Quasielastic Contribution Research Articles

Systematic study of Δ (1232) resonance excitations using single isobaric charge-exchange reactions induced by medium-mass projectiles of Sn

The fragment separator FRS has been for the first time used to measure the (n,p) and (p,n)-type isobaric charge-exchange cross sections of stable 112,124Sn isotopes accelerated at 1A GeV with an uncertainty of 3% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic contribution can be associated to the excitation of isobar {\Delta}(1232) resonances and to the pion emission in s-wave, both in the target and projectile nuclei, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. The data lead to interesting results where we observe a clear quenching of the quasi-elastic component and their comparisons to theoretical calculations demonstrate that the baryonic resonances can be excited in the target and projectile nuclei. To go further in this investigation, we propose to study the excitation of baryonic resonances taking advantage of the combination of high-resolving power magnetic spectrometers with the WASA calorimeter. These new measurements will allow us to determine the momenta of the ejectiles and pions emitted in coincidence after the single isobaric charge-exchange collisions, providing us unique opportunities to study the evolution of the baryonic resonance dynamics with the neutron-proton asymmetry through the use of exotic radioactive ion beams.

Revisiting rescattering contributions to overline{B} (s) \u2192 {D}_{(s)}^{left(ast right)}M decays

Motivated by the reported discrepancies between experimental data and Standard Model predictions for the branching ratios of the color-allowed decays overline{B} 0 → D(*)+K− and {overline{B}}_s^0 → {D}_s^{left(ast right)+}{pi}^{-} , we study final-state rescattering effects on overline{B} (s) → {D}_{(s)}^{left(ast right)}P and overline{B} (s) → D(s)V, where P(V) is a light pseudoscalar (vector) meson. We consider quasi-elastic rescatterings in the framework of SU(3) and U(3) flavor symmetries, and find that the effects cannot explain the measured branching ratios of the color-allowed and color-suppressed decays simultaneously. We also perform global fits to the overline{B} (s) → {D}_{(s)}^{left(ast right)}P and overline{B} (s) → D(s)V data, allowing for new physics contributions to the Wilson coefficient a1 associated with the color-allowed tree amplitudes. It is shown that the fits prefer a downward shift of mathcal{O} (10%) in a1 even in the presence of the quasi-elastic rescattering contributions.

Isobaric charge-exchange reactions: a tool to study the excitation of baryonic resonances in exotic nuclear matter

Isobaric charge-exchange reactions induced by beams of 112Sn have been investigated at the GSI facility using the fragment separator FRS. The high-resolving power of this spectrometer makes it possible to obtain the isobaric charge-exchange cross sections with an uncertainty of 3.5% and to separate quasi-elastic and inelastic contributions in the missing-energy spectra, in which the inelastic component is associated to the in-medium excitation of baryonic resonances such as the Δ resonance. We report on the results obtained for the (p,n) channel excited by using different targets that cover a large range in neutron excess. In addition, we also compare the missing-energy spectra with an intranuclear cascade model coupled to a de-excitation code to investigate the in-medium effects in the production of baryonic resonances.

Excitation of baryonic resonances in stable medium-mass nuclei of Sn

Isobaric charge-exchange reactions induced by beams of 112Sn have been investigated at the GSI facilities using the fragment separator FRS. The high-resolving power of this spectrometer makes it possible to obtain the isobaric charge-exchange cross sections with an accuracy of 3% and to separate quasi-elastic and inelastic contributions in the missing-energy spectra, in which the inelastic component is associated to the in-medium excitation of baryonic resonances such as the Δ resonance. We report on the results obtained for the (p,n) and (n,p) channels excited by using different targets that cover a large range in neutron excess.

Dynamics of an Anisotropic Metaphosphate LiNaKCsPO3Glass by Inelastic X‐Ray Scattering

To clarify the mechanism of the entropic shrinkage of a metaphosphate LiNaKCsPO3glass, high‐resolution inelastic X‐ray scattering is carried out in the momentum transfer (Q) range from 1.6 to 15.9 nm−1by changing the stretched sample rod directions perpendicular and parallel to the X‐ray scattering plane. Phonon excitations are found only in a lowQrange below about 3 nm−1, and the so‐called Boson peaks are observed in theQregion beyond 5.6 nm−1. These excitations exhibit mostly no differences in the rod direction. A spectral enhancement at the prepeak position in the total X‐ray scattering spectrum is due to the quasielastic contributions. The direction difference in the width of the quasielastic peak becomes largely broadened near the prepeak region, which may be owing to a low excitation energy of the phosphate chains across the chain direction.

Study of Δ excitations in medium-mass nuclei with peripheral heavy ion charge-exchange reactions

Isobaric single charge-exchange reactions, changing nuclear charges by one unit but leaving the mass partitions unaffected, have been for the first time investigated by peripheral collisions of 112Sn ions accelerated up to 1A GeV at the GSI facilities. The high-resolving power of the FRS spectrometer allows us to obtain (p,n)-type isobaric charge-exchange cross sections with an uncertainty of 3.5% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic component is associated to the excitation of the Δ(1232) isobar resonance and the emission of pions in s-wave both in the target and projectile nucleus, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. An apparent shift of the Δ-resonance peak of ∼63 MeV is observed when comparing the missing-energy spectra obtained from the measurements with proton and carbon targets. A detailed analysis, performed with a theoretical model for the reactions, indicates that this observation can be simply interpreted as a change in the relative magnitude between the contribution of the excitation of the resonance in the target and in the projectile.

Boosting Quantum Vacuum Signatures by Coherent Harmonic Focusing.

We show that coherent harmonic focusing provides an efficient mechanism to boost all-optical signatures of quantum vacuum nonlinearity in the collision of high-intensity laser fields, thereby offering a promising route to their first experimental detection. Assuming two laser pulses of given parameters at our disposal, we demonstrate a substantial increase of the number of signal photons measurable in experiments where one of the pulses undergoes coherent harmonic focusing before it collides with the fundamental-frequency pulse. Imposing a quantitative criterion to discern the signal photons from the background of the driving laser photons and accounting for the finite purity of polarization filtering, we find that signal photons arising from inelastic scattering processes constitute a promising signature. By contrast, quasielastic contributions which are conventionally assumed to form the most prospective signal remain background dominated. Our findings may result in a paradigm shift concerning which photonic signatures of quantum vacuum nonlinearity are accessible in experiment.

Flexible lipid nanomaterials studied by NMR spectroscopy.

Our review addresses how material properties emerge from atomistic-level interactions in the case of lipid membrane nanostructures. We summarize advances in solid-state nuclear magnetic resonance (NMR) spectroscopy in conjunction with alternative small-angle X-ray and neutron scattering methods for investigating lipid flexibility and dynamics. Solid-state 2H NMR is advantageous in that it provides atomistically resolved information about the order parameters and mobility of phospholipids within liquid-crystalline membranes. Bilayer deformation in response to external perturbations occurs over a range of length scales and allows one to disentangle how the bulk material properties emerge from atomistic forces. Examples include structural parameters such as the area per lipid and volumetric thickness together with the moduli for elastic deformation. Membranes under osmotic stress allow one to further distinguish collective undulations and quasielastic contributions from short-range noncollective effects. Our approach reveals how membrane elasticity involves length scales ranging from the bilayer dimensions on down to the size of the flexible lipid segments. Collective lipid interactions of the order of the bilayer thickness and less occur in the liquid-crystalline state. Emergence of lipid material properties is significant for models of lipid-protein forces acting on the mesoscopic length scale that play key roles in biomembrane functions.

Emergence of Membrane Material Parameters Revealed by Solid-State 2H NMR Spectroscopy

The emergence of the material properties of lipid membranes is a topic of current interest in quantitative biophysics. At the smallest length scale, lipid membranes are collections of atoms whose dynamics can be traced by molecular dynamics simulations. At cellular length scales, they are continuous hydrophobic barriers, which together with membrane proteins regulate trafficking and cell signaling. Somewhere in this broad range, material properties emerge from the ensemble of atoms. How can we understand this emergence behavior? Here we show that solid-state 2H NMR spectroscopy is powerful, because as opposed to typical scattering experiments it provides information over a range of length scales. Specifically, solid-state 2H NMR provides atomistically resolved order parameters and dynamics of flexible phospholipids within the liquid-crystalline bilayer [1]. By measuring the membrane response to osmotic stress we can disentangle how bulk material properties emerge from atomistic-level interactions. Examples include structural parameters such as the area per lipid and the volumetric thickness plus the associated moduli for elastic deformation. Data for samples under osmotic stress allow an insightful analysis of intermembrane interactions by distinguishing between collective undulatory and quasi-elastic contributions at large length scales versus short-range non-collective (molecular) effects. By calculating the area elastic modulus over a substantial range of osmotic pressures, collective bilayer properties are found to emerge over very short length scales, on the order of the bilayer thickness or even less. Notably the emergence of lipid material properties on this length scale determines what model is most appropriate to study lipid-protein interactions [2]. A continuum flexible surface model (FSM) for lipid-protein interactions on the mesoscopic length scale can optimally capture the essential material features that govern biomembrane functions. [1] J.Kinnun et al. (2015) Biochim.Biophys.Acta 1848, 256. [2] M.F.Brown (2017) Annu.Rev.Biophys. 46, 379.

Magnetic excitations in the ground state of Yb2Ti2O7

We report an extensive study on the zero field ground state of a powder sample of the pyrochlore $\mathrm{Yb_2Ti_2O_7}$. A sharp heat capacity anomaly that labels a low temperature phase transition in this material is observed at 280 mK. Neutron diffraction shows that a \emph{quasi-collinear} ferromagnetic order develops below $T_\mathrm{c}$ with a magnetic moment of $0.87(2)\mu_\mathrm{B}$. High resolution inelastic neutron scattering measurements show, below the phase transition temperature, sharp gapped low-lying magnetic excitations coexisting with a remnant quasielastic contribution likely associated with persistent spin fluctuations. Moreover, a broad inelastic continuum of excitations at $\sim0.6$ meV is observed from the lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has vanished and a broad quasielastic conventional paramagnetic scattering takes place at the observed energy range. Finally, we show that the exchange parameters obtained within the framework of linear spin-wave theory do not accurately describe the observed zero field inelastic neutron scattering data.

Charged-current inclusive neutrino cross sections in the superscaling model including quasielastic, pion production and meson-exchange contributions

Charged current inclusive neutrino-nucleus cross sections are evaluated using the superscaling model for quasielastic scattering and its extension to the pion production region. The contribution of two-particle-two-hole vector meson-exchange current excitations is also considered within a fully relativistic model tested against electron scattering data. The results are compared with the inclusive neutrino-nucleus data from the T2K and SciBooNE experiments. For experiments where , the three mechanisms considered in this work provide good agreement with the data. However, when the neutrino energy is larger, effects from beyond the Δ also appear to be playing a role. The results show that processes induced by vector two-body currents play a minor role in the inclusive cross sections at the kinematics considered.

Low-energy excitations and quasielastic contribution to electron-nucleus and neutrino-nucleus scattering in the continuum random-phase approximation

We present a detailed study of a continuum random phase approximation approach to quasielastic electron-nucleus and neutrino-nucleus scattering. The formalism is validated by confronting ($e,e'$) cross-section predictions with electron scattering data for the nuclear targets $^{12}$C, $^{16}$O, and $^{40}$Ca, in the kinematic region where quasielastic scattering is expected to dominate. We examine the longitudinal and transverse contributions to $^{12}$C($e,e'$) and compare them with the available data. Further, we study the $^{12}$C($\nu_{\mu},\mu^{-}$) cross sections relevant for accelerator-based neutrino-oscillation experiments. We pay special attention to low-energy excitations which can account for non-negligible contributions in measurements, and require a beyond-Fermi-gas formalism.

Crystal field manifestation in inelastic neutron scattering, magnetic susceptibility and specific heat of the antiferromagnetic CeCoAl4

Inelastic and quasielastic excitations in the neutron scattering on the compounds CeCo1−xCuxAl4 (x=0, 0.05, 0.1) have been studied above and below the antiferromagnetic ordering temperature. The quasielastic contribution disappears below the Néel temperature, TN=13.5K, and its linewidth Γ/2 is below TN, therefore these results suggest that Kondo screening is not relevant in these Ce compounds. Based on the example of CeCoAl4 we show that the inelastic excitations provide crystal electric field energy levels scheme, which in consistent way describes both the magnetic susceptibility and the specific heat. The inelastic neutron scattering spectrum below TN is interpreted as the splitting of the crystal electric field levels by the internal molecular field.

Two particle–hole excitations in charged current quasielastic antineutrino-nucleus scattering

We evaluate the quasielastic and multinucleon contributions to the antineutrino-nucleus scattering cross section and compare our results with the recent MiniBooNE data. We use a local Fermi gas model that includes RPA correlations and gets the multinucleon part from a systematic many body expansion of the W boson selfenergy in the nuclear medium. The same model had been quite successful for the neutrino cross section and contains no new parameters. We have also analyzed the relevance of 2p2h events for the antineutrino energy reconstruction.

Raman spectroscopy of racemic ibuprofen: Evidence of molecular disorder in phase II

Low- and high-frequency Raman experiments in the 5–200cm−1 and 600–1800cm−1 ranges were carried out in the crystalline and amorphous states of ibuprofen. Low-frequency investigations indubitably reveal the existence of a molecular disorder in the metastable phase (phase II), through the observation of quasielastic contribution below 30cm−1, and the absence of phonon peaks in the Raman susceptibility which mimics the density of vibrational states of an amorphous state. High-frequency Raman spectra indicate a local order in phase II similar to that in the glassy state. Both dynamic and static molecular disorder could contribute to the Raman signatures of the disorder in crystalline phase II. Raman investigations suggest that phase II can be considered as a transient metastable state in the devitrification process of ibuprofen upon heating from a far from equilibrium state toward the stable phase I.

Inclusive charged-current neutrino-nucleus reactions

We present a model for weak charged-current induced nuclear reactions at energies of interest for current and future neutrino oscillation experiments. This model is a natural extension of the work in Refs. [1,2], where the quasielastic contribution to the inclusive electron and neutrino scattering on nuclei was analyzed. The model is based on a systematic many-body expansion of the gauge boson absorption modes that includes one, two, and even three-body mechanisms, as well as the excitation of $\ensuremath{\Delta}$ isobars. The whole scheme has no free parameters, besides those previously adjusted to the weak pion production off the nucleon cross sections in the deuteron, since all nuclear effects were set up in previous studies of photon, electron, and pion interactions with nuclei. We have discussed at length the recent charged-current quasielastic MiniBooNE cross section data, and showed that two-nucleon knockout mechanisms are essential to describing these measurements.

Measurement of low-energy neutrino cross-sections with the PEANUT experiment

The PEANUT experiment was designed to study the NuMi neutrino beam at Fermilab. The detector uses a hybrid technique, being made of nuclear emulsions and scintillator trackers. Emulsion films act as a micrometric tracking device and are interleaved with lead plates used as passive material. The detector is designed to precisely reconstruct the topology of neutrino interactions and hence to measure the different contributions to the cross section. We present here the full reconstruction and analysis of 147 neutrino interactions and the measurement of the quasi-elastic, resonance and deep-inelastic contributions to the total charged current cross section at the energies of the NuMi neutrino beam. This technique could be applied for beam monitoring in future neutrino facilities, and this paper shows its proof-of-principle.

Superscaling of non-quasielastic electron-nucleus scattering

The present study focuses on the superscaling behavior of electron-nucleus cross sections in the region lying above the quasielastic peak, especially the region dominated by electroexcitation of the $\ensuremath{\Delta}$. Non-quasielastic cross sections are obtained from all available high-quality data for $^{12}\mathrm{C}$ by subtracting effective quasielastic cross sections based on the superscaling hypothesis. These residuals are then compared with results obtained within a scaling-based extension of the relativistic Fermi gas model, including an investigation of violations of scaling of the first kind in the region above the quasielastic peak. A way to potentially isolate effects related to meson-exchange currents by subtracting both impulsive quasielastic and impulsive inelastic contributions from the experimental cross sections is also presented.

Cross sections and analyzing powers for(p,n)reactions onHe3andHe4at 346 MeV

The cross sections and analyzing powers for $(p,n)$ reactions on $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ have been measured at a bombarding energy of ${T}_{p}=346$ MeV and reaction angles of ${\ensuremath{\theta}}_{\mathrm{lab}}=9.{4}^{\ifmmode^\circ\else\textdegree\fi{}}\text{\ensuremath{-}}{27}^{\ifmmode^\circ\else\textdegree\fi{}}$. The energy transfer spectra for ${}^{3}\mathrm{He}(p,n)$ at large ${\ensuremath{\theta}}_{\mathrm{lab}}$ ($\ensuremath{\geqslant}{16}^{\ifmmode^\circ\else\textdegree\fi{}}$) are dominated by quasielastic contributions and can be reasonably reproduced by plane-wave impulse approximation (PWIA) calculations for quasielastic scattering. By contrast, the known $L=1$ resonances in $^{4}\mathrm{Li}$ are clearly observed near the threshold in the ${}^{4}\mathrm{He}(p,n)$ spectra. Because these contributions are remarkable at small angles, the energy spectra are significantly different from those expected for quasielastic scattering. The data are compared with the PWIA calculations, and it is found that the quasielastic contributions are dominant at large ${\ensuremath{\theta}}_{\mathrm{lab}}$ ($\ensuremath{\geqslant}{22}^{\ifmmode^\circ\else\textdegree\fi{}}$). The nuclear correlation effects on the quasielastic peak for ${}^{4}\mathrm{He}(p,n)$ are also discussed.

Quasi-Elastic Neutron Scattering Studies on Clay Interlayer-Space Highlighting the Effect of the Cation in Confined Water Dynamics

It has long been realized that cations play a critical role in the readsorption of water into the interlayer region in clay minerals. To explore possible differences in the water dynamics related to the presence of cations in clays, and to examine the dynamics of its surface water, which plays a prominent role in diffusion of water in clay barriers a comparative study was carried out to highlight differences between water dynamics in montmorillonite and halloysite. Whereas montmorillonite has interlayer cations that interact with interlayer water, and which can rehydrate after dehydration at temperature, halloysite has no interlayer cations. Water is found in both interlayers and on the surface of these clay particles. In this study we show that by combining incoherent inelastic neutron scattering (quasi-elastic and elastic fixed window) and neutron spin echo, it was possible to discriminate the dynamics of surface water (by collapsing the interlayer region by heating and rehydrating the surface layer) from interlayer water. The analysis of the elastic fixed window scans in the temperature range 5−300 K revealed an extension of water dynamics in montmorillonite to lower temperatures than in halloysite. These differences suggested mechanisms that cations (Na+ in this case) in the interlayer regions facilitate water mobility allowing interlayer water to be readmitted to montmorillonite. Finally it was shown that the occurrence of magnetic fluctuations, caused by the presence of paramagnetic Fe3+ ions in the crystalline clay lattice, gave rise to a quasi-elastic contribution that disrupted the evaluation of water diffusion computed from such measurements. Therefore previous estimates of water diffusion coefficients might have been overestimated in recent literature.