38 research outputs found
First measurement of direct photoproduction on the proton
We report on the results of the first measurement of exclusive
meson photoproduction on protons for GeV and GeV. Data were collected with the CLAS detector at the Thomas
Jefferson National Accelerator Facility. The resonance was detected via its
decay in the channel by performing a partial wave analysis of the
reaction . Clear evidence of the meson
was found in the interference between and waves at GeV. The -wave differential cross section integrated in the mass range of
the was found to be a factor of 50 smaller than the cross section
for the meson. This is the first time the meson has been
measured in a photoproduction experiment
Search for the pentaquark in the reactions and
The exclusive reactions and have been studied in the photon energy range 1.6--3.8 GeV, searching
for evidence of the exotic baryon in the decays and . Data were collected with the CLAS detector at
the Thomas Jefferson National Accelerator Facility. The integrated luminosity
was about 70 pb. The reactions have been isolated by detecting the
and proton directly, the neutral kaon via its decay to
and the neutron or neutral kaon via the missing mass technique. The mass and
width of known hyperons such as , and were
used as a check of the mass determination accuracy and experimental resolution.
Approximately 100,000 's and 150,000 's were observed in
the and final state respectively. No evidence
for the pentaquark was found in the or invariant mass
spectra. Upper limits were set on the production cross section of the reaction
as functions of center-of-mass angle,
and masses. Combining the results of the two reactions, the 95% C.L.
upper limit on the total cross section for a resonance peaked at 1540 MeV was
found to be 0.7 nb. Within most of the available theoretical models, this
corresponds to an upper limit on the width, ,
ranging between 0.01 and 7 MeV.Comment: 1 tex file (16 pages) + 23 figures (25 eps files
Novel genetic loci associated with hippocampal volume
The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness