A. M. Cartacci

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.

Charged charmed particle lifetime

Abstract We present the lifetime values obtained for D ± and Λ c + , photoproduced in nuclear emulsion in the WA58 experiment. In photohadronic interactions, pairs of charmed particles are produced. Out of 20 charged charmed particles used for lifetime evaluation, 17 have their charmed partner seen emulsion, being then essentially free from any background. The values of the lifetime are τ D ± = (3.91 −1.25 +2.35 ) × 10 −13 s, τ Λ c + = (2.22 −0.75 +1.34 ) × 10 −13 s.

Observation of pairs of charmed particles produced by high-energy photons in nuclear emulsions coupled with a magnetic spectrometer

Abstract Preliminary results of an experiment using nuclear emulsions exposed to a tagged photon beam at the CERN SPS (experiment WA58) are presented. Six events showing pairs of charmed particles have been found. One of these has been interpreted as an associated production of Λc+ and D 0. The mean lifetime of the neutral D meson based on three events is τ0 = (0.58−0.2+0.8 × 10−13 s,, whereas a statistical analysis of eight charged charmed particles, assumed to be D mesons, leads to an estimate of the mean lifetime of τ± ≈ 4.4 × 10−13 s.

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.

Partial-wave analyses of the (3π)-system in the reaction π−p → π−π−π+p at 11.2 GeV/c

Abstract The results are presented of two partial-wave analyses of the (3π) − system in 30 000 events of the reaction π − p → π − π − π + p at 11.2 GeV/ c . Both techniques incorporate the assumptions of the isobar model and are (a) the University of Illinois program which fits in terms of the (3π) density matrix elements and (b) an amplitude parametrisaton including possible effects of both spin non-flip and spin flip at the baryon vertex. The results obtained with these independent programs are found to be very close. The proportions of contributing states, their t -dependence and the phases of off-diagonal density matrix elements are discussed for the mass range 0.9 M (3 π ) 1.9 GeV/ c 2 . The A 1 phenomenon is investigated in the context of a recent model; values of the mass, width and cross sections for the A 1 , A 2 , A 3 states are given, and an interesting variation in the 2 + P M =1 wave is observed at high masses.

Measurement of the lifetime of neutral charmed mesons

Abstract The lifetime of neutral charmed particles photoproduced in emulsion has been measured. The lifetime value presented here was obtained from a sample of 22D 0 mesons, 18 of which have their charmed partner seen in emulsion. The sample is essentially background-free. The result obtained is τ D 0 =(2.11 +1.21 -0.63 )×10 13 s The D 0 mass derived from 8 3C events is m D 0 = 1856 ± 36 MeV/ c 2 .

On the difference in the range-energy relation for positive and negative particles

SummaryMeasurements were made on the final products of the reactions K−+p → Σ−+π+ and K−+p → Σ+π−, produced in nuclear emulsion by K−-mesons at rest. From measured pion momentum the expected energies for the hyperons were computed and the expected ranges for Σ+ and Σ- were obtained using the existing range-energy relations. For Σ+ the measured range was (822.0±1.4) μm and the expected range (816±ll)μm; for Σ- (709.2±l. )μm and (685±6) μm respectively. For the Σ− there is an evident disagreement between the two values. Such results confirm the hypothesis suggested by Barkas of a different behaviour in the energy loss of negative and positive particles.RiassuntoSi sono eseguite misure sulle particelle emesse nelle reazioni K−+p → Σ-+π++ e K−+p → Σ++π− prodotte da K− a ripoeo in emulsione mucleare. Dall’impulso misurato dei pioni sono state ricavate le energie previste per gli iperoni e usando le relazioni percorso-energia già note si sono ottenuti i percorsi aspettati per il Σ+ e Σ−. Per il Σ+ si è trovato (822.0±1.4) μm per il percorso misurato e (816±11)μm per il percorso aspettato. Per il Σ− (709.2±1) μm e (685±6) μm rispettivamente. Per il Σ− c’è un evidente disaccordo tra i due valori. Tali risultati confermano l’ipotesi di Barkas di un differente comportamento nella perdita di energia per particelle positive e negative.

Study of A2− → ηπ− in the reaction π−p → π−π−π+π0p at 11.2 GeV/c

SummaryThe analysis of A2−→ηπ− at 11.2 GeV/c confirms that A2− is essentially produced by natural-parity exchange. In the differential cross-section as a function oft′ there is evidence of the dip at smallt′ values. The branching ratio (A2→ηπ)/(A2→ϱπ) is 0.18±0.05.RiassuntoL’analisi del decadimento A2−→ηπ− nel sistema di Gottfried-Jackson conferma che il mesone A2− è essenzialmente prodotto mediante scambio di parità naturale. La sezione d’urto differenziale mostra un decremento per piccoli valori dit′. Il rapporto di decadimento (A2→ηπ)/(A2→ϱπ) risulta essere 0.18±0.05.РеэюмеАналиэ A2−→ηπ− при 11.2 ГзВ/c подтверждает, что A2− преимушественно рождается в реэультате обмена с естественной четностью в системе Готтфри-да-Джексона. В дифференциальном поперечном сечении, как функцииt′, имеется провал при малыхt′. Отнощение ветвей распадов (A2→ηπ)/(A2→ϱπ) составляет 0.18±0.05.

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.