A Study of Charged D* Mesons Produced in e⁺e⁻ Annihilation at E꜀ₘ = 29 GeV

Citation

Yamamoto, Hitoshi (1986) A Study of Charged D* Mesons Produced in e⁺e⁻ Annihilation at E꜀ₘ = 29 GeV. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/nms8-7v38. https://resolver.caltech.edu/CaltechTHESIS:04152019-093410294

Abstract

Charged D* mesons produced in e⁺e^- annihilation at a center-of-mass energy of 29 GeV have been studied with the DELCO detector at the PEP storage ring. The selection criteria of D* candidates exploit the π/K separation capability in the momentum range from 2.6 GeV/c to 9.2 Ge VIc provided by the gas Čerenkov counter. The data correspond to an integrated luminosity of 147 pb^-1.

We have measured the total production cross section of D*^± to be [0.16±0.02(statistical)±0.02(systematic)] nb [x ≡ P_D*/(E²_beam-M²_D*)^1/2 > 0.35], and (0.18 ± 0.02 ± 0.03) nb (x > 0) if the contribution from bottom quarks is subtracted. The branching fractions used are Br(D*⁺ → D⁰π⁺) = 64% and Br(D⁰ → K^-π⁺) = 3%. The systematic errors due to the branching ratios are not included in the errors. With Br(D⁰ → K^-π⁺) = 4.9%, which is a recent measurement by the MARK III group, the above two cross sections become 0.10±0.02±0.02 nb (x > 0.35) and 0.11±0.02±0.02 nb (x > 0 and after the subtraction of the contribution from b quarks).

The charm fragmentation function is harder than that for light quarks, and the shape is found to be consistent with the prediction of the string model with a uniform string-breaking probability. Assuming the string model, the string-breaking probability is determined to be (0.019 ± 0.05 ± 0.09) GeV².

We have also determined the lifetime of D⁰ meson which is detected in the D* decay, with the result τ_D⁰ = (5.3 ± 1.7^+0.6_-0.5) x 10^-13 sec. Together with the semileptonic branching fraction of D⁰ measured elsewhere, the semileptonic decay rate of D⁰ is estimated to be (1.4 ± 0.5) x 10¹¹ sec^-1, which corresponds to an effective charm quark mass of (1.54 ± 0.12) GeV/c².

Using part of the D* candidates, we have set an upper limit on D⁰-D̅⁰ mixing: r ≡ P(D⁰ → D̅⁰)/P(D⁰ → D⁰ or D̅⁰) < 8.3% (90% c.l.), leading to a stringent limit on charm-changing neutral currents.

Thesis Files