Revisiting πΆ and πΆβ’π violation in π β π + π - β’π 0 decay
The decay π β π + β’π β β’π 0 is an ideal process in which to study flavor-conserving πΆ and πΆβ’π violation beyond the Standard Model. We deduce the πΆ- and πΆβ’π-odd quark operators that contribute to π β π + β’π β β’π 0 originating from the mass-dimension-six Standard Model effective field theory. The corresponding hadron-level operators that generate a nonvanishing πΌ = 0 amplitude at order π 6 in the chiral effective theory are presented for the first time, to the best of our knowledge, in addition to the leading-order operators ascribed to the πΌ = 2 final state. By fitting the KLOE-2 and the most recent BESIII experimental data, we determine the coefficients of the lowest-order πΌ = 0 and πΌ = 2 amplitudes and estimate the potential new physics energy scale. We also perform an impact study of the future π β π + β’π β β’π 0 experiments.