342 research outputs found
Decays of the tau lepton
No full textPrevious measurements of the branching fractions of the tau lepton result in a discrepancy between the inclusive branching fraction and the sum of the exclusive branching fractions to final states containing one charged particle. The sum of the exclusive branching fractions is significantly smaller than the inclusive branching fraction. In this analysis, the branching fractions for all the major decay modes are measured simultaneously with the sum of the branching fractions constrained to be one. The branching fractions are measured using an unbiased sample of tau decays, with little background, selected from 207 pb/sup -1/ of data accumulated with the Mark II detector at the PEP e/sup +/e/sup -/ storage ring. The sample is selected using the decay products of one member of the ..gamma../sup +/..gamma../sup -/ pair produced in e/sup +/e/sup -/ annihilation to identify the event and then including the opposite member of the pair in the sample. The sample is divided into subgroups according to charged and neutral particle multiplicity, and charged particle identification. The branching fractions are simultaneously measured using an unfold technique and a maximum likelihood fit. The results of this analysis indicate that the discrepancy found in previous experiments is possibly due to two sources. First, the leptonic branching fractions measured in this analysis are about one standard deviation higher than the world average. The measured leptonic branching fractions correspond to a tau lifetime of (3.0 +- 0.2) x 10/sup -13/ s. Secondly, the total branching fraction to one charged hadron plus at least one neutral particle is measured to be (7 +- 3)% higher than the branching fraction expected from a combination of previous measurements and theoretical predictions. It is shown that decay modes involving the eta are not expected to contribute more than 3% to this excess
The role of intestinal stearoyl-CoA desaturase 1 in intestinal and systemic lipid and energy metabolism
No full textStearoyl-CoA desaturase 1 (SCD) is an endoplasmic reticulum-residing enzyme that converts saturated fatty acids into monounsaturated fatty acids through the insertion of a double bond at the 9 position. This conversion of saturated fatty acids (SFA) to monounsaturated fatty acids (MUFA) is a key and highly regulated step in lipid metabolism because the MUFA products of SCD1 are the preferred substrates for the synthesis of other lipid species, including triacylglycerols (TAG), cholesterol esters (CE), phospholipids (PL), and diacylglycerols (DAG). Prior studies have shown that disruptions to SCD1 lead to alterations in esterified lipids, protection from diet-induced obesity, increased energy expenditure and improved glucose tolerance. Given the important roles the intestine plays in the digestion, absorption, and secretion of nutrients into the body, and as a regulatory and signaling organ, the specific contributions of intestinal SCD1 to systemic lipid metabolism and energy balance were investigated. SCD1 gene and protein expression was found to be expressed along the length of the intestine, with the greatest expression in the distal small intestine and colon. Intestinal SCD1 is also regulated in a nutritional manner, as seen in mice fasted then refed a high-sucrose diet which upregulates SCD1 in each segment of the intestine, particularly in the distal intestine. Given the spatial and nutritional regulation of intestinal SCD1, we generated intestine-specific knockout (iKO) mice to assess the specific contribution of intestinal SCD1 to whole-body lipid and energy metabolism. This deletion did not have significant impacts on body weights, body composition, intestinal fat absorption or motility. Lipidomic analyses of the intestine revealed that intestinal SCD1 modulates intestinal lipid content particularly TAGs and CEs in the proximal and distal small intestine. Intestinal SCD1 also regulates plasma lipid content and hepatic lipid composition, with notable reductions in the 14:1/14:0 desaturation ratio. This reduction in myristoleate may mediate reductions in hepatic expression of the Pgc1a-Sirt1 axis and fatty acid oxidation. Given prior reports of Scd1 deficient animals being protected from diet-induced obesity due to increased energy expenditure, and our findings that intestinal SCD1 regulates intestinal and systemic lipid metabolism, the role of intestinal SCD1 in systemic energy balance was investigated. iKO mice were maintained on a chow diet or fed a 45% high-fat diet (HFD) for metabolic profiling. Chow fed iKO mice had increased plasma and hepatic bile acid content and decreased fecal bile acid excretion. Notably, expression of apical sodium dependent bile acid transporter (Asbt) was increased in iKO mice, potentially mediating increased ileal uptake of bile acids. This altered bile acid profile was associated with increased expression of Takeda G protein-coupled receptor 5 (TGR5) signaling targets, including Dio2 in brown adipose tissue and plasma glucagon-like peptide 1 (GLP-1). iKO mice on a HFD had reduced metabolic efficiency due to decreased weight gain despite increased food consumption. HFD-fed iKO mice had increased energy expenditure and improved glucose tolerance. Altogether, these studies indicate an important role of intestinal SCD1 on modulating intestinal and whole-body lipid content and composition and suggest a role for intestinal SCD1 in the regulation of bile acid and energy homeostasis.Ph.D.Includes bibliographical reference
The BaBar detector
No full textThis is the pre-print version of the Article. The official published version can be accessed from the link below. Copyright @ 2002 Elsevier.BABAR, the detector for the SLAC PEP-II asymmetric e+e− B Factory operating at the (4S) resonance, was designed to allow comprehensive studies of CP-violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagnetic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and in a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems , VME- and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.This work has been supported by the US Department of Energy and the National Science
Foundation, the Natural Sciences and Engineering Research Council (Canada), the Institute of High Energy Physics (P.R. China), le Commisariat a l’Energie Atomique and Institut National de Physique Nucl´eaire et de Physique des Particules (France), Bundesministerium fur Bildung und Forschung (Germany), Istituto Nazionale di Fisica Nucleare (Italy), the Research Council of
Norway, the Ministry of Science and Technology of the Russian Federation, and the Particle Physics and Astronomy Research Council (United Kingdom). In addition, individuals have received support from the Swiss National Foundation, the A.P. Sloan Foundation, the Research Corporation, and the Alexander von Humboldt Foundation
Dalitz plot analyses of B-0 -> (D-DK+)-K-0 and B+-> (D)over-bar(-)D(0)K(+) decays
No full text© 2015, APS Journal
Measurement of Collins asymmetries in inclusive production of charged pion pairs in e+e− annihilation at BABAR
No full textWe present measurements of Collins asymmetries in the inclusive process e+e−→ππX, where π stands for charged pions, at a center-of-mass energy of 10.6 GeV. We use a data sample of 468 fb−1 collected by the BABAR experiment at the PEP-II B factory at SLAC, and consider pairs of charged pions produced in opposite hemispheres of hadronic events. We observe clear asymmetries in the distributions of the azimuthal angles in two distinct reference frames. We study the dependence of the asymmetry on several kinematic variables, finding that it increases with increasing pion momentum and momentum transverse to the analysis axis, and with increasing angle between the thrust and beam axis
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Studies of helium based drift chamber gases for high-luminosity low energy machines
No full textFuture high luminosity low energy machines will need low mass tracking chambers to order to minimize multiple scattering of the relatively low momentum tracks produced at these facilities. A drift chamber using a helium based gas rather than a conventional argon based gas would greatly reduce the amount of multiple scattering. This paper summarizes measurements of the drift velocity and position resolution for gas mixtures of helium with CO{sub 2} and isobutane and helium with DME. Good spatial resolutions are obtained. A design of a drift chamber with only 0.12% of a radiation length (gas plus wire) over a 60 cm tracking distance is presented
Opportunities and requirements for experimentation at high energy e/sup +/e/sup /minus// collider
No full textOver the past fifteen years of high-energy physics, electron-positron annihilation has been the most productive of all reactions probing the fundamental interactions. The e/sup +/e/sup /minus// annihilation process is unique in offering at the same time copious production of novel particles, low backgrounds from more conventional physics, and the most efficient use of the energy which an accelerator provides. These features have allowed the detailed characterization of the charm and bottom quark-antiquark systems and the unambiguous discovery of gluon jets---the crucial ingredients in the establishment of Quantum Chromodynamics as the correct theory of the strong interactions---as well as the discovery of the tau lepton and confirmation of the weak and electromagnetic properties of all the quarks and leptons at high energy. Over the past few years, experiments will begin at SLC and LEP, and we anticipate new discoveries from the detailed study of the Z/sup 0/ resonance. It is time, then to begin to think out how one might continue this mode experimentation to still higher energies. This document is the report of a committee convened by the Director of SLAC, Burton Richter, to set out the major physics goals of an e/sup +/e/sup /minus// collider in the energy range 600 GeV-1 TeV, corresponding to the next feasible step in accelerator technology. The committee was charged with the task of outlining the main experiments that such a collider might carry out and the requirements which those experiments place on the accelerator design. 106 refs., 105 figs., 13 tabs
A measurement of the charged and neutral B meson lifetimes using fully reconstructed decays
No full textThe author first notes that Google, the trade mark, the project, the utilization - the "googling"- are social facts proven by the numbers – number of net surfers, of requests, of uses- and by the signs of adhesion - linguistics, economic, social. A socio linguistic analysis of the speeches of the persons in charge of Google and of users indicate that the social fact "googling" results in the emergence of a culture and a world community which shares it. They are supported by the language and also by the myths that were created and largely maintained by the owners the mark "Google Inc". The conclusion is that the current organization of the market of services on the Internet makes that Google Inc. is almost the only institution to know the population of the googlers. In order not to be subjected to this monopoly, however comfortable it is, the author proposes to develop a research program on the uses and users of Google
The BaBar detector: Upgrades, operation and performance
No full textContains fulltext :
121729.pdf (Author’s version preprint ) (Open Access
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