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%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In this paper, we present the form factor
measurement in the virtual photon mass range 1 GeV <
< 2 GeV in the
process. Measurements are based on the data acquired by the SND detector at the VEPP-2000
...collider in Novosibirsk. The obtained form factor is approximated in the vector meson dominance (VMD) model. The joint fitting of the form factor obtained in the SND and NA60 experiments is also performed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A striking discrepancy between the results for the ratio of electric and magnetic form factors of the proton obtained by two approaches: the Rosenbluth extraction from the unpolarized cross section ...and the double-polarization measurements has led to a serious re-examination of the role played by two-photon exchange diagrams. The evaluation of such diagrams could not be done in model-independent way, which means an experimental verification is required. One of the direct ways to do this is to measure the ratio of positron-proton and electron-proton elastic scattering cross-sections for identical kinematics. Such a measurement has been performed at the VEPP-3 storage ring at Novosibirsk. There were two runs at beam energies of 1.6 and 1.0 GeV at several ranges of scattering angle. The measurements covered the transferred momentum Q2 up to 1.5 GeV2 and the virtual photon polarization parameter ϵ down to 0.2 . The VEPP-3 experimental approach is described and the results of the measurements are presented.
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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A method for circular e−/e+ accelerator beam energy measurement is proposed. A coordinate of an electron (or a positron) in a focusing magnetic spectrometer built in a circular accelerator depends on ...its energy, two spectrometer parameters, and the circulating beam energy. The spectrometer parameters can be determined using minimum electron energies from Compton backscattering with two laser wavelengths, and a coordinate detector for photons. The photon detector is calibrated separately at well-known beam energy. The VEPP-4M collider has appropriate equipment for the method implementation: built-in focusing magnetic spectrometer, Compton calibration system with two lasers and a photon coordinate detector. Thus, the proposed technique could be implemented with minimum efforts; tests and further upgrade are planned. The beam energy can be defined with expected uncertainty better than 10−4.
The tagging system of the KEDR detector is a symmetrical focusing magnetic spectrometer for electrons and positrons scattered at small angles; it is embedded into the lattice of the VEPP-4M collider ...and intended for two-photon processes study. It measures scattered electron energy with resolution ΔE/E0=0.03% 0.6% (E0 is the beam energy). For precise energy scale calibration two methods are used: tagging of bremsstrahlung electron/positron by the photon energy measured by BGO calorimeter, and direct calibration using Compton backscattering spectrum edge. This report covers design and current status of the calibration system.
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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
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Chinese physics C,
12/2013, Volume:
37, Issue:
12
Journal Article
Peer reviewed
Open access
Data sets were collected with the BESⅢ detector at the BEPCⅡ collider at the center-of-mass energy of √s=3.650 GeV during May 2009 and at √s=3.773 GeV from January 2010 to May 2011. By analyzing the ...large angle Bhabha scattering events, the integrated luminosities of the two data sets are measured to be （44.49±0.02±0.44） pb-1 and （2916.94±0.18±29.17） pb-1, respectively, where the first error is statistical and the second error is systematic.
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