1,163 research outputs found
Z lineshape and forward-backward asymmetries
Preliminary but close to final results on the Z lineshape and
Forward-Backward asymmetries from the four LEP experiments are presented.
Combined values extracted from ALEPH. DELPHI, L3 and OPAL data recorded at
energies around the Z pole are discussed.Comment: 5 pages, 6 figures, sunbmitted to the Vancouver conference, ICHEP'9
Recent results from NA48/2 on decays and interpretation in terms of scattering lengths
Preliminary results from a new measurement of the decay by the Na48/2 collaboration at the CERN SPS are reported. An unprecedented sample of more than 670000 decays in both charged modes have been collected in 2003. The form factors of the hadronic current (F, G, H) and phase shift () of the scattering have been measured using a model independent method and their variation with the ππ mass has been investigated. First evidence for a non zero term is reported. Thanks to a sizeable acceptance at large mass, a low background and a very good resolution, an improved accuracy can be reached when extracting the scattering length . Using more elaborated theory inputs and another NA48/2 result from decays, a consistent picture can be drawn for the scattering lengths and , in good agreement with Chiral Perturbation Theory predictions
Experimental status of the isoscalar S wave at low energy: pole and scattering length
The experimental results obtained in the last few years on kaon decays
(K and, above all, Ke4 decays) allow a reliable, model independent
determination of low energy scattering in the S0 wave. Using them and,
eventually, other sets of data, it is possible to give a precise
parametrization of the S0 wave as well as to find the scattering length and
effective range parameter. One can also perform an extrapolation to the pole of
the " resonance" []. We obtain the results
and, for the pole, M_\sigma=484\pm17 \mev,\quad\gammav_\sigma/2=
255\pm10 {\rm MeV}.Comment: Plain TeX;4 figures; improved data used; version to appear in Phys.
Rev.
Lattice QCD calculation of scattering length
We study s-wave pion-pion () scattering length in lattice QCD for
pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered
fermion formulation, we calculate the four-point functions for isospin
I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order
to extrapolate our simulation results. Extrapolating to the physical pion mass
gives the scattering lengths as and for isospin I=2 and 0 channels, respectively. Our lattice
simulation for scattering length in the I=0 channel is an exploratory
study, where we include the disconnected contribution, and our preliminary
result is near to its experimental value. These simulations are performed with
MILC 2+1 flavor gauge configurations at lattice spacing fm.Comment: Remove some typo
The sigma and f_0(980) from Ke4 + pi-pi scatterings data
We systematically reconsider, within an improved "analytic K-matrix model",
the extraction of the sigma = f_0(600) and f_0(980) masses, widths and hadronic
couplings using new Ke4 = K-->pi-pi e nu_e data on pi-pi phase shift below 390
MeV and different sets of pi-pi--> pi-pi / K-K scatterings data from 400 MeV to
1.4 GeV. Our results are summarized in Tables 1, 2 and 5. In units of MeV, the
complex poles are: M_sigma=452(12) - i 260(15) and M_f=981(34) -i 18(11), which
are comparable with some recent high-precision determinations and with PDG
values. Besides some other results, we find: |g_{sigma K+K-}|/|g_{sigma
pi+pi-}|=0.37(6) which confirms a sizeable g_{sigma K+K-} coupling found
earlier, and which disfavours a large pi-pi molecule or four-quark component of
the sigma, while its broad pi-pi width (relative to the one of the rho-meson)
cannot be explained within a \bar qq scenario. The narrow pi-pi width of the
f_0(980) and the large value: |g_{f K+K-}|/|g_{f pi+pi-}|=2.59(1.34), excludes
its pure (\bar uu+\bar dd) content. A significant gluonium component eventually
mixed with \bar qq appears to be necessary for evading the previous
difficulties.Comment: 9 pages, 3 figures, 6 table
First Observation and Measurement of the Decay K+- -> pi+- e+ e- gamma
Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e-
gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7
estimated background events. With K+- -> pi+- pi0D as normalisation channel,
the branching ratio is determined in a model-independent way to be Br(K+- ->
pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x
10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass
allow a comparison with predictions of Chiral Perturbation Theory.Comment: 13 pages, 3 figures. Accepted for publication in Phys.Lett.
Empirical parameterization of the K+- -> pi+- pi0 pi0 decay Dalitz plot
As first observed by the NA48/2 experiment at the CERN SPS, the \p0p0
invariant mass (M00) distribution from \kcnn decay shows a cusp-like anomaly
at M00=2m+, where m+ is the charged pion mass. An analysis to extract the pi pi
scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively,
has been recently reported. In the present work the Dalitz plot of this decay
is fitted to a new empirical parameterization suitable for practical purposes,
such as Monte Carlo simulations of K+- -> pi+- pi0 pi0 decays.Comment: 9 pages, 3 figures
Search for direct CP-violation in K+- --> pi+-pi0pi0 decays
A search for direct CP-violation in K+- --> pi+-pi0pi0 decays based on 47.14
million events has been performed by the NA48/2 experiment at the CERN SPS. The
asymmetry in the Dalitz plot linear slopes A_g=(g^+ - g^-)/(g^+ + g^-) is
measured to be A_g=(1.8 +- 2.6).10^{-4}. The design of the experiment and the
method of analysis provide good control of instrumental charge asymmetries in
this measurement. The precision of the result is limited by statistics and is
almost one order of magnitude better than that of previous measurements by
other experiments.Comment: 14 page
ChPT tests at the NA48 and NA62 experiments at CERN
The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of
rare kaon decays in the Ke4 modes: Ke4(+-) ()
and Ke4(00) () with nearly one percent
background contamination. The detailed study of form factors and branching
rates, based on these data, has been completed recently. The results brings new
inputs to low energy strong interactions description and tests of Chiral
Perturbation Theory (ChPT) and lattice QCD calculations. In particular, new
data support the ChPT prediction for a cusp in the invariant mass
spectrum at the two charged pions threshold for Ke4(00) decay. New final
results from an analysis of about 400 rare
decay candidates collected by the NA48/2 and NA62 experiments at CERN during
low intensity runs with minimum bias trigger configurations are presented. The
results include a model-independent decay rate measurement and fits to ChPT
description.Comment: XIIth International Conference on Heavy Quarks and Leptons 2014,
Mainz, German
Recent NA48/2 and NA62 results
The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented
statistics of rare kaon decays in the modes: () and ()
with nearly one percent background contamination. It leads to the improved
measurement of branching fractions and detailed form factor studies. New final
results from the analysis of 381 rare decay
candidates collected by the NA48/2 and NA62 experiments at CERN are presented.
The results include a decay rate measurement and fits to Chiral Perturbation
Theory (ChPT) description.Comment: Prepared for the Proceedings of "Moriond QCD and High Energy
Interactions. March 22-29 2014." conferenc
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