J.M. Brunet

The Barrel Ring Imaging Cherenkov counter of DELPHI

Abstract A short explanation is given of the Barrel Ring Imaging CHerenkov (BRICH) detector and its performance. We discuss in brief some of the requirements to run this detector. Special attention is paid to the functioning of the Cherenkov photon detector — a photosensitive gas-filled drift chamber where the photoelectrons drift to a MWPC of special construction. We illustrate the BRICH performance with some preliminary results.

Operation, optimisation, and performance of the DELPHI RICH detectors

The Ring Imaging Cherenkov detectors of DELPHI represent a large-scale particle identification system which covers almost the full angular acceptance of DELPHI. The combination of liquid and gas radiators (C4F10, C5F12, and C6F14) provides particle identification over the whole secondary particle momentum spectrum at LEP I and LEP II. Continuing optimisation on the hardware as well as on the online and offline software level have resulted in a stable operation of the complete detector system for more than five years at full physics performance.

The DELPHI pixels

Abstract To improve tracking in the very forward direction for running at LEP200, the angular acceptance of the DELPHI Vertex detector has been extended from 45° to 11° with respect to the beam axis. Pixel detector crowns cover the region between 25° and 13°. Due to very tight space and material thickness constraints it was necessary to develop new techniques (integrated busses in the detector substrate, high density layout on Kapton, etc.). About 1000 cm 2 of pixels are already installed and working in DELPHI. Techniques, tests and production of these detectors will be described, as well as the main problems encountered during this work.

Measurement of Deep Inelastic Compton Scattering of High-energy Photons

Abstract We present the first results on inclusive photo-production of prompt photons at high transverse momenta. The data were taken in an open spectrometer at CERN using a high intensity photon beam energy between 50 and 150 GeV. After subtracting the yield of photons from indirect sources, a clear excess is observed for transverse momenta above 2.5 GeV c Deep inelastic Compton scattering with appropriate QCD corrections account for this excess. The data disfavour the gauge integer charge quark models so far proposed.

Measurement ofJ/ψ and ψ′ real photoproduction on lithium-6 at a mean energy of 90 GeV

Inelastic and elasticJ/ψ (3097) photoproduction on Li6 are measured at a mean γ energy of 90 GeV in an open spectrometer. TheJ/ψ are identified by their decays intoμ+μ− ore+e−. A signal of ψ′(3685) intoμ+μ− andJ/ψπ+π− is also seen. The inelastic cross-section withZ=Eψ/Eγ<0.9 is compared in shape and magnitude with the colour singlet model of photon-gluon fusion.

High energy photoproduction of large transverse-momentum π0 mesons: A quantitative test of QCD

Abstract The first results on inclusive photoproduction of π 0 at transverse momenta up to 4 GeV/ c , using incident γ energies between 50 and 150 GeV are presented. A comparison is made with inclusive π 0 production obtained, in the same experiment, with incident π − . Using the π − data to parametrize the hadronic behaviour of the photon, significant differences are observed in quantitative agreement with QCD Compton scattering and corrections thereof.

New data on the reaction K−p→Λπ0 from 1.934 to 2.516 GeV/c and partial-wave analysis for this reaction between 2070 MeV and 2436 MeV CMS energy

Abstract We present the results of a formation experiment for the reaction K − p → Λπ 0 in the cms energy between 2200 and 2436 MeV with a total statistics of 10 eV/μb. A partial-wave analysis including these new data gives evidence for the existence of three resonances in the P 3 , D 5 and G 9 (or H 11 ) states in this mass region.

K+p elastic scattering in the intermediate momentum range region (2.1 to 2.7 GeV/c)

Abstract Preliminary results on total and differential K + p elastic cross-sections are presented at 2.11, 2.31, 2.53, 2.72 GeV/ c incident K + momenta. A Legendre polynomial analysis of the s -channel does not require more than a G-wave. On the other hand, a good description is obtained by extrapolating t -channel Regge pole calculations to these low energies. A reasonable agreement is found down to t =−0.7 (GeV/ c ) 2 .

The DELPHI very forward tracker for LEP200

Abstract The design of a new silicon tracker detector for the forward region in the DELPHI experiment is presented. It consists of two layers of macropixel and two layers of ministrip detectors in both the forward directions. The motivations and the requirements for this detector will be shown together with test beam results.

Current achievements of the DELPHI ring imaging Cherenkov detector

Abstract The DELPHI experiment has already collected 2.5 million Z 0 decays with the ring imaging Cherenkov detector (RICH) operational. This detector, covering most of the solid angle, is designed to perform π K separation from 0.8 to 20 GeV/ c and K/p separation from 0.8 to 35 GeV/ c . After a brief detector description we discuss the actual operating conditions, the data monitoring and the signal treatment. The collected data from Z 0 decays and the detector response to signals from the calibration system are used to evaluate the performance of the RICH system.