Decay Branching Ratios Research Articles

Semirelativistic study of the semileptonic decays of Bq mesons to orbital excited heavy tensors

Based on the method of solving the complete Salpeter equation, we study the semileptonic decays of a 0− heavy meson to 1P, 2P, or 3P heavy-tensor mesons, Bq→(c¯q)(nP)ℓ+νℓ (q=u,d,s,c;n=1,2,3). The obtained branching ratio of B(B→D2⋆(2460)ℓ+νℓ) agrees with the experimental data. We predict B(Bs0→Ds2⋆−(1P)ℓ+νℓ)=3.76×10−3 and B(Bc+→χc2(1P)ℓ+νℓ)=1.82×10−3. The branching ratios of decays to 2P and 3P final states are found to be very small. The ratios R(D¯2⋆0)=0.045, R(Ds2⋆)=0.048 and R(χc2)=0.059 are also obtained. This study focuses on the contribution of relativistic corrections. The wave function of the pseudoscalar includes nonrelativistic S-wave and relativistic P-wave. While for a tensor, it contains nonrelativistic P-wave and relativistic P-, D-, and F-waves in its wave function. We find the individual contributions of relativistic partial waves are significant in the decay B→D2⋆(2460)ℓ+νℓ, but the overall contribution of the relativistic effect is 24.4%, which is small due to cancellation. Similarly, for the decay Bs0→Ds2⋆−(1P)ℓ+νℓ, the contribution of the relativistic effect is 28.8%. While for Bc+→χc2(1P)ℓ+νℓ, the individual contributions of relativistic partial waves and the overall relativistic correction are both small, the later of which is 22.1%. Published by the American Physical Society 2024

Search for a Neutron Dark Decay in ^{6}He.

Neutron dark decays have been suggested as a solution to the discrepancy between bottle and beam experiments, providing a dark matter candidate that can be searched for in halo nuclei. The free neutron in the final state following the decay of ^{6}He into ^{4}He+n+χ provides an exceptionally clean detection signature when combined with a high efficiency neutron detector. Using a high-intensity ^{6}He^{+} beam at Grand Accélérateur National d'Ions Lourds, a search for a coincident neutron signal resulted in an upper limit on a dark decay branching ratio of Br_{χ}≤4.0×10^{-10} (95% C.L.). Using the dark neutron decay model proposed originally by Fornal and Grinstein, we translate this into an upper bound on a dark neutron branching ratio of O(10^{-5}), improving over global constraints by one to several orders of magnitude depending on m_{χ}.

First observation and study of the K±→ π0π0μ±ν decay

The NA48/2 experiment at CERN reports the first observation of the K± → π0π0μ±ν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV2/c4 is measured to be (0.65 ± 0.03) × 10−6. The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10−6, in agreement with chiral perturbation theory predictions.

Charmonium decays of beauty baryons in the perturbative QCD approach

Motivated by recent advances in experimental measurements of heavy baryon decays, the charmonium decays of single b baryon are investigated systematically in the framework of perturbative QCD approach. We calculate the decay branching ratios and helicity amplitudes as well as many pertinent decay asymmetry parameters that characterize the angular decay distributions. In particular, we estimate the fragmentation fractions of b quark to b baryons based on the current world averages of the branching ratio multiplied by fragmentation fraction. Some of the featured results are compared with the predictions of other approaches and experimental data. We also evaluate the branching ratios and angular asymmetries of the Σb and Ξb′ decay modes, which have neither been measured experimentally nor calculated theoretically. Our results could be helpful for a future experimental search for them and provide deeper insights in the understanding of the dynamics of heavy-flavor weak decay processes. Published by the American Physical Society 2024

Search for a CP-odd Higgs boson decaying into a heavy CP-even Higgs boson and a Z boson in the ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} and νν¯bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \\overline{\ u}b\\overline{b} $$\\end{document} final states using 140 fb−1 of data collected with the ATLAS detector

A search for a heavy CP-odd Higgs boson, A, decaying into a Z boson and a heavy CP-even Higgs boson, H, is presented. It uses the full LHC Run 2 dataset of pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV collected with the ATLAS detector, corresponding to an integrated luminosity of 140 fb−1. The search for A → ZH is performed in the ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} and νν¯bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \\overline{\ u}b\\overline{b} $$\\end{document} final states and surpasses the reach of previous searches in different final states in the region with mH > 350 GeV and mA > 800 GeV. No significant deviation from the Standard Model expectation is found. Upper limits are placed on the production cross-section times the decay branching ratios. Limits with less model dependence are also presented as functions of the reconstructed m(tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document}) and m(bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ b\\overline{b} $$\\end{document}) distributions in the ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} and νν¯bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \\overline{\ u}b\\overline{b} $$\\end{document} channels, respectively. In addition, the results are interpreted in the context of two-Higgs-doublet models.

Dark photon effects with the kinetic and mass mixing in Z -boson decay processes

Motivated by the most recent measurement of tau polarization in Z→τ+τ− by CMS, we have introduced a new U(1)X gauge boson field X, which can have renormalizable kinetic mixing with the standard model U(1)Y gauge boson field Y. In addition to the kinetic mixing of the dark photon, denoted as σ, there may also be mass mixing introduced by the additional Higgs doublet with a vacuum expectation value participating in U(1)X and electroweak symmetry breaking simultaneously. The interaction of the Z boson with the SM leptons is modified by the introduction of the mixing ratio parameter ε, which quantifies the magnitude of both the mass and kinetic mixing of the dark photon. Initially, we use the tau lepton as an example to explore the Z-boson phenomenology of the dark photon model with both kinetic and mass mixing. The goal is to determine the allowed parameter regions by taking into account constraints from the vector and axial-vector couplings gV,Aτ, the decay branching ratio Br(Z→τ−τ+) and tau-lepton polarization in Z→τ−τ+. We found that the mixing ratio plays important role in the Z-boson features by choosing different ε values. Furthermore, we aim to generalize our analysis from the tau-lepton case to include all fermions by conducting global fits. This allows us to identify viable regions by incorporating relevant fermion constraints and the W/Z mass ratio. Correspondingly, we obtain the fit results with the kinetic mixing parameter σ=0.074±0.021, mixing ratio ε=−1.37±0.46, and dark photon mass mX=275±39 GeV. Our global analysis indicates a preference for a dark photon mass larger than mZ. Published by the American Physical Society 2024

Radiative decay branching ratio of the Hoyle state

Radiative decay branching ratio of the Hoyle state

Measurement of the K+ → π+γγ decay

A sample of 3984 candidates of the K+→π+γγ decay, with an estimated background of 291±14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61±0.17)×10−7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process K+→π+a, a→γγ is also reported.

Study of Bs0→TT(a2(1320), K2*(1430), f2(1270), f2′(1525)) in the perturbative QCD approach

In the present study, the calculations of two-body decays Bs0→TT [T denotes tensor mesons, a2(1320), K2*(1430), f2(1270), f2′(1525)] in the perturbative QCD approach are presented. The ensuing predictions encompass branching ratios, polarization fractions, and direct CP violations, all elucidated in comprehensive detail. It is discerned that (1) for pure annihilation decay, the longitudinal polarization is around 90.0%, whereas the transverse polarizations manifest comparatively diminutive magnitudes. (2) The direct CP asymmetry is directly proportional to the interference between the tree and penguin contributions. For most of the decays investigated within this discourse, the direct CP asymmetry remains modest in magnitude. (3) There are precisely six distinct categories of Feynman diagrams for Bs0→TT, because the tensor mesons cannot be produced through the (V±A) currents or (S±P) density, thereby prohibiting factorizable emission diagrams. The nonfactorizable and annihilation contributions are ascertained to be pivotal in these decay modes. The calculated branching ratios of our calculation for Bs0→TT are at the order of 10−6 and 10−7, which can be tested in the LHCb and Belle II experiments. (4) Mixing exists for the f2(1270) and f2′(1525), just as the η and η′ mixing, the branching ratios about the mixing angle θ are given in this work. However, it is different from f1(1285)−f1(1420), the mixing angle is notably small, thereby resulting in only marginal alterations in the decay branching ratios. Published by the American Physical Society 2024

DDEP re-evaluation of the radioactive decay scheme of 137Cs

A complete re-evaluation of the 137Cs β‒ decay scheme has been performed within the scope of the Decay Data Evaluation Project (DDEP), taking full advantage of the most recent measurements. An evaluated half-life of 30.018 (22) years is recommended, along with a full revision of the β‒ decay branching ratios that also results in a re-evaluation of the absolute emission probability of the 662-keV gamma ray to give a value of 85.01 (20)%. Recommendations for new measurements are also suggested.

Radiative Decay Branching Ratio of the Hoyle State in 12C via Charged Particle Coincidence Techniques

The properties of the Hoyle state in 12C (7.654 MeV, 0+) affect the rate at which carbon, one of the most abundant elements in the Universe, is forged in stars. Recent experiments reported values of its radiative decay branching ratio that are in tension, posing major implications especially in the astrophysical domain. This work reports on an almost background-free measurement of the radiative decay branching ratio of the Hoyle state that exploits charged particle coincidence techniques. The experiment adopts several methodologies to minimize the background and identify the rare signal associated with the radiative decay. Large care is devoted to having under full control two of the major sources of systematic errors in particle-coincidence experiments: the coincidence efficiency and the spurious coincidence rate. We find a radiative decay branching ratio of Γrad/Γtot = 4.2(6) · 10−4. The new finding helps to resolve the tension between recent data published in the literature.

Chelation chemistry of manganese-52 for PET imaging applications

IntroductionDue to its decay and chemical properties, interest in manganese-52 has increased for development of long-lived PET radiopharmaceuticals. Its long half-life of 5.6 days, low average positron energy (242 keV), and sufficient positron decay branching ratio make it suitable for radiolabeling macromolecules for investigating slow biological processes. This work aims to establish suitable chelators for manganese-52 that can be radiolabeled at mild conditions through the evaluation of commercially available chelators. MethodsManganese-52 was produced through the nuclear reaction NatCr(p,n)52Mn by irradiation of natural chromium targets on a TR24 cyclotron followed by purification through ion exchange chromatography. The radiolabeling efficiencies of chelators: DOTA, DiAmsar, TETA, DO3A, NOTA, 4′-Formylbenzo-15-crown-5, Oxo-DO3A, and DFO, were assessed by investigating the impact of pH, buffer type, and temperature. In vitro stability of [52Mn]Mn(DO3A)−, [52Mn]Mn(Oxo-DO3A)−, and [52Mn]Mn(DOTA)2− were evaluated in mouse serum. The radiocomplexes were also evaluated in vivo in mice. Crystals of [Mn(Oxo-DO3A)]− were synthesized by reacting Oxo-DO3A with MnCl2 and characterized by single crystal X-ray diffraction. ResultsYields of 185 ± 19 MBq (5.0 ± 0.5 mCi) (n = 4) of manganese-52 were produced at the end of a 4 h, 15 μA, bombardment with 12.5 MeV protons. NOTA, DO3A, DOTA, and Oxo-DO3A chelators were readily radiolabeled with >96 % radiochemical purity at all conditions. Manganese radiocomplexes of Oxo-DO3A, DOTA, and DO3A remained stable in vitro up to 5 days and exhibited different biodistribution profiles compared to [52Mn]MnCl2. The solid-state structure of Mn-Oxo-DO3A complex was determined by single-crystal X-ray diffraction. ConclusionsDO3A and Oxo-DO3A are suitable chelators for manganese-52 which are readily radiolabeled at mild conditions with high molar activity, and demonstrate both in vitro and in vivo stability.

Search for the Zγ decay mode of new high-mass resonances in pp collisions at [formula omitted] TeV with the ATLAS detector

This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The s=13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb−1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.

Semileptonic decays B_{c} meson to S-wave charmonia and X(3872) within the covariant light-front approach

In this work, we investigate the semileptonic decays of B_{c} meson to eta _{c}(1S,2S,3S), psi (1S,2S,3S) and X(3872) within the framework of covariant light-front quark model (CLFQM). We combine the helicity amplitudes via the corresponding form factors to obtain the branching ratios of the semileptonic decays B_{c}rightarrow eta _{c}(1S, 2S, 3S)ell nu _{ell }, B_{c}rightarrow psi (1S, 2S, 3S))ell nu _{ell } and B_{c}rightarrow X(3872)ell nu _{ell }, with ell =e,mu ,tau . In view of the R_{J/Psi } anomaly released by the LHCb collaboration, it is necessary to systematically calculate the ratios R_X with X=psi (1S,2S,3S),eta _c(1S,2S,3S),X(3872), which are helpful for checking the lepton flavor universality (LFU). We also take into account another two physical observables, the longitudinal polarization fraction f_{L} and the forward–backward asymmetry A_{FB}, which can provide new clues for understanding the R_{J /Psi } anomaly. Such theoretical predictions are necessary and interesting, and can be tested in future LHCb experiments.

CP asymmetries in B meson two-body baryonic decays

We study the CP-odd and CP-even observables of the B mesons decaying into a baryon and antibaryon. We estimate these observables through the P03 model and chiral selection rule. The decay branching ratio of B+→pΛ‾ is calculated to be (2.31±0.69)×10−7, which is consistent with the current experiments. The effects of the B−B‾ oscillations are considered, which largely suppress the direct CP asymmetries in the Bs0 decays. We suggest the experiments to visit Bs0→Λ(→pπ−)Λ‾(→p‾π+), where the time-averaged CP-odd observables are estimated to be large. The direct CP asymmetries of B+→pΛ‾ and B0→pp‾ are found to be (26.2±7.9)% and (−3.1±0.9)% for a positive strong phase and (−36.9±11.1)% and (4.2±1.3)% for a negative strong phase, respectively.

Search for a new heavy scalar particle decaying into a Higgs boson and a new scalar singlet in final states with one or two light leptons and a pair of τ-leptons with the ATLAS detector

A search for a new heavy scalar particle X decaying into a Standard Model (SM) Higgs boson and a new singlet scalar particle S is presented. The search uses a proton-proton (pp) collision data sample with an integrated luminosity of 140 fb−1 recorded at a centre-of-mass energy of s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with the ATLAS detector at the Large Hadron Collider. The most sensitive mass parameter space is explored in X mass ranging from 500 to 1500 GeV, with the corresponding S mass in the range 200–500 GeV. The search selects events with two hadronically decaying τ-lepton candidates from H → τ+τ− decays and one or two light leptons (ℓ = e, μ) from S → VV (V = W, Z) decays while the remaining V boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section σ(pp → X → SH) assuming the same SM-Higgs boson-like decay branching ratios for the S → VV decay. Upper limits on the visible cross-sections σ(pp → X → SH → WWττ) and σ(pp → X → SH → ZZττ) are also set in the ranges 3–26 fb and 6–33 fb, respectively.

PANDORA Project for the study of photonuclear reactions below A=60

Photonuclear reactions of light nuclei below a mass of A=60 are planned to be studied experimentally and theoretically with the PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project. Two experimental methods, virtual photon excitation by proton scattering and real photo absorption by a high-brilliance gamma -ray beam produced by laser Compton scattering, will be applied to measure the photoabsorption cross sections and decay branching ratio of each decay channel as a function of the photon energy. Several nuclear models, e.g. anti-symmetrized molecular dynamics, mean-field and beyond-mean-field models, a large-scale shell model, and ab initio models, will be employed to predict the photonuclear reactions. The uncertainty in the model predictions will be evaluated based on the discrepancies between the model predictions and experimental data. The data and predictions will be implemented in the general reaction calculation code, TALYS. The results will be applied to the simulation of the photo-disintegration process of ultra-high-energy cosmic rays in inter-galactic propagation.

Search for pair-produced vector-like top and bottom partners in events with large missing transverse momentum in pp collisions with the ATLAS detector

A search for pair-produced vector-like quarks using events with exactly one lepton (e or mu ), at least four jets including at least one b-tagged jet, and large missing transverse momentum is presented. Data from proton–proton collisions at a centre-of-mass energy of sqrt{s}=13 text {TeV}, recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb^{-1}, are analysed. Vector-like partners T and B of the top and bottom quarks are considered, as is a vector-like X with charge +5/3, assuming their decay into a W, Z, or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section of T and B quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 text {TeV} assuming mass-degenerate vector-like quarks and branching ratios corresponding to the weak-isospin doublet model, and 1.47 text {TeV} (1.46 text {TeV}) for exclusive T rightarrow Zt (B/X rightarrow Wt) decays. In addition, lower limits on the T and B quark masses are derived for all possible branching ratios.

Multi-species thermalization cascade of energetic particles in the early universe

Heavy long-lived particles are abundant in BSM physics and will, under generic circumstances, get to dominate the energy density of the universe. The resulting matter dominated era has to end through the decay of the heavy matter component particles of mass M, and before the universe cools down to a temperature of a few MeV, in order not to upset the successful predictions of Big Bang Nucleosynthesis. The process of thermalization of their decay products, of initial energy ∼ M/2, into a thermal bath of temperature T primarily involves near-collinear splittings of energetic particles into two particles with lower energy. The correct treatment of these processes requires the inclusion of coherence effects which suppress the splitting rate. We write down and numerically solve the resulting coupled Boltzmann equations including all gauge bosons and fermions of the unbroken phase of the Standard Model (SM). We then comment on the dependence of the nonthermal spectra on the ratio M/T, as well as on the matter decay rate and branching ratios into various SM particles.

Search for an axion-like particle with forward proton scattering in association with photon pairs at ATLAS

A search for forward proton scattering in association with light-by-light scattering mediated by an axion-like particle is presented, using the ATLAS Forward Proton spectrometer to detect scattered protons and the central ATLAS detector to detect pairs of outgoing photons. Proton-proton collision data recorded in 2017 at a centre-of-mass energy of sqrt{s} = 13 TeV were analysed, corresponding to an integrated luminosity of 14.6 fb−1. A total of 441 candidate events were selected. A search was made for a narrow resonance in the diphoton mass distribution, corresponding to an axion-like particle (ALP) with mass in the range 150–1600 GeV. No excess is observed above a smooth background. Upper limits on the production cross section of a narrow resonance are set as a function of the mass, and are interpreted as upper limits on the ALP production coupling constant, assuming 100% decay branching ratio into a photon pair. The inferred upper limit on the coupling constant is in the range 0.04–0.09 TeV−1 at 95% confidence level.