Measurement of the CP-violation Parameter sin2\phi_1 with a New Tagging Method at the \Upsilon(5S) Resonance.

Abstract

WereportameasurementoftheCP-violationparametersin21attheð5SÞresonanceusinganew taggingmethod,called‘‘B-tagging.’’Inð5SÞdecayscontaininganeutralBmeson,achargedB,anda chargedpion,theneutralBisreconstructedintheJ=cK0S CP-eigenstatedecaychannel.Theinitialflavor oftheneutralBmesonatthemomentoftheð5SÞdecayisoppositetothatofthechargedBandmaythus beinferredfromthechargeofthepionwithoutreconstructingthechargedB.Fromtheasymmetry betweenB-þandB-taggedJ=cK0S yields,wedeterminesin21 ¼0:570:58ðstatÞ0:06ðsystÞ. Theresultsarebasedon121fb1ofdatarecordedbytheBelledetectorattheKEKBeþecollider.