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Register a new userTowards understanding $bbar{b}$ production in $gammagamma$ collisions
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Jiri.Chyla
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Understanding the data on the total cross section $sigma_{tot}($e$^+$e$^-to$e$^+$e$^-bbar{b})$ measured at LEP2 represents a serious challenge for perturbative QCD. In order to unravel the origins of the discrepancy between data and theory, we investigate the dependence of four contributions to this cross section on $gammagamma$ collision energy. As the reliability of the existing calculations of $sigma_{tot}($e$^+$e$^-to$e$^+$e$^-bbar{b})$ depends, among other things, on the stability of calculations of the cross section $sigma_{tot}(gammagammato bbar{b})$ with respect to variations of the renormalization and factorization scales, we investigate this aspect in detail. We show that in most of the region relevant for the LEP2 data the existing QCD calculations of $sigma_{tot}(gammagammato bbar{b})$ do not exhibit a region of local stability and should thus be taken with caution. The source of this instability is suggested and its phenomenological implications for LEP2 data are discussed.
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We study the single production of sneutrinos with two leptons (or jets) via $gammagamma$ collision in an R-parity ($R_{p}$) violating supersymmetric model. The subsequent decays of the sneutrino are also considered. The single production of sneutrinos may provide a significant test of supersymmetry and $R_p$-violation with flavour conserving and flavour changing final states. If such processes coming from $R_p$ violation are not detected, the parameter space of the model will be strongly constrained at the future Linear Collider.
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.
The cross section of bottom quark-antiquark ($bbar{b}$) production in $p$+$p$ collisions at $sqrt{s}=510$ GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider. The results are based on the yield of high mass, like-sign muon pairs measured within the PHENIX muon arm acceptance ($1.2<|y|<2.2$). The $bbar{b}$ signal is extracted from like-sign dimuons by utilizing the unique properties of neutral $B$ meson oscillation. We report a differential cross section of $dsigma_{bbar{b}rightarrow mu^pmmu^pm}/dy = 0.16 pm 0.01~(mbox{stat}) pm 0.02~(mbox{syst}) pm 0.02~(mbox{global})$ nb for like-sign muons in the rapidity and $p_T$ ranges $1.2<|y|<2.2$ and $p_T>1$ GeV/$c$, and dimuon mass of 5--10 GeV/$c^2$. The extrapolated total cross section at this energy for $bbar{b}$ production is $13.1 pm 0.6~(mbox{stat}) pm 1.5~(mbox{syst}) pm 2.7~(mbox{global})~mu$b. The total cross section is compared to a perturbative quantum chromodynamics calculation and is consistent within uncertainties. The azimuthal opening angle between muon pairs from $bbar{b}$ decays and their $p_T$ distributions are compared to distributions generated using {sc ps pythia 6}, which includes next-to-leading order processes. The azimuthal correlations and pair $p_T$ distribution are not very well described by {sc pythia} calculations, but are still consistent within uncertainties. Flavor creation and flavor excitation subprocesses are favored over gluon splitting.
Kinematic correlations for pairs of beauty hadrons, produced in high energy proton-proton collisions, are studied. The data sample used was collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3 fb$^{-1}$. The measurement is performed using inclusive $brightarrow J/psi X$ decays in the rapidity range $2<y^{J/psi}<4.5$. The observed correlations are in good agreement with theoretical predictions.
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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