4,488 research outputs found
The final measurement of by NA48
The direct CP violation parameter Re() has been measured
from the decay rates of neutral kaons into two pions using the NA48 detector at
the CERN SPS. The 2001 running period was devoted to collecting additional data
under varied conditions compared to earlier years (1997-99). The 2001 data
yield the result: Re()=.
Combining this result with that published from the 1997,98 and 99 data, an
overall value of Re()= is
obtained from the NA48 experiment.Comment: 5 pages, 3 figures. Proceedings for the ICHEP02 conferenc
The isospin symmetry breaking effects in decays
The Fermi-Watson theorem is generalized to the case of two coupled channels
with different masses and applied to final state interaction in
decays. The impact of considered effect on the phase of the scattering
is estimated and shown that it can be crucial for scattering lengths extraction
from experimental data on decays
K^+ -> pi^+pi^0e^+e^-: a novel short-distance probe
We study the decay K^+ -> pi^+ pi^0 e^+ e^-, currently under analysis by the
NA62 Collaboration at CERN. In particular, we provide a detailed analysis of
the Dalitz plot for the long-distance, gamma^*-mediated, contributions
(Bremsstrahlung, direct emission and its interference). We also examine a set
of asymmetries to isolate genuine short-distance effects. While we show that
charge asymmetries are not required to test short distances, they provide the
best environment for its detection. This constitutes by itself a strong
motivation for NA62 to study K^- decays in the future. We therefore provide a
detailed study of different charge asymmetries and the corresponding estimated
signals. Whenever possible, we make contact with the related processes K^+ ->
pi^+ pi^0 gamma and K_L -> pi^+ pi^- e^+ e^- and discuss the advantages of K^+
-> pi^+ pi^0 e^+ e^- over them.Comment: 25 pages, 6 figure
Direct CP violation in neutral kaon decays
The final result is presented of the NA48 Experiment performed at CERN SPS
neutral kaon beams on the direct CP violation parameter Re(epsilon'/epsilon),
as maesured from the decay rates of neutral kaons into two pions. The data
collected in years 1997-2001 yield the evidence for direct CP violation with
Re(epsilon'/epsilon)=(14.7+-2.2)10^-4. Description of expermental method and
systematics, comparison with world data and some discussion of implications for
theory are given.Comment: 5 pp., 3 figs, presented on behalf of NA48 Collaboration at PASCOS
2003 Conference, Mumbai, India, 2-8 Jan 2003, to appear in Praman
Radiative corrections to neutral pion-pair production
We calculate the one-photon loop radiative corrections to the neutral
pion-pair photoproduction process . At leading
order this reaction is governed by the chiral pion-pion interaction. Since the
chiral contact-vertex depends only on the final-state
invariant-mass it factors out of all photon-loop diagrams. We give analytical
expressions for the multiplicative correction factor
arising from eight classes of contributing one-photon loop diagrams. An
electromagnetic counterterm has to be included in order to cancel the
ultraviolet divergences generated by the photon-loops. Infrared finiteness of
the virtual radiative corrections is achieved (in the standard way) by
including soft photon radiation below an energy cut-off . The
radiative corrections to the total cross section vary between and
for center-of-mass energies from threshold up to . The finite part of
the electromagnetic counterterm gives an additional constant contribution of
about , however with a large uncertainty.Comment: 10 pages, 6 figures, submitted to Eur. Phys. J.
Soft-photon corrections in multi-body meson decays
The effects due to soft-photon emission (and the related virtual corrections)
in multi-body decays of B, D, and K mesons are analysed. We present analytic
expressions for the universal O(alpha) correction factors which can be applied
to all multi-body decay modes where a tight soft-photon energy cut in the
decaying-particle rest-frame is applied. All-order resummations valid in the
limit of small and large velocities of the final-state particles are also
discussed. The phenomenological implications of these correction factors in the
distortion of Dalitz-plot distributions of K -> 3 pi decays are briefly
analysed.Comment: 8 pages, 2 figures (v2: minor modifications - published version
Two-pion production in deuteron-deuteron collisions at low energies
The cross section for the dd -> 4He pi pi reaction is estimated near
threshold in a two-step model where a pion created in a first interaction
produces a second pion in a subsequent interaction. This approach, which
describes well the rates of 2pi and eta production in the pd -> 3He pi pi and
dd -> 4He eta reactions, leads to predictions that are much too low compared to
experiment. Alternatives to this and the double-Delta model will have to be
sought to explain these data.Comment: 5 pages with 4 postscript figure
Two-loop representations of low-energy pion form factors and pi-pi scattering phases in the presence of isospin breaking
Dispersive representations of the pi-pi scattering amplitudes and pion form
factors, valid at two-loop accuracy in the low-energy expansion, are
constructed in the presence of isospin-breaking effects induced by the
difference between the charged and neutral pion masses. Analytical expressions
for the corresponding phases of the scalar and vector pion form factors are
computed. It is shown that each of these phases consists of the sum of a
"universal" part and a form-factor dependent contribution. The first one is
entirely determined in terms of the pi-pi scattering amplitudes alone, and
reduces to the phase satisfying Watson's theorem in the isospin limit. The
second one can be sizeable, although it vanishes in the same limit. The
dependence of these isospin corrections with respect to the parameters of the
subthreshold expansion of the pi-pi amplitude is studied, and an equivalent
representation in terms of the S-wave scattering lengths is also briefly
presented and discussed. In addition, partially analytical expressions for the
two-loop form factors and pi-pi scattering amplitudes in the presence of
isospin breaking are provided.Comment: 57 pages, 12 figure
The sigma and f_0(980) from K_e4+pi-pi, gamma-gamma scatterings, J/psi, phi to gamma sigma_B and D_s to l nu sigma_B
We extract the pole positions, hadronic and gamma-gamma widths of sigma and
f_0(980, from pi-pi and gamma-gamma scattering data using an improved analytic
K-matrix model. Our results favour a large gluon component for the sigma and a
\bar ss or/and gluon component for the f_0(980) but neither a large four-quark
nor a molecule component. Gluonium sigma_B production from J/psi, phi radiative
and D_s semi-leptonic decays are also discussed.Comment: 4 pages, 5 figures, 6 tables, talk given by X.-G. Wang at QCD 10
(25th anniversary) 28th june-2nd july 2010 (Montpellier - FR
The electromagnetic effects in decay
The final state interaction of pions in decay allows one to obtain
the value of the isospin and angular momentum zero scattering length
.We take into account the electromagnetic interaction of pions and
isospin symmetry breaking effects caused by different masses of neutral and
charged pions and estimate the impact of these effects on the procedure of
scattering length extraction from decay.Comment: 8 pages,1 figur
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