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Register a new userThe implications of final L3 measurement of $sigma_{tot}(gammagammato bbar{b}
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Jiri Chyla
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he excess of data on the total cross section of $bar{b}b$ production in $gammagamma$ collisions over QCD predictions, observed by L3, OPAL and DELPHI Collaborations at LEP2, has so far defied explanation. The recent final analysis of L3 data has brought important new information concerning the dependence of the observed excess on the $gammagamma$ collisions energy $W_{gammagamma}$. The implications of this dependence are discussed.
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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.
Though the neutron mass is larger than the proton mass and obviously one expects in $e^+e^-$ annihilation a creation of more $p bar p$ pairs in comparison with $n bar n$ at the same energy, just the opposite inequality for the corresponding total cross sections $sigma_{tot}(e^+e^- to n bar n) > sigma_{tot}(e^+e^- to p bar p)$ has been revealed in the analysis of only the present time existing proton electromagnetic form factors data by the unitary and analytic approach.
We discuss thw relations between the elastic and inelastic cross-sections valid for the shadow and reflective modes of the elastic scattering. Considerations are based on the unitarity arguments. It is shown that the redistribution of the total interaction probability between the elastic and inelastic interactions can lead to increasing ratio of $sigma_{el}(s)/sigma_{tot}(s)$ at the LHC energies in presence of the reflective scattering mode. The form of the inelastic overlap function becomes peripheral due to the negative feedback. In the absorptive scattering mode, the mechanism of this increase is a different one since the impact parameter dependence of the inelastic interactions probability is central in this case. A short notice is also given on the slope parameter and the leading contributions to its energy dependence in the both modes.
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.
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.
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