Bryan Fulsom

25 May 2018

Abstract: This figure shows the invariant mass distribution of K^0_S → π+ π- in 5 pb^{-1} of collision data. Events are required to contain at least three good tracks to reject beam induced background, Bhabha scattering, and other low multiplicity background sources. The charged pion tracks from the K^0_S candidates are required to have a z-direction impact parameter, z0, in the range of -4 to 6 cm to ensure the tracks originate from near the interaction region. A vertex fitter based on a Kalman algorithm is used to fit the vertex to reject candidates where the tracks do not originate from near a common decay point. The internal document reference is BELLE2-NOTE-PH-2018-001.