The NA62 experiment collected the world’s largest dataset of charged kaon decays in 2016–2018, leading to the first measurement of the branching ratio of the ultra-rare
decay, based on 20 candidates. ...The radiative kaon decay
(
) is studied with the data recorded in 2017–2018, achieving the most precise measurements of the
branching ratio and
-asymmetry. Preliminary results from an analysis of the flavour-changing neutral current
decay led to the most precise determination of the form-factor parameters
and
using data collected in 2017–2018. New preliminary results are obtained from an analysis of the
decay using data collected in 2016–2018 with a minimum-bias trigger, leading to an unprecedented sensitivity. This analysis can be naturally extended to search for the
,
process, where
is a short-lived axion-like particle. The NA62 dataset is exploited to search for light feebly interacting particles (heavy neutral leptons) in Kaon decays. Dedicated trigger lines are employed to collect di-lepton final states, which allowed establishing new stringent upper limits on the rates of lepton flavour and lepton number violating kaon decays. NA62 can also be run as a beam-dump experiment, by removing the Kaon production target and moving the upstream collimators into a ‘‘closed’’ position. Analyses of the data taken in beam-dump mode are performed to search for visible decays of exotic mediators, with a particular emphasis on Dark Photon Models.
Observation of K+→π+π0π0γ decay Artamonov, A. V.; Bychkov, V. N.; Donskov, S. V. ...
The European physical journal. C, Particles and fields,
04/2024, Letnik:
84, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The
K
+
→
π
+
π
0
π
0
γ
decay is observed by the OKA collaboration. About 60 events of the decay observed with signal:noise
≈
1
. The branching ratio obtained by normalization to
K
+
→
π
+
π
0
π
0
is ...measured to be
(
3.7
±
0.9
(
s
t
a
t
)
±
0.3
(
s
y
s
t
)
)
×
10
-
6
for
E
γ
∗
>
10
MeV
. The branching ratio,
γ
energy spectrum and angular distribution are consistent with ChPT prediction.
A high-statistics data sample of the
K
+
decays is recorded by the OKA collaboration. A missing mass analysis is performed to search for a light invisible pseudoscalar axion-like particle (ALP)
a
in ...the decay
K
+
→
π
+
π
0
a
. No signal is observed, and the upper limits for the branching ratio of the decay are calculated. The
90
%
confidence level upper limit changes from
2.5
·
10
-
6
to
2
·
10
-
7
for the ALP mass from 0 to 200 MeV/
c
2
, except for the region of
π
0
mass, where the upper limit is
4.4
·
10
-
6
.
Crilin (Crystal Calorimeter with Longitudinal Information) is a semi-homogeneous, longitudinally segmented electromagnetic calorimeter based on high-
Z
, ultra-fast crystals with UV-extended SiPM ...readout. The Crilin design has been proposed as a candidate solution for both a future Muon Collider barrel ECAL and for the Small Angle Calorimeter of the HIKE experiment. As a part of the Crilin development program, we have carried out beam tests of small (10 × 10 × 40 mm
3
) lead fluoride (PbF
2
) and ultra-fast lead tungstate (PbWO
4
, PWO-UF) crystals with 120 GeV electrons at the CERN SPS to study the light yield, timing response, and systematics of light collection with a proposed readout scheme. For a single crystal of PbF
2
, corresponding to a single Crilin cell, a time resolution of better than 25 ps is obtained for
>
3 GeV of deposited energy. For a single cell of PWO-UF, a time resolution of better than 45 ps is obtained for the same range of deposited energy. This timing performance fully satisfies the design requirements for the Muon Collider and HIKE experiments. Further optimizations of the readout scheme and crystal surface preparation are expected to bring further improvements.
Study of K+→π0e+νγ decay with OKA setup Polyarush, A. Yu; Akimenko, S. A.; Artamonov, A. V. ...
The European physical journal. C, Particles and fields,
02/2021, Letnik:
81, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Results of a study of the
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
e
3
decay are calculated for different cuts on
E
γ
∗
and
c
o
s
Θ
e
γ
∗
. In particular, the branching ratio for
E
γ
∗
>
30
MeV and
Θ
e
γ
∗
>
20
∘
is measured R =
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
.))
×
10
-
2
, which is in a good agreement with ChPT
O
(
p
4
)
calculations.
The charge-exchange reaction
,
,
is studied on the upgraded VES facility (U-70, Protvino) upon the interaction of a 29 GeV/
c
meson beam with a beryllium target. There are 905 events of the
system ...selected. The distribution over the invariant mass of the
system,
, shows a near-threshold signal with a mass of
M
~ 1.9 GeV/
c
2
. A five-particle partial wave analysis (PWA) reveals that the scalar state (
) dominates in this mass region. Under the assumption of the resonant nature of the signal, the following values of its mass and width are obtained:
M
= 1819 ± 27 MeV/
c
2
and Γ = 167 ± 18 MeV/
c
2
.
The
T
-odd correlation
, which is the mixed product of the momenta of
,
, and γ in the system of rest of the kaon divided by
, has been measured in the
K
+
→ π
0
e
+
ν
e
γ radiative decay among 101 ...200 candidate events detected at the OKA setup. The asymmetry of the distribution in
is characterized by the ratio
, where
is the number of events with positive (negative) ξ. The value
= (+0.1 ± 3.9(stat.) ± 1.7(syst.)) × 10
–3
or
(90% C.L.) has been obtained.
On the statistics of ~1.7 × 10
8
interactions of positively charged kaons on copper nuclei, coherent events of the
K
+
π
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) →
K
+
γ is determined. When studying the mass spectrum of the
K
+
π
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
exp
/
A
th
= 0.9 ± 0.24(stat.) ± 0.3(syst.).
Search for heavy neutrino in K+→μ+νH decay Sadovsky, A. S.; Kurshetsov, V. F.; Filin, A. P. ...
The European physical journal. C, Particles and fields,
02/2018, Letnik:
78, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A high statistics data sample of the
K
+
→
μ
+
ν
μ
decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search for the decay channel
K
+
→
μ
+
ν
H
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
ν
H
<
375
)
MeV
/
c
2
. As a result, upper limits on the branching ratio and on the value of the mixing element
|
U
μ
H
|
2
are obtained.
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