Evidence for Direct CP Violation in $B\pm \to \eta h\pm$ and Observation of $B0 \to \eta K0$.

Abstract

WereportmeasurementsofthebranchingfractionsandCPasymmetriesforB!h(h¼Kor) andtheobservationofthedecayB0!K0fromthefinaldatasampleof772106BBpairscollected withtheBelledetectorattheKEKBasymmetric-energyeþecollider.Themeasuredbranchingfractions areBðB!KÞ¼ð2:120:230:11Þ106,BðB!Þ¼ð4:070:260:21Þ106, andBðB0!K0Þ¼ð1:27þ0:33 0:29 0:08Þ106,wherethelastdecayisobservedforthefirsttime withasignificanceof5.4standarddeviations().WealsofindevidenceforCPviolationinthechargedB modes,ACP ðB!KÞ¼0:380:110:01andACP ðB!Þ¼0:190:060:01with significancesof3:8and3:0,respectively.Forallmeasurements,thefirstandseconduncertaintiesare statisticalandsystematic,respectively.