We report results from the analysis of the
(
) decay by the NA48/2 collaboration at the CERN SPS, based on the total statistics of 1.13 million decays collected in 2003–2004. The hadronic form ...factors in the S- and P-wave and their variation with energy are obtained. The phase difference between the S- and P-wave states of the
ππ
system is accurately measured and allows a precise determination of
and
, the I = 0 and I = 2 S-wave
ππ
scattering lengths:
. Combination of this result with the other NA48/2 measurement obtained in the study of
decays brings an improved determination of
and the first precise experimental measurement of
, providing a stringent test of Chiral Perturbation Theory predictions and lattice QCD calculations. Using constraints based on analyticity and chiral symmetry, even more precise values are obtained:
and
.
The magnetic spectrometer of the CERN experiment NA48 uses a conventional dipole magnet with a gap of 2.40 m and a field integral of 0.83 Tm, equivalent to a transverse momentum change of charged ...particles of 250 MeV/
c. This paper introduces the magnet and compares three-dimensional calculations of the magnetic field with the measured field map.
We report on the measurement of the direct emission (DE) and interference (INT) terms of the K±→π±π0γ decay by the NA48/2 experiment at the CERN SPS. From the data collected during 2003 and 2004 ...about 600k such decay candidates have been selected. The relative amounts of DE and INT with respect to the internal bremsstrahlung (IB) contribution have been measured in the range \(0<T^{*}_{\pi }<80\) MeV: \\begin{array}{l}\mathrm{Frac_{\mathrm{DE}}}{(0<T^{*}_{\pi }<80~\mathrm{MeV})}\\3pt\quad =(3.32\pm0.15_{\mathrm{stat}}\pm 0.14_{\mathrm{sys}})\times10^{-2},\\3pt\mathrm{Frac_{\mathrm{INT}}}{(0<T^{*}_{\pi }<80~\mathrm{MeV})}\\3pt\quad =(-2.35\pm 0.35_{\mathrm{stat}}\pm0.39_{\mathrm{sys}})\times10^{-2}\end{array}\ where \(T^{*}_{\pi }\) is the kinetic energy of the charged pion in the kaon rest frame. This is the first observation of an interference term in K±→π±π0γ decays, thus allowing the normalised electric and magnetic amplitudes to be measured, giving XE=(−24±6) GeV−4, and XM=(254±9) GeV−4.In addition, a limit on the CP violating asymmetry in the K+ and K− branching ratios for this channel has been determined to be less than 1.5×10−3 at 90% confidence level.
As first observed by the NA48/2 experiment at the CERN SPS, the π0π0 invariant mass (M00) distribution from K±→π±π0π0 decay shows a cusp-like anomaly at M00=2m+, where m+ is the charged pion mass. An ...analysis to extract the ππ 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±→π±π0π0 decays.
The decay asymmetries of the weak radiative hyperon decays
Ξ
0
→
Λ
γ
and
Ξ
0
→
Σ
0
γ
have been measured with high precision using data of the NA48/1 experiment at CERN. From about 52 000
Ξ
0
→
Λ
γ
...and 15 000
Ξ
0
→
Σ
0
γ
decays, we obtain for the decay asymmetries
α
Ξ
0
→
Λ
γ
=
−
0.704
±
0.019
stat
±
0.064
syst
and
α
Ξ
0
→
Σ
0
γ
=
−
0.729
±
0.030
stat
±
0.076
syst
, respectively. These results are in good agreement with previous experiments, but more precise.
A total of 368 415 Ξ0→Λπ0 and 31 171 Ξ0¯→Λ¯π0 were selected from data recorded in the NA48/1 experiment during 2002 data taking. From this sample, the polarization of Ξ0 and Ξ0¯ hyperons was measured ...to be PΞ0=−0.102±0.012(stat)±0.008(syst) and PΞ0¯=−0.01±0.04(stat)±0.008(syst). The dependence of PΞ0 on the Ξ0 transverse momentum with respect to the primary proton beam is also presented. With the same data sample, the ratio of Ξ0¯ and Ξ0 fluxes in proton collisions at 400 GeV/c on a beryllium target was measured.
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