Absolute Branching Ratios Research Articles

Decay study of Be11 with an optical time-projection chamber

The β decay of one-neutron halo nucleus Be11 was investigated using the Warsaw Optical Time Projection Chamber (OTPC) detector to measure β-delayed charged particles. The results of two experiments are reported. In the first one, carried out in LNS Catania, the absolute branching ratio for β-delayed α emission was measured by counting incoming Be11 ions stopped in the detector and the observed decays with the emission of α particle. The result of 3.27(46)% is in good agreement with the literature value. In the second experiment, performed at the HIE-ISOLDE facility at CERN, bunches containing several hundreds of Be11 ions were implanted into the OTPC detector followed by the detection of decays with the emission of charged particles. The energy spectrum of β-delayed α particles was determined in the full energy range. It was analyzed in the R-matrix framework and was found to be consistent with the literature. The best description of the spectrum was obtained assuming that the two 3/2+ and one 1/2+ states in B11 are involved in the transition. The search for β-delayed emission of protons was undertaken. Only the upper limit for the branching ratio for this process of (2.2±0.6stat±0.6sys)×10−6 could be determined. This value is in conflict with the result published by Ayyad [] but does agree with the limit reported by Riisager []. Published by the American Physical Society 2024

Reactivity of the Ethenium Cation (C2H5+) with Ethyne (C2H2): A Combined Experimental and Theoretical Study.

The gas-phase reaction between the ethyl cation (C2H5+) and ethyne (C2H2) is re-investigated by measuring absolute reactive cross sections (CSs) and branching ratios (BRs) as a function of collision energy, in the thermal and hyperthermal energy range, via tandem-guided ion beam mass spectrometry under single collision conditions. Dissociative photoionization of C2H5Br using tuneable VUV radiation in the range 10.5-14.0 eV is employed to generate C2H5+, which has also allowed us to explore the impact of increasing (vibrational) excitation on the reactivity. Reactivity experiments are complemented by theoretical calculations, at the G4 level of theory, of the relative energies and structures of the most relevant stationary points on the reactive potential energy hypersurface (PES) and by mass-analyzed ion kinetic energy (MIKE) spectrometry experiments to probe the metastable decomposition from the [C4H7]+ PES and elucidate the underlying reaction mechanisms. Two main product channels have been identified at a centre-of-mass collision energy of ∼0.1 eV: (a) C3H3++CH4, with BR = 0.76±0.05 and (b) C4H5++H2, with BR = 0.22±0.02. A third channel giving C2H3+ in association with C2H4 is shown to emerge at both high internal excitation of C2H5+ and high collision energies. From CS measurements, energy-dependent total rate constants in the range 4.3×10-11-5.2×10-10 cm3·molecule-1·s-1 have been obtained. Theoretical calculations indicate that both channels stem from a common covalently bound intermediate, CH3CH2CHCH+, from which barrierless and exothermic pathways exist for the production of both cyclic c-C3H3+ and linear H2CCCH+ isomers of the main product channel. For the minor C4H5+ product, two isomers are energetically accessible: the three-member cyclic isomer c-C3H2(CH3)+ and the higher energy linear structure CH2CHCCH2+, but their formation requires multiple isomerization steps and passages via transition states lying only 0.11 eV below the reagents' energy, thus explaining the smaller BR. Results have implications for the modeling of hydrocarbon chemistry in the interstellar medium and the atmospheres of planets and satellites as well as in laboratory plasmas (e.g., plasma-enhanced chemical vapor deposition of carbon nanotubes and diamond-like carbon films).

Combined experimental and computational study of the reactivity of the methanimine radical cation (H2CNH˙+) and its isomer aminomethylene (HCNH2˙+) with propene (CH3CHCH2).

The gas phase reactivity of the radical cation isomers H2CNH˙+ (methanimine) and HCNH2˙+ (aminomethylene) with propene (CH3CHCH2) has been investigated by measuring absolute reactive cross sections and product branching ratios, under single collision conditions, as a function of collision energy (in the range ∼0.07-11.80 eV) using guided ion beam mass spectrometry coupled with VUV photoionization for selective isomer generation. Experimental results have been merged with theoretical calculations to elucidate reaction pathways and structures of products. The H2CNH˙+ isomer is over a factor two more reactive than HCNH2˙+. A major channel from both isomers is production of protonated methanimine CH2NH2+via hydrogen-atom transfer reaction but, while H2CNH˙+ additionally gives charge and proton transfer products, the HCNH2˙+ isomer leads instead to protonated vinylimine CH2CHCHNH2+, produced alongside CH3˙ radicals. The reactions have astrochemical implications in the build up of chemical complexity in both the interstellar medium and the hydrocarbon-rich atmospheres of planets and satellites.

Semileptonic decay of Ξc→Ξℓ+νℓ from light-cone QCD sum rules

Semileptonic decay processes of $\Xi_c \to \Xi\ell\nu_\ell$ are studied by light-cone QCD sum rules in this paper. The six form factors of $\Xi_c \to \Xi$ semileptonic transition matrix elements are calculated by this method with the light-cone distribution amplitudes of $\Xi$ baryon up to twist six. With the six form factors, the absolute branching ratios of $\Xi_c^0 \to \Xi^- \ell^+ \nu_\ell$ and $\Xi_c^+ \to \Xi^0 \ell^+ \nu_\ell$ are calculated by the helicity amplitudes formalism of semileptonic differential decay widths. The ratios of absolute branching ratios of electron and muon final states processes give the proof of lepton flavor universality. Our results are in accordance with the recent experimental and theoretical reports.

Remarks on the precise measurement of the X(3872) mass and its counting rate

The lineshapes of specific production experiments of the exotic state such as $X(3872)$ with $J^{PC}=1^{++}$ quantum numbers involving triangle singularities have been found to become highly sensitive to the binding energy of weakly bound states, thus offering in principle the opportunity of benchmark determinations. We critically analyze recent proposals to extract accurately and precisely the $X(3872)$ mass, which overlook an important physical effect by regarding their corresponding production lineshapes as a sharp mass distribution and, thus, neglecting the influence of initial nearby continuum states in the $1^{++}$ channel. The inclusion of these states implies an effective cancellation mechanism which operates at the current and finite experimental resolution of the detectors so that one cannot distinguish between the $1^{++}$ bound-state and nearby $D \bar D^*$ continuum states with the same quantum numbers. In particular, we show that the lineshape for resolutions above 1 MeV becomes rather insensitive to the binding energy unless high statistics is considered. The very existence of the observed bumps is a mere consequence of short distance correlated $\bar D D^*$ pairs, bound or unbound. The cancellation also provides a natural explanation for a recent study reporting missing but unknown decay channels in an absolute branching ratio global analysis of the $X(3872)$.

Gamma-ray spectrometry in the decays of odd-mass Pt isotopes produced by neutron irradiation of natural Pt

In order to clarify the data on the energies and intensities of the γ rays emitted in the decays of the odd-mass Pt isotopes, which are often used as monitors in experiments to measure cross sections or excitation functions, a new spectrometric study has been undertaken of the decays of 191,193,195,197,199Pt using samples produced in the neutron irradiation of natural Pt. Energy values have been determined by comparison to known calibration sources down to an uncertainty of 10 eV for the strongest lines, and relative intensities often to an uncertainty of 1%. More precise absolute branching ratios were determined for several cases. New and more precise values for the half-lives were also determined.

Measurement of the structure of potential cluster bands and absolute branching ratios of high-energy states in 18O*

The investigation of nuclei with potential α-cluster structure is of great importance to the understanding of nuclear structure, both in the testing of theoretical models and for the study of the synthesis of elements in stars. The 18O nucleus is an excellent candidate to test for such a system, and an experiment has been performed in order to determine the validity of proposed cluster bands in 18O, by measuring absolute branching ratios for high-energy excited states. In order to accurately measure these branching ratios, Monte-Carlo techniques have been employed allowing for the precision reproduction of data gathered throughout the experiment. An in-depth description of the considerations required when simulated data for these experiments and comparisons between features in real and simulated data are presented.

Almost medium-free measurement of the Hoyle state direct-decay component with a TPC

Background: The structure of the Hoyle state, a highly $\alpha$-clustered state at 7.65 MeV in $^{12}\mathrm{C}$, has long been the subject of debate. Understanding if the system comprises of three weakly-interacting $\alpha$-particles in the 0s orbital, known as an $\alpha$-condensate state, is possible by studying the decay branches of the Hoyle state. Purpose: The direct decay of the Hoyle state into three $\alpha$-particles, rather than through the $^{8}\mathrm{Be}$ ground state, can be identified by studying the energy partition of the 3 $\alpha$-particles arising from the decay. This paper provides details on the break-up mechanism of the Hoyle stating using a new experimental technique. Method: By using beta-delayed charged-particle spectroscopy of $^{12}\mathrm{N}$ using the TexAT (Texas Active Target) TPC, a high-sensitivity measurement of the direct 3 $\alpha$ decay ratio can be performed without contributions from pile-up events. Results: A Bayesian approach to understanding the contribution of the direct components via a likelihood function shows that the direct component is $<0.043\%$ at the 95\% confidence level (C.L.). This value is in agreement with several other studies and here we can demonstrate that a small non-sequential component with a decay fraction of about $10^{-4}$ is most likely. Conclusion: The measurement of the non-sequential component of the Hoyle state decay is performed in an almost medium-free reaction for the first time. The derived upper-limit is in agreement with previous studies and demonstrates sensitivity to the absolute branching ratio. Further experimental studies would need to be combined with robust microscopic theoretical understanding of the decay dynamics to provide additional insight into the idea of the Hoyle state as an $\alpha$-condensate.

Primary γ -ray intensities and γ -strength functions from discrete two-step γ -ray cascades in radiative proton-capture experiments

Background: Reaction rates of radiative capture reactions can play a crucial role in the nucleosynthesis of heavy nuclei in explosive stellar environments. These reaction rates depend strongly on $\ensuremath{\gamma}$-ray decay widths in the reaction products, which are, for nonresonant capture reactions at high excitation energies, derived from the $\ensuremath{\gamma}$-ray strength function and the nuclear level density. Recently, the ratio method was applied to primary $\ensuremath{\gamma}$ rays observed from ($d,p$) reactions and nuclear resonance fluorescence measurements to extract the dipole strength in atomic nuclei and to test the generalized Brink-Axel hypothesis.Purpose: The purpose of this work is to apply the ratio method to primary $\ensuremath{\gamma}$-ray intensities of the $^{63,65}\mathrm{Cu}(p,\ensuremath{\gamma})$ reactions to extract $\ensuremath{\gamma}$-ray strength information on the nuclei $^{64,66}\mathrm{Zn}$. The impact of spin distribution, total $\ensuremath{\gamma}$-ray decay widths, level densities, and width fluctuations on the application of the ratio method will be discussed. Additionally, by comparing the relative $\ensuremath{\gamma}$-ray strength at different excitation energies, conclusions on the validity of the generalized Brink-Axel hypothesis can be made.Method: The radiative proton capture reaction measurements have been performed at the HORUS $\ensuremath{\gamma}$-ray spectrometer of the University of Cologne at one excitation energy for each reaction. Primary $\ensuremath{\gamma}$-ray intensities have been determined by normalizing secondary $\ensuremath{\gamma}$-ray transitions in two-step cascades using their absolute branching ratio. The ratio method was applied to the measured primary $\ensuremath{\gamma}$-ray intensities as well as to previous measurements by Erlandsson $et$ $al.$ at different excitation energies.Results: The relative strength function curve for $^{64}\mathrm{Zn}$ from our measurement shows no significant deviation from the previous measurement at a different excitation energy. The same is true for $^{66}\mathrm{Zn}$ where both measurements were at almost the same excitation energy. Absolute $\ensuremath{\gamma}$-strength function values have been obtained by normalizing the relative curves to quasiparticle random phase approximation calculations because of the absence of experimental data in the respective energy region.Conclusion: The generalized Brink-Axel hypothesis, i.e., the independence of the strength function on the excitation energy, seems to hold in the studied energy region and nuclei. The method to obtain primary $\ensuremath{\gamma}$-ray intensities from two-step cascade spectra was shown to be a valuable and sensitive tool although its uncertainties are connected to the knowledge of the low-energy level scheme of the investigated nucleus. The scaling in the ratio method should be taken with care, because the relative strength is not a simple sum of ${f}_{E1}$ and ${f}_{M1}$ but a somewhat complex linear combination dependent on the excitation energy of the nucleus.

Clustering in $^{18}$O - absolute determination of branching ratios via high-resolution particle spectroscopy

The determination of absolute branching ratios for high-energy states in light nuclei is an important and useful tool for probing the underlying nuclear structure of individual resonances: for example, in establishing the tendency of an excited state towards \alphaα-cluster structure. Difficulty arises in measuring these branching ratios due to similarities in available decay channels, such as (\mathbf{^{18}}18O,\mathbf{n}𝐧) and (\mathbf{^{18}}18O,\mathbf{2n}2𝐧), as well as differences in geometric efficiencies due to population of bound excited levels in daughter nuclei. Methods are presented using Monte Carlo techniques to overcome these issues.

State-selected ion-molecule reactions with VUV synchrotron radiation : the O2 + + C3H6 case

SynopsisO2 + molecular ion is produced by photoionization close to threshold at SOLEIL, DESIRS beam line. By means of coincidence methods, ions are prepared in selected vibrational and electronic states (X, v=0,3,15 and a, v=3). Their reactivity with the propene in single collision regime is studied in the guided ion beam in-strument CERISES, adding ability to vary the collision energy. Absolute reaction cross section and branching ratio are recorded for the 5 most intense reactive channels, described as dissociative charge transfer. Contrasted effects of internal and collision energy are observed.

Validation of Geant4’s G4NRF module against nuclear resonance fluorescence data from 238U and 27Al

G4NRF (Jordan and Warren, 2007; Vavrek et al., 2018a) is a simulation module for modeling nuclear resonance fluorescence (NRF) interactions in the Geant4 framework (Allison et al., 2016). In this work, we validate G4NRF against both absolute and relative measurements of three NRF interactions near 2.2 MeV in 238U and 27Al using the transmission NRF data from the experiments described in Vavrek et al. (2018b). Agreement between the absolute NRF count rates observed in the data and predicted by extensive Geant4+G4NRF modeling validate the combined Geant4+G4NRF to approximately 15–20% in the 238U NRF transitions and 10% in 27Al, for an average 14% discrepancy across the entire study. The difference between simulation and experiment in relative NRF rates, as expressed as ratios of count rates in various NRF lines, is found at the level of ≲3%, and is statistically identical to zero. Inverting the analysis, approximate values of the absolute level widths and branching ratios for 238U and 27Al are also obtained.

Electron-Induced Chemistry in the Condensed Phase

Electron–molecule interactions have been studied for a long time. Most of these studies have in the past been limited to the gas phase. In the condensed-phase processes that have recently attracted attention from academia as well as industry, a theoretical understanding is mostly based on electron–molecule interaction data from these gas phase experiments. When transferring this knowledge to condensed-phase problems, where number densities are much higher and multi-body interactions are common, care must be taken to critically interpret data, in the light of this chemical environment. The paper presented here highlights three typical challenges, namely the shift of ionization energies, the difference in absolute cross-sections and branching ratios, and the occurrence of multi-body processes that can stabilize otherwise unstable intermediates. Examples from recent research in astrochemistry, where radiation driven chemistry is imminently important are used to illustrate these challenges.

Size-dependent proton localization in hydrated uracil clusters: A joint experimental and theoretical study.

A collision-induced dissociation study of hydrated protonated uracil (H2O)n=1-15UH+ clusters is reported. The mass-selected clusters collide with water molecules and rare gases at a controlled center of mass collision energy. From these measurements, absolute fragmentation cross sections and branching ratios are extracted as a function of the uracil hydration. For small clusters, up to n = 4, we observe that only neutral water molecules are evaporated upon collisions, whereas, for larger clusters, neutral uracil is also evaporated: this transition in the nature of the evaporation products is interpreted considering the lowest-energy isomers of each species that are obtained from a combination of density-functional based tight-binding and MP2 calculations. The simulations show that in (H2O)1-4UH+ the proton is located on the uracil molecule or on a water molecule strongly bound to uracil whereas, in larger clusters, the proton is bound to water molecules far from uracil. This correlation between the structure of the low-energy isomers and the experimental fragmentation channel suggests that dissociation may occur in a very short time after collisions so that energy has not enough time to be redistributed among all degrees of freedom and the ground-state geometry of the parent cluster partly determines the nature of the favored fragmentation channels. Of course, thermal dissociations originating from long lived, thus thermalized, collision complexes cannot be ruled out but they are not expected to play the major role since the experimental results can be satisfactorily accounted for by assuming that the fragmentation processes are mainly impulsive.

Recent KLOE results on kaon physics

A short review of two measurements recently published by KLOE/KLOE-2 collaborations is presented. Namely the most stringent limits of the CPT-violating parameters Δaμ for neutral kaons, and the absolute branching ratio of K+→π+π−π+(γ) decay. In addition a discussion of starting KLOE-2 project is performed.

Experimental and theoretical study of the [formula omitted] ([formula omitted]) [formula omitted] excited states of D2: Absolute absorption cross sections and branching ratios for ionization, dissociation and fluorescence

The absolute absorption cross sections for photoexcitation of D2 to N=0 Rydberg levels have been measured at a resolution of 0.001nm in the 123,500–135,000cm−1 spectral range. The experimental energies and line intensities are compared with ab initio multichannel quantum defect (MQDT) calculations of the n⩾4npσ1Σu+N=0 levels of D2. The calculations provide theoretical values of level positions, line intensities and autoionization widths. They are based on quantum–mechanical clamped-nuclei potential energy curves and dipole transition moments available for the lowest Rydberg members of the npσ series. The overall agreement between experiment and theory is good. The decay dynamics of the excited N=0 Rydberg levels is discussed based on the observed quantum yields for ionization, dissociation and fluorescence, and is compared with the yields previously observed in the analogous states of the H2 isotopomer.

Υ(nS)→Bc⁎π,Bc⁎KDecays with Perturbative QCD Approach

Besides the traditional strong and electromagnetic decay modes,Υ(nS)meson can also decay through the weak interactions within the standard model of elementary particle. With anticipation of copiousΥ(nS)data samples at the running LHC and coming SuperKEKB experiments, the two-body nonleptonic bottom-changingΥ(nS)→Bc⁎π,Bc⁎Kdecays (n=1,2,3) are investigated with perturbative QCD approach firstly. The absolute branching ratios forΥ(nS)→Bc⁎πandBc⁎Kdecays are estimated to reach up to about10-10and10-11, respectively, which might possibly be measured by the future experiments.

Experimental and theoretical study of the [formula omitted] ([formula omitted]) excited states of D2: Absolute absorption cross sections and branching ratios for ionization, dissociation and fluorescence

The absolute absorption cross section and the branching ratios for the competing decay channels fluorescence, dissociation, and ionization of photoexcited long-lived 1Πu- superexcited molecular levels in D2 have been measured with a spectral resolution of 0.001nm from the ionization threshold of D2 up to the D(n=1)+D(n=3) dissociation limit. The experimental energies and absorption line intensities are compared with fully ab initio multichannel quantum defect theory (MQDT) calculations Glass-Maujean et al. (2011) which are based on quantum-chemical potential energy curves and transition moments of Wolniewicz and collaborators Wolniewicz and Staszewska (2003) and http://fizyka.umk.pl/ftp/pub/publications/ifiz/luwo. The overall agreement between experiment and theory is good. The branching ratios for the competing decay channels are also reproduced by the calculations including their substantial variations from level to level. A comparison of the vibronic interactions in the isotopomers H2 and D2 is made.

Measurement of the absolute branching ratio of the K+ → π+π−π+ (γ) decay with the KLOE detector

The absolute branching ratio of the K+ → π+π−π+ (γ) decay, inclusive of final- state radiation, has been measured using ~17 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory. The result is:BR(K+ → π+π−π+ (γ)) = 0.05565 ± 0.00031stat ± 0.00025syst

Measurement of the absolute branching ratio of the [formula omitted] decay with the KLOE detector

The absolute branching ratio of the K+→π+π−π+(γ) decay, inclusive of final-state radiation, has been measured using ∼17 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory. The result is:BR(K+→π+π−π+(γ))=0.05565±0.00031stat±0.00025syst a factor ≃ 5 more precise with respect to the previous result. This work completes the program of precision measurements of the dominant kaon branching ratios at KLOE.