arXiv subjects

J. R. Batley

Publications and source records attributed to J. R. Batley.

13 recordsLinked to original sources

arXiv2024

First observation and study of the $K^{\pm} \rightarrow π^{0} π^{0} μ^{\pm} ν$ decay

The NA48/2 experiment at CERN reports the first observation of the $K^{\pm} \rightarrow π^{0} π^{0} μ^{\pm} ν$ 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 $0.03$~GeV$^2/c^4$ is measured to be $(0.65 \pm 0.03) \times 10^{-6}$. The extrapolation to the full kinematic space, using a specific model, is found to be $(3.45 \pm 0.16) \times 10^{-6}$, in agreement with chiral perturbation theory predictions.

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arXiv2016

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(+-) ($K^\pm \to π^+ π^- e^\pm ν$) and Ke4(00) ($K^\pm \to π^0 π^0 e^\pm ν$) 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 $π^0π^0$ invariant mass spectrum at the two charged pions threshold for Ke4(00) decay. New final results from an analysis of about 400 $K^\pm \to π^\pm γγ$ 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.

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arXiv2014

Recent NA48/2 and NA62 results

The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented statistics of rare kaon decays in the $K_{e4}$ modes: $K_{e4}(+-)$ ($K^\pm \to π^+ π^- e^\pm ν$) and $K_{e4}(00)$ ($K^\pm \to π^0 π^0 e^\pm ν$) 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 $K^\pm \to π^\pm γγ$ 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.

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arXiv2013

Measurement of the branching ratio of the decay $Ξ^{0}\rightarrow Σ^{+} μ^{-} \barν_μ$

From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 $Ξ^{0}\rightarrow Σ^{+} μ^{-} \barν_μ$ candidates with a background contamination of $30.8 \pm 4.2$ events. From this sample, the BR($Ξ^{0}\rightarrow Σ^{+} μ^{-} \barν_μ$) is measured to be $(2.17 \pm 0.32_{\mathrm{stat}}\pm 0.17_{\mathrm{syst}})\times10^{-6}$.

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arXiv2010

New Precise Measurements of the $\xilamgam$ and $\xisiggam$ Decay Asymmetries

The decay asymmetries of the weak radiative Hyperon decays Xi0 \to Lambda gamma and Xi0 \to Sigma0 gamma have been measured with high precision using data of the NA48/1 experiment at CERN. From about 52000 Xi0 \to Lambda gamma and 15000 Xi0 \to Sigma0 gamma decays, we obtain for the decay asymmetries alpha(Xi0 \to Lambda gamma) = -0.704 +/- 0.019(stat) +/- 0.064(syst) and alpha(Xi0 \to Sigma0 gamma) = -0.729 +/- 0.030(stat) +/- 0.076(syst), respectively. These results are in good agreement with previous experiments, but more precise.

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arXiv2010

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.

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arXiv2007

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.

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arXiv2007

Search for direct CP violating charge asymmetries in $K^\pm\toπ^\pmπ^+π^-$ and $K^\pm\toπ^\pmπ^0π^0$ decays

A measurement of the direct CP violating charge asymmetries of the Dalitz plot linear slopes $A_g=(g^+-g^-)/(g^++g^-)$ in $K^\pm\toπ^\pmπ^+π^-$ and $K^\pm\toπ^\pmπ^0π^0$ decays by the NA48/2 experiment at CERN SPS is presented. A new technique of asymmetry measurement involving simultaneous $K^+$ and $K^-$ beams and a large data sample collected allowed a result of an unprecedented precision. The charge asymmetries were measured to be $A^c_g=(-1.5\pm2.2)\times10^{-4}$ with $3.11\times 10^9$ $K^{\pm}\toπ^\pmπ^+π^-$ decays, and $A^n_g=(1.8\pm1.8)\times10^{-4}$ with $9.13\times 10^7$ $K^{\pm}\toπ^\pmπ^0π^0$ decays. The precision of the results is limited mainly by the size of the data sample.

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arXiv2007

Measurements of Charged Kaon Semileptonic Decay Branching Fractions K^+- -> pi^0 mu^+- nu and K+- -> pi^0 e^+- nu and Their Ratio

Measured ratios of decay rates for Ke3/K2π, K\mu3/K2πand K\mu3/Ke3 are presented. These measurements are based on K^+- decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are Ke3/K2π= 0.2470 +/- 0.0009 (stat) +/- 0.0004 (syst) and K\mu3/K2π= 0.1637 +/- 0.0006 (stat) +/- 0.0003 (syst). Using the PDG average for the K^+- -> π^+-π^0 normalisation mode, both values are found to be larger than the current values given by the Particle Data Book and lead to a larger magnitude of the |V_{us}| CKM element than previously accepted. When combined with the latest Particle Data Book value of |V_{ud}|, the result is in agreement with unitarity of the CKM matrix. In addition, a new measured value of K\mu3/Ke3 = 0.663 +/- 0.003(stat) +/- 0.001(syst) is compared to the semi-empirical predictions based on the latest form factor measurements.

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arXiv2006

Search for direct CP violation in the decays K\pm \to 3π\pm

We report a measurement of the direct CP violation asymmetry parameter $A_g$ in charged kaon decays $K^\pm\toπ^\pmπ^+π^-$ by the NA48/2 experiment at the CERN SPS. The experiment has been designed not to be limited by systematics in the asymmetry measurement. Using $1.67\times 10^9$ such decays collected during the 2003 run, the charge asymmetry in the Dalitz plot linear slope parameter $g$ has been measured to be $A_g=(1.7\pm2.9)\times 10^{-4}$. The precision of the result is limited by the statistics used.

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arXiv2004

Observation of the rare decay K_S -> pi^0mu^+mu^-

A search for the decay K_S -> pi^0mu^+mu^- has been made by the NA48/1 Collaboration at the CERN SPS accelerator. The data were collected during 2002 with a high-intensity K_S beam. Six events were found with a background expectation of 0.22^+0.18_-0.11 event. Using a vector matrix element and unit form factor, the measured branching ratio is B(K_S -> pi^0mu^+mu^-)=[2.9^+1.5_-1.2(stat)+/-0.2(syst)]x10^{-9}.

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arXiv2004

Measurement of the Branching Ratio and Form Factors for the Decay \boldmath $K_L\toπ^{\pm}π^0e^{\mp}ν_e(\barν_e)

The $K_L\toπ^{\pm}π^0e^{\mp}ν_e(\barν_e)$ decay was investigated with the NA48 detector at CERN SPS using a beam of long-lived neutral kaons. The branching ratio $Br(K_L\toπ^{\pm}π^0e^{\mp}ν_e(\barν_e))=(5.21\pm 0.07_{stat}\pm 0.09_{syst})\times 10^{-5}$ was fixed from a sample of 5464 events with 62 background events. The form factors $\bar{f}_s$, $\bar{f}_p$, $λ_g$ and $\bar{h}$ were found to be in agreement with previous measurements but with higher accuracy. The coupling parameter of the chiral Lagrangian $L_3=(-4.1\pm 0.2)\times 10^{-3}$ was evaluated from the data.

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arXiv2002

A precision measurement of direct CP violation in the decay of neutral kaons into two pions

The direct CP violation parameter Re(epsilon'/epsilon) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997-99). The new data yield the result: Re(epsilon'/epsilon) = (13.7 +/- 3.1) times 10^{-4}. Combining this result with that published from the 1997, 98 and 99 data, an overall value of Re(epsilon'/epsilon) = (14.7 +/- 2.2) times 10^{-4} is obtained from the NA48 experiment.

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