Münster 2017 – wissenschaftliches Programm
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T: Fachverband Teilchenphysik
T 52: CP-Verletzung und Mischungswinkel 2
T 52.1: Vortrag
Dienstag, 28. März 2017, 16:45–17:00, JUR 490
Measurement of the Branching Fractions of Semileptonic Kaon Decays and Extraction of the CKM Parameter |Vus| — •Mario Vormstein — Institut für Physik, Joahannes Gutenberg-Universität, Mainz, Deutschland
Semileptonic kaon decays (Kl3+=K+ → π0 l+ ν with l=e,µ) provide a clean way to extract the parameter |Vus| of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. It is one of the fundamental parameters of the Standard Model and is only accessible via experimental measurement. The NA62 collaboration collected K+ decay data in 2007 which are analyzed in the presented work. In total 28 · 106 Kµ 3+, 37 · 106 Ke3+, and 2 · 106 K2π+ candidates were extracted from the data set and used to compute the ratios of branching fractions Br(Kµ3+)/Br(K2π+), Br(Ke3+)/ Br(K2π+), and Br(Kµ3+)/Br(Ke3+). The semileptonic branching fractions Br(Kµ3+) = 3.321(19) % and Br(Ke 3+) = 5.027(22) % follow from the world average of Br(K 2 π+) measurements. They are used to extract the CKM parameter |Vus| = 0.2219(10). The new |Vus| result leads to the unitarity relation |Vud |2 + |Vus|2 + |Vub|2 = 0.9983(6) which disagrees by 2.8 standard deviations with the CKM unitarity prediction.
The e−µ lepton universality is tested with the ratio of the semileptonic branching fractions Br(Kµ3+)/Br(Ke3+) and agrees with the Standard Model prediction.