Decay Branching Ratios Research Articles

Laser-assisted nuclear decay spectroscopy of Au176,177,179

A study of the laser-ionized and mass-separated neutron-deficient isotopes Au 176 , 177 , 179 was performed using the Resonance Ionization Laser Ion Source and the Windmill detection setup at ISOLDE, CERN. New and improved data on complex fine-structure α decays of the three isotopes were deduced, providing insight into the low-lying levels in the daughter nuclei Ir 172 , 173 , 175 . New information on the properties of β -decay daughter products Pt 177 , 179 was also obtained. From the first in-source laser spectroscopy measurements of the hyperfine structure in the atomic 267.6-nm transition of Au 176 , the nuclear magnetic moments for both high- and low-spin α -decaying states were deduced. Together with the values determined from the additivity relations, they were used to propose the most probable spins and configurations for both states. The α -decay branching ratios were determined as b α ( Au ls 176 ) = 58 ( 5 ) % and b α ( Au hs 176 ) = 29 ( 5 ) % .

Measurements of Higgs properties from CMS

<p indent=0mm>The Large Hadron Collider (LHC) exhibits the highest colliding energy in the world. The compact muon solenoid (CMS) is one of the main experiments conducted on the LHC, and its objective is to discover the Higgs boson and new particles. In this report, the discovery of the Higgs Boson and the measurements of Higgs properties using CMS RUN2 data were briefly presented. Higgs production modes—ggH, VBF, VH, and ttH—were observed using the CMS, and decay modes— ZZ to four leptons, diphotons, WW, ττ, and bb—were discovered using the CMS. Higgs coupling with vector bosons and third-generation fermions t, b, and τ were measured. Moreover, the Higgs mass, width, decay branching ratio, spin and parity, cross-section, and differential cross-section were studied. The results are consistent with those obtained using the standard model within an error range. The results are mainly obtained using 2016 data, and the errors are large. Nevertheless, the results will be improved when all RUN2 data analyses are published.

Decay spectroscopy of Sc50 and Sc50m to Ti50

The $\beta$ decay of the isomeric and ground state of $^{50}$Sc to the semi-magic nucleus $^{50}_{22}$Ti$_{28}$ has been studied using a $^{50}$Ca beam delivered to the GRIFFIN $\gamma$-ray spectrometer at the TRIUMF-ISAC facility. $\beta$-decay branching ratios are reported to 16 excited states with a total of 38 $\gamma$-ray transitions linking them. These new data significantly expands the information available over previous studies. Relative intensities are measured to less than 0.001$\%$ that of the strongest transition with the majority of $\gamma$-ray transitions observed here in $\beta$ decay for the first time. The data are compared to shell-model calculations utilizing both phenomenologically-derived interactions employed in the ${\it pf}$ shell as well as a state-of-the-art, ${\it ab~initio}$ based interaction built in the valence-space in-medium similarity renormalization group framework.

Effect of initial 3α cluster configurations in C12 on the direct decay of its Hoyle state

We investigate the implications of initial $3\ensuremath{\alpha}$ configurations in $^{12}\mathrm{C}$ corresponding to different decay modes of its Hoyle state on the penetrability ratios. Considering the second ${2}^{+}$ (10.03 MeV) state to be a collective excitation of the Hoyle state, the direct $3\ensuremath{\alpha}$ decay width for the Hoyle state has been calculated using the ratio of the barrier penetration probability of the Hoyle state to the ${2}^{+}$ state. Semiclassical Wentzel--Kramers--Brillouin (WKB) approximation has been employed to determine the penetrability ratio, resulting in an upper limit on the branching ratio of the direct decay of the Hoyle state in ``equal phase-space'' ($\mathrm{DD}\ensuremath{\phi}$) mode as $\frac{{\mathrm{\ensuremath{\Gamma}}}_{3\ensuremath{\alpha}}}{\mathrm{\ensuremath{\Gamma}}}&lt;3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. However, this limit for ``linear chain'' (DDL) decay is $\frac{{\mathrm{\ensuremath{\Gamma}}}_{3\ensuremath{\alpha}}}{\mathrm{\ensuremath{\Gamma}}}&lt;2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$, which is one order of magnitude smaller than the $\mathrm{DD}\ensuremath{\phi}$ decay and the limit for ``equal energy'' (DDE) decay is $\frac{{\mathrm{\ensuremath{\Gamma}}}_{3\ensuremath{\alpha}}}{\mathrm{\ensuremath{\Gamma}}}&lt;1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, which is greater than both $\mathrm{DD}\ensuremath{\phi}$ and DDL decays. It implies that the limit on direct decay probability is strongly dependent on the initial configuration of the $3\ensuremath{\alpha}$ cluster. A further probe using a bent-arm-like $3\ensuremath{\alpha}$ initial configuration shows that the direct decay probability is maximum when the angle of the bent arm is $\ensuremath{\approx}{120}^{\ensuremath{\circ}}$, an important ingredient for understanding the Hoyle-state structure.

First measurement of proton decay from a transfer reaction to Na21

Decay protons from excited states in $^{21}\mathrm{Na}$ populated through a previously reported $^{24}\mathrm{Mg}(p,\ensuremath{\alpha})^{21}\mathrm{Na}$ transfer reaction [Cha et al., Phys. Rev. C 96, 025810 (2017)] were analyzed to extract the proton branching ratios of the energy levels. By utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched $^{24}\mathrm{Mg}$ solid targets, the decay protons were detected in coincidence with $\ensuremath{\alpha}$ particles from the $(p,\ensuremath{\alpha})$ reaction using a silicon strip detector array. Proton decay branching ratios of several $^{21}\mathrm{Na}$ levels were deduced for the $p0$ and $p1$ decay channels to the ground and first excited states in $^{20}\mathrm{Ne}$, respectively.

Semileptonic decay of Bc to ηc and J/ψ on the light front

We study the semileptonic decay of the $B_c (0^-)$ to charmonia through the bottom-to-charm-quark electroweak current in the framework of basis light-front quantization. Explicitly, we calculate the weak transition form factors for processes of $B_c$ decaying into $\eta_c$ or $J/\psi$ based on the corresponding initial and final valence light-front wave functions both obtained from the basis light-front quantization. We also present the corresponding differential decay width and branching ratios, as well as the branching ratios for decays into the $\eta_c'$ and the $\psi'$. We observe unphysical frame dependence of the calculated form factors, which is attributed to only including the valence light-front wave functions. Based on the analysis of current component, we propose a preferred set of frames to calculate these form factors.

Discriminating the HTM and MLRSM models in collider studies via doubly charged Higgs boson pair production and the subsequent leptonic decays * *The research has been supported by the Polish National Science Center (NCN) under grant 2015/17/N/ST2/04067, COST (European Cooperation in Science and Technology) Action CA16201 PARTICLEFACE and the research activities co-financed by the funds granted under the Research Excellence

We present a case study for the doubly charged Higgs boson pair production in and pp colliders with their subsequent decays to four charged leptons. We consider the Higgs Triplet Model ( ), which is not restricted by the custodial symmetry, and the Minimal Left-Right Symmetric Model ( ). These models include scalar triplets with different complexities of scalar potentials and, because of experimental restrictions, completely different scales of non-standard triplet vacuum expectation values. In both models, a doubly charged Higgs boson can acquire a mass of hundreds of gigaelectronvolts, which can be probed at the HL-LHC, future , and hadron colliders. We take into account a comprehensive set of constraints on the parameters of both models coming from neutrino oscillations, LHC, , and low-energy lepton flavor violating data and assume the same mass of . Our finding is that the pair production in lepton and hadron colliders is comparable in both models, though more pronounced in the . We show that the decay branching ratios can be different within both models, leading to distinguishable four-lepton signals, and that the strongest are events yielded by the . Typically, we find that the signals are one order of magnitude larger those in the . For example, the signal for 1 TeV mass results in a clearly detectable significance of for the HL-LHC and for the FCC-hh. Finally, we provide quantitative predictions for the dilepton invariant mass distributions and lepton separations, which help to identify non-standard signals.

Effective field theory approach to lepton number violating τ decays * *Supported in part by the Grants No. NSFC-12035008, No. NSFC-11975130, by The National Key Research and Development Program of China under Grant No. 2017YFA0402200, by the CAS Center for Excellence in Particle Physics (CCEPP). XDM is supported by the MOST (109-2112-M-002-017-MY3, 109-2811-M-002-535)

We continue our endeavor to investigate lepton number violating (LNV) processes at low energies in the framework of effective field theory (EFT). In this work we study the LNV tau decays , where and denote the lowest-lying charged pseudoscalars . We analyze the dominant contributions in a series of EFTs from high to low energy scales, namely the standard model EFT (SMEFT), the low-energy EFT (LEFT), and the chiral perturbation theory ( ). The decay branching ratios are expressed in terms of the Wilson coefficients of dimension-five and -seven operators in SMEFT and the hadronic low-energy constants. These Wilson coefficients involve the first and second generations of quarks and all generations of leptons; thus, they cannot be explored in low-energy processes such as nuclear neutrinoless double beta decay or LNV kaon decays. Unfortunately, the current experimental upper bounds on the branching ratios are too weak to set useful constraints on these coefficients. Alternatively, if we assume the new physics scale is larger than 1 TeV, the branching ratios are well below the current experimental bounds. We also estimate the hadronic uncertainties incurred in applying to decays by computing one-loop chiral logarithms and attempt to improve the convergence of chiral perturbation by employing dispersion relations in the short-distance part of the decay amplitudes.

Low-energy excitations and gamma -decay branchings in ^{124}Sn via (p,p\u2019gamma ) at E_p={15},,hbox {MeV}

The dipole response of the proton-magic nucleus {}^{124}hbox {Sn} was previously investigated with electromagnetic and hadronic probes. Different responses were observed revealing the so-called isospin splitting of the Pygmy Dipole Resonance (PDR). Here we present the results of a new study of {}^{124}hbox {Sn} using inelastic proton scattering at low energies to test an additional probe possibly exciting states of the PDR. The response to the new probe as well as the gamma -decay behavior of excited states were studied. The {}^{124}hbox {Sn}(p,p’gamma ) experiment was performed at E_p = {15},,hbox {MeV} using the combined spectroscopy setup SONIC@HORUS at the Tandem accelerator of the University of Cologne. Proton-gamma coincidences were recorded, enabling a state-to-state analysis due to the excellent energy resolution for both particles and gamma rays. J=1 states in the PDR region were populated in the present inelastic proton scattering experiment. Many gamma -decay branching ratios could be determined.

Candidates for the 5α condensed state in 20Ne

We conducted the coincidence measurement of α particles inelastically scattered from 20Ne at 0° and decay charged particles in order to search for the alpha-particle condensed state. We compared the measured excitation-energy spectrum and decay branching ratio with the statistical-decay-model calculations, and found that the newly observed states at Ex=23.6, 21.8, and 21.2 MeV in 20Ne are strongly coupled to a candidate for the 4α condensed state in 16O. This result presents the first strong evidence that these states are the candidates for the 5α condensed state.

Phenomenology of JPC=3−− tensor mesons

We study the strong and radiative decays of the anti-quark-quark ground state $J^{PC} = 3^{--}$ ($n^{2 S + 1} L_J = 1^3 D_3$) nonet {$\rho_{3} (1690)$, $K_{3}^{\ast} (1780)$, $\phi_{3} (1850)$, $\omega_{3} (1670)$} in the framework of an effective quantum field theory approach, based on the $SU_\mathrm{V}(3)$-flavor-symmetry. The effective model is fitted to experimental data listed by the Particle Data Group. We predict numerous experimentally unknown decay widths and branching ratios. An overall agreement of theory (fit and predictions) with experimental data confirms the $\bar{q} q$ nature of the states and qualitatively validates the effective approach. Naturally, experimental clarification as well as advanced theoretical description is needed for trustworthy quantitative predictions, which is observed from some of the decay channels. Besides conventional spin-$3$ mesons, theoretical predictions for ratios of strong and radiative decays of a hypothetical glueball state $G_3 (4200)$ with $J^{PC} = 3^{--}$ are also presented.

Beam particle tracking with a low-mass mini time projection chamber in the PEN experiment

The international PEN collaboration aims to obtain the branching ratio for the pion electronic decay π+→e+νe(γ), aka πe2, to a relative precision of 5×10−4 or better. The PEN apparatus comprises a number of detection systems, all contributing vital information to the PEN event reconstruction. This paper discusses the design, performance, and Monte Carlo simulation of the mini time projection chamber (mTPC) used for pion, muon, and positron beam particle tracking. We also review the use of the extracted trajectory coordinates in the analysis, in particular in constructing observables critical for discriminating background processes, and in maximizing the fiducial volume of the target in which decay event vertices can be accepted for branching ratio extraction without introducing bias.

Absolute Mo96(p,n)Tc96m+g cross sections and a new branching for the Tc96m decay

Background: Radionuclides in the Mo-Tc region play an important role in modern medical diagnostics. These applications require a $\ensuremath{\gamma}$-emitting radioisotope that is injected into the patient. Various production methods of those radionuclides have been investigated in the past; among them are ($p,x$) reactions on natural or enriched molybdenum. Reliable estimations for the produced activity of the radionuclides and radioactive byproducts are required. Therefore, either precise theoretical calculations or a firm experimental database for the nuclear production reactions are needed. In addition, experimental cross-section data of proton-induced reactions on heavy nuclei are very valuable to test nuclear models that enter theoretical calculations of reaction rates relevant for nuclear astrophysics.Purpose: The present paper reports on experimental cross sections of the $^{96}\mathrm{Mo}(p,n)^{96m+g}\mathrm{Tc}$ reaction. The contribution of the ground-state population as well as for the population of the metastable state in $^{96}\mathrm{Tc}$ are determined individually. The obtained results are very valuable to test existing models that enter statistical model calculations. In addition, the present work aims at remeasuring the branching ratio of the decay of the metastable state $^{96m}\mathrm{Tc}$.Method: Highly enriched $^{96}\mathrm{Mo}$ targets were irradiated with protons at energies between ${E}_{p}=3.9\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ and ${E}_{p}=5.4\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$, which are slightly above the ($p,n$) threshold (${E}_{th}=3.8\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$). By employing an offline analysis, the $\ensuremath{\gamma}$-ray decay of the reaction product was investigated and reaction cross sections were calculated by means of the activation technique.Results: Individual reaction cross sections for the production channel of the metastable state ${\ensuremath{\sigma}}_{m}$ and the ground state ${\ensuremath{\sigma}}_{gs}$ as well as the branching of the $^{96m}\mathrm{Tc}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{96}\mathrm{Tc}$ decay were determined.Conclusion: The measured cross sections are in good agreement with previously measured cross sections as well as with recent Hauser-Feshbach calculations. The new branching ratio for the direct decay of $^{96m}\mathrm{Tc}$ into $^{96}\mathrm{Mo}$ amounts to $4.1{\phantom{\rule{0.16em}{0ex}}}_{\ensuremath{-}0.34}^{+0.39}\phantom{\rule{0.16em}{0ex}}%$ compared to previously reported $2\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}0.5%$.

β−γ spectroscopy of the Os195 nucleus

The $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy of $^{195}\mathrm{Os}$ nucleus was performed at the KEK isotope separation system (KISS). The radioactive isotope of $^{195}\mathrm{Os}$ was produced by the multinucleon transfer reactions of $^{136}\mathrm{Xe}$ beams and $^{198}\mathrm{Pt}$ target. The isotope of interest was separated and extracted by using KISS, which is an argon-gas-cell based laser ion source with a mass separator. Those extracted isotopes are implanted into an aluminized mylar tape, which is surrounded by the multisegmented proportional gas counter (MSPGC) and four clover-type high-purity germanium (HPGe) detectors for the $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy. 27 $\ensuremath{\gamma}$-ray peaks were observed in coincidence with internal conversion electrons and x rays detected by the MSPGC. 21 of them were identified as $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays of the $^{195}\mathrm{Os}$ ground state, where the energies of 19 $\ensuremath{\gamma}$-ray peaks agree with the literature values of transitions observed in $^{195}\mathrm{Ir}(n,\ensuremath{\gamma})$ reactions and two $\ensuremath{\gamma}$-ray peaks were newly found. The $\ensuremath{\beta}$-decay branching ratios of the $^{195}\mathrm{Os}$ ground state were deduced. The obtained log-$ft$ values range from $5.99(4)$ to $7.56(22)$, indicating all $\ensuremath{\beta}$-decay channels are the first forbidden transitions. It suggests that the spin-parity of the $^{195}\mathrm{Os}$ ground state is $3/{2}^{\ensuremath{-}}$, which is consistent with the systematical expectation. The $\ensuremath{\beta}$-decay half-life of the $^{195}\mathrm{Os}$ ground state was evaluated to be 6.5(4) min, which agrees well to the previously known value 6.5(11) min.

Evidence against the Efimov effect in C12 from spectroscopy and astrophysics

Background: The Efimov effect is a universal phenomenon in physics whereby three-body systems are stabilized via the interaction of an unbound two-body sub-systems. A hypothetical state in $^{12}\mathrm{C}$ at 7.458 MeV excitation energy, comprising of a loose structure of three $\alpha$-particles in mutual two-body resonance, has been suggested in the literature to correspond to an Efimov state in nuclear physics. The existence of such a state has not been demonstrated experimentally. Method: Using the combined data sets from two recent experiments, one with the TexAT TPC to measure $\alpha$-decay and the other with Gammasphere to measure $\gamma$-decay of states in $^{12}\mathrm{C}$ populated by $^{12}\mathrm{N}$ and $^{12}\mathrm{B}$ $\beta$-decay respectively, we achieve high sensitivity to states in close-proximity to the $\alpha$-threshold in $^{12}\mathrm{C}$. Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95\% C.L. $\gamma$-decay branching ratio is determined as a function of the $\beta$-decay feeding strength relative to the Hoyle state. In parallel, calculations of the triple-alpha reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around $5 \times 10^{7}$ K. Conclusion: From decay spectroscopy - at the 95\% C.L., the Efimov state cannot exist at 7.458 MeV with any $\gamma$-decay branching ratio unless the $\beta$-strength is less than 0.7\% of the Hoyle state. This limit is evaluated for a range of different excitation energies and the results are not favorable for existence of the hypothetical Efimov state in $^{12}\mathrm{C}$. Furthermore, the triple-alpha reaction rate with the inclusion of a state between 7.43 and 7.53 MeV exceeds the rate required for stars to undergo the red giant phase.

Evaluation of the K35(p,γ)Ca36 reaction rate using the Ca37(p,d)Ca36 transfer reaction

Background: A recent sensitivity study has shown that the K35(p,γ)Ca36 reaction is one of the ten (p,γ) reaction rates that could significantly impact the shape of the calculated x-ray burst light curve. Its reaction rate used up to now in type I x-ray burst calculations was estimated using an old measurement for the mass of Ca36 and theoretical predictions for the partial decay widths of the first 2+ resonance with arbitrary uncertainties. Purpose: In this work, we propose to reinvestigate the K35(p,γ)Ca36 reaction rate, as well as related uncertainties, by determining the energies and decay branching ratios of Ca36 levels, within the Gamow window of x-ray bursts, in the 0.5 to 2 GK temperature range. Method: These properties were studied by means of the one-neutron pickup transfer reaction Ca37(p,d)Ca36 in inverse kinematics using a radioactive beam of Ca37 at 48 MeV nucleon−1. The experiment was performed at the GANIL facility using the liquid hydrogen target CRYPTA, the MUST2 charged particle detector array for the detection of the light charged particles, and a zero degree detection system for the outgoing heavy recoil nuclei. Results: The atomic mass of Ca36 is confirmed and new resonances have been proposed together with their proton decay branching ratios. This spectroscopic information, used in combination with very recent theoretical predictions for the γ-decay width, were used to calculate the K35(p,γ)Ca36 reaction rate. The recommended rate of the present work was obtained within a uncertainty factor of 2 at 1σ. This is consistent with the previous estimate in the x-ray burst temperature range. A large increase of the reaction rate was found at higher temperatures due to two newly discovered resonances. Conclusions: The K35(p,γ)Ca36 thermonuclear reaction rate is now well constrained by the present work in a broad range of temperatures covering those relevant to type I x-ray bursts. Our results show that the K35(p,γ)Ca36 reaction does not affect the shape of the x-ray burst light curve, and that it can be removed from the list of the few influential proton radiative captures reactions having a strong impact on the light curve.Received 18 January 2021Accepted 12 April 2021DOI:https://doi.org/10.1103/PhysRevC.103.055809©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsExplosive burningNuclear astrophysicsNuclear physics of explosive environmentsNucleon induced nuclear reactionsProton emissionRadiative captureTransfer reactionsProperties20 ≤ A ≤ 38Nuclear PhysicsGravitation, Cosmology & Astrophysics

Study on pure annihilation type B→Vγ decays

We investigate the pure annihilation type radiative $B$ meson decays $B^0 \to \phi \gamma$ and $B_s \to \rho^0(\omega)\gamma$ in the soft-collinear effective theory. We consider three types of contributions to the decay amplitudes, including the direct annihilation topology, the contribution from the electro-magnetic penguin operator and the contribution of the neutral vector meson mixings. The numerical analysis shows that the decay amplitudes are dominated by the $\omega-\phi$ mixing effect in the $B^0 \to \phi\gamma$ and $B_s \to \omega\gamma$ modes. The corresponding decay branching ratios are enhanced about three orders of magnitudes relative to the pure annihilation type contribution in these two decay channels. The decay rate of $B_s \to \rho^0\gamma$ is much smaller than that of $B_s \to \omega\gamma$ because of the smaller $\rho^0-\phi$ mixing. The predicted branching ratios $B(B^{0}\rightarrow\phi\gamma)=(3.99^{+1.67}_{-1.46} )\times10^{-9},\,B(B_s\rightarrow\omega\gamma)=(2.01^{+0.81}_{-0.71} )\times10^{-7}$ are to be tested by the Belle-II and LHC-b experiments.

Predicting the [formula omitted] bound states as the partners of [formula omitted

In this work, we investigate the SU(3) flavor symmetry, heavy quark spin symmetry and their breaking effects in the di-meson systems. We prove the existence of the [D‾s∗Ds∗]0++, [D‾s∗Ds/D‾sDs∗]1+-, and [D‾s∗Ds∗]1+- bound states as the consequence of two prerequisites in the SU(3) flavor symmetry and heavy quark spin symmetry. The first prerequisite, the X(3872) as the weakly D‾∗D/D‾D∗ bound state is supported by its mass and decay branching ratios. The second prerequisite, the existence of the [D‾sDs]0++ bound state is supported by the lattice QCD calculation and the observation of χc0(3930) by the LHCb Collaboration. We hope the future experimental analyses can search for these bound states in the B→D(s)(*)D‾(s)(*)h processes (h denotes the light hadrons). The [D‾s∗Ds∗]0++ bound state is also expected to be reconstructed in the J/ψϕ final state in the B→J/ψϕK decay.

Colored scalar mediated nucleon decays to an invisible fermion

We investigate nucleon decays to light invisible fermion mediated by the coloured scalar $\bar S_1= (\bar 3, 1, -2/3)$ and compare them with the results coming from the mediation of $S_1 = (\bar 3,1,1/3)$. In the case of $\bar S_1= (\bar 3, 1, -2/3)$ up-like quarks couple to the invisible fermion, while in the case of $S_1 = (\bar 3,1,1/3)$ the down-like quarks couple to the invisible fermion. For the mass of invisible fermion smaller than the mass $m_p - m_K$, proton (neutron) can decay to $K$ and invisible fermion and the masses of $\bar S_1$ and $S_1$ are in the region $\sim 10^{15}$ GeV. The decays of nucleons to pions and invisible fermion can occur at the tree-level, but in the case of $\bar S_1$ they come from dimension-9 operator and are therefore suppressed by several orders of magnitude compared to the decays into kaons. For the invisible fermion mass in the range $(937.8 \, {\rm MeV},\, 938.8 \, {\rm MeV})$, decay of neutron $n \to\chi \gamma$ induced by $\bar S_1$ is possible at the loop level, while the proton remains stable. The branching ratio of such decay is $\le 10^{-6}$, which does not explain neutron decay anomaly, but is in agreement with the Borexino experiment bound. We comment on low-energy processes with the nucleon-like mass of $\chi$ in the final state as $\Lambda \to \chi \gamma$ and heavy hadron decays to invisibles.

Semileptonic weak decays of antitriplet charmed baryons in the light-front formalism

We systematically study the semileptonic decays of ${\bf B_c} \to {\bf B_n}\ell^+ \nu_{\ell}$ in the light-front constituent quark model, where ${\bf B_c}$ represent the anti-triplet charmed baryons of $(\Xi_c^0,\Xi_c^+,\Lambda_c^+)$ and ${\bf B_n}$ correspond to the octet ones. We determine the spin-flavor structures of the constituents in the baryons with the Fermi statistics and calculate the decay branching ratios (${\cal B}$s) and averaged asymmetry parameters ($\alpha$s) with the helicity formalism. In particular, we find that ${\cal B}( \Lambda_c^+ \to \Lambda e^+ \nu_{e}, ne^+ \nu_{e})=(3.55\pm1.04, 0.36\pm0.15)\%$, ${\cal B}( \Xi_c^+ \to \Xi^0 e^+ \nu_{e},\Sigma^0 e^+ \nu_{e},\Lambda e^+ \nu_{e})=(11.3\pm3.35), 0.33\pm0.09,0.12\pm0.04\%$ and ${\cal B}( \Xi_c^0 \to \Xi^- e^+ \nu_{e},\Sigma^- e^+ \nu_{e})=(3.49\pm0.95,0.22\pm0.06)\%$. Our results agree with the current experimental data. Our prediction for ${\cal B}( \Lambda_c^+ \to n e^+ \nu_{e})$ is consistent with those in the literature, which can be measured by the charm-facilities, such as BESIII and BELLE. Some of our results for the $\Xi_c^{+(0)}$ semileptonic channels can be tested by the experiments at BELLE as well as the ongoing ones at LHCb and BELLEII.