Features ofsignal (I)Signal meansJ/y→pKA+c.c.A signal (very strong constraint)z/sAoeuaDataMC(b)a400050020001.1251.151.17GeV/c2111.1251.151.17GeV/c82After selection, the clear A signal in data shows high purity ofsignal
Features of signal (I) Signal means • Λ signal (very strong constraint) After selection, the clear Λ signal in data shows high purity of signal. J / → pK + c.c. Data MC
Features of signal (ID)Four charged tracks, no photon, no pio Three heavy particles: p, pbar, KaonSo kinematics (with correct mass assignment) providesvery strong constraint in the event selection, M pkpx = M iwand p. =o in the kinematic fit can reject mostbackground events
Features of signal (II) • Four charged tracks, no photon, no pi0 • Three heavy particles: p, pbar, Kaon • So kinematics (with correct mass assignment) provides very strong constraint in the event selection, and in the kinematic fit can reject most background events. M pKp = M J / Pmiss = 0
Key points in event selectionKeep High purity of signal (A mass as a control)Efficiency as high as possibleSystematic uncertainties from selection criteriaas small as possibleLow momentum feature should be considered
Key points in event selection Keep • High purity of signal ( Λ mass as a control) • Efficiency as high as possible • Systematic uncertainties from selection criteria as small as possible Low momentum feature should be considered
EventSelectionFour good charged tracks (Pxy>50 MeV)PID: Kaon-ID and at least one proton-ID 4-C kinematic fitPID information is used in the mass assignmentRemove..pkZ +c.c.events with combinedinformation of Emiss and Mpk missno requirement on A vertex reconstruction
Event Selection • Four good charged tracks ( Pxy>50 MeV ) • PID: Kaon-ID and at least one proton-ID • 4-C kinematic fit PID information is used in the mass assignment • Remove events with combined information of Emiss and Mpk_miss no requirement on Λ vertex reconstruction pK + c.c