| 1. |
- Aktas, A, et al.
(författare)
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Inclusive production of D+, D-0, D-s(+) and D*(+) mesons in deep inelastic scattering at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 447-459
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 < Q(2) < 100 GeV2, inelasticity 0.05 < y < 0.7, D meson transverse momenta p(t)( D) greater than or equal to 2.5 GeV and pseudorapidity |eta( D)| less than or equal to 1.5. The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons containing the light quarks u, d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process.
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| 2. |
- Aktas, A, et al.
(författare)
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Measurement of F-2(c(c)over-bar) and F-2(b(b)over-bar) at high Q(2) using the H1 vertex detector at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 40:3, s. 349-359
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Tidskriftsartikel (refereegranskat)abstract
- Measurements are presented of inclusive charm and beauty cross sections in e(+)p collisions at HERA for values of photon virtuality Q(2) > 150 GeV2 and of inelasticity 0.1 < y < 0.7. The charm and beauty fractions are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. The data are divided into four regions in Q(2) and Bjorken x, and values for the structure functions F-2(c (c) over bar) and F-2(b (b) over bar) are obtained. The results are found to be compatible with the predictions of perturbative quantum chromodynamics.
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| 3. |
- Aktas, A, et al.
(författare)
-
Measurement of prompt photon cross sections in photoproduction at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 437-445
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented on the photoproduction of isolated prompt photons, inclusively and associated with jets, in the gammap center of mass energy range 142 < W < 266 GeV. The cross sections are measured for the transverse momentum range of the photons 5 < E. T < 10 GeV and for associated jets with E-T(jet) > 4.5 GeV. They are measured differentially as a function of E-T(gamma), E-T(jet), the pseudorapidities eta(gamma) and eta(jet) and estimators of the momentum fractions x(gamma) and x(p) of the incident photon and proton carried by the constituents participating in the hard process. In order to further investigate the underlying dynamics, the angular correlation between the prompt photon and the jet in the transverse plane is studied. Predictions by perturbative QCD calculations in next to leading order are about 30% below the inclusive prompt photon data after corrections for hadronisation and multiple interactions, but are in reasonable agreement with the results for prompt photons associated with jets. Comparisons with the predictions of the event generators PYTHIA and HERWIG are also presented.
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| 4. |
- Aktas, A, et al.
(författare)
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Search for light gravitinos in events with photons and missing transverse momentum at HERA
- 2005
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 616:1-2, s. 31-42
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Tidskriftsartikel (refereegranskat)abstract
- A search for gravitinos produced in e(+/-)p collisions is performed using the H1 detector at HERA. The data were taken at a centre-of-mass energy of 319 GeV and correspond to an integrated luminosity of 64.3 pb(-1) for e(+)p collisions and 13.5 pb(-1) for e(-)p collisions. If R-parity is not conserved, the t-channel exchange of a selectron can produce a neutralino, which, in models where the gravitino is the lightest supersymmetric particle, subsequently decays into a photon and a light gravitino. The resulting event signature, which involves an isolated photon, a jet and missing transverse energy, is analysed for the first time at HERA. No deviation from the Standard Model is found. Exclusion limits on the cross section and on R-parity-violating Yukawa couplings are derived in a Gauge Mediated Supersymmetry Breaking scenario. The results are independent of the squark sector. Neutralinos and supersymmetric partners of the left-handed electron with masses up to 112 GeV and 164 GeV, respectively, can be ruled out at the 95% confidence level for R-parity-violating couplings lambda' equal to 1, in some parts of the parameter space of the considered model.
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| 5. |
- Engqvist, Martin, 1983, et al.
(författare)
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Two D-2-hydroxy-acid dehydrogenases in arabidopsis thaliana with catalytic capacities to participate in the last reactions of the methylglyoxal and β-oxidation pathways
- 2009
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 284:37, s. 25026-25037
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Tidskriftsartikel (refereegranskat)abstract
- The Arabidopsis thaliana locus At5g06580 encodes an ortholog to Saccharomyces cerevisiae D-lactate dehydrogenase (AtD-LDH). The recombinant protein is a homodimer of 59-kDa subunits with one FAD per monomer. A substrate screen indicated that AtD-LDH catalyzes the oxidation of D- and L-lactate, D-2-hydroxybutyrate, glycerate, and glycolate using cytochrome c as an electron acceptor. AtD-LDH shows a clear preference for D-lactate, with a catalytic efficiency 200- and 2000-fold higher than that for L-lactate and glycolate, respectively, and a Km value for D-lactate of ∼160 μM. Knock-out mutants showed impaired growth in the presence of D-lactate or methylglyoxal. Collectively, the data indicated that the protein is a D-LDH that participates in planta in the methylglyoxal pathway. Web-based bioinformatic tools revealed the existence of a paralogous protein encoded by locus At4g36400. The recombinant protein is a homodimer of 61-kDa subunits with one FAD per monomer. A substrate screening revealed highly specific D-2-hydroxyglutarate (D-2HG) conversion in the presence of an organic cofactor with a Km value of ∼580 μM. Thus, the enzyme was characterized as a D-2HG dehydrogenase (AtD-2HGDH). Analysis of knock-out mutants demonstrated that AtD-2HGDH is responsible for the total D-2HGDH activity present in A. thaliana. Gene coexpression analysis indicated that AtD-2HGDH is in the same network as several genes involved in β-oxidation and degradation of branched-chain amino acids and chlorophyll. It is proposed that AtD-2HGDH participates in the catabolism of D-2HG most probably during the mobilization of alternative substrates from proteolysis and/or lipid degradation.
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