Weak Decays Research Articles

Probing effects of new physics in {varLambda}_b^0to {varLambda}_c^{+}{mu}^{-}{overline{v}}_{mu } decays

We present, for the first time, the six-fold differential decay density expression for {varLambda}_b^0to {varLambda}_c^{+}mu {ell}^{-}{overline{v}}_{ell } , taking into account the polarisation of the {varLambda}_b^0 baryon and a complete basis of new physics operators. Using the expected yield in the current dataset collected at the LHCb experiment, we present sensitivity studies to determine the experimental precision on the Wilson coefficients of the new physics operators with {varLambda}_b^0to {varLambda}_c^{+}{mu}^{-}{overline{v}}_{mu } decays in two scenarios. In the first case, unpolarised {varLambda}_b^0to {varLambda}_c^{+}{mu}^{-}{overline{v}}_{mu } decays with {varLambda}_c^{+} → pK + π− are considered, whereas polarised {varLambda}_b^0to {varLambda}_c^{+}{mu}^{-}{overline{v}}_{mu } decays with {varLambda}_c^{+} → p{K}_{mathrm{S}}^0 are studied in the second. For the latter scenario, the experimental precision that can be achieved on the de-termination of {varLambda}_b^0 polarisation and {varLambda}_c^{+} weak decay asymmetry parameter is also presented.

Polarization in (quasi-)two-body decays and new physics

We consider two-body and quasi-two-body decays of the type f_1 rightarrow f_2 B, where f_1 and f_2 are spin-1/2 fermions and B a spin-0 or spin-1 boson. After recalling the non-covariant formalism for decay amplitudes, we derive the expression of the differential decay width and of the polarizations of the final spinning particles, both on- and off-shell. We find an intriguing geometrical interpretation of the results about the polarization. We also illustrate some methods for measuring the polarizations of the resonances and for optimizing data analysis. Then we propose applications to semi-leptonic weak decays, with a major attention to the T-odd component of the polarization; this may help to find, simultaneously, possible time-reversal violations and hints to physics beyond the standard model. We suggest also a CPT test. Last, we discuss some T-odd observables for the production process of f_1 and for the study of the strong final state interactions of non-leptonic decays.

Polarization in decays * * Supported by the National Natural Science Foundation of China (11875262, 11805037, 11705078), Joint Large-Scale Scientific Facility Funds of the NSFC and CAS (U1832121), Shanghai Pujiang Program (18PJ1401000) and Open Research Program of Large Research Infrastructures (2017), Chinese Academy of Sciences

Measurements of decay asymmetry parameters of charmed baryons, e.g., , provide more data to test the W-emission and W-exchange mechanisms controlled by strong and weak interactions. Taking advantage of the spin polarization in charmed baryon decays, we investigate the possibility to measure weak decay asymmetry parameters in the process. We analyze the transverse polarization spontaneously produced in this process and the spin transfer in the subsequent decays. The sensitivity to measure the asymmetry parameters is estimated for the decay .

Stability of Nearly Optimal Decompositions in Fourier Analysis

We consider the existence problem for near-minimizers for the distance functional (or E-functional in the interpolation terminology) that are stable under the action of certain operators. In particular, stable near-minimizers for the couple (L1, Lp) are shown to exist when the operator is the projection to wavelets and these wavelets satisfy only some weak decay conditions at infinity.

Performance studies for collective flow measurements with CBM at FAIR

We present recent results from CBM performance studies for measurements of the directed (v1) flow of π+, Ʌ and . For the performance studies we use the CBMROOT environment for Monte-Carlo simulations and event reconstruction. The Kalman Filter Particle Finder (KFParticleFinder) package is used for hyperon reconstruction via their weak decays, and the Projectile Spectator Detector (PSD) for event plane determination. A status of the fast simulator implementation for the PSD calorimeter response, which is required for high statistics simulation, is also presented.

Investigation of a Confined C‐Class Flare in an Arch Filament System Close to a Regular Sunspot

AbstractA moderate C1.1 class confined flare is investigated here, which occurred on 24 September 2013 at 22:56 UT, in an arch filament system close to a regular, unipolar sunspot. Spectropolarimetric observations from the Tenerife Infrared Polarimeter at the 70‐cm German Vacuum Tower Telescope were combined with data from the Helioseismic Magnetic Imager and the Atmospheric Imaging Assembly to identify the processes that triggered the flare. The legs of this arch filament were anchored in the leading sunspot and the network flux region of opposite polarity. The flare was driven by small‐scale, flux cancellation at the weak neutral line underlying the arch filament, which resulted in two small flaring events within an hour of the C1.1 flare. Flux cancellation was facilitated by the moat flow from the leading sunspot wherein small‐scale magnetic fragments stream toward patches of preexisting flux. The cancellation of flux led to the destabilization of the arch filament, which was seen as an increase in the twist along the arch filament. The horizontal fields across the weak neutral line decay rapidly, which cannot prevent the filament from rising that results in a two‐ribbon flare at the neutral line. The arch filament unwinds as it rises but is confined by the higher, overlying fields between the two polarities of the active region that decay much more slowly.

The New Results from Multi-quark Exotic States Searches at D0 Experiment

Recent results from a search for multi-quark exotic states at D0 experiment (FNAL, USA) are presented. This includes the new data for possible tetraquark state X(5568) decaying to , in the channels with semileptonic decays of mesons. Also, result from the J/ψπ system analysis and an evidence for exotic charged charmoniumlike state Zc(3900) in semiinclusive weak decays of B-flavored hadrons are presented as well.

The role of Lattice QCD in searches for violations of fundamental symmetries and signals for new physics

This document is one of a series of whitepapers from the USQCD collaboration. Here, we discuss opportunities for Lattice Quantum Chromodynamics (LQCD) in the research frontier in fundamental symmetries and signals for new physics. LQCD, in synergy with effective field theories and nuclear many-body studies, provides theoretical support to ongoing and planned experimental programs in searches for electric dipole moments of the nucleon, nuclei and atoms, decay of the proton, $n$-$\overline{n}$ oscillations, neutrinoless double-$\beta$ decay of a nucleus, conversion of muon to electron, precision measurements of weak decays of the nucleon and of nuclei, precision isotope-shift spectroscopy, as well as direct dark matter detection experiments using nuclear targets. This whitepaper details the objectives of the LQCD program in the area of Fundamental Symmetries within the USQCD collaboration, identifies priorities that can be addressed within the next five years, and elaborates on the areas that will likely demand a high degree of innovation in both numerical and analytical frontiers of the LQCD research.

Weak decays of doubly heavy baryons: Decays to a system of π mesons

We consider exclusive weak decays of doubly heavy baryons with spin $J=1/2$ with production of a leptonic pair or a set of light mesons. Using the QCD factorization theorem and spectral functions approach, we obtain theoretical predictions for the partial probabilities of these decays and distributions over various kinematic variables. According to the obtained results, partial probabilities of some of the considered decays are large enough to be observed experimentally.

Kaon Photoproduction and the Λ Decay Parameter α_{-}.

The weak decay parameter α_{-} of the Λ is an important quantity for the extraction of polarization observables in various experiments. Moreover, in combination with α_{+} from Λ[over ¯] decay it provides a measure for matter-antimatter asymmetry. The weak decay parameter also affects the decay parameters of the Ξ and Ω baryons and, in general, any quantity in which the polarization of the Λ is relevant. The recently reported value by the BESIII Collaboration of 0.750(9)(4) is significantly larger than the previous PDG value of 0.642(13) that had been accepted and used for over 40years. In this work we make an independent estimate of α_{-}, using an extensive set of polarization data measured in kaon photoproduction in the baryon resonance region and constraints set by spin algebra. The obtained value is 0.721(6)(5). The result is corroborated by multiple statistical tests as well as a modern phenomenological model, showing that our new value yields the best description of the data in question. Our analysis supports the new BESIII finding that α_{-} is significantly larger than the previous PDG value. Any experimental quantity relying on the value of α_{-} should therefore be reconsidered.

Testing SU(3) flavor symmetry in semileptonic and two-body nonleptonic decays of hyperons

The semileptonic decays and two-body nonleptonic decays of light baryon octet ($T_8$) and decuplet ($T_{10}$) consisting of light $u,d,s$ quarks are studied with the SU(3) flavor symmetry in this work. We obtain the amplitude relations between different decay modes by the SU(3) irreducible representation approach, and then predict relevant branching ratios by present experimental data within $1 \sigma$ error. We find that the predictions for all branching ratios except $\mathcal{B}(\Xi\rightarrow \Lambda^0\pi)$ and $\mathcal{B}(\Xi^*\rightarrow \Xi\pi)$ are in good agreement with present experimental data, that implies the neglected $C_+$ terms or SU(3) breaking effects might contribute at the order of a few percent in $\Xi\rightarrow \Lambda^0\pi$ and $\Xi^*\rightarrow \Xi\pi$ weak decays. We predict that $\mathcal{B}(\Xi^{-}\rightarrow \Sigma^0\mu^-\bar{\nu}_\mu)=(1.13\pm0.08)\times10^{-6}$, $\mathcal{B}(\Xi^{-}\rightarrow\Lambda^0\mu^-\bar{\nu}_\mu)=(1.58\pm0.04)\times10^{-4}$, $\mathcal{B}(\Omega^-\rightarrow\Xi^0\mu^-\bar{\nu}_\mu)=(3.7\pm1.8)\times10^{-3}$, $\mathcal{B}(\Sigma^-\rightarrow \Sigma^0e^-\bar{\nu}_e)=(1.35\pm0.28)\times10^{-10}$, $\mathcal{B}(\Xi^-\rightarrow \Xi^0e^-\bar{\nu}_e)=(4.2\pm2.4)\times10^{-10}$. We also study $T_{10}\to T_8 P_8$ weak, electromagnetic or strong decays. Some of these decay modes could be observed by the BESIII, LHCb and other experiments in the near future. Due to the very small life times of $\Sigma^0$, $\Xi^{*0,-}$, $\Sigma^{*0,-}$ and $\Delta^{0,-}$, the branching ratios of these baryon weak decays are only at the order of $\mathcal{O}(10^{-20}-10^{-13}$), which are too small to be reached by current experiments. Furthermore, the longitudinal branching ratios of $T_{8A} \to T_{8B} \ell^- \bar{\nu}_\ell~(\ell=\mu,e)$ decays are also given.

Multiple Shape Coexistence in ^{110,112}Cd.

From detailed spectroscopy of ^{110}Cd and ^{112}Cd following the β^{+}/electron-capture decay of ^{110,112}In and the β^{-} decay of ^{112}Ag, very weak decay branches from nonyrast states are observed. The transition rates determined from the measured branching ratios and level lifetimes obtained with the Doppler-shift attenuation method following inelastic neutron scattering reveal collective enhancements that are suggestive of a series of rotational bands. In ^{110}Cd, a γ band built on the shape-coexisting intruder configuration is suggested. For ^{112}Cd, the 2^{+} and 3^{+} intruder γ-band members are suggested, the 0_{3}^{+} band is extended to spin 4^{+}, and the 0_{4}^{+} band is identified. The results are interpreted using beyond-mean-field calculations employing the symmetry conserving configuration mixing method with the Gogny D1S energy density functional and with the suggestion that the Cd isotopes exhibit multiple shape coexistence.

A general decay estimate for the nonlinear transmission problem of weak viscoelastic equations with time-varying delay

The transmission of waves over a body composed of two different materials is considered in this paper. One component is a simple elastic part, while the other is a weak viscoelastic component with time-varying delay and damping effect. Besides, one part of the boundary is controlled by a nonlinear memory source term, while the other part is clamped. Under the influence of time-varying delay and damping effect, we derive a general decay estimate of the energy when the memory kernels in the internal weak viscoelasticity and boundary source decay simultaneously.

Weak decays in the light-front quark model with two schemes to deal with the polarization of diquark

Thanks to the remarkable achievements of the LHC, a large database on baryons has been accumulated. There is therefore now the opportunity to precisely study baryons, particularly heavy baryons. By analyzing the data, the quark–diquark structure, which has been the subject of intensive discussions, can be tested. In this work the decay widths of weak transitions are calculated in terms of the light-front quark model. To carry out the calculations, the quark–diquark picture is employed where an axial-vector diquark composed of two light quarks serves as a spectator in the processes concerned. The first step of this work is to construct the vertex functions for and Σb, then the relevant form factors are derived. It is shown that under the heavy quark limit the Isgur–Wise functions for the transition are re-deduced. Indeed, the question of how to properly depict the polarization (ϵμ) of the diquark is slightly tricky. In this work, we apply two schemes to explicitly determine the momentum-dependence of the diquark. The corresponding numerical results are presented which will be testified by future experiments.

Weak decays * * Supported by the National Natural Science Foundation of China (11875122 and 11475055) and the Program for Innovative Research Team in University of Henan Province (19IRTSTHN018)

Motivated by the rapid development of heavy flavor physics experiments, we study the tree-dominated nonleptonic ( ) decays within the factorization approach. The relevant transition form factors are calculated by employing the covariant light-front quark model. Helicity amplitudes are calculated and analyzed in detail, and a very clear hierarchical structure is presented. The branching fractions are computed and discussed. Numerically, the CKM-favored and decays have relatively large branching fractions, , and could be observed by LHC and Belle-II experiments in the future.

The decays τ → (K,K(1460))ντ and the value of the weak decay constants FK and FK′ in the extended NJL model

In the extended Nambu–Jona-Lasinio (NJL) model, the decay widths of [Formula: see text], [Formula: see text] are calculated. The contributions from intermediate axial-vector mesons [Formula: see text], [Formula: see text] and the first radially excited state [Formula: see text] are taken into account. Estimates for the weak decay constants [Formula: see text] and [Formula: see text] are given. Predictions are made for the width of [Formula: see text] decay and [Formula: see text] constant.

Coherence length of neutrino oscillations in a quantum field-theoretical approach

We consider a novel quantum field-theoretical approach to the description of processes passing at finite space-time intervals based on the Feynman diagram technique in the coordinate representation. The most known processes of this type are neutrino and neutral kaon oscillations. The experimental setting of these processes requires one to adjust the rules of passing to the momentum representation in the Feynman diagram technique in accordance with it, which leads to a modification of the Feynman propagator in the momentum representation. The approach does not make use of wave packets, both initial and final particle states are described by plane waves, which simplifies the calculations considerably. We consider neutrino oscillation processes, where the neutrinos are produced in three-particle weak decays of nuclei and detected in the charged-current interaction with nuclei or in the charged- and neutral-current interactions with electrons. Particular examples are considered and it is shown that the momentum spread of the produced neutrinos and the energy dependence of the differential cross section of the detection process result in the suppression of neutrino oscillation, which is characterized by a coherence length specific for a pair of production and detection processes. This coherence length turns out to be much less than the coherence length in the standard quantum-mechanical approach defined by the quantum uncertainty of neutrino momentum.

Fully heavy tetraquark {bb {bar{c}} {bar{c}}}: lifetimes and weak decays

We study the lifetime and weak decays of the full-heavy S-wave 0^+ tetraquark T^{{bb}}_{{{bar{c}}{bar{c}}}}. Using the operator product expansion rooted in heavy quark expansion, we find a rather short lifetime, at the order (0.1-0.3)times 10^{-12}s depending on the inputs. With the flavor SU(3) symmetry, we then construct the effective Hamiltonian at the hadron level, and derive relations between decay widths of different channels. According to the electro-weak effective operators, we classify different decay modes, and make a collection of the golden channels, such as T_{{{bar{c}} {bar{c}}}}^{{bb}}rightarrow B^- K^0 B_c^- for the charm quark decay and T_{{{bar{c}} {bar{c}}}}^{{bb}}rightarrow B^-D^- for the bottom quark decay. Our results for the lifetime and golden channels are helpful to search for the fully-heavy tetraquark in future experiments.

Radial Spectrum of Light Mesons in Planar QCD Sum Rules and the Scalar Sigma-Meson

In the framework of spectral sum rules in the planar limit of quantum chromodynamics, we propose two new methods for calculating the spectra of light mesons based on using linear radial Regge trajectories and the simplest quark-antiquark operators interpolating meson states. Both methods predict a resonance near 500 MeV in the scalar-isoscalar channel, which hypothetically corresponds to the lightest scalar hadron. the σ-meson. This can mean that the quark-antiquark component is strongly dominating in its structure even if the σ-meson is a tetraquark state. In one of the methods, we obtain a reasonable agreement with experimental data using only two input parameters: the phenomenological value of the gluon condensate and the weak decay constant of the pion. In this case, the predicted quark condensate value agrees well with contemporary lattice computation results.

A study of ΔC = 1 decays of bottom mesons involving axial-vector meson

We study the two-body charmed nonleptonic weak decays of the bottom meson to an axial-vector meson and a pseudoscalar meson using the non-relativistic quark model. We employ the factorization hypothesis to obtain the branching ratios of these decays. First, we calculate the axial-vector (JP=1+) emitting form factors for B→D1/D_1 transitions in the non-relativistic Isgur-Scora-Grinstein-Wise quark model. Later, we use the heavy quark symmetry constraints to obtain the B→D11/2/D13/2 form factors and consequently, calculated their branching ratios. For a comparative analysis, we extract τ1/2(ω) and τ3/2(ω) form factors from the recent lattice QCD results to get a qualitative estimate of B→D11/2/D13/2 form factors. We find that the calculated branching ratios are in fair agreement with the available experimental data in both the scenarios. Also, we observe that, despite of 1/mQ suppression in heavy quark limit, the color-suppressed contribution to these decays can not be ignored.