Search for Flavor-Changing Neutral-Current Decays of Charm Mesons

The Standard Model of particle physics forbids Flavor-Changing Neutral-Current (FCNC) decays at first order but does allow higher order processes to mimic such decays. Searches for these rare decays have been conducted on strange quarks in the Kaon system with the required sensitivity to reach second order decay rates, although no first order decays were found. Searches on up-like quarks have just begun by comparison, leaving a large window for new physics. Extensions to the Standard Model could allow for FCNC decays in up-like quarks while respecting limits set for down-like quarks. This study reports on the details of the search for the charm meson FCNC decays D^0tol^+/-l ^mp, D^+/-topi ^+/-l^+/-l^ mp, and D_sp{s}{ +/-}torm K^+/-l ^+/-l^mp in the data set from Fermilab hadroproduction experiment E791. No signals above background were found. Consequently, 90% C.L. upper limits on their branching fractions were set: B(D^0tomu^+/-mu ^mp)<2.6times10^{-6}, B(D^0to e^+/- e^{mp}<9.3times10^ {-6}, B(D^+/-to pi^+/-mu^+/-mu ^mp)<1.7times10^{-5}, B(D^+/-topi^ +/- e^+/- e^mp)<6.5times10 ^{-5} B(D_sp{s }{+/-}to K^+/- e^ +/- e^mp)<K^{+/-} mu^{+/-}mu^mp<2.4 times10^{-4}, and B(D _sp{s}+/-to K^+/- e^+/- e^mp<4.7times10^ {-4}, These limits include upward corrections due to systematic errors.