Brief Introduction to KLOE Experiment

　　KLOE (K LOng Experiment) is one of the 3 experiments being carried out at the electron positron collider of DAFNE at Laboratori Nazionale di Frascati (LNF), Instituto Nazionale di Fisica Nucleare (INFN), Italy. It aims at the study of kaon physics. The other two experiments are respectively FINUDA for the research on super nucleus and DEAR for studying kaonic hydrogen. The main objective of KLOE is to detect the direct CP violation during kaon decay. The measurement sensitivity of CP violation parameter （x¢/x）can reach 10-4. DAFNE optimizes its total energy to F meson mass, namely, 1020MeV／C2. It is the only electron positron collider operating in Φenergy region in the world, called Φ factory. Its designed luminosity is 5×l032cm-2s-1，with an annual supply to KLOE of 5×l010 F. Both DAFNE and the KLOE detector began to operate in April 1999.

　　KLOE at LNF, NA48 at CERN and KTEV at FNAL are the 3 experiments being carried out on kaon physics. KLOE is the only kaon experiment that the Institute of High Energy Physics (IHEP), the Chinese Academy of Sciences (CAS), has joined as a full member in addition to the research institutions from Italy, Germany, the United States, Israel, Russia, etc.

In 1993, IHEP officially joined the KLOE collaboration by invitation and signed the agreement on collaboration between IHEP, CAS and LNF, INFN.

KLOE detector is a universal spectrometer installed at DAFNE. It consists of a large effective tracking chamber, an electromagnetic calorimeter and a superconducting coil.

　　The large effective tracking chamber is used to measure the charged K° decay products. It adopts helium (90% helium + 10 % isobutene) as working gas and its drift chamber with a thin wall is 3.5 m in length and 4 m in diameter. There are 52,140 wires in the drift chamber. The walls of the drift chamber are made of materials with low atomic weight. The main performances of the tracking chamber are: the space resolution: 200mm (in the directions of r and f), 2mm (in z direction); the momentum resolution: dpt／pt／pt／pt／pt＝O.5％.

　　The electromagnetic calorimeter is used for time measurement and particle identification. It consists of the barrel and the end cap. It is a lead scintillating fiber sampling calorimeter. Its main performances are as follows: the shower vertex position resolution: 1 cm; the energy resolution: dE／E＝5％/ÖE（GeV）and the time resolution: dt＝66ps／ÖE（GeV）

　　The tracking chamber and electromagnetic calorimeter are inside a superconducting coil, which provides a field of 6,000 gauss along the z direction.

Goal of KLOE Experiment

　　Since the discovery of CP violation in 1964, the neutral kaon has become the means of research on CP violation. These neutral kaons are the decay products of F mesons produced by DAFNE. F meson usually decays into a kaon pair. This kind of decay provides an important stage for CP violation. A deeper understanding of CP violation is very important for particle physics and cosmology. Although B meson has become a new means of research on CP violation with the construction of B factory, kaon produced from F meson decay is purer and does not contain background. The interference production of two kinds of neutral kaons with different life has opened up a new field for the precise measurement of their interference.

　　The K K pair produced from F meson decay is in a well-defined quantum state (Jpc=1--). The neutral kaon pair forms a pair of short life kaon and long life kaon, which is very suitable for the study of CP violation. Compared with other experiments on CP violation, the uncertainty of the relativistic fluxes of short life kaon and long life kaon does not exist in the KLOE experiment. KLOE is the only experiment on CP violation during kaon decay being carried out at an electron positron collider in the world, which possesses a unique capability in the study of decay time interference of the two neutral kaons - ks and kL . By measuring the relativistic output of ks and kL → two charged and neutral p mesons, many precision measurements can be made of CP violation.

　　KLOE detector is optimized for the research on CP violation of kaons. The lead scintillating fiber structure of the electromagnetic calorimeter is brand-new, which can best detect photon and electron. The lower limit of photon detection energy is Eg » 20MeV. The tracking chamber is of a thin wall structure and adopts helium (90% He + 10％ Isobutane) as the working gas. The thin wall structure provides very good transparency for photons. It minimizes multi-scatterings and provides good detection of charged particles with low momentum. The KLOE detector design ensures that the path length of ks and kL decays can be measured to the required accuracy.

Content of KLOE International Collaboration

　　In 1993, IHEP officially joined the KOLE collaboration and signed a cooperative　 agreement with LNF. At the end of 1997, IHEP group was formed in China. And from 1998, it received financial support from National Natural Science Foundation of China (NSFC). In 1999, the KLOE collaboration was incorporated in the Agreement of Cooperation on Science and Technology between the People’s Republic of China and Italy.

　　According to the collaborative agreement between IHEP and LNF, the collaborative items are as follows:

　　During the construction of KLOE detector, some scientists from IHEP will be sent to LNF to join in the construction of the electromagnetic calorimeter and the tracking chamber and also in the research on related electronics, mechanical parts and technologies.

　　When KLOE is in operation, IHEP will join in data taking and data analysis. IHEP group will transplant and establish KLOE simulation and analyzing environment at IHEP, and analyze the data obtained from KLOE experiment.