Measurement of the K~0 Charge Radius and a CP- Violating Asymmetry and a Search for CP-Violating E1 Direct Photon Emission in the Rare Decay K_L → π~+π~-e~+e~-

摘要

Using the complete KTeV data set of 5241 candidate K_L→ π~+π~-e~+e~- decays (including an estimated background of 204 ± 14 events), we have measured the coupling g_(CR) = 0.163 ± 0.014(stat) ± 0.023(syst) of the CP conserving charge radius process and from it determined a K~0 charge radius of < r_(K~0)~2 > = [-0.077 ± 0.007(stat) ± 0.011(syst)]f m~2. We have determined a first experimental upper limit of 0.04 (90% C.L.) for the ratio (|g_(E1)|)/(|g_(M1)|) of the couplings for the E1 and M1 direct photon emission processes. We also report the measurement of |g_(M1)| including a vector form factor |g_(M1)|(1 + (a_1/a_2)/((m_ρ~2-M_K~2)+2M_KE_γ~*)), where |g_(M1)| = 1.11 ± 0.12(stat) ± 0.08(syst) and a_1/a_2 = [-0.744 ± 0.027(stat) ± 0.032(syst)] GeV~2/c~2. Finally, a CP-violating asymmetry of [13.6 ± 1.4(stat) ± 1.5(syst)]% in the CP and T odd angle φ between the decay planes of the e~+e~- and π~+π~- pairs in the K_L center of mass is reported.