Status of the Pierre Auger Observatory

1. Status of the Pierre Auger Observatory Rebeca López1, Humberto Salazar1, Arturo Fernandez1, Luis Villasenor2, Arnulfo Zepeda3 1Benemérita Universidad Autónoma de Puebla, 72570, Puebla, Puebla. 2Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, 58000, Morelia, Mich. 3Departamento de Física, Cinvestav, Apartado Postal 14-740, 07000, México, D.F., México . Abstract The quest for the origin, composition and acceleration mechanism of the ultrahigh energy cosmic rays, the particles with the highest energy (E 1018eV) so far detected from outer space, has led an international collaboration to design and built a gigantic cosmic ray detector called the Pierre Auger Observatory which, once finished, will address the main questions behind these enigmatic particles. The construction of the Pierre Auger Observatory began in March 1999 and now it is the first and the only one existing hybrid cosmic ray detector in the world. In addition, it has become the largest running surface array on the Earth, although it has not been completed yet. In the following lines, the present status of the Pierre Auger Observatory will be described . The detector assembly building at the Auger campus, which is located in the town of Malargüe. The central data acquisition system is in the central building, at the Auger campus. • Thethird and present stage:Production • The project has also completedthe pre-production phase (100 WCD and 2 FD), checking, in this way, the performance of the final design.Now, the project is inthe full-production phase, under which the complete FD and SD will be finished. • Status of the Surface detector • On May 28 of 2004, the 337th running Cherenkov detector • joinned the surface array. Since last January, the Pierre • AugerObservatory, is the largestrunning array of the world. • There are about 371 Cherenkov detectors deployed in the field, • from which, about 337 of them are operational. • The running stations are already taken data. • Introduction • What are the ultra high energy cosmic • rays (UHECR)? • What we know is that they are very energetic particles • (E  1018eV) which arrive to the Earth from the outer • space. • But, their origin, composition and acceleration mechanism • remain still a mystery. • The Pierre Auger Observatory (PAO) and the quest for the UHECR • To shed light on the mystery of the UHECR, it is necessary • to have a detector of kilometric size, such as the Pierre • Auger Observatory,since the flux of cosmic rays with • energy above 1020 eV it is too low: of the order of • 1 particle/( km2century). • An international collaboration from about 13 countries, • including Mexico, is participating now in the construction • of this observatory. • The main features of the observatory are briefly described. • below: • Goal: to collect several UHECR eventswith unprecedent • statistics in order to know theirspectrum, arrival directions • and composition. • Location:to allow a full sky coverage, it will consistof two • similar instruments located in both hemispheres. In • the southern hemisphere, thePAO is being deployed • in Malargüe, Mendoza Province, Argentina. • Size:To compensate the low fluxof UHECR's, its total • size will be of the order of 6000 km2. • Detection techniques: Itwillbe of hybrid type, that is, • each observatory will use two complementary techniques • based on the detection ofthesecondary air shower • generatedby the interaction of the UHECR with the • atmosphere: • Status of the southern PAO • The construction of the southern Pierre Auger Observatory began • in March1999. From that date, several advances have been • accomplished in its construction. The main stages of the project, up • to now, are shown below: • The first stage:The Engineering Array (EA) • The first phasewas finished during 2001 with the deployment of • a prototypedetector called theEngineering Array (EA). • Description: The EA is a subset of the PAO and is composed by • 40 water Cherenkov detectors, and twoprototypefluorescence • telescopes, the latter onesoverlooking the Cherenkov detectors • from Los Leoneshill. • Size:The surface detectors cover an area of 46km2. The full planned Southern PAO (left) and the EA (right). • Goal: This prototype wasconstructed to help the Pierre Auger • Collaboration to testseveral aspects of the observatory and • improve them.For example: • Performance of the initial design. • Deployment strategy. • Communication and data acquisition systems. • Components and subsystems, etc. • Status:Accomplished. Now, the Cherenkov detectors of the EA • are part of the Observatory and the two prototype telescopes • have been dismantled to allow installation of the final design • telescopes. The SD at the beginning of May29 2004. The EA is shown inside the shaded region in gray. • Status of the Fluorescence detectors • Three fluorescence buldings have already been constructed at Los • Leones, Coihueco and Los Morados hills, and planning for the • construction ofthe fourth one at LomaAmarilla has begun. • There are six final design fluorescence telescopes in operation • at Los Leones. Twoare operational at Coihueco. • In order to perform atmospheric and calibration measurements it • was constructed a Central Laser Facility (CLF). This instrument is • located almost equidistantly from the Coihueco, Los Leones and • Los Morados hills. • Data acquisition and performance of the PAO • The observatory has been taking data since the construction of • the EA, in July 2001. • The data collected by the EA during the first stage was very • important for checkingboth the performance of the EA and • the methods of data analysis.In particular, in hybrid mode, it • detected more than 70 eventswithenergy 1018 eV. • The data acquired on UHECR has shown that the detectors, • communications and data acquisition systems perform as well or • better than expected. • The number of detected UHECR is growing up! • At this stage, the statistics is not enough yet to make relevant • physical conclusions about the UHECR. Upper figure: final design fluorescence telescope (left) at Los Leones building (right). The Central Laser Facility (left). Spectacular hybrid event recorded on Octuber 2003 (right). The event, which struck 11 tanks inthe array, was reconstructed with an energy of 25.4 Eev.