From 1310.6 x 10(6) J/psi and 448.1 x 10(6) psi (3686) events collected with the BESIII experiment, we report the first observation of Sigma(+) and (Sigma) over bar (-) spin polarization in e(+)e(-) ...-> J/psipsi(3686) -> Sigma(+)(Sigma) over bar (-) decays. The relative phases of the form factors Delta Phi have been measured to be (-15.5 +/- 0.7 +/- 0.5)degrees and (21.7 +/- 4.0 +/- 0.8)degrees with J/psi and psi(3686) data, respectively. The nonzero value of Delta Phi allows for a direct and simultaneous measurement of the decay asymmetry parameters of Sigma(+)-> p pi(0) (alpha(0) = -0.998 +/- 0.037 +/- 0.009) and (Sigma) over bar (-)-> (p) over bar pi(0) ((alpha) over bar (0) = 0.990 +/- 0.037 +/- 0.011), the latter value being determined for the first time. The average decay asymmetry, (alpha(0 )- (alpha) over bar (0))/2, is calculated to be -0.994 +/- 0.004 +/- 0.002. The CP asymmetry A(CP,Sigma) = (alpha(0) + (alpha) over bar (0))/(alpha(0) - (alpha) over bar (0)) = -0.004 +/- 0.037 +/- 0.010 is extracted for the first time, and is found to be consistent with CP conservation.
The process Formula omitted is studied in the center-of-mass energy range 1.17-2.00 GeV using data with an integrated luminosity of 201 pb Formula omitted collected by the SND detector at the ...VEPP-2000 Formula omitted collider. The Formula omitted cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the Formula omitted intermediate state. Our result on the Formula omitted cross section is consistent with the Formula omitted measurement in the Formula omitted mode. The search for radiative processes contributing to the Formula omitted cross section is performed, and no significant signal is observed.
Calibration of the calorimeter signal waveform in the SND detector Achasov, M.N.; Bogdanchikov, A.G.; Druzhinin, V.P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Letnik:
936
Journal Article
Recenzirano
The new spectrometric channel for the Spherical Neutral Detector (SND) electromagnetic calorimeter (EMC) is described. It provides measurement of the calorimeter signal arrival time and amplitude ...with 1 ns and 250 keV resolutions, respectively. The new electronics is useful for reliable detection of low-speed anti-neutrons from the e+e−→nn̄ reaction near threshold and needed for increasing the EMC operation rate. The algorithm of determination of signal parameters (time, amplitude) is based on invariability of the signal waveform. We present the procedure of the waveform calibration using signals from cosmic-muon and Bhabha scattering events.
Based on an e+e− collision data sample corresponding to an integrated luminosity of 567 pb−1 taken at the center-of-mass energy of s=4.6 GeV with the BESIII detector, we measure the absolute ...branching fraction of the inclusive decay Λc+→Λ+X to be B(Λc+→Λ+X)=(38.2−2.2+2.8±0.9)% using the double-tag method, where X refers to any possible final state particles. In addition, we search for direct CP violation in the charge asymmetry of this inclusive decay for the first time, and obtain ACP≡B(Λc+→Λ+X)−B(Λ¯c−→Λ¯+X)/B(Λc+→Λ+X)+B(Λ¯c−→Λ¯+X)=(2.1−6.6+7.0±1.6)%, a statistically limited result with no evidence of CP violation.
Using a data sample of ${e}^{+}{e}^{{-}}$ collisions corresponding to an integrated luminosity of $567\text{ }\text{ }{\mathrm{pb}}^{{-}1}$ collected at a center-of-mass energy of $\sqrt{s}=4.6\text{ ...}\text{ }\mathrm{GeV}$ with the BESIII detector, we measure the absolute branching fraction of the inclusive semileptonic ${\mathrm{{\Lambda}}}_{c}^{+}$ decay with a double-tag method. We obtain $\mathcal{B}({\mathrm{{\Lambda}}}_{c}^{+}{\rightarrow}X{e}^{+}{{\nu}}_{e})=(3.95\pm{}0.34\pm{}0.09)%$, where the first uncertainty is statistical and the second systematic. Using the known ${\mathrm{{\Lambda}}}_{c}^{+}$ lifetime and the charge-averaged semileptonic decay width of nonstrange charmed mesons (${D}^{0}$ and ${D}^{+}$), we obtain the ratio of the inclusive semileptonic decay widths $\mathrm{{\Gamma}}({\mathrm{{\Lambda}}}_{c}^{+}{\rightarrow}X{e}^{+}{{\nu}}_{e})/\overline{\mathrm{{\Gamma}}}(D{\rightarrow}X{e}^{+}{{\nu}}_{e})=1.26\pm{}0.12$.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring, the cross section of the inclusive process e + e − → η + X , normalized by the total cross section of e + e ...− → hadrons , is measured at eight center-of-mass energy points from 2.0000 to 3.6710 GeV. These are the first measurements with momentum dependence in this energy region. Our measurement shows a significant discrepancy compared to the existing fragmentation functions. To address this discrepancy, a new QCD analysis is performed at the next-to-next-to-leading order with hadron mass corrections and higher twist effects, which can explain both the established high-energy data and our measurements reasonably well. Published by the American Physical Society 2024
The Spherical Neutral Detector (SND) is an experiment for e+e− annihilation study at low energies 0.2−2 GeV. The light quark anti−quark bound states are the main subject of study at these energies. ...They express themselves as resonances in the e+e− hadronic cross sections. Hadronic cross sections could be recalculated to hadronic vacuum polarization (HVP). The Standard Model predictions today are limited by HVP which is not calculable with modern QCD theory. In this talk we present the review of the hadronic cross sections measurements at SND and new measurements: e+e− → π+π−, π0γ, π+π−π0, ωπ0, K+K−η, η, KsKLπ0, π+π−π0η, ωπ0η e.t.c.
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