Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLambda beta-decay in-medium
50
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Under the working hypothesis that the structure of a bound hadron is modified by its interactions with other hadrons, one may expect to see changes in carefully chosen observables. In the light of a recent proposal to measure the axial charge in the strangeness changing beta-decay of a bound Lambda hyperon, we examine the size of the change expected within the quark-meson coupling model. It is predicted to be significant.
rate research
Read More
We discuss a novel effect in neutrinoless double beta (0{ u}{beta}{beta}) decay related with the fact that its underlying mechanisms take place in the nuclear matter environment. We study the neutrino exchange mechanism and demonstrate the possible impact of nuclear medium via Lepton Number Violating (LNV) 4-fermion interactions of neutrino with quarks from decaying nucleus. The net effect of these interactions is generation of an effective in-medium Majorana neutrino mass matrix. The enhanced rate of the 0{ u}{beta}{beta}-decay can lead to the apparent incompatibility of observations of the 0{ u}{beta}{beta}-decay with the value of the neutrino mass determined or restricted by the {beta}-decay and cosmological data. The effective neutrino masses and mixing are calculated for the complete set of the relevant 4-fermion neutrino-quark operators. Using experimental data on the 0{ u}{beta}{beta}-decay in combination with the {beta}-decay and cosmological data we evaluate the characteristic scales of the LNV operators: {Lambda} > 2.4 TeV.
The sensitivity of polarisation-asymmetry correlation experiments to charged currents of right-handed chirality contributing to allowed $beta$-decay is considered in the most general context possible, independently of any type of approximation nor of any specific model for physics beyond the Standard Model of the electroweak interactions. Results are then particularised to general Left-Right Symmetric Models, and experimental prospects offered by mirror nuclei are assessed explicitly on general grounds. In order of decreasing interest, the cases of $^{17}$F, $^{41}$Sc and $^{25}$Al are the most attractive, providing sensitivities better or comparable to allowed pure Gamow-Teller transitions, with the advantage however, that recoil order corrections are smaller in the case of super-allowed decays.
We analyze neutrinoless double beta decay ($0 ubetabeta$) within the framework of the Standard Model Effective Field Theory. Apart from the dimension-five Weinberg operator, the first contributions appear at dimension seven. We classify the operators and evolve them to the electroweak scale, where we match them to effective dimension-six, -seven, and -nine operators. In the next step, after renormalization group evolution to the QCD scale, we construct the chiral Lagrangian arising from these operators. We develop a power-counting scheme and derive the two-nucleon $0 ubetabeta$ currents up to leading order in the power counting for each lepton-number-violating operator. We argue that the leading-order contribution to the decay rate depends on a relatively small number of nuclear matrix elements. We test our power counting by comparing nuclear matrix elements obtained by various methods and by different groups. We find that the power counting works well for nuclear matrix elements calculated from a specific method, while, as in the case of light Majorana neutrino exchange, the overall magnitude of the matrix elements can differ by factors of two to three between methods. We calculate the constraints that can be set on dimension-seven lepton-number-violating operators from $0 ubetabeta$ experiments and study the interplay between dimension-five and -seven operators, discussing how dimension-seven contributions affect the interpretation of $0 ubetabeta$ in terms of the effective Majorana mass $m_{beta beta}$.
Neutrinoless double beta decay, which is a very old and yet elusive process, is reviewed. Its observation will signal that lepton number is not conserved and the neutrinos are Majorana particles. More importantly it is our best hope for determining the absolute neutrino mass scale at the level of a few tens of meV. To achieve the last goal certain hurdles have to be overcome involving particle, nuclear and experimental physics. Nuclear physics is important for extracting the useful information from the data. One must accurately evaluate the relevant nuclear matrix elements, a formidable task. To this end, we review the sophisticated nuclear structure approaches recently been developed, which give confidence that the needed nuclear matrix elements can be reliably calculated. From an experimental point of view it is challenging, since the life times are long and one has to fight against formidable backgrounds. If a signal is found, it will be a tremendous accomplishment. Then, of course, the real task is going to be the extraction of the neutrino mass from the observations. This is not trivial, since current particle models predict the presence of many mechanisms other than the neutrino mass, which may contribute or even dominate this process. We will, in particular, consider the following processes: (i)The neutrino induced, but neutrino mass independent contribution. (ii)Heavy left and/or right handed neutrino mass contributions. (iii)Intermediate scalars (doubly charged etc). (iv)Supersymmetric (SUSY) contributions. We will show that it is possible to disentangle the various mechanisms and unambiguously extract the important neutrino mass scale, if all the signatures of the reaction are searched in a sufficient number of nuclear isotopes.
We elaborate on the dichotomy between the description of the semileptonic decays of heavy hadrons on the one hand and the semileptonic decays of light hadrons such as neutron $beta$ decays on the other hand. For example, almost without exception the semileptonic decays of heavy baryons are described in cascade fashion as a sequence of two two-body decays $B_1 to B_2 + W_{rm off-shell}$ and $W_{rm off-shell} to ell + u_ell$ whereas neutron $beta$ decays are analyzed as true three-body decays $n to p + e^- +bar u_e$. Within the cascade approach it is possible to define a set of seven angular observables for polarized neutron $beta$ decays as well as the longitudinal, transverse and normal polarization of the decay electron. We determine the dependence of the observables on the usual vector and axial vector form factors. In order to be able to assess the importance of recoil corrections we expand the rate and the $q^2$ averages of the observables up to NLO and NNLO in the recoil parameter $delta=(M_n-M_p)/(M_n+M_p)= 0.689cdot 10^{-3}$. Remarkably, we find that the rate and three of the four parity conserving polarization observables that we analyze are protected from NLO recoil corrections when the second class current contributions are set to zero.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
