K0L reconstruction for improved resolution in strong phase measurement at BESIII
ABSTRACT :
Central goal of flavour physics is to precisely determine the extent of CP violation in the quark sector. Observation of CP violation in weakly interacting neutral kaon systems has paved path for corresponding searches in B± mesons. φ3 is the least precisely known phase of all the phases of CKM unitarity triangle that contains direct information about CP violation in weak interactions. φ3 can be extracted from interference of the tree level decays B± → D0K± and B± → ¯D 0K±, with D0 and D¯ 0 decaying to self-conjugate three body final states, K0 S/Lπ+π−. The problem then depends upon measuring precisely the strong phase difference ∆δD, between D0 and D¯ 0 decays, which can further be represented by the parameters ci and si . BESIII collider experiment in Beijing, aims to precisely determine ci and si by colliding e+e− beams at ψ(3770) center-of-mass energy with the highest integrated luminosity of 2.9 fb−1 , accumulated by any charm factory till date and ensures much lower background and uncertainties in the analysis. Although D0 → K0Lπ+π− is an important decay mode to improve the sensitivity on ci and si , reconstructing K0L , as opposed to K0S , is a more challenging task because of its longer lifetime and hence negligible decay rate in the detector. This work focuses on utilizing the information on part of hadronic shower produced by some K0L’s and the missing momentum technique to reconstruct K0L , along with certain optimized selection cuts to suppress background. Use of loose selection cut (i.e. π0 , η veto) is suggested instead of the nominal high purity tight cut to achieve a signal purity of 79% and reconstruction efficiency of 68%. We further propose to perform the first amplitude analysis of K0Lπ+π− for sensitive measurement of ci and si using the same K0L reconstruction algorithm.​