5,089 research outputs found
Sphaleron Effects Near the Critical Temperature
We discuss one-loop radiative corrections to the sphaleron-induced baryon
number-violating transition rate near the electroweak phase transition in the
standard model. We emphasize that in the case of a first-order transition a
rearrangement of the loop expansion is required close to the transition
temperature. The corresponding expansion parameter, the effective 3-dimensional
gauge coupling approaches a finite dependent value at the critical
temperature.
The
(Higgs mass) dependence of the 1-loop radiative corrections is discussed in
the framework of the heat kernel method. Radiative corrections are small
compared to the leading sphaleron contribution as long as the Higgs mass is
small compared to the W mass. To 1-loop accuracy, there is no Higgs mass range
compatible with experimental limits where washing-out of a B+L asymmetry could
be avoided for the minimal standard model with one Higgs doublet.Comment: 17 pages, RevTeX, (4 figures in a separate uuencoded file),
HD-THEP-93-23re
Skyrmion Multi-Walls
Skyrmion walls are topologically-nontrivial solutions of the Skyrme system
which are periodic in two spatial directions. We report numerical
investigations which show that solutions representing parallel multi-walls
exist. The most stable configuration is that of the square -wall, which in
the limit becomes the cubically-symmetric Skyrme crystal. There is
also a solution resembling parallel hexagonal walls, but this is less stable.Comment: 7 pages, 1 figur
Trakhtenbrot's Theorem in Coq, A Constructive Approach to Finite Model Theory
We study finite first-order satisfiability (FSAT) in the constructive setting
of dependent type theory. Employing synthetic accounts of enumerability and
decidability, we give a full classification of FSAT depending on the
first-order signature of non-logical symbols. On the one hand, our development
focuses on Trakhtenbrot's theorem, stating that FSAT is undecidable as soon as
the signature contains an at least binary relation symbol. Our proof proceeds
by a many-one reduction chain starting from the Post correspondence problem. On
the other hand, we establish the decidability of FSAT for monadic first-order
logic, i.e. where the signature only contains at most unary function and
relation symbols, as well as the enumerability of FSAT for arbitrary enumerable
signatures. All our results are mechanised in the framework of a growing Coq
library of synthetic undecidability proofs
Measurement of the hadronic photon structure function F_{2}^{γ} at LEP2
The hadronic structure function of the photon F_{2}^{γ} (x, Q²) is measured as a function of Bjorken x and of the photon virtuality Q² using deep-inelastic scattering data taken by the OPAL detector at LEP at e⁺e⁻ centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F_{2}^{γ} are extended to an average Q² of 〈Q²〉=780 GeV² using data in the kinematic range 0.15<x<0.98. The Q² evolution of F_{2}^{γ} is studied for 12.1<〈Q²〉<780 GeV² using three ranges of x. As predicted by QCD, the data show positive scaling violations in F_{2}^{γ} with F_{2}^{γ} (Q²)/α = (0.08±0.02⁺⁰·⁰⁵_₀.₀₃) + (0.13±0.01⁺⁰·⁰¹_₀.₀₁) lnQ², where Q² is in GeV², for the central x region 0.10–0.60. Several parameterisations of F_{2}^{γ} are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data
Measurement of the charm structure function F_{2,c)^{γ} of the photon at LEP
The production of charm quarks is studied in deep-inelastic electron–photon scattering using data recorded by the OPAL detector at LEP at nominal e⁺e⁻ centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D* mesons using their decays into D⁰π with the D⁰ observed in two decay modes with charged particle final states, Kπ and Kπππ. The cross-section σ^{D*} for production of charged D* in the reaction e⁺e⁻→e⁺e⁻D*Χ is measured in a restricted kinematical region using two bins in Bjorken x, 0.00140.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x<0.1 the measured cross-section is 43.8±14.3±6.3±2.8 pb with a next-to-leading order prediction of 17.0⁺²·⁹_₂.₃ pb
Measurement of triple gauge boson couplings from W⁺W⁻ production at LEP energies up to 189 GeV
A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pb⁻¹. After combining with our previous measurements at centre-of-mass energies of 161–183 GeV we obtain κ = 0.97_{-0.16}^{+0.20}, g_{1}^{z} = 0.991_{-0.057}^{+0.060} and λ = -0.110_{-0.055}^{+0.058}, where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their Standard Model values. These results are consistent with the Standard Model expectations
Baseline variability in onshore near surface gases and implications for monitoring at CO2 storage sites
The measurement of gas concentrations and fluxes in the soil and atmosphere is a powerful tool for monitoring geological carbon capture and storage (CCS) sites because the analyses are made directly in the biosphere in which we live. These methods can be used to both find and accurately quantifying leaks, and are visible and tangible data for public and ecosystem safety. To be most reliable and accurate, however, the measurements must be interpreted in the context of natural variations in gas concentration and flux. Such baseline data vary both spatially and temporally due to natural processes, and a clear understanding of their values and distributions is critical for interpreting near-surface gas monitoring techniques. The best example is CO2 itself, as the production of this gas via soil respiration can create a wide range of concentrations and fluxes that must be separated from, and not confused with, CO2 that may leak towards the surface from a storage reservoir. The present article summarizes baseline studies performed by the authors at various sites having different climates and geological settings from both Europe and North America, with focus given to the range of values that can result from near surface processes and how different techniques or data processing approaches can be used to help distinguish a leakage signal from an anomalous, shallow biogenic signal
Tests of model of color reconnection and a search for glueballs using gluon jets with a rapidity gap
Gluon jets with a mean energy of 22 GeV and purity of 95% are selected from
hadronic Z0 decay events produced in e+e- annihilations. A subsample of these
jets is identified which exhibits a large gap in the rapidity distribution of
particles within the jet. After imposing the requirement of a rapidity gap, the
gluon jet purity is 86%. These jets are observed to demonstrate a high degree
of sensitivity to the presence of color reconnection, i.e. higher order QCD
processes affecting the underlying color structure. We use our data to test
three QCD models which include a simulation of color reconnection: one in the
Ariadne Monte Carlo, one in the Herwig Monte Carlo, and the other by Rathsman
in the Pythia Monte Carlo. We find the Rathsman and Ariadne color reconnection
models can describe our gluon jet measurements only if very large values are
used for the cutoff parameters which serve to terminate the parton showers, and
that the description of inclusive Z0 data is significantly degraded in this
case. We conclude that color reconnection as implemented by these two models is
disfavored. The signal from the Herwig color reconnection model is less clear
and we do not obtain a definite conclusion concerning this model. In a separate
study, we follow recent theoretical suggestions and search for glueball-like
objects in the leading part of the gluon jets. No clear evidence is observed
for these objects.Comment: 42 pages, 18 figure
Scaling violations of quark and gluon jet fragmentation functions in e+e- annihilations at sqrt(s) = 91.2 and 183-209 GeV
Flavour inclusive, udsc and b fragmentation functions in unbiased jets, and
flavour inclusive, udsc, b and gluon fragmentation functions in biased jets are
measured in e+e- annihilations from data collected at centre-of-mass energies
of 91.2, and 183-209 GeV with the OPAL detector at LEP. The unbiased jets are
defined by hemispheres of inclusive hadronic events, while the biased jet
measurements are based on three-jet events selected with jet algorithms.
Several methods are employed to extract the fragmentation functions over a wide
range of scales. Possible biases are studied in the results are obtained. The
fragmentation functions are compared to results from lower energy e+e-
experiments and with earlier LEP measurements and are found to be consistent.
Scaling violations are observed and are found to be stronger for the
fragmentation functions of gluon jets than for those of quarks. The measured
fragmentation functions are compared to three recent theoretical
next-to-leading order calculations and to the predictions of three Monte Carlo
event generators. While the Monte Carlo models are in good agreement with the
data, the theoretical predictions fail to describe the full set of results, in
particular the b and gluon jet measurements.Comment: 46 pages, 17 figures, Submitted to Eur. Phys J.
Performance of a Large-Area GEM Detector Prototype for the Upgrade of the CMS Muon Endcap System
Gas Electron Multiplier (GEM) technology is being considered for the forward
muon upgrade of the CMS experiment in Phase 2 of the CERN LHC. Its first
implementation is planned for the GE1/1 system in the region of the muon endcap mainly to control muon level-1 trigger rates
after the second long LHC shutdown. A GE1/1 triple-GEM detector is read out by
3,072 radial strips with 455 rad pitch arranged in eight -sectors.
We assembled a full-size GE1/1 prototype of 1m length at Florida Tech and
tested it in 20-120 GeV hadron beams at Fermilab using Ar/CO 70:30 and
the RD51 scalable readout system. Four small GEM detectors with 2-D readout and
an average measured azimuthal resolution of 36 rad provided precise
reference tracks. Construction of this largest GEM detector built to-date is
described. Strip cluster parameters, detection efficiency, and spatial
resolution are studied with position and high voltage scans. The plateau
detection efficiency is [97.1 0.2 (stat)]\%. The azimuthal resolution is
found to be [123.5 1.6 (stat)] rad when operating in the center of
the efficiency plateau and using full pulse height information. The resolution
can be slightly improved by 10 rad when correcting for the bias due
to discrete readout strips. The CMS upgrade design calls for readout
electronics with binary hit output. When strip clusters are formed
correspondingly without charge-weighting and with fixed hit thresholds, a
position resolution of [136.8 2.5 stat] rad is measured, consistent
with the expected resolution of strip-pitch/ = 131.3 rad. Other
-sectors of the detector show similar response and performance.Comment: 8 pages, 32 figures, submitted to Proc. 2014 IEEE Nucl. Sci.
Symposium, Seattle, WA, reference adde
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