Recent Results in Rare and Semileptonic Kaon Decays from NA48

Abstract

Recent results are presented on rare neutral kaon decays from the NA48/1 collaboration, and on semileptonic charged kaon decays from the NA48/2 collaboration. Using data taken on 2002, NA48/1 has measured the CP conserving component of the decay K 0 → π 0 π + π − . For the λ parameter describing this decay the values Re ( λ ) = 0.038 ± 0.008 s t a t ± 0.006 s y s t and Im ( λ ) = − 0.013 ± 0.005 s t a t ± 0.004 s y s t have been obtained. This is consistent with previous measurements and with chiral perturbation theory predictions. NA48/1 has also measured the BR ( K s → π ± e ∓ ν ) = ( 6.8 ± 0.2 s t a t ± 0.2 s y s t ) 10 −4 , consistent with Δ S = Δ Q . Using data collected during eight hours minimum bias run on 2003, the NA48/2 collaboration has measured BR ( K ± → π 0 e ± ν ) = ( 5.14 ± 0.02 s t a t ± 0.06 s y s t ) 10 −2 , where the channel K ± → π 0 π ± has been used as normalization. From the same data sample, the ratio of K ± → π 0 μ ± ν to K ± → π 0 e ± ν has been obtained. This results on BR ( K ± → π 0 μ ± ν ) = ( 3.462 ± 0.018 s t a t ± 0.006 s y s t ± 0.011 λ + , λ 0 ± 0.068 n o r m ) . From semileptonic decays the value of the CKM matrix element V u s can be extracted. The values of V u s | f + ( 0 ) | obtained by NA48/2 from electron and muon channels are compatible. The result on K 0 → π 0 π + π − is final, and all the other results presented here are preliminary.