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Register a new userBranching fraction measurement of $J/psi rightarrow K_S K_L$ and search for $J/psi rightarrow K_S K_S$
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Using a sample of $1.31 times 10^{9}$ $J/psi$ events collected with the BESIII detector at the BEPCII collider, we study the decays of $J/psi rightarrow K_S K_L$ and $K_S K_S$. The branching fraction of$J/psirightarrow K_S K_L$ is determined to be ${cal B}(J/psi rightarrow K_S K_L)=(1.93pm0.01~(rm{stat.})pm0.05~(rm{syst.}))times10^{-4}$, which significantly improves on previous measurements. No clear signal is observed for the $J/psi rightarrow K_S K_S$ process, and the upper limit at the 95% confidence level for its branching fraction is determined to be ${cal B}(J/psi rightarrow K_S K_S)<1.4times10^{-8}$, which improves on the previous searches by two orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.
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The $B_s^0to J/psi K_S^0$ branching fraction is measured in a data sample corresponding to 0.41$fb^{-1}$ of integrated luminosity collected with the LHCb detector at the LHC. This channel is sensitive to the penguin contributions affecting the sin2$beta$ measurement from $B^0to J/psi K_S^0$ The time-integrated branching fraction is measured to be $BF(B_s^0to J/psi K_S^0)=(1.83pm0.28)times10^{-5}$. This is the most precise measurement to date.
This paper reports the first measurement of the effective B_s^0 -> J/{psi} K_S^0 lifetime and an updated measurement of its time-integrated branching fraction. Both measurements are performed with a data sample, corresponding to an integrated luminosity of 1.0 fb^{-1} of pp collisions, recorded by the LHCb experiment in 2011 at a centre-of-mass energy of 7 TeV. The results are: tau_J/{psi}K_S^0 = 1.75 +/- 0.12 (stat) +/- 0.07 (syst) and BR(B_s^0 -> J/{psi} K_S^0) = (1.97 +/- 0.23) X 10^{-5}. For the latter measurement, the uncertainty includes both statistical and systematic sources.
Using $pp$ collision data collected by LHCb at center-of-mass energies $sqrt{s}$ = 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$, the ratio of the branching fraction of the $B_c^+ rightarrow psi(2S)pi^+$ decay relative to that of the $B_c^+ rightarrow J/psipi^+$ decay is measured to be 0.268 $pm$ 0.032 (stat) $pm$ 0.007 (syst) $pm$ 0.006 (BF). The first uncertainty is statistical, the second is systematic, and the third is due to the uncertainties on the branching fractions of the $J/psi rightarrow mu^+mu^-$ and $psi(2S) rightarrow mu^+mu^-$ decays. This measurement is consistent with the previous LHCb result, and the statistical uncertainty is halved.
A measurement of the branching fraction of the decay $B_s^0 to K_S^0 K_S^0$ is performed using proton-proton collision data corresponding to an integrated luminosity of 5 $fb^{-1}$ collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be BR($B_s^0 to K_S^0 K_S^0$) = [8.3 $pm$ 1.6 (stat) $pm$ 0.9 (syst) $pm$ 0.8 (norm) $pm$ 0.3 ($f_s/f_d$)] $times 10^{-6}$ , where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode $B^0 to phi K_S^0$ and the ratio of hadronization fractions $f_s/f_d$. This is the most precise measurement of this branching fraction to date. Furthermore, a measurement of the branching fraction of the decay $B^0 to K_S^0 K_S^0$ is performed relative to that of the $B_s^0 to K_S^0 K_S^0$ channel, and is found to be $frac{BR(B^0 to K_S^0 K_S^0)}{BR(B_s^0 to K_S^0 K_S^0)}$ = [7.5 $pm$ 3.1 (stat) $pm$ 0.5 (syst) $pm$ 0.3 ($f_s/f_d$)] $times 10^{-2}$.
The first measurements of the coherence factor R_{K_S^0Kpi} and the average strong--phase difference delta^{K_S^0Kpi} in D^0 to K_S^0 K^mppi^pm decays are reported. These parameters can be used to improve the determination of the unitary triangle angle gamma in B^- rightarrow $widetilde{D}K^-$ decays, where $widetilde{D}$ is either a D^0 or a D^0-bar meson decaying to the same final state, and also in studies of charm mixing. The measurements of the coherence factor and strong-phase difference are made using quantum-correlated, fully-reconstructed D^0D^0-bar pairs produced in e^+e^- collisions at the psi(3770) resonance. The measured values are R_{K_S^0Kpi} = 0.70 pm 0.08 and delta^{K_S^0Kpi} = (0.1 pm 15.7)$^circ$ for an unrestricted kinematic region and R_{K*K} = 0.94 pm 0.12 and delta^{K*K} = (-16.6 pm 18.4)$^circ$ for a region where the combined K_S^0 pi^pm invariant mass is within 100 MeV/c^2 of the K^{*}(892)^pm mass. These results indicate a significant level of coherence in the decay. In addition, isobar models are presented for the two decays, which show the dominance of the K^*(892)^pm resonance. The branching ratio {B}(D^0 rightarrow K_S^0K^+pi^-)/{B}(D^0 rightarrow K_S^0K^-pi^+) is determined to be 0.592 pm 0.044 (stat.) pm 0.018 (syst.), which is more precise than previous measurements.
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