Search results for "Matrix"
showing 10 items of 3205 documents
New information on β-delayed neutron emission from Be-12, Be-14
1999
17 pages, 3 tables, 5 figures, 1 appendix.-- PACS nrs.: 23.40.Hc; 27.20.+n.
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.
Testing refined shell-model interactions in thesdshell: Coulomb excitation ofNa26
2015
Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal $sd$ interaction (USD) describing nuclei within the $sd$ shell yielded two new interactions---USDA and USDB---causing changes in the theoretical description of these nuclei.Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus $^{26}\mathrm{Na}$ with 7 valence neutrons and 3 valence protons outside the doubly-magic ${}^{16}\mathrm{O}$ core is used a…
Precision measurements of B(D+→μ+νμ), the pseudoscalar decay constant fD+, and the quark mixing matrix element |Vcd|
2014
We report a measurement of the branching fraction B(D+ -> mu(+)nu(mu)) = [3.71 +/- 0.19(stat) +/- 0.06(sys)] x 10(-4) based on 2.92 fb(-1) of data accumulated at root s = 3.773 GeV with the BESIII detector at the BEPCII collider. This measurement, in conjunction with the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cd vertical bar determined from a global Standard Model fit, implies a value for the weak decay constant f(D+) = (203.2 +/- 5.3 +/- 1.8) MeV. Additionally, using this branching fraction measurement together with a lattice QCD prediction for f(D+), we find vertical bar V-cd vertical bar 0.2210 +/- 0.0058 +/- 0.0047. In either case, these are the most precise results for…
General Multipole Expansion of Polarization Observables in Deuteron Electrodisintegration
2002
Formal expressions are derived for the multipole expansion of the structure functions of a general polarization observable of exclusive electrodisintegration of the deuteron using a longitudinally polarized beam and/or an oriented target. This allows one to exhibit explicitly the angular dependence of the structure functions by expanding them in terms of the small rotation matrices $d^j_{m'm}(\theta)$, whose coefficients are given in terms of the electromagnetic multipole matrix elements. Furthermore, explicit expressions for the coefficients of the angular distributions of the differential cross section including multipoles up to $L_{max}=3$ are listed in tabular form.
The Axial Charge Renormalization in a Relativistic Description of Finite Nuclei
1994
Starting from a realistic One-Boson-Exchange model of the nucleon nucleon interaction the relativistic mean field for nucleons is determined within the Dirac Brueckner Hartree Fock approach for finite nuclei. The matrix elements of the axial charge operator evaluated for the solutions of the Dirac equation with this selfenergy are investigated. These matrix elements are enhanced with respect to the equivalent non relativistic ones obtained from the solutions of the Schr\"odinger equation with the non relativistic equivalent potential. The present results confirm at a qualitative level the results for the axial charge renormalization obtained with perturbative approaches. However, the result…
Short-range correlations and neutrinoless double beta decay
2007
In this work we report on the effects of short-range correlations upon the matrix elements of neutrinoless double beta decay. We focus on the calculation of the matrix elements of the neutrino-mass mode of neutrinoless double beta decays of 48Ca and 76Ge. The nuclear-structure components of the calculation, that is the participant nuclear wave functions, have been calculated in the shell-model scheme for 48Ca and in the proton-neutron quasiparticle random-phase approximation (pnQRPA) scheme for 76Ge. We compare the traditional approach of using the Jastrow correlation function with the more complete scheme of the unitary correlation operator method (UCOM). Our results indicate that the Jast…
Relativistic two-body processes in axial-charge transitions
1995
We study the contribution of two-body meson-exchange processes to axial charge transitions for nuclei in the lead, tin and oxygen regions. We conduct calculations in the Dirac-Hartree (the Walecka model) and the relativistic Hartree (where the full one-nucleon-loop effects are included) approximations. We present results indicating that one- and two-body processes enhance the matrix elements of the axial-charge operator by some (100+-20)% in all three regions studied. This agrees well with the fit of eighteen first-forbidden beta-decay transitions conducted by Warburton in the lead region. We also discuss some sensitivities present in the calculation.
Reparametrization invariance ofBdecay amplitudes and implications for new physics searches inBdecays
2005
When studying $B$ decays within the standard model (SM), it is customary to use the unitarity of the CKM matrix in order to write the decay amplitudes in terms of only two of the three weak phases which appear in the various diagrams. Occasionally, it is mentioned that those two weak phases can be used in order to describe any decay amplitude, even beyond the standard model. Here we point out that, when describing a generic decay amplitude, the two weak phases can be chosen completely at will, and we study the behavior of the decay amplitudes under changes in the two weak phases chosen as a basis. Of course, physical observables cannot depend on such reparametrizations. This has an impact o…
Measurements of theB→D*form factors using the decayB¯0→D*+e−ν¯e
2006
We measure the dependence of (B) over bar (0)-> D(*+)e(-)(B) over bar (e) on the decay angles and momentum transfer. The data sample consists of similar to 86x10(6) B (B) over bar -pairs accumulated on the Upsilon(4S) resonance by the BABAR detector at the asymmetric e(+)e(-) collider PEP-II. We specify the three form factors by two ratios R-1 and R-2, and by a single parameter rho(2) characterizing the polynomial representing h(A1), the function which describes the momentum-transfer dependence of the form factor A(1). We determine R-1, R-2, and rho(2) using an unbinned maximum likelihood fit to the full decay distribution. The results are R-1=1.396 +/- 0.060 +/- 0.035 +/- 0.027, R-2=0.885 …