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Register a new userZ lineshape and forward-backward asymmetries
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Authors
B. Bloch-Devaux
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Preliminary but close to final results on the Z lineshape and Forward-Backward asymmetries from the four LEP experiments are presented. Combined values extracted from ALEPH. DELPHI, L3 and OPAL data recorded at energies around the Z pole are discussed.
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We examine the O(alpha_s) forward-backward asymmetries for the production process e+ e- --> gamma,Z --> q qbar (g), tagging the outgoing heavy-quark jet at center-of-momentum energies off the Z-peak. The complicated analytic results are reduced to simple polynomial forms that provide excellent approximations. For charm and bottom quark, a full dynamical cancellation gives O(alpha_s) zeros in the forward-backward asymmetry close to the Z-peak. We conclude with a detailed numerical analysis of our results.
We suggest that the forward-backward asymmetry $(A_{FB})$ of the charged leptons in $ggto Htogamma Ztogamma ell^-ell^+$ process could be used to probe the CP violating $Hgamma Z$ coupling when the interference from $ggtogamma Ztogamma ell^-ell^+$ process is included. With CP violation in $Hgamma Z$ coupling, the interference effect leads to a non-vanishing $A_{FB}$, which is also sensitive to the strong phase differences. The resonant and non-resonant strong phases together make $A_{FB}(hat{s})$ change sign around Higgs mass $M_H$. For phenomenology study, we suggest the integral over one-side mass region below $M_H$ to magnify the $A_{FB}$ strength.
We suggest that the forward-backward asymmetry $(A_{FB})$ of the charged lepton in $ggto Htogamma Ztogamma ell^-ell^+$ process could be used to probe the CP violating $Hgamma Z$ coupling when the interference from $ggtogamma Ztogamma ell^-ell^+$ process is included. With CP violation in $Hgamma Z$ coupling, the interference effect leads to a non-vanishing $A_{FB}$, which is also sensitive to the strong phase differences. The resonant and non-resonant strong phases together make $A_{FB}(hat{s})$ change sign around Higgs mass $M_H$. For phenomenology study, we suggest the integral over one-side mass region below $M_H$ to magnify the $A_{FB}$ strength.
Precision determinations of Standard Model (SM) Electro-Weak (EW) parameters at the Large Hadron Collider (LHC) are dominated by uncertainties due to Parton Distribution Functions (PDFs). Reweighting and profiling techniques are routinely employed to treat this. We explore approaches based on combining measurements of charged current and neutral current Drell-Yan (DY) asymmetries to improve PDF uncertainties. We present the results of a numerical analysis performed with the open-source platform xFitter. PDF uncertainties are examined for lepton-charge and forward-backward asymmetries in regions of transverse and invariant masses near the vector-boson peak, based on LHC Run III and HL-LHC luminosity scenarios. We discuss the complementarity of the asymmetries in reducing PDF uncertainties in observables relevant to both SM and Beyond the SM (BSM) physics.
We address the impact of future measurements of charged and neutral current Drell-Yan (DY) asymmetries and their combination on Parton Distribution Functions (PDFs) uncertainties. We quantify the reduction of PDF uncertainties using the QCD tool xFitter. We examine the effects of such reduced PDF errors on both Standard Model (SM) and Beyond SM (BSM) observables.
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