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Register a new userWould a Deeply Bound $bbar b bbar b$ Tetraquark Meson be Observed at the LHC?
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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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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.
A feasibility study for an experimental analysis searching for $tbar{t}H(Hrightarrow bbar{b})$ production at the LHC and its high luminosity phase is presented in this note. Unlike search strategies currently being used in experimental collaborations, the present analysis exploits jet substructure techniques and focuses on the reconstruction of boosted Higgs bosons, to obtain sensitivity to the signal in a simple cut-based analysis. The $tbar{t} +$ jets background may be constrained in the proposed analysis through a control region with very small signal contamination. Using this analysis strategy, the $tbar{t}H(Hrightarrow bbar{b})$ process could be observed at the LHC, in the semi-leptonic channel alone, with a significance of $5.41pm 0.12$ for $mathcal{L}=300,mbox{fb}^{-1}$. For the same integrated luminosity, in the High Luminosity LHC scenario with an upgraded detector, a significance of $6.13pm 0.11$ may be obtained. The top Yukawa coupling could be measured with a 35% uncertainty using $mathcal{L}=300,mbox{fb}^{-1}$ of LHC data and of 17% at the HL-LHC scenario with $mathcal{L}=3000,mbox{fb}^{-1}$. In the same luminosity scenarios, the signal strength is equally expected to have a 18$%$ and 5$%$ uncertainty, respectively. Finally, it was found that re-clustered jets may be used without loss of efficiency.
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.
We analyse three different New Physics scenarios for Delta F=2 flavour-changing neutral currents in the quark sector in the light of recent data on neutral-meson mixing. We parametrise generic New Physics contributions to B_q-Bbar_q mixing (q=d,s), in terms of one complex quantity Delta_q, while three parameters Delta_K^tt, Delta_K^ct and Delta_K^cc are needed to describe K-Kbar mixing. In Scenario I, we consider uncorrelated New Physics contributions in the B_d, B_s, and K sectors. In this scenario, it is only possible to constrain the parameters Delta_d and Delta_s whereas there are no non-trivial constraints on the kaon parameters. In Scenario II, we study the case of Minimal Flavour Violation (MFV) and small bottom Yukawa coupling and Scenario III is the generic MFV case with large bottom Yukawa couplings. Our quantitative analyses consist of global CKM fits within the Rfit frequentist statistical approach, determining the Standard Model parameters and the new physics parameters of the studied scenarios simultaneously. We find that the recent measurements indicating discrepancies with the Standard Model are well accomodated in Scenarios I and III with new mixing phases, with a slight preference for Scenario I that permits different new CP phases in the B_d and B_s systems. Within our statistical framework, we find evidence of New Physics in both B_d and B_s systems. The Standard-Model hypothesis Delta_d=Delta_s=1 is disfavoured with p-values of 3.6 sigma and 3.3 sigma in Scenarios I and III, respectively. We also present an exhaustive list of numerical predictions in each scenario. In particular, we predict the CP phase in B_s -> J psi phi and the difference between the B_s and B_d semileptonic asymmetries, which will be both measured by the LHCb experiment.
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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