0000000000248320
AUTHOR
G. Pierazzini
First measurement of the rate K0L → πμνγ
Abstract In a preliminary version of the NA48 experiment at the CERN SPS, in which an iron-scintillator sandwich calorimeter was used as a photon detector, the ratio of K L → πμνγ and K L → πμν decays was measured. The branching ratio BR(K L →πμνγ, E γ ∗ ≥30 MeV )/(K L → πμν ) is found to be (2.08±0.17 +0.16 −0.21 )×10 −3 , where the first error is statistical and the second systematic. The result is in agreement with theoretical predictions.
Measurement of the branching ratios of the decays Ξ0→Σ+e−ν¯e and Ξ0¯→Σ+¯e+νe
Abstract From 56 days of data taking in 2002, the NA48/1 experiment observed 6316 Ξ 0 → Σ + e − ν ¯ e candidates (with the subsequent Σ + → p π 0 decay) and 555 Ξ 0 ¯ → Σ + ¯ e + ν e candidates with background contamination of 215 ± 44 and 136 ± 8 events, respectively. From these samples, the branching ratios BR ( Ξ 0 → Σ + e − ν ¯ e ) = ( 2.51 ± 0.03 stat ± 0.09 syst ) × 10 −4 and BR ( Ξ 0 ¯ → Σ + ¯ e + ν e ) = ( 2.55 ± 0.14 stat ± 0.10 syst ) × 10 −4 were measured allowing the determination of the CKM matrix element | V us | = 0.209 −0.028 +0.023 . Using the Particle Data Group average for | V us | obtained in semileptonic kaon decays, we measured the ratio g 1 / f 1 = 1.20 ± 0.05 of the …
Search for direct CP violation in the decays K-+/- -> 3 pi(+/-)
Abstract We report a measurement of the direct CP violation asymmetry parameter A g in charged kaon decays K ± → π ± π + 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 × 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 ± 2.9 ) × 10 −4 . The precision of the result is limited by the statistics used.
First observation and study of the K± → π±π0e+e− decay
The NA48/2 experiment at CERN reports the first observation of the K-+/- -> pi(+/-)pi(0)e(+)e(-) decay from an exposure of 1.7 x 10(11) 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-+/- -> pi(+/-)pi(0)e(+)e(-)) = (4.24 +/- 0.14) x 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.
Search for the dark photon in π0 decays
A sample of $1.69\times 10^7$ fully reconstructed $\pi^0\to\gamma e^+e^-$ decay candidates collected by the NA48/2 experiment at CERN in 2003--2004 is analysed to search for the dark photon ($A'$) production in the $\pi^0\to\gamma A'$ decay followed by the prompt $A'\to e^+e^-$ decay. No signal is observed, and an exclusion region in the plane of the dark photon mass $m_{A'}$ and mixing parameter $\varepsilon^2$ is established. The obtained upper limits on $\varepsilon^2$ are more stringent than the previous limits in the mass range $9~{\rm MeV}/c^2<m_{A'}<70~{\rm MeV}/c^2$. The NA48/2 sensitivity to the dark photon production in the $K^\pm\to\pi^\pm A'$ decay is also evaluated.
Measurement of the polarization of the Ξ0 (Ξ0¯) hyperon beam by the NA48/1 experiment
Abstract A total of 368 415 Ξ 0 → Λ π 0 and 31 171 Ξ 0 ¯ → Λ ¯ π 0 were selected from data recorded in the NA48/1 experiment during 2002 data taking. From this sample, the polarization of Ξ 0 and Ξ 0 ¯ hyperons was measured to be P Ξ 0 = − 0.102 ± 0.012 (stat) ± 0.008 (syst) and P Ξ 0 ¯ = − 0.01 ± 0.04 (stat) ± 0.008 (syst) . The dependence of P Ξ 0 on the Ξ 0 transverse momentum with respect to the primary proton beam is also presented. With the same data sample, the ratio of Ξ 0 ¯ and Ξ 0 fluxes in proton collisions at 400 GeV / c on a beryllium target was measured.
New precise measurements of the and decay asymmetries
Abstract 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.
Measurement of the quadratic slope parameter in the K-L -> 3 pi(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 -> 3\pi^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 -> 3\pi^0 -> 6\gamma decays. This is the most precise measurement of any of the Dalitz plot slope parameters in the charged and neutral kaon decays so far.
Study of the K±→π±γγ decay by the NA62 experiment
Abstract A study of the dynamics of the rare decay K ± → π ± γ γ has been performed on a sample of 232 decay candidates, with an estimated background of 17.4 ± 1.1 events, collected by the NA62 experiment at CERN in 2007. The results are combined with those from a measurement conducted by the NA48/2 Collaboration at CERN. The combined model-independent branching ratio in the kinematic range z = ( m γ γ / m K ) 2 > 0.2 is B MI ( z > 0.2 ) = ( 0.965 ± 0.063 ) × 10 − 6 , and the combined branching ratio in the full kinematic range assuming a Chiral Perturbation Theory description is B ( K π γ γ ) = ( 1.003 ± 0.056 ) × 10 − 6 . A detailed comparison of the results with the previous measurements…
Search for the decay KS → π0γγ
Abstract A search for the decay K S → π 0 γγ has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity K S beam, an upper limit for the branching ratio BR ( K S → π 0 γγ , z ⩾0.2) −7 has been obtained at 90% confidence level, where z = m γγ 2 / m K 0 2 .
Precision measurement of the ratio of the charged kaon leptonic decay rates
A precision measurement of the ratio RK of the rates of kaon leptonic decays K+- --> e nu and K+- --> mu nu with the full data sample collected by the NA62 experiment at CERN in 2007-2008 is reported. The result, obtained by analysing ~150000 reconstructed K+- --> e nu candidates with 11% background contamination, is RK = (2.488+-0.010)*10^{-5}, in agreement with the Standard Model expectation.
Measurement of the Dalitz plot slope parameters of the K±→π±π+π− decay
Abstract The distribution of the K ± → π ± π + π − decays in the Dalitz plot has been measured by the NA48/2 experiment at the CERN SPS with a sample of 4.71 × 10 8 fully reconstructed events. With the standard Particle Data Group parameterization the following values of the slope parameters were obtained: g = ( − 21.134 ± 0.017 ) % , h = ( 1.848 ± 0.040 ) % , k = ( − 0.463 ± 0.014 ) % . The quality and statistical accuracy of the data have allowed an improvement in precision by more than an order of magnitude, and are such as to warrant a more elaborate theoretical treatment, including pion–pion rescattering, which is in preparation.