2,951 research outputs found
A Tentative Description of Z_c,b States in Terms of Metastable Feshbach Resonances
We attempt a description of the recently discovered Z_{c,b} states in terms
of Feshbach resonances arising from the interaction between the `closed'
subspace of hadrocharmonium levels and the `open' one of open-charm/beauty
thresholds. We show how the neutrality of the X(3872) might be understood in
this scheme and provide a preliminary explanation of the pattern of the
measured total widths of X,Z_{c,b}.Comment: To appear in the proceedings of The 6th International Workshop on
Charm Physics (CHARM 2013
Higher-order QED corrections to single-W production in electron-positron collisions
Four-fermion processes with a particle lost in the beam pipe are studied at
LEP to perform precision tests of the electroweak theory. Leading higher-order
QED corrections to such processes are analyzed within the framework of the
Structure Functions (SF) approach. The energy scale entering the QED SF is
determined by inspection of the soft and collinear limit of the O(alpha)
radiative corrections to the four-fermion final states, paying particular
attention to the process of single-W production. Numerical predictions are
shown in realistic situations for LEP experiments and compared with existing
results. A Monte Carlo event generator, including exact tree-level matrix
elements, vacuum polarization, higher-order leading QED corrections and
anomalous trilinear gauge couplings, is presented.Comment: LaTeX (using elsart), 21 pages, 8 .ps figure
Light Pair Correction to Bhabha Scattering at Small Angle
This work deals with the computation of electron pair correction to small
angle Bhabha scattering, in order to contribute to the improvement of
luminometry precision at LEP/SLC below 0.1% theoretical accuracy. The exact QED
four-fermion matrix element for , including all
diagrams and mass terms, is computed and different Feynman graph topologies are
studied to quantify the error of approximate calculations present in the
literature. Several numerical results, obtained by a Monte Carlo program with
full matrix element, initial-state radiation via collinear structure functions,
and realistic event selections, are shown and critically compared with the
existing ones. The present calculation, together with recent progress in the
sector of purely photonic corrections, contributes to achieve a
total theoretical error in luminometry at the 0.05% level, close to the current
experimental precision and important in view of the final analysis of the
electroweak precision data.Comment: LaTeX2e, 28 pages, 8 figures include
Light-Pair Corrections to Small-Angle Bhabha Scattering in a Realistic Set-up at LEP
Light-pair corrections to small-angle Bhabha scattering have been computed in
a realistic set-up for luminosity measurements at LEP. The effect of
acollinearity and acoplanarity rejection criteria has been carefully analysed
for typical calorimetric event selections. The magnitude of the correction,
depending on the details of the considered set-up, is comparable with the
present experimental error.Comment: 6 pages, LaTeX (elsart.sty), 4 tables, 1 figur
Full one-loop electroweak corrections to e+e- to 3 jets at linear colliders
We describe the impact of the full one-loop electroweak terms of O(alpha_s
alpha_EM^3) entering the electron-positron into three-jet cross-section from
sqrt(s)=M_Z to TeV scale energies. We include both factorisable and
non-factorisable virtual corrections and photon bremsstrahlung. Their
importance for the measurement of alpha_S from jet rates and shape variables is
explained qualitatively and illustrated quantitatively, also in presence of
b-tagging.Comment: 6 pages, to appear in the proceedings of the workshop "LC09 -- e+e-
Physics at the TeV scale and the Dark Matter Connection", 21-24 September
2009, Perugia (Italy). Minor corrections, references added
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