Based on a sample of 300 million K-S mesons produced in phi -> KLKS decays recorded by the KLOE experiment at the DA Phi NE e(+)e(-) collider we have measured the branching fraction for the decay ...K-S -> pi mu nu. The K-S mesons are identified by the interaction of K-L mesons in the detector. The K-S -> pi mu nu decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of K-L -> pi mu nu decays. A fit to the reconstructed muon mass distribution finds 7223 +/- 180 signal events. Normalising to the K-S -> pi(+)pi(-) decay events the result for the branching fraction is B(K-S -> pi mu nu) = (4.56 +/- 0.11(stat) +/- 0.17(syst)) x 10(-4). It is the first measurement of this decay mode and the result allows an independent determination of vertical bar V-us vertical bar and a test of the lepton-flavour universality. (c) 2020 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Based on an integrated luminosity of 1.61 fb(-1)e(+)e(-) collision data collected with the KLOE detector at DA Phi NE, the Frascati phi -factory, a search for the P- and CP-violating decay eta -> ...pi (+)pi (-) has been performed. Radiative phi -> eta gamma decay is exploited to access the eta mesons. No signal is observed in the pi (+)pi (-) invariant mass spectrum, and the upper limit on the branching fraction at 90% confidence level is determined to be B(eta -> pi (+)pi (-)) < 4.9 x 10(-6), which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get B(<eta> -> pi (+)pi (-)) < 4.4 x 10(-6) at 90% confidence level.
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)°.
The ratio Rη=Γ(η→π+π−γ)/Γ(η→π+π−π0) has been measured by analysing 22 million ϕ→ηγ decays collected by the KLOE experiment at DAΦNE, corresponding to an integrated luminosity of 558 pb−1. The η→π+π−γ ...proceeds both via the ρ resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, Rη=0.1856±0.0005stat±0.0028syst, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the η→π+π−γ decay could be described in a model-independent approach in terms of a single free parameter, α. The determined value of the parameter α is α=(1.32±0.08stat−0.09syst+0.10±0.02theo) GeV−2.
Charmed-meson production by 350 GeV/c π
− particles incident on copper and tungsten targets has been studied in the WA92 experiment, performed at the CERN Ω′ spectrometer. Results obtained are ...reported and discussed. Reconstruction of decays from the set D
0 → K
−
π
+ D
0 → K
−
π
−
π
+
π
+, D
s
+ →
φπ
+ and charge conjugates has yielded a sample of 7280 ± 108 charmed mesons, produced with
χ
F
> 0, (
χ
F
) = 0.18 and〈
p
T
2〉 = 1.86 (
GeV/
c)
2. Assuming a relationship
σ =
σ
0
A
α
between the cross section, σ, per nucleus of mass
A and the nucleonic cross section,
σ
0 the α value found for the detected charmed particles is 0.95 ± 0.06 ± 0.03. Taking
α = 1, the measured cross sections per nucleon for
χ
F
> 0 production are 7.78 ± 0.14 ± 0.52
μb for
D
0/
D
0, 3.28 ± 0.08 ± 0.29 μ
b
for D
+/D
− and 1.29 ± 0.16 ± 0.33
μb for D
s
+/D
s
−. Differential cross sections with respect to
χ
F
and
p
T
2 have been determined for the various types of charmed meson, and particle-antiparticle asymmetries have been analysed.
A
bstract
The three precision measurements of the cross section
σ
(
e
+
e
−
→
π
+
π
−
γ(γ)) using initial state radiation by the KLOE collaboration provide an important input for the prediction of ...the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. We present the construction of these covariance matrices and use them to determine a combined KLOE measurement for
σ
(
e
+
e
−
→
π
+
π
−
γ(γ)). We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range 0
.
10
< s <
0
.
95 GeV
2
of
$$ {a}_{\mu}^{\pi^{+}{\pi}^{-}}=\left(489.8\pm {1.7}_{\mathrm{stat}}\pm {4.8}_{\mathrm{sys}}\right)\times {10}^{-10} $$
a
μ
π
+
π
−
=
489.8
±
1.7
stat
±
4.8
s
y
s
×
10
−
10
.
Data vectors and covariance matrices are available at
http://www.lnf.infn.it/kloe/ppg/
ppg_2017/ppg_2017.html
.
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.
Using 1.63 fb(-1) of integrated luminosity collected by the KLOE experiment about 7 x 10(4) K-S -> pi(+/-)e(-/+)nu decays have been reconstructed. The measured value of the charge asymmetry for ...this decay is A(S) = (-4.9 +/- 5.7(stat) +/- 2.6(syst)) x 10(-3) which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives A(S) = (3.8 +/- 5.0(stat) +/- 2.6(syst)) x 10(-3) and, together with the asymmetry of the K-L semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.
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