The recent precise measurements of the e+e− → K+K− and e+e− → KSKL cross sections and the hadronic spectral function of the τ− → K−KSντ decay are used to extract the isoscalar and isovector ...electromagnetic kaon form factors and their relative phase in a model independent way. The experimental results are compared with a fit based on the vector-meson-dominance model.
The recent precise measurements of the
e
+
e
–
→
K
S
K
L
and
e
+
e
–
→
K
+
K
–
cross sections and the hadronic spectral function of the τ
–
→
K
–
K
S
ν
τ
decay are used to extract the isoscalar and ...isovector electromagnetic kaon form factors and their relative phase in a model-independent way. The experimental results are compared with a fit based on the vector-meson-dominance model.
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 SND is a non-magnetic detector at the VEPP-2000 e+e− collider (BINP, Novosibirsk) designed for hadronic cross-section measurements in the center-of-mass energy range up to 2 GeV. The important ...part of the detector is a segmented electromagnetic calorimeter (EMC) with three layers of NaI(Tl) counters. The EMC signal shaping and digitizing electronics based on FADC allow one to obtain both the signal amplitude and the arrival time. We describe the EMC signal processing and how the EMC measured time is applied in event reconstruction and physics analysis.
The SND is a non-magnetic detector deployed at the VEPP-2000
e
+
e
−
collider (BINP, Novosibirsk) for hadronic cross-section measurements in the center of mass energy range below 2 GeV. The important ...part of the detector is a hodoscopic electromagnetic calorimeter (EMC) with three layers of NaI(Tl) counters. EMC signal shaping and digitizing electronics based on FADC allow us to obtain both the energy deposition and the signal arrival time. We demonstrate how EMC time is applied to detect background pileup and cosmic events.
New measurement of the
e
+
e
−
→
nn
̅cross section based on the data set recorded in 2017 with the SND detector at the VEPP-2000
e
+
e
−
collider is presented.Inthe energyrangefromthe ...thresholdupto2GeVthe cross section is almost flat. Its average value is 0.5 nb. The polar angle distribution indicates dominanceof the magnetic formfactor
GM
.
A novel method of studying e{sup +}e{sup -} annihilation into hadrons using initial state radiation at e{sup +}e{sup -} colliders is described. After a brief history of the method, its theoretical ...foundations are considered. Numerous experiments in which exclusive cross sections of e{sup +}e{sup -} annihilation into hadrons below the center-of-mass energy of 5 GeV have been measured are presented. Some applications of the experimental results to fundamental tests of the standard model are listed.
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.
We study the process e+e−→π+π−ηγ, where the photon is radiated from the initial state. About 8000 fully reconstructed events of this process are selected from the BABAR data sample with an integrated ...luminosity of 469 fb−1. Using the π+π−η invariant mass spectrum, we measure the e+e−→π+π−η cross section in the e+e− center-of-mass energy range from 1.15 to 3.5 GeV. The cross section is well described by the Vector-Meson dominance model with four ρ-like states. We observe 49±9 events of the J/ψ decay to π+π−η and measure the product ΓJ/Ψ→e+e−BJ/Ψ→π+π−η=2.34±0.43stat±0.16syst eV.
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