4 research outputs found
The status of the ARGO experiment at YBJ
The ARGO-YBJ experiment, located at Yangbajing, Tibet, China, performed by a wide Sino-Italian
collaboration, is designed to study cosmic rays, sub-TeV gamma ray sources and GeV Gamma Ray
Burst (GRB) emission in the northern hemisphere, by means of detecting small size EAS (Extensive Air
Shower) using a full coverage RPC (Resistive Plate Chamber) carpet. The central carpet of the detector
is installed and put into operation to date, with 1900m2 of the carpet already operating since December
2004. With a trigger multiplicity of ≥60 hits, corresponding to a primary mode energy of 2 TeV, the
angular resolution of EAS measurements is < 1o for showers with more than 500 recorded hits. We report
the preliminary results of data taking performed during 2005: the all-sky survey for gamma ray sources
and the search for GRBs, as well as the cosmic ray spectrum up to about 100TeV. The Forbush decrease
of the cosmic ray flux during January, 2005 is observed using the ARGO data
Measurement of the CP violating asymmetry amplitude sin 2beta
We present results on time-dependent CP-violating asymmetries in neutral B
decays to several CP eigenstates. The measurements use a data sample of about
88 million Y(4S) --> B Bbar decays collected between 1999 and 2002 with the
BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We study
events in which one neutral B meson is fully reconstructed in a final state
containing a charmonium meson and the other B meson is determined to be either
a B0 or B0bar from its decay products. The amplitude of the CP-violating
asymmetry, which in the Standard Model is proportional to sin2beta, is derived
from the decay-time distributions in such events. We measure sin2beta = 0.741
+/- 0.067 (stat) +/- 0.034 (syst) and |lambda| = 0.948 +/- 0.051 (stat) +/-
0.030 (syst). The magnitude of lambda is consistent with unity, in agreement
with the Standard Model expectation of no direct CP violation in these modes.Comment: 7 pages, 2 postscript figures, submitted to PR