9 research outputs found
Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction
We report the first measurement of the target-normal single-spin asymmetry in
deep-inelastic scattering from the inclusive reaction
He on a polarized He gas target.
Assuming time-reversal invariance, this asymmetry is strictly zero in the Born
approximation but can be non-zero if two-photon-exchange contributions are
included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron
beam, covers a range of GeV, GeV and
. Neutron asymmetries were extracted using the effective nucleon
polarization and measured proton-to-He cross section ratios. The measured
neutron asymmetries are negative with an average value of for invariant mass GeV, which is non-zero at the
level. Our measured asymmetry agrees both in sign and magnitude
with a two-photon-exchange model prediction that uses input from the Sivers
transverse momentum distribution obtained from semi-inclusive deep-inelastic
scattering.Comment: This is the final edited version as published in PR
Probing the Repulsive Core of the Nucleon-Nucleon Interaction via the 4He(e,e'pN) Triple-Coincidence Reaction
We studied simultaneously the 4He(e,e'p), 4He(e,e'pp), and 4He(e,e'pn)
reactions at Q^2=2 [GeV/c]2 and x_B>1, for a (e,e'p) missing-momentum range of
400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a
proton or neutron recoiling almost back to back to the missing momentum,
leaving the residual A=2 system at low excitation energy. These data were used
to identify two-nucleon short-range correlated pairs and to deduce their
isospin structure as a function of missing momentum in a region where the
nucleon-nucleon force is expected to change from predominantly tensor to
repulsive. Neutron-proton pairs dominate the high-momentum tail of the nucleon
momentum distributions, but their abundance is reduced as the nucleon momentum
increases beyond ~500 MeV/c. The extracted fraction of proton-proton pairs is
small and almost independent of the missing momentum in the range we studied.
Our data are compared with ab-initio calculations of two-nucleon momentum
distributions in 4He.Comment: 6 pages, 2 figure
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Expanding the diversity of mycobacteriophages: insights into genome architecture and evolution.
Mycobacteriophages are viruses that infect mycobacterial hosts such as Mycobacterium smegmatis and Mycobacterium tuberculosis. All mycobacteriophages characterized to date are dsDNA tailed phages, and have either siphoviral or myoviral morphotypes. However, their genetic diversity is considerable, and although sixty-two genomes have been sequenced and comparatively analyzed, these likely represent only a small portion of the diversity of the mycobacteriophage population at large. Here we report the isolation, sequencing and comparative genomic analysis of 18 new mycobacteriophages isolated from geographically distinct locations within the United States. Although no clear correlation between location and genome type can be discerned, these genomes expand our knowledge of mycobacteriophage diversity and enhance our understanding of the roles of mobile elements in viral evolution. Expansion of the number of mycobacteriophages grouped within Cluster A provides insights into the basis of immune specificity in these temperate phages, and we also describe a novel example of apparent immunity theft. The isolation and genomic analysis of bacteriophages by freshman college students provides an example of an authentic research experience for novice scientists
Expanding the diversity of mycobacteriophages: insights into genome architecture and evolution.
Mycobacteriophages are viruses that infect mycobacterial hosts such as Mycobacterium smegmatis and Mycobacterium tuberculosis. All mycobacteriophages characterized to date are dsDNA tailed phages, and have either siphoviral or myoviral morphotypes. However, their genetic diversity is considerable, and although sixty-two genomes have been sequenced and comparatively analyzed, these likely represent only a small portion of the diversity of the mycobacteriophage population at large. Here we report the isolation, sequencing and comparative genomic analysis of 18 new mycobacteriophages isolated from geographically distinct locations within the United States. Although no clear correlation between location and genome type can be discerned, these genomes expand our knowledge of mycobacteriophage diversity and enhance our understanding of the roles of mobile elements in viral evolution. Expansion of the number of mycobacteriophages grouped within Cluster A provides insights into the basis of immune specificity in these temperate phages, and we also describe a novel example of apparent immunity theft. The isolation and genomic analysis of bacteriophages by freshman college students provides an example of an authentic research experience for novice scientists