Direct measurements of charmed-D-meson hadronic branching fractions.
نویسندگان
چکیده
A new technique is applied to data collected at the +(3770) resonance to derive charmed D meson branching fractions without relying on the measurement of D production cross sections. Measurements are presented for three decay modes of the Do (K-n+, K-?r-w+r+ and K-7r+r ") and four decay modes of the D+ (K-7r+rr+, K-x+r+~~, Kt?r+ and Kfr+7r "). The resulting branching fractions are significantly larger than previous measurements. The exclusive production of Dom and D+D-pairs at the $(3770) resonance provides a unique opportunity to measure charmed D meson branching fractions directly. Previous measurements at this resonance of D hadronic branching fractions lb3 have relied on a determination of the charm production cross section (a~) to normalize observed D meson production rates. However, the kinematics of DD pair production at the $~(3770) makes it possible to measure D branching fractions independent of 0~. The results obtained by this method differ significantly from earlier results. The data were collected with the Mark III detector4 at the e+e-storage ring SPEAR at an average energy of @ = 3.768 GeV. We assume that events containing charmed D mesons arise solely from DD production, so that the detection of a single D in an event implies that the recoiling system is a monochromatic D. 5 The data are searched for events containing either one or two reconstructed D mesons. For this analysis, three Do decay channels (K-z+, K-z-z+~+ and K-z+zO) and four D+ decay channels (K-z+z+, K-7rr+zr+no, Kt7rr+ and Kfz+z') are considered. By comparing the number of times a single D (or D) is reconstructed (single-tags) with the number of fully reconstructed Dn events (double-tags), the individual D meson branching fractions can be derived independently of a~. Single-tag reconstruction proceeds as follows. Charged particles are required to satisfy 1 cos01 < 0.85 (w h ere 8 is the polar angle with respect to the beam) to insure reliable drift chamber measurements. A charged particle which enters the time-of-flight (TOF) system (I cos 01 < 0.75) is identified as either a z or K, according to which predicted time is closer to the measured time. Unidentified tracks are assumed to be pions. Showers with energies greater than 0.050 GeV 2 are used as photon candidates. Neutral kaons are detected through the decay K; + X+C, where the 7rIT+rT-invariant mass is required to lie within 0.0156 GeV/c2 of the Kf mass. Appropriate combinations of charged tracks and photons …
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عنوان ژورنال:
- Physical review letters
دوره 56 20 شماره
صفحات -
تاریخ انتشار 1986