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Register a new user$Z to tautau$ and $W to tau u_tau$ Cross-Sections at the LHC
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Philip Ilten
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Measurements of the $Z to tautau$ and $W to tau u_tau$ cross-sections at the LHC with data taken at $sqrt{s} = 7$ TeV are reported for the ATLAS, CMS, and LHCb experiments. All results are found to agree with the Standard Model.
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We present an update on the status of the W and Z cross sections in proton-antiproton collisions at 1.96 TeV on behalf of the DZero and CDF collaborations. Preliminary studies of the differential cross sections with different jet multiplicities and as a function of jet transverse energy are also presented.
The precise determination of the $B_c to tau u_tau$ branching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element $|V_{cb}|$ and probing new physics models. In this paper, we discuss the potential of measuring the processes of $B_c to tau u_tau$ with $tau$ decaying leptonically at the proposed Circular Electron Positron Collider (CEPC). We conclude that during the $Z$ pole operation, the channel signal can achieve five $sigma$ significance with $sim 10^9$ $Z$ decays, and the signal strength accuracies for $B_c to tau u_tau$ can reach around 1% level at the nominal CEPC $Z$ pole statistics of one trillion $Z$ decays assuming the total $B_c to tau u_tau$ yield is $3.6 times 10^6$. Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the $b to ctau u$ transition. If the total $B_c$ yield can be determined to $mathcal{O}(1%)$ level of accuracy in the future, these results also imply $|V_{cb}|$ could be measured up to $mathcal{O}(1%)$ level of accuracy.
The most recent results for W and Z boson production cross sections and asymmetries are presented from the CDF and D0 collaborations using Run II data taken at the Fermi National Accelerator Laboritory (FNAL) Tevatron. Data set sizes range from 72pb^(-1) to 226pb^(-1), and results range from published to preliminary. Results presented agree with the Standard Model and world averages within errors.
In a combined study of the decay spectra of $tau^-to K_Spi^- u_tau$ and $tau^-to K^-eta u_tau$ decays within a dispersive representation of the required form factors, we illustrate how the $K^*(1410)$ resonance parameters, defined through the pole position in the complex plane, can be extracted with improved precision as compared to previous studies. While we obtain a substantial improvement in the mass, the uncertainty in the width is only slightly reduced, with the findings $M_{K^{*prime}}=1304 pm 17,$MeV and $Gamma_{K^{*prime}} = 171 pm 62,$MeV. Further constraints on the width could result from updated analyses of the $Kpi$ and/or $Keta$ spectra using the full Belle-I data sample. Prospects for Belle-II are also discussed. As the $K^-pi^0$ vector form factor enters the description of the decay $tau^-to K^-eta u_tau$, we are in a position to investigate isospin violations in its parameters like the form factor slopes. In this respect also making available the spectrum of the transition $tau^-to K^-pi^0 u_tau$ would be extremely useful, as it would allow to study those isospin violations with much higher precision.
We consider QCD radiative corrections to $W^+W^-$ production at the LHC and present the first fully differential predictions for this process at next-to-next-to-leading order (NNLO) in perturbation theory. Our computation consistently includes the leptonic decays of the $W$ bosons, taking into account spin correlations, off-shell effects and non-resonant contributions. Detailed predictions are presented for the different-flavour channel $pptomu^+e^- u_mu {bar u}_e+X$ at $sqrt{s}=8$ and $13$ TeV. In particular, we discuss fiducial cross sections and distributions in the presence of standard selection cuts used in experimental $W^+W^-$ and $Hto W^+W^-$ analyses at the LHC. The inclusive $W^+W^-$ cross section receives large NNLO corrections, and, due to the presence of a jet veto, typical fiducial cuts have a sizeable influence on the behaviour of the perturbative expansion. The availability of differential NNLO predictions, both for inclusive and fiducial observables, will play an important role in the rich physics programme that is based on precision studies of $W^+W^-$ signatures at the LHC.
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