Three-body Decay Research Articles

Exploring the manifestation and nature of a dineutron in two-neutron emission using a dynamical dineutron model

Emission of two neutrons or two protons in reactions and decays is often discussed in terms of "dineutron" or "diproton" emission. The discussion often leans intuitively on something described by Migdal-Watson approximation. In this work we propose a way to formalize situations of dineutron emission. It is demonstrated that properly formally defined dineutron emission may reveal properties which are drastically different from those traditionally expected, and properties which are actually observed in three-body decays.

Three-body decays B→ϕ(ρ)Kγ in perturbative QCD approach

We study the three-body radiative decays $B\to \phi(\rho) K\gamma$ induced by a flavor-changing neutral current in the perturbative QCD approach. Pseudoscalar-vector ($PV$) distribution amplitudes (DAs) are introduced for the final-state $\phi K$ ($\rho K$) pair to capture important infrared dynamics in the region with a small $PV$-pair invariant mass. The dependence of these $PV$ DAs on the parton momentum fraction is parametrized in terms of the Gegenbauer polynomials, and the dependence on the meson momentum fraction is derived through their normalizations to time-like $PV$ form factors. In addition to the dominant electromagnetic penguin, the subleading chromomagnetic penguin, quark-loop and annihilation diagrams are also calculated. After determining the $PV$ DAs from relevant branching-ratio data, the direct $CP$ asymmetries and decay spectra in the $PV$-pair invariant mass are predicted for each $B\to \phi(\rho) K\gamma$ mode.

Effective Majorana mass matrix from tau and pseudoscalar meson lepton number violating decays

An observation of any lepton number violating process will undoubtedly point towards the existence of new physics and indirectly to the clear Majorana nature of the exchanged fermion. In this work, we explore the potential of a minimal extension of the Standard Model via heavy sterile fermions with masses in the [0.1 − 10] GeV range concerning an extensive array of “neutrinoless” meson and tau decay processes. We assume that the Majorana neutrinos are produced on-shell, and focus on three-body decays. We conduct an update on the bounds on the active-sterile mixing elements, left|{U}_{ell }{{}_{{}_{alpha}}}_4{U}_{ell }{{}_{{}_{beta}}}_4right| , taking into account the most recent experimental bounds (and constraints) and new theoretical inputs, as well as the effects of a finite detector, imposing that the heavy neutrino decay within the detector. This allows to establish up-to-date comprehensive constraints on the sterile fermion parameter space. Our results suggest that the branching fractions of several decays are close to current sensitivities (likely within reach of future facilities), some being already in conflict with current data (as is the case of K+ → ℓα+ℓβ+π−, and τ− → μ+π−π−). We use these processes to extract constraints on all entries of an enlarged definition of a 3 × 3 “effective” Majorana neutrino mass matrix mναβ.

Weak decays of doubly heavy baryons: multi-body decay channels

The newly-discovered Xi _{cc}^{++} decays into the Lambda _{c}^+ K^-pi ^+pi ^+, but the experimental data has indicated that this decay is not saturated by any two-body intermediate state. In this work, we analyze the multi-body weak decays of doubly heavy baryons Xi _{cc}, Omega _{cc}, Xi _{bc}, Omega _{bc}, Xi _{bb} and Omega _{bb}, in particular the three-body nonleptonic decays and four-body semileptonic decays. We classify various decay modes according to the quark-level transitions and present an estimate of the typical branching fractions for a few golden decay channels. Decay amplitudes are then parametrized in terms of a few SU(3) irreducible amplitudes. With these amplitudes, we find a number of relations for decay widths, which can be examined in future.

Model-independent partial wave analysis using a massively-parallel fitting framework

The functionality of GooFit, a GPU-friendly framework for doing maximum-likelihood fits, has been extended to extract model-independent -wave amplitudes in three-body decays such as D+ → h+h+h−. A full amplitude analysis is done where the magnitudes and phases of the -wave amplitudes are anchored at a finite number of m2(h+h−) control points, and a cubic spline is used to interpolate between these points. The amplitudes for -wave and -wave intermediate states are modeled as spin-dependent Breit-Wigner resonances. GooFit uses the Thrust library, with a CUDA backend for NVIDIA GPUs and an OpenMP backend for threads with conventional CPUs. Performance on a variety of platforms is compared. Executing on systems with GPUs is typically a few hundred times faster than executing the same algorithm on a single CPU.

Performance studies of GooFit on GPUs vs RooFit on CPUs while estimating the statistical significance of a new physical signal

In order to test the computing capabilities of GPUs with respect to traditional CPU cores a high-statistics toy Monte Carlo technique has been implemented both in ROOT/RooFit and GooFit frameworks with the purpose to estimate the statistical significance of the structure observed by CMS close to the kinematical boundary of the J/ψϕ invariant mass in the three-body decay B+ → J/ψϕK+. GooFit is a data analysis open tool under development that interfaces ROOT/RooFit to CUDA platform on nVidia GPU. The optimized GooFit application running on GPUs hosted by servers in the Bari Tier2 provides striking speed-up performances with respect to the RooFit application parallelised on multiple CPUs by means of PROOF-Lite tool. The considerable resulting speed-up, evident when comparing concurrent GooFit processes allowed by CUDA Multi Process Service and a RooFit/PROOF-Lite process with multiple CPU workers, is presented and discussed in detail. By means of GooFit it has also been possible to explore the behaviour of a likelihood ratio test statistic in different situations in which the Wilks Theorem may or may not apply because its regularity conditions are not satisfied.

Three-body fragmentation of multiply charged nitrous oxide induced by Ar8+ - and Xe15+ -ion impact

We study multiple ionization and subsequent dissociation of nitrous oxide $({\mathrm{N}}_{2}\mathrm{O})$ in collisions with 1 a.u. ${\mathrm{Ar}}^{8+}$ and ${\mathrm{Xe}}^{15+}$ ions. The experiments are performed by using a recoil ion momentum spectrometer (RIMS) equipped with a position- and time-sensitive detector which allows the measurement of the momenta of fragment ions in coincidence. By measuring the momentum vectors of the recoiling fragment ions various important parameters, such as kinetic energy release and those related to molecular structure prior to fragmentation, have been derived. Furthermore, the projectile-charge-state dependence of the fragmentation dynamics of ${\mathrm{N}}_{2}\mathrm{O}$ is investigated and a very mild dependence has been noticed in a few channels. In addition, we also study the concerted and sequential mechanisms in the three-body decay of ${\mathrm{N}}_{2}{\mathrm{O}}^{q+}$ (where $q\phantom{\rule{4pt}{0ex}}\ensuremath{\le}7)$. It has been observed that ${\mathrm{N}}_{2}{\mathrm{O}}^{q+}$ breaks up mainly in a concerted manner except for the ${\mathrm{N}}_{2}{\mathrm{O}}^{3+}\ensuremath{\rightarrow}{\mathrm{N}}^{+}+{\mathrm{N}}^{+}+{\mathrm{O}}^{+}$ (1,1,1) and ${\mathrm{N}}_{2}{\mathrm{O}}^{4+}\ensuremath{\rightarrow}{\mathrm{N}}^{2+}+{\mathrm{N}}^{+}+{\mathrm{O}}^{+}$ (2,1,1) channels. For both these channels, the presence of an intermediate rotating ${\mathrm{NO}}^{2+}$ has been identified. Furthermore, by using Dalitz plot analysis, we have been able to separate various mutually mixed channels of highly charged ${\mathrm{N}}_{2}{\mathrm{O}}^{q+}$.

Search for right-handed neutrinos from dark matter annihilation with gamma-rays

Several extensions of the Standard Model contain right-handed (sterile) neutrinos in the GeV-TeV mass range. Due to their mixing with the active neutrinos, they may give rise to novel effects in cosmology, neutrino physics, and collider searches. In addition, right-handed neutrinos can also appear as final states from dark matter annihilations, with important implications for dark matter indirect detection searches. In this paper, we use current data from the Fermi Large Area Telescope (6-year observation of dwarf spheroidal galaxies) and H.E.S.S. (10-year observation of the Galactic center) to constrain the annihilation of dark matter into right-handed neutrinos. We consider right-handed neutrino with masses between 10 GeV and 1 TeV, including both two-body and three-body decays, to derive bounds on the dark matter annihilation rate, ⟨ σ v⟩, as a function of the dark matter mass. Our results show, in particular, that the thermal dark matter annihilation cross section, 3× 10−26 cm3 s−1 , into right-handed neutrinos is excluded for dark matter masses smaller than 200 GeV.

Three-body decays of Ds+ → η(η′)π+π0

In this paper, we investigate the three-body decays of [Formula: see text] meson to [Formula: see text] and [Formula: see text] final state mesons, using a simple model based on the framework of the factorization approach. As we know, there are tree and emission-annihilation diagrams for these decay modes in the factorization approach. We calculate the total [Formula: see text] and [Formula: see text] branching ratios, including the nonresonant and resonances contributions, and in view of the [Formula: see text] mixing, by applying the Dalitz plot analysis and obtain [Formula: see text] and [Formula: see text], while the experimental values are [Formula: see text] and [Formula: see text], respectively. The branching ratios obtained in our model are partly compatible with the experimental results.

Three-Body Decay of Λc*(2595) and Λc*(2625) with consideration of Σc(2455)π and Σc*(2520)π in intermediate States

Three-body decay of charmed baryons $\Lambda^*_c(2595)$ and $\Lambda^*_c(2625)$ into $\Lambda_c \pi \pi$ are studied with effective Lagrangians in which the coupling constants are extracted from the non-relativistic quark model. We take into account sequential processes going through $\Sigma_c (2455)$ and $\Sigma^*_c (2520)$ in intermediate states. The total decay widths are sensitive to the coupling of $\Lambda^*_c$ with $\Sigma_c \pi$ open channel and to $\Sigma^*_c \pi$ closed channel. We find that $\Lambda_c^*(2595)$ and $\Lambda_c^*(2625)$ with $\lambda$ mode assignment can explain nicely the experimental data. We also show invariant mass distributions of $\Lambda_c^*(2595)$ and $\Lambda_c^*(2625)$ decays which are significantly different for various quark configurations.

Decays of the vector glueball

We calculate two- and three-body decays of the (lightest) vector glueball into (pseudo)scalar, (axial-)vector, as well as pseudovector and excited vector mesons\textbf{ }in the framework of a model of QCD. While absolute values of widths cannot be predicted because the corresponding coupling constants are unknown, some interesting branching ratios can be evaluated\textbf{ }by setting the mass of the yet hypothetical vector glueball to $3.8$ GeV as predicted by quenched Lattice QCD\textbf{.} We find that the decay mode $\omega\pi\pi$ should be one of the largest (both through the decay chain $\mathcal{O}\rightarrow b_{1}\pi\rightarrow$ $\omega\pi\pi$ and through the direct coupling $\mathcal{O}\rightarrow\omega\pi\pi$)$.$ Similarly, the (direct and indirect) decay into $\pi KK^{\ast}(892)$ is sizable. Moreover, the decays into $\rho\pi$ and $K^{\ast}(892)K$ are, although subleading, possible and could play a role in explaining the $\rho\pi$ puzzle of the charmonium state $\psi(2S)$ thank to a (small) mixing with the vector glueball. The vector glueball can be directly formed at the ongoing BESIII experiment as well as at the future PANDA experiment at the FAIR facility. If the width is sufficiently small ($\lesssim100$ MeV) it should not escape future detection. It should be stressed that the employed model is based on some inputs and simplifying assumptions: the value of glueball mass (at present, the quenched lattice value is used), the lack of mixing of the glueball with other quarkonium states, and the use of few interaction terms. It then represents a first step toward the identification of the main decay channels of the vector glueball, but shall be improved when corresponding experimental candidates and/or new lattice results will be available.

Alpha-clustering effects on 16O( $\gamma$ γ ,np)14N in the quasi-deuteron region

Photonuclear reaction in the quasi-deuteron regime has been investigated in an extended Quantum Molecular Dynamics model at a photon energy of 70-120 MeV. Particularly, the reaction channel of 16O( $\gamma$ ,np)14N is focused where 16O is considered as having different $\alpha$ -clustering configurations as well as regular spherical structure. Because of three-body decay from the above photonuclear reaction, we can investigate many observables including the recoil momentum, missing energy, pair momentum/energy and opening angle of ejected neutron and proton, hyper-angle and hyper-radius distributions, etc. These quantitative results demonstrate an obvious difference among different initial configurations of 16O, which can be attributed to the spatial-momentum correlation of a neutron-proton pair inside the nucleus. The results illustrate that photonuclear reaction is a good tool to explore different $\alpha$ -clustering structures.

Decay properties of P -wave charmed baryons from light-cone QCD sum rules

We study decay properties of the $P$-wave charmed baryons using the method of light-cone QCD sum rules, including the $S$-wave decays of the flavor $\mathbf{\bar 3}_F$ $P$-wave charmed baryons into ground-state charmed baryons accompanied by a pseudoscalar meson ($\pi$ or $K$) or a vector meson ($\rho$ or $K^*$), and the $S$-wave decays of the flavor $\mathbf{6}_F$ $P$-wave charmed baryons into ground-state charmed baryons accompanied by a pseudoscalar meson ($\pi$ or $K$). We study both two-body and three-body decays which are kinematically allowed. We find two mixing solutions from internal $\rho$- and $\lambda$-mode excitations, which can well describe both masses and decay properties of the $\Lambda_c(2595)$, $\Lambda_c(2625)$, $\Xi_c(2790)$ and $\Xi_c(2815)$. We also discuss the possible interpretations of $P$-wave charmed baryons for the $\Sigma_c(2800)$, $\Xi_c(2930)$, $\Xi_c(2980)$, and the recently observed $\Omega_c(3000)$, $\Omega_c(3050)$, $\Omega_c(3066)$, $\Omega_c(3090)$, and $\Omega_c(3119)$.

Constraining secret gauge interactions of neutrinos by meson decays

Secret coupling of neutrinos to a new light vector boson, $Z'$, with a mass smaller than 100 MeV is motivated within a myriad of scenarios which are designed to explain various anomalies in particle physics and cosmology. Due to the longitudinal component of the massive vector boson, the rates of three-body decay of charged mesons ($M$) such as the pion and the kaon to the light lepton plus neutrino and $Z'$ ($M \to l \nu Z'$) are enhanced by a factor of $(m_M/m_{Z'})^2$. On the other hand, the standard two body decay $M \to l \nu$ is suppressed by a factor of $(m_l/m_M)^2$ due to chirality. We show that in the case of ($M \to e \nu Z^\prime$), the enhancement of $m_M^4/m_e^2 m_{Z^\prime}^2\sim 10^8-10^{10}$ relative to two-body decay ($M \to e \nu$) enables us to probe very small values of gauge coupling for $\nu_e$. The strongest bound comes from the $R_K\equiv Br(K \to e +\nu)/Br(K \to \mu +\nu)$ measurement in the NA62 experiment. The bound can be significantly improved by customized searches for signals of three-body charged meson decay into the positron plus missing energy in the NA62 and/or PIENU data.

In-flight cLFV conversion: {e-mu }, {e-tau } and {mu -tau } in minimal extensions of the standard model with sterile fermions

We revisit charged lepton flavour in-flight conversions, in which a beam of electrons or muons is directed onto a fixed target, e + N rightarrow mu +N, e + N rightarrow tau +N and mu + N rightarrow tau +N, focusing on elastic interactions with a nucleus N. After a general discussion of this observable, we carry a full phenomenological analysis in the framework of minimal Standard Model extensions via sterile neutrinos, with a strong emphasis on the rôle of the increasingly more stringent constraints arising from other (low-energy) charged lepton flavour-violation observables. Despite the potential interest of this observable, in particular in the light of certain upcoming facilities with the capability of very intense lepton beams, our study suggests that due to current bounds on three-body decays (ell _i rightarrow 3 ell _j) and mu -e conversion in nuclei, the expected number of conversions in such a minimal framework is dramatically reduced. An experimental observation of such a conversion would thus signal the presence of another source of flavour violation, possibly at tree level.

Dark sectors and enhanced h \u2192 \u03c4 \u03bc transitions

LHC searches with τ leptons in the final state are always inclusive in missing-energy sources. A signal in the flavor-violating Higgs decay search, h → τ μ, could therefore equally well be due to a flavor conserving decay, but with an extended decay topology with additional invisible particles. We demonstrate this with the three-body decay h → τ μφ, where φ is a flavorful mediator decaying to a dark-sector. This scenario can give thermal relic dark matter that carries lepton flavor charges, a realistic structure of the charged lepton masses, and explain the anomalous magnetic moment of the muon, (g − 2)μ, while simultaneously obey all indirect constraints from flavor-changing neutral currents. Another potentially observable consequence is the broadening of the collinear mass distributions in the h → τ μ searches.

Amplitude analysis of D0→K−π+π+π−

We present an amplitude analysis of the decay D0→K−π+π+π− based on a data sample of 2.93 fb−1 acquired by the BESIII detector at the ψ(3770) resonance. With a nearly background free sample of about 16000 events, we investigate the substructure of the decay and determine the relative fractions and the phases among the different intermediate processes. Our amplitude model includes the two-body decays D0→K¯*0ρ0, D0→K−a1+(1260) and D0→K1−(1270)π+, the three-body decays D0→K¯*0π+π− and D0→K−π+ρ0, as well as the four-body nonresonant decay D0→K−π+π+π−. The dominant intermediate process is D0→K−a1+(1260), accounting for a fit fraction of 54.6%.Received 3 February 2017DOI:https://doi.org/10.1103/PhysRevD.95.072010© 2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHadronic decaysPhysical SystemsCharmed mesonsParticles & Fields

Decay width of the d⁎(2380)→NNπ process in a chiral constituent quark model

The width of three-body single-pion decay process d⁎→NNπ0,± is calculated by using the d⁎ wave function obtained from our chiral SU(3) constituent quark model calculation. The effect of the dynamical structure on the width of d⁎ is taken into account in both the single ΔΔ channel and coupled ΔΔ+CC two-channel approximations. Our numerical result shows that in the coupled-channel approximation, namely, the hidden-color configuration being considered, the obtained partial decay width of d⁎→NNπ is about several hundred keV, while in the single ΔΔ channel it is just about 2∼3 MeV. We, therefore, conclude that the partial width in the single-pion decay process of d⁎ is much smaller than the widths in its double-pion decay processes. Our prediction may provide a criterion for judging different interpretations of the d⁎ structure, as different pictures for the d⁎ may result quite different partial decay width.

The three-body decays B(s) → ρf0(X)→ρπ−π+ in pQCD factorization approach

In this paper, we study three-body decays B(s)→ρf0(X)→ρπ−π+ in the perturbative QCD (pQCD) factorization approach. By using two-pion distribution amplitudes (DAs), these decays can proceed mainly via quasi-two-body channels. The Flatté model for the f0(980) resonance and the Breit–Wigner formula for the f0(500), f0(1500), and f0(1790) resonances are adopted to parameterize the time-like scalar form factors. We also use Bugg's model for the wide f0(500) as a comparison. We evaluate S-wave resonance contributions, and show the contributions to the B(s)→ρπ+π− decay spectrums with respect to the two-pion invariant mass M(π+π−). The pQCD prediction of B→ρf0(500) is B(B0→ρ0f0(500))=4.43×10−8, B(B+→ρ+f0(500))=3.84×10−8 for Breit–Wigner model, and B(B0→ρ0f0(500))=4.91×10−8, B(B+→ρ+f0(500))=4.07×10−8 for Bugg's model. We also predict other resonance contributions B(Bs→ρ0f0(980))=8.91×10−8, B(Bs→ρ0f0(1500))=1.43×10−8 and B(Bs→ρ0f0(1790))=2.78×10−9. This study in pQCD approach can provide a ready reference to the running and forthcoming experiments. Further improvements in theories and experiments are expected so that we can understand the inner structure of the scalar mesons f0.

AMS-02 positron excess and indirect detection of three-body decaying dark matter

We consider indirect detection of meta-stable dark matter particles decaying into a stable neutral particle and a pair of standard model fermions. Due to the softer energy spectra from the three-body decay, such models could potentially explain the AMS-02 positron excess without being constrained by the Fermi-LAT gamma-ray data and the cosmic ray anti-proton measurements. We scrutinize over different final state fermions, paying special attention to handling of the cosmic ray background and including various contributions from cosmic ray propagation with the help of the LIKEDM package. It is found that primary decays into an electron-positron pair and a stable neutral particle could give rise to the AMS-02 positron excess and, at the same time, stay unscathed against the gamma-ray and anti-proton constraints. Decays to a muon pair or a mixed flavor electron-muon pair may also be viable depending on the propagation models. Decays to all other standard model fermions are severely disfavored.