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Nuclear Interactions of 400 GeV Protons in Emulsion

  • Otterlund, I.
  • Bolta Alandete, José Miguel
  • Sanchis Lozano, Miguel Ángel
  • Bravo Sánchez, Laura
  • Niembro Bárcena, Ramón
  • Ruiz Jimeno, Alberto
  • Villar García, Eugenio
We report on 400 GeV proton-emulsion nucleus reactions and compare the results to hadron-nucleus reactions at smaller energies. In particular we present results on the emission of fast target protons (essentially grey track particles) and on their correlation with the number of collisions inside the nucleus, ν, with the number of charged evaporated particles (essentially black track particles) and with the number of pions produced (essentially shower particles). We observe that the main features of the 200¿400 GeV data are very similar. However, we find that the mean shower-particle multiplicity at 400 GeV is essentially higher than expected from the simple independent particle model prediction 〈ns〉 = 〈nch〉[1 + 0.5(〈ν〉 − 1)]. The shower particle multiplicities do not seem to follow a target mass dependence of the form 〈ns〉 = 〈nch〉 Aα with α = 0.14 or α = 0.19 as has been suggested in the literature. The pseudo-rapidity distribution shows limiting target and projectile fragmentation. The shower-particle multiplicity in the ¿central region¿ increases linearity with 〈ν〉 but faster than 0.5〈ν〉 times the corresponding multiplicity in pp reactions.
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Charged Charmed Particle Lifetime

  • Adamovich, M. I.
  • Bolta Alandete, José Miguel
  • Castillo Giménez, María Victoria
  • Higón Rodríguez, Emilio
  • Martínez Mora, Juan A.
  • Sanchis Lozano, Miguel Ángel
  • Senent Pérez, Fernando
  • Bravo Sánchez, Laura
  • Niembro Bárcena, Ramón
  • Ruiz Jimeno, Alberto
  • Villar García, Eugenio
We present the lifetime values obtained for D± and Λc+, 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 τD± = (3.91−1.25+2.35) × 10−13 s, τΛc+ = (2.22−0.75+1.34) × 10−13 s.
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Measurement of the Lifetime of Neutral Charmed Mesons

  • Adamovich, M. I.
  • Bolta Alandete, José Miguel
  • Castillo Giménez, María Victoria
  • Higón Rodríguez, Emilio
  • Martínez Mora, Juan A.
  • Sanchis Lozano, Miguel Ángel
  • Senent Pérez, Fernando
  • Bravo Sánchez, Laura
  • Niembro Bárcena, Ramón
  • Ruiz Jimeno, Alberto
  • Villar García, Eugenio
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 tau D0=(2.11 {+1.21}/{-0.63})×10 13s The D 0 mass derived from 8 3C events is mD 0 = 1856 ± 36 MeV/ c2.
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Measurement of Charmed Particle Lifetimes and Decay Branching Ratios

  • Adamovich, M. I.
  • Bolta Alandete, José Miguel
  • Castillo Giménez, María Victoria
  • Higón Rodríguez, Emilio
  • Salt Cairols, José
  • Sanchis Lozano, Miguel Ángel
  • Bravo Sánchez, Laura
  • Niembro Bárcena, Ramón
  • Ruiz Jimeno, Alberto
  • Villar García, Eugenio
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, bar D0) = (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.
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Cross sections and some features of charm photoproduction at γ energies of 20-70 GeV

  • Adamovich, M. I.
  • Bolta Alandete, José Miguel
  • Castillo Giménez, María Victoria
  • Higón Rodríguez, Emilio
  • Salt Cairols, José
  • Sanchis Lozano, Miguel Ángel
  • Bravo Sánchez, Laura
  • Niembro Bárcena, Ramón
  • Ruiz Jimeno, Alberto
  • Villar García, Eugenio
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.
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Associated Photoproduction Of Charmed Lambda(c)+ Baryons And Anti-d Mesons And Weak Decays Of The Lambda(c)+ Baryon

  • Adamovich, M. I.
  • Bolta Alandete, José Miguel
  • Castillo Giménez, María Victoria
  • Higón Rodríguez, Emilio
  • Salt Cairols, José
  • Sanchis Lozano, Miguel Ángel
  • Bravo Sánchez, Laura
  • Niembro Bárcena, Ramón
  • Ruiz Jimeno, Alberto
  • Villar García, Eugenio
Data on associated photoproduction.
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