Effective Leptonic Weak Mixing Angle Research Articles

A new analysis of the pQCD contributions to the electroweak parameter ρ using the single-scale approach of principle of maximum conformality

It has been observed that conventional renormalization scheme and scale ambiguities for the pQCD predictions can be eliminated by using the principle of maximum conformality (PMC). However, being the intrinsic nature of any perturbative theory, there are still two types of residual scale dependences due to uncalculated higher-order terms. In the paper, as a step forward of our previous work Wang et al. (2014) [16], we reanalyze the electroweak ρ parameter by using the PMC single-scale approach. Using the PMC conformal series and the Padé approximation approach, we observe that the residual scale dependence can be greatly suppressed and then a more precise pQCD prediction up to N4LO-level can be achieved, e.g. Δρ|PMC≃(8.204±0.012)×10−3, where the errors are squared averages of those from unknown higher-order terms and Δαs(MZ)=±0.0010. We then predict the magnitudes of the uncertainties of the W-boson mass and the effective leptonic weak-mixing angle: δMW|N4LO=−0.26 MeV and δsin2⁡θeff|N4LO=0.14×10−5, which are well below the precision anticipated for the future electron-position colliders such as FCC, CEPC and ILC. Thus by measuring those parameters, it is possible to test SM with high precision.

Tests of the electroweak sector with precision measurements and diboson final states at the ATLAS Experiment.

The electroweak sector of the Standard Model can be tested either via precision measurements of fundamental observables or via direct tests of its underlying gauge structure. The ATLAS collaboration has recently released a measurement of the effective leptonic weak mixing angle using data collected at a centre-of-mass energy of 8 TeV. The result has a precision similar to that of the most precise individual measurements. The high integrated luminosity delivered by the LHC during Run-2 has allowed ATLAS to measure integrated and differential cross-sections for several kinematic observable of W±Z production in pp collisions and to observe vector boson scattering processes with WZ and same-sign WW final states. The results from these milestone analyses as well as their interpretation in the context of the Standard Model are presented in this proceeding.

Direct determination of sin2ϑeffℓ at hadron colliders

We discuss the renormalization of the electroweak Standard Model at 1-loop using the leptonic effective weak mixing angle as one of the input parameters. We evaluate the impact of this choice in the prediction of the forward-backward asymmetry for the neutral current Drell-Yan process. The proposed input scheme is suitable for a direct determination of the effective leptonic weak mixing angle from the experimental data.

Standard Model: Electroweak Physics with CMS and ATLAS at 13 TeV

This paper presents cross section measurements for inclusive W/Z boson production, and W/Z boson production in association with jets and diboson production, performed by the CMS [1] and ATLAS [2] collaborations using proton-proton (pp) collisions data at a centre-of-mass energy of at LHC. Differential and total production cross sections for various processes, are computed and compared to higher order predictions of the standard model (SM). Recent results on effective leptonic weak mixing angle are also presented.

Measurement of the weak mixing angle using the forward\u2013backward asymmetry of Drell\u2013Yan events in mathrm {p}mathrm {p} collisions at 8,text {TeV}

A measurement is presented of the effective leptonic weak mixing angle (sin ^2theta ^{ell }_{text {eff}}) using the forward–backward asymmetry of Drell–Yan lepton pairs (mu mu and mathrm {e}mathrm {e}) produced in proton–proton collisions at sqrt{s}=8,text {TeV} at the CMS experiment of the LHC. The data correspond to integrated luminosities of 18.8 and 19.6{{,text {fb}^{-1}}} in the dimuon and dielectron channels, respectively, containing 8.2 million dimuon and 4.9 million dielectron events. With more events and new analysis techniques, including constraints obtained on the parton distribution functions from the measured forward–backward asymmetry, the statistical and systematic uncertainties are significantly reduced relative to previous CMS measurements. The extracted value of sin ^2theta ^{ell }_{text {eff}} from the combined dilepton data is sin ^2theta ^{ell }_{text {eff}} =0.23101pm 0.00036,text {(stat)} pm 0.00018,text {(syst)} pm 0.00016,text {(theo)} pm 0.00031,text {(parton distributions in proton)}=0.23101 pm 0.00053.

QCD improved electroweak parameterρ

In the present paper, we make a detailed analysis for the QCD corrections to the electroweak $\rho$ parameter by applying the principle of maximum conformality (PMC). As a comparison, we show that under the conventional scale setting, we have $\Delta\rho|_{\rm N^3LO} = \left(8.257^{+0.045}_{-0.012}\right) \times10^{-3}$ by varying the scale $\mu_{r}\in[M_{t}/2$, $2M_{t}]$. By defining a ratio, $\Delta R=\Delta\rho/3X_t-1$, which shows the relative importance of the QCD corrections, it is found that its scale error is $\sim \pm9 \%$ at the two-loop level, which changes to $\sim\pm4\%$ at the three-loop level and $\sim \pm 2.5\%$ at the four-loop level, respectively. These facts well explain why the conventional scale uncertainty constitutes an important error for estimating the $\rho$ parameter. On the other hand, by applying the PMC scale setting, the four-loop estimation $\Delta\rho|_{\rm N^3LO}$ shall be almost fixed to $8.228\times10^{-3}$, which indicates that the conventional scale error has been eliminated. We observe the pQCD convergence for the $\rho$ parameter has also been greatly improved due to the elimination of the divergent renormalon terms. As applications of the present QCD improved $\rho$ parameter, we show the shifts of the $W$-boson mass and the effective leptonic weak-mixing angle due to $\Delta\rho$ can be reduced to $\delta M_{W}|_{\rm N^3LO} =0.7$ MeV and $\delta \sin^2{\theta}_{\rm eff}|_{\rm N^3LO}=-0.4\times10^{-5}$.

FeynHiggs: A program for the calculation of MSSM Higgs-boson observables – Version 2.6.5

FeynHiggs is a Fortran code for the calculation of physical observables in the field of high-energy physics. FeynHiggs calculates various observables in the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM) for real or complex parameters. These observables comprise Higgs-boson masses, mixing angles, couplings, Tevatron/LHC production cross-sections, branching ratios, as well as some additional observables such as Δ ρ, M W , the effective leptonic weak mixing angle, ( g − 2 ) μ , BR( b → s γ ), electric dipole moments. New version program summary Program title: FeynHiggs v2.6.5 Catalogue identifier: ADKT_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADKT_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GPL No. of lines in distributed program, including test data, etc.: 156 455 No. of bytes in distributed program, including test data, etc.: 1 058 758 Distribution format: tar.gz Programming language: Fortran 77, C, Mathematica Computer: Intel/AMD, PowerPC, Alpha Operating system: Linux, Windows (Cygwin), Mac OS, Tru64 Unix RAM: insignificant (typically a few MB) Classification: 11.5 Catalogue identifier of previous version: ADKT_v1_0 Journal reference of previous version: Comput. Phys. Comm. 124 (2000) 76 Does the new version supersede the previous version?: Yes Nature of problem: The experimental searches for Higgs bosons have to be compared with theory predictions at a high level of accuracy. Radiative corrections are especially important in the Minimal Supersymmetric Standard Model (MSSM). Solution method: High-precision calculations (mostly based on the Feynman-diagrammatic approach) for various Higgs-boson observables in the MSSM are implemented. The program takes the basic model parameters as input and evaluates many MSSM Higgs-boson observables relevant for experimental Higgs-boson physics. Reasons for new version: Existing calculations have been refined (e.g., by the inclusion of complex parameters); many new observables have been implemented. Summary of revisions: Input parameters are now allowed to be complex, and non-minimal flavor violation is permitted. Besides the Higgs-boson masses also branching ratios and hadron-collider production cross-sections are calculated. Restrictions: Several observables are still missing and have to be implemented. Running time: The command-line frontend, which invokes essentially all FeynHiggs functions, takes 200 ms a single point in parameter space On a 3 GHz AMD CPU.

Bosonic corrections to the effective leptonic weak mixing angle at the two-loop level

Details of the recent calculation of the two-loop bosonic corrections to the effective leptonic weak mixing angle are presented. In particular, the expansion in the difference of the W and Z boson masses is studied and some of the master integrals needed are given in analytic form.

Complete Two-Loop Electroweak Fermionic Corrections to the Effective Leptonic Weak Mixing Anglesin2θeffleptand Indirect Determination of the Higgs Boson Mass

We present a complete calculation of the contributions to the effective leptonic weak mixing angle, sin((2)theta;(lept)(eff), generated by closed fermion loops at the two-loop level of the electroweak interactions. This quantity is the source of the most stringent bound on the mass M(H) of the standard model Higgs boson. The size of the corrections with respect to known partial results varies between -4 x 10(-5) and -8 x 10(-5) for a realistic range of M(H) from 100 to 300 GeV. This translates into a shift of the predicted (from sin((2)theta;(lept)(eff) alone) central value of M(H) by +19 GeV, to be compared with the shift induced by a recent change in the measured top quark mass which amounts to +36 GeV.

Two-loop Fermionic Electroweak Corrections to the Effective Leptonic Weak Mixing Angle in the Standard Model

We give some details of the recently completed calculation of the full two-loop fermionic corrections to the effective leptonic weak mixing angle. Among others, we describe the C++ library DiaGen/IdSolver, which was used to reduce the two-loop light fermion vertex diagrams to linear combinations of master integrals with rational function coefficients.