63 research outputs found
The dimensional stability of glass-fibre reinforced Polyamide 66 during hydrolysis conditioning
Injection moulded glass-fibre reinforced polyamide 66 composites based on two glass fibre products with different sizing formulations and unreinforced polymer samples have been characterised both dry as moulded and during conditioning in a water-glycol mixture at 70°C for a range of times up to 400 hours. The results reveal that hydrothermal ageing in water-glycol mixtures causes significant changes in the weight and dimensions of these materials. All conditioned materials showed a time dependent weight increase which could be characterised as pseudo-Fickian. The weight change could be well modelled by a Fickian diffusion process with a time dependent diffusion coefficient. It was not apparent that changing the glass fibre sizing affected the dimensional stability of the composites. There was a strong correlation between the swelling of these samples and the level of fluid absorption. The composites exhibited different levels of swelling depending on direction. These effects were well in line with the influence of fibres on restriction of the matrix deformation in the fibre direction. These differences correlated well with the average fibre orientation with respect to the various direction axes
The thermo-mechanical performance of glass-fibre reinforced Polyamide 66 during glycol-water hydrolysis conditioning
Injection moulded glass-fibre reinforced polyamide 66 composites based on two glass fibre products with different sizing formulations and unreinforced polymer samples have been characterised by dynamic mechanical analysis and unnotched Charpy impact testing both dry as moulded and during conditioning in a glycol-water mixture at 70°C for a range of times up to 400 hours. Simultaneously weight and dimension changes of these materials have been recorded. The results reveal that hydrothermal ageing in glycol-water mixtures causes significant changes in the thermo-mechanical performance of these materials. It is shown that mechanical performance obtained after conditioning at different temperatures can be superimposed when considered as a function of the level of fluid absorbed by the composite polymer matrix
Charmless Three-Body Baryonic B Decays
Motivated by recent data on B-> p pbar K decay, we study various charmless
three-body baryonic B decay modes, including Lambda pbar pi, Sigma0 pbar pi, p
pbar pi, p pbar Kbar0, in a factorization approach. These modes have rates of
order 10^{-6}. There are two mechanisms for the baryon pair production,
current-produced and transition. The behavior of decay spectra from these
baryon production mechanisms can be understood by using QCD counting rules.
Predictions on rates and decay spectra can be checked in the near future.Comment: 26 pages, 9 figures; version to appear in Phys. Rev.
An estimate of the flavour singlet contributions to the hyperfine splitting in charmonium
We explore the splitting between flavour singlet and non-singlet mesons in
charmonium. This has implications for the hyperfine splitting in charmonium
Strong coupling of excited heavy mesons
We compute the strong coupling constant , where () is the wave state, by QCD sum rules and by light-cone sum rules. The two methods give
compatible results in the limit , with a rather large value of
the coupling constant. We apply the results to the calculation of the hadronic
widths of the positive parity and states and to the chiral loop
contribution to the ratio .Comment: 31 pages, RevTeX, 4 figures appended as uuencoded fil
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
Direct Measurements of Absolute Branching Fractions for D0 and D+ Inclusive Semimuonic Decays
By analyzing about 33 data sample collected at and around 3.773
GeV with the BES-II detector at the BEPC collider, we directly measure the
branching fractions for the neutral and charged inclusive semimuonic decays
to be and , and determine the ratio of the two branching
fractions to be
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
QCD moment sum rules for Coulomb systems: the charm and bottom quark masses
In this work the charm and bottom quark masses are determined from QCD moment
sum rules for the charmonium and upsilon systems. To illustrate the special
character of these sum rules when applied to Coulomb systems we first set up
and study the behaviour of the sum rules in quantum mechanics. In our analysis
we include both the results from nonrelativistic QCD and perturbation theory at
next-next-to-leading order. The moments are evaluated at different values of
q^2 which correspond to different relative influence among the theoretical
contributions. In the numerical analysis we obtain the masses by choosing
central values for all input parameters. The error is estimated from a
variation of these parameters. First, the analysis is performed in the pole
mass scheme. Second, we employ the potential-subtracted mass in intermediate
steps of the calculation to then infer the quark masses in the MS-scheme. Our
final results for the pole- and MS-masses are: M_c = 1.75 \pm 0.15 GeV,
m_c(m_c) = 1.19 \pm 0.11 GeV, M_b = 4.98 \pm 0.125 GeV and m_b(m_b) = 4.24 \pm
0.10 GeV.Comment: 55 pages, 12 figures. References added, discussions extended. To
appear in Phys. Rev.
Search for jet extinction in the inclusive jet-pT spectrum from proton-proton collisions at s=8 TeV
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articles title, journal citation, and DOI.The first search at the LHC for the extinction of QCD jet production is presented, using data collected with the CMS detector corresponding to an integrated luminosity of 10.7ââfbâ1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The extinction model studied in this analysis is motivated by the search for signatures of strong gravity at the TeV scale (terascale gravity) and assumes the existence of string couplings in the strong-coupling limit. In this limit, the string model predicts the suppression of all high-transverse-momentum standard model processes, including jet production, beyond a certain energy scale. To test this prediction, the measured transverse-momentum spectrum is compared to the theoretical prediction of the standard model. No significant deficit of events is found at high transverse momentum. A 95% confidence level lower limit of 3.3 TeV is set on the extinction mass scale
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