A
bstract
The cross section of the process
e
+
e
−
→
π
+
π
−
has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000
e
+
e
−
collider VEPP-2000 in the energy region 525
...<
s
<
883 MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb
−
1
. The systematic uncertainty of the cross section determination is 0.8% at
s
>
0
.
600 GeV. The
ρ
meson parameters are obtained as
m
ρ
= 775
.
3 ± 0
.
5 ± 0
.
6 MeV, Γ
ρ
= 145
.
6 ± 0
.
6 ± 0
.
8 MeV,
B
ρ
→
e
+
e−
×
B
ρ
→
π
+
π−
= (4
.
89 ± 0
.
02 ± 0
.
04) × 10
−
5
, and the parameters of the
e
+
e
−
→
ω
→
π
+
π
−
process, suppressed by
G
-parity, as
B
ω
→
e
+
e−
×
B
ω
→
π
+
π−
= (1
.
32 ± 0
.
06 ± 0
.
02) × 10
−
6
and and
ϕ
ρω
= 110
.
7 ± 1
.
5 ± 1
.
0 degrees.
The process
e
+
e
-
→
n
n
¯
is studied in the experiment at the VEPP-2000
e
+
e
-
collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) electromagnetic ...calorimeter is used to select
n
n
¯
events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity.
The process
e
+
e
-
→
η
η
γ
is studied in the center-of-mass energy range 1.17–2.00 GeV using data with an integrated luminosity of 201 pb
-
1
collected by the SND detector at the VEPP-2000
e
+
e
-
...collider. The
e
+
e
-
→
η
η
γ
cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the
ϕ
η
intermediate state. Our result on the
e
+
e
-
→
η
η
γ
cross section is consistent with the
e
+
e
-
→
ϕ
η
measurement in the
ϕ
→
K
+
K
-
mode. The search for radiative processes contributing to the
e
+
e
-
→
η
η
γ
cross section is performed, and no significant signal is observed.
Results are presented from measuring the
cross section and effective neutron timelike form factor. Data are collected in 2020–2021 at the VEPP-2000
collider in the 1891 to 2007 MeV center-of-mass ...range of energies. The general purpose nonmagnetic SND detector is used to detect neutron–antineutron events. The time-of-flight approach is used to select
events. The measured cross section is 0.4–0.6 nbn. The neutron form factor in the investigated range of energies varies from 0.3 to 0.2.
In the experiment with the SND detector at the VEPP-2000
e
+
e
–
collider the cross section for the process
e
+
e
–
→ ηπ
+
π
–
has been measured in the center-of-mass energy range from 1.22 to 2.00 ...GeV. Obtained results are in agreement with previous measurements and have better accuracy. The energy dependence of the
e
+
e
–
→ ηπ
+
π
–
cross section has been fitted with the vector-meson dominance model. From this fit the product of the branching fractions
B
(ρ(1450) → ηπ
+
π
–
)
B
(ρ(1450) → π
+
π
–
) has been extracted and compared with the same products for (ρ(1450) → ωП
0
and (ρ(1450) → π
+
π
–
decays. The obtained cross section data have been also used to test the conservation of vector current hypothesis.
Study of the Process in the Energy Range GeV Achasov, M. N.; Barnyakov, A. Yu; Beloborodov, K. I. ...
Physics of atomic nuclei,
2023/12, Letnik:
86, Številka:
6
Journal Article
Recenzirano
The
cross section is measured in the center-of-mass energy range from 1.07 to 2.00 GeV in the decay channel
,
. The data set with an integrated luminosity of 242 pb
accumulated in the experiment with ...the SND detector at the VEPP-2000
collider is analyzed.
Aim.
Analysis of the influence of species, sex, and age of genus Anas and Aythya individuals on their sensitivity to low pathogenic avian influenza viruses (LPAIV) in the south of Western ...Siberia.
Material and Methods.
Infestation of ducks with the influenza virus was determined by cloacal swabs obtained from 5014 individuals of ducks belonging to the genus Anas and Aythya during the autumn migration period in the south of Western Siberia. Isolation of influenza A virus isolates was carried out according to standard WHO methods. The distribution of infected individuals was estimated with ꭓ
2
. Relative risk (RR) was used to estimate the risk of infection for each individual species.
Results.
Among the examined ducks, the distribution between species differed between infected and uninfected individuals. The common teal was under greater risk of being infected with the avian influenza virus. In this species, the sex of the individual influenced the probability of infestation both in young individuals and the whole age spectrum.
Conclusions.
Individual characteristics of wild dabbling and diving ducks (species, sex, age) affect their infestation with low‐pathogenic avian influenza virus during the autumn migration period in the south of Western Siberia.
The process
is studied in the range of center-of-mass (c.m.) collision energies between 1.05 and 2.00 GeV on the basis of data corresponding to an integrated luminosity of 94.5 pb
that were ...accumulated in an experiment with the SND detector at the VEPP-2000
collider. The cross section for this process was measured for the first time and was found to receive a dominant contribution from the mechanism of a transition through an
intermediate state. The cross section measured for the process
agrees with the results of earlier measurements in the channel
. At a level of 5.7 standard deviations (5.7
), it is established that the process
is not fully described by hadronic intermediate states of the
type. The cross section was measured for this missing contribution, which may be generated by radiative processes—for example,
. It ranges from 15 to 20 pb over a broad energy interval extending from 1.3 to 1.9 GeV.
Search for the Process with the SND Detector Achasov, M. N.; Barnyakov, A. Yu; Beloborodov, K. I. ...
Physics of atomic nuclei,
09/2020, Letnik:
83, Številka:
5
Journal Article
Recenzirano
The results of searches for the process
in an experiment with the SND detector at the VEPP-2000 electron–positron collider are presented. The data used in these searches and based on an integrated ...luminosity of about 87 pb
were accumulated at c.m. energies
between 1.15 and 2 GeV. The upper limits of
pb for
GeV and
pb for
GeV were set at a 90
confidence level.
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