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.
We have measured the cross section σ(e+e−→π+π−γ(γ)) at DAΦNE, the Frascati ϕ-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<Mππ<0.975 GeV. For the latter we find Δππaμ=(387.2±0.5stat±2.4exp±2.3th)×10−10.
We have measured the cross section σ(e+e−→π+π−γ) at an energy W=mϕ=1.02 GeV with the KLOE detector at the electron–positron collider DAΦNE. From the dependence of the cross section on the invariant ...mass of the two-pion system, we extract σ(e+e−→π+π−) for the mass range 0.35<s<0.95 GeV2. From this result, we calculate the pion form factor and the hadronic contribution to the muon anomaly, aμ.
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 ∼1.4×109ϕ 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)°.
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 present a precise measurement of the ratio RK=Γ(K→eν(γ))/Γ(K→μν(γ)) and a study of the radiative process K→eνγ, 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 RK=(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→eνγ)/dEγ for photon energies 10<Eγ< 250 MeV. Results are compared with predictions from theory.
We have studied the η→π+π−e+e−(γ) decay using about 1.7 fb−1 collected by the KLOE experiment at the DAΦNE ϕ-factory. This corresponds to about 72 millions η mesons produced in ϕ radiative decays. We ...have measured the branching ratio, inclusive of radiative effects, with 4% accuracy: BR(η→π+π−e+e−(γ))=(26.8±0.9Stat.±0.7Syst.)×10−5. We have obtained the first measurement of the CP-odd ππ–ee decay planes angular asymmetry, Aϕ=(−0.6±2.5Stat.±1.8Syst.)×10−2.
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 measured, with the KLOE detector, the spectrum of π+π− invariant mass in a sample of 6.7×105e+e−→π+π−γ events with the photon at large polar angle (θγ>45°) at a centre of mass energy s around the ...ϕ mass. We observe in this spectrum a clear contribution from the intermediate process ϕ→ f0(980)γ. A sizeable effect is also observed in the distribution of the pion forward–backward asymmetry. We use different theoretical models to fit the spectrum and we determine the f0 mass and coupling constants to the ϕ, to π+π− and to KK¯.
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