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.
The KLOE electromagnetic calorimeter Adinolfi, M; Ambrosino, F; Antonelli, A ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2002, Volume:
482, Issue:
1-2
Journal Article
Peer reviewed
The KLOE detector was designed primarily for the study of CP violation in neutral kaon decays at DAΦNE, the Frascati φ-factory. The detector consists of a tracker and an electromagnetic calorimeter. ...A lead-scintillating-fiber sampling calorimeter satisfies best the requirements of the experiment, providing adequate energy resolution and superior timing accuracy. We describe in the following the construction of the calorimeter, its calibration and how the calorimeter information is used to obtain energy, point of entry and time of the arrival of photons, electrons and charged particles. With e+e− collision data at DAΦNE for an integrated luminosity of some 2pb−1 we find for electromagnetic showers, an energy resolution of 5.7%/E(GeV) and a time resolution of 54/E(GeV) ps. We also present a measurement of efficiency for low energy photons.
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¯.
We have measured the fully inclusive K+→μ+ν(γ) absolute branching ratio with the KLOE experiment at DAΦNE, the Frascati ϕ-factory. From some 865 283 K+→μ+ν(γ) decays obtained from a sample of ...∼5.2×108, ϕ-meson decays, we find BR(K+→μ+νμ(γ))=0.6366±0.0009stat.±0.0015syst., 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 present a measurement of the KL lifetime using the KLOE detector. From a sample of ∼4×108KSKL pairs following the reaction e+e−→ϕ→KSKL we select ∼15×106KL→π0π0π0 decays tagged by KS→π+π− events. ...From a fit of the proper time distribution we find τL=(50.92±0.17stat±0.25syst) ns. This is the most precise measurement of the KL lifetime performed to date.
The FENICE experiment was built in 1990 at the
e
+e
−
collider ADONE in Frascati to perform the first measurement of the electromagnetic form factor of the neutron in the time like-region, measuring ...the cross section of the reaction:
e
+e
−
→
nn̄. The non-magnetic apparatus allowed the detection of
nn̄ and
pp̄ as well as multihadronic events.
Results are presented on the first measurement of the neutron form factor from
q
2 = 3.69 to
q
2 = 5.95 for a total integrated luminosity of about 500 nb
−1, together with new results on the proton form factor in the same
q
2 region and a new measurement of the total
e
+e
−
→
hadrons cross section, close to the nucleon-antinucleon threshold.
The neutron form factor turns out to be greater or equal than the proton one, and there are indications of a narrow vector resonance close to the nucleon-antinucleon threshold.
The angular distribution of antiprotons and antineutrons has allowed to check the presence of the electric form factor contributions.
The general behaviour of the neutron time-like form factor is rather unexpected. A proposal to perform another measurements using of an asymmetric
e
+
e
− collider is briefly discussed.
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