We report results from a new measurement of the K
e4
decay K
±
→π
+
π
-
e
±
ν by the NA48/2 collaboration at the CERN SPS, based on a partial sample of more than 670 000 K
e4
decays in both charged ...modes collected in 2003. The form factors of the hadronic current (F,G,H) and ππ phase difference (δ=δ
s
-δ
p
) have been measured in ten independent bins of the ππ mass spectrum to investigate their variation. A sizeable acceptance at large ππ mass, a low background and a very good resolution contribute to an improved experimental accuracy, a factor two better than in the previous measurement, when extracting the ππ scattering lengths a
0
0
and a
0
2
. Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained in the plane (a
0
0
,a
0
2
): a
0
0
=0.233±0.016stat±0.007syst,a
0
2
=-0.0471±0.011stat±0.004syst. The presence of potentially large isospin effects is also considered and will allow comparison with precise predictions from Chiral Perturbation Theory.
The apeNEXT project Belletti, F.; Bodin, F.; Boucaud, Ph ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2006, Volume:
559, Issue:
1
Journal Article
Peer reviewed
Open access
Numerical simulations in theoretical high-energy physics (Lattice QCD) require huge computing resources. Several generations of massively parallel computers optimised for these applications have been ...developed within the APE (array processor experiment) project. Large prototype systems of the latest generation,
apeNEXT, are currently being assembled and tested. This contribution explains how the
apeNEXT architecture is optimised for Lattice QCD, provides an overview of the hardware and software of
apeNEXT, and describes its new features, like the SPMD programming model and the C compiler.
We present the results of a high statistics lattice calculation of hadronic form factors relevant for
D- and
B-meson semi-leptonic decays into light pseudoscalar and vector mesons. The results have ...been obtained by averaging over 170 gauge field configurations, generated in the quenched approximation, at
β = 6.0, on a 18
3 × 64 lattice, using the
O(
α)-improved SW-Clover action. From the study of the matrix element 〈 K
−|J
μ|D
0 〉, we obtain
f
+(0) = 0.78 ± 0.08 and from the matrix element 〈
K
∗0|J
μ|D
+ 〉 we obtain
V(0) = 1.08 ± 0.22, A
i(0) = 0.67 ± 0.11 and A
2(0) = 0.49 ± 0.34. We also obtain the ratios
V(0)
A
1(0)
= 1.6 ± 0.3
and
A
2(0)
A
1(0)
= 0.7 ± 0.4
. Our predictions for the different form factors are in good agreement with the experimental data, although, in the case of
A
2(0), the errors are still too large to draw any firm conclusion. With the help of the Heavy Quark Effective Theory (HQET) we have also extrapolated the lattice results to
B-meson decays. The form factors follow a behaviour compatible with the HQET predictions. Our results are in agreement with a previous lattice calculation, performed at
β = 6.4, using the standard Wilson action.
The NA48/2 experiment at CERN reports the first observation of the K±→π±π0e+e− decay from an exposure of 1.7×1011 charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% ...background contamination allows the determination of the branching ratio in the full kinematic region, BR(K±→π±π0e+e−)=(4.24±0.14)×10−6. The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated.
Computing for LQCD: apeNEXT Belletti, F.; Lonardo, A.; Rossetti, D. ...
Computing in science & engineering,
2006-Jan.-Feb., 2006-01-00, 20060101, 2006, Volume:
8, Issue:
1
Journal Article
Peer reviewed
apeNEXT is the latest in the APE collaboration's series of parallel computers for computationally intensive calculations such as quantum chromo dynamics on the lattice. The authors describe the ...computer architectural choices that have been shaped by almost two decades of collaboration activity.
A measurement of the form factors of charged kaon semileptonic decays is presented, based on 4.4 × 106K± → π0e±νe (K e3 ± ) and 2.3 × 106K± → π0μ±νμ (K μ3 ±) decays collected in 2004 by the NA48/2 ...experiment. The results are obtained with improved precision as compared to earlier measurements. The combination of measurements in the K e3 ± and K μ3 ± modes is also presented.
A sample of more than one million K +/- ? p + p - e +/- ? (K e 4) decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in ...2003-2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of K e 4 gamma decays, is measured to be BR (K e 4) = (4.257 +/- 0.016 exp +/- 0.031 ext) X 10 - 5 with a total relative error of 0.8 % . This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the pp scattering lengths conducted on the same data sample. The overall form factor normalization f s = 5.705 +/- 0.017 exp +/- 0.031 ext is obtained with a total relative precision of 0.6 % .
Abstract The NA48/2 experiment at CERN reports the first observation of the K ± → π 0 π 0 μ ± ν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. ...The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV2/c 4 is measured to be (0.65 ± 0.03) × 10 −6. The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10 −6, in agreement with chiral perturbation theory predictions.
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