Strangeness Changing Research Articles

Strangeness-changing nonlepton decays of the kaons, hyperons, and the Ω− particle

We try to understand the strangeness changing nonleptonic decays of kaons, hyperons, and the Ω− particle in terms of the modern, renormalized weak Hamiltonian expressed as a sum of four-quark Wilson operators, including the so-called penguin operators c5O5 and c6O6 arising from gluon radiative corrections. It is found that these decays, including the long-standing s-wave/p-wave puzzle in hyperon decays, can be understood if the Wilson coefficient [Formula: see text] has a sign opposite to that obtained from short-distance perturbative quantum chromodynamics calculations and has an effective value such that [Formula: see text].

Baryon momentum effects in resonance dominated strangeness changing nuclear reactions

Explicit inclusion of the baryon momentum operator in the input t K −N → Λπ amplitude in impulse approximation calculations of (K −, π −) reactions results in significant (angular dependent) reductions compared to earlier results. Agreement between theory and experiment is improved.

The price of natural parity conservation in the neutral current sector

We study the requirement that the neutral current sector in SU(2) L ⊗ SU(2) R ⊗ U(1) gauge models be naturally parity conserving in the tree approximation, and therefore calculable. A class of models which reproduces automatically the Weinberg-Salam neutrino neutral current phenomenology cannot be made natural in this sense and at the same time compatible with charged current phenomenology. At best one has small but uncalculable violations of both Weinberg-Salam neutrino phenomenology and parity conservation in neutral currents, as well as proliferation of fermion and scalar fields and possible difficulties with neutral strangeness changing transitions. A second class of models has calculable p parity violation in neutral currents and allows a more restricted fermion and scalar sector, but the Weinberg-Salam neutrino phenomenology does not emerge naturally. For the latter class we evaluate the parity violation induced by radiative corrections, relevant to atomic physics experiments. While technically calculable, it is not practically so, because of their dependence on unknown parameters of the Higgs sector. We also discuss radiative corrections to Cabibbo universality in these models.

Universal Neutral Current Interactions and Urbaryon-Lepton Correspondence

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Search for strangeness changing neutral currents induced by neutrinos in gargamelle

A sample of 9930 neutrino neutral current interactions has been examined for single strange particle production. No signal in the channels νN → νγX and νN → ν| gS 0X, where X means non-strange hadrons, has been found. This yields an upper limit of 5.4 × 10 −3 to a 90% confidence level on the ratio [( ν → νΓX) + ( ν → νΣ 0X)]/[ ν → ν + anything]

Strange particle production by antineutrinos

Cross sections are presented for antineutrino production of Λ, Σ 0 and K 0 in strangeness changing reactions. Associated production reactions ( ΔS = 0) have been observed in the charged and the neutral current channels. For the elastic reaction v p → μ +Λ , estimates have been made of the axial transition form factor.

Universality in weak interactions—The cabibbo suppression

An SU3 gauge model of weak interactions, which generates the Cabibbo suppression spontaneously and consistently, is presented. Out of the eight currents, a triplet couples to relatively light gauge bosons and satisfies the commutation relations of the SU2-universality algebra of Gell-Mann. The other five couple to necessarily very massive gauge bosons. The leptons have a realistic mass spectrum and the (bare) quarks are massless. The theory as it stands does not encompass charm and cannot suppress strangeness changing neutral currents; both these deficiencies require a larger gauge group for their correction.

Difficulties with a quantum chromodynamic formulation of non-leptonic decays

A new model for non-leptonic weak interactions has been recently proposed which is based on the introduction of a right handed charm and strangeness changing weak current. We show that this model can be made to fit the data on B→ B′ π and B→ B′ γ decays only if several ad hoc assumptions of large SU 3 breaking are made. We also review the success of the conventional Cabibbo current-current model in fitting all of the non-leptonic data.

Theory of CP violation based on the charm and strangeness changing righthanded weak current

If the charged weak current contains the righthanded current ( c ̄ s) R , the quark mass term can be the origin of CP violation, which is then intimately related to the origin of the dominating |ΔI| = 1 2 and | ΔS| = 1 nonleptonic weak interaction. The electric dipole moment of the neutron is predicted to be of the order of 10 −25 ecm.

A righthanded weak current and quantum chromodynamics as the origin of the dominant nonleptonic weak interaction

If a new charm and strangeness changing righthanded weak current is introduced, one obtains within quantum chromodynamics a new term in the nonleptonic weak Hamiltonian, corresponding to the decay s → d + glue. It is proposed that this interaction gives rise to the |ΔI| = 1 2 enhancement and other hitherto unexplained properties of the nonleptonic weak decays of strange particles.

Radiative decays as a test for right-handed currents

It is shown that the purity violating amplitude for the decays Σ + → pγ and Ξ − → Σ −γ vanish in the SU(3) symmetry limit if the charged weak currents possess a U spin symmetry for strangeness changing processes. This applies to Cabibbo currents and their SU (4) generalization. Assuming an asymptotically free model for the strong interactions this result applies to all models with only left-handed charged currents. Observation of a large parity violating amplitude would indicate right-handed charged weak currents. Tests involving other radiative decays are also considered.

Some Comments on Strangeness Changing Processes and Masses of Higgs' Scalars in Gauge Theories

It is pointed out in this paper that it is not necessary to assume that the physical Higgs' scalar is very massive in order to avoid conflict with low branching ratios for certain strangeness changing decays. Results of an explicit higher order calculation in the context of a SU(2) × U(1) model in which the Glashow, Illiopoulos, Maiani mechanism is operative, are presented.

General approach to Weinberg's model with three triplet quarks

We classify all possible SU(2) × U(1) gauge models with three triplet quarks according to the representations of the quarks, requiring the validity of the Cabibbo theory and absence of strangeness changing neutral processes in lowest order. Then we investigate in detail the questions of lepton-hadron universality, ΔS ≠ 0 neutral processes in higher orders, and strong interactions. Characteristic differences between the various types of models show up. Further we give the predictions for the ratios R and R of neutral to charged ν and ν cross sections below color threshold. Only a rather small region of the R- R plane is accessible by the totality of all the models. The experimental points lie within this region, and more precise measurements could well discriminate between the various types of models.

Models for the weak parity-violating vector meson exchange potential and the circular polarization in n + p → d + γ

We propose three models which lead to a p.v. nucleon-nucleon interaction mediated by charged and neutral vector mesons. Besides the ad hoc hypothesis of octet dominance, we consider two quark models (the Bose quark and colour Fermi quark model), which give a dynamical explanation of the ΔI = 1 2 rule in strangeness changing hyperon decays. They lead to p.v. potentials with different isospin dependence. We also derive the weak NN̄ ρ° coupling from a SU(2) × U(1) gauge theory with neutral currents. The circular polarization P γ of the γ-quanta in the capture of thermal neutrons on protons is calculated for these different models. The Reid hard-core (HC) and soft-core (SC) potentials have been chosen to take into account the strong interaction. Then the naively factorized Cabbibo current-current interaction with charged rho exchange only gives P γ HC = −2.7 × 10 −8 and P γ SC = −2.1 × 10 −8. The strong octet dominance and Bose quark model lead to a vanishing circular polarization | P γ | ≈ (1–4) × 10 −9. The colour Fermi quark model enhances the circular polarization and gives P γ ≈ −5 × 10 −8.

A chiral SU(4) × SU(4) gauge theory of weak and electromagnetic interactions

A lepton hadron analogy is considered based on the gauge group SU(4) L × SU(4) R × U(1), which is broken entirely spontaneously. The model satisfies the physical requirements of the V-A theory, muon-electron universality, no neutral strangeness changing currents, the Cabibbo structure for the SU(3) currents, and triangle anomalies can be avoided. The contribution of the existing neutral currents to various neutrino processes are calculated.

Weak currents and Gnomes

A weak hadronic current is constructed using fields of conventional quantum numbers. The neutral component of this current has no strangeness changing part.

Bounds on the K ℓ3 scalar form factor from low-energy K π phase shift

Upper and lower bounds on the scalar form factor of K ℓ3 decay are calculated using the analytic properties of the form factor, the experimental low-energy S-wave K π phase shift, and an estimate of the propagator Δ( t) of the divergence of the strangeness changing current at zero momentum. We release the condition given by the soft-pion theorem on ⨍(m K 2) that we considered in a previous work. For this reason the new bounds are less restrictive. However they are sufficiently strong to be inconsistent with some experimental data irrespective of the fit used for K π scattering.

Bounds for K ℓ3 decay parameters

The extremum of the integral ∫ ∞ f( x) ‖ F ( x)‖ 2 d x is determined for the case when the values taken by the function F ( x) 1 at three points are known. The result is applied to the K ℓ3 problem, the function F ( x) being replaced by the form factor f +( q 2)+ f −( q 2) q 2( m K 2− m π 2) of the divergence of the strangeness changing vector current.

Bounds on the form factor of K ℓ3 decay

We derive bounds on the form factor f( t) of K ℓ3 decay valid from the origin to the threshold ( m π + m K) 2. If we use as input the soft-pionn theorem of f ±( t) and a bound on the propagator Δ(0) of the divergence of the strangeness changing current at zero momentum, we obtain an upper and lower bound, which are close together but which do not fit with experiment; by allowing Δ(0) to vary as a free parameter, there is then better agreement. We also discuss some bounds for the decay parameters.

Use of equal-time commutators involving the symmetric energy-momentum tensor for the derivation of sum rules

We emphasize the central role that second-order Schwinger terms in equal-time commutators involving the energy density T oo play in determining the scaling behaviour of local operators. Thereby a new derivation is given of the fact (recently derived by Chanowitz) that the time component of a conserved current has dimensions 3 if it has a dimension at all and if a state | A〉 exists such that 〈A| J o|A〉 ≠ 0. Assuming that the time component of the non-conserved strangeness changing vector current V μ K has a dimension we show by saturation of the matrix element 〈π + ( q) | [ K o , V o K (0) | K + ( q)〉 (with K μ the conformal charges) in the infinite momentum frame that the root mean square gravitational factor radii (i.e. the slope of the gravitational form factor G 1( t) at t = 0) of π and K are the same. In this case, Regge theory is used to justify the infinite momentum limit. Formal application of this limit also shows that the dimensions of ∂ μ V μ K and V k K (if any) should be 2 and 3, respectively. This result is less reliable since in this case Regge theory implies invalidity of the procedure. Analogous results hold under somewhat stronger assumptions for η too. We discuss the consequences of SU(3) and our results for tensor meson dominance and find that a (numericaly possible small) subtraction that depends on the SU(3) index M must be present in the pseudo-scalr-tensor meson form factor G 1 M( t). Our results are in at least approximate agreement with SU(3) for 2 + → 0 −0 − and allow us to predict - correct within the errors - a value for the width f → K K . They also agree with what is known about f → ηη and f′ → ηη. The assumptions include neglect of contributions from the K A, i.e. the doubtful Q-range 1240–1400 MeV.