Cascade Decay Research Articles

The measurable angular distribution of {Lambda}_b^0to {Lambda}_c^{+}left(to {Lambda}^0{pi}^{+}right){tau}^{-}left(to {pi}^{-}{v}_{tau}right){overline{v}}_{tau } decay

In {Lambda}_b^0to {Lambda}_c^{+}left(to {Lambda}^0{pi}^{+}right){tau}^{-}{overline{v}}_{tau } decay, the solid angle of the final-state particle τ− cannot be determined precisely since the decay products of the τ− include an undetected ντ. Therefore, the angular distribution of this decay cannot be measured. In this work, we construct a measurable angular distribution by considering the subsequent decay τ−→ π−ντ. The full cascade decay is {Lambda}_b^0to {Lambda}_c^{+}left(to {Lambda}^0{pi}^{+}right){tau}^{-}left(to {pi}^{-}{v}_{tau}right){overline{v}}_{tau } . The three-momenta of the final-state particles Λ0, π+, and π− can be measured. Considering all Lorentz structures of the new physics (NP) effective operators and an unpolarized initial Λb state, the five-fold differential angular distribution can be expressed in terms of ten angular observables {mathcal{K}}_ileft({q}^2,{E}_{pi}right) . By integrating over some of the five kinematic parameters, we define a number of observables, such as the Λc spin polarization {P}_{Lambda_c}left({q}^2right) and the forward-backward asymmetry of π− meson AFB(q2), both of which can be represented by the angular observables {hat{mathcal{K}}}_ileft({q}^2right) . We provide numerical results for the entire set of the angular observables {hat{mathcal{K}}}_ileft({q}^2right) and {hat{mathcal{K}}}_i both within the Standard Model and in some NP scenarios, which are a variety of best-fit solutions in seven different NP hypotheses. We find that the NP which can resolve the anomalies in overline{B}to {D}^{left(ast right)}{tau}^{-}{overline{v}}_{tau } decays has obvious effects on the angular observables {hat{mathcal{K}}}_ileft({q}^2right) , except {hat{mathcal{K}}}_{1 ss}left({q}^2right) and {hat{mathcal{K}}}_{1 cc}left({q}^2right) .

A Mathematical Model of Two-Way Heterodiffusion Processes with Cascade Decay of Migrating Particles

We construct a mathematical model of mass transfer processes with regard for the local structure of the medium and cascade decay of foreign particles migrating in two different ways. For a specific scheme of cascade decay, we deduce the mass balance relations for the components of the system and obtain linear equations of state and kinetic relations. The conditions for the intensities of mass production in different components of the system are established. The key systems of the model equations of two-way heterodiffusion with cascade decay of migrating particles are obtained in the case where the decay of substance in the current stage serves as a mass source in the next stage.

Simulation of a quantum jump in three-level systems using photonic Gaussian modes

Multilevel quantum systems lose coherence due to quantum jumps. One example is the spontaneous decay between the internal levels of an atom. In this work, we propose and implement a way to simulate experimentally a three-level system under a quantum jump using a three-mode photonic system. We simulated three different dynamics of spontaneous decay in a three-level atomic system: cascade decay, $\mathrm{\ensuremath{\Lambda}}$ decay, and $V$ decay. With an attenuated light coherent source at photon level, we have prepared photons in a three-path superposition state, which was encoded in parallel Gaussian modes. By programming a spatial light modulator (SLM) for producing periodical phase modulation, we were able to implement the corresponding dynamical maps for quantum jumps in terms of the Kraus operator decomposition. Our results have verified experimentally the variation of the population levels and the decoherence effects caused by quantum jumps in the three decay configurations of the three-level system.

Bifurcation of excited state trajectories toward energy transfer or electron transfer directed by wave function symmetry

This work explores the concept that differential wave function overlap between excited states can be engineered within a molecular chromophore. The aim is to control excited state wave function symmetries, so that symmetry matches or mismatches result in differential orbital overlap and define low-energy trajectories or kinetic barriers within the excited state surface, that drive excited state population toward different reaction pathways. Two donor-acceptor assemblies were explored, where visible light absorption prepares excited states of different wave function symmetry. These states could be resolved using transient absorption spectroscopy, thanks to wave function symmetry-specific photoinduced optical transitions. One of these excited states undergoes energy transfer to the acceptor, while another undertakes a back-electron transfer to restate the ground state. This differential behavior is possible thanks to the presence of kinetic barriers that prevent excited state equilibration. This strategy can be exploited to avoid energy dissipation in energy conversion or photoredox catalytic schemes.

Ligand field states dominate excited state decay in trans-[Ru(py)4Cl2] MLCT chromophores

In this contribution, the ultrafast excited state dynamics of a family of trans-[Ru(L)4Cl2] metal to ligand charge transfer chromophores, where L = pyridine, 4-tert-butylpyridine, 4-methoxypyridine and 4,4′-bipyridine, are studied using a combination of femtosecond transient absorption spectroscopy and (TD)DFT theoretical methods. Ligand field states were directly observed and found to dominate the excited state decay cascade, leading to ligand photosubstitution. The internal conversion process that feeds ligand field states, indirectly after light absorption, occurs prior to thermal relaxation in <2 ps for L = pyridine, 4-tert-butylpyridine and 4-methoxypyridine, suggesting a downhill process. This is consistent with DFT calculations, that indicate the lowest triplet is a ligand field state. The exception is for L = 4,4′-bpy, where a slower internal conversion of 34 ps points to a thermally relaxed population undergoing an uphill process with a small energy barrier. Matching this notion, DFT yields a metal to ligand charge transfer character for the lowest triplet of this compound.

Optimal readout of superconducting qubits exploiting high-level states

High-fidelity initialization, manipulation, and measurement of qubits are important in quantum computing. For the Google’s Sycamore processor, the gate fidelity of single- and two-qubit logic operations has improved to>99.6%, whereas single-shot measurement fidelity remains at the level of 97%, which severely limits the application of the superconducting approach to large-scale quantum computing. The current measurement scheme relies on the dispersive interaction between the qubit and the readout resonator, which was proposed back in 2004. However, the measurement fidelity is limited by the trade-off between the state separation and relaxation time of the two-level system. Recently, an exciting phenomenon was observed experimentally, wherein the separation-decay limit could be alleviated by exploiting the cascade decay nature of the higher levels; however, the mechanism and effectiveness of this phenomenon are still unclear. Herein, we present a theoretical tool to extract different types of errors in high-level states encoding dispersive measurement. For the realistic parameters of Google’s Sycamore processor, the use of state |2〉 is sufficient to suppress 92% of the decay readout error on average, where the total readout error is dominated by the background thermal excitation. We also show counter-intuitively that, the assistance of high-level states is effective in the measurement of logic 0, where there is no decay process.

Search for top squark pair production using dilepton final states in {text {p}}{text {p}} collision data collected at sqrt{s}=13,text {TeV}

A search is presented for supersymmetric partners of the top quark (top squarks) in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from {text {b}}quarks, and missing transverse momentum. The search uses data from proton-proton collisions at sqrt{s}=13,text {TeV} collected with the CMS detector, corresponding to an integrated luminosity of 137,{text {fb}}^{-1}. Hypothetical signal events are efficiently separated from the dominant top quark pair production background with requirements on the significance of the missing transverse momentum and on transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced lightest top squarks. For top squarks decaying exclusively to a top quark and a lightest neutralino, lower limits are placed at 95% confidence level on the masses of the top squark and the neutralino up to 925 and 450,text {GeV}, respectively. If the decay proceeds via an intermediate chargino, the corresponding lower limits on the mass of the lightest top squark are set up to 850,text {GeV} for neutralino masses below 420,text {GeV}. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1.4,text {TeV} and 900,text {GeV} respectively for the top squark and the lightest neutralino.

Ball Lightning as Source of High-Energy Particles When It Enters a Dense Medium

Experiments have been carried out to study the anomalous passage of laboratory-produced ball lightning through solid-state sheets. The passing of the ball lightning within the standard model can be explained by cascading generation of particles at entering of high-energetic protons of the ball lightning into a dense matter. The process of energy conversion of its own poloidal magnetic field of the ball lightning into the kinetic energy of its charged particles occurs in this case. The energy of protons becomes sufficient for the generation of charged pions and their subsequent cascade decay. The decay of pions leads to the appearance of negative and positive muons, as well as muon antineutrino and muon neutrino. This fact is confirmed by the presence of a passed ball lightning and a high potential of variable polarity in the region above the solid-state sheet after the ball lightning passing through it. The dark ball lightning also found was in the experiments. The laboratory ball lightning opens up new perspectives in many areas of research and applications and may have a positive impact on attempts to solve the energy problem based on muon-catalyzed nuclear fusion.

Implementation of the ATLAS-SUSY-2018-31 analysis in the MadAnalysis 5 framework (sbottoms with multi-bottoms and missing transverse energy; 139 fb−1)

We present the implementation, in the MadAnalysis 5 framework, of the ATLAS-SUSY-2018-31 search for new physics, and document the validation of this implementation. This analysis targets, with 139 fb[Formula: see text] of proton–proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, the production of a pair of supersymmetric bottom squarks when they further decay through a cascade decay involving the second lightest neutralino and a Standard Model Higgs boson. The validation of our work is based on three benchmark scenarios targeting different kinematic configurations. The first of them considers a new physics spectrum leading to the presence of high-[Formula: see text] [Formula: see text]-jets originating from sbottom decays, whereas the last two, that differ by the neutralino mass spectrum, are dedicated to the compressed regime and thus yield the presence of soft [Formula: see text]-jets in the final state. We obtain an agreement between the MadAnalysis 5 predictions and the official ATLAS results at the level of 20–30%, the largest discrepancies being related to cases exhibiting a poor Monte Carlo numerical precision at the level of the official ATLAS results.

Effective field theory in AdS: Continuum regime, soft bombs, and IR emergence

We consider a scalar field in a slice of Lorentzian five-dimensional AdS at arbitrary energies. We show that the presence of bulk interactions separates the behavior of the theory into two different regimes: Kaluza-Klein and continuum. We determine the transition scale between these regimes and show that UV-brane correlation functions are independent of IR-brane-localized operators for four-momenta beyond this transition scale. The same bulk interactions that induce the transition also give rise to cascade decays. We study these cascade decays for the case of a cubic self-interaction in the continuum regime. We find that the cascade decay progresses slowly towards the IR region and gives rise to soft spherical final states, in accordance with former results from both gravity and CFT. We identify a recursion relation between integrated squared amplitudes of different leg numbers and thus evaluate the total rate. We find that cascade decays in the continuum regime are exponentially suppressed. This feature completes the picture of the IR brane as an emergent sector as seen from the UV brane. We briefly discuss consistency with the holographic dual description of glueballs and some implications for dark sector models.

Femtosecond fragmentation of CS2 after sulfur 1s ionization: interplay between Auger cascade decay, charge delocalization, and nuclear motion

We present a combined experimental and theoretical study of the fragmentation of molecular CS2 after sulfur 1s Auger cascade decay, consisting of electron–multi-ion coincidence spectra of charged fragments and theoretical simulations combining density functional theory and molecular dynamics. On the experimental side, a procedure for a complete determination of all sets of ions formed is described. For many of the fragmentation channels, we observed a higher charge in one of the sulfur atoms than the other atoms. Based on these observations and the theoretical simulations where the time scale of the nuclear motion and decay is taken into account, we propose that KLL Auger decay after the 1s core hole creation, via 2p double hole states, results in highly charged and strongly repulsive states with one localized core hole. These localized core holes are sufficiently long-lived that some will decay after fragmentation of the molecular ion, thereby efficiently impeding charge exchange between the fragments.

Signatures of a flavor changing Z′ boson in Bq → γZ′

Rare B meson decays offer an opportunity to probe a light hidden Z′ boson. In this work we explore a new channel Bq→γZ′ (q=d,s) followed by a cascade decay of Z′ into an invisible (neutrino or dark matter) or charged lepton pair ℓ+ℓ− (ℓ=e,μ). The study is based on a simplified effective model where the down quark sector has tiny flavor-changing neutral current couplings with Z′. For the first time, we calculate BR(Bq→γZ′) at the leading power of 1/mb and 1/Eγ. Confronting with the strong constraints from semi-invisible decays of B meson, we find that the branching ratio for Bd→invisible+γ can be larger than its Standard Model background prediction, leaving a large room for new physics, in particular for light dark matter. Additionally, the branching ratio for Bd→e+e−γ can also be sizable when the corresponding flavor violating Z′ coupling to quarks is of the axial-vector type. On the other hand, the predicted branching ratios of Bd→μ+μ−γ and Bs→ℓ+ℓ−γ are severely constrained by the experimental measurements.

Decay heating power of various types of plutonium

Analysis of the influence of the decay heating power of plutonium is one of the important tasks of the process in design of nuclear reactors, nuclear waste disposal or mechanical analysis of nuclear explosive devices. The paper simulated the decay heating power of some isotopes by means of cascade decay dynamics, then numerical regression was done and some formulae were obtained describing the heating power of the isotopes respectively. Furthermore, the paper reached to a common formula describing the heating power of all kinds of plutonium, and the heating powers of various types of plutonium used in fields of nuclear energy, nuclear waste disposal or military were obtained. Comparing with other calculation methods, calculating the heating power of various types of plutonium using this common formula raised in the paper could result in higher precision and more efficient, and because of the time-dependence, the common formula could also be used in thermal-related analysis of plutonium considering the storage time.

Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using sqrt{s} = 13 TeV proton-proton collisions recorded by ATLAS in Run 2 of the LHC

Results of a search for new particles decaying into eight or more jets and moderate missing transverse momentum are presented. The analysis uses 139 fb−1 of proton-proton collision data at sqrt{s} = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. The selection rejects events containing isolated electrons or muons, and makes requirements according to the number of b-tagged jets and the scalar sum of masses of large-radius jets. The search extends previous analyses both in using a larger dataset and by employing improved jet and missing transverse momentum reconstruction methods which more cleanly separate signal from background processes. No evidence for physics beyond the Standard Model is found. The results are interpreted in the context of supersymmetry-inspired simplified models, significantly extending the limits on the gluino mass in those models. In particular, limits on the gluino mass are set at 2 TeV when the lightest neutralino is nearly massless in a model assuming a two-step cascade decay via the lightest chargino and second-lightest neutralino.

Theoretical investigation of an intense ultrashort xuv pulse-induced Auger cascade in krypton

This paper theoretically investigates an Auger cascade triggered upon exposure of a Kr atom to an intense ultrashort xuv laser. In the first step of the cascade, Auger electrons are released from a coherent superposition of core-excited states to form an intermediate ionic state, which further decays through the Auger process to form a double ionic final state. Results show that the interference due to electrons released from a coherent superposition of closely spaced core-excited states, in their common continuum, in the first step of the cascade significantly modifies the line shape of the coincidence spectrum of the two Auger electrons of the cascade. The variation of the laser peak intensity not only influences the peak magnitude and linewidth but also induces a peak shift in the coincidence electron spectrum; further, the high-intensity-induced Rabi oscillations between ground and core-excited state induce line-shape splitting in the coincidence electron spectrum of the two Auger electrons, thereby manifesting the effect of Rabi oscillations even for the second Auger electron of the cascade. This work shows that the inter-related decay widths of the core-excited state and intermediate ionic state significantly influence the line shape of the coincidence electron spectrum of a cascade decay. The angular distribution of the second electron released from the cascade system of krypton is also investigated.

Search for decaying heavy dark matter in an effective interaction framework: a comparison of γ-ray and radio observations

We investigate and compare the possibilities of observing decaying dark matter (DM) in γ-ray and radio telescopes. The special emphasis of the study is on a scalar heavy DM particle with mass in the trans-TeV range. DM decays, consistent with existing limits on the lifetime, are assumed to be driven by higher dimensional effective operators. We consider both two-body decays of a scalar dark particle and a dark sector having three-body decays, producing two standard model particles. It is found that the Fermi-LAT data on isotropic γ-ray background provides the best constraints so far, although the CTA telescope may be more effective for decays where one or two photons are directly produced. In all cases, deeper probes of the effective operators are possible in the upcoming SKA radio telescope with a few hundred hours of observation, using the radio synchrotron flux coming from energetic electrons produced in the decay cascades within dwarf spheroidal galaxies. Finally, we estimate how the SKA can constrain the parameter space spanned by the galactic magnetic field and the diffusion coefficient, if observations consistent with γ-ray data actually take place.

Time-Resolved Exploration of a photoCORM {Ru(bpy)} Model Compound.

The carbon monoxide (CO)-photoreleasing molecule [Ru(Me3[9]aneN3)(bpy)(CO)]2+ (RuCO2+; bpy = 2,2'-bipyridine) was prepared and structurally characterized. The photochemical behavior was studied in unprecedented detail for this type of system, using a combination of steady-state and ultrafast transient absorption experiments, which unveiled that 3MLCT and 3dd excited states participate in the decay cascade of photoexcited RuCO2+. Theoretical calculations yield a consistent picture, providing details of the electronic structure of the transient species involved. Our results suggest that the photorelease of CO involves excited states of different electronic nature that are populated sequentially and in parallel. This complex scenario strengthens the idea that the rational design of a good photoCORM is a difficult task to carry out solely using the tools provided by chemical intuition: it is necessary to control by design factors that favor the population of specific photoactive electronic states with respect to those that are not.

Effective influence estimation in twitter using temporal, profile, structural and interaction characteristics

Influence diffusion is extensively studied in social networks for product or service promotion and viral-marketing applications. This paper proposes two models for social influence estimation, namely Time Decay Features Cascade Model (TDF-C) and Time Decay Features Cascade Threshold Model (TDF-CT). These models overcome three main existing challenges - first, measure the strength of user's influence as an influencer; second, identify the set of users influenced by an influencer; third, estimate the time frame of the influence. TDF-C is an M-TAP based diffusion model, which learns influence probabilities between users using four types of features, namely temporal, interaction, structural, and profile features, and uses Independent Cascade (IC) model for influence estimation. TDF-CT is an extension of the TDF-C model, which uses temporal and interaction features to calculate the diffusion through the Progressive Feedback Estimation (PFE) model in place of IC model. PFE model is a fusion of two diffusion models, i.e., Linear Threshold (LT) and Independent Cascade. TDF-CT handles the limitations of the contemporary diffusion models, i.e., IC and LT. The efficacy of proposed models is evaluated with respect to existing models Independent Cascade (IC), Time Constant Cascade (TC-C), Time Decay Cascade (TD-C), and Time-Depth Decay Cascade (TDD-C). Experimental evaluation over two benchmark datasets namely Darwin and MelCup17 reveal that proposed models are able to make the predictions very close to the real-time in a given time frame. TDF-CT and TDF-C are most suitable for applications requiring high precision and high recall, respectively. Results of spread shape establish the efficacy of models to spread the influence with good coverage of the social network. Results are obtained with improved accuracy by up to 39%.

On the substantial anomalous absorption regime at the extraordinary wave decay into trapped and propagating upper hybrid waves

We analyze the strong nonlinear regime of low power-threshold parametric decay instability (PDI) of a pump extraordinary wave. The PDI leads to the excitation of two upper hybrid (UH) waves only one of which is trapped in the vicinity of the local maximum of a non-monotonic density profile. The pump depletion and the multi-step secondary decays of the localized daughter UH wave are treated as the mechanisms leading to the instability saturation. It is shown that in the case of the even-step secondary cascade decay of trapped primary UH wave the pump wave depletion is responsible for the transition of a nonlinear phenomenon into a stationary regime, and the strong anomalous absorption is possible.

Construction of a thorium/actinium generator at the Canadian Nuclear Laboratories

Targeted Alpha Therapy (TAT) has demonstrated considerable promise in the treatment of a range of cancers in both preclinical and, more recently clinical research. In particular, work with the alpha-emitting radionuclide 225Ac has been effectively employed due to the relatively rapid decay cascade that leads to 4 alpha and 2 beta emissions. One limitation for TAT has been caused by access to the vital radionuclide. Traditionally, 225Ac has been sourced from thorium/actinium generators based on the alpha decay of stockpiles of 229Th. 229Th is itself the alpha-decay product from 233U. Due to proliferation issues associated with 233U, only three thorium/actinium generators have been reported in the literature, capable of supporting clinical research. This paper describes the construction and operation of a thorium/actinium radionuclide generator at the Canadian Nuclear Laboratories, capable of supporting preclinical and limited clinical research in the area of TAT. Thorium was recovered and purified by a combination of anion exchange and extraction chromatography from aged 233U stockpiles. A separation scheme for 225Ra and 225Ac has been developed, based upon the chemical composition of the thorium material to allow for regular, routine milkings capable of supplying up to 3.7 GBq (100 mCi) of radiochemically pure 225Ac annually. This routine separation is accomplished using a combination of anion exchange chromatography to separate Ac and Ra isotopes from Th and extraction chromatography employing TEVA and DGA-N resins to separate actinium from radium and breakthrough thorium.