355 research outputs found
A Study of Event Shapes and Determinations of alpha_s using data of e^+e^- Annihilations at sqrt{s} = 22 to 44 GeV
Data recorded by the JADE experiment at the PETRA e^+e^- collider were used
to measure the event shape observables thrust, heavy jet mass, wide and total
jet broadening and the differential 2-jet rate in the Durham scheme. For the
latter three observables, no experimental results have previously been
presented at these energies. The distributions were compared with resummed QCD
calulations (O(alpha_s^2)+NLLA), and the strong coupling constant alpha_s(Q)
was determined at different energy scales Q=sqrt{s}. The results,
\alpha_s(22 GeV) = 0.161 ^{+0.016}_{-0.011},
\alpha_s(35 GeV) = 0.143 ^{+0.011}_{-0.007},
\alpha_s(44 GeV) = 0.137 ^{+0.010}_{-0.007}, are in agreement with previous
combined results of PETRA albeit with smaller uncertainties. Together with
corresponding data from LEP, the energy dependence of alpha_s is significantly
tested and is found to be in good agreement with the QCD expectation.
Similarly, mean values of the observables were compared to analytic QCD
predictions where hadronisation effects are absorbed in calculable power
corrections.Comment: 36 pages, LaTeX2e, 34 .eps-files included, submitted to Z. Phys. C,
revised version, with comments of referee included and some typos corrected,
accepted for publicatio
Metabolic engineering of Bacillus methanolicus and Corynebacterium glutamicum for the production of cadaverine from methanol
Pfeifenschneider J. Metabolic engineering of Bacillus methanolicus and Corynebacterium glutamicum for the production of cadaverine from methanol. Bielefeld: Universität Bielefeld; 2015
Transaldolase in Bacillus methanolicus: Biochemical Characterization and Biological Role in Ribulose Monophosphate Cycle
Pfeifenschneider J, Markert B, Stolzenberger J, Brautaset T, Wendisch VF. Transaldolase in Bacillus methanolicus: Biochemical Characterization and Biological Role in Ribulose Monophosphate Cycle. BMC Microbiology. 2020;20: 63.Background
The Gram-positive facultative methylotrophic bacterium Bacillus methanolicus uses the sedoheptulose-1,7-bisphosphatase (SBPase) variant of the ribulose monophosphate (RuMP) cycle for growth on the C1 carbon source methanol. Previous genome sequencing of the physiologically different B. methanolicus wild-type strains MGA3 and PB1 has unraveled all putative RuMP cycle genes and later, several of the RuMP cycle enzymes of MGA3 have been biochemically characterized. In this study, the focus was on the characterization of the transaldolase (Ta) and its possible role in the RuMP cycle in B. methanolicus.
Results
The Ta genes of B. methanolicus MGA3 and PB1 were recombinantly expressed in Escherichia coli, and the gene products were purified and characterized. The PB1 Ta protein was found to be active as a homodimer with a molecular weight of 54 kDa and displayed KM of 0.74 mM and Vmax of 16.3 U/mg using Fructose-6 phosphate as the substrate. In contrast, the MGA3 Ta gene, which encodes a truncated Ta protein lacking 80 amino acids at the N-terminus, showed no Ta activity. Seven different mutant genes expressing various full-length MGA3 Ta proteins were constructed and all gene products displayed Ta activities. Moreover, MGA3 cells displayed Ta activities similar as PB1 cells in crude extracts.
Conclusions
While it is well established that B. methanolicus can use the SBPase variant of the RuMP cycle this study indicates that B. methanolicus possesses Ta activity and may also operate the Ta variant of the RuMP
A Measurement of the QCD Colour Factors using Event Shape Distributions at sqrt(s)=14 GeV to 189 GeV
Measurements of the QCD colour factors C_A and C_F and of the number of
active quark flavours n_f in the process e+e- -> hadrons at high energy are
presented. They are based on fits of O(alpha_S**2)+NLLA QCD calculations to
distributions of the event shape observables 1-T, C, B_T and B_W measured at
centre-of-mass energies from 14 GeV to 189 GeV. Hadronisation effects are
approximated with power correction calculations which also depend on the QCD
gauge structure. In this approach potential biases from hadronisation models
are reduced. Our results for individually measured quantities are n_f = 5.64 +-
1.35, C_A = 2.88 +- 0.27 and C_F = 1.45 +- 0.27 in good agreement with QCD
based on the SU(3) symmetry group where n_f=5 for the energies considered here,
C_A=3 and C_F=4/3. From simultaneous fits of C_A and C_F we find C_A = 2.84 +-
0.24 and C_F = 1.29 +- 0.18, which is also in good agreement with the QCD
expectation.Comment: accepted by European Journal of Physics
Measurement of the longitudinal and transverse cross-section in e^+e^- annihilation at sqrt(s)=35-44 GeV
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.
Colour reconnections in Herwig++
We describe the implementation details of the colour reconnection model in
the event generator Herwig++. We study the impact on final-state observables in
detail and confirm the model idea from colour preconfinement on the basis of
studies within the cluster hadronization model. Moreover, we show that the
description of minimum bias and underlying event data at the LHC is improved
with this model and present results of a tune to available data.Comment: 19 pages, 21 figures, 2 tables. Matches with published versio
Electroweak corrections to hadronic event shapes and jet production in e+e- annihilation
We present a complete calculation of the electroweak O(alpha^3 alpha_s)
corrections to three-jet production and related event-shape observables at
electron--positron colliders. The Z-boson resonance is described within the
complex-mass scheme, rendering the calculation valid both in the resonance and
off-shell regions. Higher-order initial-state radiation is included in the
leading-logarithmic approximation. We properly account for the corrections to
the total hadronic cross section and for the experimental photon isolation
criteria. To this end we implement contributions of the quark-to-photon
fragmentation function both in the slicing and subtraction formalism. The
effects of the electroweak corrections on various event-shape distributions and
on the three-jet rate are studied. They are typically at the few-per-cent
level, and remnants of the radiative return are found even after inclusion of
appropriate cuts.Comment: 47 pages, 20 figure
Event shapes in e+e- annihilation and deep inelastic scattering
This article reviews the status of event-shape studies in e+e- annihilation
and DIS. It includes discussions of perturbative calculations, of various
approaches to modelling hadronisation and of comparisons to data.Comment: Invited topical review for J.Phys.G; 40 pages; revised version
corrects some nomenclatur
A Measurement of Rb using a Double Tagging Method
The fraction of Z to bbbar events in hadronic Z decays has been measured by
the OPAL experiment using the data collected at LEP between 1992 and 1995. The
Z to bbbar decays were tagged using displaced secondary vertices, and high
momentum electrons and muons. Systematic uncertainties were reduced by
measuring the b-tagging efficiency using a double tagging technique. Efficiency
correlations between opposite hemispheres of an event are small, and are well
understood through comparisons between real and simulated data samples. A value
of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is
statistical and the second systematic. The uncertainty on Rc, the fraction of Z
to ccbar events in hadronic Z decays, is not included in the errors. The
dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the
deviation of Rc from the value 0.172 predicted by the Standard Model. The
result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the
Standard Model.Comment: 42 pages, LaTeX, 14 eps figures included, submitted to European
Physical Journal
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.
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