Abstract A high statistics data sample of the $$K^{+}\rightarrow \mu ^{+}\nu _{\mu }$$ K+→μ+νμ decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search ...for the decay channel $$K^{+}\rightarrow \mu ^{+}\nu _{H}$$ K+→μ+νH with a hypothetic stable heavy neutrino in the final state. The obtained missing mass spectrum does not show peaks that could be attributed to existence of stable heavy neutrinos in the mass range $$(270< m_{\nu _{H}} < 375)$$ (270<mνH<375) MeV$$/c^{2}$$ /c2 . As a result, upper limits on the branching ratio and on the value of the mixing element $$|U_{\mu H}|^{2}$$ |UμH|2 are obtained.
We present the measurement of the intrinsic hadronic contamination at the CERN SPS H4 beamline configured to transport electrons and positrons at 100 GeV/c. The analysis, performed using data ...collected by the NA64-e experiment in 2022, is based on calorimetric measurements, exploiting the different interaction mechanisms of electrons and hadrons in the NA64 detector. We determined the contamination by comparing the results obtained using the nominal electron/positron beamline configuration with those from a dedicated setup, in which only hadrons impinged on the detector. We also obtained an estimate of the relative protons, anti-protons and pions yield by exploiting the different absorption probabilities of these particles in matter. We cross-checked our results with a dedicated Monte Carlo simulation for the hadron production at the primary T2 target, finding a good agreement with the experimental measurements.
Abstract
Results of a study of the
$$K^+ \rightarrow \pi ^{0} e^{+} \nu \gamma $$
K
+
→
π
0
e
+
ν
γ
decay at OKA setup are presented. More than 32,000 events of this decay are observed. The ...differential spectra over the photon energy and the photon–electron opening angle in kaon rest frame are presented. The branching ratios, normalized to that of
$$K_{e3}$$
K
e
3
decay are calculated for different cuts on
$$E^*_\gamma $$
E
γ
∗
and
$$cos\Theta ^{*}_{e\gamma }$$
c
o
s
Θ
e
γ
∗
. In particular, the branching ratio for
$$E^{*}_{\gamma }>30$$
E
γ
∗
>
30
MeV and
$$\Theta ^{*}_{e \gamma }>20^{\circ }$$
Θ
e
γ
∗
>
20
∘
is measured R =
$$\frac{Br(K^+ \rightarrow \pi ^{0} e^{+} \nu _{e} \gamma ) }{Br(K^+ \rightarrow \pi ^{0} e^{+} \nu _{e})} $$
B
r
(
K
+
→
π
0
e
+
ν
e
γ
)
B
r
(
K
+
→
π
0
e
+
ν
e
)
= = (0.587±0.010(
stat
.)±0.015(
syst
.))
$$\times 10^{-2}$$
×
10
-
2
, which is in a good agreement with ChPT
$$O(p^{4})$$
O
(
p
4
)
calculations.
Abstract Results of a study of the $$K^+ \rightarrow \pi ^{0} e^{+} \nu \gamma $$ K + → π 0 e + ν γ decay at OKA setup are presented. More than 32,000 events of this decay are observed. The ...differential spectra over the photon energy and the photon–electron opening angle in kaon rest frame are presented. The branching ratios, normalized to that of $$K_{e3}$$ K e 3 decay are calculated for different cuts on $$E^*_\gamma $$ E γ ∗ and $$cos\Theta ^{*}_{e\gamma }$$ c o s Θ e γ ∗ . In particular, the branching ratio for $$E^{*}_{\gamma }>30$$ E γ ∗ > 30 MeV and $$\Theta ^{*}_{e \gamma }>20^{\circ }$$ Θ e γ ∗ > 20 ∘ is measured R = $$\frac{Br(K^+ \rightarrow \pi ^{0} e^{+} \nu _{e} \gamma ) }{Br(K^+ \rightarrow \pi ^{0} e^{+} \nu _{e})} $$ B r ( K + → π 0 e + ν e γ ) B r ( K + → π 0 e + ν e ) = = (0.587±0.010(stat.)±0.015(syst.)) $$\times 10^{-2}$$ × 10 - 2 , which is in a good agreement with ChPT $$O(p^{4})$$ O ( p 4 ) calculations.
On the statistics of ~1.7 x 10.sup.8 interactions of positively charged kaons on copper nuclei, coherent events of the K.sup.+pi.sup.0 system production are selected. The cross sections for the ...Coulomb and coherent strong components and their interference in the region of the K*(892) meson are measured. The partial width for the decay K*(892) right arrow K.sup.+gamma is determined. When studying the mass spectrum of the K.sup.+pi.sup.0 system, an effect which can be interpreted as the interference of the chiral anomaly and the K*(892) s-channel amplitudes is found. This gives an estimate for the ratio of the observed amplitude of the chiral anomaly to the theoretical one: A.sub.exp/A.sub.th = 0.9 ± 0.24(stat.) ± 0.3(syst.).
A class of models of a "dark sector" of particles consider new very weak interaction between the ordinary and dark matter transmitted by U'(1) gauge bosons A' (dark photons) mixing with ordinary ...photons. If such A's exist, they could be searched for in a light-shining-through-a-wall experiment in a high energy electron beam from the CERN SPS. A proposed search project suggests detection of the e+e- pairs produced in the A ' -> e+e - decays with a very small opening angle. Coordinate detectors based on the thin-wall drift tubes with a minimal material budget and a two-hit resolution for e+ and e- tracks separated by more than 0.5 mm are considered as an option for detecting such events.
Abstract A precise measurement of the vector and axial-vector form factors difference $$F_V-F_A$$ FV-FA in the $$K^+\rightarrow {\mu ^+}{\nu _{\mu }}{\gamma }$$ K+→μ+νμγ decay is presented. About 95K ...events of $$K^+\rightarrow {\mu ^+}{\nu _{\mu }}{\gamma }$$ K+→μ+νμγ are selected in the OKA experiment. The result is $$F_V-F_A=0.134\pm 0.021(stat)\pm 0.027(syst)$$ FV-FA=0.134±0.021(stat)±0.027(syst) . Both errors are smaller than in the previous $$F_V-F_A$$ FV-FA measurements.
Study of the decay K+→π+π-π+γ in the OKA experiment Shapkin, M. M.; Akimenko, S. A.; Artamonov, A. V. ...
The European physical journal. C, Particles and fields,
04/2019, Letnik:
79, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A high statistics data sample of the decays of
K
+
mesons to three charged particles was accumulated by the OKA experiment in 2012 and 2013. This allowed to select a clean sample of about 450 events ...with
K
+
→
π
+
π
-
π
+
γ
decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the
K
+
→
π
+
π
-
π
+
γ
, with
E
γ
∗
>
30
MeV
is equal to
(
0.71
±
0.05
)
×
10
-
5
. The measured differential branching fraction over photon energy is compared with the prediction of the chiral perturbation theory to
O
(
p
4
)
. A search for an up-down asymmetry of the photon with respect to the hadronic system decay plane is also performed.
A precise measurement of the vector and axial-vector form factors difference
F
V
-
F
A
in the
K
+
→
μ
+
ν
μ
γ
decay is presented. About 95K events of
K
+
→
μ
+
ν
μ
γ
are selected in the OKA ...experiment. The result is
F
V
-
F
A
=
0.134
±
0.021
(
s
t
a
t
)
±
0.027
(
s
y
s
t
)
. Both errors are smaller than in the previous
F
V
-
F
A
measurements.
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