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Register a new userMeasurement of the energy dependence of the $e^+e^-to Bbar{B}$, $Bbar{B}^*$ and $B^*bar{B}^*$ exclusive cross sections
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We report the first measurement of the exclusive cross sections $e^+e^-to Bbar{B}$, $e^+e^-to Bbar{B}^*$, and $e^+e^-to B^*bar{B}^*$ in the energy range from 10.63 GeV to 11.02 GeV. The $B$ mesons are fully reconstructed in a large number of hadronic final states and the three channels are identified using a beam-constrained-mass variable. The shapes of the exclusive cross sections show oscillatory behavior with several maxima and minima. The results are obtained using data collected by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider.
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We present NLO QCD results for W/Z gauge boson production with bottom quark pairs at the Tevatron including full bottom-quark mass effects. We study the impact of QCD corrections on both total cross-section and invariant mass distribution of the bottom-quark pair. Including NLO QCD corrections greatly reduces the dependence of the tree-level cross-section on the renormalization and factorization scales. We also compare our calculation to a calculation that considers massless bottom quarks and find that the bottom-quark mass effects amount to about 8-10% of the total NLO QCD cross-section and can impact the shape of the bottom-quark pair invariant mass distribution, in particular in the low invariant mass region.
We report the analysis of the three-body e+e- => B B-bar pi, B B*-bar pi, and B* B*-bar pi processes, including the first observation of the Zb+-(10610) =>[B B*-bar+c.c.]+- and Zb+-(10650) => [B*B*-bar]+- transitions. We measure visible cross sections for the three-body production of sigma_vis(e+e- => [B B*-bar+c.c.]+-pi-+=(11.2+-1.0(stat.)+-1.2(syst.)) pb and sigma_vis(e+e- => [B*B*-bar]+-pi-+)=(5.61+-0.73(stat.)+-0.66(syst.)) pb and set a 90% C.L. upper limit of sigma_vis(e+e- => [BB-bar]+-pi-+)<2.1 pb. The results are based on a 121.4 1/fb data sample collected with the Belle detector at a center-of-mass energy near the Y(5S) peak.
We indicated in our previous work that for QED the role of the scalar potential which appears at the loop level is much smaller than that of the vector potential and in fact negligible. But the situation is different for QCD, one reason is that the loop effects are more significant because $alpha_s$ is much larger than $alpha$, and secondly the non-perturbative QCD effects may induce a sizable scalar potential. In this work, we phenomenologically study the contribution of the scalar potential to the spectra of charmonia, bottomonia and $bbar c(bar b c)$ family. Taking into account both vector and scalar potentials, by fitting the well measured charmonia and bottomonia spectra, we re-fix the relevant parameters and test them by calculating other states of not only the charmonia, bottomonia, but also further the $bbar c$ family. We also consider the Lamb shift of the spectra.
There has been much theoretical speculation about the existence of a deeply bounded tetra-bottom state. Such a state would not be expected to be more than a GeV below $UpsilonUpsilon$ threshold. If such a state exists below the $eta_beta_b$ threshold it would be narrow, as Zweig allowed strong decays are kinematically forbidden. Given the observation of $Upsilon$ pair production at CMS, such a state with a large branching fraction into $Upsilon Upsilon^*$ is likely discoverable at the LHC. The discovery mode is similar to the SM Higgs decaying into four leptons through the $Z Z^*$ channel. The testable features of both production and the four lepton decays of such a tetra-bottom ground state are presented. The assumptions required for each feature are identified, allowing the application of our results more generally to a resonance decaying into four charged leptons (through the $UpsilonUpsilon^*$ channel) in the same mass region.
A search for the decays $B^0_sto e^+e^-$ and $B^0to e^+e^-$ is performed using data collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$, $8$ and $13,text{TeV}$, corresponding to integrated luminosities of $1$, $2$ and $2,text{fb}^{-1}$, respectively. No signal is observed. Assuming no contribution from $B^0to e^+e^-$ decays, an upper limit of $mathcal{B}(B^0_sto e^+e^-)<9.4,(11.2)times10^{-9}$ is obtained at $90,(95),%$ confidence level. If no $B^0_sto e^+e^-$ contribution is assumed, a limit of $mathcal{B}(B^0to e^+e^-)<2.5,(3.0)times10^{-9}$ is determined at $90,(95),%$ confidence level. These upper limits are more than one order of magnitude lower than the previous values.
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