The development of the new spectrometric channel for the SND electromagnetic calorimeter is described. The time resolution of about 1 ns is achieved at an energy deposition in the calorimeter crystal ...of 100 MeV . The amplitude resolution is about 250 keV.
Recent results on
e
+
e
−
annihilation to hadrons from SND experiment at VEPP-2000 collider are presented. Corresponding data set is about 200 pb
−1
of integrated luminosity collected at the energy ...region below 2 GeV. The processes
e
+
e
−
→ π
+
π
−
, π
0
γ, ωπ
0
, π
+
π
−
π
0
, ηπ
+
π
−
π
0
,
η
, π
+
π
−
4π
0
have been studied. Searches for
e
+
e
−
annihilation to
C
-even resonances η and
f
1(1285) were done.
Using a data sample corresponding to an integrated luminosity of 2.93 fb−1 recorded by the BESIII detector at a center-of-mass energy of 3.773 GeV, we present an analysis of the decays D0 → π−π0e+νe ...and D+ → π−π+e+νe. By performing a partial wave analysis, the π+π− S-wave contribution to D+ → π−π+e+νe is observed to be (25.7 ± 1.6 ± 1.1)% with a statistical significance greater than 10σ, besides the dominant P-wave contribution. This is the first observation of the S-wave contribution. We measure the branching fractions B(D0 → ρ−e+νe) = (1.445 ± 0.058 ± 0.039) × 10−3, B(D+ → ρ0e+νe) = (1.860 ± 0.070 ± 0.061) × 10−3, and B(D+ → f0(500)e+νe, f0(500) → π+π−) = (6.30 ± 0.43 ± 0.32) × 10−4. An upper limit of B(D+ → f0(980)e+νe, f0(980) → π+π−) < 2.8 × 10−5 is set at the 90% confidence level. We also obtain the hadronic form factor ratios of D → ρe+νe at q2 = 0 assuming the single-pole dominance parametrization: rV = {V(0)/A1(0)} = 1.695 ± 0.083 ± 0.051, r2 = {A2(0)/A1(0)} = 0.845 ± 0.056 ± 0.039.
Using a data set of 2.93 fb taken at a center-of-mass energy root s = 3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a ...dark photon. We examine the initial state radiation reactions e(+)e(-) -> e(+)e(-) gamma(ISR) and e(+)e(-) -> mu(+)mu(-) gamma(ISR) for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/c(2) and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range.
Using 1310.6×106 J/ψ and 447.9×106 ψ(3686) events collected with the BESIII detector at the BEPCII e+e− collider, the branching fractions and the angular distributions of J/ψ and ψ(3686) decays to ...ΛΛ¯ and Σ0Σ¯0 final states are measured. The branching fractions are determined, with much improved precision, to be 19.43±0.03±0.33, 11.64±0.04±0.23, 3.97±0.02±0.12 and 2.44±0.03±0.11 for J/ψ→ΛΛ¯, J/ψ→Σ0Σ¯0, ψ(3686)→ΛΛ¯ and ψ(3686)→Σ0Σ¯0, respectively. The polar angular distributions of ψ(3686) decays are measured for the first time, while those of J/ψ decays are measured with much improved precision. In addition, the ratios of branching fractions B(ψ(3686)→ΛΛ¯)B(J/ψ→ΛΛ¯) and B(ψ(3686)→Σ0Σ¯0)B(J/ψ→Σ0Σ¯0) are determined to test the “12% rule.”
Using e+e− annihilation data corresponding to an integrated luminosity of 3.19 fb−1 collected at a center-of-mass energy of 4.178 GeV with the BESIII detector, we measure the absolute branching ...fractions BDs+→ηe+νe = (2.323±0.063stat ± 0.063syst)% and BDs+→η′e+νe = (0.824±0.073stat ± 0.027syst)% via a tagged analysis technique, where one Ds is fully reconstructed in a hadronic mode. Combining these measurements with previous BESIII measurements of BD+→η(′)e+νe, the η−η′ mixing angle in the quark flavor basis is determined to be ϕP = (40.1±2.1stat ± 0.7syst)°. From the first measurements of the dynamics of Ds+ → η(′)e+νe decays, the products of the hadronic form factors f+η(′)(0) and the Cabibbo-Kobayashi-Maskawa matrix element |Vcs| are determined with different form factor parametrizations. For the two-parameter series expansion, the results are f+η(0)|Vcs| = 0.4455±0.0053stat±0.0044syst and f+η′(0)|Vcs|=0.477±0.049stat±0.011syst.
We report the first observation of D+→τ+ντ with a significance of 5.1σ. We measure B(D+→τ+ντ)=(1.20±0.24stat±0.12syst)×10−3. Taking the world average B(D+→μ+νμ)=(3.74±0.17)×10−4, we obtain ...Rτ/μ=Γ(D+→τ+ντ)/Γ(D+→μ+νμ)=3.21±0.64stat±0.43syst., which is consistent with the standard model expectation of lepton flavor universality. Using external inputs, our results give values for the D+ decay constant fD+ and the Cabibbo-Kobayashi-Maskawa matrix element |Vcd| that are consistent with, but less precise than, other determinations.
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