138 research outputs found
Eleven Years of QCD at LEP
Studies of hadronic final states of annihilations, observed at the
Large Electron Positron Collider LEP at CERN, are reviewed. The topics included
cover measurements of , hadronic event shapes and hadronisation
studies, tests of asymptotic freedom and of the non-Abelian gauge structure of
QCD, differences between quark and gluon jets, tests of power corrections and
selected results of two-photon scattering processes. The improvements obtained
at LEP are demonstrated by comparing to results from the pre-LEP era. This
article consists of a reproduction of slides presented at the LEPFest in
October 2000, supplemented by a short descriptive text and a list of relevant
references.Comment: 10 pages of text plus reproduction of 27 transparencies presented at
the LEPFest at CERN, October 2000. To be published in Eur. Phys. Jour
(direct) C; a higher resolution version of the viewgraphs can be obtained
from: http://www.mppmu.mpg.de/~bethke/LEPQCDtalk-higres.pd
Experimental Tests of Asymptotic Freedom
Quantum Chromodynamics (QCD), the gauge field theory of the Strong
Interaction, has specific features, asymptotic freedom and confinement, which
determine the behaviour of quarks and gluons in particle reactions at high and
at low energy scales. QCD predicts that the strong coupling strength \as
decreases with increasing energy or momentum transfer, and vanishes at
asymptotically high energies. In this review, the history and the status of
experimental tests of asymptotic freedom are summarised. The world summary of
measurements of \as is updated, leading to an unambiguous verification of the
running of \as and of asymptotic freedom, in excellent agreement with the
predictions of QCD. Averaging a set of measurements balanced between different
particle processes and the available energy range, results in a new and
improved world average of \amz = 0.1189 \pm 0.0010 .Comment: 38 pages, 18 figure
at Zinnowitz 2004
A review of measurements of is given, representing the status of
April 2004. The results prove the energy dependence of and are in
excellent agreement with the expectations of Quantum Chromodynamics, QCD.
Evolving all results to the rest energy of the boson, the world average
of is determined from measurements which are based on QCD
calculations in complete NNLO perturbation theory, giving Comment: 8 pages, 4 figures, talk presented at the workshop Loops and Legs in
Quantum Field Theory, April 2004, Zinnowitz (Germany
QCD Tests at Colliders
A short review of the history and a 'slide-show' of QCD tests in
annihilation is given. The world summary of measurements of is
updated.Comment: Revised version: some references added and corrected; world summary
of extended by result from polarized structure functions. 9 pages,
15 EPS figures; contribution to the CQD Euroconference 97 (Montpellier 1997
Data Preservation in High Energy Physics - why, how and when?
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 in NNLO QCD are reviewed.Comment: 5 pages, 3 figures; presentation given at the QCD10, Montpellier,
France, June 201
Wer fischt was? – Gemischte Bodenfischereien und ihre Auswirkungen auf die wichtigsten Nutzfischbestände in der Nordsee
Cod, haddock, whiting, saithe, plaice, sole and Norway lobster are 7 main target species of the demersal mixed fisheries in the North Sea, Skagerrak and Eastern Channel. Gadoids and Norway lobsters are mainly taken in the nor-thern North Sea by towed gears except beam trawls while the flatfish fisheries are conducted in the southern North Sea mainly using beam trawls. Recently, the central North Sea appears less fished by demersal gears. Towed nets including seines and beam trawls equipped with meshes of more than 100 mm resp. more than 80 mm were identified as the main gears effecting the depleted cod and reduced plaice stocks. The saithe sector, using towed nets with meshes of more than110 mm, longlines, gill nets and others, appears to affect the 7 species to a lesser extend. These results support the interim effort limitations by gear types, vessel and month as enforced by the European Commission since 2003. TAC regulations alone are considered inefficient to sustainably harvest stocks by mixed fisheries. A fleet-effort management method is developed estimating the fleets’ effects based on the sum of partial exploitation rates of the species in mixed fisheries weighted by the ratio of the precautionary reference Bpa and the actual SSB size as ecological quality objective. Applying such fleet effort management could result in increased catch possibilities of some stocks by fleets selecting mainly few and non-overexploited stocks while respecting precautionary management constraints in minimum SSB or maximum exploitation rates at the same time
Experimental Tests of Asymptotic Freedom
Measurements which probe the energy dependence of , the coupling
strength of the strong interaction, are reviewed. Jet counting in
annihilation, combining results obtained in the centre of mass energy range
from 22 to 133 GeV, provides direct evidence for an asymptotically free
coupling, without the need to determine explicit values of . Recent
results from jet production in and in collisions,
obtained in single experiments spanning large ranges of momentum transfer,
, are in good agreement with the running of as predicted by
QCD. Mass spectra of hadronic decays of -leptons are analysed to probe
the running in the very low energy domain, . An update of the world summary of measurements of
consistently proves the energy dependence of and results in a
combined average of .Comment: 11 pages, 8 Figures, LaTeX. To appear in Proc. of QCD Euroconference
96 at Montpellier, France, July 199
The 2009 World Average of
Measurements of , the coupling strength of the Strong Interaction
between quarks and gluons, are summarised and an updated value of the world
average of is derived. Building up on previous reviews,
special emphasis is laid on the most recent determinations of . These
are obtained from -decays, from global fits of electroweak precision data
and from measurements of the proton structure function \F_2, which are based
on perturbative QCD calculations up to ; from hadronic event
shapes and jet production in \epem annihilation, based on
QCD; from jet production in deep inelastic scattering and from
decays, based on QCD; and from heavy quarkonia based on
unquenched QCD lattice calculations. Applying pragmatic methods to deal with
possibly underestimated errors and/or unknown correlations, the world average
value of results in . The
measured values of , covering energy scales from Q \equiv \mtau
= 1.78 GeV to 209 GeV, exactly follow the energy dependence predicted by QCD
and therefore significantly test the concept af Asymptotic Freedom.Comment: 14 pages, 7 figure
Status Report of the DPHEP Study Group: Towards a Global Effort for Sustainable Data Preservation in High Energy Physics
Data from high-energy physics (HEP) experiments are collected with
significant financial and human effort and are mostly unique. An
inter-experimental study group on HEP data preservation and long-term analysis
was convened as a panel of the International Committee for Future Accelerators
(ICFA). The group was formed by large collider-based experiments and
investigated the technical and organisational aspects of HEP data preservation.
An intermediate report was released in November 2009 addressing the general
issues of data preservation in HEP. This paper includes and extends the
intermediate report. It provides an analysis of the research case for data
preservation and a detailed description of the various projects at experiment,
laboratory and international levels. In addition, the paper provides a concrete
proposal for an international organisation in charge of the data management and
policies in high-energy physics
- …