A. Quareni-Vignudelli

Cross sections and some features of charm photoproduction at γ energies of 20-70 GeV

Abstract We report some results on charm photoproduction at γ energies ranging from 20 to 70 GeV. 36 events with pairs of charmed particles have been found in emulsions. The computed total cross section is (230±57)nb/nucleon. Frequencies of different production channels and some distributions are presented and compared with the predictions from a photon-gluon fusion model with string fragmentation.

A ϱ−π− enhancement at 1.32 GeV observed in 5 GeV/c π−d interactions

Abstract In the reaction π−d → p p π−π−πo at 5.04 GeV′c, a ϱ−π− enhancement at 1.32 GeV is observed. Its statistical significance is about 4 standard deviations. The production cross-section (15 μ b) excludes its identification with the (ϱoπ±) A2 resonance.

ϱπ resonances in π+π−πo system

Abstract Results on the analysis of neutral ϱπ system from π + d interactions at 5.1 GeV/ c are presented. Evidence for a new isoscalar resonance (ϱπ) is reported. Its mass, width and cross section are M = 1.636 GeV, Γ = 0.112 GeV and σ = 53 μ b, respectively. There is no evidence for H and A 1 o resonance production.

Ao2 production in π+d interaction

Abstract In ( π + π − π 0 ) invariant mass from the reaction π + d→p s p π + π − π o at 5.1 GeV/ c in the 81 cm Saclay D.B.C. exposed at CERN PS, we observed a peak at 1.32 ± 0.01 GeV with Γ = 0.12 ± 0.02 GeV. This peak has a ϱπ structure and corresponds to a T = 1, J P = 2 + resonant state.

Measurement of Charmed-Particle Lifetimes and Decay Branching Ratios

The lifetimes of charmed hadrons photoproduced in nuclear emulsion have been computed from a practically background-free sample of 44 neutral particle decays and 42 charged-particle decays including 27D±, 11Λc+, 1Ds+ and 3 ambiguous decays. The values obtained are τ(D0, 0) = (3.6-0.8+1.2 ± 0.7) 10-13 s, τ(D±) = (5.0-1.0+1.5 ± 1.9) 10-13 s, τ(Λc+) = = (2.3-0.6+0.9 ± 0.4) 10-13 s. Branching ratios of various decay topologies were also obtained.

Nππ enhancements observed in the reaction π−n → pπ−π−πo at 5 GeV/c

Abstract In the search for nucleon resonance production in the reaction π−d → (ps)pπ−π−πo at 5 GeV/c, the (pπ−πo) and (pπ−π−) spectra are investigated. Signals are observed in the 1.7 GeV region; however their characteristics do not fully agree with what is known on nucleon resonance structures from phase shift analysis. While these discrepancies are not as significative as that reported in the preceding letter; they also point toward difficulties in correlating resonant structures in production reactions to those observed in formation processes.

An experimental study of longitudinal and azimuthal correlations between pairs of mesons produced in π−p collisions at 11.2 GeV/c and their possible interdependence

SummaryAzimuthal and longitudinal correlations between charged mesons have been studied on a large sample of four- and six-prong events produced in π−p collisions at 11.2 GeV/c in the 2 m CERN HBC. The effect introduced by the ρ-meson has been investigated. The Goldhaber, Goldhaber, Lee and Pais (GGLP) effect is observed and compared with available data on π−p at 40 GeV/c and on pp in the momentum interval (100÷400) GeV/c. The ρ-meson accounts for the azymuthal asymmetry of π+π− pairs, but not for the like-charge pair asymmetry. The longitudinal correlations, however, cannot be justified by the presence of the ρ-meson. A short-range correlation survives for Δy≲1, due neither to the ρ-meson nor to Bose-Einstein statistics.RiassuntoSi studiano le correlazioni longitudinali e azimutali tra coppie di mesoni carichi prodotti nelle interazioni con 4 e 6 particelle cariche nello stato finale. Si utilizzano i dati di un esperimento di ampia statistica di π−p a 11.2 GeV/c nella camera a bolle di 2 m del CERN, riempita con idrogeno. Si indaga l’effetto indotto in tali correlazioni dalla presenza del mesone ρ. Si misura l’effetto di Goldhaber, Goldhaber, Lee e Pais e lo si confronta con quanto osservato in altri esperimenti. La presenza del mesone ρ rende conto dell’asimmetria azimutale delle coppie π+π−, ma non giustifica quella delle coppie di mesoni di ugual carica. Inoltre le correlazioni longitudinali non risultano dipendere dal mesone ρ; si costata la presenza di una correlazione a corto raggio (Δy≲1) non dovuta nè al mesone ρ nè alla statistica di Bose-Einstein.РеэюмеИэучаются аэимутальные и продольные корреляции между эаряжен-ными меэонами на больщой выборке четырех- и щестилучевых событий, обраэо-ванных при π−p соударениях при 11.2 ГзB/c в 2M водородной пуэырьковой камере в ЦЕРНе. Исследуется зффект, обусловленный ρ меэоном. Наблюдается зффект Голдхабера, Голдхабера, Ли и Пейса. Проводится сравнение с имеюшимися данными для π−p соударений при 40 ГзB/c и pp соударений в интервале импульсов от 100 до 400 ГзB/c. ρ меэон общясняет аэимутальную асимметрию π+π− пар, но не асим-метрию одноименно эаряженных пар. Однако продольные корреляции не могут быть общяснены наличием ? меэона. Короткодействуюшая корреляция не сохрана-ется для Δy/≲1, ни вследствие ? меэона, ни вследствие статистики Боэе-Эйщтейна.

A High Resolution Telescope Using CCD Photodiodes Arrays

A relatively new approach to the problem of high spatial resolution in vertices reconstruction is here reported.

A 3 + production in π+d interactions at 5.1 GeV/c

ConclusionsThe present experiment confirms the production of the A3 resonance. The mass valueM = (1.673±0.040) GeV is in fairly good agreement with that found at different energies, but the width Г = (0.24±0.05) GeV is larger.The analysis shows a dominant fπ decay mode.The slope of the differential cross-section is similar to that found at higher energy, while the total cross-section is higher in comparison with that found at different incident energies.

Observations of nucleon isobars in the reaction π−n →{pπ−}π−πo at 5 GeV/c

Abstract In the reaction π − d → (p s )p π − π − π o at 5 GeV/ c the {p π − } final state spectrum is investigated. A signal is seen at the position of the D 13 -state central mass, namely 1518 MeV; its width is about three times narrower than the width of this D 13 -state as firmly established by formation experiments. A qualitative explanation of this discrepancy is proposed.