Origin of the D*−K+ excess around 2.7 GeV

Ascertain whether the broad excess of the M(D*−K+) distribution around 2.7 GeV observed in the B+ → D*− D+ K+ decay analysis is caused by an additional D*−K+ resonance or instead by mismodeling of one or more nonresonant components in the baseline amplitude model used for the simultaneous unbinned maximum-likelihood fit.

Background

In comparing the baseline amplitude model with data, the authors observe that the model overshoots the M(D*−K+) spectrum in a broad region around 2.7 GeV in the B+ → D*− D+ K+ channel. An attempt to add a D*−K+ resonance to account for this discrepancy yields unstable fits, with widths becoming very large due to interference with nonresonant components.

Fixing the putative resonance mass and width to 2750 MeV and 100 MeV, respectively, improves the likelihood most when J^P = 1^+, but the authors ultimately treat the discrepancy as a source of systematic uncertainty because they cannot determine whether it is due to an additional resonance or to mismodeling of one or more nonresonant contributions. This unresolved attribution motivates determining the true origin of the excess.