B. de Raad

«Glancing» collisions of pions with protons at 6.1 and 18.1 GeV/c

SummaryAn analysis is presented of inelastic hydrogen-like interactions with two or four charged prongs. An event was accepted only if one of the prongs was due to a slow recoil proton and if no strange particles were associated with it. The interactions were oberved in the large propane/freon bubble chamber of the École Polytechnique. Due to the adopted selection criteria, there was ≈75% detection probability for neutral pions through convesion of at least one of its decay photons. The analysis was carried out using the one-particle-exchange model as a guide, and the features of the events were found to be consistent with it. In a proportion of the events there was a secondary negative pion of almost the full primary momentum; this can be explained by diffraction off the exchanged virtual pion. In about 72% of the inelastic interactions with two charged prongs only one neutral pion was emitted.RiassuntoSi sono studiate in questo lavoro interazioni idrogenoidi con due e quattro rami utilizzando eventi a cui non erano associate particelle strane ed in cui uno dei secondari era riconoscibile come protone lento. Le interazioni, fotografate nella camera a bolle dell’École Politechnique, sono state selezionate in modo che la probabilità di rivelare un mesone π neutro dalla materializzazione di almeno uno dei fotoni di decadimento fosse del 72% circa. La nostra analisi è stata svolta in base al modello di scambio di una particella e le caratteristiche degli eventi sono risultate in accordo col modello stesso. In una parte degli eventi vi è un pione secondario negativo con impulso molto vicino a quello del pione incidente il che può essere interpretato sulla base di una diffrazione sul pione virtuale scambiato. Si è osservato che in circa il 72% delle interazioni anelastiche a due rami viene emesso un solo pione neutro.

Status of magnetic horn and neutrino beam

The magnetic horn is a focusing device that accepts particles of widely varying momentum and with large emission angles. It is intended to focus e (as Fe/sup 59 and K mesons coming from a target before they decay into neutrinos in order to produce a high-intensity neutrino beam. The proton beam from the CPS will be ejected and focused on an external target inside the horn. The ejection apparatus, transport channel, and horn are described. Curves show the estimated neutrino flux per circulating proton for different currents in the horn. (A.G.W.)

The Damper for the Transverse Instabilities of the SPS

For beam intensities above 1012 protons per pulse in the SPS, collective transverse beam instabilities develop with frequencies between 15 kHz and 3 MHz because of the resistive wall effect of the vacuum chamber1). An active feedback system2) with an electrostatic deflector has been installed in the SPS for damping the resistive wall instabilities in both the vertical and horizontal planes. Measurements have been made to determine the threshold and growth rate of these instabilities. As a novel application, the damper can be used also for the excitation of small coherent betatron oscillations. A phase-locked loop tracks the beam oscillations and provides a continuous display of the betatron wavenumber Q during the cycle.

Extraction from the CERN SPS

The experimental programme requires three different modes of extraction from the SPS : fast extraction (burst duration from 3 ¿s to 23 ¿s), slow resonant extraction (spill duration 0.5 s to 2 s) and fast resonant extraction (spill duration shorter than 3 ms). All three modes have been successfully tested and brought into operation. Fast extraction of the full beam is 100% efficient. By fast beam shaving, fractions as low as 1% of the circulating beam can be extracted in a fairly stable way. Third-integer extraction is used to produce slow spills of 700 ms or more. The efficiency of resonant extraction is currently some 97%. The spill duty factor at present amounts to about 40%. Fast resonant spills of less than 2 ms were achieved with both integer and half-integer extraction. The different modes of extraction are consecutively performed during each accelerator cycle. At present, a 1 s third-integer spill at 200 GeV/c is followed by a fast shaving extraction at 210 GeV/c and by a fast or fast resonant extraction of the remaining protons at 400 GeV/c.

The CERN SPS Proton-Antiproton Collider

The SPS now operates for about 40% of the time as a proton-antiproton collider at a centre of mass energy of 630 GeV. Towards the end of 1984 the SPS achieved a peak luminosity of 3.6×1029cm-2s-1, with a luminosity lifetime of 28 hours and an average integrated luminosity of 5nb-1 per day. This report reviews the operational experience and limitations of the collider and describes the improvements which will be implemented to increase its luminosity by an order of magnitude.

Correlations in strange-particle pairs produced by π of 6, 11 and 18 GeV/c

SummaryInteractions of π− of 6.1, 11.6 and 18.1 GeV/c from the CERN PS on protons or quasi-free neutrons have been studied in the Ecole Polytechnique one-meter bubble chamber filled with a mixture 86% propane C3H8-14% freon CF3Br (by volume). Interactions have been selected in which two neutral strange particles are visible in order to study correlations among the strange particles and to study separately the behaviour of the K10’s from the reactions: π−+N → K0 + -K0+nπ +N, π−+N → K0+Λ(Σ0)+nπ. It is found that πp c.m.s longitudinal and transverse momentum distributions are similar for the K10’s from K0-K0 and from K0Y0 pairs. They tend to go forward in the c.m.s., small momenta being most probable. The baryon (A or nucleon) tends to go backward in the c.m.s. but with longitudinal momentum distributed roughly uniformly from slightly forward to the maximum kinematically possible backward. The K10’s of K10K10 pairs tend to have relative energy which is only a small fraction of that available with a distribution roughly independent of the π− beam momentum and of the πp c.m.s. momentum of the K10K10 system. This effect does not seem to be due to phase-space limitations arising from backward peaking of the nucleon. We have too few events to decide whether this low-energy peaking of theQ-values is due to a resonance near 1.1 GeV or to a strong low-energy K0-K0 inter-action. Clear evidence of K* (0.89 GeV) and to a lesser degree of Y1* (1.39 GeV) are seen in K0A production. (47±15)% of all K10π+ systems are (K*)+, (30±20)% of all Λπ systems are Y1*. No evidence is seen of K* production in K10K10 producing jets.RiassuntoSi sono studiate le interazioni di π− di 6.1, 11.6 e 18.1 GeV/c del PS del CERN su protoni o neutroni quasi liberi nella camera a bolle di un metro dell’École Poly-technique riempita con una miscela di 86% di propano C3H8 e 14% di freon CF3Br (in volume). Si sono scelte interazioni in cui sono visibili due particelle strane neutre, allo scopo di studiare le correlazioni fra le particelle strane e di esaminare separatamente il comportamento dei K10 dalla reazione π−−+N → K0+−K0+nπ+N, π−+N → → K0+Λ(Σ0)+ nπ. Si trova che le distribuzioni dell’impulso longitudinale e trasversale nel s.c.m. dei πp sono simili per i K10 provenienti sia dalle coppie K0−K che dalle coppie K0Y0. Essi tendono ad andare avanti nel s.c.m., e gli impulsi più piccoli sono i più probabili. Il barione (Λ o nucleone) tende ad andare all’indietro nel s.c.m. ma con impulso longitudinale distribuito in modo grossolanamente uniforme da legger-mente in avanti a massimo indietro cinematicamente possibile. I K10 delle coppie K10K10 tendono ad avere un’energia relativa che è solo una piccola frazione di quella disponibile con una distribuzione grossolanamente indipendente dall’impulso del f ascio di π− e dall’impulso del sistema K10K10 nel s.c.m. πp. Questo effetto non sembra dovuto a limitazioni di spazio delle fasi derivanti dal picco all’indietro del nucleone. Si hanno pochi elementi per decidere se questo picco di bassa energia dei valoriQ è dovuto ad una risonanza prossima a 1.1 GeV o ad una forte interazione K0−K0 di bassa energia. Nella produzione di K0A si notano chiaramente i segni del K* (0.89 GeV) ed in grado minore del Y1* (139 GeV). II (47±15)% dei sistemi K10π+ sono (K*)+, il (30±20)% dei sistemi Λπ sono Y1*. Non si vedono segni di produzione di K* nei K10K10 che producono getti.

Methods to compute the optics of beam transfer channels

Abstract In the course of the design of the beam transfer channels for the Intersecting Storage Rings project at CERN, Geneva, a computer programme has been developed capable of performing all the operations necessary for the design of extensive beam transport systems, viz., the matching of phase-space ellipses and momentum compaction and the computation of beam envelopes along a channel, trajectories of particles, transfer matrices, betatron parameters of periodic magnetic lattices, and geometry of central orbits.

Experimental utilization of proton storage rings

The addition of 25-Bev proton storage rings to the CERN proton synchrotron for possible use in experiments with colliding beams was studied. Possible storage ring parameters are summarized. The layout of the interaction region and the magnets required are discussed. Detectors for possible use with colliding beams are considered, and a possible arrangement of spark chambers around the interaction region is shown. (A.G.W.)