L3 + Cosmics Experiment

%RE4 %title\\ \\The L3+C experiment takes advantage of the unique properties of the L3 muon spectrometer to get an accurate measurement of cosmic ray muons 30 m underground. A new muon trigger, readout and DAQ system have been installed, as well as a scintillator array covering the upper surfaces of the L3 magnet for timing purposes. The acceptance amounts to 200 $m^2 sr$. The data are collected independently in parallel with L3 running. In spring 2000 a scintillator array will be installed on the roof of the SX hall in order to estimate the primary energy of air showers associated with events observed in L3+C.\\ \\The cosmic ray muon momentum spectrum, the zenith angular dependence and the charge ratio are measured with high accuracy between 20 and 2000 GeV/c. The results will provide new information about the primary composition, the shower development in the atmosphere, and the inclusive pion and kaon (production-) cross sections (specifically the "$\pi$/K ratio") at high energies. These data will also help to solve problems related to the ``atmospheric neutrino puzzle'' (prediction of the absolute number of upward going muons above 10 GeV to be observed underground).\\ \\Other fundamental issues of cosmic ray and astroparticle physics are being investigated : Burst signals of point sources or gamma ray bursts (GRB) may be detected and the associated muons analyzed. The primary composition of cosmic rays in the knee region can be estimated through the recording of muon families. Observing the moon shadow with muons may enable one to set a flux limit for primary anti-protons near 1 TeV (the earth magnetic field acting as a momentum analyzer). Exotic events have been recorded by many different experiments. Measuring the momentum spectra of the particles should reveal clues to the processes involved. By recording time variations, meteorological effects as well as sideral anisotropies can be studied. Coincident events observed by other detectors situated far away are also within the experimental objectives we intend to explore.\\ \\Presently the experiment is collecting continuously 500 events/s (the $4\cdot 10^9$ event mark has been reached mid September 99).\\ \\