20 research outputs found
Long-lived connection between southern Siberia and northern Laurentia in the Proterozoic
Precambrian supercontinents Nuna-Columbia (1.7 to 1.3 billion years ago) and Rodinia (1.1 to 0.7 billion years ago) have been proposed. However, the arrangements of crustal blocks within these supercontinents are poorly known. Huge, dominantly basaltic magmatic outpourings and intrusions, covering up to millions of square kilometres, termed Large Igneous Provinces, typically accompany (super) continent breakup, or attempted breakup and offer an important tool for reconstructing supercontinents. Here we focus on the Large Igneous Province record for Siberia and Laurentia, whose relative position in Nuna-Columbia and Rodinia reconstructions is highly controversial. We present precise geochronology—nine U–Pb and six Ar–Ar ages—on dolerite dykes and sills, along with existing dates from the literature, that constrain the timing of emplacement of Large Igneous Province magmatism in southern Siberia and northern Laurentia between 1,900 and 720 million years ago. We identify four robust age matches between the continents 1,870, 1,750, 1,350 and 720 million years ago, as well as several additional approximate age correlations that indicate southern Siberia and northern Laurentia were probably near neighbours for this 1.2-billion-year interval. Our reconstructions provide a framework for evaluating the shared geological, tectonic and metallogenic histories of these continental blocks
Production asymmetry of D-s from 600 GeV/c Sigma(-) and pi(-) beam
The production of D-S(-) relative to D-S(+) as a function of x(F) with 600 GeV/c Sigma(-) beam is measured in the interval 0.15 < x(F) < 0.7 by the SELEX (E781) experiment at Fermilab. The integrated charge asymmetries with 600 GeV/c Sigma(-) beam (0.53 +/- 0.06) and pi(-) beam (0.06 +/- 0.11) are also compared. The results show the Sigma(-) beam fragments play a role in the production of D-S(-), as suggested by the leading quark model. (C) 2003 Elsevier Science B.V. All rights reserved
Measurement of the D-s(+/-) lifetime
We report a precise measurement of the D-s(+/-) meson lifetime. The data were taken by the SELEX experiment (E781) spectrometer using 600 GeV/c Sigma (-), pi (-) and p beams. The measurement has been done using 918 reconstructed D-s(+/-). The lifetime of the D-s(+/-) s is measured to be 472.5 +/- 17.2 +/- 6.6 fs, using K*(892)K-0(+/-) and phi pi (+/-) decay modes. The lifetime ratio of D-s(+/-) to D-0 is 1.145 +/- 0.049. (C) 2001 Elsevier Science B.V. All rights reserved
First observation of the doubly charmed baryon Xi(+)(cc)
We observe a signal for the doubly charmed baryon Xi(cc)(+) in the charged decay mode Xi(cc)(+)-->Lambda(c)(+)K(-)pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence
First measurement of pi(-)e ->pi(-)e gamma pion virtual compton scattering
Pion virtual compton scattering (VCS) via the reaction pi(-)e-->pi(-)egamma was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 GeV/c pi(-) beam incident on target atomic electrons, detecting the incident pi(-) and the final state pi(-), electron and gamma. Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (=9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predictions. The corresponding pi(-) VCS experimental cross section is sigma=38.8+/-13 nb, in agreement with the theoretical expectation of sigma=34.7 nb
Hadronic production of Lambda c from 600 GeV/c pi(-), Sigma(-) and p beams
We present data from Fermilab experiment E781 (SELEX) on the hadroproduction asymmetry for (Lambda) over bar((c)) over bar compared to Lambda(c)(+) as a function of x(F), and on p(t)(2) distributions for Lambda(c)(+). These data were measured in the same apparatus using incident pi(-),Sigma(-) beams at 600 GeV/c and proton beam at 540 GeV/c. The asymmetry is studied as a function of x(F). In the forward hemisphere with x(F) greater than or equal to 0.2 both baryon beams exhibit very strong preference for producing charm baryons rather than charm antibaryons, while the pion beam asymmetry is much smaller. In this energy regime the results show that beam fragments play a major role in the kinematics of Lambda(c) formation, as suggested by the leading quark picture. (C) 2002 Published by Elsevier Science B.V
Isotopic geochronological evidence for the Paleoproterozoic age of gold mineralization in Archean greenstone belts of Karelia, the Baltic Shield
Radiative decay width of the a(2)(1320)(-) meson
Coherent pi (+)pi (-)pi (-) production in the interactions of a beam of 600GeV pi (-) mesons with C, Cu and Pb nuclei has been studied with the SELEX facility (Experiment E781 at Fermilab). The a(2)(1320) meson signal has been detected in the Coulomb (low q(2)) region. The Primakoff formalism used to extract radiative decay width of this meson yields Gamma = 284 +/- 25 +/- 25 keV, which is the most precise measurement to date. (C) 2001 Elsevier Science B.V. All rights reserved
Observation of a narrow charm-strange meson D-sJ(+)(2632)-> D-s(+)eta and (DK+)-K-0
We report the first observation of a charm-strange meson D-sJ(+)(2632) at a mass of 2632.5+/-1.7 MeV/c(2) in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D(s)(+)eta and (DK+)-K-0. In the D(s)(+)eta decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4+/-3.3 MeV/c(2). There is a corresponding peak of 21 events over a background of 6.9 at 2631.5+/-2.0 MeV/c(2) in the decay mode (DK+)-K-0. The decay width of this state is <17 MeV/c(2) at 90% confidence level. The relative branching ratio Gamma((DK+)-K-0)/Gamma(D(s)(+)eta) is 0.14+/-0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D(s)(+)eta decay mode