Theoretical Expectations For High Mass Photon Pairs in L+ L- Gamma Gamma Events at LEP/SLC

Recently, the L3 collaboration has reported the observation of four events in the reactions e+ e- --> L+ L- + (2 Photons), L = e, mu, tau, with the invariant photon pair mass near 60 GeV in a data sample collected in the L3 detector corresponding to 950,000 produced Z0's. More recently, more data from the other LEP collaborations have become available. In this paper, we use the Monte Carlo genrator YFS3 and our recent exact results on e+ e- --> L+ L- + (2 Photons) to assess the QED expectations for such L3-type high mass photon pair events in e+ e- --> L+ L- + (n Photons) near the Z0 resonance.Comment: 9 pages (LaTeX + 6 uu-encoded figures), UTHEP-93-1002 (version with corrected preprint number

Multiple photon effects in fermion-(anti)fermion scattering at SSC energies

We use the theory of Yennie, Frautschi and Suura to realize, via Monte Carlo methods, the process f\,\bbbarf\to f'\,\bbbarf'+n\gamma at SSC and LHC energies, where $f$ and $f'$ are quarks or leptons. QED infrared divergences are canceled to all orders in perturbation theory. The resulting Monte Carlo event generator, SSC-YFS2, is used to study the effects of initial-state photon radiation on these processes in the SSC environment. Sample Monte Carlo data are presented and discussed. We find that the respective multiple-photon effects must be taken into account in discussing precise predictions for SSC physics processes.Comment: 14 pages + 8 figures + 1 tabl

Precision Predictions for (Un)Stable W+W- Pair Production At and Beyond LEP2 Energies Beyond LEP2 Energies

We present precision calculations of the processes e+e- -> 4-fermions in which the double resonant W+W- intermediate state occurs. Referring to this latter intermediate state as the 'signal process', we show that, by using the YFS Monte Carlo event generators YFSWW3-1.14 and KORALW1.42 in an appropriate combination, we achieve a physical precision on the signal process, as isolated with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge invariance of our calculations and we compare our results with those of other authors where appropriate. In particular, sample Monte Carlo data are explicitly illustrated and compared with the results of the program RacoonWW of Dittmaier {\it et al.}. In this way, we show that the total (physical plus technical) precision tag for the WW signal process cross section is 0.4 per cent for 200 GeV, for example. Results are also given for 500 GeV with an eye toward the LC.Comment: 19 pages, 2 figs;corrected Tab. 3;improved refs.,figs.,text;improved refs.,text;improved tex

CLEO Contributions to Tau Physics

We review many of the contributions of the CLEO experiment to tau physics. Topics discussed are: branching fractions for major decay modes and tests of lepton universality; rare decays; forbidden decays; Michel parameters and spin physics; hadronic sub-structure and resonance parameters; the tau mass, tau lifetime, and tau neutrino mass; searches for CP violation in tau decay; tau pair production, dipole moments, and CP violating EDM; and tau physics at CLEO-III and at CLEO-c.Comment: Invited talk at the Seventh International Workshop on Tau Lepton Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 14 pages, LaTeX, 21 eps figure

Final State Radiative Effects for the Exact O(alpha) YFS Exponentiated (Un)Stable W+W- Production At and Beyond LEP2 Energies

We present the LL final state radiative effects for the exact O(alpha) YFS exponentiated (un)stable WW pair production at LEP2/NLC energies using Monte Carlo event generator methods. The respective event generator, version 1.12 of the program YFSWW3, wherein both Standard Model and anomalous triple gauge boson couplings are allowed, generates n(\gamma) radiation both from the initial state and from the intermediate W+ W- and generates the LL final state W decay radiative effects. Sample Monte Carlo data are illustrated.Comment: 16 pages, 8 figures, 2 table

Polarized Moller Scattering Asymmetries

The utility of polarized electron beams for precision electroweak studies is described. Parity violating Moller scattering asymmetries in e-e- --> e-e- are discussed. Effects of electroweak radiative corrections and the running sin^2(theta_W(Q^2)) are reviewed. The sensitivity of E158 (a fixed target e-e- experiment at SLAC) and future e-e- collider studies to ``new physics'' is briefly outlined.Comment: Updated Fig.

CLEO Results on Tau Michel Parameters

We present measurements of the tau Michel Parameters made by the CLEO experiment. Three different analyses are performed: a spin-independent lepton spectrum analysis and a second spin-dependent analysis using $\ell^\pm$ \vs\ $\pi^\mp\pi^0$ events, and a third spin-dependent analysis using $\pi^+$ \vs\ $\pi^-$ events. the results are used to derive limits on the general four-fermion couplings, the mass of the charged Higgs in the MSSM, and a right-handed $W$ in left-right models. Many of these measurements are more precise than the PDG world averages.Comment: Invited talk at the TAU'98 Workshop, 14-17 September 1998, Santander, Spain. 7 pages, 7 figures, LaTeX -> postscrip

Radiative Tau Lepton Pair Production as a Probe of Anomalous Electromagnetic Couplings of the Tau

We calculate the squared matrix element for the process e+ e- --> tau+ tau- gamma allowing for anomalous magnetic and electric dipole moments at the tau tau gamma vertex. No interferences are neglected and no approximations of light fermion masses are made. We show that anomalous moments affect not only the cross section, but also the shape of the photon energy and angular distributions. We also demonstrate that in the case of the anomalous magnetic dipole moment, the contribution from interference involving Standard Model and anomalous amplitudes is significant compared to the contribution from anomalous amplitudes alone. A program to perform the calculation is available and it may be employed as a Monte Carlo generator.Comment: 14 pages, 8 figures submitted to Nuclear Physics

Gauge Invariant YFS Exponentiation of (Un)stable W+W−W^+W^- Production At and Beyond LEP2 Energies

We present the theoretical basis and sample Monte Carlo data for the YFS exponentiated calculation of $e^+e^- \rightarrow W^+ W^- \rightarrow f_1\bar f'_1 + \bar f_2 f'_2$ at and beyond LEP2 energies, where the left-handed parts of $f_i$ and $f'_i$ are the respective upper and lower components of an $SU_{2L}$ doublet, $i=1,2$. The problem of gauge invariance of the radiation from the unstable charged spin~1 $W^{\pm}$ is solved in an entirely physical manner. Our formulas are illustrated in a proto-typical YFS Monte Carlo event generator YFSWW2, wherein both Standard Model and anomalous triple gauge boson couplings are allowed.Comment: Latex replaces postscript, 17 page

Measuring the FSR--inclusive pi+pi- cross section

Final state radiation (FSR) in pion--pair production cannot be calculated reliably because of the composite structure of the pions. However, FSR corrections have to be taken into account for a precise evaluation of the hadronic contribution to g-2 of the muon. The role of FSR in both energy scan and radiative return experiments is discussed. It is shown how FSR influences the pion form factor extraction from experimental data and, as a consequence, the evaluation of a_mu^had. In fact the O(alpha) FSR corrections should be included to reach the precision we are aiming at. We argue that for an extraction of the desired FSR--inclusive cross section sigma^(gamma)_had a photon--inclusive scan measurement of the ``e+e- to pi+pi- + photons'' cross section is needed. For exclusive scan and radiative return measurements in contrast we have to rely on ad hoc FSR models if we want to obtain either sigma^(gamma)_had or the FSR--exclusive cross section sigma^(0)_had. We thus advocate to consider seriously precise photon--inclusive energy scan measurements at present and future low energy e+e- facilities. Then together with radiative return measurements from DAFNE and BABAR and forthcoming scan measurements at VEPP-2000 we have a good chance to substantially improve the evaluation of a_mu^had in the future.Comment: 18 pages, 13 Figure