Recent results in electromagnetic excitation of nucleon resonance are presented, and confronted with theoretical predictions. Preliminary data in the search for missing states are discussed as well. ...Resonance electroproduction has rich applications in nucleon structure studies at intermediate and large distances. Resonances play an important role in understanding the spin structure of the nucleon. More than 80% of the helicity-dependent integrated total photoabsorption cross-section difference (GDH integral) is a result of the excitation of the {Delta}(1232). At Q{sup 2} = 1 GeV{sup 2}, about 40% of the first moment {Lambda}{sub 1}{sup P}(Q{sup 2}) = {integral}{sub 0}{sup 1} g{sub 1}(x, Q{sup 2})dx for the proton is due to contributions of the resonance region at W < 2 GeV. Conclusions regarding the nucleon spin structure for Q{sup 2} < 2 GeV{sup 2} must therefore be regarded with some scepticism if contributions of baryon resonances are not taken into account.
Hadron physics has been an essential part of the physics program with the CLAS detector in experimental hall B at Thomas Jefferson National Accelerator Facility (Jefferson Lab). With the 12 GeV ...upgrade of the CEBAF machine, hadron physics in Hall B will be extended to a new domain of higher mass resonances and the range of higher transferred momentum using up to 11 GeV electron beams and the upgraded CLAS12 detector. In this paper, status of the hall B superconducting magnets for the 12 GeV upgrade is presented.
Hard two-body photodisintegration of 3He Pomerantz, I; Ilieva, Y; Amaryan, M J ...
Physical review letters,
2013-Jun-14, Letnik:
110, Številka:
24
Journal Article
Recenzirano
We have measured cross sections for the γ(3)He → pd reaction at photon energies of 0.4-1.4 GeV and a center-of-mass angle of 90°. We observe dimensional scaling above 0.7 GeV at this center-of-mass ...angle. This is the first observation of dimensional scaling in the photodisintegration of a nucleus heavier than the deuteron.
The helicity-dependent observable E for the reaction γd → ηn(p) with a spectator proton was recently measured in this paper by the A2 Collaboration at MAMI in Mainz. The data were interpreted as ...further evidence for a narrow resonance with spin and parity JP = 1/2+ (P11 wave). However, a full partial-wave analysis without any narrow resonance leads to an excellent description of the data. Finally, imposing a narrow resonance with the properties suggested by the A2 Collaboration leads to a significant deterioration of the fit quality: there is no need for a narrow resonance.
The electroexcitation amplitudes or $\gamma_vpN^*$ electrocouplings of the $N(1440)1/2^+$, $N(1520)3/2^-$, and $\Delta(1600)3/2^+$ resonances were obtained for the first time from the $ep \to ...e'\pi^+\pi^-p'$ differential cross sections measured with the CLAS detector at Jefferson Lab within the range of invariant mass $W$ of the final state hadrons from 1.4–1.7~GeV for photon virtualities $Q^2$ from 2.0--5.0~GeV$^2$. A good description of the nine independent one-fold differential $\gamma_v p\to \pi^+\pi^-p'$ cross sections achieved within the data-driven Jefferson Lab-Moscow State University (JM) meson-baryon reaction model in each bin of ($W$,$Q^2$) allows for separation of the resonant and non-resonant contributions. The electrocouplings were determined in the fits of the $\pi^+\pi^-p$ cross sections within three overlapping $W$ intervals with a substantial contribution from each of the three resonances listed above. Consistent results on the electrocouplings extracted from the data in these $W$ intervals provide evidence for their reliable extraction. These studies extend information on the electrocouplings of the $N(1440)1/2^+$ and $N(1520)3/2^-$ available from this channel over a broader range of $Q^2$. The electrocouplings of the $\Delta(1600)3/2^+$, which decays preferentially into $\pi\pi N$ final states, have been determined for the first time. Here, the reliable extraction of the electrocouplings for these states is also supported by the description of the $\pi^+\pi^-p$ differential cross sections with $Q^2$-independent masses and total/partial hadronic decay widths into the $\pi\Delta$ and $\rho p$ final states.
We present the first determination of the proton mechanical radius. The result was obtained by employing a novel theoretical approach that connects experimental data of deeply virtual Compton ...scattering with the spin = 2 interaction that is characteristic of gravity coupling with matter. We find that the proton mechanical radius is significantly smaller than its charge radius, consistent with the latest Lattice QCD computation.
•Astaxanthin is a powerful antioxidant that acts in the combat of free radicals.•SEDS is a promising technique for application in encapsulation of active principles.•The experiments do not exceeded ...308K to prevent degradation of the carotenoid.•The precipitation pressure had influence on the particle size formed.•Increase in the biomass:solvent ratio improved the encapsulation.
The objective of this work was to investigate the effectiveness of supercritical carbon dioxide as anti-solvent for the encapsulation of astaxanthin from Haematococcus pluvialis in co-polymer poly(hydroxybutirate-co-hydroxyvalerate) (PHBV) with dichloromethane as organic solvent using the solution enhanced dispersion by supercritical fluids (SEDS) technique. For the co-precipitation experiments of astaxanthin in PHBV the parameters tested were precipitation pressures of 80 and 100bar, the biomass containing astaxanthin: dichloromethane ratio (5, 8 and 10mgmL−1) at the carotenoid extraction step, PHBV concentration of 20mgmL−1 at the organic solution, keeping constant the temperature at 308K, solution flow rate, 1mLmin−1, and anti-solvent flow rate at 20mLmin−1. For the co-precipitation experiments the results showed that smaller particles (mean particle size of 0.128μm) were obtained at the highest pressure tested (100bar), while the highest encapsulation efficiency (48.25%) was obtained when using 10mgmL−1 of biomass containing astaxanthin:solvent ratio.
The Heavy Photon Search experiment took its first data in a 2015 engineering run using a 1.056 GeV, 50 nA electron beam provided by CEBAF at the Thomas Jefferson National Accelerator Facility, ...searching for a prompt, electroproduced dark photon with a mass between 19 and 81 MeV/c2. A search for a resonance in the e+e− invariant mass distribution, using 1.7 days (1170 nb−1) of data, showed no evidence of dark photon decays above the large QED background, confirming earlier searches and demonstrating the full functionality of the experiment. Upper limits on the square of the coupling of the dark photon to the standard model photon are set at the level of 6×10−6. Future runs with higher luminosity will explore new territory.
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