Observation of the W -Annihilation Process Ds+ →ωρ+ and Measurement of Ds+ →φρ+ in Ds+ →π+π+π-π0π0 Decays

We present the first amplitude analysis and branching fraction measurement of the decay Ds+→π+π+π-π0π0, using e+e- collision data collected with the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV corresponding to an integrated luminosity of 7.33 fb-1, and report the first observation of the pure W-annihilation decay Ds+→ωρ+ with a branching fraction of (0.99±0.08stat -0.07+0.05syst)%. In comparison to the low significance of the D wave in the decay Ds+→φρ+, the dominance of the D wave over the S and P waves, with a fraction of (51.85±7.28stat -7.90+4.83syst)% observed in the decay Ds+→ωρ+, provides crucial information for the "polarization puzzle,"as well as for the understanding of charm meson decays. The branching fraction of Ds+→π+π+π-π0π0 is measured to be (4.41±0.15stat±0.13syst)%. Moreover, the branching fraction of Ds+→φρ+ is measured to be (3.98±0.33stat -0.19+0.21syst)%, and the Rφ=B(φ→π+π-π0)/B(φ→K+K-) is determined to be (0.222±0.019stat -0.016+0.016syst), which is consistent with the previous measurement based on charm meson decays, but deviates from the results from e+e- annihilation and K-N scattering experiments by more than 3σ.