Three-body decays of charged D mesons
(Contact person: Natasha Miladinovic,

Loose cuts for D+->K-pi+pi+ reconstruction:
mass plot:

The histogram has been fit with a double Gaussian and a radiative tail for the signal and a second order polynomial for the background. Reflections from Ds, D*+, Lambdac decays have not been explicitly modeled in the fit.

D+->K-pi+pi+ Dalitz plot:

In a Dalitz plot, the invariant mass squared of one track combination is plotted versus the invariant mass square of another track combination. In decays of a pseudoscalar particle to 3 pseudoscalar daughters, the Dalitz plot contains all the non-trivial physics information of the decay. If the decay amplitude is a constant, the Dalitz plot will be homogeneously populated.

We use the sidebands to subtract the background. Since the sidebands have a larger reconstructed mass, they occupy a different region in the Dalitz plot than the signal, which complicates the side-band subtraction. We use the following trick: we rescale the invariant mass of each track pair with the ratio of the reconstructed Q-value and the true Q-value of the decay.

D+->K-pi+pi+ Dalitz plot:

The K*0(890) resonance can be clearly recognized.

Optimized cuts for D+->pi-pi+pi+ reconstruction:
The branching ratio of D+ -> pi-pi+pi+ is about 30 times smaller than to K-pi+pi+. With the same loose cuts as for K-pi+pi+, the background is too high to be acceptable. We study the sidebands for the properties of the background and a MC sample for the properties of the signal and tighten the cuts to get the best value for the significance S/sqrt(S+B): D+ -> K-pi+pi+ mass plot with tight cuts:

The yield of D+ -> K-pi+pi+ has been reduced from about 2.8 million to 1.6 million using the tight cuts.

D+ -> pi-pi+pi+ mass plot with tight cuts:

To the right of the D+ -> pi-pi+pi+ is the Ds -> pi-pi+pi+ peak with a similar yield.

A Dalitz plot for the D+ -> pi-pi+pi+ decay is made in a similar way as for D+ -> K-pi+pi+.

D+ -> pi-pi+pi+ Dalitz plot:

The Dalitz plot clearly shows the rho0(770)->pi+pi- and f0(980)->pi+pi- intermediate resonances.