Using a sample of about 10(10) J/Psi events collected at a center-of-mass energy root s = 3.097 GeV with the BESIII detector, the electromagnetic Dalitz decays J/Psi -> e(+)e(-) pi(+)pi(-) eta', ...with eta' -> gamma pi(+)pi(-) and eta' -> pi(+)pi(-) eta, have been studied. The decay J/Psi -> e(+)e(-) X(1835) is observed with a significance of 15 sigma, and also an e(+)e(-) invariant-mass dependent transition form factor of J/Psi -> e(+)e(-) X(1835) is presented for the first time. The intermediate states X(2120) and X(2370) are also observed in the pi(+)pi(-) eta' invariant-mass spectrum with significances of 5.3 sigma and 7.3 sigma. The corresponding product branching fractions for J/Psi -> e(+)e(-) X, X -> pi(+) pi(-) eta' X = X(1835), X(2120), and X(2370) are reported.
We present the first measurements of the electric and magnetic form factors of the neutron in the timelike (positive q^{2}) region as function of four-momentum transfer. We explored the differential ...cross sections of the reaction e^{+}e^{-}→nover ¯n with data collected with the BESIII detector at the BEPCII accelerator, corresponding to an integrated luminosity of 354.6 pb^{-1} in total at twelve center-of-mass energies between sqrts=2.0-2.95 GeV. A relative uncertainty of 18% and 12% for the electric and magnetic form factors, respectively, is achieved at sqrts=2.3935 GeV. Our results are comparable in accuracy to those from electron scattering in the comparable spacelike region of four-momentum transfer. The electromagnetic form factor ratio R_{em}≡|G_{E}|/|G_{M}| is within the uncertainties close to unity. We compare our result on |G_{E}| and |G_{M}| to recent model predictions, and the measurements in the spacelike region to test the analyticity of electromagnetic form factors.
A
bstract
Based on 4.5 fb
−
1
data taken at seven center-of-mass energies ranging from 4.600 to 4.699 GeV with the BESIII detector at the BEPCII collider, we measure the branching fractions of
Λ
c
+
...→
Σ
+
+
hadrons
relative to
Λ
c
+
→
Σ
+
π
+
π
−
. Combining with the world average branching fraction of
Λ
c
+
→
Σ
+
π
+
π
−
, their branching fractions are measured to be (0
.
377
±
0
.
042
±
0
.
020
±
0
.
021)% for
Λ
c
+
→
Σ
+
K
+
K
−
, (0
.
200
±
0
.
023
±
0
.
011
±
0
.
011)% for
Λ
c
+
→
Σ
+
K
+
π
−
, (0
.
414
±
0
.
080
±
0
.
030
±
0
.
023)% for
Λ
c
+
→
Σ
+
ϕ
and (0
.
197
±
0
.
036
±
0
.
009
±
0
.
011)% for
Λ
c
+
→ Σ
+
K
+
K
−
(non-
ϕ
). In all the above results, the first uncertainties are statistical, the second are systematic and the third are from external input of the branching fraction of
Λ
c
+
→
Σ
+
π
+
π
−
. Since no signal for
Λ
c
+
→
Σ
+
K
+
π
−
π
0
is observed, the upper limit of its branching fraction is determined to be 0.13% at the 90% confidence level.
Using (10.087±0.044)×10^{9} J/ψ events collected with the BESIII detector at the BEPCII storage ring, the processes Λp→Λp and Λover ¯p→Λover ¯p are studied, where the Λ/Λover ¯ baryons are produced ...in the process J/ψ→ΛΛover ¯ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in -0.9≤cosθ_{Λ/Λover ¯}≤0.9 are measured to be σ(Λp→Λp)=(12.2±1.6_{stat}±1.1_{syst}) and σ(Λover ¯p→Λover ¯p)=(17.5±2.1_{stat}±1.6_{syst}) mb at the Λ/Λover ¯ momentum of 1.074 GeV/c within a range of ±0.017 GeV/c, where the θ_{Λ/Λover ¯} are the scattering angles of the Λ/Λover ¯ in the Λp/Λover ¯p rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for Λp→Λp, and a strong forward peak for Λover ¯p→Λover ¯p. We present an approach to extract the total elastic cross sections by extrapolation. The study of Λover ¯p→Λover ¯p represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.Using (10.087±0.044)×10^{9} J/ψ events collected with the BESIII detector at the BEPCII storage ring, the processes Λp→Λp and Λover ¯p→Λover ¯p are studied, where the Λ/Λover ¯ baryons are produced in the process J/ψ→ΛΛover ¯ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in -0.9≤cosθ_{Λ/Λover ¯}≤0.9 are measured to be σ(Λp→Λp)=(12.2±1.6_{stat}±1.1_{syst}) and σ(Λover ¯p→Λover ¯p)=(17.5±2.1_{stat}±1.6_{syst}) mb at the Λ/Λover ¯ momentum of 1.074 GeV/c within a range of ±0.017 GeV/c, where the θ_{Λ/Λover ¯} are the scattering angles of the Λ/Λover ¯ in the Λp/Λover ¯p rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for Λp→Λp, and a strong forward peak for Λover ¯p→Λover ¯p. We present an approach to extract the total elastic cross sections by extrapolation. The study of Λover ¯p→Λover ¯p represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.
A
bstract
Using a sample of (10
.
09
±
0
.
04)
×
10
9
J/ψ
decays collected with the BESIII detector, partial wave analyses of the decay
J
/
ψ
→
γ
K
S
0
K
S
0
π
0
are performed within the
K
S
0
K
S
0
...π
0
invariant mass region below 1.6 GeV/
c
2
. The covariant tensor amplitude method is used in both mass independent and mass dependent approaches. Both analysis approaches exhibit dominant pseudoscalar and axial vector components, and show good consistency for the other individual components. Furthermore, the mass dependent analysis reveals that the
K
S
0
K
S
0
π
0
invariant mass spectrum for the pseudoscalar component can be well described with two isoscalar resonant states using relativistic Breit-Wigner model, i.e., the
η
(1405) with a mass of
1391.7
±
0.7
−
0.3
+
11.3
MeV/
c
2
and a width of
60.8
±
1.2
−
12.0
+
5.5
MeV, and the
η
(1475) with a mass of
1507.6
±
1.6
−
32.2
+
15.5
MeV/
c
2
and a width of
115.8
±
2.4
−
10.9
+
14.8
MeV. The first and second uncertainties are statistical and systematic, respectively. Alternate models for the pseudoscalar component are also tested, but the description of the
K
S
0
K
S
0
π
0
invariant mass spectrum deteriorates significantly.
A
bstract
Using 6
.
32 fb
−
1
of
e
+
e
−
collision data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we perform an amplitude analysis of the decay
D
...s
+
→ K
+
π
+
π
−
and determine the amplitudes of the various intermediate states. The absolute branching fraction of
D
s
+
→ K
+
π
+
π
−
is measured to be (6
.
11
±
0
.
18
stat
.
±
0
.
11
syst
.
)
×
10
−
3
. The branching fractions of the dominant intermediate processes
D
s
+
→ K
+
ρ
0
, ρ
0
→ π
+
π
−
and
D
s
+
→ K
*
(892)
0
π
+
, K
*
(892)
0
→ K
+
π
−
are determined to be (1
.
96
±
0
.
19
stat
.
±
0
.
23
syst
.
)
×
10
−
3
and (1
.
85
±
0
.
12
stat
.
±
0
.
13
syst
.
)
×
10
−
3
, respectively. The intermediate resonances
f
0
(500),
f
0
(980), and
f
0
(1370) are observed for the first time in this channel.
Using (10 087±44)×10^{6} J/ψ events collected with the BESIII detector, the radiative hyperon decay Σ^{+}→pγ is studied at an electron-positron collider experiment for the first time. The absolute ...branching fraction is measured to be (0.996±0.021_{stat}±0.018_{syst})×10^{-3}, which is lower than its world average value by 4.2 standard deviations. Its decay asymmetry parameter is determined to be -0.652±0.056_{stat}±0.020_{syst}. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by 78% and 34%, respectively.
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