Reaction Amplitude Research Articles

Helicity-dependent reaction γd → π0d near the η-threshold and its contribution to the E-asymmetry and the GDH sum rule for the deuteron

The helicity-dependent coherent π0-photoproduction in the reaction γd → π0d near the η-threshold is investigated. The calculations are performed within an approach which includes the reaction amplitudes of the impulse approximation (IA), two-step process with intermediate πN- and ηN-rescattering, and the higher order terms in the multiple scattering series for the intermediate ηNN interaction. The contribution of γd → π0d to the deuteron spin asymmetry is calculated and its contribution to the Gerasimov–Drell–Hearn (GDH) integral is explicitly evaluated by integration up to a photon energy of 900 MeV. In addition, the helicity E-asymmetry is calculated. The results revealed that the doubly polarized differential cross-sections and the helicity E-asymmetry are sensitive to the interference of rescattering effects, specially at photon energies 600–800 MeV and extreme backward pion angles. The sensitivity of the obtained results for the GDH integral to the choice of NN potential model governing the deuteron wave function is discussed. We find that the deviation among results obtained for the deuteron GDH integral using different deuteron wave functions is quite large.

Nearside-farside, local angular momentum and resummation theories: Useful tools for understanding the dynamics of complex-mode reactions

A valuable tool for understanding the dynamics of direct reactions is Nearside-Farside (NF) scattering theory. It makes a decomposition of the (resummed) partial wave series for the scattering amplitude, both for the differential cross section (DCS) and the Local Angular Momentum (LAM). This paper makes the first combined application of these techniques to complex-mode reactions. We ask if NF theory is a useful tool for their identification, in particular, can it distinguish complex-mode from direct-mode reactions? We also ask whether NF theory can identify NF interference oscillations in the full DCSs of complex-mode reactions. Our investigation exploits the fact that accurate quantum scattering matrix elements have recently become available for complex-mode reactions. We first apply NF theory to two simple models for the scattering amplitude of a complex-mode reaction: One involves a single Legendre polynomial; the other involves a single Legendre function of the first kind, whose form is suggested by complex angular momentum theory. We then study, at fixed translational energies, four state-to-state complex-mode reactions. They are: S(1D) + HD → SH + D, S(1D) + DH → SD + H, N(2D) +H2 → NH + H, and H+ + D2 → HD + D+. We compare the NF results for the DCSs and LAMs with those for a state-to-state direct reaction, namely, F + H2 → FH + H. We demonstrate that NF theory is a valuable tool for identifying and analyzing the dynamics of complex-mode reactions.

Tactile processing in children and adolescents with obsessive–compulsive disorder

Many obsessive–compulsive disorder (OCD) patients experience sensory phenomena, such as bodily sensations and “just-right” perceptions accompanying compulsions. We studied tactile processing in OCD by psychophysical experiments targeting the somatosensory cortex. Thirty-two children and adolescents with OCD (8 tic-related, 19 with sensory phenomena (SP)) and their sex- and age-matched controls participated in the study. After clinical assessments, two questionnaires were completed for sensory problems (Sensory Profile and Touch Inventory for Elementary-School-Aged Children). The psychophysical experiments consisted of five tasks: simple reaction time, choice reaction time, dynamic (detection) threshold, amplitude discrimination, and amplitude discrimination with single-site adaptation. The tactile stimuli were sinusoidal mechanical vibrations (frequency: 25 Hz) applied on the fingertips. Just-noticeable differences (JNDs) were found in amplitude discrimination tasks. There was no difference between the OCD group and controls in detection thresholds. However, the OCD group (especially young males) had worse amplitude discrimination (i.e., higher JNDs) than controls. Young OCD participants had reduced adaptation than young controls. Tic-related OCD participants and those with SP had higher detection thresholds than those without. Additionally, the OCD group reported more problems than controls in the Emotional/Social subset of the Sensory Profile questionnaire. The discrimination results show altered tactile processing in OCD at suprathreshold levels. This can be explained by a scaling factor modifying the sensory signal with decreasing slope at higher input levels to achieve normal Weber fractions internally. Quadratic discriminant analysis gave the best positive (76%) and negative (60%) predictive values for classifying individuals (into “OCD” or “control” groups) based on psychophysical data alone.

Type 2 diabetes and cardiac autonomic neuropathy screening using dynamic pupillometry.

To determine if changes in pupillary response are useful as a screening tool for diabetes and to assess whether pupillometry is associated with cardiac autonomic neuropathy. We conducted a cross-sectional study with participants drawn from two settings: a hospital and a community site. At the community site, individuals with newly diagnosed diabetes as well as a random sample of control individuals without diabetes, confirmed by oral glucose tolerance test, were selected. Participants underwent an LED light stimulus test and eight pupillometry variables were measured. Outcomes were diabetes, defined by oral glucose tolerance test, and cardiac autonomic dysfunction, determined by a positive readout on two of four diagnostic tests: heart rate response to the Valsalva manoeuvre; orthostatic hypotension; 30:15 ratio; and expiration-to-inspiration ratio. The area under the curve, best threshold, sensitivity and specificity of each pupillometry variable was calculated. Data from 384 people, 213 with diabetes, were analysed. The mean (±sd) age of the people with diabetes was 58.6 (±8.2) years and in the control subjects it was 56.1 (±8.6) years. When comparing individuals with and without diabetes, the amplitude of the pupil reaction had the highest area under the curve [0.69 (sensitivity: 78%; specificity: 55%)]. Cardiac autonomic neuropathy was present in 51 of the 138 people evaluated (37.0%; 95% CI 28.8-45.1). To diagnose cardiac autonomic neuropathy, two pupillometry variables had the highest area under the curve: baseline pupil radius [area under the curve: 0.71 (sensitivity: 51%; specificity: 84%)], and amplitude of the pupil reaction [area under the curve: 0.70 (sensitivity: 82%; specificity: 55%)]. Pupillometry is an inexpensive technique to screen for diabetes and cardiac autonomic neuropathy, but it does not have sufficient accuracy for clinical use as a screening tool.

Amplitude extraction in pseudoscalar-meson photoproduction: towards a situation of complete information

A complete set for pseudoscalar-meson photoproduction is a minimum set of observables from which one can determine the underlying reaction amplitudes unambiguously. The complete sets considered in this work involve single- and double-polarization observables. It is argued that for extracting amplitudes from data, the transversity representation of the reaction amplitudes offers advantages over alternate representations. It is shown that with the available single-polarization data for the Λ reaction, the energy and angular dependence of the moduli of the normalized transversity amplitudes in the resonance region can be determined to a fair accuracy. Determining the relative phases of the amplitudes from double-polarization observables is far less evident.

Asymptotic normalization coefficients and spectroscopic factors from deuteron stripping reactions

We present the analysis of three deuteron stripping reactions, $^{14}\mathrm{C}(d,p)^{15}\mathrm{C},^{58}\mathrm{Ni}(d,p)^{59}\mathrm{Ni}$, and $^{116}\mathrm{Sn}(d,p)^{117}\mathrm{Sn}$ using the combined method [A. M. Mukhamedzhanov and F. M. Nunes, Phys. Rev. C 72, 017602 (2005)], in which each reaction is analyzed at low and significantly higher energies. At low energies all these reactions are peripheral and the experimental asymptotic normalization coefficients (ANCs) are determined with accuracy about $10%$. At higher energies we determine the spectroscopic factors (SFs) by fixing the normalization of the peripheral parts of the reaction amplitudes governed by the ANCs found from the low-energy data. The combined method imposes a strict limitation on the variation of the geometrical parameters of the single-particle potential, which can be arbitrarily taken in the standard approach. By checking the compatibility of the ANCs and SFs using the combined method we reveal the flaw in the contemporary nuclear reaction theory in treating the nuclear interior, which is the most crucial part in the determination of the SFs.

Aggression and the Acoustic Startle Response in Young Rats Genetically Predisposed to Aggression and Nonaggressive Rats

The aim of the present work was to study the relationship between expression of the reflex startle reaction and fear-induced aggression. The extent of aggressive reactions towards humans and the amplitude of the acoustic startle response were studied in adult and 15-day-old Norway rats bred for 70 generations for a high level of fear-induced aggression towards humans and in animals without such aggression. Adult rats of the aggressive strain demonstrated a high level of aggression and a significantly greater reflex startle amplitude than rats bred for the absence of aggression. In contrast to 15-day-old rat pups of the nonaggressive strain, pups of the highly aggressive strain showed clear aggression directed towards humans, though these reactions were weaker than those of adults of this strain. There were no differences in the amplitudes of the acoustic startle reaction between aggressive and nonaggressive rat pups. Adult aggressive rats showed a significant decrease in the amplitude of the acoustic startle reaction on sequential presentations of the sound stimulus, while 15-day-old rat pups of the aggressive strain showed no change in the acoustic startle reflex. The amplitude of the acoustic startle reflex on sequential presentations of the sound stimulus decreased significantly in both adult and 15-day-old nonaggressive rats. Thus, protective-defensive aggression in rats genetically predisposed to fear-induced aggression appears quite early ‐ these animals displayed marked aggressive responses against humans by the moment of eye opening. The startle reflex is one of the elements of a complex behavior ‐ protective-defensive aggression ‐ an element which does not play a significant role in aggression in young rats but is involved in age-related increases in aggression.

Reliability of dynamic balance simultaneously with cognitive performance in patients with ACL deficiency and after ACL reconstructions and in healthy controls.

To determine the intra- and inter-session reliability of balance and cognitive performance in anterior cruciate ligament-deficient (ACLD) and ACL-reconstructed (ACLR) and matched athletes. Using SMART EquiTest, recovery reactions of the groups were assessed during single-leg standing, following medium and large forward perturbations with and without performing a cognitive (Stroop) task. The outcomes included reaction time (RT), latency and amplitude for balance and error ratio (ER) and RT for cognitive performance. The participants of each group repeated the tests 2-7 days after the first session. Intraclass correlation coefficient (ICC) and standard error of measurement were computed in order to assess relative and absolute reliability, respectively. Single- and dual-task balance measures had moderate to very high reliability in ACLD (ICC = 0.63-0.88), ACLR (ICC = 0.62-0.93) and control (ICC = 0.69-0.98) athletes. The ICCs for RT of Stroop were between 0.87 and 0.90 in ACLD, between 0.70 and 0.74 in ACLR and between 0.66 and 0.70 in controls and for ER of Stroop were between 0.36 and 0.90 in ACLD, between 0.42 and 0.49 in ACLR and between 0.41 and 0.51 in controls. Balance measures and RT of the cognitive task in single- and dual-task conditions have acceptable reliability and may be incorporated into the evaluation of physical and mental function of athletes following ACL injury and reconstruction. ER of the cognitive task is less reliable which needs to be considered in future research. Prognostic study, case-control, Level III.

Investigation of summation mechanisms in the pupillomotor system.

To ascertain whether the pupillary response amplitude shows spatial summation of responses with increasing size of retinal stimulation, and to examine the pupillary responses for evidence of surround inhibition, analogous to that found in the receptive fields of the retinal ganglion cells. By means of infrared-video-pupillography, the pupil reaction to stimuli of increasing size (1-15°) was measured in 30 normal subjects. Four different retinal locations (0°, 20° and 40° eccentricity on the upper temporal retina and 20° eccentricity on the lower nasal retina) were examined at four different stimulus luminances (17, 47, 87 and 140 cd/m(2)). When the average log amplitude of the pupil light reaction from the 30 subjects is plotted as a function of the log area of the stimulus, a bi-linear response is observed, which is most pronounced for the two higher luminances. The intersection points of the two linear responses are 2.01° in the fovea, 2.80° at 20° upper temporal retina, 2.85° at 20° lower nasal retina and 4.86° at 40° upper temporal retina. This study suggests that pupillomotor summation areas consist of both summation and inhibitory zones. They show larger diameters than receptive fields of retinal ganglion cells and do not appear to reflect pupillary summation areas of the pretectal olivary nucleus luminance neurons.

Model-independent aspects of the reactionK¯+N→K+Ξ

Various model-independent aspects of the $\bar{K} N \to K \Xi$ reaction are investigated, starting from the determination of the most general structure of the reaction amplitude for $\Xi$ baryons with $J^P=\frac12^\pm$ and $\frac32^\pm$ and the observables that allow a complete determination of these amplitudes. Polarization observables are constructed in terms of spin-density matrix elements. Reflection symmetry about the reaction plane is exploited, in particular, to determine the parity of the produced $\Xi$ in a model-independent way. In addition, extending the work of Biagi $\mathrm{\textit{et al. } [Z. Phys.\ C \textbf{34}, 175 (1987)]}$, a way is presented of determining simultaneously the spin and parity of the ground state of $\Xi$ baryon as well as those of the excited $\Xi$ states.

Complete sets of observables in pseudoscalar-meson photo-production

Pseudoscalar-meson photoproduction is characterized by four complex reaction amplitudes. A complete set is a minimum theoretical set of observables that allow to determine these amplitudes unambiguously. It is studied whether complete sets remain complete when experimental uncertainty is involved. To this end, data from the GRAAL Collaboration and simulated data from a realistic model, both for the $\gamma p \to K^+ \Lambda$ reaction, are analyzed in the transversity representation of the reaction amplitudes. It is found that only the moduli of the transversity amplitudes can be determined without ambiguity but not the relative phases.

TRANSITION FORM FACTORS: A UNIQUE OPPORTUNITY TO CONNECT NON-PERTURBATIVE STRONG INTERACTIONS TO QCD

Meson-photoproduction measurements and their reaction-amplitude analyses can establish more sensitively, and in some cases in an almost model-independent way, nucleon excitations and non-resonant reaction amplitudes. However, to investigate the strong interaction from explored — where meson-cloud degrees of freedom contribute substantially to the baryon structure — to still unexplored distance scales — where quark degrees of freedom dominate and the transition from dressed to current quarks occurs — we depend on experiments that allow us to measure observables that are probing this evolving non-perturbative QCD regime over its full range. Elastic and transition form factors are uniquely suited to trace this evolution by measuring elastic electron scattering and exclusive single-meson and double-pion electroproduction cross sections off the nucleon. These exclusive measurements will be extended to higher momentum transfers with the energy-upgraded CEBAF beam at JLab to study the quark degrees of freedom, where their strong interaction is responsible for the ground and excited nucleon state formations. After establishing unprecedented high-precision data, the imminent next challenge is a high-quality analysis to extract these relevant electrocoupling parameters for various resonances that then can be compared to state-of-the-art models and QCD-based calculations. Recent results will demonstrate the status of the analysis and of their theoretical descriptions, and an experimental and theoretical outlook will highlight what shall and may be achieved in the new era of the 12-GeV upgraded transition form factor program.

EXTRACTION OF THE Λ(1405) POLES FROM π0Σ0 PHOTOPRODUCTION DATA

In this contribution we review a work where we showed how to extract the position of the two Λ(1405) poles from experimental photoproduction data which have been measured recently in the γp → K+π0Σ0 reaction at Jefferson Lab. Using a potential motivated by chiral dynamics but with free parameters, we solve the Bethe Salpeter equation in the coupled channels [Formula: see text] and πΣ in isospin I=0 and parameterize the amplitude for the photonuclear reaction in terms of a linear combination of the πΣ → πΣ and [Formula: see text] scattering amplitudes in I=0, with a different linear combination for each energy. Good fits to the data are obtained which lead to two poles at 1385 - 68i MeV and 1419 - 22i MeV, similar to those found in the chiral unitary approach.

STATUS OF MESON PHOTOPRODUCTION EXPERIMENTS WITH CLAS

A large part of the experimental program in Hall B of the Jefferson Lab is dedicated to baryon spectroscopy. Meson photoproduction experiments are essential part of this program. CEBAF Large Acceptance Spectrometer (CLAS) and availability of circularly and linearly polarized tagged photon beams in combination with longitudinally and transversely polarized frozen spin targets provide unique conditions for this type of experiments. For the first time, a complete or nearly complete measurement became possible and will allow model independent extraction of the reaction amplitude. The measurements were complete with both proton and deuteron targets. An overview of the collected experimental data will be presented.

Speed of processing in the primary motor cortex: A continuous theta burst stimulation study

‘Temporally urgent’ reactions are extremely rapid, spatially precise movements that are evoked following discrete stimuli. The involvement of primary motor cortex (M1) and its relationship to stimulus intensity in such reactions is not well understood. Continuous theta burst stimulation (cTBS) suppresses focal regions of the cortex and can assess the involvement of motor cortex in speed of processing. The primary objective of this study was to explore the involvement of M1 in speed of processing with respect to stimulus intensity. Thirteen healthy young adults participated in this experiment. Behavioral testing consisted of a simple button press using the index finger following median nerve stimulation of the opposite limb, at either high or low stimulus intensity. Reaction time was measured by the onset of electromyographic activity from the first dorsal interosseous (FDI) muscle of each limb. Participants completed a 30min bout of behavioral testing prior to, and 15min following, the delivery of cTBS to the motor cortical representation of the right FDI. The effect of cTBS on motor cortex was measured by recording the average of 30 motor evoked potentials (MEPs) just prior to, and 5min following, cTBS. Paired t-tests revealed that, of thirteen participants, five demonstrated a significant attenuation, three demonstrated a significant facilitation and five demonstrated no significant change in MEP amplitude following cTBS. Of the group that demonstrated attenuated MEPs, there was a biologically significant interaction between stimulus intensity and effect of cTBS on reaction time and amplitude of muscle activation. This study demonstrates the variability of potential outcomes associated with the use of cTBS and further study on the mechanisms that underscore the methodology is required. Importantly, changes in motor cortical excitability may be an important determinant of speed of processing following high intensity stimulation.

A model for soft high-energy scattering: Tensor pomeron and vector odderon

A model for soft high-energy scattering is developed. The model is formulated in terms of effective propagators and vertices for the exchange objects: the pomeron, the odderon, and the reggeons. The vertices are required to respect standard rules of QFT. The propagators are constructed taking into account the crossing properties of amplitudes in QFT and the power-law ansätze from the Regge model. We propose to describe the pomeron as an effective spin 2 exchange. This tensor pomeron gives, at high energies, the same results for the pp and pp̄ elastic amplitudes as the standard Donnachie–Landshoff pomeron. But with our tensor pomeron it is much more natural to write down effective vertices of all kinds which respect the rules of QFT. This is particularly clear for the coupling of the pomeron to particles carrying spin, for instance vector mesons. We describe the odderon as an effective vector exchange. We emphasise that with a tensor pomeron and a vector odderon the corresponding charge-conjugation relations are automatically fulfilled. We compare the model to some experimental data, in particular to data for the total cross sections, in order to determine the model parameters. The model should provide a starting point for a general framework for describing soft high-energy reactions. It should give to experimentalists an easily manageable tool for calculating amplitudes for such reactions and for obtaining predictions which can be compared in detail with data.

CONTRIBUTION OF P11 (1440) RESONANCE TO THE d(e, e′ π+)nn REACTION INCLUDING NN FINAL STATE INTERACTION

The effect of P11(1440) (Roper) resonance on the response functions for the positivelly charged pion electroproduction from the deuteron is studied using the well known spectator model. The amplitude for the elementary reaction γ* N→π+ N is taken from MAID2003 model. The effect of the NN interaction subsystem in the final state interaction (FSI) is included. Two values for the four momentum transferred Q2 are used. A small effect of the Roper resonance on the structure functions is found.

Broadening of ρ(→ e+e−) meson produced coherently in the photonuclear reaction

The $e^+e^-$ invariant mass distribution spectra are calculated to estimate the hadron parameters of the $\rho$ meson produced coherently in the photonuclear reaction. The elementary reaction occurring in the nucleus is considered to proceed as $ \gamma N \to \rho^0 N ; ~ \rho^0 \to e^+e^- $. We describe the elementary $\rho$ meson photoproduction by the experimentally determined reaction amplitude $ f_{ \gamma N \to \rho^0 N } $. The $\rho$ meson propagator is presented by the eikonal form, and the $\rho$ meson nucleus optical potential $V_{O\rho}$ appearing in it is estimated using the "$t\varrho$" approximation. The $\rho$ meson nucleon scattering amplitude $ f_{ \rho N } $ extracted from the measurements is used to generate this potential. The calculated $e^+e^-$ invariant mass distribution spectra are compared with those measured at Jefferson Laboratory. The calculated results for the transparency ratio are also presented.

Kinetic Mechanism of DNA Polymerization Catalyzed by Human DNA Polymerase ε

Eukaryotes require highly accurate and processive DNA polymerases to ensure faithful and efficient replication of their genomes. DNA polymerase ε (Polε) has been shown to catalyze leading-strand DNA synthesis during replication in vivo, but little is known about the kinetic mechanism of polymerization catalyzed by this replicative enzyme. To elucidate this mechanism, we have generated a truncated, exonuclease-deficient mutant of the catalytic subunit of human Polε (Polε exo-) and carried out pre-steady-state kinetic analysis of this enzyme. Our results show that Polε exo-, as other DNA polymerases, follows an induced-fit mechanism when catalyzing correct nucleotide incorporation. Polε exo- binds DNA with a Kd(DNA) of 79 nM and dissociates from the E·DNA binary complex with a rate constant of 0.021 s(-1). Although Polε exo- binds a correct incoming nucleotide weakly with a Kd(dTTP) of 31 μM, it catalyzes correct nucleotide incorporation at a fast rate constant of 248 s(-1) at 20 °C. Both a large reaction amplitude difference (42%) between pulse-chase and pulse-quench assays and a small elemental effect (0.9) for correct dTTP incorporation suggest that a slow conformational change preceding the chemistry step limits the rate of correct nucleotide incorporation. In addition, our kinetic analysis shows that Polε exo- exhibits low processivity during polymerization. To catalyze leading-strand synthesis in vivo, Polε likely interacts with its three smaller subunits and additional replication factors in order to assemble a replication complex and significantly enhance its polymerization processivity.

Two-nucleon scattering: Merging chiral effective field theory with dispersion relations

We consider two-nucleon scattering close to threshold. Partial-wave amplitudes are obtained by an analytic extrapolation of subthreshold reaction amplitudes calculated in a relativistic formulation of chiral perturbation theory. The constraints set by unitarity are used in order to stabilize the extrapolation. Neutron-proton phase shifts are analyzed up to laboratory energies $T_{{\rm lab}}\simeq250$ MeV based on the next-to-next-to-next-to-leading order expression for the subthreshold amplitudes. We find a reasonably accurate description of the empirical S- and P-waves and a good convergence of our approach. These results support the assumption that the subthreshold nucleon-nucleon scattering amplitude may be computed perturbatively by means of the chiral expansion. The intricate soft scales that govern the low-energy nucleon-nucleon scattering are generated dynamically via a controlled analytic continuation.