《粒子物理与核物理实验方法（二）》KinematicFit.pdf

Kinematic Fitting?October 5, 2007Contents1 Introduction12 General algorithm13 Common Kinematic Constraints Invariant mass and energy-momentum constraints . . . . . . . . . . . . . . . . . . . . . . . . Reconstruction ofK0Sand Λ decay vertex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kinematic constraints for charm tag reconstructions . . . . . . . . . . . . . . . . . . . . . . . 54 Applying Kalman ?lter technique in kinematic ?tting Constraint with covariance matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Constraint with virtual particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Limitation of Kinematic Fitting 71 IntroductionKinematic ?tting is a mathematical procedure in which one uses the physical law governing a particleinteraction or decay to improve the measurements describing the process. For example, considering thedecay chains,ψ(3770)→D0D0, whereD0decays to the CP eigenstateK0Sπ0andD0decays to the hadronicmodeK?π+. There are several constraints can be applied: (1) theπ+π?pair fromK0Sdecay efrom mon space point(2×2?3 = 1 constraint); (2) the momentum vector ofπ+π?pair must bealigned with the position vector of the decay vertex to the interaction point(3?1 = 2 constraints); (3) themass ofγγpair can be forced to be equal to theπ0mass(1 constraint); (4) energy-momentum