We present a study of the high rotational bands (J > 2) of H2 toward 4 early type galactic stars: HD 73882, HD 192639, HD 206267, and HD 207538. In each case, the velocity dispersion - characterized ...by the spectrum fitting parameter b - increases with the level of excitation, a phenomenon that has previously been detected by the Copernicus and IMAPS observatories. In particular, we show with 4 sigma confidence that for HD 192639 it is not possible to fit all J levels with a single b value, and that higher b values are needed for the higher levels. The amplitude of the line broadening, which can be as high as 10 km s^-1, makes explanations such as inhomogeneous spatial distribution unlikely. We investigate a mechanism in which the broadening is due to the molecules that are rotationally excited through the excess energy acquired after their formation on a grain (H2-formation pumping). We show that different dispersions would be a natural consequence of this mechanism. We note however that such process would require a formation rate 10 times higher then what was inferred from other observations. In view of the difficulty to account for the velocity dispersion as thermal broadening (T would be around 10,000 K), we conclude then that we are most certainly observing some highly turbulent warm layer associated with the cold diffuse cloud. Embedded in a magnetic field, it could be responsible for the high quantities of CH+ measured in the cold neutral medium.
We report on a detailed study of longitudinal strength in the nucleon resonance region, presenting new results from inclusive electron-proton cross sections measured at Jefferson Lab Hall C in the ...four-momentum transfer range 0.2 < Q^2 < 5.5 GeV^2. The data have been used to accurately perform 167 Rosenbluth-type longitudinal / transverse separations. The precision R = sigma_L / sigma_T data are presented here, along with the first separate values of the inelastic structure functions F_1 and F_L in this regime. The resonance longitudinal component is found to be significant, both in magnitude and in the existence of defined mass peaks. Additionally, quark-hadron duality is here observed above Q^2 = 1 GeV^2 in the separated structure functions independently.
Phys.Rev.Lett.101:042501,2008 We report new measurements of the neutron charge form factor at low momentum
transfer using quasielastic electrodisintegration of the deuteron.
Longitudinally polarized ...electrons at an energy of 850 MeV were scattered from
an isotopically pure, highly polarized deuterium gas target. The scattered
electrons and coincident neutrons were measured by the Bates Large Acceptance
Spectrometer Toroid (BLAST) detector. The neutron form factor ratio
$G^{n}_{E}/G^{n}_{M}$ was extracted from the beam-target vector asymmetry
$A_{ed}^{V}$ at four-momentum transfers $Q^{2}=0.14$, 0.20, 0.29 and 0.42
(GeV/c)$^{2}$.
The quasielastic (e,eprimep) reaction was studied on targets of deuterium, carbon, and iron up to a value of momentum transfer Q2 of 8.1 (GeV/c)2. A nuclear transparency was determined by comparing ...the data to calculations in the plane-wave impulse approximation. The dependence of the nuclear transparency on Q2 and the mass number A was investigated in a search for the onset of the color transparency phenomenon. We find no evidence for the onset of color transparency within our range of Q2. A fit to the world's nuclear transparency data reflects the energy dependence of the free-proton-nucleon cross section.
Phys.Rev.Lett.98:052301,2007 We report the first precision measurement of the proton electric to magnetic
form factor ratio from spin-dependent elastic scattering of longitudinally
polarized ...electrons from a polarized hydrogen internal gas target. The
measurement was performed at the MIT-Bates South Hall Ring over a range of
four-momentum transfer squared $Q^2$ from 0.15 to 0.65 (GeV/c)$^2$.
Significantly improved results on the proton electric and magnetic form factors
are obtained in combination with previous cross-section data on elastic
electron-proton scattering in the same $Q^2$ region.
We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 ...MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio \(G^{n}_{E}/G^{n}_{M}\) was extracted from the beam-target vector asymmetry \(A_{ed}^{V}\) at four-momentum transfers \(Q^{2}=0.14\), 0.20, 0.29 and 0.42 (GeV/c)\(^{2}\).
We report on a detailed study of longitudinal strength in the nucleon
resonance region, presenting new results from inclusive electron-proton cross
sections measured at Jefferson Lab Hall C in the ...four-momentum transfer range
0.2 < Q^2 < 5.5 GeV^2. The data have been used to accurately perform 167
Rosenbluth-type longitudinal / transverse separations. The precision R =
sigma_L / sigma_T data are presented here, along with the first separate values
of the inelastic structure functions F_1 and F_L in this regime. The resonance
longitudinal component is found to be significant, both in magnitude and in the
existence of defined mass peaks. Additionally, quark-hadron duality is here
observed above Q^2 = 1 GeV^2 in the separated structure functions
independently.
Polarized electrons in the MIT-Bates South Hall Ring Zwart, T.; Akdogan, T.; Dow, K. ...
PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268),
2001, Letnik:
5
Conference Proceeding
Odprti dostop
The MIT-Bates facility is pursuing a vigorous spin physics program in its 1 GeV electron storage ring. The combination of polarized beams, polarized internal targets and a large acceptance ...spectrometer will allow world class measurements of important nuclear physics quantities including G/sup N//sub E/ and T/sub 20/. Toward this end we have constructed and installed a Siberian Snake to preserve longitudinal electron polarization at the internal target, a laser back-scattering Compton polarimeter to accurately measure the stored electron polarization and an RF coil for resonantly flipping the electron spin which will provide an important systematic check of all measured polarization dependent asymmetries. The status of the stored polarized beam and results from all these polarization handling devices are presented below.
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