The Character of Z-pole Data Constraints on Standard Model Parameters

Despite the impressive precision of the Z-pole measurements made at LEP and SLC, the allowed region for the principle Standard Model parameters responsible for radiative corrections (the mass of the Higgs, the mass of the top and alpha(Mz)) is still large enough to encompass significant non-linearities. The nature of the experimental constraints therefore depends in an interesting way on the "accidental" relationships among the various measurements. In particular, the fact that the Z-pole measurements favor values of the Higgs mass excluded by direct searches leads us to examine the effects of external Higgsstrahlung, a process ignored by the usual precision electroweak calculations.Comment: 9 pages, 6 figures, REVTeX format; added reference in section IV; added paragraph on widths and a few cosmetic changes to correspond to published versio

ft Value of O14 and the Universality of the Fermi Interaction

The conserved-vector-current theory of the strangeness-conserving weak decays predicts that GV, the vector coupling constant in nuclear beta decay, should be equal to Gμ, the coupling constant in the muon decay. To make possible a more precise comparison of GV and Gμ, the ft value of O14 has been remeasured. The endpoint energy of the positron decay has been determined by measuring the Q values of the reactions C12(He3, n)O14 and C12(He3, p)N14* (2.311-MeV state), using the same techniques and equipment where possible in order to minimize the uncertainty in the difference of the Q values. The results of these measurements are Qn=-1148.8±0.6 keV and Qp=2468.4±1.0 keV, which yield Emax(β+)=1812.6±1.4 keV, all energies relative to the Li7(p, n)Be7 threshold assumed as 1880.7±0.4 keV. The half-life of O14 has also been remeasured as 71.00±0.13 sec, which implies a partial half-life of 71.43±0.15 sec for the transition to the 2.311-MeV state of N14. Averaged with the recent half-life measurement of Hendrie and Gerhart, we obtain an ft value of 3075±10 sec for the O14 decay, after correcting for nuclear form factors, electron screening, and K-capture competition. With the radiative corrections of Kinoshita and Sirlin, the value obtained for GV is (1.4025±0.0022)×10^-49 erg-cm^3, where the quoted error is experimental in origin. This is to be compared with the value computed from recent muon decay measurements, Gμ=(1.4312±0.0011)×10^-49 erg-cm^3, which is (2.0±0.2)% larger. As there appear to be several possible theoretical explanations for this small discrepancy, the present results are consistent with the conserved-vector-current hypothesis

Searching for Anomalous Weak Couplings of Heavy Flavors at the SLC and LEP

The existence of anomalous electric($\tilde \kappa$) and/or magnetic($\kappa$) dipole moment couplings between the heavy flavor fermions ($c,b,\tau$) and the $Z$ boson can cause significant shifts in the values of several electroweak observables currently being probed at both the SLC and LEP. Using the good agreement between existing data and the predictions of the Standard Model we obtain strict bounds on the possible strength of these new interactions for all of the heavy flavors. The decay $Z\rightarrow b\bar b$, however, provides some possible hint of new physics. The corresponding anomalous couplings of $\tau$'s to photons is briefly examined.Comment: 21 pages, 14 figs(available on request), LaTex, SLAC-PUB-667

The order O(αˉ αˉs)O(\bar{\alpha}~\bar{\alpha}_s) and O(αˉ2)O(\bar{\alpha}^2) corrections to the decay width of the neutral Higgs boson to the bˉb\bar{b}b pair

We present the analytical expressions for the contributions of the order $O(\bar{\alpha}~\bar{\alpha}_s)$ and $O(\bar{\alpha}^2)$ corrections to the decay width of the Standard Model Higgs boson into the $\bar{b}b$-pair. The numerical value of the mixed QED and QCD correction of order $O(\bar{\alpha}~\bar{\alpha}_s)$ is comparable with the previously calculated terms in the perturbative series for $\Gamma(H^0\to\bar{b}b)$.Comment: LaTeX 5 pages, accepted for publication in Pisma Zh. Eksp. Teor. Fiz. v 66, N5 (1997

Electroweak Physics, Experimental Aspects

Collider measurements on electroweak physics are summarised. Although the precision on some observables is very high, no deviation from the Standard Model of electroweak interactions is observed. The data allow to set stringent limits on some models for new physics.Comment: Plenary Talk at the UK Phenomenology Workshop on Collider Physics, Durham, 199

Master integrals for massive two-loop Bhabha scattering in QED

We present a set of scalar master integrals (MIs) needed for a complete treatment of massive two-loop corrections to Bhabha scattering in QED, including integrals with arbitrary fermionic loops. The status of analytical solutions for the MIs is reviewed and examples of some methods to solve MIs analytically are worked out in more detail. Analytical results for the pole terms in epsilon of so far unknown box MIs with five internal lines are given.Comment: 23 pages, 5 tables, 12 figures, references added, appendix B enlarge

QED Corrections to Neutrino Electron Scattering

We evaluate the O(alpha) QED corrections to the recoil electron energy spectrum in the process nu_l + e --> nu_l + e (+gamma), where (+gamma) indicates the possible emission of a photon and l=e, mu or tau. The soft and hard bremsstrahlung differential cross sections are computed for an arbitrary value of the photon energy threshold. We also study the O(alpha) QED corrections to the differential cross section with respect to the total combined energy of the recoil electron and a possible accompanying photon. Their difference from the corrections to the electron spectrum is investigated. We discuss the relevance and applicability of both radiative corrections, emphasizing their role in the analysis of precise solar neutrino electron scattering experiments.Comment: 14 pages + 10 figures. Minimal changes, published versio

Searching For Anomalous τνW\tau \nu W Couplings

The capability of current and future measurements at low and high energy $e^+e^-$ colliders to probe for the existence of anomalous, CP conserving, $\tau \nu W$ dipole moment-type couplings is examined. At present, constraints on the universality of the tau charged and neutral current interactions as well as the shape of the $\tau \to \ell$ energy spectrum provide the strongest bounds on such anomalous couplings. The presence of these dipole moments are shown to influence, e.g., the extraction of $\alpha_s(m_\tau^2)$ from $\tau$ decays and can lead to apparent violations of CVC expectations.Comment: 24 pages, 9 figure

Can We Observe Weak Anomalous Couplings of Heavy Quarks Through Three Jet Events?

The rates and corresponding jet distributions for the decay $Z\to b\bar bg$ and the process $e^+e^-\to t\bar tg$ may be sensitive to anomalous dipole-like couplings of heavy quarks to the photon and $Z$. In the $b$-quark case, after updating our previous analysis on the constraints imposed by current experiments on $Zb\bar b$ anomalous couplings, we show that the variation of these couplings within their presently allowed ranges leads to rather minor modifications to the Standard Model expectations for $Z\to b\bar bg$ observables. In the $t$-quark case, significant deviations from the Standard Model predictions for $t\bar tg$ production at the Next Linear Collider are possible.Comment: 26 pages with 9 embedded figures; gzipped, uuencoded postscript file. To obtain a copy of this paper send e-mail to [email protected]

Combined Description of N‾N\bf{\overline{N}N} Scattering and Annihilation With A Hadronic Model

A model for the nucleon-antinucleon interaction is presented which is based on meson-baryon dynamics. The elastic part is the $G$-parity transform of the Bonn $NN$ potential. Annihilation into two mesons is described in terms of microscopic baryon-exchange processes including all possible combinations of $\pi,\eta,\rho,\omega,a_0,f_0,a_1,f_1,a_2,f_2,K,K^*$. The remaining annihilation part is taken into account by a phenomenological energy- and state independent optical potential of Gaussian form. The model enables a simultaneous description of nucleon-antinucleon scattering and annihilation phenomena with fair quality.Comment: revised version, REVTEX, 9 pages, 10 figures available from this URL ftp://ikp113.ikp.kfa-juelich.de/pub/kph140/nucl-th.9411014.u