700 research outputs found

    Heavy Flavour Physics at HERA

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    New results with increased statistics are presented for heavy flavour production at Q20. Cross sections for Dstar production, F2charm, the gluon density in the proton, and inelastic J/psi production are discussed and compared to theoretical calculations. A first measurement of the b anti-b cross section is reported.Comment: 11 pages, 11 figures, Contribution to `Workshop on Heavy Quarks at Fixed Target, October 199

    Data Preservation in High Energy Physics - why, how and when?

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    Long-term preservation of data and software of large experiments and detectors in high energy physics is of utmost importance to secure the heritage of (mostly unique) data and to allow advanced physics (re-)analyses at later times. Summarising the work of an international study group, motivation, use cases and technical details are given for an organised effort to secure and enable future use of past, present and future experimental data. As a practical use case and motivation, the revival of JADE data and the corresponding latest results on measuring őĪs\alpha_s in NNLO QCD are reviewed.Comment: 5 pages, 3 figures; presentation given at the QCD10, Montpellier, France, June 201

    Fragmentation functions using e+e- data from PETRA and LEP

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    We investigate fragmentation of charged particles in e+e- annihilation at 22, 35 and 44 GeV in terms of their polar angle and momentum distributions. From the angular distribution the ratio of longitudinal to total hadronic cross-section was determined at an average energy scale of 36.6 GeV to be ŌÉL/ŌÉtot=0.076¬Ī0.013\sigma_L / \sigma_{tot} = 0.076 \pm 0.013. At next-to-leading order this yields őĪS(36.6GeV)=0.150¬Ī0.025 \alpha_S (36.6 GeV) = 0.150 \pm 0.025 . The őĺ=ln‚Ā°(1/x)\xi = \ln (1/x) distributions were used in conjunction with OPAL data from 91-208 GeV to study the scale dependence of the maximum position, őĺ0\xi_0. We studied flavour dependence of őĺ0\xi_0 as a possible explanation of this problem, using direct flavour dependent measurements of őĺ0\xi_0 at 91 GeV by OPAL.Comment: 4 pages, 4 figures. Talk given by M. Blumenstengel at QCD 02, Montpellier, France, July 200

    Vergleichende Untersuchungen √ľber den Einflu√ü des hydrostatischen Druckes auf √úberlebensf√§higkeit und Stoffwechselintensit√§t mariner Evertebraten und Teleosteer

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    1. In experiments of one hour's duration the pressure resistance of marine invertebrates and fish was examined by determining the number of surviving specimens. The results (LD50-data) show great (probably specific) differences in resistance to pressure. Young Pleuronectes platessa and Platichthys flesus, Neomysis vulgaris and decapod crustaceans (Eupagurus bernhardus, Crangon crangon, Carcinus maenas) are relatively sensible to pressure. The highest levels of pressure resistance can be observed on echinoderms (Asterias rubens, Psammechinus miliaris), molluscs (Mytilus edulis, Modiolus modiolus, Mya arenaria, Cyprina islanica, Littorina littorea), Jaera albifrons and Nereis diversicolor. 2. Gammarus oceanicus, G. duebeni and Crangon crangon are more sensible to pressure at 15¬į and 20¬į C than at 5¬į C. 3. The resistance to pressure of G. oceanicus becomes greater with increase of salinity as well as of osmotic concentration in the external medium. 4. The pressure resistance of G. oceanicus changes with the seasons, being obviously influenced by the stage of maturity of the gonades and the size of the animals. Crangon crangon is more sensitive to pressure at higher temperatures in summer than at lower ones in winter. 5. Asterias rubens and Littorina littorea decrease in weight at increasing sublethal pressures. 6. The frequency of cardiac beat of G. oceanicus, G. duebeni and young Zoarces viviparus was studied under pressure. Relatively little increase of pressure temporarily stimulates the heart-beat, whereas a decrease of pressure stops the beat or can slow it down for a short time. The heart-beat of Gammarus is accelerated after decompression. These effects of pressure also depend on the temperature. 7. Under pressure in short- and long-termed experiments the O2-consumption of diverse species wasmeasured in steadily running sea-water. Increasing pressure by steps (100-300 atm) Asterias rubens, Henricia sanguinolenta, Ophiura texturata and Psammechinus miliaris react every time with initial "shock-like" reduction of O2-consumption. At 100-200 atm Carcinus maenas, Hyas araneus, Nereis diversicolor and Platichthys flesus initially accelerate their metabolism. Constant pressures of 200 and 300 atm lower the O2-consumption below the normal rates. 8. The slight changes in metabolism of some eurybathic echinoderms under a step by step increase of pressure (100-300 atm) and a gradual recovery of O2-consumption during long-termed exposure to pressure may be looked upon as an adaptation to pressure

    Measurement of the longitudinal and transverse cross-section in e^+e^- annihilation at sqrt(s)=35-44 GeV

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    An investigation of the polar angle distribution of charged hadrons is presented using data taken by the JADE experiment at the PETRA e^+e^- collider at centre-of-mass energies of 35 and 44 GeV. From fits to the polar angle distribution the longitudinal, sigma_L, and transverse, sigma_T, cross-section relative to the total hadronic are determined at an average energy scale of 36.6 GeV. The results are sigma_L/sigma_tot = 0.067 +/- 0.013, sigma_T/sigma_tot = 0.933 -/+ 0.013 where total errors are given and the results are exactly anti-correlated. Using the next-to-leading order QCD prediction for the longitudinal cross-section, the value alpha_S(36.6 GeV) = 0.150 +/- 0.025 of the strong coupling constant is obtained in agreement with the world average value of alpha_S evolved to an energy scale of 36.6 GeV.Comment: 12 pages, LaTeX2e, 5 .eps-files included, pennames.sty included, submitted to Phys. Lett.

    Production of J/psi Mesons at HERA

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    Inelastic and diffractive production of J/psi mesons at HERA is reviewed. The data on inelastic photoproduction are described well within errors by the Colour Singlet Model in next-to-leading order. A search for colour octet processes predicted within the NRQCD/factorisation approach is conducted in many regions of phase space. No unambiguous evidence has been found to date. Diffractive elastic production of J/psi mesons has been measured in the limit of photoproduction up to the highest photon proton center of mass energies. The increase of the cross section is described by pQCD models. At larger Q^2, the W dependence is found to be similar to that observed in photoproduction. First analyses of data at high t yield a powerlike dependence on |t|. A LO BFKL calculation gives a good description of the data.Comment: 14 pages, 12 figures, contribution to Ringberg 200

    J/psi Inclusive Production in ep Deep-Inelastic Scattering at DESY HERA

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    We calculate the cross section of J/psi plus jet associated production in ep deep-inelastic scattering within the factorization formalism of nonrelativistic quantum chromodynamics. Our analytic results disagree with previous analyses, both for the colour-singlet and colour-octet channels. Our theoretical predictions agree reasonably well with recent data taken by the H1 Collaboration at DESY HERA, significantly better than those obtained within the colour-singlet model.Comment: 27 pages (Latex), 9 figures (Postscript), to appear in Nucl. Phys.

    Measurement of the strong coupling alpha_S from the three-jet rate in e+e- - annihilation using JADE data

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    We present a measurement of the strong coupling alpha_S using the three-jet rate measured with the Durham algorithm in e+e- -annihilation using data of the JADE experiment at centre-of-mass energies between 14 and 44 GeV. Recent theoretical improvements provide predictions of the three-jet rate in e+e- -annihilation at next-to-next-to-leading order. In this paper a measurement of the three-jet rate is used to determine the strong coupling alpha_s from a comparison to next-to-next-to-leading order predictions matched with next-to-leading logarithmic approximations and yields a value for the strong coupling alpha_S(MZ) = 0.1199+- 0.0010 (stat.) +- 0.0021 (exp.) +- 0.0054 (had.) +- 0.0007 (theo.) consistent with the world average.Comment: 27 pages, 8 figure
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