19,991 research outputs found
Tau polarization effects in the CNGS tau-neutrino appearance experiments
We studied tau polarization effects on the decay distributions of tau
produced in the CNGS tau-neutrino appearance experiments. We show that energy
and angular distributions for the decay products in the laboratory frame are
significantly affected by the tau polarization. Rather strong azimuthal
asymmetry about the tau momentum axis is predicted, which may have observable
consequences in experiments even with small statistics.Comment: 5 pages, 6 eps figures, espcrc2.sty; Proceedings of the 4th
International Workshop on Neutrino-Nucleus Interactions in the Few GeV Region
(NuInt05), September 26-29, 2005, Okayama, Japa
Probing the CP nature of the Higgs bosons by top-pair production at photon linear colliders
We study effects of heavy Higgs bosons on the top-pair production process at
photon linear colliders. The interference patterns between the resonant
Higgs-production amplitudes and the continuum QED amplitudes are examined. The
patterns tell us not only the CP nature of the Higgs bosons but also the phase
of the --Higgs vertex which gives new information about the Higgs
couplings to new charged particles. We point out that it is necessary to use
circularly polarized photon beams to produce efficiently heavy Higgs bosons
whose masses exceed the electron beam energy, and show that the above
interference patterns of the production amplitudes can be studied by observing
top decay angular distributions. Analytic expressions for the helicity
amplitudes for the sequential process are presented in
terms of the generic production amplitudes.Comment: 34 pages, LATEX file with 6 PS figures, comments adde
Looking Beyond the Standard Model through Precision Electroweak Physics
The most important hint of physics beyond the Standard Model (SM) from the
1995 precision electroweak data is that the most precisely measured quantities,
the total, leptonic and hadronic decay widths of the and the effective weak
mixing angle, , measured at LEP and SLC, and the quark-lepton
universality of the weak charged currents measured at low energies, all agree
with the predictions of the SM at a few level. By taking into
account the above constraints I examine implications of three possible
disagreements between experiments and the SM predictions. It is difficult to
interpret the 11\% (2.5-) deficit of the -partial-width ratio
, since it either implies an unacceptably large
or a subtle cancellation among hadronic decay widths in order to
keep all the other successful predictions of the SM. The 2\% (3-)
excess of the ratio may indicate the presence of a new
rather strong interaction, such as the top-quark Yukawa coupling in the
supersymmetric (SUSY) SM or a new interaction responsible for the large
top-quark mass in the Technicolor scenario of dynamical electroweak symmetry
breaking. Another interpretation may be additional tree-level gauge
interactions that couple only to the third generation of fermions. A common
consequence of these attempts is a rather small , \alpha_s(\mz
)_{\msbar}=0.104\pm 0.08. The 0.17\% (1-) deficit ...Comment: Talk presented at Yukawa International Seminar (YKIS)~'95, 23 pages,
uuencoded compressed tar file of LaTeX file and 13 EPS files (uses
ptptex.sty,wrapfig.sty,psfig.sty,axodraw.sty) PostScript version of complete
paper available at ftp://ftp.kek.jp/kek/preprints/TH/TH-463/kekth463.ps.g
Sum rules for helicity amplitudes from BRS invariance
The BRS invariance of the electroweak gauge theory leads to relationships
between amplitudes with external massive gauge bosons and amplitudes where some
of these gauge bosons are replaced with their corresponding Nambu-Goldstone
bosons. Unlike the equivalence theorem, these identities are exact at all
energies. In this paper we discuss such identities which relate the process
to and production. By using
a general form-factor decomposition for , and amplitudes, these identities are
expressed as sum rules among scalar form factors. Because these sum rules may
be applied order by order in perturbation theory, they provide a powerful test
of higher order calculations. By using additional Ward-Takahashi identities we
find that the various contributions are divided into separately gauge-invariant
subsets, the sum rules applying independently to each subset. After a general
discussion of the application of the sum rules we consider the one-loop
contributions of scalar-fermions in the Minimal Supersymmetric Standard Model
as an illustration.Comment: 37 pages, including 16 figure
SUSY Particles Searches at LEP and Interpretations within the MSSM
Searches for R-parity conserving supersymmetric particles have been performed
in e+e- data collected by LEP detectors, at centre-of-mass energies up to
209GeV, corresponding to an integrated luminosity of 3.1fb-1. The results and
their interpretation in the context of MSSM frameworks are briefly reviewed.Comment: 4 pages, 5 figures. To be published in Proceedings of 'ICHEP02 - 31st
International Conference on High Energy Physics', 24-31 July 2002, Amsterda
The Decay of Tau Leptons Produced in Neutrino-Nucleon Scatterings
Energy and angular distributions of the tau decay products in the
CERN-to-Gran Sasso appearance experiments are studied for the decay
modes and (l=e or mu). We find that the
decay particle distributions in the laboratory frame are significantly affected
by the tau polarization. Rather strong azimuthal asymmetry of and
about the tau momentum axis is predicted, which may have observable
consequences even at small statistics experiments.Comment: 14 pages, 6 eps figures; comments on Fig. 1 added, Fig. 4 improved to
see clearl
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