The article deals with the study of a torque electric drive at low negative air temperatures used as part of the enclosing structure of a ventilated underground building. The increasing of the ...efficiency of the torque electric drive of the enclosing structure is analyzed, a simulation model of the torque electric drive is developed and a model of the control system of the enclosing structure in the language of MATLAB&Simulink is designed. A software model in the form of Arduino software package was developed to study the drive operation of the ventilated underground of building enclosure structure in the permafrost zone.
Hadrons in the nuclear medium Sargsian, M M; Arrington, J; Bertozzi, W ...
Journal of physics. G, Nuclear and particle physics,
03/2003, Letnik:
29, Številka:
3
Journal Article
Elastic electron-proton scattering (e-p) and the spectroscopy of hydrogen atoms are the two methods traditionally used to determine the proton charge radius, r
. In 2010, a new method using muonic ...hydrogen atoms
found a substantial discrepancy compared with previous results
, which became known as the 'proton radius puzzle'. Despite experimental and theoretical efforts, the puzzle remains unresolved. In fact, there is a discrepancy between the two most recent spectroscopic measurements conducted on ordinary hydrogen
. Here we report on the proton charge radius experiment at Jefferson Laboratory (PRad), a high-precision e-p experiment that was established after the discrepancy was identified. We used a magnetic-spectrometer-free method along with a windowless hydrogen gas target, which overcame several limitations of previous e-p experiments and enabled measurements at very small forward-scattering angles. Our result, r
= 0.831 ± 0.007
± 0.012
femtometres, is smaller than the most recent high-precision e-p measurement
and 2.7 standard deviations smaller than the average of all e-p experimental results
. The smaller r
we have now measured supports the value found by two previous muonic hydrogen experiments
. In addition, our finding agrees with the revised value (announced in 2019) for the Rydberg constant
-one of the most accurately evaluated fundamental constants in physics.
We summarize the ongoing scientific program of the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and give an outlook into future opportunities. The program addresses important topics ...in nuclear, hadronic, and electroweak physics, including nuclear femtography, meson and baryon spectroscopy, quarks and gluons in nuclei, precision tests of the standard model and dark sector searches. Potential upgrades of CEBAF and their impact on scientific reach are discussed, such as higher luminosity, the addition of polarized and unpolarized positron beams, and doubling the beam energy.
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, Letnik:
346, Številka:
6209
Journal Article
Recenzirano
Odprti dostop
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.
The CLAS forward electromagnetic calorimeter Amarian, M.; Asryan, G.; Beard, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2001, Letnik:
460, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab utilizes six iron-free superconducting coils to provide an approximately toroidal magnetic field. The six sectors are instrumented ...individually to form six independent spectrometers. The forward region (8°<
θ<45°) of each sector is equipped with a lead–scintillator electromagnetic sampling calorimeter (EC), 16
radiation lengths thick, using a novel triangular geometry with stereo readout. With its good energy and position resolution, the EC is used to provide the primary electron trigger for CLAS. It is also used to reject pions, reconstruct π° and η decays and detect neutrons. This paper treats the design, construction and performance of the calorimeter.
We report a new extraction of nucleon resonance couplings using π− photo-production cross sections on the neutron. The world database for the process γn → π−p above 1 GeV has quadrupled with the ...addition of new differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab in Hall B. Differential cross sections from CLAS have been improved with a new final-state interaction determination using a diagrammatic technique taking into account the SAID phenomenological NN and πN final-state interaction amplitudes. Resonance couplings have been extracted and compared to previous determinations. With the addition of these new cross sections, significant changes are seen in the high-energy behavior of the SAID cross sections and amplitudes.
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