118659723
Search for TeV-antiprotons in space from the shadowing of cosmic rays by the moon with the L3+C detector
A search for antiprotons in the primary cosmic ray flux has been performed by observing the Moon shadow with the muon data collected by the L3+C experiment at CERN during 1999 and 2000. The angular resolution ofthe detector and its dependences on the muon energy and zenith angle are obtained at the event level with a Monte Carlo simulation and the analysis of real double muon data using a maximum likelihood method. The Moon shadow effect is observed in three muon momentum bands > 100 GeV/c, 65 100 GeV/c and 30 65 GeV/c with a significance of 7.0 0",5.80" and 5.2 0" respectively. Two dimensional maximum likelihood analyses are performed, both with binned data and unbinned data. The unbinned method gives a smaller uncertainty on the measurement of the antiproton to proton ratio. For a muon momentum cut at 70 GeV/c, the antiproton to proton ratio is measured to be -0.12 ±O.ll and an upper limit ofthis ratio is estimated to be 0.08 (at 90% confidence level) for primary energies in the range 0.8 TeV to 2.4 TeV. In addition, the above mentioned angular resolution is confirmed by the Moon shadow observation and the pointing precision of the detector is determined to be better than 0.1 0 •
116433269
A Search for Astrophysical Point Sources and a Solar Anisotropy measurement
The L3 detector at LEP, CERN, has been employed for the search of point sources through the observation of muons with energies above 20, 30, 50, and 100 GeV. Excesses lasting for only one day, as well as steady emissions of single muon events pointing to a particular direction in the sky were searched for in the data obtained from mid July to October 1999 and from April to November 2000. Special attention was also given to a selection of known γ-sources. No statistically significant excess has been observed for any direction or particular source in the time periods considered. In addition a dedicated study of the angular distribution of muons above 20 GeV revealed evidence for a Solar anisotropy of the primary flux.
14866078
The asymmetric structure of the Galactic halo
Using the stellar photometry catalogue based on the latest data release (DR4) of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using star counts is carried out for selected areas of the sky. The sample areas are selected along a circle at a Galactic latitude of +60 ◦ , and 10 strips of high Galactic latitude along different longitudes. Direct statistics of the data show that the surface densities of l from 180 ◦ to 360 ◦ are systematically higher than those of l from 0 ◦ to 180 ◦ , defining a region of overdensity (in the direction of Virgo) and another one of underdensity (in the direction of Ursa Major) with respect to an axisymmetric model. It is shown by comparing the results from star counts in the (g r) colour that the density deviations are due to an asymmetry of the stellar density in the halo. Theoretical models for the surface density profile are built and star counts are performed using a triaxial halo of which the parameters are constrained by observational data. Two possible reasons for the asymmetric structure are discussed.
119233618
The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
We present a support vector machine classifier to identify the K giant stars from the LAMOST survey directly using their spectral line features. The completeness of the identification is about 75% for tests based on LAMOST stellar parameters. The contamination in the identified K giant sample is lower than 2.5%. Applying the classification method to about two million LAMOST spectra observed during the pilot survey and the first year survey, we select 298,036Kgiant candidates. The metallicities of the sample are also estimated with an uncertainty of 0.13 similar to 0.29 dex based on the equivalent widths of Mgb and iron lines. A Bayesian method is then developed to estimate the posterior probability of the distance for the K giant stars, based on the estimated metallicity and 2MASS photometry. The synthetic isochrone-based distance estimates have been calibrated using 7 globular clusters with a wide range of metallicities. The uncertainty of the estimated distance modulus at K = 11 mag, which is the median brightness of the K giant sample, is about 0.6 mag, corresponding to similar to 30% in distance. As a scientific verification case, the trailing arm of the Sagittarius stream is clearly identified with the selected K giant sample. Moreover, at about 80 kpc from the Sun, we use our K giant stars to confirm a detection of stream members near the apo-center of the trailing tail. These rediscoveries of the features of the Sagittarius stream illustrate the potential of the LAMOST survey for detecting substructures in the halo of the Milky Way.