8 research outputs found
UBVI CCD Photometry of the Old Open Cluster Berkeley 17
Photometric UBVI CCD photometry is presented for NGC 188 and Berkeley 17.
Color-magnitude diagrams (CMDs) are constructed and reach well past the
main-sequence turn-off for both clusters. Cluster ages are determined by means
of isochrone fitting to the cluster CMDs. These fits are constrained to agree
with spectroscopic metallicity and reddening estimates. Cluster ages are
determined to be 7.0+/-0.5 Gyr for NGC 188, and 10.0+/- 1.0 Gyr for Berkeley
17, where the errors refer to uncertainties in the relative age determinations.
These ages are compared to the ages of relatively metal-rich inner halo/thick
disk globular clusters and other old open clusters. Berkeley 17 and NGC 6791
are the oldest open clusters with an age of 10 Gyr. They are 2 Gyr younger than
the thick disk globular clusters. These results confirm the status of Berkeley
17 as one of the oldest known open cluster in the Milky Way, and its age
provides a lower limit to the age of the Galactic disk.Comment: to appear in AJ; 28 pages, 9 figure
Emerging technologies in physics education
Three emerging technologies in physics education are evaluated from the
interdisciplinary perspective of cognitive science and physics education
research. The technologies - Physlet Physics, the Andes Intelligent Tutoring
System (ITS), and Microcomputer-Based Laboratory (MBL) Tools - are assessed
particularly in terms of their potential at promoting conceptual change,
developing expert-like problem-solving skills, and achieving the goals of the
traditional physics laboratory. Pedagogical methods to maximize the potential
of each educational technology are suggested.Comment: Accepted for publication in the Journal of Science Education and
Technology; 20 page
Maverick dark matter at colliders
Assuming that dark matter is a weakly interacting massive particle (WIMP)
species X produced in the early Universe as a cold thermal relic, we study the
collider signal of pp or ppbar -> XXbar + jets and its distinguishability from
standard-model background processes associated with jets and missing energy. We
assume that the WIMP is the sole particle related to dark matter within reach
of the LHC--a "maverick" particle--and that it couples to quarks through a
higher dimensional contact interaction. We simulate the WIMP final-state signal
XXbar + jet and dominant standard-model (SM) background processes and find that
the dark-matter production process results in higher energies for the colored
final state partons than do the standard-model background processes, resulting
in more QCD radiation and a higher jet multiplicity. As a consequence, the
detectable signature of maverick dark matter is an excess over standard-model
expectations of events consisting of large missing transverse energy, together
with large leading jet transverse momentum and scalar sum of the transverse
momenta of the jets. Existing Tevatron data and forthcoming LHC data can
constrain (or discover!) maverick dark matter.Comment: 11 pages, 7 figure