Search

Recent theory results on direct production of resonances with positive charge conjugation in electron-positron annihilation are reviewed. The strong model dependence is emphasized, with predictions varying between 0.03 eV and 0.43 eV for the charmonium state with $J^{PC} = 1^{++}$ and between 0.16 eV and 4.25 eV for the state with $J^{PC} = 2^{++}$. For the state with $J^{PC} = 0^{++}$ the cross section is of $\cal{O}$ $(m^2_e/M^2_{\chi})$ and thus negligeable for all practical purpose. The importance of the relative phase of the production amplitude is emphasized., Comment: 7 pages, 6 figures

Theory results on precision measurements in electron-positron annihilation at low and high energies are collected. These cover pure QCD calculations as well as mixed electroweak and QCD results, involving light and heavy quarks. The impact of QCD corrections on the $W$-boson mass is discussed and, last not least, the status and the perspectives for the Higgs boson decay rate into $b\bar b$, $c\bar c$ and into two gluons., Comment: 9 pages, LaTeX (PoS style), to appear in the proceedings of `DIS 2016', DESY, Hamburg (Germany), April 2016

Direct, resonant production of the charmonium states $\chi_{c1}$ and $\chi_{c2}$ in electron-positron annihilation is investigated. Depending on details of the model, a sizeable variation of the prediction for the production cross section is anticipated. It is demonstrated that resonant production could be observed under favorable circumstances.

A brief discussion of massive tadpole diagrams and their phenomenological consequences is presented. This includes predictions of the $\rho$ parameter and, as a consequence, the mass of the $W$ boson, implications on the charm and bottom quark masses from the moments, i.e. the derivatives of the current correlators, and the Higgs boson decay rate. A fairly consistent picture emerges, with $m_c(3 {GeV})=0.986\pm0.013$ GeV and $m_b(m_b)=3.610\pm0.016$ GeV. Furthermore, fairly stringent predictions for the Higgs decay rate into photons and gluons are obtained, which will be interesting in increasingly precise experiments., Comment: 12 pages, Contribution to the Proceedings of the Final Meeting of the Collaborative Research Centre / Transregio 9 "Computational Particle Physics", Durbach, Germany, September 2014, to appear in Nucl. Phys. (Proc. Suppl.), v2: Fig.10 updated, reference added

We provide a qualitative and quantitative unified picture of the charge asymmetry in top quark pair production at hadron colliders in the SM and summarise the most recent experimental measurements., Comment: 8 pages, 3 figures. Presented at 8th International Workshop on the CKM Unitarity Triangle (CKM 2014), Vienna, Austria, September 8-12, 2014

The detailed study of vector-boson pair production processes at the LHC will lead to a better understanding of electroweak physics. As pointed out before, a consistent inclusion of higher-order electroweak effects in the analysis of corresponding experimental data may be crucial to properly predict the relevant phenomenological features of these important reactions. Those contributions lead to dramatic distortions of invariant-mass and angular distributions at high energies, but may also significantly affect the cross section near threshold, as is the case e.g. for Z-pairs. For this reason, we present an analysis of the next-to-leading-order electroweak corrections to WW, WZ and ZZ production at the LHC, taking into account mass effects as well as leptonic decays. Hence, our predictions are valid in the whole kinematic reach of the LHC and, moreover, respect the spin correlations of the leptonic decay products at NLO accuracy. Starting from these fixed-order results, a simple and straight-forward method is motivated to combine the electroweak corrections with state-of-the-art Monte Carlo predictions, focusing on a meaningful combination of higher-order electroweak and QCD effects. To illustrate our approach, the electroweak corrections are implemented in the HERWIG++ generator, and their phenomenological effects within a QCD environment are studied explicitly., Comment: 30 pages, 15 figures

Building on earlier work on electroweak corrections to W-pair production, the first calculation of the full electroweak one-loop corrections to on-shell ZZ, W$^{\pm}$Z and $\gamma\gamma$ production at hadron colliders is presented, explicitly taking into account the full vector-boson mass dependence. As a consequence, our results are valid in the whole energy range probed by LHC experiments. Until now, the electroweak corrections have only been known in dedicated high-energy approximations limited to a specific kinematic regime, in particular requiring high boson transverse momenta. Therefore, our results comprise an important and so far missing ingredient to improve on the theory predictions for these fundamental Standard-Model benchmark processes also at intermediate energies and small scattering angles, where actually the bulk of events is located. In case of Z-pair production we have also included the leptonic decays and the associated weak corrections in our analysis. For this particular channel, corrections of about -4% are observed even close to the production threshold. For hard scattering processes with momentum transfers of several hundred GeV one finds large negative corrections which may amount to several tens of percent and lead to significant distortions of transverse-momentum and rapidity distributions., Comment: 29 pages, 13 figures, 9 tables

Vector-boson pair production ranks among the most important Standard-Model benchmark processes at the LHC, not only in view of on-going Higgs analyses. These processes may also help to gain a deeper understanding of the electroweak interaction in general, and to test the validity of the Standard Model at highest energies. In this work, the first calculation of the full one-loop electroweak corrections to on-shell W-boson pair production at hadron colliders is presented. We discuss the impact of the corrections on the total cross section as well as on relevant differential distributions. We observe that corrections due to photon-induced channels can be amazingly large at energies accessible at the LHC, while radiation of additional massive vector bosons does not influence the results significantly., Comment: 29 pages, 15 figures, 4 tables; some references and comments on \gamma\gamma -> WW added; matches version published in JHEP

Theoretical predictions for Bhabha scattering at the two-loop level require the inclusion of hadronic vacuum polarization in the photon propagator. We present predictions for the contributions from reducible amplitudes which are proportional to the vacuum polarization $\pi(q^2)$ and from irreducible ones where the vacuum polarization appears in a loop representing vertex or box diagrams. The second case can be treated by using dispersion relations with a weight function proportional to the $R$-ratio as measured in electron-positron annihilation into hadrons and kernels that can be calculated perturbatively. We present simple analytical forms for the kernels and, using two convenient parametrizations for the function $R(s)$, numerical results for the quantities of interest. As a cross check we evaluate the corresponding corrections resulting from light and heavy lepton loops and we find perfect agreement with previous calculations. For the hadronic correction our result are in good agreement with a previous evaluation., Comment: 22 pages, 13 figures, 3 tables, references added

New data for the total cross section $\sigma(e^+e^-\to{hadrons})$ in the charm and bottom threshold region are combined with an improved theoretical analysis, which includes recent four-loop calculations, to determine the short distance $\bar{\rm MS}$ charm and bottom quark masses. A detailed discussion of the theoretical and experimental uncertainties is presented. The final result for the $\bar{\rm MS}$-masses, $m_c(3 {GeV})=0.986(13)$ GeV and $m_b(10 {GeV})=3.609(25)$ GeV, can be translated into $m_c(m_c)=1.286(13)$ GeV and $m_b(m_b)=4.164(25)$ GeV. This analysis is consistent with but significantly more precise than a similar previous study., Comment: 29 pages

We present the complete analytical result for the two-loop logarithmically enhanced contributions to the high energy asymptotic behavior of the vector form factor and the four-fermion cross section in a spontaneously broken SU(2) gauge model. On the basis of this result we derive the dominant two-loop electroweak corrections to the neutral current four-fermion processes at high energies. Previously neglected effects of the gauge boson mass difference are included through the next-to-next-to-leading logarithmic approximation., Comment: 29 pages, 6 figures. Bernd Jantzen was Bernd Feucht in previous publications. v2: references added, version in Nucl. Phys. B. v3: soft anomalous dimension matrix and dependent results corrected. v4: missing 2-loop NNLL mass-splitting terms in Eq. (62) completed and a few numerical results in Eqs. (63), (66), (70) corrected

We present the complete analytical result for the two-loop logarithmically enhanced contributions to the high energy asymptotic behavior of the vector form factor and the four-fermion cross section in a spontaneously broken SU(2) gauge model. On the basis of this result we derive the dominant two-loop electroweak corrections to the neutral current four-fermion processes at high energies., Comment: LaTeX, 5 pages, 2 figures. Bernd Jantzen was Bernd Feucht in previous publications. v2 & v3: Eqs. (3,4) and numerical results corrected. v4: minor correction (one number) in numerical results, Eq. (5)

The two-loop Sudakov form factor is computed in a U(1) model with a massive gauge boson and a $U(1)\times U(1)$ model with mass gap. We analyze the result in the context of hard and infrared evolution equations and establish a matching procedure which relates the theories with and without mass gap setting the stage for the complete calculation of the dominant two-loop corrections to electroweak processes at high energy., Comment: Latex, 5 pages, 2 figures. Bernd Feucht is Bernd Jantzen in later publications. (The contents of the paper is unchanged.)

We present an analysis of two-loop mixed QCD and electroweak corrections to the decay of the Z boson into light quarks. We find that the naive factorization of QCD and electroweak corrections does not describe correctly the two-loop effects. The nonfactorizable corrections shift the width of the Z boson by approximately -0.55(3) MeV and increase the central value of the strong coupling constant determined at LEP by 0.001., Comment: 9 pages, Revtex

Calculations of radiative corrections to the top quark width are reviewed. QCD effects are discussed for $t-\bar t$ systems produced in $e^+e^-$ annihilation near the energy threshold.}, Comment: Karlsruhe Univ. preprint TTP 93-21, 6p., 2 figures not included (Talk presented by M. Je\.zabek at the Workshop on Physics and Experiments at Linear $e^+e^-$ Colliders, Waikoloa, Hawaii, April 1993)