2,449 research outputs found
On the theoretical uncertainties in the muon anomalous magnetic moment
I present a fairly detailed discussion of various contributions to the
anomalous magnetic moment of the muon a_mu. I try to give an unbiased
evaluation of the validity of the SM prediction for this quantity and to point
out some delicate issues involved in its calculation. I conclude that the
theory uncertainties in the SM prediction for the muon anomalous magnetic
moment are underestimated and a great deal of work will be required to reduce
these uncertainties to the level required by experiment.Comment: 12 pages, revte
Complementarity of a Low Energy Photon Collider and LHC Physics
We discuss the complementarity between the LHC and a low energy photon
collider. We mostly consider the scenario, where the first linear collider is a
photon collider based on dual beam technology like CLIC.Comment: 29 pages, 37 figure, LP-200
Exclusive hadronization in gamma* gamma -> pi pi
We perform a QCD analysis of exclusive two-meson production in gamma* gamma
collisions in the kinematical domain of large photon virtuality Q^2 and small
hadronic invariant mass W^2. In these kinematics the amplitude factorizes into
a perturbative subprocess gamma* gamma -> q qbar and a two-meson distribution
amplitude. This opens the way to study new hadronic matrix elements related
with the physics of hadronization and confinement.Comment: 5 pages, 1 figure. Talk given at PHOTON 99, Freiburg, Germany, 23-27
May 1999. Eq. (8) correcte
QED radiative corrections to the decay pi^0 to e^+e^-
We reconsider QED radiative corrections (RC) to the
decay width. One kind of RC investigated earlier has a renormalization group
origin and can be associated with the final state interaction of electron and
positron. It determines the distribution of lepton pair invariant masses in the
whole kinematic region. The other type of RC has a double-logarithmic character
and is related to almost on-mass-shell behavior of the lepton form factors. The
total effect of RC for the decay is estimated to be
3.2% and for the decay is 4.3%.Comment: 12 pages, 3 figure
Symmetry-breaking corrections to heavy-to-light B meson form factors at large recoil
Recently it has been shown that symmetries emerging in the heavy quark and
large recoil energy limit impose various relations on form factors that
parametrise the decay of B mesons into light mesons. These symmetries are
broken by perturbative effects. In this paper we discuss the structure of
heavy-to-light form factors including such effects and compute
symmetry-breaking corrections to first order in the strong coupling. As an
application of our results we consider the forward-backward asymmetry zero in
the rare decay B -> V l^+ l^- and the possibility to constrain potential new
physics contributions to the Wilson coefficient C_9.Comment: 30 pages, LaTeX (typos in eq. (44), (46) corrected
Two photon decay of the pseudoscalars, the chiral symmetry breaking corrections
The extrapolation of the decay amplitudes of the pseudoscalar mesons into two
photons from the soft meson limit where it is obtained from the axial-anomaly
to the mass shell involves the contribution of the 0^ - continuum. These chiral
symmetry breaking corrections turn out to be large. The effects of these
corrections on the calculated pi ^0 decay rate, on the values of the
singlet-octet mixing angle and on the ratios f_8 / f_pi and f_0 / f_pi are
discussed. The implications for the transition form factors gamma gamma* -->
pseudoscalars are also evaluated and confronted with the available experimental
data.Comment: Computational errors straightened and study of the implications on
the form factors of the transitions gamma gamma* --> pseudoscalars adde
Detecting and Studying Higgs Bosons at a Photon-Photon Collider
We examine the potential for detecting and studying Higgs bosons at a
photon-photon collider facility associated with a future linear collider. Our
study incorporates realistic \gam\gam luminosity spectra based on the most
probable available laser technology. Results include detector simulations. We
study the cases of: a) a SM-like Higgs boson; b) the heavy MSSM Higgs bosons;
c) a Higgs boson with no couplings from a general two Higgs doublet
model.Comment: 52 pages, 26 figures, revised version with new appendi
Second moment of the pion's distribution amplitude
We present preliminary results from the QCDSF/UKQCD collaborations for the
second moment of the pion's distribution amplitude with two flavours of
dynamical fermions. We use nonperturbatively determined renormalisation
coefficients to convert our results to the MSbar scheme at 5 GeV^2. Employing a
linear chiral extrapolation from our large pion masses >550 MeV, we find
=0.281(28), leading to a value of a_2=0.236(82) for the second Gegenbauer
moment.Comment: 6 pages, 5 figures, 1 table. To appear in: Procs. of the Workshop on
Light-Cone QCD and Nonperturbative Hadron Physics 2005 (LC 2005), Cairns,
Australia, 200
Higgs Physics with a gamma gamma Collider Based on CLIC 1
We present the machine parameters and physics capabilities of the CLIC Higgs
Experiment (CLICHE), a low-energy collider based on CLIC 1, the
demonstration project for the higher-energy two-beam accelerator CLIC. CLICHE
is conceived as a factory capable of producing around 20,000 light Higgs bosons
per year. We discuss the requirements for the CLIC 1 beams and a laser
backscattering system capable of producing a total (peak)
luminosity of cms with GeV. We show how CLICHE could be used to measure accurately
the mass, , and decays of a light Higgs boson.
We illustrate how these measurements may distinguish between the Standard Model
Higgs boson and those in supersymmetric and more general two-Higgs-doublet
models, complementing the measurements to be made with other accelerators. We
also comment on other prospects in and physics with
CLICHE.Comment: 34 pages, 20 figures, Latex. submitted to Eur. Phys. Jou
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