New measurements of the and branching ratios
Introduction
This Letter describes new measurements of charm semileptonic decay rates into the and Ds+→φμ+ν final states relative to the hadronic decay rates D+→K−π+π+ and Ds+→φπ+, respectively. The width sets the scale of the A1(0) form factor describing these decays [2] and therefore tests Lattice Gauge and quark model calculations. Such tests of the overall form factor scale are particularly relevant to the determination of CKM matrix element ratios such as |Vcd/Vcs|2 which relates to (for example) . The Ds+→φμ+ν process has been frequently used to estimate the Ds+ branching ratios via assumptions about Γ(Ds+→φℓ+νℓ) since no high statistics double tag deduced branching fractions for the Ds+ presently exist. Frequently the Ds+ yields are established by counting Ds+→φπ+ decays making a good measurement of Γ(Ds+→φμ+ν)/Γ(Ds+→φπ+) important.
Recently the CLEO Collaboration obtained a new measurement of that is somewhat higher than previous measurements. They state in Ref. [3], that their new value implies an increase in the ratio bringing it more in line with early quark model estimates and in considerable discrepancy with the ISGW2 model [4]. This Letter discusses a more precise determination of the from FOCUS and provides a first measurement of this ratio that includes the effects of the interfering s-wave described in our recent Letter [1]. The interference of this s-wave amplitude with the dominant contribution to D+→K−π+μ+ν significantly distorts the angular decay distributions thus affecting the reconstruction efficiency for this state. Throughout this Letter, unless explicitly stated otherwise, the charge conjugate is also implied when a decay mode of a specific charge is stated.
Section snippets
Experimental and analysis details
The data for this Letter were collected in the Wideband photoproduction experiment FOCUS during the Fermilab 1996–1997 fixed-target run. In FOCUS, a forward multi-particle spectrometer is used to measure the interactions of high energy photons on a segmented BeO target. The FOCUS detector is a large aperture, fixed-target spectrometer with excellent vertexing and particle identification. Most of the FOCUS experiment and analysis techniques have been described previously [5]. The FOCUS muon
Analysis of the final state
Fig. 1 shows the K−π+ mass distributions and fits of the signal we obtained using two selections of the cuts described above. A very strong (896) signal is present for both samples. To assess the level of non-charm backgrounds, we plot the “right-sign” (where the kaon and muon have the opposite charge) and “wrong-sign” K−π+ mass distributions separately in Fig. 1(a) and (c) for the sample with the baseline cuts and the sample with baseline, out-of-material, and isolation cuts, respectively.
Analysis of the final state
Fig. 3 shows the K−K+ mass distributions that we obtained using two versions of the cuts described above. Fig. 3(a) and (c) compare the K+K− mass spectra for Ds+→φμ+ν candidates and in a charm background Monte Carlo normalized to the observed number of Ds+→φπ+ events where the Ds+→φμ+ν contribution is excluded. The use of the out-of-material and isolation cuts both significantly reduces the φ background level and increases the agreement between the observed and that predicted background from
Summary
Table 1 summarizes measurements of the branching fraction for electrons and muons. Our measurement is the first one to include the effects on the acceptance due to changes in the decay angular distribution brought about by the s-wave interference [1]. After correcting the muon numbers by a factor of 1.05 to compare to electrons according to the prescription of Ref. [8], we find that all values in the table are consistent with their weighted average (0.62±0.02) with a
Acknowledgements
We wish to acknowledge the assistance of the staffs of Fermi National Accelerator Laboratory, the INFN of Italy, and the physics departments of the collaborating institutions. This research was supported in part by the US National Science Foundation, the US Department of Energy, the Italian Istituto Nazionale di Fisica Nucleare and Ministero dell'Università e della Ricerca Scientifica e Tecnologica, the Brazilian Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico, CONACyT-México,
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