Improved bounds on the radius and curvature of the K$ \pi$ scalar form factor and implications to low-energy theorems

We obtain stringent bounds in the 〈r ² -c plane where these are the scalar radius and the curvature parameters of the scalar K form factor, respectively, using analyticity and dispersion relation constraints, the knowledge of the form factor from the well-known Callan-Treiman point , as well as at , which we call the second Callan-Treiman point. The central values of these parameters from a recent determination are accomodated in the allowed region provided the higher loop corrections to the value of the form factor at the second Callan-Treiman point reduce the one-loop result by about 3% with . Such a variation in magnitude at the second Callan-Treiman point yields 0.12 fm² 〈r ² 0.21 fm²and 0.56 GeV^-4 c 1.47 GeV^-4and a strong correlation between them. A smaller value of shifts both bounds to lower values.     

Electromagnetic form factors of the $\Delta(1232)$ excitation

In the resonance region we have precisely determined the electromagnetic properties of the -resonance, in particular the E2/M1 ratio . For pion electroproduction recent experimental data from Mainz, Bates, Bonn and JLab for Q² up to 4.0 (GeV/c)² have been analyzed with the isobar model MAID. The extracted E2/M1 ratio shows, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and becomes positive with increasing Q². This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as . At high Q², the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached. The electromagnetic-transition form factors of the excitation are parameterized and fitted to the electroproduction data. This also shows a zero-crossing of the electric form factor G_E^* at (GeV/c)².Received: 1 November 2002, Published online: 15 July 2003PACS:   13.40.Gp Electromagnetic form factors - 13.60.Le Meson production - 14.20.Gk Baryon resonances with S=0 - 25.20.Lj Photoproduction reactions     

Partial wave analysis of $\bar pp \to \bar \Lambda \Lambda$

A partial wave analysis of PS185 data for is presented. A ³ S ₁ cusp is identified in the inverse process at threshold, using detailed balance to deduce cross sections from . Partial wave amplitudes for ³ P ₀, ³ F ₃, ³ D ₃ and ³ G ₃ exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the data then provide evidence for a new I = 0, J ^PC = 1^- resonance with mass MeV, MeV, coupling to both ³ S ₁ and ³ D ₁.Received: 4 June 2004, Published online: 9 July 2004     

Anomalous $\eta/\eta^\prime$ decays: the triangle and box anomalies

We examine the decay modes within the context of the hidden local symmetry (HLS) model. Using numerical information derived in previous fits to the and Ve ⁺ e ^- decay modes in isolation and the lineshape determined in a previous fit to the pion form factor, we show that all aspects of these decays can be predicted with fair accuracy. Freeing some parameters does not improve the picture. This is interpreted as strong evidence in favor of the box anomaly in the decays, which occurs at precisely the level expected. We also construct the set of equations defining the amplitudes for and at the chiral limit, as predicted from the anomalous HLS Lagrangian appropriately broken. This provides a set of four equations depending on only one parameter, instead of three for the traditional set. This is also shown to match the (two-angle, two-decay-constant) - mixing scheme recently proposed and is also fairly well fulfilled by the data. The information returned from the fits also matches expectations from previously published fits to the decay modes in isolation.Received: 29 June 2003, Revised: 17 September 2003, Published online: 4 November 2003     

Dilepton-tagged $Q\overline{Q}+\mathrm{jet}$ events at the LHC

We propose a new method for identifying and isolating events through semileptonic decays of the pair. Employing these decay dileptons to tag the jet in a specific kinematic region provides a clean signature of jets associated with heavy-quark production. The measurement, in both pp and heavy-ion collisions, is essential for addressing heavy-quark fragmentation in vacuum and in a dense medium. We present next-to-leading order calculations of production (leading order in production) in TeV pp collisions at the LHC and discuss the feasibility of the measurement in heavy-ion collisions at TeV.     

Intermediate energy elastic scattering of protons on 24Mg in the $ \alpha$ -cluster model with dispersion

The -cluster model with dispersion has been developed for the case of the ²⁴Mg nucleus. The ²⁴Mg nucleus is considered as composed of the core ( ¹⁶O nucleus) and two -clusters that form a dumbbell configuration and are arranged with the most probability inside the core. In the calculations the -cluster structure of the core has been taken into account. On the basis of the multiple diffraction scattering theory the differential cross-section and the polarization observables for the elastic p - ²⁴Mg scattering at 800 and 250MeV have been calculated. The results obtained are in agreement with the existing experimental data.     

K-forbidden allowed $ \beta$ transitions in heavy nuclei

The role of the band quantum number K in influencing the character of allowed transitions in heavy deformed nuclei is examined. The conditions for the occurrence of K -forbidden decays in this region are explored. Specific cases of “allowed” decays proceeding via K = 2 to K = 6 channels are presented to illustrate the phenomenon. The listed K = 2 transitions, which by themselves contribute over 10% of all the presently known allowed transitions for A 228 nuclei, are seen to have an average , which is clearly outside the normal range for allowed transitions. It is concluded that, wherever the -connected states can be confidently labelled using the quantum numbers, the K -forbiddenness is in general as significant as that involving the other two (spin and parity) quantum numbers.     

$\overline pp$ annihilation into four charged pions at rest and in flight

The spin-parity analysis of the data on the annihilation reaction at rest in liquid and in gaseous hydrogen at 3 bar pressure and in flight at momentum of MeV/c, collected by the Obelix spectrometer at the LEAR complex of CERN, is presented. The relative branching ratios and are obtained. It is also shown that the inclusion of the exotic meson , J^PC = 1^{- +} , mass and width , GeV/c², in its decay to , improves the fit and some implications of these results are briefly discussed. The relative S and P-wave annihilation percentages in four charged pions at two target densities are obtained.Received: 2 December 2003, Published online: 23 April 2004     

Intermediate-energy proton- 20Ne elastic scattering in the $ \alpha$ + 16O model of 20Ne

The ground state of ²⁰Ne is described as the clustering structure of + ¹⁶ O . The cluster wave function with an analytical and simple form is presented. Based on this model, the intermediate-energy proton- ²⁰Ne elastic scattering is calculated and compared with the experimental data.     

Leptoproduction of $\varrho$ mesons within Regge approach

A model describing the leptoproduction of mesons is considered. For the amplitude of the photon dissociation into a pair, the light-cone wave function is used. Scattering of the colorless pair off the nucleon is computed within reggeon exchange phenomenology. The transition of the scattered quark and antiquark into the final meson is treated with the aid of the parton-hadron duality concept. Numerical calculations of and r⁰⁴₀₀ describe the world data at Q² < 4 GeV² rather reasonably. The calculations of the meson spin density matrix show that the computed matrix elements except r⁰⁴₀₀ are in good agreement with the available experimental data at Q² up to 8 GeV² and the total mass of the system greater than 4 GeV. The Regge phenomenology predictions at the highest experimentally available energies agree with both the HERA data and calculations performed within the perturbative QCD approach even for very high Q² ( -20 GeV²). The predicted scale of the S-channel helicity non-conservation is in reasonable agreement with the experimental data.Received: 18 September 2003, Revised: 17 December 2003, Published online: 13 February 2004     

The $\eta_{c}(2980)$ formation in two-photon collisions at LEP energies

production in interactions has been detected via its decays into ,K ⁺ K ^- K ⁺ K ^- and in the data taken with the DELPHI detector at LEP1 and LEP2 energies. The two-photon radiative width averaged over all observed decay channels is = 13.9 2.0 (stat.) 1.4(syst.) 2.7 (BR) keV. No direct decay channel has been observed. An upper limit < 5.5 keV at 95% confidence level has been evaluated for this decay mode.Received: 3 July 2003, Published online: 7 November 2003     

Effect of top quark spin on the unparticle couplings in $\gamma\gamma \to t\bar{t}$

We investigate the potential of γ γ collisions to probe scalar unparticle couplings via top–antitop quark pair production. We find 95% confidence level limits on the unparticle couplings with an integrated luminosity of 500 fb⁻¹ and an energy of  TeV. We investigate the effect of the top quark spin polarization on the unparticle couplings. It is shown that spin polarization of the top quark leads to a significant improvement in the sensitivity limits.     

Molecular dynamics in nanophase-separated comb-like poly( $ \upalpha$- n-alkyl $ \upbeta$-L-aspartate)s

A series of poly( -n-alkyl -L-aspartates) which are nanophase self-assembled comb-like polymers has been studied by dielectric spectroscopy in a broad frequency range ( 10^-23×10⁶ Hz), with n-alkyls side chains of various lengths, 10n18. In every member of the series the same relaxations were identified after the decomposition of the experimental isothermal trace in up to three peaks with relaxation times distributions. The strength, width and average relaxation time for all the relaxation modes were determined for each material. Besides the local low temperature, Arrhenius modes, two relaxation modes, and , present a cooperative character whose dynamics are not affected by the side chains melting. The relaxation is a polyethylene-like glass transition of the amorphous side chains and its dynamics is strongly dependent on the n value due to the increasing restrictions imposed by the self-assembled confinement. The strength of the relaxation mode increases as the lateral chains loose their 2D order. The restricted chopstick motion of the rigid rods is thought to be the origin of the mode; this motion is hindered at temperatures where the cage size decreases as a result of the increasing disorder with temperature.     

Towards a model-independent determination of the $\phi\to \gamma f_0$ coupling

A guide to the composition of the enigmatic f ₀(980) and a ₀(980) states is their formation in -radiative decays. Precision data are becoming available from the KLOE experiment at the DA NE machine at Frascati, as well as results from SND and CMD-2 at VEPP-2M at Novosibirsk. We show how the coupling of the f ₀(980) to this channel can be extracted from these, independently of the background provided by production. To do this we use the fact that the behaviour of both the f ₀(980) and cannot be determined by these data alone, but is strongly constrained by experimental results from other hadronic processes as required by unitarity. We find that the resulting coupling for the is GeV with a background that is quite unlike that assumed if unitarity is neglected. This provides an object lesson in how unitarity teaches us to add resonances. Not surprisingly the result is crucially dependent on the pole position of the f ₀(980), for which there are still sizeable uncertainties. At present this leads to an uncertainty in the branching ratio which can only be fixed by further precision data on the f ₀(980). Nevertheless, the is now the same order of magnitude as the experimental .Received: 25 March 2003, Published online: 5 September 2003     

Polarisation in sfermion decays: determining $\tan\beta$ and trilinear couplings

The basic parameters of supersymmetric theories can be determined at future e ⁺ e ^- linear colliders with high precision. We investigate in this report how polarisation measurements in and or decays to leptons and t quarks plus neutralinos or charginos can be used to measure (in particular for large values) and to determine the trilinear couplings , A _t and A _b in sfermion pair production.Received: 17 April 2003, Revised: 3 July 2003, Published online: 29 August 2003     

ZZ production in e+ e- int eractions at $\sqrt{s} =$ 183-209 G eV

Measurements of on-shell ZZ production are described, using data from the DELPHI experiment at LEP in e ⁺ e ^- collisions at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 665 pb^-1. Results obtained in each of the final states , , , , , l ⁺ l ^- l ⁺ l ^-, and (with ) are presented. The measured production cross-sections are consistent with the Standard Model expectations. These results update and supersede those already published at 183 and 189 GeV.Received: 3 March 2002, Revised: 28 May 2003, Published online: 19 September 2003     

Forward $\pi^\circ$ production and associated transverse energy flow in deep-inelastic scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to which give rise to high transverse momentum -mesons are studied with the H1 experiment at HERA. The inclusive cross section for -mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the and of the four-momentum transfer Q ² and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward -meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Received: 8 April 2004, Revised: 7 July 2004, Published online: 30 July 2004Dedicated to the memory of Krzysztof Rybicki     

CP asymmetry in $B \rightarrow \phi K_{S}$ in a general two-Higgs-doublet model with fourth-generation quarks

We discuss the time-dependent CP asymmetry of the decay in an extension of the standard model with both a two Higgs doublet and additional fourth-generation quarks. We show that, although the standard model with a two Higgs doublet and the standard model with fourth-generation quarks alone are not likely to largely change the effective from the decay , the model with both an additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor-changing Yukawa interactions between neutral Higgs bosons and the heavy fourth-generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from processes such as and , this model can lead to an effective as large as - 0.4 in the CP asymmetry of .Received: 25 March 2004, Revised: 20 April 2004, Published online: 18 June 2004     

Photoproduction of $ \eta$ -mesons off neutrons from a deuteron target

A formalism is developed for the partial-wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of and mesons. Different interpretations of a dip-bump structure of the photoproduction cross-section in the 1670MeV region are presented and discussed. Helicity amplitudes for two low-mass S₁₁ states are determined.