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Abstract

The H.E.S.S., experiment (High Energy Stereoscopic System) is an array of four imaging Cherenkov telescopes designed to detect gamma-rays in the energy domain above 100 GeV. The telescopes utilise the stereoscopic approach, in which particle showers in the atmosphere are observed by several telescopes simultaneously, connected by a central trigger system at the hardware level. This approach greatly reduces the background of the instrument and thereby allows one to decrease the energy threshold and improve the sensitivity of the system. The functionality and performance of the central trigger of H.E.S.S., is presented. Making use of the reduced energy threshold and the improved sensitivity, a survey of the inner part of the Milky way in very high energy gamma-rays, was conducted in 2004 with H.E.S.S. at an unprecedented sensitivity level. The Galactic plane between +- 30deg, in longitude and +-3deg, in latitude relative to the Galactic centre was observed for a total of 230 hours, reaching an average flux sensitivity of 3% of the Crab nebula at energies above 200 GeV. Fourteen new sources were detected at a significance level greater than 4 sigma in addition to three previously known sources in this area. Detailed spectral and morphological information for these new sources are provided, along with a discussion on possible counterparts in other wavelength bands. The distribution in galactic latitude of the detected sources appears to be consistent with a scale height in the galactic disc for the parent population of less than 100 parsec.