Search results for "Functional analysis"
showing 10 items of 1059 documents
Shell model and octupole states in148Gd from in-beam experiments
1990
Through (α, 4n) and (τ, 3n) reactions the high-spin states in the two-neutron nucleus148Gd were populated up toI π=21− at 7.2 MeV, including numerous states above the yrast line. The148Gd energy spectrum is interpreted in terms of the spherical shell model. Identification of the (νf 7/2 i 1 3/2)10− state gives the νi 13/2 single particle energy free of octupole admixtures as 2.1(1) MeV. Eight high-spin states between 1.2 and 3.7 MeV were identified as the couplings of the two valence-particles to the146Gd octupole phonon, and three above-lying levels are assigned as double-octupole excitations including a 12+ state which decays by anE3-E3 stretched cascade. All these octupole levels can be …
Eta bound states in nuclei
2002
The energies and widths of bound states of the $\eta$ meson in different nuclei are obtained using the results for its selfenergy in a nuclear medium, which is evaluated in a selfconsistent manner using techniques of unitarized chiral perturbation theory. We find bound states in all studied nuclei (from $^{12}{C}$ on) and the half widths obtained are larger than the separation of the levels, what makes the experimental observation of peaks unlikely. We have paid a special attention to the region of nuclei where only the $1s$ state appears and the binding energies are of the order of magnitude of the half width, which would magnify the chances that some broad peak could be observed. This is …
Radiative production of the Λ(1405) resonance in K− collisions on protons and nuclei
1999
We have carried a theoretical study of the K^- p\to M B \gamma reaction with M B = K^-p, \bar{K}^0 n, \pi^- \Sigma^+, \pi^+ \Sigma^-, \pi^0 \Sigma^0, \pi^0 \Lambda, for K^- lab. momenta between 200 and 500 MeV/c, using a chiral unitary approach for the strong K^-p interaction with its coupled channels. The \Lambda(1405) resonance, which is generated dynamically in this approach, shows up clearly in the d\sigma/dM_I spectrum, providing new tests for chiral symmetry and the unitary approach, as well as information regarding the nature of the resonance. The photon detection alone, summing all channels, is shown to reproduce quite accurately the strength and shape of the \Lambda(1405) resonance…
Final State Interaction Effects in 3He(e ,e'p)
2003
Abstract Asymmetries in quasi-elastic 3 He ( e → , e ′ p ) have been measured at a momentum transfer of 0.67 (GeV/ c ) 2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3 He -ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.
Chromomagnetic dipole-operator corrections inB¯→XsγatO(β0αs2)
2010
We calculate the fermionic corrections to the photon-energy spectrum of $\overline{B}\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ which arise from the self-interference of the chromomagnetic dipole operator ${Q}_{8}$ at next-to-next-to-leading order by applying naive non-Abelianization. The resulting $\mathcal{O}({\ensuremath{\beta}}_{0}{\ensuremath{\alpha}}_{s}^{2})$ correction to the $\overline{B}\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ branching ratio amounts to a relative shift of $+0.12%$ ($+0.27%$) for a photon-energy cut of 1.6 GeV (1.0 GeV). We also comment on the potential size of resummation and nonperturbative effects related to ${Q}_{8}$.
Dependence of lepton pair emission on EoS and initial state
1998
We present results from a hydrodynamic calculation for thermal emission of lepton pairs in central lead-lead collisions at the CERN SPS energy. Dependence of the emission on the initial conditions and Equation of State (EoS) is considered and the spectra are compared with CERES data and calculated distribution of Drell--Yan pairs.
NUCLEAR-STRUCTURE EFFECTS ON DOUBLE BETA DECAYS TO 0+ STATES IN 76Ge
2011
Neutrinoless double beta (0νββ) decay of 76 Ge to the ground state and first excited 0+ state in 76 Se is discussed in terms of the associated nuclear matrix elements. The effects arizing from the size of the single-particle model space and the occupancies of the individual orbits are discussed in the framework of the (higher) quasiparticle random-phase approximation with effective, G -matrix-derived nuclear forces. It is found that the orbital occupancies play a role for the size of the nuclear matrix element. Contrary to the ground-state transition the transition to the first excited 0+ state does not depend sensitively on the size of the model space.
X(2175)as a resonant state of theϕKK¯system
2008
We perform a Faddeev calculation for the three-meson system $\ensuremath{\phi}K\overline{K}$, taking the interaction between two pseudoscalar mesons and between a vector and a pseudoscalar meson from the chiral unitary approach. We obtain a neat resonance peak around a total mass of 2150 MeV and an invariant mass for the $K\overline{K}$ system around 970 MeV, very close to the ${f}_{0}(980)$ mass. The state appears in $I=0$ and qualifies as a $\ensuremath{\phi}{f}_{0}(980)$ resonance. We enlarge the space of states including $\ensuremath{\phi}\ensuremath{\pi}\ensuremath{\pi}$, since $\ensuremath{\pi}\ensuremath{\pi}$ and $K\overline{K}$ build up the ${f}_{0}(980)$, and find moderate changes…
The N*(1710) as a resonance in the ππN system
2008
We study the $\pi \pi N$ system by solving the Faddeev equations, for which the input two-body $t$-matrices are obtained by solving the Bethe-Salpeter equation in the coupled channel formalism. The potentials for the $\pi \pi$, $\pi N$ sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the $\pi\pi N$ system with a mass of $1704 - i 375/2$ MeV and with quantum numbers $I=1/2$, $J^\pi =1/2^+$. We identify this state with the $N^*(1710)$. This peak is found where the energies of the $\pi \pi$ sub-system fall in the region of the $\sigma$ resonance. We d…
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…