7,499 research outputs found

    Measurement of the fraction of t-tbar production via gluon-gluon fusion in p-pbar collisions at sqrt(s)=1.96 TeV

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    We present a measurement of the ratio of t-tbar production cross section via gluon-gluon fusion to the total t-tbar production cross section in p-pbar collisions at sqrt{s}=1.96 TeV at the Tevatron. Using a data sample with an integrated luminosity of 955/pb recorded by the CDF II detector at Fermilab, we select events based on the t-tbar decay to lepton+jets. Using an artificial neural network technique we discriminate between t-tbar events produced via q-qbar annihilation and gluon-gluon fusion, and find Cf=(gg->ttbar)/(pp->ttbar)<0.33 at the 68% confidence level. This result is combined with a previous measurement to obtain the most precise measurement of this quantity, Cf=0.07+0.15-0.07.Comment: submitted to Phys. Rev.

    Measurement of Resonance Parameters of Orbitally Excited Narrow B^0 Mesons

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    We report a measurement of resonance parameters of the orbitally excited (L=1) narrow B^0 mesons in decays to B^{(*)+}\pi^- using 1.7/fb of data collected by the CDF II detector at the Fermilab Tevatron. The mass and width of the B^{*0}_2 state are measured to be m(B^{*0}_2) = 5740.2^{+1.7}_{-1.8}(stat.) ^{+0.9}_{-0.8}(syst.) MeV/c^2 and \Gamma(B^{*0}_2) = 22.7^{+3.8}_{-3.2}(stat.) ^{+3.2}_{-10.2}(syst.) MeV/c^2. The mass difference between the B^{*0}_2 and B^0_1 states is measured to be 14.9^{+2.2}_{-2.5}(stat.) ^{+1.2}_{-1.4}(syst.) MeV/c^2, resulting in a B^0_1 mass of 5725.3^{+1.6}_{-2.2}(stat.) ^{+1.4}_{-1.5}(syst.) MeV/c^2. This is currently the most precise measurement of the masses of these states and the first measurement of the B^{*0}_2 width.Comment: 7 pages, 1 figure, 1 table. Submitted to Phys.Rev.Let

    Search for lepton flavor violating decays of a heavy neutral particle in p-pbar collisions at root(s)=1.8 TeV

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    We report on a search for a high mass, narrow width particle that decays directly to e+mu, e+tau, or mu+tau. We use approximately 110 pb^-1 of data collected with the Collider Detector at Fermilab from 1992 to 1995. No evidence of lepton flavor violating decays is found. Limits are set on the production and decay of sneutrinos with R-parity violating interactions.Comment: Figure 2 fixed. Reference 4 fixed. Minor changes to tex

    Th e role of prescribed burning in maintenance of an endangered plant species, Lomatium bradshawii.

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    Abstract. Responses of a federally listed endangered plant species, Lomatium bradshawii, to the use of fire as a management tool for maintaining remnant wetland prairies were evaluated at two public land areas in the Willamette Valley of western Oregon. Areas containing L. bradshawii were treated with two or three fall season prescribed burns during a nine-year period. Foliar crown area, height, umbellets, and schizocarps of 150 L. bradshawii at Rose Prairie and 250 at Fisher Butte and the recruitment and density of L. bradshawii in 2-m 2 plots at both sites were documented during 1988-1996. When both sites were considered together, crown area, height, umbellets, and schizocarps per plant initially responded positively to burn treatments, but increases were not consistent across years or sites. Crown area tended to increase and then decline after each burn. Burning initially enhanced schizocarp production at both sites; schizocarps declined one or two years after burning but remained much higher in the burn treatments than in controls until 1996. Seedling production was not correlated with schizocarp production at either site. Umbellet and schizocarp production were not correlated with January-June temperatures or precipitation at the nearest weather station. Burning accentuated differences in size and reproductive capacity of L. bradshawii at the two sites and differentially affected recruitment and density. Random resampling of L. bradshawii in 1997 indicated that effects of repeated burning during the previous eight years were hard to detect. At Rose Prairie, foliar crown area, height, number of leaves, umbellets, and schizocarps in 1997 were similar or lower with burning than in unburned controls. At Fisher Butte, L. bradshawii in the two burn treatment were similar to control plants, but three burns significantly increased foliar crown area, number of leaves, and schizocarps. Monitoring recovery for one or two years after a burn may only capture the initial stimulation provided by burning and may foster unrealistically high expectations concerning the viability of an endangered plant population

    Big sugar in southern Africa : rural development and the perverted potential of sugar/ethanol exports

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    This paper asks how investment in large-scale sugar cane production has contributed, and will contribute, to rural development in southern Africa. Taking a case study of the South African company Illovo in Zambia, the argument is made that the potential for greater tax revenue, domestic competition, access to resources and wealth distribution from sugar/ethanol production have all been perverted and with relatively little payoff in wage labour opportunities in return. If the benefits of agro-exports cannot be so easily assumed, then the prospective 'balance sheet' of biofuels needs to be re-examined. In this light, the paper advocates smaller-scale agrarian initiatives

    Differentiating normal and problem gambling: a grounded theory approach.

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    A previous study (Ricketts &amp; Macaskill, 2003) delineated a theory of problem gambling based on the experiences of treatment seeking male gamblers and allowed predictions to be made regarding the processes that differentiate between normal and problem gamblers. These predictions are the focus of the present study, which also utilised a grounded theory approach, but with a sample of male high frequency normal gamblers. The findings suggest that there are common aspects of gambling associated with arousal and a sense of achievement. The use of gambling to manage negative emotional states differentiated normal and problem gambling. Perceived self-efficacy , emotion management skills and perceived likelihood of winning money back were intervening variables differentiating problem and normal gamblers.</p

    Routine activities and proactive police activity: a macro-scale analysis of police searches in London and New York City

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    This paper explored how city-level changes in routine activities were associated with changes in frequencies of police searches using six years of police records from the London Metropolitan Police Service and the New York City Police Department. Routine activities were operationalised through selecting events that potentially impacted on (a) the street population, (b) the frequency of crime or (c) the level of police activity. OLS regression results indicated that routine activity variables (e.g. day of the week, periods of high demand for police service) can explain a large proportion of the variance in search frequency throughout the year. A complex set of results emerged, revealing cross-national dissimilarities and the differential impact of certain activities (e.g. public holidays). Importantly, temporal frequencies in searches are not reducible to associations between searches and recorded street crime, nor changes in on-street population. Based on the routine activity approach, a theoretical police-action model is proposed
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