Abstract
The process
$$e^+e^-\rightarrow n{\bar{n}}$$
e
+
e
-
→
n
n
¯
is studied in the experiment at the VEPP-2000
$$e^+e^-$$
e
+
e
-
collider with the SND detector. The technique of the time ...measurements in the multichannel NaI(Tl) electromagnetic calorimeter is used to select
$$n{\bar{n}}$$
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
-
→
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.
Abstract
Using the 1.32
$$\hbox {pb}^{-1}$$
pb
-
1
statistics collected at the
$$J/\psi $$
J
/
ψ
peak with the KEDR detector at the VEPP-4M
$$e^{+}e^{-\, }$$
e
+
e
-
collider, we measured the ...branching fractions of
$$J/\psi $$
J
/
ψ
meson decays to the final states 2(
$$\pi ^{+}\pi ^{-})\pi ^{0}$$
π
+
π
-
)
π
0
,
$$K^{+}K^{-}\pi ^{+}\pi ^{-}\pi ^{0}$$
K
+
K
-
π
+
π
-
π
0
, 2(
$$\pi ^{+}\pi ^{-})$$
π
+
π
-
)
and
$$K^{+}K^{-}\pi ^{+}\pi ^{-}$$
K
+
K
-
π
+
π
-
. The results obtained for the decays
$$J/\psi \rightarrow $$
J
/
ψ
→
2(
$$\pi ^{+}\pi ^{-})\pi ^{0}$$
π
+
π
-
)
π
0
,
$$J/\psi \rightarrow K^{+}K^{-}\pi ^{+}\pi ^{-}\pi ^{0}$$
J
/
ψ
→
K
+
K
-
π
+
π
-
π
0
contradict the measurements performed by other groups in the last century, but agree well with recent results of BABAR and BESIII collaborations.
Upgrade of beam energy measurement system at BEPC-II 张建勇 蔡啸 莫晓虎 郭迪舟 刘佰奇 M. N. Achasov A. A. Krasnov N.Yu. Muchnoi E. E. Pyata E. V. Mamoshkina F. A. Harris
Chinese Physics C, High Energy Physics and Nuclear Physics/Chinese physics C,
07/2016, Letnik:
40, Številka:
7
Journal Article
Recenzirano
Odprti dostop
The beam energy measurement system is of great importance for both BEPC-II accelerator and BES-III detector. The system is based on measuring the energies of Compton back-scattered photons. In order ...to meet the requirements of data taking and improve the measurement accuracy, the system has continued to be upgraded, which involves the updating of laser and optics subsystems, replacement of a view-port of the laser to the vacuum insertion subsystem, the use of an electric cooling system for a high purity germanium detector, and improvement of the data acquisition and processing subsystem. The upgrade system guarantees the smooth and efficient measurement of beam energy at BEPC-II and enables accurate offline energy values for further physics analysis at BES-III.
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
...<
$$ \sqrt{s} $$
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
$$ \sqrt{s} $$
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 beam energy measurement system (BEMS) for the upgraded Beijing electron–positron collider BEPC-II is described. The system is based on measuring the energies of Compton back-scattered photons. ...The relative systematic uncertainty of the electron and positron beam energy determination is estimated as 2×10−5. The relative uncertainty of the beam's energy spread is about 6%.
The results of a beam test of a prototype of the BELLE CsI(Tℓ) calorimeter are reported. The test used beams of photons with energies spanning the range from 20 MeV to 5.4 GeV, produced at ROKK-1M ...facility of the Budker Institute of Nuclear Physics. The single-counter energy-equivalent noise was measured to be ∼200 keV. The design goals for the energy resolution, e.g. 4% at 20 MeV and 1.7% at 5.4 GeV, were achieved using the sum of energy deposits in a 5×5 crystal matrices with a single crystal energy threshold of 0.5 MeV; the summed energy deposit measured in the array corresponds to 97±2% of the incident photon energy over the entire energy range. The average position resolution for 470 MeV energy photons was measured to be 8 mm.
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