Measurement of the positive muon lifetime and determination of the Fermi constant to part-per-million precision.

We report a measurement of the positive muon lifetime to a precision of 1.0 ppm; it is the most precise particle lifetime ever measured. The experiment used a time-structured, low-energy muon beam and a segmented plastic scintillator array to record more than 2×10(12) decays. Two different stopping target configurations were employed in independent data-taking periods. The combined results give τ(µ(+)) (MuLan)=2 196 980.3(2.2) ps, more than 15 times as precise as any previous experiment. The muon lifetime gives the most precise value for the Fermi constant: G(F) (MuLan)=1.166 378 8(7)×10(-5) GeV(-2) (0.6 ppm). It is also used to extract the µ(-)p singlet capture rate, which determines the proton's weak induced pseudoscalar coupling g(P).

Improved measurement of the positive-muon lifetime and determination of the Fermi constant.

The mean life of the positive muon has been measured to a precision of 11 ppm using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which was surrounded by a scintillator detector array. The result, tau(micro)=2.197 013(24) micros, is in excellent agreement with the previous world average. The new world average tau(micro)=2.197 019(21) micros determines the Fermi constant G(F)=1.166 371(6)x10(-5) GeV-2 (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling g(P).

Polychlorinated biphenyls: in vivo and in vitro modifications of cholesterol and fatty acid biosynthesis.

Aroclor 1254 (0.1 percent w/w) administered in the diet caused moderate to severe vacuolar degeneration of periportal hepatocytes, heptocyte enlargement, lipid accumulation, and necrosis of the liver. The incorporation of [2-14C]mevalonate into nonsaponifiable lipids was inhibited 18 percent and 26 percent after 14 days and 30 days, respectively. Biosynthesis of cholesterol from [2-14C]acetate and [2-14C]mevalonate was decreased by 51 percent and 31 percent respectively after 30 days, but no significant inhibition was observed after 14 days of feeding Aroclor 1254. [2-14C]Acetate incorporation into non-saponifiable lipids was 1.66 times greater in homogenates from Aroclor-treated rats than in those from control rats. Similar results were obtained when 3H2O, Mevalonate-14C, and acetate-2-14C were incubated in vivo. The conversion of [2-14C-A1acetate to fatty acids was decreased 43 percent by Aroclor 1254 (0.1 percent w/w, dietary) and 73 percent by Aroclor 1254, 500 ppm, in vitro. The in vitro incorporation of each [2-14C]acetate, [2-14C]mevalonate and [1-14C]isopentenyl pyrophosphate into cholesterol was inhibited by Aroclor 1254. There was no inhibition of the conversion of [1-14C]mevalonate to CO2, indicating that there was no inhibition of mevalonate-5-pyrophosphate anhydrodecarboxylase. Fatty acid synthase was not inhibited by PCB. Citrate cleavage enzyme was inhibited by Aroclor 1254. When ATP and citrate concentrations were varied, the Ki's were 5.3 X 10(-5)M and 11.5 X 13(-5)M, respectively. Acetyl CoA carboxylase activity was not inhibited by 1000 ppm Aroclor 1254 in vitro. Inhibition of citrate cleavage enzyme is a possible explanation for the observed decrease in fatty acid synthesis. There was an apparent diversion of acetate from fatty acid synthesis into the formation of non-saponifiable lipids, accompanied by an inhibition of the biosynthesis of cholesterol per se.