Analysis Of Electroweak Data Research Articles

First results on precision constraints on Z - Z′ mixing with ATLAS and CMS diboson production data at the LHC at 13 TeV and predictions for Run II

The study of electroweak boson pair production provides a powerful tool to search for new phenomena beyond the Standard Model (SM). Extra neutral vector bosons Z′ decaying to charged gauge vector boson pairs W+W- are predicted in many scenarios of new physics, including models with an extended gauge sector. The diboson production allows to place stringent constraints on the Z-Z′ mixing parameter ξ and Z′ mass, MZ′. We present the Z′ exclusion region in the ξ - MZ′ plane for the first time by using data comprised of pp collisions at √s = 13 TeV and recorded by the ATLAS and CMS detectors at the CERN LHC, with integrated luminosities of 36.1 and 35.9 fb-1, respectively. The exclusion region has been significantly extended compared to that obtained from the previous analysis performed with Tevatron data, as well as with LHC data collected at 7 and 8 TeV. Also, we found that these constraints on the Z-Z′ mixing factor are more severe than those derived from the global analysis of electroweak data. Further improvement on the constraining of this mixing can be achieved from the analysis of data to be collected at higher luminosity expected in Run II.

Probing Z−Z′ mixing with ATLAS and CMS resonant diboson production data at the LHC at s=13 TeV

The study of electroweak boson pair production provides a powerful test of the spontaneously broken gauge symmetry of the Standard Model (SM) and can be used to search for new phenomena beyond the SM. Extra neutral vector bosons $Z'$ decaying to charged gauge vector boson pairs $W^+W^-$ are predicted in many scenarios of new physics, including models with an extended gauge sector. The diboson production allows to place stringent constraints on the $Z$-$Z'$ mixing factor $\xi$ and $Z'$ mass, $M_{Z'}$. We present the $Z'$ exclusion region in the $\xi-M_{Z'}$ plane for the first time by using data comprised of $pp$ collisions at $\sqrt{s}=13$ TeV and recorded by the ATLAS and CMS detectors at the CERN LHC, with integrated luminosities of 13.2 and 35.9 fb$^{-1}$, respectively. The exclusion region has been significantly extended compared to that obtained from the previous analysis performed with Tevatron data as well as with LHC data collected at 7 and 8 TeV. Also, we found that these constraints on the $Z$-$Z'$ mixing factor are more severe than those derived from the global analysis of electroweak data. Further improvement on the constraining of this mixing can be achieved from the analysis of data to be collected at higher luminosity.

Comparing electroweak data with a decoupling model

Present data, both from direct Higgs search and from analysis of electroweak data, are starting to become rather restrictive on the possible values for the mass of the standard model Higgs. We discuss a new physics scenario based on a model with decoupling (both in a linear and in a non-linear version) showing how it allows for an excellent fit to the present values of the ϵ parameters and how it widens the allowed ranges for the Higgs mass (thought as elementary in the linear version, or as composite in the non-linear one).

Globalχ2analysis of electroweak data in SO(10) SUSY GUTs

We present the details of a global ${\ensuremath{\chi}}^{2}$ analysis of electroweak data, including fermion masses and mixing angles, in SO(10) SUSY GUTs. Just as precision electroweak data are used to test the standard model, the well-determined standard model parameters are the precision electroweak data for testing theories beyond the standard model. In this paper we use the latest experimentally measured values for these parameters. We study several models discussed in the literature. One of these models provides an excellent fit to the low energy data with ${\ensuremath{\chi}}^{2}\ensuremath{\sim}1$ for three degrees of freedom. We present graphs of constant ${\ensuremath{\chi}}^{2}$ contours as functions of position in soft SUSY-breaking parameter space, as well as our predictions for a few selected points in parameter space. We also study the sensitivity of our results to changes in various parameters. Finally, we discuss the consequences of our work in the context of a general MSSM analysis at the $Z$ scale.

Analysis of electroweak precision data and prospects for future improvements

We update our previous work on an analysis of the electroweak data by including new and partly preliminary data available up to the 1996 summer conferences. The new results on the Z partial decay widths into b and c hadrons now offer a consistent interpretation of all data in the minimal standard model. The value extracted for the strong interaction coupling constant \alpha_s(mZ) agrees well with determinations in other areas. New constraints on the universal parameters S, T and U are obtained from the updated measurements. No signal of new physics is found in the S,T,U analysis once the SM contributions with mt \sim 175GeV and those of not a too heavy Higgs boson are accounted for. The naive QCD-like technicolor model is now ruled out at the 99%CL even for the minimal model with SU(2)_{TC}. In the absence of a significant new physics effect in the electroweak observables, constraints on masses of the top quark, mt, and Higgs boson, mH, are derived as a function of \alpha_s and the QED effective coupling $\bar{\alpha}(m_Z^2)$. The preferred range of mH depends rather strongly on the actual value of mt: mH 130GeV for mt=180GeV at 95%CL. Prospects due to forthcoming improved measurements of asymmetries, the mass of the weak boson W mW, mt and $\bar{\alpha}(m_Z^2)$ are discussed. Anticipating uncertainties of 0.00020 for $\sbar^2(m_Z^2)$, 20MeV for mW, and 2GeV for mt, the new physics contributions to the S,T,U parameters will be constrained more severely, and, within the SM, the logarithm of the Higgs mass can be constrained to about +-0.35. The better constraints on S,T,U and on mH within the minimal SM should be accompanied with matching precision in $\bar{\alpha}(m_Z^2)$.