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Register a new userProbe CP violation in $Hto gamma Z$ through forward-backward asymmetry
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Xia Wan
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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.
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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.
The Higgs boson discovered at the LHC opened a new chapter for particle physics. Its properties need to be studied in detail to distinguish a purely standard model (SM) Higgs boson from one of many scalars in an enlarged Higgs sector. The CMS collaboration has reported a possible lepton flavor violating (LFV) signal $htomutau$, which if confirmed, implies that the Higgs sector is larger than in the SM. New physics responsible for this type of decay may, in general, also introduce other observable effects such as charge-parity (CP) violation in $hto tautau$. We study two types of models that single out the third generation and can induce large $h to mutau$ rates with different consequences for CP violation in $h to tau tau$. Predictions for the size of the CP violating couplings require knowledge of the lepton Yukawa matrices and we discuss this in the context of two different textures considering all existing constraints.
The forward-backward (FB) asymmetry of $b$ quarks in $e^+e^-$ collisions at the Z pole measured at LEP, $A_{FB}^{0,b} = 0.0992pm0.0016$, remains today the electroweak precision observable with the largest disagreement (2.4$sigma$) with respect to the Standard Model prediction, $(A_{FB}^{0,b})_{_{rm th}} = 0.1030 pm 0.0002$. Beyond the dominant statistical uncertainties, QCD effects, such as $b$-quark showering and hadronization, are the leading sources of $A_{FB}^{0,b}$ systematic uncertainty, and have not been revised in the last twenty years. We reassess the QCD uncertainties of the eight original $A_{FB}^{0,b}$ LEP measurements, using modern parton shower PYTHIA-8 and PYTHIA-8 + VINCIA simulations with nine different implementations of soft and collinear radiation as well as of parton fragmentation. Our analysis, combined with NNLO massive $b$-quark corrections independently computed recently, indicates total propagated QCD uncertainties of $sim$0.7% and $sim$0.3% for the lepton-charge and jet-charge analyses, respectively, that are about a factor of two smaller than those of the original LEP results. Accounting for such updated QCD effects leads to a new $A_{FB}^{0,b} = 0.0996pm0.0016$ average, with a data-theory tension slightly reduced from 2.4$sigma$ to 2.1$sigma$. Confirmation or resolution of this long-term discrepancy requires a new high-luminosity $e^+e^-$ collider collecting orders-of-magnitude more data at the Z pole to significantly reduce the $A_{FB}^{0,b}$ statistical uncertainties.
We study the impact of the inclusion of Neutral Current (NC) DY data from LHC mapped in the Forward-Backward Asymmetry ($A_{rm FB}$) observable on PDF uncertainties, using the open source platform texttt{xFitter}. We find that $A_{rm FB}$ enables new PDF sensitivity at current and future luminosity stages of LHC.
We investigate the impact of high-statistics Drell-Yan (DY) measurements at the LHC on the study of non-perturbative QCD effects from parton distribution functions (PDF). We present the results of a PDF profiling analysis based on the neutral-current DY forward-backward asymmetry, using the open source fit platform xFitter.
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