Nonconserving Decay Research Articles

Main results and perspectives on other rare processes with DAMA experiments

Development of low radioactive technique allows to investigate many other rare nuclear and subnuclear processes: double [Formula: see text] decay, rare [Formula: see text] and [Formula: see text] decays, and to search for hypothetical particles and processes like axions, charge nonconserving decays, the nucleon, di-nucleon and tri-nucleon decays into invisible channels, to test the Pauli principle. Here, we present results of the rare processes searches and development of instrumentation for low counting experiments.

KK-number non-conserving decays: Signal of [formula omitted] excitations of extra-dimensional models at the LHC

In the simplest universal extra-dimensional models Kaluza–Klein (KK) parity distinguishes the states with odd and even KK-number. We calculate the coupling of a 2n-level top quark to a top quark and the Higgs scalar (both n=0 states), absent at the tree level, which is mediated by strong interactions at one-loop. We show that the strength of this coupling is independent of n. We observe that the decay due to this coupling, which conserves KK-parity, can be a few per cent of the phase space suppressed decay to two n-level states which proceeds through tree-level couplings. We explore the prospects of verification of this result at the Large Hadron Collider through the production of a second-level KK top–antitop pair both of which subsequently decay to a zero mode top quark/antiquark and a Higgs boson.

New Limit for the Lepton-Family-Number Nonconserving Decayμ+→e+γ

An experiment has been performed to search for the muon- and electron-number nonconserving decay μ+→e+γ. The upper limit for the branching ratio is found to be Γ(μ+→e+γ)/ Γ(μ+→e+νν¯)<1.2×10−11 with 90% confidence.Received 10 May 1999DOI:https://doi.org/10.1103/PhysRevLett.83.1521©1999 American Physical Society

The neutron yesterday, today, and tomorrow

The current status of the study of the fundamental properties of the neutron is discussed. Experimental results on the neutron lifetime, β-decay angular correlations, electric dipole moment, and form factor are presented, and comparison with theory is made. Major experimental techniques are described. Exotic neutron features, such as the electric charge, baryon number nonconserving decays, etc., are discussed. The properties and applications of ultracold neutrons, and related problems, are discussed in detail. Some new ideas are suggested and research programs outlined.

Status of BNL E791: Study of very rare KL0 decays

BNL E791 is a search for the lepton-number non-conserving decay K L 0 → μe. During the 1988 run, the apparatus was also sensitive to the decays K L 0 → μμ, K L 0 → ee, and K L 0 → π 0 ee. Preliminary limits on the branching fractions from this run are: B( K L 0 → μe) < 3 × 10 −10 and B( K L 0 → ee) < 3 × 10 −10. For the decay K L 0 → μμ, we identified 87 candidate events. We expect to reach a single-event sensitivity in the 10 −11 range in the future.

Second class current effects in Tau-Lepton decay

The matrix element for the G-parity nonconserving decay τ→ η+ π+ ν τ is calculated in the standard electroweak theory. The ηπ final state is assumed to be dominated by the a 0(980) resonance, which is described by an excited q q state of the MIT bag model. The branching ratio B( τ→ η+ π+ ν τ , while quite model dependent, is very small (<10 −4) for all reasonable values of the bag radius and quark masses. Consequently, the decay mode is a negligible background in τ decay and can be ruled out as being responsible for the “missing” one-prong events in τ decay.

Upper limits on charm-changing neutral-current interactions.

We report on a search for charm-changing neutral-current decays and lepton-family-number--nonconserving decays of charmed hadrons using inclusive and exclusive decays of charmed hadrons into oppositely charged dileptons. We find no evidence for such interactions. The upper limits on the branching ratio for inclusive charm decay to dileptons are B(c..-->..X..mu../sup +/..mu../sup -/) ..Xe/sup +/e/sup -/) ..X..mu../sup +- /e/sup minus-or-plus/)<3.7 x 10/sup -3/ at 90% confidence level. Upper bounds are also presented for the branching ratios of several exclusive modes

The milano experiment on lepton number nonconservation in double beta-decay of76Ge

An underground experiment carried out in the Mont Blanc Tunnel with two (GeLi) diodes acting as source and detector of neutrinoless double beta-decay of76Ge is reported. No evidence has been found for this lepton nonconserving decay either to the ground state or to the first excited state of76Se, and lower limits of 3.3 -1023 and 2.7.1022 y have been found for the corresponding half-lifetimes at the 68% confidence level. For double beta-decay accompanied by two neutrinos or by a majoron, limits have been obtained which are less stringent by four and three orders of magnitude, respectively. The results on neutrinoless double beta-decay are discussed in terms of the role played by possible massive Majorana neutrinos or by weak righthanded currents.

Unsuppressed electroweak fermion number non-conservation in decays of heavy particles

It is argued that the electroweak fermion number non-conservation associated with the θ-vacuum structure and the triangle anomaly can be unsuppressed if there exist fermions (or bound states of fermions) with masses of order M W/ α w (a few TeV), the relevant processes being the decays of these heavy particles. We give a quantum mechanical example, discuss the decay of a techni-baryon (within the Skyrme model) and propose a scenario for the decay of a heavy fermion in the standard electroweak theory. We also discuss possible observable signatures of the anomalous fermion number non-conserving decays.

Measurement of theCP-nonconserving decay,KL0→2π0

The rate of the $\mathrm{CP}$-nonconserving decay ${K}_{L}^{0}\ensuremath{\rightarrow}2{\ensuremath{\pi}}^{0}$ has been measured using a monoenergetic $K$ beam and a nearly-$4\ensuremath{\pi}$-solid-angle detector system employing lead-plate spark chambers and shower counters. Final results based on a detailed analysis of the complete data set are given. The branching ratio of ${K}_{L}^{0}\ensuremath{\rightarrow}2{\ensuremath{\pi}}^{0}$ is determined relative to three different normalizations, ${K}_{L}^{0}\ensuremath{\rightarrow}3{\ensuremath{\pi}}^{0}$, ${K}_{L}^{0}\ensuremath{\rightarrow}\mathrm{all}\mathrm{charged}\mathrm{decay}\mathrm{modes}$, and ${K}_{L}^{0}\ensuremath{\rightarrow}{K}_{S}^{0}$ using a beryllium regenerator. From the ${K}_{L}^{0}\ensuremath{\rightarrow}2{\ensuremath{\pi}}^{0}$ rate we find the $\mathrm{CP}$-nonconserving parameter ${|{\ensuremath{\eta}}_{00}|}^{2}=[14.1\ifmmode\pm\else\textpm\fi{}1.9(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.5(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$.

Note on divergenceless currents and muon polarization in K μ3 decays

The hypothesis of conserved current in weak interaction is examined for the strangeness non-conserving decays. This hypothesis enables the unambiguous calculation of the longitudinal polarization of a muon in Kμ3 decay as a function of the pion energy. Its dependence on the muon energy is also studied. The result is compared with that of Okun and Martinyan who did not use a conserved current.