The last decade has seen a marked shift in how the internal structure of hadrons is understood. Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and ...progress with lattice-regularised QCD have provided strong indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in the flavour-separation of the proton’s electromagnetic form factors; and phenomenology suggests that diquark correlations might be critical to the formation of exotic tetra- and penta-quark hadrons. A broad spectrum of such information is evaluated herein, with a view to consolidating the facts and therefrom moving toward a coherent, unified picture of hadron structure and the role that diquark correlations might play.
The CLAS detector at Jefferson Lab has provided the dominant part of all available worldwide data on exclusive meson electroproduction off protons in the resonance region. New results on the γυpN* ...transition amplitudes (electrocouplings) are available from analyses of the CLAS data and will be presented. Their impact on understanding of hadron structure will be discussed emphasizing the credible access to the dressed quark mass function that has been achieved for the first time by a combined analysis of the experimental results on the electromagnetic nucleon elastic and N → N* transition form factors. We will also discuss further convincing evidences for a new baryon state N′ (1720)3/2+ found in a combined analysis of charged double pion photo- and electroproduction cross sections off the protons.
The analysis of the nine 1-fold differential cross sections for the γr,vp→π+π−p photo- and electroproduction reactions obtained with the CLAS detector at Jefferson Laboratory was carried out with the ...goal to establish the contributing resonances in the mass range from 1.6 GeV to 1.8 GeV. In order to describe the photo- and electroproduction data with Q2-independent resonance masses and hadronic decay widths in the Q2 range below 1.5 GeV2, it was found that an N′(1720)3/2+ state is required in addition to the already well-established nucleon resonances. This work demonstrates that the combined studies of π+π−p photo- and electroproduction data are vital for the observation of this resonance. The contributions from the N′(1720)3/2+ state and the already established N(1720)3/2+ state with a mass of 1.745 GeV are well separated by their different hadronic decays to the πΔ and ρp final states and the different Q2-evolution of their photo-/electroexcitation amplitudes. The N′(1720)3/2+ state is the first recently established baryon resonance for which the results on the Q2-evolution of the photo-/electrocouplings have become available. These results are important for the exploration of the nature of the “missing” baryon resonances.
Here, we present the first measurement of dihadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, ...carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the gibuu model, which suggests that hadrons form near the nuclear surface and undergo multiple scattering in nuclei.These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei.
Given the rapidly increasing demographic of older adults, it is vital to implement effective behavioral strategies to improve physical function to maintain activities of daily living. However, ...changing physical activity in older adults remains extremely difficult. The current trial tested the efficacy of a novel, 6-month, home-based, DVD-delivered exercise program focusing on flexibility, balance, and toning on the physical function of older adults.
Older adults (N = 307) were recruited from 83 towns and cities throughout central Illinois. The trial consisted of 4 waves of recruitment and randomization from May 2010 through January 2012. Inclusion criteria included being inactive, at least 65 years of age, English speaking, providing physician's consent, and willingness to be randomized. Eligible participants were randomly assigned to 1 of 2 treatment conditions: the exercise intervention or a healthy aging, attentional control. Functional assessments were completed at baseline and following the 6-month DVD intervention. Measures included the Short Physical Performance Battery, assessments of flexibility and strength, and self-reported functional limitations.
Participants in the DVD intervention condition demonstrated significant improvements in the Short Physical Performance Battery (p = .005), lower extremity flexibility (p = .04), and upper body strength (p = .003). There were no effects of the intervention on self-reported functional limitations.
The exercise intervention produced a clinically significant improvement in the Short Physical Performance Battery and improvements in flexibility and strength, demonstrating the effectiveness of a low-cost DVD exercise program in improving physical function in older adults.
The CLAS12 Forward Time-of-Flight system Carman, D.S.; Clark, L.; De Vita, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2020, Volume:
960, Issue:
C
Journal Article
Peer reviewed
Open access
The Forward Time-of-Flight system for the large-acceptance CLAS12 spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility is described. The system is positioned at distances in ...the range from 6.2 m to 7.2 m from the beam–target interaction point and spans laboratory polar angles from 5∘→45∘ and nearly the full azimuth. The system consists of 540 individual scintillation counters with double-ended readout that range in length from 17 cm to 426 cm of discrete widths of 6 cm, 15 cm, and 22 cm, and of discrete thicknesses of 5 cm and 6 cm. The effective counter time resolution for passing charged particles varies from 50 ps for the shortest counters at small angles to 200 ps for the longest counters at large angles. The detectors are part of the forward-angle particle identification system for CLAS12 during offline event reconstruction and are a component of the online data acquisition trigger to select final state event topologies with forward-going charged particles.
We measured the triple coincidence A(e,e^{'}np) and A(e,e^{'}pp) reactions on carbon, aluminum, iron, and lead targets at Q^{2}>1.5 (GeV/c)^{2}, x_{B}>1.1 and missing momentum >400 MeV/c. This was ...the first direct measurement of both proton-proton (pp) and neutron-proton (np) short-range correlated (SRC) pair knockout from heavy asymmetric nuclei. For all measured nuclei, the average proton-proton (pp) to neutron-proton (np) reduced cross-section ratio is about 6%, in agreement with previous indirect measurements. Correcting for single-charge exchange effects decreased the SRC pairs ratio to ∼3%, which is lower than previous results. Comparisons to theoretical generalized contact formalism (GCF) cross-section calculations show good agreement using both phenomenological and chiral nucleon-nucleon potentials, favoring a lower pp to np pair ratio. The ability of the GCF calculation to describe the experimental data using either phenomenological or chiral potentials suggests possible reduction of scale and scheme dependence in cross-section ratios. Our results also support the high-resolution description of high-momentum states being predominantly due to nucleons in SRC pairs.
Momentum sharing in imbalanced Fermi systems Hen, O.; Sargsian, M.; Weinstein, L. B. ...
Science (American Association for the Advancement of Science),
10/2014, Volume:
346, Issue:
6209
Journal Article
Peer reviewed
Open access
The atomic nucleus is composed of two different kinds of fermions: protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority of ...fermions (usually neutrons) to have a higher average momentum. Our high-energy electron-scattering measurements using 12C, 27Al, 56Fe, and 208Pb targets show that even in heavy, neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few-body systems to neutron stars and may also be observable experimentally in two-spin–state, ultracold atomic gas systems.
Abstract Introduction In the present study, we examined the influence of a home-based, DVD-delivered exercise intervention on daily sedentary time and breaks in sedentary time in older adults. ...Methods Between 2010 and 2012, older adults (i.e., aged 65 or older) residing in Illinois ( N = 307) were randomized into a 6-month home-based, DVD-delivered exercise program (i.e., FlexToBa ; FTB) or a waitlist control. Participants completed measurements prior to the first week (baseline), following the intervention period (month 6), and after a 6 month no-contact follow-up (month 12). Sedentary behavior was measured objectively using accelerometers for 7 consecutive days at each time point. Differences in daily sedentary time and breaks between groups and across the three time points were examined using mixed-factor analysis of variance (mixed ANOVA) and analysis of covariance (ANCOVA). Results Mixed ANOVA models revealed that daily minutes of sedentary time did not differ by group or time. The FTB condition, however, demonstrated a greater number of daily breaks in sedentary time relative to the control condition ( p = .02). ANCOVA models revealed a non-significant effect favoring FTB at month 6, and a significant difference between groups at month 12 ( p = .02). Conclusions While overall sedentary time did not differ between groups, the DVD-delivered exercise intervention was effective for maintaining a greater number of breaks when compared with the control condition. Given the accumulating evidence emphasizing the importance of breaking up sedentary time, these findings have important implications for the design of future health behavior interventions.
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