M. G. Dagliana

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.

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 .

Photometric analysis of the tracks in the nuclear emulsions

SummaryThe dependence of the photometric width of a track on the degree of development has been investigated in G-5 nuclear plates, developed by the standard procedure. It is found that the width varies with the development only through an additive term, which is independent of the nature and velocity of the particle which produced the track.RiassuntoÈ stata presa in esame la dipendenza della larghezza fotometrica delle tracce dello sviluppo, in emulsioni Ilford G-5 sviluppate col procedimento standard. Sono state esaminate tracce di ioni Carbonio e di particelle α reperite in lastre sviluppate differentemente. I risultati sperimentali sono in accordo con una espressione del tipo λ + λ0 + λ1(β,Z), dove la dipendenza dello sviluppo è localizzata nel termine λ0 indipendente daβ e daZ.

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.

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.

Fotometria dei nuclei pesanti relativistici

RiassuntoViene atudiato il profilo fotometrico delle tracce di nuclei pesanti relativistici. Un modello di traccia costituito da una parte centrale di granuli direttamente impressionati e da una parte periferica in cui l’annerimento è dovuto agli elettroni secondari viene confermato sperimentalmente. Si discute la possibilità di usare la semilarghezza fotometrica come parametro per l’individuazione della carica del nucleo pesante.SummaryThe photometric profile of the tracks of relativistic heavy nuclei in nuclear emulsions has been studied. A model for the track is developed according to which the track is made up of a central part of grains directly affected by the heavy nuclei and of a peripheral part in which the darkening is due to the secondary electrons. The experimental results are in accord with this model. By measuring the darkening at a distance of more than 3.5 μm from the axis of the track a method is proposed for the identification of the chargeZ of the heavy nuclei. This method appears to compete favourably with other standard methods. The possibility of using the half width as a parameter for the identification of the charge of heavy nuclei is also discussed.