Graham Wallace Wilson

Atmospheric consequences of cosmic ray variability in the extragalactic shock model: 2. Revised ionization levels and their consequences

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Improved measurement of the lifetime of the τ lepton

Abstract A new measurement of the τ lifetime is presented. It uses data collected with the Opal detector during 1994, which almost doubles the size of the Opal τ sample. Two statistically independent techniques are used: an impact parameter analysis of one-prong decay tracks and a fit to the decay length distribution of three-prong decays. The lifetime obtained from the 1994 data by combining the results of these methods is τ τ = 289.7 ± 2.5 (stat)± 1.5 (sys) fs. When combined with the previous Opal τ lifetime measurement the improved τ lifetime is τ τ = 289.2 ± 1.7 (stat.) ± 1.2 (sys.) fs.

Search for Diphoton Events with Large Missing Transverse Energy in 6.3 fb(-1) of p(p)over-bar Collisions at root s=1.96 TeV

We report a search for diphoton events with large missing transverse energy produced in pp collisions at √s=1.96u2009u2009TeV. The data were collected with the D0 detector at the Fermilab Tevatron Collider and correspond to 6.3u2009u2009fb(-1) of integrated luminosity. The observed missing transverse energy distribution is well described by the standard model prediction, and 95% C.L. limits are derived on two realizations of theories beyond the standard model. In a gauge-mediated supersymmetry breaking scenario, the breaking scale Λ is excluded for Λ<124u2009u2009TeV. In a universal extra dimension model including gravitational decays, the compactification radius R(c) is excluded for R(c)(-1)<477u2009u2009GeV.

Atmospheric consequences of cosmic‐ray variability in the extragalactic shock model

[1]xa0It has been suggested that galactic shock asymmetry induced by our galaxys infall toward the Virgo Cluster may be a source of periodicity in cosmic-ray exposure as the solar system oscillates normally to the galactic plane, thereby inducing an observed terrestrial periodicity in biodiversity. There are a number of plausible mechanisms by which cosmic rays might affect terrestrial biodiversity. Here we investigate one of these mechanisms, the consequent ionization and dissociation in the atmosphere, resulting in changes in atmospheric chemistry, which culminate in the depletion of ozone and a resulting increase in the dangerous solar UVB flux on the ground. We estimate the enhancement of cosmic-ray intensity for a range of reasonable parameters of the galactic wind and galactic magnetic field, and use these to compute steady-state atmospheric effects. At the lower end of this range, we find that the effects are far too small to be of serious consequence. At the upper end of this range, the level of ozone depletion approaches that currently experienced due to anthropogenic effects such as accumulated chlorofluorocarbons, i.e., ∼2.1% global average loss of ozone column density. We discuss some of the possible effects. While much smaller intensity than the atmospheric effects of a nearby galactic gamma-ray burst, the duration of the effects would be about 106 times greater. Current ozone depletion is a documented stress on the biosphere; it is not clear whether its consequences would be severe if of extended duration. We conclude that, for estimates at the upper end of the reasonable range of the cosmic-ray variability over geologic time, the mechanism of atmospheric ozone depletion may provide a small additional stress, enhancing the impact of other events. However, in order to account for large fluctuations in biodiversity correlated with cosmic-ray flux, other mechanisms should be investigated.

Multi-lepton signals from the top-prime quark at the LHC

A bstractWe analyze the collider signatures of models with a vector-like top-prime quark and a massive color-octet boson. The top-prime quark mixes with the top quark in the Standard Model, leading to richer final states than ones that are investigated by experimental collaborations. We discuss the multi-lepton final states, and show that they can provide increased sensitivity to models with a top-prime quark and gluon-prime. Searches for new physics in high multiplicity events are an important component of the LHC program and complementary to analyses that have been performed.

The DO central track trigger

An overview of the system architecture and algorithms used for the DO Central Track Trigger (CTT) in the Run 2 of the Fermilab Tevatron Proton-Antiproton Collider is presented. This system uses information from the newly commissioned Central Fiber Tracker and Preshower Detectors to generate Level 1 trigger decisions. It also generates lists of seed tracks and preshower clusters that are sent to the Level 1 Muon Trigger, L2 Silicon Track Trigger, and Central and Forward Preshower Level 2 preprocessors. The system consists of modular boards which utilize field-programmable gate arrays (FPGAs) to implement trigger algorithms. The system delivers trigger decisions every 132 ns, based on input data flowing at a maximum sustained rate of 475 gigabits per second. The first results of trigger efficiency studies are presented.

An improved measurement of the BS0 lifetime

Abstract This letter presents an updated measurement of the lifetime of the B s 0 meson using 3.6 million hadronic Z 0 decays recorded by the OPAL detector at LEP from 1990 to 1994. A sample of B s 0 decays is obtained using D s − l + combinations, where the D s − is reconstructed in either the φπ − or K ∗0 K − decay mode. From 79 ± 13 D x l combinations attributed to B s 0 decays in this data sample, we measure τ (B s 0 ) = 1.54 −0.21 +0.25 ± 0.06 ps, where the errors are statistical and systematic, respectively.

Experimental studies of unbiased gluon jets from e ¿ e ¿ annihilations using the jet boost algorithm

We present the first exptl. results based on the jet boost algorithm, a technique to select unbiased samples of gluon jets in e+e- annihilations, i.e. gluon jets free of biases introduced by event selection or jet finding criteria. Our results are derived from hadronic Z0 decays obsd. with the OPAL detector at the LEP e+e- collider at CERN. First, we test the boost algorithm through studies with HERWIG Monte Carlo events and find that it provides accurate measurements of the charged particle multiplicity distributions of unbiased gluon jets for jet energies larger than about 5 GeV, and of the jet particle energy spectra (fragmentation functions) for jet energies larger than about 14 GeV. Second, we apply the boost algorithm to our data to derive unbiased measurements of the gluon jet multiplicity distribution for energies between about 5 and 18 GeV, and of the gluon jet fragmentation function at 14 and 18 GeV. In conjunction with our earlier results at 40 GeV, we then test QCD calcns. for the energy evolution of the distributions, specifically the mean and first two nontrivial normalized factorial moments of the multiplicity distribution, and the fragmentation function. The theor. results are in global agreement with the data, although the factorial moments are not well described for jet energies below about 14 GeV. [on SciFinder (R)]

Search for stopped gluinos from pp collisions at √{s)=1.96 TeV

Long-lived, heavy particles are predicted in a number of models beyond the standard model of particle physics. We present the first direct search for such particles decays, occurring up to 100 h after their production and not synchronized with an accelerator bunch crossing. We apply the analysis to the gluino (g), predicted in split supersymmetry, which after hadronization can become charged and lose enough momentum through ionization to come to rest in dense particle detectors. Approximately 410 pb(-1) of pp collisions at square root(s) = 1.96 TeV collected with the D0 detector during Run II of the Fermilab Tevatron collider are analyzed in search of such stopped gluinos decaying into a gluon and a neutralino (chi(1)(0)). Limits are placed on the (gluino cross section) x (probability to stop) x [BR(g --> g chi(1)(0))] as a function of the gluino and chi(1)(0) masses, for gluino lifetimes from 30 micros-100 h.

Measurement of the B(0)(s) Lifetime Using Semileptonic Decays

We report a measurement of the Bs(0) lifetime in the semileptonic decay channel Bs(0) --> Ds- mu+ nuX (and its charge conjugate), using approximately 0.4 fb(-1) of data collected with the D0 detector during 2002-2004. Using 5176 reconstructed Ds- mu+ signal events, we have measured the Bs(0) lifetime to be tau(Bs(0))=1.398+/-0.044(stat)(-0.025)(+0.028)(syst) ps. This is the most precise measurement of the Bs(0) lifetime to date.