872 research outputs found
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
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
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 and 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 , with
validity for center of mass energies from lepton threshold to 1TeV, that
is for LEP1, LEP2, SLC, future Linear Colliders, -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
precision.Comment: Invited talk presented at Mini-Workshop ``Electroweak Physics Data
and the Higgs Mass'', DESY Zeuthen, Germany, February 28 - March 1, 200
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