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Department of Cosmic Rays and Chronology |
GROUP OF LEPTONS
A. Galactic cosmic rays
Members of the Group
Anderson Fauth (Faculty), Armando Turtelli (Invited Professor), Carlos Escobar (Faculty), José Augusto Chinellato (Faculty), Reinaldo Rigitano (Faculty),
Hélio Nogima (PostDoc Fellow), Hugo Reis (PostDoc Fellow), Marcelo Leigui (PostDoc Fellow at INFN/Torino, Italy),
Fernando Catalani (PhD student), , Ernesto Kemp (Ph.D. Student),
Luís Gustavo dos Santos (Ph.D. Student).
L V D
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This group is a member of the LVD Collaboration (Large Volume Detector at Gran Sasso) since its beginning, as a result of a former
collaboration we had with the group of Prof. Carlo Castagnoli, Istituto di Cosmogeofisica del CNR, in the city of Torino .
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The aim of the collaboration is the study of neutrino emission from collapsing stars and the study of muons deep underground.
The detector is installed in the Laboratori Nazionali del Gran Sasso, Italy. It consists mainly of steel tanks with liquid scintillator and a shield of streamer tubes. Members of this Department participate mainly in the construction of the detector, its maintenance, in the development of the software for data analysis and in data analysis. These activities are performed in a close relationship with our colleagues from the Italian Istituto Nazionale di Fisica Nucleare, Torino Section. Further details on this experiment can be found here
in English or here
in Portuguese (em português).
Two members of our group have also participated in some activities of the EAS-TOP Collaboration: Hélio Nogima and Anderson Fauth. This Collaboration is studying Extensive Air Showers with an huge array installed at Campo Imperatore. The array comprehends plastic scintillator, Air Cerenkov Telescopes, Radio and a streamer tube Hadronic Calorimeter.
More information can be obtained in the site of EAS-TOP.
The funding for our participation in these experiments comes from the Italian
INFN ("Fondi FAI") and Brazilian agencies
FAPESP , FAEP/UNICAMP and CNPQ, to which we are very grateful.
Some pictures from the Gran Sasso region.
Pierre Auger Observatory
The history of cosmic ray research is a romantic story of scientific adventure. For three quarters of a century,
cosmic ray researchers have climbed mountains, dived into deep mines and long tunnels, ridden hot-air balloons,
and traveled to the remote corners of the earth in the tantalising quest to understand these fast-moving
particles from space. Their endless explorations have solved scientific mysteries and revealed many more.
We will mention just a few of those pioneers: the intrepid Viktor Hess, with his balloon flights in the beginning of this century; Millikan (and Compton),
going around the world measuring the intensity of the radiation; Anderson, the discoverer of the antimatter; Pierre Auger, the discoverer of the big showers of particles; Lattes, Occhialini and Powel, elucidating the mistery of Yukawa's meson;
Fermi, proposing a theory for the acceleration mechanism.
2. Cosmic rays?
Cosmic rays are fast-moving particles from space that constantly bombard the earth from all directions.
Each second, about 200 cosmic ray particles with energies of a few million electron volts (10
6eV) strike every square meter of the earth. While these low-energy cosmic rays
are plentiful, cosmic ray at higher energies are far rarer. Above the energy of 1018eV, only one particle each week falls on an area of one square kilometer. Above the energy of
1020eV, only one particle falls on a square kilometer in a century! To find
and measure these rare events, a high-energy cosmic ray study needs to wait centuries or to build a truly giant detector.
3. Their energy
Most of the cosmic-ray particles are either the nuclei of atoms, or electrons. Of the nuclei, most are single protons
-the nuclei of hydrogen atoms- but a few are much heavier, ranging up to the nuclei of lead atoms.
Cosmic ray
particles travel at nearly the speed of light, which means they have very high energy. Some of them, in fact, are
the most energetic of any particles ever observed in nature. The highest-energy cosmic rays have a hundred million
times more energy than the particles produced in the world's most powerful particle accelerator.
No one knows the source of the highest-energy cosmic ray particles. Most lower-energy cosmic ray particles that strike
the earth come from within our own galaxy, the Milky Way. Many probably come from the exploding stars we call Supernovae.
Over time, some cosmic ray particles pick up energy from moving magnetic fields they encouter as they wander
around the galaxy.
The great Italian physicist Enrico Fermi first provided an explanation for the acceleration of most cosmic
rays. In Fermi's cosmic ray accelerator the protons "bounce" off moving magnetic clouds in space. Despite the random
directions of both the cosmic rays and the clouds, over time the cosmic rays gain energy. This process is well understood
for low-energy cosmic rays accelerated by magnetic fields produced by the sun. In our galaxy, scientists believe that
the strong moving magnetic fields produced in supernovae explosions provide the energy for acceleration.
4. Present situation
Presently, there is suggestive evidence from a number of experiments that above 1020 eV the cosmic rays are
protons. If so, an origin within our own galaxy can be excluded as the protons would propagate
rectilinearly and sources within our galaxy would be readily identified. By contrast, the arrival direction
distribution is isotropic, within the limited statistics, even beyond 1020eV where only a handful of
events have been detected. This result is extremely paradoxical as sources at large distances (beyond
about 30 Mpc) are strongly excluded by the existence of such events. The point is that above 4x1019
eV protons and heavier nuclei interact with the primordial 2.7 K microwave background radiation (from the Big Bang)
through well-understood reactions of particle and nuclear physics and are rapidly degraded in energy.
The existence of the most energetic event yet detected, 3x1020 eV, implies that it must have
originated within 20 Mpc of the earth. However the arrival directions of this event and others of similar
energy do not point to any unusually energetic objects within our galaxy or elsewhere and the lack of
appropriate electromagnetic acceleration processes has even led to speculation that the particles are
created in the collapse of massive cosmic strings which are topological relics of the early universe.
5. The Pierre Auger Collaboration
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Scientists believe that the very highest-energy cosmic ray particles come from sources beyond the Milky Way - but where?
Something out there -no one knows what and where- is hurling incredibly energetic particles around the universe. Do these particles come from some unknown superpowerful cosmic explosion? From a huge black hole sucking stars to their violent deaths? From the collapse of massive invisible relics from the origin of the universe? We don't yet know the answers, but we do know that solving the mystery of high-energy cosmic rays will take scientists another step forward in understanding the universe.
The results obtained so far derive from the independent efforts of groups in four different nations and
are based on only a few hundred records above 1019 eV. To increase this sample significantly
requires an international effort in which all the nations historically involved, and others, are eager to
participate. In this scenario was born the Pierre Auger Project. |
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So, a multinational
group of physicists presented a detailed proposal for a new cosmic ray observatory, the Pierre Auger
Project, named in honor of the discoverer of air showers. The new observatory will use a giant
array of detectors to study large numbers of air showers from the very
highest-energy cosmic rays, above 1019eV. Tracing high-energy
cosmic rays to their unknown source will advance the understanding of the origin and evolution
of the universe.
6. Pierre Auger Observatory
To measure cosmic rays particles directly requires sending detectors to heights above most of the earth's atmospherre, using high-flying balloons and satellites. However, we can also detect cosmic rays indirectly on the surface of the earth by observing the showers of particles they produce in the air. An air shower occurs when a fast-moving cosmic ray particles strikes an air molecule high in the atmosphere, creating a violent collision. Fragments fly out from this collision and collide with more air molecules, in a cascade that continues until the energy of the original particle is spread among millions of particles raining down upon the earth on an area of about 16 km2. The atmosphere absorbs the great part of the energy of the cosmic ray particles in this process and makes it possible to detect and measure them.
By measuring two different features of an air shower, scientist at the Pierre Auger Observatory will be able to determine the direction and energy of the original incoming cosmic ray particle. In the first part of the detection system, 1800 particle detector stations will form a giant regular array, or grid, covering about 3500 km2. The detector stations will be about 1.5 km apart, and each will be about the size of a small one-car garage. Each station will be self-contained and operate on solar power. Instruments in each station will measure the number of particles passing through. Shower particles from a high-energy cosmic ray will reach several stations at the same time. When particles strike a station, a small computer will confer by radio with computers in neighboring stations to decide whether the particles are part of a large shower. If so, information about the shower will be transmitted by radio to a central data center. At the data center, computers will combine the measurements of the number of particles and their time of arrival at each station to determine the direction and energy of the original cosmic ray that set off the shower. The detector will measure about 50 cosmic-ray events a year with energies above 1020eV, along with large numbers of lower-energy ones.
A second detection system will make use of the faint glow caused by the collisions of shower particles with air molecules during cosmic-ray air showers. On dark, moonless nights, in a remote and dry site, finely tuned light sensors can measure this fluorescence. A collection of light sensors pointing around the sky in all directions makes an effective air shower detector, observing an air shower as a trace of light across the sky. The total amount of light depends on the number of particles in the shower and, in turn, on the energy. The shape and direction of the light trace helps determine the cosmic ray's direction and indicates what kind of particle the original cosmic ray might have been. The first fluorescence detector built by the University of Utah was called "fly's eye".
The Pierre Auger Observatory will build two Giant Detectors, one in the Northern and another in the
Southern Hemisphere.
The detectors will be installed in
Argentina (the first to be constructed) and in the USA.
The Secretary of the Collaboration is Dr. Murat Boratav
, the Spokesman is Prof. Jim Cronin ,
the Site Manager (South) is Dr. Alberto Etchegoyen
and the Chairman is Prof. Carlos Escobar .
The complete organization of the Collaboration can be found
here .
The Collaboration Board meets twice in the year, news about the last meeting , held in Morelia, Mexico, from Jan 11th to 15th, 1999, can be found here.
7. Brazilian participation
In Brazil, the following Institutions are involved in the Project: University of São Paulo,
Laboratório de Física Experimental (LAFEX/CBPF),
Pontíficia Universidade Católica do Rio de Janeiro,
Universidade Federal da Bahia ,
Universidade Federal Fluminense,
Universidade Federal da Paraíba e
Universidade do Estado do Rio de Janeiro, and the Universidade Estadual de Campinas.
In this University, the Centro de Ensino e Pesquisa em Agricultura (CEPAGRI) and the Deaprtment of Cosmic Rays and Chronology are involved in the project. CEPAGRI's participation is mainly concerned with studies on the atmospheric transmission.
In this Department, are involved in the Pierre Auger Project: Anderson Fauth, Armando Turtelli, Carlos Escobar,
Carola Dobrigkeit Chinellato,
Edison Hiroyuki Shibuya,
José Augusto Chinellato, Marcelo Guzzo, Renato Biral (Post Doc), Hélio Nogima (Post Doc, now at Salt Lake City), Hugo Reis (PostDoc Fellow) and the PhD students Luís Gustavo dos Santos, Ernesto Kemp and Fernando Catalani.
C. Escobar, A. Fauth, M. Guzzo and E.H. Shibuya made a series of tests with the tank shown in the link below and came to the conclusion that it is more indicated to use a plastic tank (PVC + BaSO4), customized for this Group by
Sansuy S/A , than to use Tivek as lining material. Complete report on their results appeared as a technical note. A brief resume is available here.
8. World-wide Auger links
You find the complete documentation about the project in the official Auger Site. Other sites are:
EASCAMP
The Track detector of Eascamp |
This is a small air shower array, working inside the campus
of Unicamp. We are studying the anisotropy of primary radiation and trying to correlate it with
the known sources in the South Galactic Hemisphere. The detector is an array of plastic
scintillators an three modules of streamer tubes, one with three layers and area of 1 m
2 , another with 5 layers and a bigger one with four layers and
an area of 4x4 m2. These modules are used
mainly for tracking. The direction of primary particle is obtained by reconstructing the arrival
direction of the shower particles, using the Time-of-Flight technique, with fast TDC (nominal
resolution of 0.5 ns). Number of particles in each scintillator module is obtained with ADC's.
The energy threshold is determined by the triggering conditions and by the size of the array
and is about a few 1014eV. |
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The angular resolution depends
mainly on the position of the shower axis respect the center of the detector, it is estimated as
4 degrees. Extensive simulations were performed in order to better estimate the errors involved
in the reconstruction algorithm and in the selection criteria for track reconstruction inside the
streamer tubes modules.
Single and multiple particle tracks inside the streamer
module
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Armando Turtelli, Inácio Malmonge Martin (Faculty), Anatoly Gusev (Visiting Professor from Moscow State University),
Galina Pugatcheva (MSU, Visiting Professor),
Wagner Eduardo Alves, Márcio do Carmo Vieira, Dirceu Emeterio Passos Jr., Marcelo Dantas de Carvalho and Marcelo Hermannson Canela (Undergraduate Students).
Balloon-borne detectors
Balloon
launching |
Since 1988, a joint program
with the Institute Lebedev was established for launching
rubber balloons, the so called IKAR Sonds, for monitoring the solar activity in the Region of
the Brazilian Magnetic Anomaly. From 1989, the collaboration includes also the launching of
stratospheric balloons for monitoring solar activity and neutral and charged particles at
30-33 km.
Interesting results were obtained in collaboration with
CEPAGRI when we tried to find a correlation between
Forbush decrease and variations in rainfalls in the tropical/subtropical regions of Brazil and
Russian territory, taking into account that ions in the upper atmosphere would work as
condensation droplets for water vapor. See, for instance, Il Nuovo Cimento C18, N.3,
pp335/341 (1995) and Geomagnetism and Aeronomy, V.36, N.4, pp.211/216.
In collaboration with the Polar Geophysical Institute of Apatity, we are also continuously
monitoring the variation of the profile of the ozone layer at tropical latitudes.
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Preliminary results show that enhanced ozone production of anthropogenic origin is not an
exception, but a regular situation, with a considerable number of episodes with ozone
concentrations exceeding the officially recognized critical level. Local meteorological
conditions may introduce strong distortions into the classical schemes. Large ozone decreases,
associated with the rainfalls, have also been observed.
Furthermore, irregular pulsations with periods from tens of seconds to tens of minutes are
detected. We are inclined to explain these phenomena assuming that photochemical haze may become
unstable on the ozone production/destruction transition regime and that the reverse, i.e. from
production to destruction, may be localized in time and space and have a form of catastrophic
instability, which in combination with other factors, such as air-transport, may give the
observed variability of fast ozone temporal structures. Further studies are necessary for a more
reliable model of local ozone dynamics.
The results of this research are usually published in the Proceedings of the International
Cosmic Ray Conferences, held biennially under the auspices of the International Union of Pure
and Applied Physics, and in specialized journals. See, for example, Atmospheric Environment
30, 2729-2738 (1996).
The launchings of stratospheric balloons are
performed in collaboration with the Balloon
Launching Sector of INPE.
Back?
Last amended Nov 10th, 2000, 0310 AM, LT.
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Most of the text about Auger was adapted from a pamphlet of the Collaboration and from a text of
Alan Watson. General information about Cosmic Rays is based also on the book: Cosmic Bullets, by Roger Clay & Bruce Dawson, 1997, Ed. Allen & Unwin, Australia.
Written with Arachnophilia and checked with
Netscape Communicator,
version 4.5
Curator: A.Turtelli
Argentina Tandar