THE LISBON COSMIC RAY TELESCOPE P. Assis, F. Barão, M. Ferreira, P. Martins, J.C. Nogueira, T. Pereira, N. Santos, J.C. Silva, P. Silva, J. Varela New Worlds in Astroparticle Physics, Faro L aboratório de I nstrumentação e Física Experimental de P artículas Projecto Ciência Viva

2 THE LISBON COSMIC RAY TELESCOPE Project Overview (Motivation, Purpose and Goals) Designing the Telescope (Monte-Carlo Simulation Results) The Telescope Stations (Detectors’ Description) Current Status (First Measures Report) Future Perspectives

3 PROJECT OVERVIEW The Lisbon Cosmic Ray Telescope (LCRT) is an array of detectors designed to measure Extensive Air Showers initiated in the atmosphere by Primary Cosmic Rays. The detectors are located in several Lisbon High Schools and are connected through the Internet to a central in L.I.P. The students have online access to the LCRT data as well as the scientific collaboration.

4 The LCRT main purposes are: Didactic (to introduce Experimental Particle Physics and Astrophysics to portuguese high school students) Outreach (to bring together scientists, students and society) Scientific (to study High Energy Cosmic Rays) Purposes

5 Figure 1 - Distribution of the Institutions involved in the LCRT project in Central Lisbon. 1 LIP Escola Secundária D. Pedro V Escola Secundária Gomes Ferreira Escola Secundária Gil Vicente Escola Sec. Maria Amália Vaz de Carvalho Escola Secundária da Amadora Escola Sec. Prof. Herculano de Carvalho Escola Secundária Luís de Freitas Branco Escola Secundária Mem Martins Escola Secundária Diogo de Gouveia Escola Secundária D.Manuel I L.I.P. Laboratório de Instrumentação e Física Experimental de Partículas I.S.T. Instituto Superior Técnico Institutions Already Involved

6 DESIGNING THE TELESCOPE The simulation results are compared step by step with experience: First telescope prototype ( L.I.P. June-July 2002 ) We have been using Monte-Carlo simulations to study: Extensive Air Shower Properties ( Corsika ref. Report FZKA 6019 ) Detectors’ Response ( Geant4 ref. )

7 Detection Method Figure 2 - Geant4 simulation of a detection module used in the LCRT. 2 A detection module consists in two scintillators intermediated by a lead plate. The use of scintillators enables the measure of the charged component of EAS; The conversion of gamma rays (E   1,022 MeV) from EAS improves the statistics in use; q q e+e+ e-e- 

8 Extensive Air Shower Properties Composition at sea level ~ 60% -  30% - e  10% -   Shower size (N) scales with primary energy (E o ) Corsika simulations With increasing distance to shower axis - R : Figure 3 - Shower Plane Geometry assumed for extensive air shower analysis. 3 - Particle density -  decreases Typical shower dimension (sea level): eV ~ 10 4 m 2 ; eV ~ 10 6 m 2 ; - Mean time of arrival -  t increases Typical delay (sea level): 50 m ~ 15 ns; 200 m ~ 99 ns; - Dispersion in time of arrival -  t increases Typical dispersion (sea level): 50 m ~ 23 ns; 200 m ~ 83 ns;

9 Detectors’ Response Geant4 simulations The mean energy deposit by a m.i.p. is 1,9 MeV The light collection efficiency is 1,2% The mean number of photons collected is 299 Figure 5 - Probability of detecting a gamma ray if the shower it starts in the lead plate deposits an amount of energy equal or superior to the energy deposited by a m.i.p. particle in the lower scintillator. Figure 4 - Light collection efficiency distribution derived from random m.i.p. incidence on a 0,5m  1m scintillator. 4 =1,2% 5 P( E=100MeV )=53%

10 Reconstruction Accuracy  2 minimization algorithms tested for: i eV  E o  eV; ii.  < 45º; iii. Array of 20 m separated detectors; Figure 7 - Influence of the GPS error in the reconstruction of a 25º inclined shower. Mean time of arrival of particles was perturbed with a 10 ns [ ] and 20 ns [//] gaussian noise. Figure 6 - Reconstruction distributions events initiated by eV vertical protons. Shaded distributions include gamma ray detection efficiency.  X  3,9 m  Y  3,7 m    0,4º  Eo /E o  34% 6    5º    10º 7

11 THE TELESCOPE STATIONS Figure 8 - Station prototype (with acrylic protection removed) built at L.I.P., July The voltage needed to feed the photomultipliers is taken from the station’s PC. Each high-school has a station consisting of 3 modules connected to a data acquisition PC. Each module is constituted by: - 2 scintillators BC-408 ( 0,5m  1m ) - 2 trapezoidal light guides ( 0,5m length ) - 2 cylindrical light guides ( 0,04 m length ) - 2 photomultipliers H high voltage transformers - 1 lead plate ( 12 mm thickness )

12 9 Each station PC has a LIP-PAD installed ( ref. P. Assis, “GPS Synchronization in Cosmic Ray Experiments” ): Signals are sampled at 100 MHz (1byte flash ADC); Events are acquired with different types of trigger (p.e. single hit, double hit, shower, etc.); Results are recorded and time tagged via GPS. Uncertainty estimated from first tests  10 ns; Figure 9 - Screen shot of an event caused by a m.i.p. crossing three superposed scintillators. Acquired by LIP-PAD at LIP, July 2002

13 CURRENT STATUS Figure 10 - Test array constructed on LIP’s backyard to measure small energy extensive air showers (July 2002). June 2001: - First scintillators were built and tested at CERN, Geneve; LIP-PAD development; June / July 2002: - First station built and tested at LIP, Lisbon; - Identification of minimum ionizing particle and photon signals; - Measurement of small energy extensive air showers; 5 m 10

14 Figure 12 - MIP Signal Type. The solid curves result from fitting the signal to a model function. Figure 13 - Gamma Ray Signal Type. The solid curves result from fiiting the signal to a model function First Results MIP and Gamma Ray signals were characterized Pb ( 12 mm ) S4S4 S1S1 S2S2 Figure 11 - Experimental Setup

Figure 14 - Energy Deposit correlation between top and bottom scintillators. Figure 15 - Comparison of mip energy deposit with a Geant4 simulation. Muons hitting the scintillator in random sites with random inclinations according to the background angle distribution were generated. Figure 16 - Gamma Ray energy deposit obtained by subtracting mip events to the full spectrum. Both curves were normalized to the same number of events before subtracting. 15 Monte-Carlo Data

16 Figure 17 - Example of a low energy extensive air shower recorded at the test array. Each one of the three scintillators is under 6 mm of lead. The scintillators form an equilateral triangle with 5 m sides. The trigger rate of this kind of events is 0,5 per hour. The signal saturation is one of the problems to be solved in the near future. 17

FUTURE PERSPECTIVES The first tests of the LCRT were successful: - Tests with time tagging will be held in I.S.T. next semester; - The Telescope installation in the High Schools will start January 2003; Detection of extremely high energy cosmic rays: - Simulation of EHECR by means of parallel computation (Linux Farm); - Validity test of actual parameterizations; Steps to be taken to Reconstruct the first Extensive Air Shower: - Determination of the method of particle counting from shower signals; - Implementation of a Neural Network to distinguish ,  and e;