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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.
Proyecto:


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.
Proyecto:


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.
Proyecto:


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.
Proyecto:


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.
Proyecto:


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.
Proyecto:


Combined Measurement of the Higgs Boson Mass in pp Collisions at √s = 7 and 8 TeV with the ATLAS and CMS Experiments

  • Aad, G.
  • Cabrillo Bartolomé, José Iban
  • Calderón Tazón, Alicia
  • Castiñeiras de Saa, Juan Ramón
  • Duarte Campderros, Jorge
  • Fernández García, Marcos
  • Gómez Gramuglio, Gervasio
  • Graziano, Alberto
  • López Virto, María Amparo
  • Marco de Lucas, Jesús
  • Marco de Lucas, Rafael José
  • Martínez Rivero, Celso
  • Matorras Weinig, Francisco
  • Muñoz Sánchez, Francisca Javiela
  • Piedra Gómez, Jonatan
  • Rodrigo Anoro, Teresa
  • Rodríguez Marrero, Ana Yaiza
  • Ruiz Jimeno, Alberto
  • Scodellaro, Luca
  • Vila Álvarez, Ivan
  • Vilar Cortabitarte, Rocío
A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H→γγ and H→ZZ→4ℓ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is mH = 125.09 ± 0.21 (stat) ±0.11 (syst)  GeV.
Proyecto:


Observation of the Associated Production of a Single Top Quark and a W Boson in pp Collisions at √s = 8  TeV

  • Chatrchyan, Serguei
  • Brochero Cifuentes, Javier Andrés
  • Cabrillo Bartolomé, José Iban
  • Calderón Tazón, Alicia
  • Chuang, S. H.
  • Duarte Campderros, Jorge
  • Fernández García, Marcos
  • Gómez Gramuglio, Gervasio
  • González Sánchez, Francisco Javier
  • Graziano, Alberto
  • López Virto, María Amparo
  • Marco de Lucas, Jesús
  • Marco de Lucas, Rafael José
  • Martínez Rivero, Celso
  • Matorras Weinig, Francisco
  • Muñoz Sánchez, Francisca Javiela
  • Piedra Gómez, Jonatan
  • Rodrigo Anoro, Teresa
  • Rodríguez Marrero, Ana Yaiza
  • Ruiz Jimeno, Alberto
  • Scodellaro, Luca
  • Vila Álvarez, Ivan
  • Vilar Cortabitarte, Rocío
The first observation of the associated production of a single top quark and a W boson is presented. The analysis is based on a data set corresponding to an integrated luminosity of 12.2  fb−1 of proton-proton collisions at √s=8  TeV recorded by the CMS experiment at the LHC. Events with two leptons and a jet originating from a b quark are selected. A multivariate analysis based on kinematic and topological properties is used to separate the signal from the dominant tt¯ background. An excess consistent with the signal hypothesis is observed, with a significance which corresponds to 6.1 standard deviations above a background-only hypothesis. The measured production cross section is 23.4 ± 5.4  pb, in agreement with the standard model prediction.
Proyecto:


Search for Flavor-Changing Neutral Currents in Top-Quark Decays t → Zq in pp Collisions at √s = 8  TeV

  • Chatrchyan, Serguei
  • Brochero Cifuentes, Javier Andrés
  • Cabrillo Bartolomé, José Iban
  • Calderón Tazón, Alicia
  • Chuang, S. H.
  • Duarte Campderros, Jorge
  • Fernández García, Marcos
  • Gómez Gramuglio, Gervasio
  • González Sánchez, Francisco Javier
  • Graziano, Alberto
  • López Virto, María Amparo
  • Marco de Lucas, Jesús
  • Marco de Lucas, Rafael José
  • Martínez Rivero, Celso
  • Matorras Weinig, Francisco
  • Muñoz Sánchez, Francisca Javiela
  • Piedra Gómez, Jonatan
  • Rodrigo Anoro, Teresa
  • Rodríguez Marrero, Ana Yaiza
  • Ruiz Jimeno, Alberto
  • Scodellaro, Luca
  • Vila Álvarez, Ivan
  • Vilar Cortabitarte, Rocío
A search for flavor-changing neutral currents in top-quark decays t → Zq is performed in events produced from the decay chain tt¯ → Zq + Wb, where both vector bosons decay leptonically, producing a final state with three leptons (electrons or muons). A data set collected with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 19.7 fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV. No excess is seen in the observed number of events relative to the standard model prediction; thus, no evidence for flavor-changing neutral currents in top-quark decays is found. A combination with a previous search at 7 TeV excludes a t → Zq branching fraction greater than 0.05% at the 95% confidence level.
Proyecto:


Evidence of b-Jet Quenching in PbPb Collisions at √sNN = 2.76  TeV

  • Chatrchyan, Serguei
  • Brochero Cifuentes, Javier Andrés
  • Cabrillo Bartolomé, José Iban
  • Calderón Tazón, Alicia
  • Duarte Campderros, Jorge
  • Fernández García, Marcos
  • Gómez Gramuglio, Gervasio
  • González Sánchez, Francisco Javier
  • Graziano, Alberto
  • López Virto, María Amparo
  • Marco de Lucas, Jesús
  • Marco de Lucas, Rafael José
  • Martínez Rivero, Celso
  • Matorras Weinig, Francisco
  • Muñoz Sánchez, Francisca Javiela
  • Piedra Gómez, Jonatan
  • Rodrigo Anoro, Teresa
  • Rodríguez Marrero, Ana Yaiza
  • Ruiz Jimeno, Alberto
  • Scodellaro, Luca
  • Vila Álvarez, Ivan
  • Vilar Cortabitarte, Rocío
The production of jets associated to bottom quarks is measured for the first time in PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair. Jet spectra are reported in the transverse momentum (pT) range of 80–250  GeV/c, and within pseudorapidity |η|<2. The nuclear modification factor (RAA) calculated from these spectra shows a strong suppression in the b-jet yield in PbPb collisions relative to the yield observed in pp collisions at the same energy. The suppression persists to the largest values of pT studied, and is centrality dependent. The RAA is about 0.4 in the most central events, similar to previous observations for inclusive jets. This implies that jet quenching does not have a strong dependence on parton mass and flavor in the jet pT range studied.
Proyecto:


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