12,065 research outputs found
Interference of Conversion and Bremsstrahlung Amplitudes in the Decay K_L -> mu^+ mu^- gamma
In the region of large mu^+ mu^- invariant mass, the decay spectrum of K_L ->
mu^+ mu^- gamma deviates from the Dalitz pair spectrum, as a result of
interference between conversion (K_L -> gamma^* gamma -> mu^+ mu^- gamma) and
bremsstrahlung amplitudes. The latter is proportional to the K_L -> mu^+ mu^-
matrix element, whose 2 gamma-absorptive part appears to dominate the observed
K_L -> mu^+ mu^- decay rate. We examine the extent to which a scrutiny of the
K_L -> mu^+ mu^- gamma spectrum in the end-point region could provide evidence
on the real part of the K_L -> mu^+ mu^- amplitude. As a by-product, we obtain
the absorptive part of the K_L -> gamma^* gamma form factor, using data on the
K_L -> pi^+ pi^- gamma spectrum.Comment: 7 pages, 4 figure
Time Evolution of Decay Spectrum in K^0, K^0 bar -> pi^+ pi^- e^+ e^-
We consider the decay K^0 (K^0 bar) -> pi^+ pi^- e^+ e^- of a neutral K meson
prepared in a state of strangeness +1 (-1). The time evolution of the state
produces remarkable time-dependent effects in the angular distribution of the
pi^+ pi^- e^+ e^- system. These effects are correlated with the time-dependence
of the photon polarization in the radiative decay K^0 (K^0 bar) -> pi^+ pi^-
gamma. We study, in particular, the CP-odd, T-odd term in the distribution d
Gamma / d phi of the angle between the pi^+ pi^- and the e^+ e^- planes. We
also give the spectrum in the case that the decaying meson is an incoherent
mixture of K^0 and K^0 bar, and discuss the case of K_S regeneration in a K_L
beam.Comment: 16 pages, 8 figures, minor typos corrected, to appear in Phys. Lett.
PCAC and the Deficit of Forward Muons in pi^+ Production by Neutrinos
The K2K experiment, using a fine-grained detector in a neutrino beam of
energy has observed two-track events that can be
interpreted as a coherent reaction or an incoherent process , the final nucleon being unobserved. The data show a significant
deficit of forward-going muons in the interval ,
where a sizeable coherent signal is expected. We attempt an explanantion of
this effect, using a PCAC formula that includes the effect of the non-vanishing
muon mass. A suppression of about 25 % is caused by a destructive interference
of the axial vector and pseudoscalar (pion-exchange) amplitudes. The incoherent
background is also reduced by 10 - 15 %. As a consequence the discrepancy
between theory and observation is significantly reduced.Comment: 4 pages including 1 figure, changes in abstract and text; version to
appear in Phys.Lett.
Status of the KTeV Experiment at Fermilab
The KTeV experiment is a fixed target experiment at Fermilab. Its primary
goal is the search for direct CP violation in the decay of neutral kaons. Its
current status and some preliminary results will be discussed.Comment: 5 pages Latex, 4 figures; to be published in the proceedings of the
XVI International Workshop on Weak Interactions and Neutrinos, WIN '97,
Capri, Italy, June 22-28, 199
Flow of entropy in the evolution of the B^0 anti B^0 system: Upper bound on CP violation from unidirectionality
We have previously studied the time-dependence of a B anti B meson mixture in
terms of its density matrix. The requirement that the absolute value of the
Stokes vector zeta(t) should evolve monotonically from its initial value
zeta(0)=0 to its final value zeta(infinity)=1 was shown to lead to an upper
bound on the CP violating overlap . In the present note we consider an
entropy variable S as an alternative measure of mixing. We show that exactly
the same upper bound emerges from the requirement that the flow of entropy is
unidirectional (dS/dt<0). We compare the entropic current dS/dt with and
without CP violation and identify certain physical features that appear when
the bound on is violated.Comment: 8 pages, 4 figures. Typos corrected, comment on entropy added. To be
published in Physical Review
Interference and Partial Width Asymmetry in Top and Antitop Decays
We re-examine the question of a possible difference in the partial decay
widths of and , induced by an intermediate scalar boson
with -violating couplings. The interference of and exchanges is
analysed by constructing the propagator matrix of the
system, and determining its absorptive part in terms of fermion loops. Results
are obtained for the partial rate difference in the channels
and , which fulfil explicitly the constraints of
invariance. These results are contrasted with those in previous work.Comment: 14 pages, report PITHA 94/1
The CP-violating asymmetry in K_L -> pi+ pi- e+ e-
We update the theoretical analysis of the CP-violating asymmetry in the decay
K_L -> pi+ pi- e+ e-, relying on chiral perturbation theory and on the most
recent phenomenological information. With the experimentally determined
magnetic amplitude and branching ratio as input, the asymmetry can be
calculated with good accuracy. The theoretical interpretation of the sign of
the asymmetry is discussed.Comment: 11 page
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