Study of the decay Ds+ --> K+ K- e+ nu

TL;DR

This study measures the form factors and branching fractions of the decay Ds+ --> K+ K- e+ nu using data from the BaBar detector, providing insights into the decay dynamics and validating theoretical models.

Contribution

It provides the first detailed measurement of the form factors and branching ratios for Ds+ --> K+ K- e+ nu decay, including the extraction of A1(0) and the decay rate comparison.

Findings

Measured form factor ratios rV and r2 with uncertainties.

Determined the total branching fraction B(Ds+ --> phi e+ nu).

Extracted the axial-vector form factor A1(0).

Abstract

Using 214 fb-1 of data recorded by the Babar detector at the PEPII electron-positron collider, we study the decay Ds+ --> K+ K- e+ nu. Except for a small S-wave contribution, the events with K+K- masses in the range 1.01-1.03 GeV/c2 correspond to phi mesons. For Ds+ --> phi e+ nu decays, we measure the relative normalization of the Lorentz invariant form factors at q2=0, rV=V(0)/A1(0)=1.849 +/- 0.060 +/- 0.095, r2=A2(0)/A1(0)=0.763 +/- 0.071 +/- 0.065 and the pol e mass of the axial-vector form factors mA=(2.28^{+0.23}_{-0.18}+/- 0.18) GeV/c2. Within the same K+K- mass range, we also measure the relative branching fraction B(Ds+ --> K + K- e+ nu)/B(Ds+ --> K+ K- pi+)=0.558 +/- 0.007 +/- 0.016, from which we obtain the total branching fraction B(Ds+ --> phi e+ nu) = (2.61 +/- 0.03 +/- 0.08 +/- 0.15)* 10^{-2}. By comparing this value with the predicted decay rate, we extract A1(0) = 0.607 +/- 0.011 +/- 0.019 +/- 0.018. The stated uncertainties are statistical, systematic, and from external inputs.