A.C. McPherson

The OPAL vertex drift chamber

Abstract A high precision vertex drift chamber has been installed in the OPAL experiment at LEP. The design of the chamber and the associated readout electronics is described. The performance of the system has been studied using cosmic ray muons and the results of these studies are presented. A space resolution of 50 μm in the drift direction is obtained using the OPAL central detector gas mixture at 4 bar.

Partial wave analysis of the K°π+π− system produced in K−p interactions at 11 GeV/c☆

Abstract We have performed a partial wave analysis of the K °π + π − system produced in the reaction K − p → K °π + π − n at 11 GeV /c and detected in the LASS spectrometer at SLAC. Results from an analysis of ≈7600 events in the K °π + π − mass range from 1090 to 2290 MeV/c2 produced at low t(∥t′∥ The JP = 2+, 3− and 4+ amplitudes show the behavior expected of the leading K∗(1430), K∗(1780) and K∗(2060) respectively. The behavior of the JP = 1+ and 2− amplitudes can be associated with the Q2(1400) and the L(1770). The 1− amplitudes exhibit behavior which indicates the existence of two resonant states, one near 1400 MeV/c2 and the other near 1800 MeV/c2. A simple Breit-Wigner model is used to fit the leading partial wave amplitudes and to compute branching ratios for the K∗(1430) and the K∗(1780).

Observation of a spin-parity 4+ K∗(2090)

Abstract High statistics data for the reaction K − p → K − π + n at 11 GeV c have been obtained in the LASS spectrometer at SLAC. A spherical harmonic moment analysis of the Kπ angular distribution displays evidence for a new K ∗ state at 2086 MeV c 2 with the spin-parity assignment, J P = 4 + .

Design and tests of the z-coordinate drift chamber system for the opal central detector at LEP

Abstract A system of drift chambers has been designed to make high resolution measurements of the z -coordinates of charged tracks at the outer radius of the OPAL central detector at LEP. The unit module of this detector is a 25 cm drift length bidirectional cell with six sense wires in a thin 50 cm wide by 29 mm high drift slot. Tests indicate that the chamber has a wide and stable electric field operating range and its performance is unaffected by small misalignments between the drift electric field and an external magnetic field. The drift cell was found to have uniform acceptance up to its geometrical boundaries, and the z -resolution for beam tracks normal to the chamber was measured to be in the range of 40–175 μm.

Observation of two non-leading strangeness-one vector mesons

Abstract We present evidence for the existence of two strange JP = 1− mesons; one at 1410 MeV/c2 coupling principally to K ∗ (892)π , and the other at 1790 MeV/c2 couplingto Kπ, K ∗ π and ϱK. The data derive from a partial wave analysis of the K 0 π + π − system produced in the reaction K − p → K 0 π + π − n at 11 GeV /c . The production mechanism and quark model assignment of each state are discussed. The state at 1410 MeV/c2 most naturally understood as the first radial excitation of the K∗(892), and the 1790 MeV/c2 object can be interpreted as the triplet D wave partner to the 3−K∗(1780).

Track fitting in the OPAL vertex detector with stereo wires

The geometry of the vertex chamber for the OPAL detector at LEP is reviewed and expressions for the coordinates of the hits are given in terms of the measured drift distance and z-coordinate. The tracks are fitted by a procedure based on the Lagrange multipliers method. The increase in the accuracy of the fit due to the use of the stereo wires is discussed.