56 research outputs found
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
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.
A new measurement of K+(e4) decay and the s-wave pi-pi-scattering length a00
A sample of 400000 events from the decay K+->pi+pi-e+nu(e)(K(e4)) has been
collected in experiment E865 at the Brookhaven AGS. The analysis of these data
yields new measurements of the K(e4) branching ratio
(4.11+-0.01+-0.11)*10**(-5)), the s-wave pi-pi scattering length
a00=0.228+-0.012+-0.003, and the form factors F, G, and H of the hadronic
current and their dependence on the invariant pi-pi mass
First observation of the decay K+ -> e+ nu mu+ mu-
Experiment 865 at the Brookhaven AGS has observed the decay K^+ -> e^+ nu
mu^+ mu^-. The branching ratio extracted is (1.72 +/- 0.37(stat) +/- 0.17(syst)
+/- 0.19(model)) x 10^{-8} where the third term in the error results from the
use of a model to extrapolate into a kinematic region dominated by background.Comment: 4 pages, 6 figures, Revtex4. Correction to figure and minor text
change
T-odd correlations in charged Kl4 decays
We analyse the sensitivity to physics beyond the SM of T-odd correlations in
decays, which do not involve the lepton polarization. We show that
a combined analysis of and decays can lead to new
constraints about CP violation in charged-current interactions,
complementary to those obtained from the transverse muon polarization in
and of comparable accuracy.Comment: 6 pages (LaTeX
An Improved upper limit on the decay K^+ -> pi^+ mu^+ e^-
Based on results of a search for the lepton-family-number-violating decay
with data collected by experiment E865 at the
Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an
upper limit on the branching ratio at (90% C.L.).
Combining the results with earlier E865 data and those of a previous
experiment, E777, an upper limit on the branching ratio of (90% C.L.) is obtained.Comment: v2: 13 pages, submitted to the Phys. Rev. D v3: 13 pages, resubmitted
to Phys. Rev. D (corrections include: a more detailed overview of the
combined analysis of the available experimntal data
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 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
New, high statistics measurement of the K+ -> pi0 e+ nu (Ke3) branching ratio
E865 at the Brookhaven National Laboratory AGS collected about 70,000 K+(e3)
events with the purpose of measuring the relative K+(e3) branching ratio. The
pi0 in all the decays was detected using the e+e- pair from pi0 -> e+e-gamma
decay and no photons were required. Using the Particle Data Group branching
ratios for the normalization decays we obtain
BR(K+(e3(gamma))=(5.13+/-0.02(stat)+/-0.09(sys)+/-0.04(norm))%, where
V_{us}$ element of the CKM matrix, and the matrix's
unitarity are discussed.Comment: 4 pages, 5 figures; final version accepted by PR
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