ترغب بنشر مسار تعليمي؟ اضغط هنا

Electroweak precision tests in the LHC era and Z-decay form factors at two-loop level

94   0   0.0 ( 0 )
 نشر من قبل Ayres Freitas
 تاريخ النشر 2014
  مجال البحث
والبحث باللغة English
 تأليف A. Freitas




اسأل ChatGPT حول البحث

The current status of electroweak precision tests after the discovery of the Higgs boson is reviewed, both from a phenomenological and from a theoretical point of view. Predictions for all Z-pole quantities are now available at the complete fermionic two-loop order within the Standard Model. The calculation of these corrections is described based on the example of the total Z-boson width. Finally, an outlook on the experimental improvements and theoretical challenges for a future high-luminosity e+e- collider is given.



قيم البحث

اقرأ أيضاً

We present Standard Model predictions for the complete set of phenomenologically relevant electroweak precision pseudo-observables related to the Z-boson: the leptonic and bottom-quark effective weak mixing angles $sin^2theta_{rm eff}^ell$, $sin^2the ta_{rm eff}^b$, the Z-boson partial decay widths $Gamma_f$, where $f$ indicates any charged lepton, neutrino and quark flavor (except for the top quark), as well as the total Z decay width $Gamma_Z$, the branching ratios $R_ell$, $R_c$, $R_b$, and the hadronic cross section $sigma_{rm had}^0$. The input parameters are the masses $M_Z$, $M_H$ and $m_t$, and the couplings $alpha_s$, $alpha$. The scheme dependence due to the choice of $M_W$ or its alternative $G_mu$ as a last input parameter is also discussed. Recent substantial technical progress in the calculation of Minkowskian massive higher-order Feynman integrals allows the calculation of the complete electroweak two-loop radiative corrections to all the observables mentioned. QCD contributions are included appropriately. Results are provided in terms of simple and convenient parameterization formulae whose coefficients have been determined from the full numerical multi-loop calculation. The size of the missing electroweak three-loop or QCD higher-order corrections is estimated. We briefly comment on the prospects for their calculation. Finally, direct predictions for the $Z{bar f}f$ vector and axial-vector form-factors are given, including a discussion of separate order-by-order contributions.
We complete the list of one loop renormalization group equations and matching conditions relevant for the computation of the electroweak precision parameters $S$ and $T$ in the three site Higgsless model. We obtain one-loop formulas for $S$ and $T$ e xpressed in terms of physical observables such as the KK gauge boson mass $M_{W}$, the KK fermion mass $M$, and the KK gauge boson ($W$) couplings with light quarks and leptons $g_{Wff}$. It is shown that these physical observables, $M_{W}$, $M$ and $g_{Wff}$ are severely constrained by the electroweak precision data. Unlike the tree level analysis on the ideally delocalized fermion, we find that perfect fermiophobity of $W$ is ruled out by the precision data. We also study the cutoff dependence of our analysis. Although the model is non-renormalizable, the dependence on the cutoff parameter $Lambda$ is shown to be non-significant.
This article presents results for the last unknown two-loop contributions to the $Z$-boson partial widths and $Z$-peak cross-section. These are the so-called bosonic electroweak two-loop corrections, where bosonic refers to diagrams without closed fe rmion loops. Together with the corresponding results for the $Z$-pole asymmetries $A_l, A_b$, which have been presented earlier, this completes the theoretical description of $Z$-boson precision observables at full two-loop precision within the Standard Model. The calculation has been achieved through a combination of different methods: (a) numerical integration of Mellin-Barnes representations with contour rotations and contour shifts to improve convergence; (b) sector decomposition with numerical integration over Feynman parameters; (c) dispersion relations for sub-loop insertions. Numerical results are presented in the form of simple parameterization formulae for the total width, $Gamma_{rm Z}$, partial decay widths $Gamma_{e,mu},Gamma_{tau},Gamma_{ u},Gamma_{u},Gamma_{c},Gamma_{d,s},Gamma_{b}$, branching ratios $R_l,R_c,R_b$ and the hadronic peak cross-section, $sigma_{rm had}^0$. Theoretical intrinsic uncertainties from missing higher orders are also discussed.
57 - Frederic Teubert 2002
This paper is an updated version of the invited plenary talk given at the XXII Physics in Collision Conference at Stanford, (June 2002). The measurements performed at LEP and SLC have substantially improved the precision of the tests of the Minimal S tandard Model. The precision is such that there is sensitivity to pure weak radiative corrections. This allows to indirectly determine the top mass (mt=178$pm$10 GeV), the W-boson mass (MW=80.368$pm$0.022 GeV), and to set an upper limit on the Higgs boson mass of 193 GeV at 95% confidence level.
We update the global fit to electroweak precision observables, including the effect of the latest measurements at hadron colliders of the $W$ and top-quark masses and the effective leptonic weak mixing angle. We comment on the impact of these measure ments in terms of constraints on new physics. We also update the bounds derived from the fit to the Higgs-boson signal strengths, including the observables measured at the LHC Run 2, and compare the improvements with respect to the 7 and 8 TeV results.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا