35 research outputs found
The Size Distributions of Asteroid Families in the SDSS Moving Object Catalog 4
Asteroid families, traditionally defined as clusters of objects in orbital
parameter space, often have distinctive optical colors. We show that the
separation of family members from background interlopers can be improved with
the aid of SDSS colors as a qualifier for family membership. Based on an
~88,000 object subset of the Sloan Digital Sky Survey Moving Object Catalog 4
with available proper orbital elements, we define 37 statistically robust
asteroid families with at least 100 members using a simple Gaussian
distribution model in both orbital and color space. The interloper rejection
rate based on colors is typically ~10% for a given orbital family definition,
with four families that can be reliably isolated only with the aid of colors.
About 50% of all objects in this data set belong to families, and this fraction
varies from about 35% for objects brighter than an H magnitude of 13 and rises
to 60% for objects fainter than this. The fraction of C-type objects in
families decreases with increasing H magnitude for H > 13, while the fraction
of S-type objects above this limit remains effectively constant. This suggests
that S-type objects require a shorter timescale for equilibrating the
background and family size distributions via collisional processing. The size
distributions for 15 families display a well-defined change of slope and can be
modeled as a "broken" double power-law. Such "broken" size distributions are
twice as likely for S-type familes than for C-type families, and are dominated
by dynamically old families. The remaining families with size distributions
that can be modeled as a single power law are dominated by young families. When
size distribution requires a double power-law model, the two slopes are
correlated and are steeper for S-type families.Comment: 50 pages, 16 figures, accepted for publication in Icaru
Prompt charm production in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV
Charm production at the LHC in pp collisions at sâ=7 TeV is studied with the LHCb detector. The decays D0âKâÏ+, D+âKâÏ+Ï+, Dâ+âD0(KâÏ+)Ï+, D+sâÏ(KâK+)Ï+, Î+câpKâÏ+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nbâ1. Differential cross-sections dÏ/dpT are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0<pT<8 GeV/c and 2.0<y<4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above pT-y range, and their ratios are reported. A combination of the five integrated cross-section measurements gives
Ï(ccÂŻ)pT<8 GeV/c,2.0<y<4.5=1419±12(stat)±116(syst)±65(frag) Όb,
where the uncertainties are statistical, systematic, and due to the fragmentation functions