-pi Compton scattering. The pion polarizabilities are key observables, and provide stringent tests of our understanding of chiral symmetry, its spontaneous breakdown, the role of explicit symmetry breaking in QCD. The chi_PT effective Lagrangian, using data from radiative pion beta decay, predicts the pion electric and magnetic polarizabilities alpha = -beta = 2.7 +- 0.4, in standard polarizability units. The polarizabilities deduced by An…
The NA48/2 and NA62-$R_K$ experiments at the CERN SPS collected large samples of charged kaon decays in flight in 2003--07. The data analysis is still on-going (with over 20 publications produced so far); the recent results from these experiments are presented. A new upper limit on the rate of a lepton number violating decay $K^\pm\toπ^\mpμ^\pmμ^\pm$ is reported: $\mathcal{B} < 8.6\times 10^{-11}$ at 90\% CL. Searches for heavy sterile neutrino $N_4$ and neutral scalar resonances ($χ$) in $K^\pm\toπμμ$ decays are reported. Upper limits on the products $\mathcal{B}(K^\pm\toμ^\pm N_4)\mathcal{B}…
COMPASS at CERN is preparing for a new series of measurements on the nucleon structure comprising deep virtual Compton scattering and hard exclusive meson production using muon beams, as well as Drell-Yan reactions using a polarised proton target and a negative pion beam. The former will mainly constrain the generalised parton distribution H and determine the transverse size of the nucleon, while the latter measurements will provide information on transverse-momentum dependent parton distribution functions. The projected results of the programme and the necessary hardware upgrades are discusse…
Recent precise measurements of CP violation parameters in kaon decays at the NA48 experiment: indirect CPV parameter $|η_{+-}|$, and charge asymmetries in $K^\pm\to3π$ decays, are presented.
This paper reviews the current status of experimental measurements of radiative kaon decays. Several experiments at BNL, CERN and FNAL have recently or will soon complete data collection; as a result, several new results are available.
Recent results and future prospects of rare kaon-decay experiments at KEK, BNL, CERN and FNAL are reviewed. Topics include lepton flavor violation, T-violating transverse muon polarization in K+{mu3}, exotic decays, K0 -> pi0 ell+ ell-, and K -> pi nu nubar.
Kaon experiments are now focusing on searching for new physics beyond the standard model. For example, CERN NA62, J-PARC KOTO and J-PARC TREK-E36 experiments are starting up to study K->pi nu nu-bar decay modes, a lepton flavor violation, and lepton universality.
The rare decay $K^\pm\toπ^\pmγγ$ has been recently measured from data samples collected by the NA48/2 and NA62 experiments at CERN. These measurements are presented, including model-independent spectrum measurements and fits to the Chiral Perturbation Theory description.
The NA62 experiment at CERN aims to make a precision measurement of the ultra-rare decay $K^{+} \rightarrow π^{+}ν\overlineν$, and relies on a differential Cherenkov detector (KTAG) to identify charged kaons at an average rate of 50 MHz in a 750 MHz unseparated hadron beam. The experimental sensitivity of NA62 to K-decay branching ratios (BR) of $10^{-11}$ requires a time resolution for the KTAG of better than 100 ps, an efficiency better than 95% and a contamination of the kaon sample that is smaller than $10^{-4}$. A prototype version of the detector was tested in 2012, during the first NA62…
Direct CP violation is studied in two pion decays of the neutral kaon. Using data collected in the first beam period in 1997, the result for the parameter Re(epsilon'/epsilon) is (18.5+/-4.5(stat)+/-5.8(syst))x10^(-4).
The NA62 experiment at CERN collected a large sample of charged kaon decays with a highly efficient trigger for decays into electrons in 2007. The kaon beam represents a source of tagged neutral pion decays in vacuum. A measurement of the electromagnetic transition form factor slope of the neutral pion in the time-like region from $1.05\times10^6$ fully reconstructed $π^0$ Dalitz decay is presented. The limits on dark photon production in $π^0$ decays from the earlier kaon experiment at CERN, NA48/2, are also reported.
Recent NA48 results from detailed studies of $K_{L,S}\to π^+ π^- e^+ e^-$ and $K_S\toπ^0 γγ$ decay modes are presented. The results are based on the data collected with the NA48 detector at the CERN SPS during the 1998-199 9 and 2000 data taking periods, respectively. Prospects for future results on charged kaon decays are briefly described.
Searches for lepton flavour and lepton number violation in kaon decays by the NA48/2 and NA62 experiments at CERN are presented. A new measurement of the helicity suppressed ratio of charged kaon leptonic decay rates $RK=BR(Ke2)/BR(Kmu2) to sub-percent relative precision is discussed. An improved upper limit on the lepton number violating K+- --> pi-+mu+-mu+- decay rate is also presented.
Searches for lepton flavour violation and lepton number violation in kaon decays by the NA62 and NA48/2 experiments at CERN are presented. A new measurement of the ratio of charged kaon leptonic decay rates $R_K=Γ(K_{e2})/Γ(K_{\mu2})$ to sub-percent relative precision is discussed. An improved upper limit on the lepton number violating $K^\pm\rightarrowπ^\mpμ^\pmμ^\pm$ decay rate is also reported. The future 10% precision measurement of the branching ratio of the ultra-rare kaon decay $K^+\rightarrowπ^+ν\barν$ with the NA62 experiment is finally reviewed.
New data from the NA49 experiment at the CERN SPS concerning hadron+proton and hadron+nucleus interactions are discussed and compared to nucleus+nucleus collisions. Detailed information on baryonic momentum distributions and nuclear enhancement factors for kaons and cascade baryons are extracted.
The NA48 experiment at CERN has performed a new measurement of direct CP violation, based on data taken in 1997 by simultaneously collecting K_L and K_S decays into pi0pi0 and pi+pi-. The result for the CP violating parameter Re(epsilon'/epsilon) is (18.5 +/- 4.5(stat)} +/- 5.8 (syst))x10^{-4}.
A precision measurement of the ratio RK of the rates of kaon leptonic decays K+- --> e nu and K+- --> mu nu with the full data sample collected by the NA62 experiment at CERN in 2007-2008 is reported. The result, obtained by analysing ~150000 reconstructed K+- --> e nu candidates with 11% background contamination, is RK = (2.488+-0.010)*10^{-5}, in agreement with the Standard Model expectation.
In the recent year many new results from kaon decays have been reported from both the NA48 experiment at CERN and the KTeV experiment at Fermilab. Both experiments have new and improved measurements of the parameter Re(epsilon'/epsilon) of direct CP violation in the neutral kaon system. Also several new results on rare and very rare K_L decays were reported. In addition, the NA48 collaboration has performed special high-intensity K_S run periods, with the first results now being available.
The final result is presented of the NA48 Experiment performed at CERN SPS neutral kaon beams on the direct CP violation parameter Re(epsilon'/epsilon), as maesured from the decay rates of neutral kaons into two pions. The data collected in years 1997-2001 yield the evidence for direct CP violation with Re(epsilon'/epsilon)=(14.7+-2.2)10^-4. Description of expermental method and systematics, comparison with world data and some discussion of implications for theory are given.
The NA62 experiment at CERN aims to use rare kaon decays to search for new phenomena beyond the Standard Model. During the current short term phase (data taking completed in years 2007-8), the ratio $R_K = Γ(K^+ \rightarrow e ν_e (γ)) / Γ(K^+ \rightarrow μν_μ (γ))$ of leptonic decay rates is studied, which tests the structure of weak interactions and lepton flavour universality. In this paper, the $R_K$ analysis is summarized, and the preliminary result is discussed, based on 59963 $K^+ \rightarrow e ν_e $ candidates collected in 2007.
Universität Bonn（波恩大学）；Helmholtz-Institut für Strahlen- und Kernphysik（亥姆霍兹射线与核物理研究所）；University of Torino（都灵大学）；Torino Section of INFN（意大利国家核物理研究院都灵分部）；CERN（欧洲核子研究中心）
The decay $K^+ \to π^+ν\barν$ is highly suppressed in the Standard Model (SM), while its rate can be predicted with minimal theoretical uncertainty. The branching ratio (BR) for this decay is thus a sensitive probe of the flavor sector of the SM; its measurement, however, is a significant experimental challenge. The primary goal of the NA62 experiment is to measure ${\rm BR}(K^+ \to π^+ν\barν)$ with $\sim$10% precision. This will require the observation of $10^{13}$ $K^+$ decays in the experiment's fiducial volume, as well as the use of high-performance systems for precision tracking, particle…
Recent results from the NA48/1 and NA48/2 experiments at the CERN SPS are presented. NA48/2 carried out data taking in 2003 and 2004 collecting charged kaon decays: branching ratios and form factors have been measured for the rare K+- to pi+-e+e-, K+- to pi+-gammagamma and K+- to pi+-e+e-gamma decays. The NA48/1 experiment has taken data in 2002 using only the Ks beam at an increased intensity measuring neutral hyperon radiative decays. Using this data, which exceeds present statistics by about one order of magnitude, a new precise measurement of the Csi_0 decay asymmetries has been obtained.
New results from NA49 on the production of strangeness in elementary and nuclear reactions are presented. New measurements of charged kaon and pion production have been obtained from 40 AGeV Pb+Pb collisions. The evolution of strange meson yields in nucleus-nucleus interactions is studied as a function of collision energy and system size. Cascade baryon yields are presented for a wide range of hadronic interactions including first measurements in p+p and centrality controlled p+Pb collisions.
In the last few years it has become possible to study low energy pi pi scattering in kaon decays to three pions, thanks to the high statistics measurement of K+- -> pi+- pi0 pi0 decays performed by the NA48/2 experiment at the CERN SPS. At the pi+ pi- threshold, the pi0 pi0 mass spectrum exhibits a Wigner-cusp, from which the S-wave pi pi scattering lengths are extracted with high precision. This measurement is complementary to the extraction of the scattering lengths from K_e4 decays, which is also performed by the NA48/2 experiment.
The direct CP violation parameter Re(epsilon'/epsilon) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997-99). The new data yield the result: Re(epsilon'/epsilon) = (13.7 +/- 3.1) times 10^{-4}. Combining this result with that published from the 1997, 98 and 99 data, an overall value of Re(epsilon'/epsilon) = (14.7 +/- 2.2) times 10^{-4} is obtained from the NA48 experiment.
High statistics sample of kaon decays collected by NA48-CERN experiment allowed two independent measurements of the pion scattering length. Methods and Results are discussed
Recent measurements of kaon decays provide new information about CKM unitarity, lepton universality, and discrete symmetries. KLOE-2, the proposed extension of the kaon physics program at Frascati, will extend the world data set on kaon decays and conduct interference measurements with neutral kaons. Meanwhile, the decays K \to πν\barν can be directly related to the CKM matrix elements with minimal theoretical uncertainty, and are the focus of a series of experiments. Several events of K+ \to π+ν\barν have been observed to date; the goal of the NA62 experiment at CERN is to perform an O(100)-e…
The ratio of the leptonic charged kaon decays $R_K= Γ(K^{\pm} \to e^{\pm}ν) / Γ(K^{\pm} \to μ^{\pm}ν)$ is sensitive to the structure of the week interactions and can be precisely calculated within the Standard Model. Presence of New Physics can introduce a shift on its value of the order of a percent. The NA62 experiment at CERN SPS used data from a dedicated run in 2007 to perform a measurement of this ratio and probe the lepton universality. The data analysis technique and the final results are presented.
Recent results and future prospects in the rare kaon-decay experiments at KEK, BNL, CERN and FNAL are reviewed. Emphasis is placed on the quark flavor dynamics in the flavor-changing neutral current processes. Experimental and data-analysis techniques developed in the rare decay experiments are discussed.
NA62, an experiment at the CERN SPS to measure the branching ratio for the decay K+ -> pi+ nu nu-bar with ~10% precision, will observe ~10^13 K+ decays in its fiducial volume, and will thus also be able to carry out a rich program to search for forbidden K+ and pi0 decays, including in particular K+ decays that violate the conservation of lepton flavor and/or number. NA62's potential performance in searches for a number of forbidden K+ and pi0 decays is discussed, with initial sensitivity estimates.
New data on the production of charged kaons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The kaons are identified by energy loss in a large TPC tracking system. Inclusive invariant cross sections are obtained in intervals from 0 to 1.7 GeV/c in transverse momentum and from 0 to 0.5 in Feynman x. Using these data as a reference, a new evaluation of the energy dependence of kaon production, including neutral kaons, is conducted over a range from 3 GeV to p+anti-p collider…
The NA62 experiment at SPS is a continuation of the long standing CERN kaon physics program. The high statistics and the unprecedent precision allow to probe the Standard Model and test the description of the strong interactions at low energy. The final results on the the lepton universality test by measuring the ratio $R_K = Γ(K^{+}\to e^{+}ν) / Γ(K^{+}\to μ^{+}ν)$ and the study of the $K^\pm\toπ^{\pm}γγ$ decay are presented. The major goal of the NA62 experiment is to perform a measurement of the $Br(K^{+} \to π^{+} ν\barν)$ with a precision of 10% in two years of data taking. The detector s…
The COMPASS experiment at CERN is well designed for light-hadron spectroscopy with emphasis on the detection of new states, in particular the search for $J^{PC}$-exotic states and glueballs. We have collected data with 190 GeV/c charged hadron beams on a liquid hydrogen and nuclear targets in 2008/09. The spectrometer features good coverage by electromagnetic calorimetry and a RICH detector further provides $π$ / $K$ separation, allowing for studying final states involving neutral particles like $π^0$ or $η$ as well as hidden strangeness, respectively. We discuss the status of ongoing analyses…
The availability of high-intensity kaon beams at the J-PARC Hadron Experimental Facility and the CERN SPS North Area, together with the abundant forward production of kaons at the LHC, gives rise to unique possibilities for sensitive tests of the Standard Model in the quark flavor sector. Precise measurements of the branching ratios for the flavor-changing neutral current decays $K\toπν\barν$ can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. Building on the success of the current generation of fixed-target experiments, initiatives are taking shape in b…
The aim of the COMPASS hadron programme is to study the light-quark hadron spectrum, and in particular, to search for evidence of hybrids and glueballs. COMPASS is a fixed-target experiment at the CERN SPS and features a two-stage spectrometer with high momentum resolution, large acceptance, particle identification and calorimetry. A short pilot run in 2004 resulted in the observation of a spin-exotic state with $J^{PC} = 1^{-+}$ consistent with the debated $\pi1(1600)$. In addition, Coulomb production at low momentum transfer data provide a test of Chiral Perturbation Theory. During 2008 and …
The European Organization for Nuclear Research (CERN) has recently approved a world-unique QCD facility in which an updated version of the external M2 beam line of the CERN SPS in conjunction with a universal spectrometer of the COMPASS experiment is used. One of its main goals is to use highly intense and energetic kaon beams to map out the complete spectrum of excited kaons with an unprecedented precision; having a broad impact not only on low-energy QCD phenomenology, but also on many high-energy particle processes where excited kaons appear, such as the study of CP violation in heavy-meson…
The main physics goal of the NA62 experiment at CERN is to precisely measure the branching ratio of the kaon rare decay $K^+\rightarrow π^+ ν\barν$. This decay is strongly suppressed in the Standard Model and its branching ratio is theoretically calculated with high accuracy. The NA62 experiment is designed to measure this decay rate with an uncertainty better than 10\%. The measurement can be a good probe of new physics phenomena, which can alter the SM decay rate. The NA62 experiment has been successfully launched in October 2014. In this document, after an introduction to the theoretical fr…
A timely and long-term programme of kaon decay measurements at a new level of precision is presented, leveraging the capabilities of the CERN Super Proton Synchrotron (SPS). The proposed programme is firmly anchored on the experience built up studying kaon decays at the SPS over the past four decades, and includes rare processes, CP violation, dark sectors, symmetry tests and other tests of the Standard Model. The experimental programme is based on a staged approach involving experiments with charged and neutral kaon beams, as well as operation in beam-dump mode. The various phases will rely o…
The decay $K^+ \to π^+ ν\barν$, with a very precisely predicted branching ratio of less than $10^{-10}$, is one of the best candidates to reveal indirect effects of new physics at the highest mass scales. The NA62 experiment at the CERN SPS is designed to measure the branching ratio of the $K^+ \to π^+ ν\barν$ with a decay-in-flight technique. NA62 took data so far in 2016-2018. Statistics collected in 2016 allowed NA62 to reach the Standard Model sensitivity for $K^+ \to π^+ ν\barν$, entering the domain of $10^{-10}$ single event sensitivity and showing the proof of principle of the experimen…
We present new sets of fragmentation functions for neutral kaons, both at leading and next-to-leading order. They are fitted to data on inclusive K^0 production in e^+e^- annihilation taken by MARK II at PEP (\sqrt s = 29 GeV) and by ALEPH at LEP. Our fragmentation functions lead to a good description of other e^+e^- data on inclusive K^0 production at various energies. They also nicely agree with the K_S^0 transverse-momentum spectra measured by H1 at the DESY ep collider HERA, by UA5 at the CERN Sp\bar pS Collider, and by CDF at the Fermilab Tevatron.
