Charge asymmetry ratio as a probe of quark flavour couplings of resonant particles at the LHC

We show how a precise knowledge of parton distribution functions, in particular those of the u and d quarks, can be used to constrain a certain class of New Physics models in which new heavy charged resonances couple to quarks and leptons. We illustrate the method by considering a left-right symmetric model with a W' from a SU(2)_R gauge sector produced in quark-antiquark annihilation and decaying into a charged lepton and a heavy Majorana neutrino. We discuss a number of quark and lepton mixing scenarios, and simulate both signals and backgrounds in order to determine the size of the expected charge asymmetry. We show that various quark-W' mixing scenarios can indeed be constrained by charge asymmetry measurements at the LHC, particularly at 14 TeV centre of mass energy.Comment: 14 pages, 3 figure

Floating in space: how to treat the weak interaction between CO molecules in interstellar ices

NWO722.017.008Theoretical Chemistr

A high stability semiconductor laser system for a 88^{88}Sr-based optical lattice clock

We describe a frequency stabilized diode laser at 698 nm used for high resolution spectroscopy of the 1S0-3P0 strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high resolution remote spectroscopy on the 88Sr clock transition by transferring the laser output over a phase-noise-compensated 200 m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7 \cdot 10^{-18} after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10^{14}. Furthermore, with an eye towards the development of transportable optical clocks, we investigate how the complete laser system (laser+optics+cavity) can be influenced by environmental disturbances in terms of both short- and long-term frequency stability.Comment: 9 pages, 9 figures, submitted to Appl. Phys.

PYTHIA 6.4 Physics and Manual

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.Comment: 576 pages, no figures, uses JHEP3.cls. The code and further information may be found on the PYTHIA web page: http://www.thep.lu.se/~torbjorn/Pythia.html Changes in version 2: Mistakenly deleted section heading for "Physics Processes" reinserted, affecting section numbering. Minor updates to take into account referee comments and new colour reconnection option

Atmospheric trace gases support primary production in Antarctic desert surface soil

LetterCultivation-independent surveys have shown that the desert soils of Antarctica harbour surprisingly rich microbial communities¹⁻³. Given that phototroph abundance varies across these Antarctic soils²·⁴, an enduring question is what supports life in those communities with low photosynthetic capacity³·⁵. Here we provide evidence that atmospheric trace gases are the primary energy sources of two Antarctic surface soil communities. We reconstructed 23 draft genomes from metagenomic reads, including genomes from the candidate bacterial phyla WPS-2 and AD3. The dominant community members encoded and expressed high-affinity hydrogenases, carbon monoxide dehydrogenases, and a RuBisCO lineage known to support chemosynthetic carbon fixation⁶·⁷. Soil microcosms aerobically scavenged atmospheric H₂ and CO at rates sufficient to sustain their theoretical maintenance energy and mediated substantial levels of chemosynthetic but not photosynthetic CO₂ fixation. We propose that atmospheric H₂, CO₂ and CO provide dependable sources of energy and carbon to support these communities, which suggests that atmospheric energy sources can provide an alternative basis for ecosystem function to solar or geological energy sources⁸·⁹. Although more extensive sampling is required to verify whether this process is widespread in terrestrial Antarctica and other oligotrophic habitats, our results provide new understanding of the minimal nutritional requirements for life and open the possibility that atmospheric gases support life on other planets.Mukan Ji, Chris Greening, Inka Vanwonterghem, Carlo R. Carere, Sean K. Bay, Jason A. Steen, Kate Montgomery, Thomas Lines, John Beardall, Josie van Dorst, Ian Snape, Matthew B. Stott, Philip Hugenholtz & Belinda C. Ferrar

Measurement of the partial widths of the Z into up- and down-type quarks

Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma decays were selected by tagging hadronic final states with isolated photon candidates in the electromagnetic calorimeter. Combining the measured rates of Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the simultaneous determination of the widths of the Z into up- and down-type quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18} MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.

Search for R-Parity Violating Decays of Scalar Fermions at LEP

A search for pair-produced scalar fermions under the assumption that R-parity is not conserved has been performed using data collected with the OPAL detector at LEP. The data samples analysed correspond to an integrated luminosity of about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An important consequence of R-parity violation is that the lightest supersymmetric particle is expected to be unstable. Searches of R-parity violating decays of charged sleptons, sneutrinos and squarks have been performed under the assumptions that the lightest supersymmetric particle decays promptly and that only one of the R-parity violating couplings is dominant for each of the decay modes considered. Such processes would yield final states consisting of leptons, jets, or both with or without missing energy. No significant single-like excess of events has been observed with respect to the Standard Model expectations. Limits on the production cross- section of scalar fermions in R-parity violating scenarios are obtained. Constraints on the supersymmetric particle masses are also presented in an R-parity violating framework analogous to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.

Measurement of the Strong Coupling alpha s from Four-Jet Observables in e+e- Annihilation

Data from e+e- annihilation into hadrons at centre-of-mass energies between 91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study the four-jet rate as a function of the Durham algorithm resolution parameter ycut. The four-jet rate is compared to next-to-leading order calculations that include the resummation of large logarithms. The strong coupling measured from the four-jet rate is alphas(Mz0)= 0.1182+-0.0003(stat.)+-0.0015(exp.)+-0.0011(had.)+-0.0012(scale)+-0.0013(mass) in agreement with the world average. Next-to-leading order fits to the D-parameter and thrust minor event-shape observables are also performed for the first time. We find consistent results, but with significantly larger theoretical uncertainties.Comment: 25 pages, 15 figures, Submitted to Euro. Phys. J.

Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2

The hadronic structure function of the photon F_2^gamma is measured as a function of Bjorken x and of the factorisation scale Q^2 using data taken by the OPAL detector at LEP. Previous OPAL measurements of the x dependence of F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted by QCD, the data show positive scaling violations in F_2^gamma. Several parameterisations of F_2^gamma are in agreement with the measurements whereas the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001, Ascona, Switzerlan

A measurement of the tau mass and the first CPT test with tau leptons

We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV using tau pairs from Z0 decays. To test CPT invariance we compare the masses of the positively and negatively charged tau leptons. The relative mass difference is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.