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Register a new userMeasurement of the forward-backward asymmetry in low-mass bottom-quark pairs produced in proton-antiproton collisions
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We report a measurement of the forward-backward asymmetry, $A_{FB}$, in $bbar{b}$ pairs produced in proton-antiproton collisions and identified by muons from semileptonic $b$-hadron decays. The event sample was collected at a center-of-mass energy of $sqrt{s}=1.96$ TeV with the CDF II detector and corresponds to 6.9 fb$^{-1}$ of integrated luminosity. We obtain an integrated asymmetry of $A_{FB}(bbar{b})=(1.2 pm 0.7)$% at the particle level for $b$-quark pairs with invariant mass, $m_{bbar{b}}$, down to $40$ GeV/$c^2$ and measure the dependence of $A_{FB}(bbar{b})$ on $m_{bbar{b}}$. The results are compatible with expectations from the standard model.
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We measure the particle-level forward-backward production asymmetry in $bbar{b}$ pairs with masses $m(bbar{b})$ larger than 150 GeV/$c^2$, using events with hadronic jets and employing jet charge to distinguish $b$ from $bar{b}$. The measurement uses 9.5/fb of ppbar collisions at a center of mass energy of 1.96 TeV recorded by the CDF II detector. The asymmetry as a function of $m(bbar{b})$ is consistent with zero, as well as with the predictions of the standard model. The measurement disfavors a simple model including an axigluon with a mass of 200 GeV/$c^2$ whereas a model containing a heavier 345 GeV/$c^2$ axigluon is not excluded.
The bottom quark forward-backward asymmetry $A_{rm{FB}}$ is a key observable in electron-positron collisions at the $Z^{0}$ peak. In this paper, we employ the Principle of Maximum Conformality (PMC) to fix the $alpha_s$-running behavior of the next-to-next-to-leading order QCD corrections to $A_{rm{FB}}$. The resulting PMC scale for this $A_{rm{FB}}$ is an order of magnitude smaller than the conventional choice $mu_r=M_Z$. This scale has the physically reasonable behavior and reflects the virtuality of its QCD dynamics, which is independent to the choice of renormalization scale. Our analyses show that the effective momentum flow for the bottom quark forward-backward asymmetry should be $mu_rll M_Z$ other than the conventionally suggested $mu_r=M_Z$. Moreover, the convergence of perturbative QCD series for $A_{rm{FB}}$ is greatly improved using the PMC. Our prediction for the bare bottom quark forward-backward asymmetry is refined to be $A^{0,b}_{rm FB}=0.1004pm0.0016$, which diminishes the well known tension between the experimental determination for this (pseudo) observable and the respective Standard Model fit to $2.1sigma$.
We report on a search for a spin-zero non-standard-model particle in proton-antiproton collisions collected by the Collider Detector at Fermilab at a center-of-mass-energy of 1.96 TeV. This particle, the $phi$ boson, is expected to decay into a bottom-antibottom quark pair and to be produced in association with at least one bottom quark. The data sample consists of events with three jets identified as initiated by bottom quarks and corresponds to $5.4~text{fb}^{-1}$ of integrated luminosity. In each event, the invariant mass of the two most energetic jets is studied by looking for deviations from the multijet background, which is modeled using data. No evidence is found for such particle. Exclusion upper limits ranging from 20 to 2 pb are set for the product of production cross sections times branching fraction for hypothetical $phi$ boson with mass between 100 and 300 GeV/$c^2$. These are the most stringent constraints to date.
We present an overview of the measurements of the like-sign dimuon charge asymmetry by the DO Collaboration at the Fermilab Tevatron proton-antiproton Collider. The results differ from the Standard Model prediction of CP violation in mixing and interference of B^0 and B^0_s by 3.6 standard deviations.
We measure the forward--backward asymmetry of the production of top quark and antiquark pairs in proton-antiproton collisions at center-of-mass energy $sqrt{s} = 1.96~mathrm{TeV}$ using the full data set collected by the Collider Detector at Fermilab (CDF) in Tevatron Run II corresponding to an integrated luminosity of $9.1~rm{fb}^{-1}$. The asymmetry is characterized by the rapidity difference between top quarks and antiquarks ($Delta y$), and measured in the final state with two charged leptons (electrons and muons). The inclusive asymmetry, corrected to the entire phase space at parton level, is measured to be $A_{text{FB}}^{tbar{t}} = 0.12 pm 0.13$, consistent with the expectations from the standard-model (SM) and previous CDF results in the final state with a single charged lepton. The combination of the CDF measurements of the inclusive $A_{text{FB}}^{tbar{t}}$ in both final states yields $A_{text{FB}}^{tbar{t}}=0.160pm0.045$, which is consistent with the SM predictions. We also measure the differential asymmetry as a function of $Delta y$. A linear fit to $A_{text{FB}}^{tbar{t}}(|Delta y|)$, assuming zero asymmetry at $Delta y=0$, yields a slope of $alpha=0.14pm0.15$, consistent with the SM prediction and the previous CDF determination in the final state with a single charged lepton. The combined slope of $A_{text{FB}}^{tbar{t}}(|Delta y|)$ in the two final states is $alpha=0.227pm0.057$, which is $2.0sigma$ larger than the SM prediction.
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