Detection of cosmic rays in the SKALTA experiment Marek Bombara (P. J. Šafárik University Košice), Kysak, August 2011

Outline Cosmic rays Detection of cosmic rays SKALTA experiment SKALTA as a barometer Student work proposals

Cosmic rays Cosmic rays are natural source of particles with high energy. Cosmic rays consist of high-energy particles (primary) coming to Earth from outer space and a shower of secondary particles created in the earth atmosphere as a consequence of interaction of primary particle with the atmosphere.

Cosmic rays The composition of charged primary particles varies with energy, however, about 86% primary particles are protons, 11% alpha particles (helium nuclei), 1% heavier nuclei and 2% electrons. Neutral primary particles are composed of photons, neutrinos and antineutrinos. Energy spectrum of cosmic rays reaches values between – eV (for comparison most powerful accelerators on the Earth can accelerate particles up to ~10 12 eV). The spectrum shows deviations like “knee” and “ankle” whose origins are still not sufficiently explained. A big mystery remains the existence of particles with energy above eV. Those particles should not exist in such a big amount as it is observed by cosmic ray experiments. Energy spectrum of primary cosmic rays

Detection of cosmic rays ➡ direct detection - by satellites, observing mostly primary cosmic rays ➡ dense network of ground detectors (e.g. Pierre Auger Observatory). There can be thousands of detectors distributed over big area (~ 1000 km 2 ), detecting whole shower of secondary cosmic rays. ➡ sparse network of ground detectors distributed over huge area (even millions km 2 ), which can not detect whole shower but can detect some very rare events occurring in Solar System, for example – fission of the nucleus into two fragments both later creating shower in the Earth atmosphere - this can be studied by correlation between two working stations (in the distance ~ 1000 km). Each detecting method is thus focused on different type of physics.

Shower absorption in different materials Atmosphere as a calorimeterLHC: ECAL CMS - PbWO4 γ

SKALTA experiment The SKALTA (SlovaKiAn Large-area coincidence Time Array) experiment measures secondary cosmic rays originating from an interaction of primary cosmic ray particle with atmosphere. The working station is composed of three scintillation detectors each with the dimensions 60x60 cm. All three detectors are connected in coincidence. The detectors are arranged into a triangle with side length of 10 m. The area of the triangle defines a minimal size of the shower and therefore a minimal energy of original primary particle (> eV). Using the time difference among the signals from the detectors the point in the sky can be localized (up to a certain resolution) from which the original primary particle came from. By the measuring of the exact time by GPS (Global Positioning System) the data from other workstations (i.e. CZELTA in Czech Republic) can be compared and long distance correlations can be studied.

SKALTA as a barometer SKALTA events per day Average atmospheric pressure at Košice Airport per day We can see anti-correlation by eye, even the distance between the locations (SKALTA and airport) is about 7 km.

SKALTA as a barometer We can quantitatively estimate the dependence of the cosmic ray flux on atmospheric pressure as: N = N 0 *e α*dp/p where N 0 is average number of detected events, dp = p - p 0, p is actual pressure and p 0 is average pressure at the place measured over very long period. By obtaining parameter α from the data we can measure (average for some time period) pressure p, if we know N. It means the SKALTA can be used as a barometer.

Student work proposals comparison of number of SKALTA events with sun activity (Exercise 1) comparison of number of SKALTA events with weather (Exercise 2) comparison of number of SKALTA events with numbers of Sunspots search in data for events incoming in very short time after each other (~seconds) - possible candidates for gamma ray bursts. Is SKALTA (or other similar stations) capable of supernova explosion detection? To find source of correlation among stations. Example:

Exercise 1: Is the cosmic ray measured by SKALTA (> eV) affected by Sun? (Or alternatively, does it come from Sun?) Proposed analysis method: Are the arrival directions of high-energy cosmic rays isotropic? Compare numbers of events (showers of secondary cosmic rays) measured by SKALTA during the day and during the night. For example: measurement for day could be noon ± 3 hours (just to be sure the Sun was shining all that time) and night measurement could be midnight ± 3 hours. The outcome of the analysis should be a plot with (day and night) event number as a function of time (minimal time unit in the plot will be 24 hours).

Exercise 2: What is the relation between secondary cosmic ray flux and air temperature and density? Proposed analysis method: The outcome of the analysis should be 3 plots with SKALTA event number, air temperature and air density as a function of time (minimal time unit in the plot will be 24 hours). Make a comparison among them and try to interpret the result. The measurement of the air temperature and air density were obtained from Hydrometeorological Institute of Slovak Academy of Sciences in Košice (In fact, air density was calculated by students from atmospheric pressure measurement.). T, ρ, p

Data analysis: two ways 1.way: by web interface using for example MS Excel, or paper, pen and calculator way: by raw data using some programming language (for example C/C++, Python, Pascal, etc.). x a c a a c a a a c c c

Caveats during analysis (to correct for) Power cut? x a c a a c a a a c c c a (not c nor x) is correct...