CEEX Exponentiation in QED

The aim is to summarize briefly on: (a) Main features of YFS Cohenetn Exclusive EXponentiation in QED, (b) Examples of recent results relevant for LEP/LC physics program.Comment: ICHEP 2002 tal

Precision calculation for e+ e- -> 2f: the KK MC project

We present the current status of the coherent exclusive (CEEX) realization of the YFS theory for the processes in e+ e- -> 2f via the KK MC. We give a brief summary of the CEEX theory in comparison to the older (EEX) exclusive exponentiation theory and illustrate recent theoretical results relevant to the LEP2 and LC physics programs.Comment: 5 pages, 4 figures, 2 diagrams - presented by BFLW at RADCOR0

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

Coherent Exclusive Exponentiation for Precision Monte Carlo Calculations

In this contribution we give a short overview of the new Coherent Exclusive Exponentiation (CEEX) which is implemented in the new \KK MC event generator for the process $e^+e^-\to f\bar{f} +n\gamma$, $f=\mu,\tau,d,u,s,c,b$ with validity for center of mass energies from $\tau$ lepton threshold to 1TeV, that is for LEP1, LEP2, SLC, future Linear Colliders, $b,c,\tau$-factories etc. In CEEX effects due to photon emission from initial beams and outgoing fermions are calculated in QED up to second-order, including all interference effects. Electroweak corrections are included in first-order, at the amplitude level. Beams can be polarized longitudinally and transversely, and all spin correlations are incorporated in an exact manner. We describe briefly the essence of CEEX as compared with older exclusive variants of the exponentiation (EEX) and present samples of the numerical results, concentrating on the question of the technical and physical precision for the total cross section and for the charge asymmetry. New results on the interference between initial and final state photon emission at LEP2 energies are also shown.Comment: new paper, not replacement for hep-ph/000635

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

Coherent Exclusive Exponentiation CEEX: the Case of the Resonant e+ e- Collision

We present the first-order coherent exclusive exponentiation (CEEX) scheme, with the full control over spin polarization for all fermions. In particular it is applicable to difficult case of narrow resonances. The resulting spin amplitudes and the differential distributions are given in a form ready for their implementation in the Monte Carlo event generator. The initial-final state interferences are under control. The way is open to the use of the exact amplitudes for two and more hard photons, using Weyl-spinor techniques, without giving up the advantages of the exclusive exponentiation, of the Yennie-Frautschi-Suura type.Comment: 14 page

QCD soft gluon exponentiation: YFS MC Approach

We develop and prove the theory of the QCD extension of the YFS Monte Carlo approach to higher order QED radiative corrections. As a corollary, a new approach to quantum gravity by one of us (B.F.L.W.) is illustrated. Semi-analytical results and preliminary explicit Monte Carlo data are presented for the processes p-bar p -> t-bar t + X at FNAL energies. We comment briefly on the implications of our results on the CDF/D0 observations and on RHIC/LHC physics.Comment: 4 pages, 2 figures, presented at ICHEP02 by BFL

Foam: Multi-Dimensional General Purpose Monte Carlo Generator With Self-Adapting Simplical Grid

A new general purpose Monte Carlo event generator with self-adapting grid consisting of simplices is described. In the process of initialization, the simplex-shaped cells divide into daughter subcells in such a way that: (a) cell density is biggest in areas where integrand is peaked, (b) cells elongate themselves along hyperspaces where integrand is enhanced/singular. The grid is anisotropic, i.e. memory of the axes directions of the primary reference frame is lost. In particular, the algorithm is capable of dealing with distributions featuring strong correlation among variables (like ridge along diagonal). The presented algorithm is complementary to others known and commonly used in the Monte Carlo event generators. It is, in principle, more effective then any other one for distributions with very complicated patterns of singularities - the price to pay is that it is memory-hungry. It is therefore aimed at a small number of integration dimensions (<10). It should be combined with other methods for higher dimension. The source code in Fortran77 is available from http://home.cern.ch/~jadac

Observables with tau leptons at LHC and LC structure of event records and Monte Carlo Algorithms

In the present report, let us adress the issues related to simulation of decays for particle embodied in full production and decay chains of Monte Carlo programs set-up for experiments such as at LHC or LC. Both technical issues related to the way how the events may be stored in event records and issues related to physics (in particular non-factorizable correlations of the Einstein-Rosen-Podolsky type) will be reviewed on the basis of practical examples. We will limit our discussion to the case of tau lepton and W boson decays, but similar problems (and solutions) may arise also in case of simulation for other intermediate states or particles. Examples related to construction of physics observables will be also given. In particular the method of measuring the CP parity properties of the h-tau-tau coupling at LC will be explained.Comment: 5 pages, 3 Postscript figures, uses espcrc2.sty, Presented at IX Workshop on A C A T in Physics Research, December 1-5, 2003, KEK, Tsukuba, Japa

Theoretical error of luminosity cross section at LEP

The aim of this note is to characterize briefly main components of theoretical error of the small angle Bhabha measurement at LEP and to discuss critically how solid these estimates really are, from todays perspective. We conclude that the existing theoretical error of the LEP luminometer process (small angle Bhabha) is rather solid, and we add some new discussion concerning the remaining uncertainties and prospects of the future improvements toward the $\le 0.025$ precision.Comment: Invited talk presented at Mini-Workshop ``Electroweak Physics Data and the Higgs Mass'', DESY Zeuthen, Germany, February 28 - March 1, 200