This book gives a comprehensive account of the development and present status of the field of soft (i.e. non-perturbative) phenomena encountered in the production of (multi-) hadronic final states by ...the collision of various types of particles at high energies. Phenomenological models used to describe the data are in general inspired by Quantum Chromo Dynamics (QCD) and the book repeatedly crosses the border — if at all existent — between soft (non-perturbative) and hard (perturbative) QCD.
Experimental data on particle correlations and fluctuations in various high-energy multiparticle collisions are presented, with special emphasis on evidence for scaling-law evolution in small ...phase-space domains. The notions of intermittency and fractality as related to the above findings are described. Phenomenological and theoretical work on the subject is reviewed.
In addition to its importance in describing high-energy processes themselves, the dynamics of multiparticle production has become part of the general field of non-linear phenomena and complex ...systems. Multiparticle dynamics is one of the rare fields of physics where
higher-order correlations are directly accessible in their full multi-dimensional characteristics under well-controlled experimental conditions. Multi-particle dynamics, therefore, is an ideal testing ground for the development of advanced statistical methods. Higher-order correlations have, indeed, been observed as particle-density fluctuations. Approximate scaling with improving resolution provides evidence for a self-similar correlation effect. Quantum-Chromodynamics branching is a good candidate for a dynamical explanation of these correlations in e
+e
− collisions at CERN/LEP and, as expected, also of those in pp collisions at future CERN/LHC energies. However, also other sources such as identical-particle Bose–Einstein interference effects contribute.
A parametrization of the Bose–Einstein correlation function of pairs of identical pions produced in hadronic e+e− annihilation is proposed within the framework of a model (the τ-model) in which ...space–time and momentum space are very strongly correlated. Using information from the Bose–Einstein correlations as well as from single-pion spectra, it is then possible to reconstruct the space–time evolution of pion production.
Electroweak measurements performed with data taken at the electron–positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total ...luminosity of about 3 fb−1 collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV.
Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron–positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose–Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, mW and ΓW, the branching fraction of W decays to hadrons, B(W→had), and the trilinear gauge-boson self-couplings g1Z, κγ and λγ are determined to be: mW=80.376±0.033GeVΓW=2.195±0.083GeVB(W→had)=67.41±0.27%g1Z=0.984−0.020+0.018κγ=0.982±0.042λγ=−0.022±0.019.
We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron–positron colliders SLC and LEP. The data consist of 17 ...million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLD experiment using a polarised beam at SLC. The measurements include cross-sections, forward–backward asymmetries and polarised asymmetries. The mass and width of the Z boson,
m
Z
and
Γ
Z
, and its couplings to fermions, for example the
ρ
parameter and the effective electroweak mixing angle for leptons, are precisely measured:
m
Z
=
91.1875
±
0.0021
GeV
,
Γ
Z
=
2.4952
±
0.0023
GeV
,
ρ
ℓ
=
1.0050
±
0.0010
,
sin
2
θ
eff
lept
=
0.23153
±
0.00016
.
The number of light neutrino species is determined to be
2.9840
±
0.0082
, in agreement with the three observed generations of fundamental fermions.
The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward–backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations.
Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark,
m
t
=
173
-
10
+
13
GeV
, and the mass of the W boson,
m
W
=
80.363
±
0.032
GeV
. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of
m
t
and
m
W
, the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than
285
GeV
at 95% confidence level.
Search for neutral MSSM Higgs bosons at LEP Casado, M.P.; Ouyang, Q.; Xu, R. ...
The European physical journal. C, Particles and fields,
09/2006, Letnik:
47, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four ...collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.
We propose a systematic study of Bose-Einstein correlations between identical hadrons coming from different W decays. Experimentally accessible signatures of these correlations as well as of possible ...color reconnection effects are discussed on the basis of two-particle inclusive densities.
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