Hadronic interactions of high energy cosmic-ray observed by emulsion chambers

Hadronic charm production in QCD

When cosmic rays (charged nuclei, photons and neutrinos of extraterrestrial origin), reach the Earth they collide with atmospheric nuclei, producing new particles. The secondaries of this interaction undergo the same process, eventually producing millions of particles that propagate through the atmosphere and reach the Earth surface. This process is known as an Extensive Air Shower (EAS).
This Ph.D thesis focuses on the production and possible detection of heavy quarks in Extensive Air Showers using the Fluorescence Detector of the Pierre Auger Observatory. Charm and bottom quark production is ubiquitous in accelerators. Since cosmic rays interactions grant access to an energy range well above that achieved at man-made accelerators, we expect those quarks to be produced copiously in cosmic ray interactions as well.
The production and propagation of heavy quarks are usually neglected in Monte-Carlo shower simulators because low energy heavy hadrons have a negligible influence in the shower development. However, there are models, such as the Intrinsic Quark model, that predict the production of heavy hadrons with large fractions of the primary energy. With such large energies, the heavy hadrons produced are able to interact with air nuclei and propagate in the atmosphere, modifying the the way the shower develops. 
Part of this thesis revolved around the study of these interactions of heavy hadrons with air nuclei in the atmosphere, using a dedicated interaction model, and the implementation of these processes in the Monte-Carlo simulator CORSIKA.
We used an large library of simulated showers generated with our modified version of CORSIKA to identify the most significant features of Extensive Air Showers where highly energetic heavy hadrons are produced.
We combined the identified features through a multivariate discriminant, namely a Boosted Decision Tree, which maximizes the separation between showers with heavy hadrons and those without them. The discriminant yields a selection efficiency that can be used to predict the expected number of event where heavy hadrons are produced. Comparing this number with the actual number of showers detected by the Pierre Auger Observatory that fulfill our selection criteria, we can derive an upper limit to the heavy quark production cross-section in the Intrinsic Quark model.
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Cuando los rayos cosmicos (nucleos cargados, fotones y neutrinos) llegan a la tierra, colisionan con nucleos de atomos en la atmosfera, generando nuevas particulas.
Los productos de esta interaccion sufren el mismo proceso, dando finalmente lugar a millones de particulas que se propagan por la atmosfera y llegan a la superficie de la tierra.
Este proceso se conoce como Cascada de Rayos Cosmicos (o \textit{Extensive Air Shower}, EAS, en ingles).
Esta tesis doctoral se centra en la produccion y la posible deteccion de quarks pesados en EAS, usando el Detector de Fluorescencia del Observatorio Pierre Auger.
Los produccion de quarks charm y bottom es mas que frecuente en los aceleradores de particulas.
Puesto que las interacciones de rayos cosmicos tienen lugar a una energia mucho mayor que la de los aceleradores, esperamos que esos quarks se produzcan copiosamente en estas interacciones.
La produccion y propagacion de quarks pesados es normalmente obviada en los generadores de cascadas Monte-Carlo, puesto que los hadrones pesados de poca energia tienen poca influencia en el desarrollo de la cascada. Existen modelos que sin embargo predicen la produccion de hadrones pesados con fracciones elevadas de energia de la particula que inicia la cascada. Unos de estos es el modelo de Quark Intrinseco. En este caso, los hadrones pesados formados son capaces de interactuar con los nucleos de aire y propagarse por la atmosfera, modificando la forma en la que la cascada se desarrolla.
Parte de esta tesis se ha dedicado al estudio de estas interacciones de los hadrones pesados, empleando un modelo de interaccion especifico, y a la implementacion de estos procesos en el generador Monte-Carlo CORSIKA.
Con la version modificada de CORSIKA hemos generado una amplia libreria de cascadas simuladas, que hemos usado para identificar las caracteristicas mas importantes de las EAS en las que se han producido hadrones pesados. Estas caracteristicas se han combinado usando un discriminante multivariable, en particular un \'Arbol de Decision, intentando maximizar la separacion entre cascadas con produccion de quarks pesados y aquellas en las que no se producen.
El resultado ultimo del discrimante es una eficiencia de seleccion que usamos para predecir el numero esperado de eventos en los que se producen hadrones pesados.
Comparando este numero con el de cascadas detectadas por el Observatorio que cumplen nuestros criterios de seleccion podemos establecer un limite superior a la seccion eficaz de produccion de quarks pesados en el modelo de Quark Intrinseco.

Heavy quark simulation and identification at the Pierre Auger observatory

This is a historical review of the discovery of naked charm particles and lifetime differences among charm species. These discoveries in the field of cosmic-ray physics were made by the innovation of nuclear emulsion techniques in Japan. A pair of naked charm particles was discovered in 1971 in a cosmic-ray interaction, three years prior to the discovery of the hidden charm particle, J/Ψ, in western countries. Lifetime differences between charged and neutral charm particles were pointed out in 1975, which were later re-confirmed by the collaborative Experiment E531 at Fermilab. Japanese physicists led by K.Niu made essential contributions to it with improved emulsion techniques, complemented by electronic detectors. This review also discusses the discovery of artificially produced naked charm particles by us in an accelerator experiment at Fermilab in 1975 and of multiple-pair productions of charm particles in a single interaction in 1987 by the collaborative Experiment WA75 at CERN.

Discovery of naked charm particles and lifetime differences among charm species using nuclear emulsion techniques innovated in Japan

The production of fragmented nuclei from relativistic56Fe beam available from LBL Bevalac at 1.88A GeV has been studied using CR-39 (DOP) passive detector placed at an angle of 60° with respect to the beam. The histogram showing the experimental frequency distribution of minor axes of the elliptic etch pit shows the presence of the fragmented nuclei produced with charge numberZ from 25 up to 21. The histogram further reveals the presence of nuclei withZ=27 and 28. The production of nuclei heavier than56Fe is possibly due to the charge exchange or pick-up phenomena.

Fragmentation of56Fe in Al at 1.88A GeV

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A New Particle Observed in High Energy Cosmic Ray Interactions

1.88 GeV/n Fe beams of LBL were vertically irradiated to the chambers composed of a pile of plastic track detector (CR-39) and nuclear emulsion plates. The charge number of projectile fragments in Fe interactions was carefully examined by use of CR-39. The angular distributions of emitted alpha particles have been investigated for several ranges of charge numbers of projectile fragments. The result of analysis shows that the emission angle distribution of alpha particles at large angles cannot be explained by the single mechanism of the fragmentation from a clean cut spectator. For events of central collisions with smaller charges of projectile fragments, the effective temperature for the production of alpha particles turns out to be much higher than that of the evaporation theory. The results are applied to the calibration of primary energy estimation by the opening angles of alpha particles.

Hisahiko Sugimoto

Papers

A New Particle Observed in High Energy Cosmic Ray Interactions

Study of Alpha Particles Emitted in Fe-Nucleus Interactions at 1.88 GeV/n

Observation of the High Energy Primary Nuclei with Balloon-Borne Emulsion Chamber

A New Particle Observed in High Energy Cosmic Ray Interactions