Measurement of the Leptonic Branching Fraction of the Dₛ Meson and Determination of Its Decay Constant

Citation

Kelsey, Michael Henderson (1996) Measurement of the Leptonic Branching Fraction of the Dₛ Meson and Determination of Its Decay Constant. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/x5qg-g497. https://resolver.caltech.edu/CaltechTHESIS:04202020-172701960

Abstract

Between February 1992 and June 1994, the Beijing Spectrometer (BES) experiment collected 24.5 pb⁻¹ of data in e⁺e⁻ collisions at a center of mass energy of 4.03 GeV, above threshold for production of Dₛ⁺Dₛ⁻ meson pairs. In this thesis, these data are searched for Dₛ⁺Dₛ⁻ events by identifying sets of charged tracks consistent with the decay channels Dₛ → Φπ,Φ → K⁺K⁻; Dₛ → K*⁰K,K*⁰ → K⁺π⁻; or Dₛ → K⁰_SK,K⁰_S → π⁺π⁻. A global maximum-likelihood technique is used, which combines particle identification detector data and a kinematic fit to each decay hypothesis, for maximum sensitivity. A sample of 190 candidates is found in the mass range 1958.5-1978.5 MeV/c², of which 76.9 ± 13.8 are estimated (from a fit to 1097 combinations with 1800 < m < 2015 MeV /c²) to be true e⁺e⁻ → Dₛ⁺Dₛ⁻ events.

This event sample is searched for leptonic decays of the Dₛ meson in the channels Dₛ → µν_µ and Dₛ → τν_τ (with τ → µν̅_µν_τ → eν̅_eν_τ, or τ → πν_τ). Five candidate decays are found. A likelihood function is formed as a product over the candidate events, where each contributes a sum over all of the leptonic decay channels, weighted according to the likelihoods of the particle identifications and the kinematics of the decay. This likelihood function is maximized with respect to the branching fraction B(Dₛ → µν_µ), or the Dₛ pseudoscalar decay constant f_Dₛ, with the results

B(Dₛ → µν_µ) = .75^+1.23_-.47 (stat) ± .06 (syst) %,

f_Dₛ = 308⁺¹⁶⁴_-189 (stat) ± 12 (syst) MeV.

Comparison of the measured value of f_Dₛ with other experimental determinations and with a variety of theoretical models is discussed, with implications for constraining those models.

Thesis Files