Brief Introduction to L3 + C

　　LEP at CERN, Geneva has a circumference of 27 kilometers. It is an electron positron collider with the highest energy in the world (the colliding energy totaling 200 GeV). L3 is one of the four experiments carried out at LEP (The other three experiments are respectively Aleph, Delphi and Opal), aiming at detecting secondary particles produced during the electron and positron annihilation to better understand the weak electro mechanism. It belongs to the frontier of high-energy physics research.

　　The international collaborative project of L3 + C is to carry out the research on an important subject concerning the frontier of non-accelerator based particle physics using L3 detector.

　　The original plan of L3 + C was only to measure the precision spectrum of cosmic ray muons and to infer atmospheric neutrino spectra. Later the Chinese physicists put forward a tentative idea of searching for unknown particles in the cosmic ray using L3 + C. In 1996, L3 group proposed to exploit L3 detector for interesting cosmic ray study. Thus a good opportunity was offered for our proposed experiment. Following contacts with Professor S. C. C. Ting and his chief assistants, L3 group agreed to accept our proposal and expressed their willingness to cooperate with us by installing 202 square meters’ scintillator detector for positioning and trigger above the large precise drift chambers and adding the parallel wire readout and DAQ system to meet the requirement of cosmic ray research. During the running of L3 experiment, by taking advantage of the large precise drift chambers and the large volume magnetic field, data of the cosmic ray muons will be collected independently and the precise muon flux measurement at 30 m underground will be available. Simultaneously unknown particles (WIMP) in cosmic rays and other new phenomena beyond the standard model of particle physics will also be searched for.

　　This international collaborative project adopts the most advanced equipment and technologies in the world, needs less investment and is helpful for cultivating a young generation of Chinese scientists. In 1998, the Institute of High Energy Physics (IHEP), the Chinese Academy of Sciences (CAS) singed a formal cooperative agreement with all research institutions involved in this experiment. The Chinese group contributed 16.6 million RMB, which accounts for only part of the total budget for this project. This is a large international collaborative project in which Chinese physicists brought excellent physics goals and made substantial contributions in many respects. As the conditions available for operating the large detector are used to the best advantage, this project has a very high ratio of performance to cost.

Research Topics of L3 + C　　 

　　L3 detector is 15.6 m high and 13.6 m long. It comprises 3 layers of high precision drift chambers installed in two wheels of 8 octants. If you look at it from the axis, you will find that it looks exactly like the Chinese Eight Trigrams. The L3 + C collaboration group upgraded the detector in the following respects:

　　1. Development of Hardware and Software

　　① 202 m2 timing scintillators (Hereafter referred to as to detector. This detector, the precision muon drift chambers and the magnetic field constitute the cosmic ray muon spectrometer.) were to be added on each of the 3 top octants (numbered 1,2 and 3) for recording the arrival time of the cosmic ray particles. The Chinese group undertook the task of developing 154 m2 timing scintillators, including the choice of scintillator, the optic fiber coating, the quality control of batch production, the module designing, the supporting structure and the implementation of installation.

　　② The 3 layers of muon drift chambers in the magnet are used for the track positioning and momentum measurement. Thus a special electronics system (L3CD) for track positioning and particle flying direction determining was developed.

　　③ A new and completely independent readout, trigger and data acquisition system was added to the existing L3 set-up. The independence of this system can avoid its interference with the L3 data taking.

　　④ The former L3 software package was improved to suit the research on cosmic ray, for example, the cross octant track reconstruction.

　　2. Data Treatment and Physics Analysis

　　① Precision measurement of the cosmic ray m spectrum and positive excess at zenith from 00 to 500 . It is expected to infer the atmospheric neutrino spectra;

　　② To search for up-going new long life particles with heavy mass;

　　③ To study the change of solar large-scale magnetic field and to extract the upper limit of the antiproton flux 1 TeV with the sun or moon shadow;

　　④ Using multi m events to study the characteristics of hadronic collision at the energy region before the “knee” and the composition of cosmic rays at the energy region of the “knee” and to search for exotic phenomena of the extensive air shower core;

　　⑤ To observe up-going muons and study the oscillation of atmospheric neutrinos;

　　⑥ To search for VHEγray burst and after glow of GRBs;

　　⑦ To observe intensity change of high energy solar cosmic ray after solar flare.