D. Hutchinson

Determination of ±s from a differential-jet-multiplicity distribution in e+e- collisions at ss =29 and 91 GeV

We measured the differential jet-multiplicity distribution in {ital e}{sup +}{ital e}{sup {minus}} annihilation with the Mark II detector. This distribution is compared with the second-order QCD prediction and {alpha}{sub {ital s}} is determined to be 0.123{plus minus}0.009{plus minus}0.005 at {radical}{ital s}{approx}{ital M}{sub {ital Z}} (at the SLAC Linear Collider) and 0.149{plus minus}0.002{plus minus}0.007 at {radical}{ital s}=29 GeV (at the SLAC storage ring PEP). The running of {alpha}{sub {ital s}} between these two center-of-mass energies is consistent with the QCD prediction.

Direct electron pair production in π−p interactions at 16 GeV/c and a model for direct lepton and photon production at low pT☆

Abstract The production of prompt electron-positron pairs in 16 GeV/c π−p collisions has been measured using the LASS spectrometer at SLAC. An excess of events is observed above the estimated contributions of direct and Dalitz decay of known resonances in the kinematic range defined by 0.1⩽x⩽0.45, 0⩽pT⩽0.8 GeV/c and 0.2⩽M(e+e−)⩽0.7 GeV/c2. The excess signal decreases slowly with increasing M, but exhibits very steep x and pT2 dependence. The contribution of this signal to the e+e− and γ/π ratios is discussed. Detailed comparisons are made between e+e− distributions and the corresponding low-mass μ+μ− distributions, and a simple production mechanism is proposed which describes the 16 GeV/c data well. The implications for direct photon production are presented, and it is shown that the model provides simultaneously a good description of the experimental data on the (e/π) and (μ/π) ratios for pT

The Mark III spectrometer

Abstract This paper describes the design, construction and performance of the Mark III, a new general purpose large solid angle spectrometer at SPEAR, the SLAC 2–8 GeV e+e− storage ring. The detector has been designed for the study of exclusive final states in e+e− annihilation, which requires large solid angle coverage combined with charged particle momentum resolution, particle identification, and photon detection efficiency at low energies.

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 + .

Observation of a direct low-mass e+e− continuum in π-p interactions at 16 GeV/c☆

Abstract The production of prompt electron-positron pairs in 16 GeV/c π-p collisions has been measured using the LASS spectrometer at SLAC. An excess of events is observed above the estimated contribution of direct and Dalitz decays of known resonances in the kinematic range defined by 0.1⩽χ⩽0.45, 0⩽p T ⩽0.8 GeV c and 0.2⩽M(e + e − )⩽0.7 GeV c 2 . The excess signal decreases slowly with increasing M, but exhibits very steep χ and pT2 dependence.

The Mark II Vertex Drift Chamber

We have completed constructing and begun operating the Mark-II drift chamber vertex detector. The chamber, based on a modified jet cell design, achieves 30 μm spatial resolution and <1000 μm track-pair resolution in pressurized CO2 gas mixtures. Special emphasis has been placed on controlling systematic errors, including the use of novel construction techniques which permit accurate wire placement. Chamber performance has been studied with cosmic ray tracks collected with the chamber located both inside and outside the Mark-II. Results on spatial resolution, average pulse shape, and some properties of CO2 mixtures are presented.

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).

The central drift chamber for the MARK III detector at SPEAR

Abstract A large cylindrical drift chamber has been constructed for the MARK III detector at SPEAR. The inner layer has a high density of sense wires for the measurement of kinks, vees, and d E d x . The outer layers have a cell design with three sense wires, giving uniform drift behavior and left/right ambiguity resolution within a cell. The chamber has both current division and stereo layers for longitudinal position measurement.

An Integrated Amplifier and Sample-and-Hold Analog Multiplexer Module

The integrated amplifier and sample-and-hold analog multiplexer-ISHAM, is a proportional wire chamber analog readout module. It includes the front-end am plifier, the gated integrator and the sample-and-hold analog multiplexer. A density of 24 channels per module was achieved in a nonstandard multilayer P.C. board. Besides the above mentioned functions, the module provides: the control circuits for the Read-In and the Read-Out of the wire signals, the control circuits for the calibration of the 24 amplifiers, and the neutral trigger information. As an additional feature, the high voltage required by each wire is also supplied. The gain is 5V output voltage @ 20 pC input signal charge. The equivalent input noise charge is 4 × 10-15 C for the channel only and 6 × 10-15 for the entire system. The nonlinearity is better than 0.1% f.s. and the crosstalk is less than 1%. The Z-position resolution achieved is 1%.