D. Bollini

e+e− Annihilation into two hadrons in the energy interval 1400–2400 MeV

Abstract The proof is given for the existence of the reaction e + e − → h ± h ∓ in the energy range 1400–2400 MeV, and its energy dependence is compared with that of e + e − → e ± e ∓ , in the same experimental conditions of observation. The exponent of the s -dependence of the ratio α = (e + e − → h ± h ∓ )/ (e + e − → e ± e ∓ ) is measured to be n = 2.08 ± 0.45, in the s -range (1.96 − 5.76) GeV 2 , on the basis of 51 e + e − → h ± h ∓ events and 8918 e + e − → e ± e ∓ events observed.

Experimental proof of the inadequacy of the peaking approximation in radiative corrections

Abstract 49 e+e− non-collinear, non-coplanar events have been observed in a study of 1824 e+e− interactions at total centre-of-mass energies from 1.6 GeV to 2.0 GeV. The inadequacy of the peaking approximation in radiative corrections is measured to be (2.8 ± 0.4)%, in these experimental conditions of observation.

A large electromagnetic shower detector with high rejection power against pions

Abstract A large electromagnetic shower detector for identification and energy measurements of γ-rmrays (between 150 and 1600 MeV) and electrons (between 400 and 1100 MeV), in the presence of high pion background, is described. The detector is based on the principle of simultaneous measurement of the spatial development of the electromagnetic cascade and of its energy release. It consists of 1) two six-gap thin-plate spark chambers for the reconstruction of the incoming particle trajectories; and 2) nine elements, each made of a lead foil, a spark chamber, and a plastic scintillator, all sandwiched together; here the shower development is studied. When used for γ-detection, a 0.5 cm Pb foil is placed in front of the thin-plate spark chambers, in order to allow the detection of the γ-conversion process and the identification of the γ-direction. The dimensions of the detector are 60 x 120 cm 2 front face, and 50 cm depth along the electromagnetic shower development. A pion rejection power of the order 5 x 10 −4 between 400 and 1100 MeV, for electron efficiencies varying from 70% to 80%, is obtained. The pion rejection efficiency in the γ-case is highly improved by the anticoincidence efficiency factor, while the γ-detection efficiency depends on the precision required in the reconstruction of the γ-ray direction. The γ-ray and electron energy resolution is about ±15%.

Proof of comparable K-pair and π-pair production from time-like photons of 1.5, 1.6, and 1.7 GeV and determination of the K-meson electromagnetic form factor☆

Abstract The observation of 21 K + K − pairs in 38 hadron pair events produced at 1.5, 1.6, and 1.7 GeV total centre-of-mass energies in e + e − annihilations, establishes that time-like photons produce K pairs and π pairs with comparable rates in this energy range. The K-meson electromagnetic form factor at a mean s -value of 2.4 GeV 2 is measured to be | F K | = 0.50±0.08. The number of e + e − pairs observed in the same angular and energy range is 5148.

Accurate position determination of particle trajectories using plastic scintillator counters

Abstract Using the CDF technique for locating charged particles in plastic scintillator counters, it has been found that the accuracy in determining the position of an incident particle in the counter is essentially a function of the distance between the two photomultipliers. Moreover it has been shown that a position resolution of Δx = ±0.15 cm and a time resolution of Δt = ±0.07 nsec can be achieved in a simple way. Finally it has been shown that it is possible to measure simultaneously the coordinates of an incident particle in two orthogonal directions. This would allow to measure particle trajectories in high rate beams, when spark chambers cannot be used.

Measurements of the polarization of high-energy muon beams

SummaryThe polarization of theM2 muon beam at the CERN SPS is studied at 220/200, 260/240, 300/280 GeV/c π+/μ+ momenta by using a lead-glass telescope and a simple trigger system to measure the positron spectrum from muon decay. A direct measurement of the polarization difference between the 220/200 GeV/c beam (forward decays, average polarization ∼−0.8) and the 300/200 GeV/c beam (backward decays, average polarization ∼+0.1) is also presented.RiassuntoLa polarizzazione del fascio di muoniM2 all’acceleratore SPS del CERN è stata studiata a 220/200, 260/240 e 300/280 GeV/c, impulsi di π+/μ+, rispettivamente. Per misurare lo spettro di energia dei positoni provenienti dal decadimento dei muoni polarizzati è stato utilizzato un semplice telescopio consistente di contatori Čerenkov di vetro al piombo e di scintillatori plastici. È stata anche eseguita una misura diretta della differenza di polarizzazione fra i fasci a 220/200 GeV/c (decadimenti in avanti, polarizzazione media ∼−0.8) e a 300/200 GeV/c (decadimenti all’indietro, polarizzazione media ∼+0.1).РезюмеИсследуется поляризацияM2 мюонного пучка в CERN SPS при π+/μ+ импульсах 220/200, 260/240, 300/280, используя телескоп из свинцового стекла и простую триггерную систему для измерения позитронного спектра из распада мюона. Также приводятся результаты прямых измерений разности поляризаций между пучком 220/200 ГэВ/с (прямые распады, средняя поляризация ∼−0.8) и пучком 300/200 ГэВ/с (обратные распады, средняя поляризация ∼+0.1).

An underground search for leptonic quarks in the cosmic radiation

SummaryThe flux of relativistic leptonic particles with charges ±e/3, ±2e/3, ±4e/3 in cosmic rays underground at 63 m w.e. was measured using a six-scintillation-counter telescope. The following upper limits were established: φ(±e/3)≤1.8·10−10 cm−2sr−1s−1, (90% confidence) φ(±2e/3)≤1.8·10−10 cm−2sr−1s−1, (90% confidence) φ(±4e/3)≤(1.1±1.8)·10−8 cm−2 sr−1 s−1, at threshold energies of (2.1±0.1) GeV, (8.5±0.6) GeV, (22±1) GeV respectively.RiassuntoSi sono misurati i flussi di particelle leptoniche relativistiche di cariche ±e/3, ±2e/3, ±4e/3 nella radiazione cosmica sottoterra con 63 m a.e. a mezzo di un telescopio formato da sei contatori plastici a scintillazione. Si sono ottenuti iseguenti limiti superiori: φ(±e/3)≤1.8·10−10 cm−2 sr−1 s−1, (90% l.c.), φ(±2e/3)≤1.8·10−10 cm−2 sr−1 s−1 (90% l.c.), φ(±4e/3)≤(1.1±1.8)·10−8 cm−2 sr−1 s−1, rispettivamente nelle condizioni di (2.1±0.1) GeV, (8.5±0.6) GeV e (22±1) GeV di energia di soglia.РезюмеГыл измерен поток релятивистских лептонных частиц с зарядами ±e/3, ±2e/3, ±4e/3 в космических лучах под землей при 63 m w.e., используя телескоп шести сцинтилляционных счетчиков. Установлены следующие верхние пределы: φ(±e/3)≤1.8·10−10 см−2 ст−1 сек−1, φ(±2e/3)≤1.8·10−10 см−2 ст−1 сек−1, φ(±4e/3)≤(1.1±1.8)·10−8 см−2 ст−1 сек−1, причем, первые два результата с достоверностью 0.9, при пороговых энергиях (2.1±0.1) ГэВ, (8.5±0.6) ГэВ, (22±1) ГэВ, соответственно.

Study of the structure of hadronic and electromagnetic showers with a segmented iron-scintillator calorimeter

Abstract The lateral development of hadronic and electromagnetic showers has been measured in an iron-scintillator calorimeter equipped with 2 cm wide hodoscopes at 20, 40 and 86 GeV c −1 .

A Review of the Results Obtained by The Bologna‐CERN Multipurpose NBC Set‐Up

The Bologna‐CERN multipurpose NBC set‐up has allowed a systematic study of some intrinsic properties of the η, S0, ρ, ω, X0, φ, and A20 mesons. These are presented in a synthetic way.