Paolo Massarotti

NA62 is a fixed-target experiment at the CERN SPS dedicated to measurements of rare kaon decays. Such measurements, like the branching fraction of the $K^{+} \rightarrow \pi^{+} \nu \bar\nu$ decay, have the potential to bring significant insights into new physics processes when comparison is made with precise theoretical predictions. For this purpose, innovative techniques have been developed, in particular, in the domain of low-mass tracking devices. Detector construction spanned several years from 2009 to 2014. The collaboration started detector commissioning in 2014 and will collect data until the end of 2018. The beam line and detector components are described together with their early performance obtained from 2014 and 2015 data.

We have measured the cross section of the radiative process e+e−→π+π−γ with the KLOE detector at the Frascati ϕ-factory DAΦNE, from events taken at a CM energy W=1 GeV. Initial state radiation allows us to obtain the cross section for e+e−→π+π−, the pion form factor |Fπ|2 and the dipion contribution to the muon magnetic moment anomaly, Δaμππ=(478.5±2.0stat±5.0syst±4.5th)×10−10 in the range 0.1<Mππ2<0.85 GeV2, where the theoretical error includes a SU(3) χPT estimate of the uncertainty on photon radiation from the final pions. The discrepancy between the Standard Model evaluation of aμ and the value measured by the Muon g-2 collaboration at BNL is confirmed.

We have measured the cross section $\sigma(e^+e^-\to\pi^+\pi^-\gamma(\gamma))$ at DA$\Phi$NE, the Frascati \phi-factory, using events with initial state radiation photons emitted at small angle and inclusive of final state radiation. We present the analysis of a new data set corresponding to an integrated luminosity of 240 pb$^{-1}$. We have achieved a reduced systematic uncertainty with respect to previously published KLOE results. From the cross section we obtain the pion form factor and the contribution to the muon magnetic anomaly from two pion states in the mass range $0.592 < M_{\pi\pi} < 0.975$ GeV. For the latter we find $\Delta a^{\pi\pi}_\mu = (387.2\pm0.5_{\rm stat}\pm2.4_{\rm exp}\pm2.3_{\rm th})\times 10^{-10}$

A precision measurement of the ratio RK of the rates of kaon leptonic decays K±→e±ν and K±→μ±ν 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±ν candidates with 11% background contamination, is RK=(2.488±0.010)×10−5, in agreement with the Standard Model expectation.

A bstract The NA62 experiment reports the branching ratio measurement $$ \mathrm{BR}\left({K}^{+}\to {\pi}^{+}\nu \overline{\nu}\right)=\left({10.6}_{-3.4}^{+4.0}\left|{}_{\mathrm{stat}}\right.\pm {0.9}_{\mathrm{syst}}\right)\times {10}^{-11} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>BR</mml:mi> <mml:mfenced> <mml:mrow> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mfenced> <mml:mrow> <mml:msubsup> <mml:mn>10.6</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mfenced> <mml:msub> <mml:mrow /> <mml:mtext>stat</mml:mtext> </mml:msub> </mml:mfenced> <mml:mo>±</mml:mo> <mml:msub> <mml:mn>0.9</mml:mn> <mml:mtext>syst</mml:mtext> </mml:msub> </mml:mrow> </mml:mfenced> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>11</mml:mn> </mml:mrow> </mml:msup> </mml:math> 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 + → $$ {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> decay, observed with a significance of 3.4 σ . The experiment achieves a single event sensitivity of (0 . 839 ± 0 . 054) × 10 − 11 , corresponding to 10.0 events assuming the Standard Model branching ratio of (8 . 4 ± 1 . 0) × 10 − 11 . This measurement is also used to set limits on BR( K + → π + 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.

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.

We have measured the ratio Rϕ=BR(ϕ→η′γ)/BR(ϕ→ηγ) by looking for the radiative decays ϕ→η′γ and ϕ→ηγ into the final states π+π−7γ and 7γ, respectively, in a sample of ∼1.4×109 ϕ mesons produced at the Frascati ϕ factory. We obtain Rϕ=(4.77±0.09stat±0.19syst)×10−3, from which we derive BR(ϕ→η′γ)=(6.20±0.11stat±0.25syst)×10−5. Assuming the η′ has zero gluonium content, we extract the pseudoscalar mixing angle in the quark-flavor basis, φP=(41.4±0.3stat±0.7syst±0.6th)°. Combining the value of Rϕ with other constraints, we estimate the fractional gluonium content of the η′ to be Z2=0.14±0.04 and the mixing angle to be φP=(39.7±0.7)°.

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.

The NA62 experiment at the CERN SPS reports the first search for $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ using the decay-in-flight technique, based on a sample of $1.21\times10^{11}$ $K^+$ decays collected in 2016. The single event sensitivity is $3.15\times 10^{-10}$, 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 $14 \times 10^{-10}$ on the $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ branching ratio at 95\% CL.

A search for heavy neutral lepton (N) production in K+→e+N decays using the data sample collected by the NA62 experiment at CERN in 2017–2018 is reported. Upper limits of the extended neutrino mixing matrix element |Ue4|2 are established at the level of 10−9 over most of the accessible heavy neutral lepton mass range 144–462 MeV/c2, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The |Ue4|2 range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/c2.

The results of a search for $\pi^0$ decays to a photon and an invisible massive dark photon at the NA62 experiment at the CERN SPS are reported. From a total of $4.12\times10^8$ tagged $\pi^0$ mesons, no signal is observed. Assuming a kinetic-mixing interaction, limits are set on the dark photon coupling to the ordinary photon as a function of the dark photon mass, improving on previous searches in the mass range 60--110 MeV/$c^2$. The present results are interpreted in terms of an upper limit of the branching ratio of the electro-weak decay $\pi^0 \to \gamma \nu \overline{\nu}$, improving the current limit by more than three orders of magnitude.

We measured, with the KLOE detector, the spectrum of pi+pi- invariant mass in a sample of 6.7 x 10^5 e+e- --> pi+pi-g events with the photon at large polar angle (theta_g>45^o) at a centre of mass energy sqrt(s) around the phi mass. We observe a clear contribution from the intermediate process phi --> f0(980)g. A sizeable effect is also observed in the distribution of the forward-backeard asymmetry. We use different theoretical models to fit the spectrum and we determine the f_0 mass and coupling constants to the phi, to pi+pi- and to KK.

We present the first observation of quantum interference in the process phi -> KS KL ->pi+pi-pi+pi-. This analysis is based on data collected with the KLOE detector at the e^+e^- collider DAFNE in 2001--2002 for an integrated luminosity of about 380pb^-1. Fits to the distribution of Delta t, the difference between the two kaon decay times, allow tests of the validity of quantum mechanics and CPT symmetry. No deviations from the expectations of quantum mechanics and CPT symmetry have been observed. New or improved limits on various decoherence and CPT violation parameters have been obtained

The NA62 experiment at CERN reports a search for the lepton number violating decays K+→π−e+e+ and K+→π−μ+μ+ using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of 2.2×10−10 and 4.2×10−11 are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.

The NA62 experiment at the CERN SPS reports a study of a sample of $4 \times10^{9}$ tagged $\pi^0$ mesons from $K^+ \to \pi^+ \pi^0 (\gamma)$, searching for the decay of the $\pi^0$ to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of $4.4 \times10^{-9}$ is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay $K^+ \to \pi^+ X$, where $X$ is a particle escaping detection with mass in the range 0.110-0.155 GeV$/c^2$ and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming $X$ to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

We have studied the Dalitz plot of the e+ e- --> pi0 pi0 gamma events collected at SQRT(s) ~ M(phi) with the KLOE detector. In the dipion invariant mass (Mpp) region below 700 MeV, the process under study is dominated by the non-resonant process e+ e- --> omega pi0 with omega --> pi0 gamma whereas, for higher Mpp values, the radiative phi decay to the f0(980) is the dominant mechanism. Different theoretical models are used to fit the Dalitz plot, taking also into account a possible contribution of the sigma(600). For each model, we extract the f0(980) mass and its coupling to pipi, KKbar and to the phi.

Among some 400 million KSKL pairs produced in e+e− annihilations at DAΦNE, ∼6500 each of KS→π+e−ν¯ and KS→π−e+ν decays have been observed with the KLOE detector. From these, the ratio Γ(KS→πeν)/Γ(KS→π+π−)=(10.19±0.13)×10−4 is obtained, improving the accuracy on BR(KS→πeν) by a factor of four and providing the most precise test of the ΔS=ΔQ rule. From the partial width Γ(KS→πeν), a value for f+K0(0)×Vus is obtained that is in agreement with unitarity of the quark-mixing matrix. The lepton charge asymmetry AS=(1.5±9.6stat±2.9syst)×10−3 is compatible with the requirements of CPT invariance. The form-factor slope agrees with recent results from semileptonic KL and K+ decays. These are the first measurements of the charge asymmetry and form-factor slope for semileptonic KS decays.

We have studied the ϕ→a0(980)γ process with the KLOE detector at the Frascati ϕ-factory DAΦNE by detecting the ϕ→ηπ0γ decays in the final states with η→γγ and η→π+π−π0. We have measured the branching ratios for both final states: Br(ϕ→ηπ0γ)=(7.01±0.10±0.20)×10−5 and (7.12±0.13±0.22)×10−5, respectively. We have also extracted the a0(980) mass and its couplings to ηπ0, K+K−, and to the ϕ meson from the fit of the ηπ0 invariant mass distributions using different phenomenological models.

We update the values of the η-η' mixing angle and of the η' gluonium content by fitting our measurement Rϕ = BR(ϕ → η'γ)/BR(ϕ → ηγ) together with several vector meson radiative decays to pseudoscalars (V → Pγ), pseudoscalar mesons radiative decays to vectors (P → Vγ) and the η' → γγ, π0 → γγ widths. From the fit we extract a gluonium fraction of ZG2 = 0.12±0.04, the pseudoscalar mixing angle ψP = (40.4±0.6)° and the ϕ−ω mixing angle ψV = (3.32±0.09)°. ZG2 and ψP are fairly consistent with those previously published. We also evaluate the impact on the η' gluonium content determination of future experimental improvements of the η' branching ratios and decay width.

We present a precise measurement of the ratio R K =Γ(K→e ν(γ))/Γ(K→μ ν(γ)) and a study of the radiative process K→e ν γ, performed with the KLOE detector. The results are based on data collected at the Frascati e + e − collider DAΦNE for an integrated luminosity of 2.2 fb−1. We find R K =(2.493±0.025stat±0.019syst)×10−5, in agreement with the Standard Model expectation. This result is used to improve constraints on parameters of the Minimal Supersymmetric Standard Model with lepton flavor violation. We also measured the differential decay rate dΓ(K→e ν γ)/dE γ for photon energies 10<E γ < 250 MeV. Results are compared with predictions from theory.

A study of the dynamics of the rare decay K±→π±γγ has been performed on a sample of 232 decay candidates, with an estimated background of 17.4±1.1 events, collected by the NA62 experiment at CERN in 2007. The results are combined with those from a measurement conducted by the NA48/2 Collaboration at CERN. The combined model-independent branching ratio in the kinematic range z=(mγγ/mK)2>0.2 is BMI(z>0.2)=(0.965±0.063)×10−6, and the combined branching ratio in the full kinematic range assuming a Chiral Perturbation Theory description is B(Kπγγ)=(1.003±0.056)×10−6. A detailed comparison of the results with the previous measurements is performed.

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 + → $$ {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> 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, and improve on current limits in the second mass range by more than an order of magnitude.

We have studied the e+e- -&gt; omegapi0 cross section in the sqrt(s) interval 1000-1030 MeV using the pi+pi-pi0pi0 and pi0pi0gamma final states with a sample of ~600 pb^-1 collected with the KLOE detector at DAFNE. By fitting the observed interference pattern around M_phi for both final states, we extract the ratio of the decay widths Gamma(omega-&gt;pi0gamma)/Gamma(omega-&gt;pi+pi-pi0) = 0.0897 +- 0.0016 and derive the branching fractions BR(omega -&gt; pi+pi-pi0)= (90.24 +- 0.19)%, BR(omega -&gt; pi0gamma) = (8.09 +- 0.14)%. The parameters describing the e+e- -&gt; omegapi0 reaction around M_ϕare also used to extract the branching fraction for the OZI and G-parity violating phi -&gt; omegapi0 decay: BR(phi-&gt;omegapi0) = (4.4 +- 0.6)x10^-5.

A precision test of lepton flavour universality has been performed by measuring the ratio RK of kaon leptonic decay rates K+ --> e+nu and K+ --> mu+nu in a sample of 59813 reconstructed K+ --> e+nu candidates with (8.71 +- 0.24)% background contamination. The result RK = (2.487 +- 0.013) * 10^{-5} is in agreement with the Standard Model expectation.

The NA62 experiment collected a large sample of charged kaon decays in 2007 with a highly efficient trigger for decays into electrons. A measurement of the $\pi^0$ electromagnetic transition form factor slope parameter from $1.11\times10^{6}$ fully reconstructed $K^\pm \to \pi^\pm \pi^0_D, \pi^0_D \to e^+ e^-\gamma$ events is reported. The measured value $a = (3.68 \pm 0.57)\times10^{-2}$ is in good agreement with theoretical expectations and previous measurements, and represents the most precise experimental determination of the slope in the time-like momentum transfer region.

The NA62 experiment recorded a large sample of $K^+ \rightarrow \mu^+ \nu_{\mu}$ decays in 2007. A peak search has been performed in the reconstructed missing mass spectrum. In the absence of a signal, limits in the range $2 \times 10^{-6}$ to $10^{-5}$ have been set on the squared mixing matrix element $|U_{\mu4} |^2$ between muon and heavy neutrino states, for heavy neutrino masses in the range 300-375 MeV/$c^2$. The result extends the range of masses for which upper limits have been set on the value of $|U_{\mu4} |^2$ in previous production search experiments.

We present a measurement of the K–π vector current form-factor parameters for the decay KL→π±e∓ν. We use 328 pb−1 of data collected in 2001 and 2002, corresponding to ∼2 million Ke3 events. Measurements of semileptonic form factors provide information about the dynamics of the strong interaction and are necessary for evaluation of the phase-space integral IKe needed to measure the CKM matrix element |Vus| for KL→π±e∓ν decays. Our result is λ+=(28.6±0.5±0.4)×10−3 for a linear fit, and λ+′=(25.5±1.5±1.0)×10−3, λ+″=(1.4±0.7±0.4)×10−3 for a quadratic fit.

We have measured the fully inclusive K+ -> mu+nu(gamma) absolute branching ratio with the KLOE experiment at DAFNE, the Frascati Phi-factory. From some 865,283 K+ -> mu+nu(gamma) decays obtained from a sample of about 5.2x10^8 Phi-meson decays, we find BR(K+ -> mu+ nu (gamma)) = 0.6366 +-0.0009(stat.) +-0.0015(syst.), corresponding to an overall fractional error of 0.27%. Using recent lattice results on the decay constants of pseudoscalar mesons one can obtain an estimate for the CKM mixing matrix element |Vus|=0.2223+-0.0026.

We describe the method of measuring the integrated luminosity of the $e^+e^-$ collider DA$\Phi$NE, the Frascati $\phi-$factory. The measurement is done with the KLOE detector selecting large angle Bhabha scattering events and normalizing them to the effective cross section. The $e^+e^- \to e^+e^-(\gamma)$ cross section is calculated using different event generators which account for the $O(\alpha)$ radiative initial and final state corrections, and the $\phi$ resonance contribution. The accuracy of the measurement is 0.6%, where 0.3% comes from systematic errors related to the event counting and 0.5% from theoretical evaluations of the cross section.

The absolute branching ratio of the K+→π+π−π+(γ) decay, inclusive of final-state radiation, has been measured using ∼17 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory. The result is:BR(K+→π+π−π+(γ))=0.05565±0.00031stat±0.00025syst a factor ≃ 5 more precise with respect to the previous result. This work completes the program of precision measurements of the dominant kaon branching ratios at KLOE.

The NA62 experiment at CERN, designed to study the ultra-rare decay $K^+ \to \pi^+\nu\overline{\nu}$, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to $\mu^+\mu^-$ pairs is reported, based on a sample of $1.4 \times 10^{17}$ protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV$/c^2$.

A bstract The NA62 experiment at CERN, designed to study the ultra-rare decay K + → π + $$ \nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> , has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ + μ − pairs is reported, based on a sample of 1 . 4 × 10 17 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV /c 2 .

We present a measurement of the KL lifetime using the KLOE detector. From a sample of 4 x 10^8 KS KL pairs following the reaction e+ e- -> phi -> KS KL we select 15 x 10^6 KL -> p0 p0 p0 decays tagged by KS -> pi+ pi- events. From a fit of the proper time distribution we find tau_L = (50.92 +- 0.17{stat} +- 0.25{syst})$ ns. This is the most precise measurement of the KL lifetime performed to date.

We present a measurement of the slope parameter α for the η→3π0 decay, with the KLOE experiment at the DAΦNE ϕ-factory, based on a background free sample of ∼17 million η mesons produced in ϕ radiative decays. By fitting the event density in the Dalitz plot we determine α=−0.0301±0.0035stat−0.0035+0.0022syst. The result is in agreement with recent measurements from hadro- and photo-production experiments.

New results concerning the scalar mesons f0(980) produced in the ϕ→ππγ decays, and the a0(980) scalar mesons in the ϕ→a0(980)γ→ηπ0γ decays, are presented.

We have studied the eta->pi+pi-e+e-(gamma) decay using about 1.7 fb^-1 collected by the KLOE experiment at the DAFNE phi-factory. This corresponds to about 72 millions eta mesons produced in phi radiative decays. We have measured the branching ratio, inclusive of radiative effects, with 4% accuracy: BR(eta->pi+pi-e+e-(gamma)) = (26.8 +/- 0.9_Stat. +/- 0.7_Syst.) x 10^-5. We have obtained the first measurement of the CP-odd pipi-ee decay planes angular asymmetry, A_phi = (-0.6 +/- 2.5_Stat. +/- 1.8_Syst.) x 10^-2.

We report the first observation of the rare eta->e+e-e+e- decay based on 1.7 fb^{-1} collected by the KLOE experiment at the DAFNE phi-factory. The selection of the e+e-e+e- final state is fully inclusive of radiation. We have identified 362 +- 29 events resulting in a branching ratio of (2.4 +- 0.2_stat+bckg +- 0.1_syst) x 10^{-5}.

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.

The first search for ultra-rare K+ decays into the π+e+e−e+e− final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017–2018. An upper limit of 1.4×10−8 at 90% CL is obtained for the branching ratio of the K+→π+e+e−e+e− decay, predicted in the Standard Model to be (7.2±0.7)×10−11. Upper limits at 90% CL are obtained at the level of 10−9 for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: K+→π+aa, a→e+e− and K+→π+S, S→A′A′, A′→e+e−.

A sample of 3984 candidates of the K+→π+γγ decay, with an estimated background of 291±14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61±0.17)×10−7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process K+→π+a, a→γγ is also reported.

Abstract The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the amount of material in the path of the beam by using hydrogen gas as the radiator medium. The detector was shown to satisfy the kaon tagging requirements in a test-beam before installation and commissioning at the experiment. The CEDAR-H performance was measured using NA62 data collected in 2023.

We have searched for the decay KS→3π0 with the KLOE experiment at DAΦNE using data from e+e− collisions at a center of mass energy W∼mϕc2 for an integrated luminosity L=450pb−1. The search has been performed with a pure KS beam obtained by tagging with KL interactions in the calorimeter and detecting six photons. We find an upper limit for the branching ratio of 1.2×10−7 at 90% C.L.

We have measured the charged kaon lifetime using a sample of 15 × 106 tagged kaon decays. Charged kaons were produced in pairs at the DAΦNE ϕ-factory, e+e− → ϕ → K+K−. The decay of a K+ was tagged by the production of a K− and viceversa. The lifetime was obtained, for both charges, from independent measurements of the decay time and decay length distributions. From fits to the four distributions we find τ = (12.347±0.030) ns.

Using a large sample of pure, slow, short lived K 0 mesons collected with KLOE detector at DAΦNE, we have measured the K S lifetime. From a fit to the proper time distribution we find τ(K S )=(89.562±0.029stat±0.043syst) ps. This is the most precise measurement to date of the short lived K 0 meson lifetime, in good agreement with the world average derived from previous measurements. We observe no dependence of the lifetime on the direction of the K S in galactic coordinates.

We present a measurement of the branching ratio of the CP violating decay KL→π+π− performed by the KLOE experiment at the ϕ factory DAΦNE. We use 328 pb−1 of data collected in 2001 and 2002, corresponding to ∼150 million tagged KL mesons. We find BR(KL→π+π−)=(1.963±0.012stat.±0.017syst.)×10−3. This branching ratio measurement is fully inclusive of final-state radiation. Using the above result, we determine the modulus of the amplitude ratio |η+−| to be (2.219±0.013)×10−3 and |ϵ| to be (2.216±0.013)×10−3.

We have studied, with the KLOE detector at the DA$Φ$NE $Φ$-Factory, the dynamics of the decay $η\toπ^+π^-π^0$ using $η$ mesons from the decay $ϕ\toηγ$ for an integrated luminosity ${\mathcal L}$ = 450 pb$^{-1}$. From a fit to the Dalitz plot density distribution we obtain a precise measurement of the slope parameters. An alternative parametrization relates the $π^+π^-π^0$ slopes to that for $η\to 3π^0$ showing the consistency of KLOE results for both channels. We also obtain the best confirmation of the $C$-invariance in the $η\toπ^+π^-π^0$ decay.

The KLOE experiment uses a fine sampling lead-scintillating fibre calorimeter to measure energy, time and position of neutral and charged particles. The overall detector consists of 88 modules organised in a barrel and two end-caps, for a total granularity of 2440 cells, read-out by photo-multipliers at both fibre ends. The chosen design of a high sampling fraction with the usage of thin lead layers and fast scintillating fibres allows to reach good efficiency for photon energies down to few MeV, good energy resolution and excellent time resolution. The design, calibration and performances of the calorimeter on efficiency, time/position/energy resolution and particle identification is reviewed. The overall calorimeter impact on kaon tagging and on physics results is also presented.

We present a precise measurement of the ratio R_K=B(K\to e\nu(\gamma))/B(K\to \mu\nu(\gamma)) and a study of the radiative process $K\to e\nu\gamma$, performed with the KLOE detector. The results are based on data collected at the Frascati $e^+e^-$ collider DAFNE for an integrated luminosity of 2.2 fb$^{-1}$. We find R_K = (2.493\pm0.025\pm0.019)x10^{-5}$, in agreement with the Standard Model expectation. This result is used to improve constraints on parameters of the Minimal Supersymmetric Standard Model with lepton flavor violation. We also measured the differential decay rate $d\Gamma(K\to e\nu\gamma)/dE_\gamma$ for photon energies $10<E_\gamma<250$ MeV. Results are compared with predictions from theory.

We have searched with the KLOE detector for the P and CP violating decay eta -> pi^+pi^- in a sample of 1.55 x 10^7 eta's from the decay phi -> eta gamma of phi mesons produced in e+e- annihilations at DAFNE. No signal is found. We obtain the upper limit BR(eta -> pi^+pi^-) < 1.3 x 10^-5 at 90% confidence level.

Using a sample of over 400 million φ→KSKL decays produced during the years 2001 and 2002 at the DAΦNE e+e- collider, the ratio RS π=Γ(KS→π+π-(γ))/Γ(KS→π0π0) has been measured with the KLOE detector. The result is RS π=2.2555±0.0012stat±0.0021corr-stat±0.0050syst, which is in good agreement with the previously published result based on the KLOE data sample from the year 2000. The average of the KLOE results is RS π=2.2549±0.0054, reducing the total error by a factor of three, to 0.25%.

We have searched for the decay phi -> K0 K0bar gamma, by detecting K_s pairs plus a photon and with the K_s-mesons decaying to pi^+ pi^-, in a sample of about 1.5x 10^9 phi-decays collected by the KLOE experiment at DAFNE. The reaction proceeds through the intermediate states f_0(980) gamma, a_0(980) gamma. We find five events with 3.2 events expected from background processes. We obtain the upper limit: BR (phi -> K0 K0bar gamma) < 1.9x10^-8 at 90% C.L. .

We present the result of a direct search for the decay KS→e+e−, obtained with a sample of e+e−→ϕ→KSKL events produced at DAΦNE, the Frascati ϕ-factory, for an integrated luminosity of 1.9 fb−1. The search has been performed using a pure KS beam tagged by the simultaneous detection of a KL interaction in the calorimeter. Background rejection has been optimized by using both kinematic and particle identification cuts. We find BR(KS→e+e−)<9×10−9 at 90% CL, which improves by an order of magnitude on the previous best limit.

Large-size Resistive Micromegas have been chosen for the upgrade of the forward muon spectrometer of the ATLAS experiment, the New Small Wheel project. These chambers, together with small-strip Thin Gap Chambers (sTGC), allow reconstruction of high-momentum muon tracks in a high-radiation environment and provide a robust low-threshold single-muon trigger. A collaboration of seven INFN units built 32 SM1 type chambers, corresponding to one fourth of the total number needed for this upgrade. Each SM1 chamber has a surface of approximately 2 m2 and four sensitive layers. The production was shared among five INFN construction sites and it was completed in fall 2020. The construction methods, as well as the results of the quality tests done on components of the detector and on the assembled chambers, are reported in the present paper.

A sample of $2.8 \times 10^4$ $K^{+} \to \pi^{+} \mu^{+} \mu^{-}$ candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017--2018. The model-independent branching fraction is measured to be $(9.15 \pm 0.08)\times 10^{-8}$, a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at $\mathcal{O}(p^6)$.

A bstract The NA62 experiment at CERN targets the measurement of the ultra-rare $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> decay, and carries out a broad physics programme that includes probes for symmetry violations and searches for exotic particles. Data were collected in 2016–2018 using a multi-level trigger system, which is described highlighting performance studies based on 2018 data.

The first search for ultra-rare $K^+$ decays into the $π^+e^+e^-e^+e^-$ final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017-2018. An upper limit of $1.4\times 10^{-8}$ at 90% CL is obtained for the branching ratio of the $K^+\toπ^+e^+e^-e^+e^-$ decay, predicted in the Standard Model to be $(7.2\pm0.7)\times 10^{-11}$. Upper limits at 90% CL are obtained at the level of $10^{-9}$ for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: $K^+\toπ^+aa$, $a\to e^+e^-$ and $K^+\toπ^+S$, $S\to A^\prime A^\prime$, $A^\prime\to e^+e^-$.

A bstract A sample of 1 . 3 × 10 5 K + → π 0 e + νγ candidates with less than 1% background was collected by the NA62 experiment at the CERN SPS in 2017–2018. Branching fraction measurements are obtained at percent relative precision in three restricted kinematic regions, improving on existing results by a factor larger than two. An asymmetry, possibly related to T-violation, is investigated with no evidence observed within the achieved precision.

A full-size prototype of a Micromegas precision tracking chamber for the upgrade of the ATLAS detector at the LHC Collider has been built between October 2015 and April 2016. This paper describes in detail the procedures followed in the construction of the components of the chamber in various INFN laboratories and the final assembly in the Laboratori Nazionali di Frascati (LNF). In addition, the results of the chamber exposure to a particle beam at SPS/H8 at CERN in June 2016 are presented. The performances obtained in the construction and the results of the test beam are compared with the requirements set in order to sustain the high radiation levels expected during the data-taking of the LHC in the next years.

We have measured the absolute branching ratio of the K+→π+π0(γ) decay, using ∼20 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory. Signal counts are obtained from the fit of the distribution of the momentum of the charged decay particle in the kaon rest frame. The result, inclusive of final-state radiation, is BR(K+→π+π0(γ))=0.2065±0.0005stat±0.0008syst.

The branching ratio for the decay $K^+ \to \pi^+\nu\bar{\nu}$ is sensitive to new physics; the NA62 experiment will measure it to within about 10%. To reject the dominant background from channels with final state photons, the large-angle vetoes (LAVs) must detect particles with better than 1 ns time resolution and 10% energy resolution over a very large energy range. Our custom readout board uses a time-over-threshold discriminator coupled to a TDC as a straightforward solution to satisfy these requirements. A prototype of the readout system was extensively tested together with the ANTI-A2 large angle veto module at CERN in summer 2010.

The NA62 experiment [1] will measure the BR(K+→π+ν) to within about 10%. To reject the dominant background from final state photons, the large-angle vetoes (LAVs) must detect particles with better than 1 ns time resolution and 10% energy resolution over a very large energy range. A low threshold, large dynamic range, Time-over-threshold based solution has been developed for the LAV front end electronics. Our custom 32 channel 9U board uses a pair of low threshold discriminators for each channel to produce LVDS logic signals. The achieved time resolution obtained in laboratory, coupled to an HPTDC based readout board, is ∼ 150 ps.

We report a preliminary measurement of the slope parameter $\alpha$ for the $\eta\to 3\piz$ decay carried out with KLOE at DA$\Phi$NE; where $\alpha$ is the parameter describing the energy dependence of the square of the matrix element for this decay. By fitting the event density in the Dalitz plot with a collected statistic of 420 pb$^{-1}$ we determine $\alpha = -0.027 \pm 0.004 (stat) ^{+0.004}_{-0.006} (syst)$. This result is consistent with current chiral perturbation theory calculations within the unitary approach.

The design, construction and test of a charged particle detector made of scintillation counters read by Silicon Photomultipliers (SiPM) is described. The detector, which operates in vacuum and is used as a veto counter in the NA62 experiment at CERN, has a single channel time resolution of 1.14 ns, a spatial resolution of ∼2.5 mm and an efficiency very close to 1 for penetrating charged particles.

This paper deals with the modeling and solution of a class of nonlinear direct problems related to a transport diffusion model with a source term. Specifically, the first part of the paper deals with the derivation of a class of transport and diffusion models (with a distributed source term) in one space dimensions with variable properties along the channel and nonlinear decay term. The second part with simulations, that is the approximation to the solution of nonlinear initial boundary value problems by generalized collocation methods. The third part develops a critical analysis mainly addressed to research perspectives on the solution of inverse problems related to the identification of the source term.

We present a measurement of the ratio R = \Gamma(\keg;\Estar>30\mev,\qstar>20^\circ)$/$\Gamma(\kegf)$ and a first measurement of the direct emission contribution in KL semileptonic decays. The measurement is done at the DAFNE phi-factory selecting phi->KL KS decays with the KLOE detector. We use 328 pb^{-1}$ of data corresponding to about 3.5 million Ke3(g) events and about 9000 radiative events. Our result is R=(924 +/- 23(stat) +/-16(syst)10^{-5} for the branching ratio and X=-2.3 +/- 1.3(stat) +/- 1.4(syst) for the parameter describing direct emission.

Using a sample of over 600 million phi->K+K- decays collected at the Dafne e+e- collider, we have measured with the KLOE detector the absolute branching ratios for the charged kaon semileptonic decays, K+/- -> p0 e nu (gamma) (Ke3) and K+/- -> p0 mu nu (gamma) (Kmu3). The results, BR(Ke3) = 0.04965 +/- 0.00038_{stat} +/- 0.00037_{syst} and BR(Kmu3) = 0.03233 +/- 0.00029_{stat} +/- 0.00026_{syst}, are inclusive of radiation. Accounting for correlations, we derive the ratio Kmu3/Ke3 = 0.6511+/-0.0064. Using the semileptonic form factors measured in the same experiment, we obtain V_{us}f_{+}(0) = 0.2141 +/- 0.0013.

The branching ratio (BR) for the decay K^+ \to \pi^+\nu\bar{\nu} is a sensitive probe for new physics. The NA62 experiment at the CERN SPS will measure this BR to within about 10%. To reject the background from dominant kaon decays with final state photons, the large-angle photon vetoes (LAVs) must detect photons of energy as low as 200 MeV with an inefficiency of less than 10^{-4}. The LAV detectors make use of lead glass blocks recycled from the OPAL electromagnetic calorimeter barrel. We describe the mechanical design and challenges faced during construction, the characterization of the lead glass blocks and solutions adopted for monitoring their performance, and the development of front-end electronics to allow simultaneous time and energy measurements over an extended dynamic range using the time over-threshold technique. Our results are based on test-beam data and are reproduced by a detailed Monte Carlo simulation that includes the readout chain.

Using 328 pb−1 of data collected at DAΦNE corresponding to ∼1.8 million KL → πμν decays, we have measured the Kμ3 form factor parameters. The structure of the K−π vector-current provides information about the dynamics of the strong interaction; its knowledge is necessary for evaluation of the phase-space integral required for measuring the CKM matrix element Vusand for testing lepton universality in kaon decays. Using a new parametrization for the vector and scalar form factors, we find λ+ = (25.7 ± 0.6) × 10−3, and λ0 = (14.0 ± 2.1) × 10−3. Our result for λ0, together with recent lattice calculations of fπ, fK and f(0), satisfies the Callan-Treiman relation.

This was the first workshop of a series which aims to discuss the status and prospects of the physics of Flavour changing and conserving processes, and addresses the scientific community involved in experiments like g -2, Mu2e, MEG, Mu3e, COMET, EDM and more generally to the physics of K and B mesons.Forty talks were presented at the Workhop, covering the theoretical status as well as the latest results of experiments in various

KLOE has measured most decay branching ratios of KS, KL and K±-mesons. It has also measured the KL and the K± lifetime and determined the shape of the form factors involved in kaon semileptonic decays. We present in the following a description of the above measurements and a well organized compendium of all of our data, with particular attention to correlations. These data provide the basis for the determination of the CKM parameter |Vus| and a test of the unitarity of the quark flavor mixing matrix. We also test lepton universality and place bounds on new physics using measurements of |Vus| from Kℓ2 and Kℓ3 decays.

The branching ratio (BR) for the decay K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> →π <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> νν̅ is a sensitive probe for new physics. The NA62 experiment at the CERN SPS will measure this BR to within about 10%. To reject the dominant background from channels with final state photons, the large-angle vetoes (LAVs) must detect photons of energy as low as 200 MeV with an inefficiency of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> , as well as provide energy and time measurements with resolutions of 10% and 1 ns for 1 GeV photons. The LAV detectors make creative reuse of lead glass blocks recycled from the OPAL electromagnetic calorimeter barrel. We describe the mechanical design and challenges faced during construction, the characterization of the lead glass blocks and solutions adopted for monitoring their performance, and the development of front-end electronics to allow simultaneous time and energy measurements over an extended dynamic range using the time-over-threshold technique. Our results are based on test-beam data and are reproduced by a detailed Monte Carlo simulation that includes the readout chain.

A bstract Measurement of the ultra-rare $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> decay at the NA62 experiment at CERN requires high-performance particle identification to distinguish muons from pions. Calorimetric identification currently in use, based on a boosted decision tree algorithm, achieves a muon misidentification probability of 1 . 2 × 10 − 5 for a pion identification efficiency of 75% in the momentum range of 15–40 GeV/ c . In this work, calorimetric identification performance is improved by developing an algorithm based on a convolutional neural network classifier augmented by a filter. Muon misidentification probability is reduced by a factor of six with respect to the current value for a fixed pion-identification efficiency of 75%. Alternatively, pion identification efficiency is improved from 72% to 91% for a fixed muon misidentification probability of 10 − 5 .

Effects of new physics in flavor could be found both in Flavor Changing Neutral Current (FCNC) processes and in Lepton Flavor Violation (LFV) modes. The former offer the possibility to deeply test the standard model in a clean environment, while the latter are sensitive to contribution from several models beyond the standard model. In the Kaon sector both FCNC and LFV will be investigated in the NA62 experiment. In addition the kaons sector is an ideal place where to look for new particles and tiny effects, in the region of hundreds of MeV/c2. In this paper prospects for exotic searches in NA62 will be presented, together with recent results from NA48/2 and NA62-RK on LFV kaon decays modes.

We present precise measurements of the eta and K0 masses using the processes phi to eta gamma, eta to gamma gamma and phi to Ks Kl, Ks to pi+ pi-. The K0 mass measurement, M_K=497.583 +/- 0.005 (stat) +/- 0.020 (syst) MeV, is in acceptable agreement with the previous measurements but is more accurate. We find m(eta) = 547.874 +/- 0.007 (stat) +/- 0.031 (syst) MeV. Our value is the most accurate to date and is in agreement with two recent measurements based on eta decays, but is inconsistent, by about 10 sigma, with a measurement of comparable precision based on eta production at threshold.

We report the measurement of the ratio $\Gamma(\eta \to \pi^+\pi^-\gamma)/\Gamma(\eta \to \pi^+\pi^-\pi^0)$ analyzing a large sample of $\phi \to \eta \gamma$ decays recorded with the KLOE experiment at the DA$\Phi$NE $e^+ e^-$ collider, corresponding to an integrated luminosity of 558 pb$^{-1}$. The $\eta \to \pi^+\pi^-\gamma$ process is supposed to proceed both via a resonant contribution, mediated by the $\rho$ meson, and a non resonant direct term, connected to the box anomaly. The presence of the direct term affects the partial width value. Our result $R_{\eta}=\Gamma(\eta \to \pi^+ \pi^- \gamma)/\Gamma(\eta \to \pi^+ \pi^- \pi^0)= 0.1838\pm 0.0005_{stat} \pm 0.0030_{syst}$ is in agreement with a recent CLEO measurement, which differs by more 3 $\sigma$ from the average of previous results.

We have measured the charged kaon lifetime using a sample of 15 \times 10^6 tagged kaon decays. Charged kaons were produced in pairs at the DA\PhiNE \phi-factory, e^+e^- \to \phi \to K^+ K^-. The decay of a K^+ was tagged by the production of a K^- and viceversa. The lifetime was obtained, for both charges, from independent measurements of the decay time and decay lenght distributions. From fits to the four distributions we find \tau = (12.347\pm0.030) ns.

The NA62 experiment at CERN SPS aims at measuring-100 events of the very rare decay K+ →π +ννˉ (BR∼8.5xlO∼10). It poses stringent requirements on PID capabilities to reject the overwhelming π+π0 (63%) and Kμ2(21%) backgrounds. The photon veto system must provide a rejection factor of 10∼8 on π0 decays. As a main γ veto detector, the NA48 liquid Kripton calorimeter will be used. To have full geometrical acceptance up to 50 mr, a set of 12 veto stations should be placed along the vacuum decay tank, with an inefficiency <10∼4 in a wide energy range (200 MeV-35 GeV). Good energy resolution (∼10% at 1 GeV) for threshold definition, good time resolution (∼1 ns) to be used at the trigger level, sensitivity to MIP for calibration with muons of the beam halo are needed. A moderate segmentation in the azimuthal angle is desirable, for reducing the counting rate and providing information on the γ direction. We performed an intense R&D program on three solutions: “spaghetti” calorimeter, lead/scintillator sandwich calorimeter, and original re-use of the existing barrel of the OPAL lead-glass e.m. calorimeter. Studies have been performed at the Frascati BTF beam and all three meet the efficiency requirements. The final choice uses a peculiar radial arrangement of lead-glasses in rings. Front-end electronics has been designed to cover the tree orders of magnitude of the signal, contributing to the trigger, and integrated in the general TDAQ, while keeping low cost and simplicity. The first five full veto stations have been constructed. Two tests have been done and problems found fixed. We will discuss about R&D for the technology choice, LAV construction, test beams results and simulation performance.

The NA62 experiment at CERN aims at the very challenging task of measuring with 10% relative error the Branching Ratio of the ultra-rare decay K+→ π+v, which is expected to occur only in about 8 out of 1011 kaon decays. This will be achieved by means of an intense hadron beam, an accurate kinematical reconstruction and a redundant veto system for identifying and suppressing all spurious events. In particular, beam induced background, caused by inelastic interactions of the hadron beam with the Si based detector which measures kaon momentum (the so called Gigatracker, GTK) can mimic the signal in case only one pion is detected downstream. To suppress this background we have designed the so called CHarged ANTIcounter (CHANTI) i.e. a series of six guard counters, to be operated in vacuum and covering a wide angular region downstream the last GTK station. CHANTI must have time resolution ∼ 1 ns, must be highly efficient in detecting charged particles and must cope with rates which in the inner part can be some kHz/cm2. We have adopted a solution based on triangularly shaped scintillator bars coupled with fast wave–length shifting fibers and individually read by means of Silicon Photomultipliers (SiPM). The full scale prototype of one counter has been built and tested using a prototype front end electronic board which allows fast amplification and individual channel fine bias setting with O(mV) resolution and 0.1% stability. We show first results on the response of the detector to minimum ionizing particles as well as on its time resolution, which are well in line with the specifications.

The NA62 experiment at the CERN SPS will measure the branching ratio for the decay K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ® π <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> v <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> to within »10%. The large-angle veto (LAV) detectors must detect photons with energies as low as 200 MeV with an inefficiency of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . After a comprehensive series of comparative studies, NA62 decided to base the LAV system on the lead-glass block/PMT assemblies recycled from the OPAL barrel calorimeter, and a prototype veto station, complete with front-end electronics, was constructed and tested in 2009. Eleven additional stations are to be constructed before data taking begins in 2012. We describe the design, construction, and testing of the LAV system, including the recovery and mechanical adaptation of the OPAL hardware, issues related to operation in high vacuum, HV distribution, and in-situ monitoring, and especially, the design of an efficient and economical system for the readout of time and energy over an extended dynamic range.

We report the newest results from the KLOE experiment on hadronic physics, such as the parameters of scalars f0 and a0, the eta meson mass measurements and dynamics, the first observation of the eta -&gt; p+p-e+e- rare decay, and study of e+e- -&gt; omega p0 cross section around the phi resonance.

The NA62 experiment at CERN SPS, aimed to measure ~80 events of very rare decay K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ¿ ¿+ ¿ anti-v (BR~8.5×10-10), poses stringent requirements on PID capabilities to reject the overwhelming K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">¿2</sub> (63%) and K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">¿2</sub> (21%) backgrounds. The photon veto system must provide a rejection factor of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> on ¿ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> decays. As main ¿ veto detector, the NA48 liquid Kr calorimeter will be used. To have full geometrical acceptance, a set of 12 veto stations will be placed along the vacuum decay tank, with an inefficiency <10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> in a wide energy range (50 MeV-35 GeV). Good energy resolution (~10% at 1 GeV) for threshold definition, good time resolution (~1 ns) to be used at the trigger level, sensitivity to mip, for calibration with muons of the beam halo are needed. We performed an intense R&D program on 3 solutions. Studies have been performed at the Frascati BTF beam and all 3 meet the efficiency requirements. The final choice uses a peculiar radial arrangement of lead glasses in rings. Studies on the front-end electronics are under way. The first full veto station has been constructed installed and tested at CERN.

Preliminary result on the charged kaon lifetime, obtained by the KLOE experiment operating at DA$Φ$NE, the Frascati $ϕ$-factory, is presented

For the upgrade of the innermost station of the forward muon spectrometer of the ATLAS experiment large Micromegas (MM) detectors of 2 and 3 m2 with 4 active layers each are foreseen. Four types of MM chambers are produced among four sites. Each sites has to deliver 32 quadruplets or 128 active planes. The tiny 120μm distance between the 600 V resistive strip anodes and the ground micro-meshes for these large areas require adequate and well adapted cleaning procedures to guarantee high voltage stability. This is particularly critical for strip shaped surfaces made from resistive material where remnants from the lithographic production processes must be completely removed. The procedure foreseen a visual inspections to be carried on during cleaning and assembly procedures; a wet cleaning procedure to remove dust and possible ionic components of salts from the anode surfaces; a dry cleaning procedure to remove dust; HV tests to be done to validate the cleaning. The cleaning procedure will be illustrated for a New Small Wheel (NSW) Outer Small Module (SM2) of 2 m2.

We describe the status of the analyses in progress on light meson spectroscopy in the KLOE experiment.We present the analyses of φ decays into f 0 ¡ 980¢ γ and a 0 ¡ 980¢ γ, the study of the Dalitz plot of the η £ π¤ π ¥ π 0 and η £ 3π 0 decays, the measurement of the branching ratio of η £ π 0 γγ, and the measurement of the ratio BrAll the presented results are based on a sample of about 450 pb¥ 1 of integrated luminosity collected during the 2001-2002 data taking.From the 2004-2005 data taking a factor 5 improvement in the integrated luminosity is expected.

The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented statistics of rare kaon decays in the $K_{e4}$ modes: $K_{e4}(+-)$ ($K^\pm \to π^+ π^- e^\pm ν$) and $K_{e4}(00)$ ($K^\pm \to π^0 π^0 e^\pm ν$) with nearly one percent background contamination. It leads to the improved measurement of branching fractions and detailed form factor studies. New final results from the analysis of 381 $K^\pm \to π^\pm γγ$ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN are presented. The results include a decay rate measurement and fits to Chiral Perturbation Theory (ChPT) description.

Rare kaon decays provide unique opportunity to test the Standard Model and probe its possible extensions. The primary goal of the NA62 experiment is the measurement of the [Formula: see text] decay with a precision of 10% in two years of data taking. The detector setup together with the analysis technique is described.

The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of rare kaon decays in the Ke4 modes: Ke4(+-) ($K^\pm \to \pi^+ \pi^- e^\pm \nu$) and Ke4(00) ($K^\pm \to \pi^0 \pi^0 e^\pm \nu$) with nearly one percent background contamination. The detailed study of form factors and branching rates, based on these data, has been completed recently. The results brings new inputs to low energy strong interactions description and tests of Chiral Perturbation Theory (ChPT) and lattice QCD calculations. In particular, new data support the ChPT prediction for a cusp in the $\pi^0\pi^0$ invariant mass spectrum at the two charged pions threshold for Ke4(00) decay. New final results from an analysis of about 400 $K^\pm \to \pi^\pm \gamma \gamma$ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN during low intensity runs with minimum bias trigger configurations are presented. The results include a model-independent decay rate measurement and fits to ChPT description.

The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of rare kaon decays in the Ke4 modes: Ke4(+-) ($K^\pm \to \pi^+ \pi^- e^\pm \nu$) and Ke4(00) ($K^\pm \to \pi^0 \pi^0 e^\pm \nu$) with nearly one percent background contamination. The detailed study of form factors and branching rates, based on these data, has been completed recently. The results brings new inputs to low energy strong interactions description and tests of Chiral Perturbation Theory (ChPT) and lattice QCD calculations. In particular, new data support the ChPT prediction for a cusp in the $\pi^0\pi^0$ invariant mass spectrum at the two charged pions threshold for Ke4(00) decay. New final results from an analysis of about 400 $K^\pm \to \pi^\pm \gamma \gamma$ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN during low intensity runs with minimum bias trigger configurations are presented. The results include a model-independent decay rate measurement and fits to ChPT description.

The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of rare kaon decays in the K e4 modes: K e4 (+-) (K ± → π + π -e ± ν) and K e4 (00) (K ± → π 0 π 0 e ± ν) with nearly one percent background contamination.The detailed study of form factors and branching rates, based on these data, has been completed recently.The results brings new inputs to low energy strong interactions description and tests of Chiral Perturbation Theory (ChPT) and lattice QCD calculations.In particular, new data support the ChPT prediction for a cusp in the π 0 π 0 invariant mass spectrum at the two charged pions threshold for K e4 (00) decay.New final results from an analysis of about 400 K ± → π ± γγ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN during low intensity runs with minimum bias trigger configurations are presented.The results include a model-independent decay rate measurement and fits to ChPT description.