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CMU
REVIEW OF SEMILEPTONIC CHARM DECAYS
DE9
DOUGLAS M. POTTER
Physics Department, Carnegie-Mellon University, Pittsburgh,
Pennsylvania, 15213, USA
ABSTRACT
The experimental status of D and D+ semileptonic decays is reviewed and compared to model
predictions. Topics covered are the form factor pole mass and decay rate for D -+ Kip, the decay
rate and form factor ratios for D -+ Kbtv, and, finally, the issue of modes other than Kbv and
K*Iv.Interest in the 3-body semileptonic decays of
charm mesons stems in part from their relative
simplicity. These decays proceed only via the
spectator model Feynman diagram, and all strong
interaction effects can be described in terms of
form factors, which can be calculated in several
different ways. By contrast, hadronic weak de-
cays can include interfering diagrams at the par-
ton level, and c-n be also be affected by final
state interactions.
Semileptonic charm decays are also important
in the determination of K-M matrix element IV6.1.
In heavy quark effective theory, measurements
of the decay modes D -+ ptv and B -. ptv,
for example, would allow extraction of the ra-
tio IT46./IVeiI. Currently, these measurements
are unavailable, and model input is required to
determine IV6.1 from measurements of the lep-
ton momentum spectrum in inclusive semilep-
tonic beauty decays. The semileptonic decays
of charm particles provide a testing ground for
the models used in this method.
The Kbv mode is the simplest semileptonic
charm decay. In the zero mass lepton limit, the
differential decay rate can be written as,
dr - GF c..Ig( 2 +(q2 2
where GF is the Fermi constant, 1V,1 j is the K-
M matrix element, q2 is the mass squared of the
virtual W, K(q2) is a known kinematic factor,
and f+(q2) is the form factor. The "monopole
ansats", in which the coupling of the virtual W
is analogous to that of the photon in the vec-
tor dominance hypothesis, is frequently used to
describe the q2 dependence of the form factor.-HEP--91-19
2 002725With this assumption, the form factor is,
f+(0)
f+(q2) 1 - g /Mp2)E
where Mpc1j; equals the mass of the D* me-
son, the nearest pole with the correct quantum
numbers. Several experiments have measured
MpotE by fitting to the q2 dependence of the
decay. Table 1 shows the results, along with the
ansats value and a prediction (BBD)[1]. The
monopole ansats appears to describe the data;
however, some models use other equally valid de-
scriptions of the q2 dependence.
Table 1: Pole mass for the form factor f+.EXPT
MARK III[2]
E691[3]
CLEO[4]
DS
BD[1 (thy)MPOLE (GeV/c2)
1.8 -v 1J-'
2.1 +0:4
2.0 +0+03
2.11
1.8 i 0.1Table 2 shows measurements and predictions
for r(Kty) . The experimental results are gen-
erally in good agreement with one another, and
all three types of models are able to describe the
data. It should be noted, however, that the ex-
perimental results for the Do may be systemat-
ically higher than those for the D+. Since the
Cabibbo favored weak current conserves strong
isospin, this effect would presumably be due to
a statistical fluctuation, or to some common sys-
tematic problem. Most of the measurements in
Table 2 are normalized to Mark III branching
ratios[5], and the average takes into account the
common systematic errors.MASTER
DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED
Presented at the Joint International Lepton-Photon Symposium
and Europhysics Conference on High Energy Physics
Geneva, Switzerland
25 July - 1 August, 1991r
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Potter, D. M. Review of Semileptonic Charm Decays, article, January 1, 1991; Pittsburgh, Pennsylvania. (https://digital.library.unt.edu/ark:/67531/metadc1057337/m1/1/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.