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The eyes of the desert

The final stage is beginning of the construction of the Pierre Auger Observatory in the west of Argentina, which has the purpose of capturing high energy cosmic rays

From Malargüe

MIGUEL BOYAYANScience at the foot of the Andes: it is possible to look beyond the plain MIGUEL BOYAYAN

One step away from the commands of the control box installed on the wall one day before, Sérgio Luiz Carmelo Barroso, a 34-year-old physicist, observes the descent of the blue chamois curtain that protects one of the telescopes of the Pierre Auger Observatory, under construction in the west of Argentina. He does not look very pleased. In the center of the thick cloth, an intense red circle forms, as an effect of the ultraviolet light that comes through a lens 5 meters in diameter. “It’s not too bad”, he consoles himself, although his plan was that no light from this sunny Sunday morning would show through the curtain. “What we want is perfection.”

Barroso and Marcelo Augusto Leigui de Oliveira, aged 33, both from the State University of Campinas (Unicamp), only reached perfection three days afterwards, when they replaced the blue curtain by a black one, capable of barring completely any light. The two researchers from São Paulo worked for weeks in the half-light, installing other control boxes and protections for the mirrors, in the midst of wide curtains of thick black plastic that separate each set of mirrors and are reminiscent of the wings of a theater. Out there, under a cobalt blue cloudless sky, the Andes display themselves clearly to the west, the peaks covered with snow, the elongated body like a block of hard wood hewed by the sharp blows of a machete.

At least 100 kilometers away, the range of the highest mountains in South America seems nearby due to the excellent visibility, which is a result of the low humidity and the almost complete absence of pollution. The climatic conditions and the breadth of this plain, whose skyline, to the east, appears to merge with an imaginary sea, made this semi-desert region of Argentina the perfect space for housing the Pierre Auger Observatory of Cosmic Rays, one of the largest and most ambitious enterprises of the history of physics, which inaugurates a new phase in this month of August. The production stage begins, the third and last, with the intensive assembly of equipment, in accordance with the standards tested and defined in the two previous stages, prototype and pre-production, which took up the last three years.

The largest open air laboratory ever designed, the Pierre Auger began in February 2000 to occupy the outskirts of Malargüe, a town with an estimated 20,000 inhabitants (and two intersections with traffic lights) 420 kilometers away from Mendoza, the nearest urban center to be endowed with regular airlines. To cover its costs, estimated at US$ 54 million, a consortium was made up with institutions from 18 countries. Brazil is participating with R$ 2.5 million, through a FAPESP thematic project (R$ 1.8 million) and of the Program for Nuclei of Excellence in Research (Pronex) of the Ministry of Science and Technology (R$ 700,000).

The chairman of the finance board, which brings together representatives of the countries, is FAPESP’s scientific director, José Fernando Perez. “The fact of the chairman being a Brazilian shows the dimension of the importance of Brazilian research for the project”, he says. The purpose of this venture that brings together 250 scientists is to detect and to interpret cosmic rays, subatomic particles with colossal energy, at least 100 million times higher than that produced in the most powerful particle accelerator, the Tevatron, in the United States. In more concrete terms, these cosmic rays have an energy equivalent to that of a soccer ball moving at 54 kilometers an hour, or of a tennis ball after being served by a professional like Gustavo Kuerten.

When it is operating at full capacity, probably three years from now, the Pierre Auger should occupy 3,000 square kilometers, twice the area of the city of São Paulo, and the results it supplies may perhaps be valuable for understanding a series of phenomena in physics, from the constitution of matter to the formation of the universe. Right away, though, it is imposing itself on the landscape at the foot of the Andes.

Contrasts
Between clumps of prickly plants that grow on a pebbly soil, the so-called Cerenkov tanks sprawl, each of them 3.7 meters in diameter. Inside them, there are 11,000 liters the purest of waters and, on the outside, a solar panel, which supplies them with energy stored in a battery made by Moura, a company from Recife, and used by a miniprocessor with a radio antenna attached. This set of equipment is given the name of surface detector, one of the resources used to record the cosmic rays in an indirect way, since when entering the atmosphere, the cosmic rays form trillions of other particles.

When they penetrate the walls of the tank and pass through the water, the particles formed by the fragmentation of the cosmic rays generate a bluish radiation called Cerenkov light. Captured by sensors, it is sent by radio waves to the observatory building, a modern construction at the entrance to Malargüe, with glass side walls, from which one can see, from afar, rows of poplars, which at this time of the year are gray and completely leafless, because of the dry and cold weather.

Up until now, 131 tanks have been set up, of which 50 are at work. Separated from each other by a regular distance of 1.5 kilometers, they are aligned with fluorescence detectors, as telescopes fitted with mirrors and photodetectors are called, the so-called fly’s eyes that record the tenuous light emitted by the nitrogen in the air after colliding with the particles in the upper atmosphere is equivalent to the energy of a 5 watt lamp at a distance of 20 kilometers. It is for being so sensitive that the fluorescence detectors only work in the dark, on moonless nights, while the tanks capture the cosmic rays the whole time. The Pierre Auger will be the first observatory to combine these two methods of observation, up until now adopted in isolation in smaller observatories, such as the Fly’s Eye, which functioned from 1981 to 1992 in the United States with 67 telescopes, and the Agasa, in Japan, with 111 surface detectors.

Today, there are two telescopes in operation, only one of them, number 4, is complete, now with the chamois curtain. They are both part of a building  or eye in the format of a semicircle, Los Leones, which occupies a hill 6 kilometers from Malargüe. Under the supervision of Carlos Escobar, from Unicamp, the Brazilian team 22 researchers from São Paulo, including two from the University of São Paulo (USP), and another ten from the Brazilian Physical Research Center (CBPF), from Rio de Janeiro, and the federal universities in the states of Rio de Janeiro (UFF) and of Bahia (UFBA) is working on the telescopes and on the installation of the tanks, which are made by Alpina, a company from São Paulo.

In Los Leones, the Brazilians are putting to work the motors and control boxes of the shutters, the doors that protect the telescopes. They still have ahead of them the assembly of the corrective lenses produced by Schwantz, from Indaiatuba, upstate São Paulo in the other four telescopes to be installed in Los Leones. Made with German glass, the convergent lenses with the format of a trapezium, 25 centimeters high, form a corrective ring along the edges of the diaphragm that regulates the entry of light, like the diaphragm of a camera, and increase the radius of the lens from 85 to 110 centimeters, without losing the quality of the image. When the shutters and the curtains are open, the tenuous light generated by the cosmic rays passes through the ultraviolet filters and the lens, hits a parabolic mirror, actually made up of 60 mirrors, and is reflected on the phototubes, sets of 440 cells of 4 centimeters each, the fly’s eyes.

Rare lights
In accordance with what had been planned, there will be four buildings of the other three, only the second, Coihueco, 60 kilometers from Los Leones, has already been built, and is at the initial stage of assembling the equipment. Together, the four constructions will have 24 telescopes, with an angle of vision that covers almost from the surface to 32o of the sky of the Southern Hemisphere. The Andean plateau will also be dotted by a total of 1,600 Cerenkov tanks, in such a way as to capture the largest number possible of these rare cosmic particles. It is calculated that one high-energy particle per square kilometer per century reaches the Earth. Accordingly, the larger the area occupied with the equipment, the greater the probability recording more events. With all the surface and fluorescence detectors in operation, it is hoped to record 20 or 30 events per year.

En route to this target, the work is intense. At the beginning of July, Slovene, Italian, French, Brazilian, American and Argentinean physicists are the majority doing postdoctoral studies and about 30 years old were assembling equipment during the day on the tanks or at Los Leones, and, at night, often up to 3 in the morning, in the workshops of the building in town. And this pace will probably become more intense as of this month, when assembly begins on a series of pieces of equipment. The intention is to arrive at December with at least 250 tanks and six telescopes in operation (four in Los Leones and two in Coihueco).

It is out of respect for the time limits that, on the same Sunday, that the two researchers from São Paulo were testing the curtains in Los Leones, Frenchmen Xavier Bertou and American Patrick Allison were putting up the tanks installed in the field, exposed to the cold wind, assembling control boxes that were more compact and had less wires than the version used in the older Cerenkov tanks the plan was for them to finish the installation of 50 new tanks in a few weeks. “It sometimes rains around here”, says Bertou, “and the prototype equipment was not properly protected from water.”

Anyone who saw them at the workshop in town, tightening bolts and dexterously assembling the new control boxes for the tanks, with parts that came from the United States, France and England, might think that were electricians, or, if you will, engineers, but hardly postdoctoral students in high energy physics. “We had to do whatever is needed”, says the 30-year-old Frenchman, diplomatically; attached to the University of Chicago, United States, Bertou seems to get little joy from the solemn nature of his post as coordinator of scientific operations. He left Paris at the beginning of last year to set himself up in Malargüe, and today does not do without his yerba mate at the end of the afternoon.

Allison, one of the youngest members of the team, is 26 years old, but looks as if he is less than 20. “This lad is a genius”, comments Argentinean Ricardo Perez, watching him testing the electronic controls for the tanks. “It is thanks to him that the Auger exists”, Perez underlines. It was the young American, who is studying for a doctorate at the University of Pennsylvania, who created the programs for communication between the surface detectors and the central office, with the exact time, the intensity and the precise location of the records of cosmic rays. Even having come to Malargüe 14 times since he joined the project, seven years ago, Allison still speaks very little Spanish. The reason, he explains, is that he gets irritated for not managing to express himself in another language as rapidly as he can in English.

Discrete, preferring to talk about the others, Perez is essential in the day to day. And not just for solving practical problems with installing the Cerenkov tanks. As the person responsible for maintenance, this 31 year old Argentinean, born in Malargüe, accompanied the assembly of the first tanks, which to start with did not work, for a simple reason: the cows on the pasture where the tanks were set up would eat the data transmission wires. It was Perez, a mining technician, who dreamt up a protective casing for the wires and the cows did not bother science ever again.

His worth goes beyond that. Perez seems to have managed to understand, respect and reconcile the style of work of the Germans, the French, the Americans and the Argentineans. “We have to value the good things and to alleviate the deficiencies of each group”, Perez observes, with a clear vision of the grandiosity of this work. For him, the fact that at least eight Cerenkov tanks have been baptized with the name Peace, in Portuguese, English, Spanish, French and even in Arabic, although the majority of the tanks have a woman’s name, following the first one named by a researcher from Rio de Janeiro, means that it is possible to leave politics aside and to establish international collaboration with common objectives, based on science.

Uncertainties
By means of Allison’s programs and the wires now protected against cattle bites (in the new electronic controls, the wires are hidden), information has arrived on about 300 episodes some recorded at the same time by 20 tanks with an energy greater than 1018 (the number 1 followed by 18 zeroes) electron-volts (eV), 1 million trillion times greater than an electron’s energy. These are preliminary results, subject to confirmation, but already at a level of energy 3,000 times higher than that of the cosmic rays detected by French physicist Pierre Victor Auger (1899-1993), on whom this project was inspired, for having recorded the first shower of particles, in 1938. The expected raw material for research is beginning to arrive. But there is an agreement between the researchers: despite the temptation, they decided not to stop to analyze the data not least because it is still regarded as too little while the construction work on the detectors is not close to being finished.

There is, though, an intriguing question that is occupying the physicist’s moments of rest. It is the difference or the discrepancy between the data recorded by the two kinds of detector: the surface detectors capture particles with twice the energy found in the fluorescence detectors, according to the methods of analysis for each kind of equipment (and they are indeed the same ones, because they have arrived at exactly the same time). “The theoretical models for analyzing the data are probably wrong”, avers Allison, faced by the impasse, which actually is seen as one of the first triumphs of this gigantic work: “If we didn’t have two kinds of detectors, we wouldn’t know that there may be something wrong”.

There are no doubts that it is a challenge to revise the conceptual bases of something whose nature is not known. What, after all, are cosmic rays? “They may be protons (particles that form the atomic nucleus), photons (particles of light) or even entire nuclei of atoms like the atomic nucleus of iron”, says Miguel Mostafa, a 33-year-old nuclear engineer who is part of the team from the University of New Mexico, United States.

Before moving, a year ago, to Albuquerque, in New Mexico, this Argentinean from Bariloche did postdoctoral studies at the University of Turin, in Italy, with Rosanna Cester who, at the age of over 70, personally accompanies the construction of the lenses for the telescopes. It was she who supervised Marcelo Oliveira’s postdoctoral studies from February 2000 to May 2001, and she is now doing the same with Michela Chiosso, who is studying for a doctor’s degree and in July was working in a container annex at Los Leones on the laser emitting device that controls the precision of the cosmic ray detectors.

“For the time being”, Mostafa goes on, taking delight in the doubts that motivate them to work, “cosmic rays can be anything, because we do not know where they come from, nor how they are formed and accelerate.” It is believed that they are particles formed within a radius of up to 3.2 million light-years (1 light-year corresponds to 9.5 trillion kilometers), on the edge of, or just beyond, our galaxy, the Milky Way, and interact with photons left over from the Big Bang, the explosion said to have originated the universe.

In a demonstration of how even basic concepts are subject to adjustments, Mostafa says that cosmic particles must enter the atmosphere in a straight line from the point at which they were formed, while American Brian Fick, a 50 year old physicist from the University of Utah, United States, and one of the leaders of the group, cogitates another possibility: “It may be that the particles are diverted by magnetic fields, which are weak, but are to be found all over the place”. The problem is that no one has yet measured the extragalactic magnetic fields, the intensity of which can vary 500 times, according to the theoretical model that is adopted.

Another point in the theory to be revised is the so-called GZK limit, an acronym from the surnames of three physicists, Kenneth Greisen, George Zatsepin and Vadem Kuzmin, who in 1966 postulated that cosmic rays with energy greater than 5 x 1018 eV would be absorbed as they traveled through space and would never be observed on Earth. But they have been. In 1993, the Fly’s Eye recorded particles with 3 x 1020 eV it is precisely particles with this level of energy that are most awaited at the Pierre Auger, because they could say whether this world record really is valid, or if there has been some mistake in the measurements.

What is now known relatively well is the process of the fragmentation of cosmic rays, the so-called particle showers. When going into the atmosphere of the Earth, coming from Heaven knows where, in just 100 microseconds this is another reason for the sophistication of the equipment, the cosmic rays collide with the particles of air, in particular nitrogen, and they are broken down, in a succession of collisions, forming some 10 trillion particles, captured by the detectors by means of the light they produce.

The axis of the shower, at a distance of up to a thousand meters from the point of the first collision, is made up of protons, electrons and photons. At the sides and in the lower regions, besides the electrons, other kinds of particles are formed, such as muons (similar to electrons, but 200 times heavier) and neutrinos, apparently with a very small mass. But reconstituting the shower in detail and finding out the direction and nature of the particle that originated it “is like discovering the color of the hair of your great-great-great-great-great-grandfather from the color of your own hair”, is Barroso’s comparison.

The privilege of putting forward more concrete hypotheses about what rays cosmic rays are perhaps belongs to Indonesian Richard Randria, an assiduous operator of the computers of the Data Acquisition Center, on the first floor of the building in town, on which the records from the surface and fluorescence detectors converge. Since he joined the project, a year and a half ago, as a member of the team from Jussieu University, in Paris, this 29-year electronic engineer, who has already lived in Guyana and in Lisbon, has made about ten programs to deal with the information on the different stages of the particle shower.

“I have to foresee the future and prepare the programs to handle a very large quantity of information”, says Randria. He knows that the information that circulates through these computers, after being analyzed, can overturn or confirm models for the interaction of atomic particles, the evolution of stars and the constitution of the universe. The prospect for contributing towards a revision of the basic laws of physics appears to be a stimulus for facing up to the plane trips to Mendoza, and then the six hours by car or bus (with luck, Randria spends 41 hours from Paris to Malargüe).

When they discover what cosmic rays are, the signs of fatigue, anxiety and unease from delayed equipment, the irritating cold and the things that are difficult to get right will probably be wiped off the scientists’s faces. “It will be a day of satisfaction, but perhaps a little sad as well”, imagines Fick, who has been working on the Auger since 1992, when this project was just an idea. At this moment, seeing the scientists working in this end of theworld, a story by the writer from Bahia João Ubaldo Ribeiro comes to mind, about a man who spent years trying to fish a robalo. The fish would always escape, and it even seemed to like the pursuit, until one day it surrendered. The man had hit the mark with his harpoon and took the fish to the table, in silence, with the impression that the fish had wanted to die on that day. Something had been lost.

Yes, indeed, science is a sort of fishing that calls for results. From these same Argentinean lands, which 150 million years ago were a gulf, they have now unearthed ichthyosaurs, marine crocodiles and skeletons that led to the conclusion that human occupation in this stretch of Argentina began some 7,000 years ago. But the physicists have no guarantee that the sky will be so generous to them. As in any scientific enterprise, the possibility is not entirely out of the question that these particles will remain enigmatic, even with the Pierre Auger working at full capacity. “It may be that we arrive at the conclusion that something even larger has to be built”, ponders Oliveira, from Unicamp. “We will only know 20 years from now.”

The Projects
1. Pierre Auger Observatory (99/05404-3); Coordinator: Carlos Ourívio Escobar Unicamp; Investment: R$ 1,884,287.12 (FAPESP) and R$ 600,000 (Pronex, MCT).
2. Pierre Auger Project; Coordinator: Ronald Cintra Shellard CBPF; Investment: R$ 100,000 (MCT)

 

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