Weak Decays Research Articles

Mathematical modeling of wave propagation in viscoelastic media with the fractional Zener model

The question of interest for the presented study is the mathematical modeling of wave propagation in dissipative media. The generalized fractional Zener model in the case of dimension d (d=1,2,3) is considered. This work is devoted to the mathematical analysis of such model: existence and uniqueness of the strong and weak solution and energy decay result which guarantees the wave dissipation. The existence of the weak solution is shown using a priori estimates for solutions which are also presented.

Branching fractions of B^-rightarrow D^-X_{0,1}(2900) and their implications

The exotic states X_{0,1}(2900) with the quark flavor of csbar{u}bar{d} are recently observed in the mass spectrum of D^+K^- in B^-rightarrow D^-D^+K^- by the LHCb collaboration. To explore the nature of X_{0,1}(2900), except for analyzing their masses and decay widths as usually did in literatures, the study of their production mechanism in B-meson weak decays would provide another important information. The amplitude of B^-rightarrow D^- X_{0,1} is non-factorizable. We consider the final-state-interaction effects and calculate them via the rescattering mechanism. The measured branching fractions of B^-rightarrow D^- X_{0,1} are revealed. It is manifested by {B}^-rightarrow Lambda _c^-Xi _c^{(prime )0} and Lambda _b^0rightarrow P_c^+K^- that the rescattering mechanism can result in the relatively large branching fractions. The similar processes of B^-rightarrow pi ^-X_{0,1} are also analyzed. The isospins of X_{0,1} can be investigated by Brightarrow DX_{0,1}^{pm ,0} decays.

Lifetime of the hypertriton

We calculate the lifetime of the hypertriton as function of the $\Lambda$ separation energy $B_\Lambda$ in an effective field theory with $\Lambda$ and deuteron degrees of freedom. We also consider the impact of new measurements of the weak decay parameter of the $\Lambda$. While the sensitivity of the total width to $B_\Lambda$ is small, the partial widths for decays into individual final states and the experimentally measured ratio $R=\Gamma_{^3\textrm{He}}/\left(\Gamma_{^3 \text{He}}+\Gamma_{pd}\right)$ show a strong dependence. For the standard value $B_\Lambda=(0.13\pm 0.05)$ MeV, we find $R=0.37\pm 0.05$, which is in good agreement with past experimental studies and theoretical calculations. For the recent STAR value $B_\Lambda=(0.41\pm0.12\pm0.11)$ MeV, we obtain $R=0.57\pm 0.11$.

Hyperon and antihyperon physics

Structure, interactions and decays of hyperons can be studied at an electron-positron collider in annihilations to a hyperon-antihyperon pair. This method already has huge impact on hyperon physics since it was used in a first modern measurement of decay asymmetry in the weak decay and the result calls for reinterpretation of all polarization results for the Λ hyperon. In the experiment by the BESIII Collaboration nearly half million events were used. The pair production process involves two (complex) hadronic form factors. The observed large relative phase ΔΦ between the form factors, (42.4±0.6±0.5)°, makes it possible to use both transverse polarization and the spin correlations of the pair to simultaneously measure decay parameters for Λ and hyperons. Of particular importance is the result for the decay asymmetry parameter α− in the most probable Λ decay used to determine Λ polarization. The new α− value from BESIII, 0.750±0.009±0.004, is 17(3)% larger than the world average of 0.642 ± 0.013 adopted by all experiments between 1978 and 2019 to determine Λ polarization from the measured asymmetry in the decay proton distribution. A comparison of the concurrently measured at BESIII α− and α+, the parameter for the charge conjugated process , results in a direct CP symmetry test for the hyperon.The reaction was studied at BESIII also outside the J/ψ resonance using 66.9 pb−1 collected at GeV. The result is the first complete determination of the time-like elastic form factors GM and GE for any baryon including the relative phase ΔΦ = arg(GE/GM ) of (37 ± 12 ± 6)°. The absolute normalization of the form factors is set by the determined Born cross section of σ Born= 119.0 ± 5.3 ± 5.1 pb. In a separate run at GeV, 1.0 MeV above threshold for , a surprisingly large cross section for of 305 ± pb was measured.

Results on 82Se 2νββ with CUPID-0 Phase I

The nucleus is an extraordinarily complex object where fundamental forces are at work. The solution of this many-body problem has challenged physicists for decades: several models with complementary virtues and flaws have been adopted, none of which has a universal predictive capability. Double beta decay is a second order weak nuclear decay whose precise measurement might steer fundamental improvements in nuclear theory. Its knowledge paves the way to a much better understanding of many body nuclear dynamics and clarifies, in particular, the role of multiparticle states. This is a useful input to a complete understanding of the dynamics of neutrino-less double beta decay, the chief physical process whose discovery may shed light to matter-antimatter asymmetry of the universe and unveil the true nature of neutrinos. Here, we report the study of 2νββ-decay in 82Se with the CUPID-0 detector, an array of ZnSe crystals maintained at a temperature close to ‘absolute zero’ in an ultralow background environment. Thanks to the unprecedented accuracy in the measurement of the two electrons spectrum, we prove that the decay is dominated by a single intermediate state. We obtain also the most precise value for the 82Se 2νββ-decay half-life of yr.

Detection prospects for the second-order weak decays of ^{124}Xe in multi-tonne xenon time projection chambers

We investigate the detection prospects for two-neutrino and neutrinoless second-order weak decays of ^{124}{mathrm{Xe}} – double-electron capture (0/2upnu text {ECEC}), electron capture with positron emission (0/2upnu text {EC}upbeta ^+) and double-positron emission (0/2upnu upbeta ^+upbeta ^+) – in multi-tonne xenon time projection chambers. We simulate the decays in a liquid xenon medium and develop a reconstruction algorithm which uses the multi-particle coincidence in these decays to separate signal from background. This is used to compute the expected detection efficiencies as a function of position resolution and energy threshold for planned experiments. In addition, we consider an exhaustive list of possible background sources and find that they are either negligible in rate or can be greatly reduced using our topological reconstruction criteria. In particular, we draw two conclusions: First, with a theoretical half-life of T_{1/2}^{2upnu text {EC}upbeta ^+} = (1.7 pm 0.6)cdot 10^{23},text {year}, the 2upnu text {EC}upbeta ^{+} decay of ^{124}Xe will likely be detected in upcoming Dark Matter experiments (e.g. XENONnT or LZ), and their major background will be upgamma -rays from detector construction materials. Second, searches for the 0upnu text {EC}upbeta ^+ decay mode will likely be background-free, and new parameter space may be within reach. To this end we investigate two different scenarios of existing experimental constraints on the effective neutrino mass. The necessary 500 kg-year exposure of ^{124}Xe could be achieved by the baseline design of the DARWIN observatory, or by extracting and using the ^{124}Xe from the tailings of the nEXO experiment. We demonstrate how a combination of ^{124}Xe results with those from 0upnu upbeta ^-upbeta ^- searches in ^{136}Xe could help to identify the neutrinoless decay mechanism.

Search of x-ray solar activity correlations with 55Fe, 60Co nucleus decay rates

Several experimental groups observed temporary modulations of some nuclei strong and weak decay constants, which are of the order of 10−3 and with periods of one year, solar day, i.e. 24 hours and some others. In our experiments the decay rates were measured for 55Fe e-capture and 60Co β-decay during 2012–2020. Altogether, six decay rate dips of the order 10−2 – 10−3 and with duration from 40 to 208 hours were found, they deviate essentially from exponential decay rate fit. It is shown that their occurrence correlate with x-ray solar flares with significant reliability. Besides, two long term deviations of 55Fe decay rate of 62 and 41 days were observed in 2017–2018, it’s argued that they are related to the change of 11 year solar cycle stages.

Global hyperon polarization in Au+Au collisions at in the STAR experiment

The Quark-Gluon Plasma (QGP), appearing in non-central nucleus-nucleus collisions is generated with large orbital angular momentum. Spin-orbit coupling aligns spin directions of produced particles with the system angular momentum, through the creation of local vorticity. Properties of hyperon weak decays lead to the way of measuring polarization, that reflects vorticity. The global polarization of Λ and hyperons was measured for Au+Au collisions at recorded with the STAR at the RHIC. However, different theoretical approaches are still in need of new experimental input to describe global polarization properly. That’s why it is important to measure the global polarization of different particle species. In this paper, we will report new results of hyperon global polarization ( and ) measurement via different methods for high-statistics Au+Au collisions at .

B-Baryon semi-tauonic decays in the Standard Model

Within the framework of HQET, Λb→Λcτν¯τ and Ωb→Ωc(⁎)τν¯τ weak decays are studied to the order of 1/mc and 1/mb. Helicity amplitudes are written down. Relevant Isgur-Wise functions given by QCD sum rule and large Nc methods are applied in the numerical analysis. The baryonic R-ratios R(Λc) and R(Ωc(⁎)) are obtained.

Electron-capture decay in isotopic transfermium chains from self-consistent calculations

Weak decays in heavy nuclei with charge numbers Z = 101–109 are studied within a microscopic formalism based on deformed self-consistent Skyrme Hartree–Fock mean-field calculations with pairing correlations. The half-lives of β+ decay and electron capture are compared with α-decay half-lives obtained from phenomenological formulas. Transfermium isotopes of Md, No, Lr, Rf, Db, Sg, Bh, Hs, and Mt that can be produced in the frontier of cold and hot fusion-evaporation channels are considered. Several isotopes are identified whose β+/EC- and α-decay half-lives are comparable. The competition between these decay modes opens the possibility of new pathways towards the islands of stability.

Energy-Dependent Chemical Potentials of Light Hadrons and Quarks Based on Transverse Momentum Spectra and Yield Ratios of Negative to Positive Particles

We describe the transverse momentum spectra or transverse mass spectra of π ± , K ± , p , and p ¯ produced in central gold-gold (Au-Au), central lead-lead (Pb-Pb), and inelastic proton-proton (pp) collisions at different collision energies range from the AGS to LHC by using a two-component (in most cases) Erlang distribution in the framework of multisource thermal model. The fitting results are consistent with the experimental data, and the final-state yield ratios of negative to positive particles are obtained based on the normalization constants from the above describing the transverse momentum (or mass) spectra. The energy-dependent chemical potentials of light hadrons ( π , K , and p ) and quarks ( u , d , and s ) in central Au-Au, central Pb-Pb, and inelastic (pp) collisions are then extracted from the modified yield ratios in which the contributions of strong decay from high-mass resonance and weak decay from heavy flavor hadrons are removed. The study shows that most types of energy-dependent chemical potentials decrease with increase of collision energy over a range from the AGS to LHC. The curves of all types of energy-dependent chemical potentials, obtained from the fits of yield ratios vs. energy, have the maximum at about 3.510 GeV, which possibly is the critical energy of phase transition from a liquid-like hadron state to a gas-like quark state in the collision system. At the top RHIC and LHC, all types of chemical potentials become small and tend to zero at very high energy, which confirms that the high energy collision system possibly changes completely from the liquid-like hadron-dominant state to the gas-like quark-dominant state and the partonic interactions possibly play a dominant role at the LHC.

The influence of an interfacial hBN layer on the fluorescence of an organic molecule.

We investigated the ability of a single layer of hexagonal boron nitride (hBN) to decouple the excited state of the organic molecule 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) from the supporting Cu(111) surface by Raman and fluorescence (FL) spectroscopy. The Raman fingerprint-type spectrum of PTCDA served as a monitor for the presence of molecules on the surface. Several broad and weak FL lines between 18,150 and 18,450 cm−1 can be detected, already from the first monolayer onward. In contrast, FL from PTCDA on a bare Cu(111) surface is present only from the second PTCDA layer onward. Hence, a single layer of hBN decouples PTCDA from the metal substrate to an extent that a weak radiative FL decay of the optical excitation can occur. The different FL lines can be ascribed to different environments of the adsorption sites, namely molecules adsorbed at surface defects, in large ordered domains, and located in the second layer.

Charmed Omega _c weak decays into Omega in the light-front quark model

More than ten Omega _c^0 weak decay modes have been measured with the branching fractions relative to that of Omega ^0_crightarrow Omega ^-pi ^+. In order to extract the absolute branching fractions, the study of Omega ^0_crightarrow Omega ^-pi ^+ is needed. In this work, we predict {{mathcal {B}}}_pi equiv {{mathcal {B}}}(Omega _c^0rightarrow Omega ^-pi ^+)=(5.1pm 0.7)times 10^{-3} with the Omega _c^0rightarrow Omega ^- transition form factors calculated in the light-front quark model. We also predict {{mathcal {B}}}_rho equiv {{mathcal {B}}}(Omega _c^0rightarrow Omega ^-rho ^+)=(14.4pm 0.4)times 10^{-3} and {{mathcal {B}}}_eequiv {{mathcal {B}}}(Omega _c^0rightarrow Omega ^-e^+nu _e)=(5.4pm 0.2)times 10^{-3}. The previous values for {{mathcal {B}}}_rho /{{mathcal {B}}}_pi have been found to deviate from the most recent observation. Nonetheless, our {{mathcal {B}}}_rho /{{mathcal {B}}}_pi =2.8pm 0.4 is able to alleviate the deviation. Moreover, we obtain {{mathcal {B}}}_e/{{mathcal {B}}}_pi =1.1pm 0.2, which is consistent with the current data.

Doubly Cabibbo-suppressed decays of antitriplet charmed baryons

Doubly Cabibbo-suppressed (DCS) nonleptonic weak decays of antitriplet charmed baryons are studied systematically in this work. The factorizable and nonfactorizable contributions can be classified explicitly in the topological-diagram approach and treated separately. In particular, the evaluation of nonfactorizable terms is based on the pole model in conjunction with current algebra. All three types of relevant non- perturbative parameters contributing factorizable and nonfactorizable terms are estimated in the MIT bag model. Branching fractions of all the DCS decays are predicted to be of order 10−4 ∼ 10−6. In particular, we find that the three modes {Xi}_c^{+}to {Sigma}^{+}{K}^0,{Sigma}^0{K}^{+} and {Xi}_c^0to {Sigma}^{-}{K}^{+} are as large as (1 ∼ 2) × 10−4, which are the most promising DCS channels to be measured. We also point out that the two DCS modes {Xi}_c^{+}to {Sigma}^{+}{K}^0 and {Xi}_c^0to {Sigma}^0{K}^0 are possible to be distinguished from {Xi}_c^{+}to {Sigma}^{+}{K}_S and {Xi}_c^0to {Sigma}^0{K}_S . The decay asymmetries for all the channels with a kaon in their final states are found to be large in magnitude and negative in sign.

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.

A family of double-beauty tetraquarks: Axial-vector state * *The work of K. A, B. B., and H. S was Supported in part by the TUBITAK (119F050)

The spectroscopic parameters and decay channels of the axial-vector tetraquark (in what follows, ) are explored using the quantum chromodynamics (QCD) sum rule method. The mass and coupling of this state are calculated using two-point sum rules by taking into account various vacuum condensates, up to 10 dimensions. Our prediction for the mass of this state confirms that it is stable with respect to strong and electromagnetic decays and can dissociate to conventional mesons only via weak transformations. We investigate the dominant semileptonic and nonleptonic decays of . In these processes, is a scalar tetraquark built of a color-triplet diquark and an antidiquark, whereas M is one of the vector mesons , , , and . To calculate the partial widths of these decays, we use the QCD three-point sum rule approach and evaluate the weak transition form factors ( ), which govern these processes. The full width and the mean lifetime of the tetraquark are computed using the aforementioned weak decays. The obtained information about the parameters of and is useful for experimental investigations of these double-heavy exotic mesons.

Theoretical study of the Ω(2012) state in the Ωc0→π+Ω(2012)−→π+(K¯Ξ)− and π+(K¯Ξπ)− decays

We report on a theoretical study of the newly observed $\Omega(2012)$ resonance in the nonleptonic weak decays of $\Omega_c^0 \to \pi^+ \bar{K}\Xi^*(1530) (\eta \Omega) \to \pi^+ (\bar{K}\Xi)^-$ and $\pi^+ (\bar{K}\Xi\pi)^-$ via final-state interactions of the $\bar{K}\Xi^*(1530)$ and $\eta \Omega$ pairs. The weak interaction part is assumed to be dominated by the charm quark decay process: $c(ss) \to (s + u + \bar{d})(ss)$, while the hadronization part takes place between the $sss$ cluster from the weak decay and a quark-antiquark pair with the quantum numbers $J^{PC} = 0^{++}$ of the vacuum, produces a pair of $\bar{K}\Xi^*(1530)$ and $\eta \Omega$. Accordingly, the final $\bar{K}\Xi^*(1530)$ and $\eta \Omega$ states are in pure isospin $I= 0$ combinations, and the $\Omega_c^0 \to \pi^+ \bar{K}\Xi^*(1530)(\eta \Omega) \to \pi^+ (\bar{K}\Xi)^-$ decay is an ideal process to study the $\Omega(2012)$ resonance. With the final-state interaction described in the chiral unitary approach, up to an arbitrary normalization, the invariant mass distributions of the final state are calculated, assuming that the $\Omega(2012)$ resonance with spin-parity $J^P = 3/2^-$ is a dynamically generated state from the coupled channels interactions of the $\bar{K}\Xi^*(1530)$ and $\eta \Omega$ in $s$-wave and $\bar{K}\Xi$ in $d$-wave. We also calculate the ratio, $R^{\bar{K}\Xi\pi}_{\bar{K}\Xi} = {\rm Br}[\Omega_c^0 \to \pi^+ \Omega(2012)^- \to \pi^+ (\bar{K}\Xi \pi)^-] / {\rm Br}[\Omega_c^0 \to \pi^+ \Omega(2012)^- \to \pi^+ (\bar{K}\Xi)^-$]. The proposed mechanism can provide valuable information on the nature of the $\Omega(2012)$ and can in principle be tested by future experiments.

Hyperon weak radiative decay * *Supported by the National Natural Science Foundation of China (11425525, 11521505), DFG and NSFC funds to the Sino-German CRC 110 “Symmetries and the Emergence of Structure in QCD” (NSFC) (11261130311), Strategic Priority Research Program of Chinese Academy of Sciences (XDB34030302), National Key Basic Research Program of China (2015CB856700); Q.W. is also supported by the research

We revisit the hyperon weak radiative decays in the framework of the non-relativistic constituent quark model. This study confirms the nonlocal feature of the hyperon weak radiative transition operators, which are dominated by the pole terms, and an overall self-consistent description of the available experimental data for the Cabibbo-favored hyperon weak radiative decays is presented. It provides a natural mechanism for evading the Hara theorem, where sizeable parity-violating contributions can come from the intermediate orbital excitations. Cancellations between pole terms also explain the significant SU(3) flavor symmetry breaking manifested by the experimental data. We also discuss several interesting selection rules arising from either the electromagnetic or the weak interaction vertices. These features suggest nontrivial relations among various hyperon decays.

Hadronic weak decays of Λc in the quark model

The hadronic weak decays of $\Lambda_c$ are studied in the framework of a constituent quark model. With the combined analysis of the Cabbibo-favored processes, $\Lambda_c\to \Lambda\pi^+$, $\Sigma^0\pi^+$ and $\Sigma^+\pi^0$, we confirm that the non-factorizable transition mechanisms play a crucial role in the understanding of their compatible branching ratios. We emphasize that the SU(3) flavor symmetry breaking effects, which is generally at the order of $1\sim 2\%$, can be amplified by the destructive interferences among the pole terms in the diagrams with internal conversion. Some contributions are sensitive to the spatial distribution of the scalar-isoscalar light-quark sector in the $\Lambda_c$, and its overlap with the light quarks in the final state hyperon. Namely, a compact diquark configuration is disfavored.

Semileptonic transition of varLambda _{b} baryon

The semileptonic transition of varLambda _b baryon is studied using the Hypercentral constituent quark model. The six-dimensional hyperradial Schrddot{o}dinger equation is solved in the variational approach to get masses and wavefunctions of heavy baryons. The matrix elements of weak decay are written in terms of the overlap integrals of the baryon wave function. The Isgur-Wise function is determined to calculate exclusive semileptonic decay varLambda _brightarrow varLambda _cell {bar{nu }}. The calculated decay rate and the branching ratio of varLambda _b baryon are consistent with other theoretical predictions and with the available experimental observations.