The dynamics of the process
e
+
e
-
→
π
+
π
-
π
0
is studied in the energy region from 1.15 to 2.00 GeV using data accumulated with the SND detector at the VEPP-2000
e
+
e
-
collider. The Dalitz plot ...distribution and
π
+
π
-
mass spectrum are analyzed in a model including the intermediate states
ρ
(
770
)
π
,
ρ
(
1450
)
π
, and
ω
π
0
. As a result, the energy dependences of the
ρ
(
770
)
π
and
ρ
(
1450
)
π
cross sections and the relative phases between the
ρ
(
770
)
π
amplitude and the
ρ
(
1450
)
π
and
ω
π
0
amplitudes are obtained. The
ρ
(
1450
)
π
cross section has a peak in the energy region of the
ω
(
1650
)
resonance (1.55–1.75 GeV). In this energy range the contributions of the
ρ
(
770
)
π
and
ρ
(
1450
)
π
states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the
ρ
(
770
)
π
cross section. We conclude that the intermediate state
ρ
(
1450
)
π
gives a significant contribution to the decay of
ω
(
1650
)
→
π
+
π
-
π
0
, whereas the
ρ
(
770
)
π
mechanism dominates in the decay
ω
(
1420
)
→
π
+
π
-
π
0
.
The process
e
+
e
-
→
η
π
0
γ
is studied in the center-of-mass energy range 1.05–2.00 GeV using data with an integrated luminosity of 94.5
pb
-
1
collected by the SND detector at the VEPP-2000
e
+
e
...-
collider. The
e
+
e
-
→
η
π
0
γ
cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the
ω
η
intermediate state. The measured cross section of the subprocess
e
+
e
-
→
ω
η
→
η
π
0
γ
is consistent with previous measurements in the
e
+
e
-
→
π
+
π
-
π
0
η
mode. It is found, with a significance of
5.6
σ
, that the process
e
+
e
-
→
η
π
0
γ
is not completely described by hadronic vector-pseudoscalar intermediate states. The cross section of this missing contribution, which can originate from radiation processes, e. g.
e
+
e
-
→
a
0
(
1450
)
γ
, is measured. It is found to be 15–20 pb in the wide energy range from 1.3 to 1.9 GeV.
The Spherical Neutral Detector (SND) is intended for study of electron–positron annihilation at the VEPP-2000 e+e− collider (BINP, Novosibirsk) in the center-of-mass energy region below 2GeV. The ...main part of the detector is a three-layer electromagnetic calorimeter based on NaI(Tl) crystals. The physics program of the SND experiment includes a high statistics study of neutron–antineutron production near threshold, for which time measurements in the calorimeter are required. In this paper we describe new shaping and digitizing calorimeter electronics, which allow to reach a time resolution of about 1ns for 100MeV signal and an amplitude resolution of about 250keV.
The process
e
+
e
-
→
K
+
K
-
π
0
is studied with the SND detector at the VEPP-2000
e
+
e
-
collider. Basing on data with an integrated luminosity of 26.4
pb
-
1
we measure the
e
+
e
-
→
K
+
K
-
π
0
...cross section in the center-of-mass energy range from 1.28 up to 2 GeV. The measured mass spectrum of the
K
π
system indicates that the dominant mechanism of this reaction is the transition through the
K
∗
(
892
)
K
intermediate state. The cross section for the
ϕ
π
0
intermediate state is measured separately. The SND results are consistent with previous measurements in the BABAR experiment and have comparable accuracy. We study the effect of the interference between the
ϕ
π
0
and
K
∗
K
amplitudes. It is found that the interference gives sizable contribution to the measured
e
+
e
-
→
ϕ
π
0
→
K
+
K
-
π
0
cross section below 1.7 GeV.
The kinetics of the pseudoliving radical polymerization of 4-vinylpyridine mediated by TEMPO is studied for the first time, and quantitative parameters characterizing the pseudoliving mechanism of ...the reaction, namely, the rate constant of reinitiation and the product of the equilibrium constant and the propagation-rate constant, are estimated. It is shown that the general kinetic features of the TEMPO-mediated polymerizations of 4-vinylpyridine and styrene (the pattern of kinetic curves and the zero reaction order with respect to the concentration of alkoxyamine) and the distinctive features of the polymerization of 4-vinylpyridine (an abnormally low rate and a high steady-state concentration of free TEMPO) are determined by three main factors: the rate of spontaneous initiation, the rate of self-termination of macroradicals, and the constant of equilibrium between active and dormant chains.
The gradient copolymers of styrene and
tert
-butyl acrylate are synthesized by pseudoliving free-radical polymerization in the presence of TEMPO. Despite the inability of
tert
-butyl acrylate to ...undergo polymerization in the presence of the nitroxide TEMPO, the introduction of styrene makes it possible to perform the process under the controlled reversible-inhibition regime. The introduction of an additional high-temperature initiator, cumene hydroperoxide, increases the yield of the copolymer, while the pseudoliving mechanism of the process is preserved. This phenomenon is confirmed by the facts that the concentration of nitroxide remains almost invariable during polymerization and that the molecular mass of the polymerization product increases with conversion. Variations in the composition of the copolymer and its molecular mass during polymerization are evidence that the gradient copolymers are formed.
The homopolymerization of vinyl acetate mediated by dithiobenzoates and trithiocarbonates as reversible addition-fragmentation chain-transfer agents is studied. The polymerization of vinyl acetate is ...characterized by some distinct features: (i) a substantial role of chain-termination reactions involving radical intermediates in the kinetics of the process that increases as the concentrations of the reversible additionfragmentation chain-transfer agent and the initiator increase and as temperature decreases and (ii) the occurrence of side reactions of chain transfer to monomers and polymers. The role of these reactions significantly increases with conversion of the monomer. Thus, in order to prepare a narrowly dispersed PVA via the reversible addition-fragmentation chain-transfer mechanism, the process should be conducted to small conversions (15–20%) at moderately high temperatures (80°C) and at a small molar excess of the reversible addition-fragmentation chain-transfer agent with respect to the initiator. A technique for the synthesis of block copolymers based on PVA and poly(
n
-butyl acrylate) via the reversible addition-fragmentation chain-transfer mechanism is developed.
The electron–ion scattering experiment ELISe is part of the installations envisaged at the new experimental storage ring at the International Facility for Antiproton and Ion Research (FAIR) in ...Darmstadt, Germany. It offers an unique opportunity to use electrons as probe in investigations of the structure of exotic nuclei. The conceptual design and the scientific challenges of ELISe are presented.
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