Square spirals, dimensionality and biopolymers

AbstractThis paper illustrates the diversity and esthetic beauty of the spatial patterns produced by a class of heuristic procedures describable by a one-parameter algorithm. While the patterns may provide insight into the structures of biopolymers and other macromolecules, the main focus of this work is the demonstration of how two-dimensional order may arise from one-dimensional processes

A Dispersive Analysis on the f0(600)f_0(600) and f0(980)f_0(980) Resonances in γγ→π+π−,π0π0\gamma\gamma\to\pi^+\pi^-, \pi^0\pi^0 Processes

We estimate the di-photon coupling of $f_0(600)$, $f_0(980)$ and $f_2(1270)$ resonances in a coupled channel dispersive approach. The $f_0(600)$ di-photon coupling is also reinvestigated using a single channel $T$ matrix for $\pi\pi$ scattering with better analyticity property, and it is found to be significantly smaller than that of a $\bar qq$ state. Especially we also estimate the di-photon coupling of the third sheet pole located near $\bar KK$ threshold, denoted as $f_0^{III}(980)$. It is argued that this third sheet pole may be originated from a coupled channel Breit-Wigner description of the $f_0(980)$ resonance.Comment: 24 pages and 13 eps figures. A nuerical bug in previous version is fixed. Some results changed. References and new figures added. Version to appear in Phys. Rev.

Lightest scalar and tensor resonances in γγ→ππ\gamma\gamma\to\pi\pi after the Belle experiment

New high statistics Belle data on the $\gamma\gamma\to\pi^+\pi^-$ reaction cross section measured in the range of pion-pair invariant masses $\sqrt{s}$ between 0.8 GeV and 1.5 GeV are analyzed to clarify the current situation around the $\sigma(600)$, $f_0(980)$, and $f_2(1270)$ resonances in $\gamma\gamma$ collisions. The present analysis shows that the direct coupling constants of the $\sigma(600)$ and $f_0(980)$ resonances to $\gamma\gamma$ are small, and the $\sigma(600)\to\gamma\gamma$ and $f_0(980)\to\gamma\gamma$ decays are four-quark transitions caused by the $\pi^+\pi^-$ and $K^+K^-$ loop mechanisms, respectively. The chiral shielding of the $\sigma(600)$ resonance takes place in the reactions $\gamma\gamma\to\pi\pi$ as well as in $\pi\pi$ scattering. Some results of a simultaneous description of the $\gamma\gamma\to\pi^+\pi^-$ and $\gamma\gamma\to\pi^0\pi^0$ Belle data are also presented. In particular, the following tentative estimate of the $f_2(1270)\to\gamma\gamma$ decay width is obtained: $\Gamma_{f_2\to\gamma\gamma}(m^2_{f_2})\approx 3.68$ keV.Comment: 14 pages, 5 figures. Fitted for the publication in Physical Review

Limits on axion and light Higgs boson production in Y(1S) decays

We have searched for axion and light Higgs boson production in the channel Y(1S) → (a0 or h0)+gamma, where the non-interacting axion a0 and the Higgs boson h0 do not decay in the detector. We find no evidence for an axion and give an upper limit, Br(Y(1S) -> a0 gamma) <4.0x10(-5) (90% CL), for long-lived axions. Combining our limit with the previous search in J/Psi decays, we are able to rule out the axion in the standard model with first order QCD corrections. Our Y(1S) data also rule out a Higgs boson with mass m<86 MeV

Exclusive channels in γγ\gamma\gamma reactions: light at the end of the tunnel?

The physics that can be learnt by studying exclusive channels in two photon interactions is recalled. This serves as an introduction to the Exclusive Reaction session of Photon'99.Comment: 9 pages,8 figures. Invited introductory talk at Photon'99, Freiburg im Br., Germany, May 199

Master Formulae Approach to Photon Fusion Reactions

We analyze the $\gamma\gamma\to \pi\pi, KK, \eta\eta, \pi\eta$ reactions through $\sqrt{s}=2$ GeV, using the master formula approach to QCD with three flavors. In this approach, the constraints of broken chiral symmetry, unitarity and crossing symmetry are manifest in all channels. The pertinent vacuum correlators are analyzed at tree level using straightforward resonance saturation methods. A one-loop chiral power counting analysis at treshold is also carried out and compared to standard chiral perturbation theory. Our results are in overall agreement with the existing data in all channels. We predict the strange meson polarizabilities and a very small cross section for $\gamma\gamma\to\eta\eta$.Comment: 19 pages LaTeX, 7 figure

Status and Prospects of Top-Quark Physics

The top quark is the heaviest elementary particle observed to date. Its large mass of about 173 GeV/c^2 makes the top quark act differently than other elementary fermions, as it decays before it hadronises, passing its spin information on to its decay products. In addition, the top quark plays an important role in higher-order loop corrections to standard model processes, which makes the top quark mass a crucial parameter for precision tests of the electroweak theory. The top quark is also a powerful probe for new phenomena beyond the standard model. During the time of discovery at the Tevatron in 1995 only a few properties of the top quark could be measured. In recent years, since the start of Tevatron Run II, the field of top-quark physics has changed and entered a precision era. This report summarises the latest measurements and studies of top-quark properties and gives prospects for future measurements at the Large Hadron Collider (LHC).Comment: 76 pages, 35 figures, submitted to Progress in Particle and Nuclear Physic

Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA

Inclusive photoproduction of D*+- mesons has been measured for photon-proton centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of 37 pb^-1. Total and differential cross sections as functions of the D* transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading order (NLO) perturbative QCD calculations using the "massive charm" and "massless charm" schemes. The measured cross sections are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured results in a kinematic region where the resolved photon contribution is significant.Comment: 32 pages including 6 figure

Angular and Current-Target Correlations in Deep Inelastic Scattering at HERA

Correlations between charged particles in deep inelastic ep scattering have been studied in the Breit frame with the ZEUS detector at HERA using an integrated luminosity of 6.4 pb-1. Short-range correlations are analysed in terms of the angular separation between current-region particles within a cone centred around the virtual photon axis. Long-range correlations between the current and target regions have also been measured. The data support predictions for the scaling behaviour of the angular correlations at high Q2 and for anti-correlations between the current and target regions over a large range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations and Monte Carlo models correctly describe the trends of the data at high Q2, but show quantitative discrepancies. The data show differences between the correlations in deep inelastic scattering and e+e- annihilation.Comment: 26 pages including 10 figures (submitted to Eur. J. Phys. C

Plastisol Foaming Process. Decomposition of the Foaming Agent, Polymer Behavior in the Corresponding Temperature Range and Resulting Foam Properties

The decomposition of azodicarbonamide, used as foaming agent in PVC - plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min-1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g -1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol-1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse