Weak Decay Widths Research Articles

Masses of doubly heavy tetraquarks QQq̄n̄ with JP = 1+

In this paper, we apply the method of QCD sum rules to study the doubly heavy tetraquark states [Formula: see text] with spin-parity [Formula: see text] and strangeness [Formula: see text] using careful estimates of the Borel and threshold parameters involved. Masses of the doubly bottom and charmed tetraquarks with isospin [Formula: see text] are computed precisely via taking into account multifarious condensates up to dimension 10. Compared with the two-heavy meson thresholds, we find that all nonstrange doubly-bottom tetraquarks and a doubly-charmed tetraquarks associated with [Formula: see text] with [Formula: see text] are stable against strong decay into two bottom mesons while a doubly-charmed tetraquark associated with current [Formula: see text] is unstable against strong decay. By the way, weak decay widths of the doubly bottom tetraquarks are also given.

$$B_c$$ meson spectroscopy motivated by general features of pNRQCD

In the present article the mass spectrum, decay constant, weak decay widths, life time and branching fraction ratios and electromagnetic transition widths are calculated for ground and radially excited $B_c$ meson. To calculate the above properties the Schr\"{o}dinger equation has been solved numerically for the potential. The potential employed consists of relativistic correction in the framework of pNRQCD, added to the Cornell potential. The calculated results are compared with available experimental and theoretical results.

Decay Properties of Conventional and Hybrid $$\boldsymbol{B}_{\boldsymbol{c}}$$ Mesons

Spectrum, radial wave functions at origin, decay constants, weak decay widths, life-time, and branching ratios for radially excited conventional and hybrid $$B_{c}$$ mesons are derived within non-relativistic quark model framework employing Schrodinger equation by shooting method. Calculated results are compared with available theoretical results and experimental observations. This work may help in identifying the new discovered $$B_{c}$$ meson states at CDF, LHCb, and ATLAS.

Magnetic field driven enhancement of the weak decay width of charged pions

We study the effect of a uniform magnetic field overrightarrow{B} on the decays {pi}^{-}to {l}^{-}{overline{nu}}_l , where l− = e−, μ−, carrying out a general analysis that includes four π− decay constants. Taking the values of these constants from a chiral effective Nambu-Jona-Lasinio (NJL) model, it is seen that the total decay rate gets strongly increased with respect to the B = 0 case, with an enhancement factor ranging from ∼ 10 for eB = 0.1 GeV2 up to ∼ 103 for eB = 1 GeV2. The ratio between electronic and muonic decays gets also enhanced, reaching a value of about 1 : 2 for eB = 1 GeV2. In addition, we find that for large B the angular distribution of outgoing antineutrinos shows a significant suppression in the direction of the magnetic field.

Effects of coupled channels on cb̄ masses and decays in NRQM with OGEP

The complete spectrum of [Formula: see text] states is obtained in a phenomenological nonrelativistic quark model (NRQM), which consists of a confinement potential and one gluon exchange potential (OGEP) as effective quark–antiquark potential with coupled channel effects. We make predictions for the radiative decay (E1 and M1) widths and weak decay widths of [Formula: see text] states in the framework of NRQM formalism.

Cb¯ spectrum and decay properties with coupled channel effects

The mass spectrum of $c\bar{b}$ states has been obtained using the phenomenological relativistic quark model (RQM) with coupled channel effects. The Hamiltonian used in the investigation has confinement potential and confined one gluon exchange potential (COGEP). In the frame work of RQM a study of M1 and E1 radiative decays of $c\bar{b}$ states has been made. The weak decay widths in the spectator quark approximation have been estimated. An overall agreement is obtained with the experimental masses and decay widths.

Mass spectra and decays of ground and orbitally excited cb̄ states in nonrelativistic quark model

The complete spectrum of [Formula: see text] states is obtained in a phenomenological nonrelativistic quark model (NRQM), which consists of a confinement potential and one gluon exchange potential (OGEP) as effective quark–antiquark potential. We make predictions for the radiative decay (E1 and M1) widths and weak decay widths of [Formula: see text] states in the framework of NRQM formalism.

Determination of non-mesonic weak decay widths of 5ΛHe and 11ΛB Hypernuclei

The recent determination of the partial decay widths for the one-proton and the two-nucleon induced Non-Mesonic Weak Decay of Λ-Hypernuclei in the A=5–16 range permitted to reconstruct the full pattern of decay widths for 5ΛHe and 11ΛB. A consistency check on 12ΛC decay widths confirms the validity of the adopted method.

First determination of the one-proton induced Non-Mesonic Weak Decay width of p-shell Λ-Hypernuclei

Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Λ-Hypernuclei (A=5–16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Γ2N/Γp, are obtained from single proton spectra, Γ2N/Γp=0.50±0.24, and from neutron and proton coincidence spectra, Γ2N/Γp=0.36±0.14stat−0.04sys+0.05sys, in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Λ decay width, Γp/ΓΛ, without resorting to Intra Nuclear Cascade models but by exploiting only experimental data, under the assumption of a linear dependence on A of the Final State Interaction contribution. This is the first systematic determination ever done and it agrees within the errors with recent theoretical calculations.

Ground state normalization in the nonmesonic weak decay of 12ΛC hypernucleus within a nuclear matter formalism

The nonmesonic weak decay width of 12 Λ C hypernucleus has been evaluated within a nuclear matter formalism, using the local density approximation. In addition to the one-body induced decay ( Λ N → n N ) , it has been also considered the two-body induced decay ( Λ N N → n N N ) . This second decay is originated from ground state correlations, where a renormalization procedure to ensure a ground state normalized to one has been implemented. Our results show that the plain addition of the two-body induced decay implies a lost in the ground state-norm, which adds ∼38% of spurious strength to the nonmesonic weak decay width. Within our scheme, it is possible to reproduce the most recent data for the nonmesonic weak decay width of 12 Λ C.

Non-mesonic weak decay of Λ hypernuclei within a nuclear matter framework

The non-mesonic weak decay of Λ hypernuclei is studied using nuclear matter. We have developed a formalism which gives a microscopic interpretation of the process of emission of particles originated in this decay. More specifically, our scheme provides a unified treatment of Γ ( Λ N → N N ) and N N ( N N N ), the Λ non-mesonic weak decay widths and the number of emitted particles (pair of particles) of kind N ( NN), respectively. We have also evaluated for the first time the quantum interference terms between the n- and p-induced weak decay amplitudes. Explicit expressions for N N and N N N are shown within the ring approximation. Using the local density approximation together with the ring approximation, we report results for the decay of the C Λ 12 hypernucleus. We have obtained values for the ratio N n / N p ( N n n / N n p ) in the range 1.4–1.6 (0.2–0.3), where no energy threshold have been employed. The n- and p-induced interference terms modify in less than ∼ 3 % these results.

Formula omitted] decay branching ratios of 5ΛHe and 12ΛC hypernuclei

We precisely measured π 0 branching ratios of 5 Λ He and 12 Λ C hypernuclei produced via the ( π + , K + ) reaction. Using these π 0 branching ratios with the π − branching ratios and lifetimes, we obtained the π 0 decay widths and the non-mesonic weak decay widths with an accuracy of ∼5% (stat) for both hypernuclei.

Chiral quark model with infrared cut-off for the description of meson properties in hot matter

A simple chiral quark model of the Nambu--Jona-Lasinio (NJL) type with a quark confinement mechanism is constructed for the description of the light meson sector of QCD at finite temperature. Unphysical quark production thresholds in the NJL model are excluded by an infrared cut-off in the momentum integration within quark loop diagrams. This chiral quark model satisfies the low energy theorems. Using the vacuum masses and decay widths of \pi- and \rho-mesons for fixing the model parameters, the properties of the \sigma- meson are derived. Within the Matsubara formalism, the model is systematically extended to finite temperatures where chiral symmetry restoration due to a dropping constituent quark mass entails a vanishing of the infrared cut-off (deconfinement) at the pion Mott temperature T_c=186 MeV. Besides of the pion mass and weak decay constant, the masses, coupling constants and decay widths of \sigma- and \rho-mesons in hot matter are investigated. The quark-antiquark decay channel of the light mesons is opened for T>T_c only and becomes particularly strong for the \rho- meson. The two-pion decay channel below T_c has almost constant width for the \rho- meson up to T_c, but for the \sigma-meson it closes below T_c such that a scalar meson state with vanishing width is obtained as a precursor of the chiral/deconfinement transition.

Chiral quark model with infrared cut-off for the description of meson properties in hot matter

A simple chiral quark model of the Nambu-Jona-Lasinio (NJL) type with a quark confinement mechanism is constructed for the description of the light-meson sector of QCD at finite temperature. Unphysical quark production thresholds in the NJL model are excluded by an infrared cut-off in the momentum integration within quark loop diagrams. This chiral quark model satisfies the low-energy theorems. Using the vacuum masses and decay widths of π- and ρ-mesons for fixing the model parameters, the properties of the σ-meson are derived. Within the Matsubara formalism, the model is systematically extended to finite temperatures where chiral symmetry restoration due to a dropping constituent quark mass entails a vanishing of the infrared cut-off (deconfinement) at the pion Mott temperature T c = 186 MeV. Besides the pion mass and weak decay constant, the masses, coupling constants and decay widths of σ- and ρ-mesons in hot matter are investigated. The quark-antiquark decay channel of the light mesons is opened for T > T c only and becomes particularly strong for the ρ-meson. The two-pion decay channel below T c has almost constant width for the ρ-meson up to T c, but for the σ-meson it closes below T c such that a scalar meson state with vanishing width is obtained as a precursor of the chiral/deconfinement transition.

MESON DECAY IN AN INDEPENDENT QUARK MODEL

Leptonic decay widths and leptonic decay constants of light vector mesons and weak leptonic decay widths and weak decay constants of light and heavy pseudoscalar mesons have been studied in a field-theoretic framework based on the independent quark model with a scalar-vector power-law potential. The results are in very good agreement with the experimental data.

Heavy quark expansion and preasymptotic corrections to decay widths in the ’t Hooft model

We address nonperturbative power corrections to inclusive decay widths of heavy flavor hadrons in the context of the 't Hooft model (two-dimensional QCD at ${N}_{c}\ensuremath{\rightarrow}\ensuremath{\infty}),$ with the emphasis on the ``spectator-dependent'' effects, i.e., those sensitive to the flavor of the spectator. The summation of exclusive widths is performed analytically using the 't Hooft equation. We show that the ${1/m}_{Q}$ expansion of both the weak annihilation and Pauli interference widths coincides with the OPE predictions to the computed orders. Violation of local duality in the inclusive widths is quantified, and the new example is identified where the OPE prediction and the actual effect are completely saturated by a single final state. The qualitative aspects of quark hadronization emerging from the analysis in the 't Hooft model are discussed. Certain aspects of the summation of spectator-independent hadronic weak decay widths are given in more detail, which were not spelled out previously. We also give some useful details of the ${1/m}_{Q}$ expansion in the 't Hooft model.

Mesonic and non-mesonic decay widths of Λ4H and Λ4He

Results are reported on precise measurements of the weak-decay processes of Λ 4 H and Λ 4 He hypernuclei formed via the 4He (K stopped −, π −) reaction. The lifetimes of Λ 4H (194 −26 +24 ps) and Λ 4He (256 ± 27 ps) were obtained. The π 0 and π − decay branching ratios of Λ 4He (0.515 ± 0.035 and 0.322 ± 0.034, respectively) were precisely determined and they are compared with recent theoretical estimates and related experimental values. Our results favor a Λ-nucleus interaction with an inner repulsive core. The non-mesonic weak decay widths of Λ 4H and Λ 4He are reexamined on the basis of our measurements and updated knowledge of the mesonic decay processes. It is found that the non-mesonic decay of Λ 4He predominantly takes place via the Λ + p → n + p process.

Explicit quark-hadron duality in heavy-light meson weak decays in the ’t Hooft model

We compute the nonleptonic weak decay width of a heavy-light meson in 1+1 spacetime dimensions with a large number of QCD colors (the 't Hooft model) as a function of the heavy quark mass. In this limit, QCD is exactly soluble, and decay modes are dominated by two-particle final states. We compare the results to the tree-level partonic decay width of the heavy quark in order to test quark-hadron duality in this universe. We find that this duality is surprisingly well satisfied in the heavy quark limit, in that the difference between the sum of exclusive partial widths and the tree-level partonic width approaches a constant as M --> infinity, and the deviation is well-fit by a small 1/M correction. We comment on the meaning of this conclusion and its implications for the use of quark-hadron duality in hadronic physics.

A WEAK DECAYS IN MEDIUM TO HEAVY HYPERNUCLEI

We compute the Λ weak decay widths in a hypernucleus as a function of the mass number A (A ≳ 50). We make a number of predictions for the mesonic and non-mesonic decays which definitely put to test the model of the "Coherent Nucleus," proposed a few years ago by one of us (G.P.).

Gravity induced particle production in earth’s gravitational field in TeV region

We discuss the production of particles via interaction with the earth’s gravitational field. Explicit calculations are done for high energy scalars passing through earth’s gravitational field. We show for example, that the width for the scalar processφ→3φ can become comparable with a typical weak decay width at an energy scale of a few TeV. (Similar conclusions can be drawn about particles that ultimately couple to some scalar field.) We speculate that similar processes may be responsible for many of the anomalies in the 10–104 TeV experimental data.