Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRevisiting the Bottom Quark Forward-Backward Asymmetry $A_{rm {FB}}$ in Electron-Positron Collisions
129
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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 $2.1sigma$.
rate research
Read More
We review in some detail the QCD corrections to the measurement of the forward-backward charge asymmetry of heavy quarks in the $mathrm{e^+e^-rightarrow Qoverline{Q}(g)}$ process at the Z pole. We show that the size of these corrections can be reduced by an order of magnitude by using simple cuts on jet acollinearity. Such a reduction is expected to lead to systematic uncertainties at the $Delta mathrm{A_{FB}^{0,Q}} approx 10^{-4}$ level, opening up the path to high precision electroweak measurements with heavy flavors at future high luminosity $mathrm{e^+e^-}$ colliders like the FCC-ee.
The leading-order accurate description of top quark pair production, as usually employed in standard Monte Carlo event generators, gives no rise to the generation of a forward--backward asymmetry. Yet, non-negligible -- differential as well as inclusive -- asymmetries may be produced if coherent parton showering is used in the hadroproduction of top quark pairs. In this contribution we summarize the outcome of our study of this effect. We present a short comparison of different parton shower implementations and briefly comment on the phenomenology of the colour coherence effect at the Tevatron.
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.
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.
We calculate the forward backward asymmetry of the top-pair production at TEVATRON up to next to leading order (NLO) in the little Higgs model (LHM). We find that the contribution of $Z_H$ can be large enough to make up the gap between standard model (SM) prediction and data. With the database of $7.65pm0.20pm0.36$ pb, therefore, the parameter space for flavor-changing coupling of $Z_H$ is constrained. Thus this model can result in the required asymmetry while the total cross section of top-pair production remaining consistent with data.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
