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NA48 Collaboration

Publications and source records attributed to NA48 Collaboration.

9 recordsLinked to original sources
arXiv2007

First observation and branching fraction and decay parameter measurements of the weak radiative decay Xi0 --> Lambda e+e-

The weak radiative decay Xi0 --> Lambda e+e- has been detected for the first time. We find 412 candidates in the signal region, with an estimated background of 15 +/- 5 events. We determine the branching fraction B(Xi0 --> Lambda e+e-) = [7.6 +/- 0.4(stat) +/- 0.4(syst) +/- 0.2(norm)] x 10^{-6}, consistent with an internal bremsstrahlung process, and the decay asymmetry parameter alpha_{XiLambdaee} = -0.8 +/- 0.2, consistent with that of Xi0 --> Lambda gamma. The charge conjugate reaction Xi0_bar --> Lambda_bar e+e- has also been observed.

hep-ex↗
arXiv2006

Measurement of the Ratio Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu) and Extraction of the CP Violation Parameter |eta+-|

We present a measurement of the ratio of the decay rates Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu), denoted as Gamma(K2pi)/Gamma(Ke3). The analysis is based on data taken during a dedicated run in 1999 by the NA48 experiment at the CERN SPS. Using a sample of 47000 K2pi and five million Ke3 decays, we find Gamma(K2pi)/Gamma(Ke3) = (4.835 +- 0.022(stat) +- 0.016(syst)) x 10^-3. From this we derive the branching ratio of the CP violating decay KL -> pi+ pi- and the CP violation parameter |eta+-|. Excluding the CP conserving direct photon emission component KL -> pi+ pi- gamma, we obtain the results BR(KL -> pi+ pi-) = (1.941 +- 0.019) x 10^-3 and |eta+-| = (2.223 +- 0.012) x 10^-3.

hep-ex↗
arXiv2004

Search for CP violation in K0 -> 3 pi0 decays

Using data taken during the year 2000 with the NA48 detector at the CERN SPS, a search for the CP violating decay K_S -> 3 pi0 has been performed. From a fit to the lifetime distribution of about 4.9 million reconstructed K0/K0bar -> 3 pi0 decays, the CP violating amplitude eta_000 = A(K_S -> 3 pi0)/A(K_L -> 3 pi0) has been found to be Re(eta_000) = -0.002 +- 0.011 +- 0.015 and Im(eta_000) = -0.003 +- 0.013 +- 0.017. This corresponds to an upper limit on the branching fraction of Br(K_S -> 3 pi0) < 7.4 x 10^-7 at 90% confidence level. The result is used to improve knowledge of Re(epsilon) and the CPT violating quantity Im(delta) via the Bell-Steinberger relation.

hep-ex↗
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.

hep-ex↗
arXiv2003

First observation of the KS->pi0 gamma gamma decay

Using the NA48 detector at the CERN SPS, 31 KS->pi0 gamma gamma candidates with an estimated background of 13.7 +- 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS->pi0 gamma gamma) = (4.9 +- 1.6(stat) +- 0.9(syst)) x 10^-8 in agreement with Chiral Perturbation theory predictions.

hep-ex↗
arXiv2002

A Measurement of the K_S Lifetime

A measurement of the K_S lifetime is presented using data recorded by the NA48 experiment at the CERN-SPS during 1998 and 1999. The K_S lifetime is derived from the ratio of decay time distributions in simultaneous, collinear K_S and K_L beams, giving a result which is approximately independent of the detector acceptance and with reduced systematic errors. The result obtained is tau_S=(0.89598 +- 0.00048 +- 0.00051)x10^(-10) s, where the first error is statistical and the second systematic.

hep-ex↗
arXiv2001

A precise measurement of the direct CP violation parameter Re(epsilon'/epsilon)

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. With 3.3 million KL->pi0pi0 events collected during the 1998 and 1999 running periods, a result of Re(epsilon'/epsilon) = (15.0 +- 2.7)x10-4 has been obtained. The result combined with the published 1997 sample is Re(epsilon'/epsilon) = (15.3 +- 2.6)x10-4.

hep-ex↗
arXiv2001

Measurement of the quadratic slope parameter in the K_L -> 3π^0 decay Dalitz plot

A value of (-6.1 +- 0.9_{stat} +- 0.5_{syst})*10^{-3} is obtained for the quadratic slope parameter h in the K_L -> 3π^0 decay Dalitz plot at the NA48 experiment at the CERN SPS. The result is based on 14.7*10^6 fully reconstructed K_L -> 3π^0 -> 6γdecays. This is the most precise measurement of any of the Dalitz plot slope parameters in the charged and neutral kaon decays so far.

hep-ex↗