Search results for "Amplitude"
showing 10 items of 1169 documents
Asymptotic properties of Born-improved amplitudes with gauge bosons in the final state
1999
For processes with gauge bosons in the final state we show how to continuously connect with a single Born-improved amplitude the resonant region, where resummation effects are important, with the asymptotic region far away from the resonance, where the amplitude must reduce to its tree-level form. While doing so all known field-theoretical constraints are respected, most notably gauge-invariance, unitarity and the equivalence theorem. The calculations presented are based on the process $f\bar{f}\to ZZ$, mediated by a possibly resonant Higgs boson; this process captures all the essential features, and can serve as a prototype for a variety of similar calculations. By virtue of massive cancel…
Matrix elements of (delta S=2) operators with Wilson fermions
2002
We test the recent proposal of using the Ward identities to compute the K0-K0bar mixing amplitude with Wilson fermions, without the problem of spurious lattice subtractions. From our simulations, we observe no difference between the results obtained with and without subtractions. In addition, from the standard study of the complete set of (delta S=2) operators, we quote the following (preliminary) results (in the MS(NDR) scheme): Bk(2 GeV)=0.70(10), < O7^{3/2}>_{K->pi pi} = 0.10(2)(1) GeV^3, < O8^{3/2}>_{K->pi pi} = 0.49(6)(0) GeV^3.
Bethe-Salpeter Approach for Meson-Meson Scattering in Chiral Perturbation Theory
1998
The Bethe-Salpeter equation restores exact elastic unitarity in the s- channel by summing up an infinite set of chiral loops. We use this equation to show how a chiral expansion can be undertaken by successive approximations to the potential which should be iterated. Renormalizability of the amplitudes in a broad sense can be achieved by allowing for an infinite set of counter-terms as it is the case in ordinary Chiral Perturbation Theory. Within this framework we calculate the $\pi \pi$ scattering amplitudes both for s- and p-waves at lowest order in the proposed expansion where a successful description of the low-lying resonances ($\sigma$ and $\rho$) and threshold parameters is obtained.…
Shape coexistence in neutron-deficient Hg isotopes studied via lifetime measurements inHg184,186and two-state mixing calculations
2014
The neutron-deficient mercury isotopes, $^{184,186}$Hg, were studied with the Recoil Distance Doppler Shift (RDDS) method using the Gammasphere array and the Koln Plunger device. The Differential Decay Curve Method (DDCM) was employed to determine the lifetimes of the yrast states in $^{184,186}$Hg. An improvement on previously measured values of yrast states up to $8^{+}$ is presented as well as first values for the $9_{3}$ state in $^{184}$Hg and $10^{+}$ state in $^{186}$Hg. $B(E2)$ values are calculated and compared to a two-state mixing model which utilizes the variable moment of inertia (VMI) model, allowing for extraction of spin-dependent mixing strengths and amplitudes.
Microscopic quasiparticle-phonon description of odd-mass127−133Xeisotopes and their β decay
1998
Quasiparticle-phonon equations of motion are solved starting from a microscopic realistic many-body Hamiltonian. In this microscopic quasiparticle-phonon model (MQPM) the relevant part of the three-quasiparticle Hilbert space may possibly be taken into account even in calculations using large single-particle bases. As an example, the MQPM is applied to the calculation of energy levels and Fermi and Gamow-Teller beta-decay transition amplitudes for transitions between odd-mass ${}^{127\ensuremath{-}133}\mathrm{Xe}$, ${}^{127\ensuremath{-}133}\mathrm{I}$, and ${}^{127\ensuremath{-}133}\mathrm{Cs}$ isotopes. Considering the fully microscopic nature of the MQPM, comparison of its results and da…
Fine structure in -decay and shape coexistence in
1999
Excited states in populated in the -decay of have been identified through -particle-conversion electron coincidences. The level scheme has been interpreted using a configuration mixing calculation, providing estimates of the mixing matrix elements, mixing amplitudes and the energies of unperturbed and unobserved levels.
Case in favor of theN*(1700)(3/2−)
2013
Using an interaction extracted from the local hidden-gauge Lagrangians, which brings together vector and pseudoscalar mesons, and the coupled channels rho N (s wave), pi N (d wave), pi Delta (s wave), and pi Delta (d wave), we look in the region ofv root s = 1400-1850 MeV and find two resonances dynamically generated by the interaction of these channels, which are naturally associated to N*(1520)(3/2(-)) and N*(1700)(3/2(-)). N*(1700)(3/2(-)) appears neatly as a pole in the complex plane. The free parameters of the theory are chosen to fit the pi N (d-wave) data. Both the real and imaginary parts of the pi N amplitude vanish in our approach in the vicinity of this resonance, which is simila…
a 0 (980)− f 0 (980) mixing in χ c1 → π 0 f 0 (980)→ π 0 π + π − and χ c1 → π 0 a 0 (980)→ π 0 π 0 η
2017
Abstract We study the isospin breaking in the reactions χ c 1 → π 0 π + π − and χ c 1 → π 0 π 0 η and its relation to the a 0 ( 980 ) − f 0 ( 980 ) mixing, which was measured by the BESIII Collaboration. We show that the same theoretical model previously developed to study the χ c 1 → η π + π − reaction (also measured by BESIII), and further explored in the predictions to the η c → η π + π − , can be successfully employed in the present study. We assume that the χ c 1 behaves as an S U ( 3 ) singlet to find the weight in which trios of pseudoscalars are created, followed by the final state interaction of pairs of mesons to describe how the a 0 ( 980 ) and f 0 ( 980 ) are dynamically generat…
Wave functions of composite hadron states and relationship to couplings of scattering amplitudes for general partial waves
2012
In this paper we present the connection between scattering amplitudes in momentum space and wave functions in coordinate space, generalizing previous work done for $s$-waves to any partial wave. The relationship to the wave function of the residues of the scattering amplitudes at the pole of bound states or resonances is investigated in detail. A sum rule obtained for the couplings provides a generalization to coupled channels, any partial wave and bound or resonance states, of Weinberg's compositeness condition, which was only valid for weakly bound states in one channel and $s$-wave. An example, requiring only experimental data, is shown for the $\ensuremath{\rho}$ meson indicating that i…
Meson exchange and isobar current effects in nuclear photon scattering
1980
Explicit expressions of meson exchange and isobar current contributions to the nuclear two-photon amplitude are derived in the non-relativistic limit. In connection with this amplitude the requirement of gauge invariance on the photon scattering amplitude and on the nuclear electromagnetic interaction operator is discussed in detail.