12 research outputs found
Design considerations for the magnetic system of a prototype x-ray free-electron laser
A number of difficult technical challenges need to be solved in the fields of accelerator and free-electron laser (FEL) technologies in order to build an X-ray FEL. One of the tasks well suited to the Advanced Photon Source Low Energy Undulator Test Line (LEUTL) is to take the intermediate step of solving some of the problems of single-pass FEL operation in the ultraviolet range. The existing Advanced Photon Source (APS) linac, in addition to its role of supply positrons for the APS storage ring, will also be used to generate the particle beam for the LEUTL. Here, the design of the magnetic system for the high gain soft x-ray free electron laser is described
Reevaluation of the hadronic contribution to the muon magnetic anomaly using new e+e- -> pi+pi- cross section data from BABAR
Using recently published, high-precision pi+pi- cross section data by the
BABAR experiment from the analysis of e+e- events with high-energy photon
radiation in the initial state, we reevaluate the lowest order hadronic
contribution a_mu[had,LO] to the anomalous magnetic moment of the muon. We
employ newly developed software featuring improved data interpolation and
averaging, more accurate error propagation and systematic validation. With the
new data, the discrepancy between the e+e- and tau-based results for the
dominant two-pion mode reduces from previously 2.4 sigma to 1.5 sigma in the
dispersion integral, though significant local discrepancies in the spectra
persist. We obtain for the e+e- based evaluation amu[had,LO] = (695.5 +- 4.1)
10^-10, where the error accounts for all sources. The full Standard Model
prediction of a_mu differs from the experimental value by 3.2 sigma.Comment: 9 pages, 7 figures. Version published in Eur. Phys. J. C. The theory
vs. experiment discrepancy increased by 0.1 \sigma, using the updated
experimental g-2 value with the new \mu_\mu/\mu_p rati
Pion and Kaon Electromagnetic Form Factors
We study the electromagnetic form factor of the pion and kaons at
low-energies with the use of Chiral Perturbation Theory. The analysis is
performed within the three flavour framework and at next-to-next-to-leading
order. We explain carefully all the relevant consistency checks on the
expressions, present full analytical results for the pion form factor and
describe all the assumptions in the analysis. From the phenomenological point
of view we make use of our expression and the available data to obtain the
charge radius of the pion obtaining , as well
as the low-energy constant . We also obtain
experimental values for 3 combinations of order constants.Comment: 50 page
Extracting Br(omega->pi^+ pi^-) from the Time-like Pion Form-factor
We extract the G-parity-violating branching ratio Br(omega->pi^+ pi^-) from
the effective rho-omega mixing matrix element Pi_{rho omega}(s), determined
from e^+e^- -> pi^+ pi^- data. The omega->pi^+ pi^- partial width can be
determined either from the time-like pion form factor or through the constraint
that the mixed physical propagator D_{rho omega}^{mu nu}(s) possesses no poles.
The two procedures are inequivalent in practice, and we show why the first is
preferred, to find finally Br(omega->pi^+ pi^-) = 1.9 +/- 0.3%.Comment: 12 pages (published version
Tests of isospin symmetry breaking at meson factories
In a model of isospin symmetry breaking we obtain the () amplitude and the isospin and
relative phase at the resonance in aproximate agreement
with experiment. The model predicts \Gamma(\phi \rightarrow \omega \pi^{0})
\approx 4 \cdot 10^{-4} \;\mbox{MeV}. We have also obtained \Gamma (\phi
\rightarrow \eta' \gamma)=5.2 \cdot 10^{-4} \;\mbox{MeV}. Measuring this
partial width would strongly constrain - mixing. The branching
ratios of the isospin violating decays
and are predicted to be and , respectively, leading to and .Comment: 11 pages 2 Figures ( not included available on request ), Latex,
Karlsruhe TTP42-9
The Dipion Mass Spectrum In e+e- Annihilation and tau Decay: A Dynamical (rho0, omega, phi) Mixing Approach
We readdress the problem of finding a simultaneous description of the pion
form factor data in e+e- annihilations and in tau decays. For this purpose, we
work in the framework of the Hidden Local Symmetry (HLS) Lagrangian and modify
the vector meson mass term by including the pion and kaon loop contributions.
This leads us to define the physical rho, omega and phi fields as linear
combinations of their ideal partners, with coefficients being meromorphic
functions of s, the square of the 4--momentum flowing into the vector meson
lines. This allows us to define a dynamical, i.e. s-dependent, vector meson
mixing scheme. The model is overconstrained by extending the framework in order
to include the description of all meson radiative (V P gamma and P gamma gamma
couplings) and leptonic (Ve+e- couplings) decays and also the isospin breaking
(omega/ phi --> pi+ pi-) decay modes. The model provides a simultaneous,
consistent and good description of the e+e- and tau dipion spectra. The
expression for pion form factor in the latter case is derived from those in the
former case by switching off the isospin breaking effects specific to e+e- and
switching on those for tau decays. Besides, the model also provides a good
account of all decay modes of the form V P gamma, Pgamma gamma as well as the
isospin breaking decay modes. It leads us to propose new reference values for
the rho^0 --> e+ e- and omega --> pi+ pi- partial widths which are part of our
description of the pion form factor. Other topics (phi --> K anti K, the rho
meson mass and width parameters) are briefly discussed. Therefore, we confirm
the 3.3 sigma discrepancy between the theoretical estimate of a_mu based on
e+e- and its direct BNL measurement.Comment: 71 pages, 8 figures. Accepted by EPJ C. Version 3: correct minor
typos, minor changes spread out into the text. Extension of Sections 12.2 and
12.3.5 and introduction of the new Appendix
Study of the process in the energy region below 0.98 GeV
The cross section of the process was measured in
the Spherical Neutral Detector (SND) experiment at the VEPP-2M collider in the
energy region below 980 MeV. This measurement was based on about
selected events. The obtained cross section was analyzed
together with the SND and DM2 data in the energy region up to 2
GeV. The -meson parameters: MeV,
MeV and nb were obtained. It was found that the experimental data cannot be
described by a sum of only , , and
resonances contributions. This can be interpreted as a
manifestation of decay, suppressed by -parity, with relative
probability .Comment: 41 pages REVTEX and 34 figure
Reevaluation of the Hadronic Contributions to the Muon g-2 and to alpha(MZ)
We reevaluate the hadronic contributions to the muon magnetic anomaly, and to
the running of the electromagnetic coupling constant at the Z-boson mass. We
include new pi+pi- cross-section data from KLOE, all available multi-hadron
data from BABAR, a reestimation of missing low-energy contributions using
results on cross sections and process dynamics from BABAR, a reevaluation of
all experimental contributions using the software package HVPTools, together
with a reanalysis of inter-experiment and inter-channel correlations, and a
reevaluation of the continuum contributions from perturbative QCD at four
loops. These improvements lead to a decrease in the hadronic contributions with
respect to earlier evaluations. For the muon g-2 we find lowest-order hadronic
contributions of (692.3 +- 4.2) 10^-10 and (701.5 +- 4.7) 10^-10 for the e+e-
based and tau-based analyses, respectively, and full Standard Model predictions
that differ by 3.6 sigma and 2.4 sigma from the experimental value. For the
e+e- based five-quark hadronic contribution to alpha(MZ) we find
Delta_alpha_had[5](MZ)=(275.7 +- 1.0) 10^-4. The reduced electromagnetic
coupling strength at MZ leads to an increase by 7 GeV in the most probable
Higgs boson mass obtained by the standard Gfitter fit to electroweak precision
data.Comment: 13 pages, 10 figures, v2 corrected missing KKpi contribution in Delta
alpha_had(MZ) evaluatio
Hadronic contributions to of the leptons and to the effective fine structure constant
The hadronic contributions to the anomalous magnetic moments of the leptons
and to the effective fine structure constant at the Z-mass are reevaluated
using all presently available data.Comment: 36 pages, 11 Postscript figures, available at
ftp://129.129.40.58/pub/preprints/vapogm2.ps.g
Study of the Process e+ e- --> pi0 pi0 gamma in c.m. Energy Range 600--970 MeV at CMD-2
The cross section of the process e+ e- --> pi0 pi0 gamma has been measured in
the c.m. energy range 600--970 MeV with the CMD-2 detector. The following
branching ratios have been determined: B(rho --> pi0 pi0 gamma)
=(5.2^{+1.5}_{-1.3} +- 0.6)x10^{-5} and B(omega --> pi0 pi0 gamma)
=(6.4^{+2.4}_{-2.0} +- 0.8)x10^{-5}. Evidence for the rho --> f0(600) gamma
decay has been obtained: B(rho --> f0(600) gamma) = (6.0^{+3.3}_{-2.7}\pm
0.9)x10^{-5}. From a search for the process e+ e- --> eta pi0 gamma the
following upper limit has been obtained: B(omega --> eta pi0 gamma) < 3.3
10^{-5} at 90% CL.Comment: 15 pages, 4 figure