Cosmic Rays: Ever Present and Useful

1. Cosmic Rays: Ever Present and Useful Anthony Gillespie Denbigh High School Mentor: Dr. Douglas Higinbotham ABSTRACT In the study of sub atomic particles, it is essential to have highly accurate detectors. One such detector is the scintillator detector. This type of detector is made up of bars of scintillating plastic with light guides that direct the light to Photomultiplier Tubes (PMTs). The PMTs can take an input of only a few photons and transform it into a measurable electrical signal. These detectors measure the light produced as charged particles pass through, or as neutral particles cause charged particles within the plastic to move, thus producing light. Because these detectors measure light, the interior of the detector must be shielded from all external sources of light, which is done by way of wrapping each bar in several layers of black electrical tape. However, one must ensure that the detectors are working properly. To do this we used a very reliable and consistent source of charged particles, cosmic rays. The flux of cosmic rays is widely known and documented as around 100 particles per m2 per second. By comparing our results of around 20 particles per second obtained by our scintillator detectors (with an area of .25m2) to the known cosmic ray flux, it was possible to determine the accuracy of our detectors. Thus we determined that our detectors were functioning properly and ready to be assembled into an array. Passing this cosmic ray test means that these detectors are one step closer to being used in an upcoming Jefferson Lab experiment. Using the Cosmic Rays Cosmic Rays Detector Construction • The always present cosmic rays were used in our experiment to test the performance of the new scintillator detectors we built • The rays were also used to calibrate the gains of the photomultiplier tubes allowing us to determine the optimum voltage for each tube • These particles constantly bombard the earth • Interaction with other particles in the atmosphere create particle showers • Known to come from a variety of sources including: solar flares, black holes, neutron stars, quasars, supernovae and radio galaxies • Most of the particles that reach the earth’s surface are muons and neutrinos • Some believe cosmic rays have a large impact on our weather: playing a large role in the creation of clouds and guiding the path of lightning • Cosmic rays affect communications with satellites especially those from solar flares • Two new layers are being added to the already existing neutron detector to be used in an upcoming Hall A experiment • 24 new scintillator bars were built and tested using cosmic rays • The bars are comprised of a piece of scintillator plastic 100x25x10cm, two light guides and two PMTs The setup we used to calibrate the gains of the PMTs Each PMT has its own specific voltage The veto layer allows the detector to filter out protons and electrons We’re adding another two layers behind the existing 4 Current Research Testing for light leaks Cosmic rays are not only useful in experiments such as this. There are experiments going on around the world involving cosmic rays, such as: Finding the Angular Distribution Neutrino Telescopes High Energy Particle Detection • Neutrinos are extremely penetrating, almost mass less particles , and so are extremely hard to detect, one way to do this is by using the earth as a giant detector • Neutrinos travelling through the earth will occasionally crash into a proton or neutron, creating a muon • These muons produce Cherenkov light as they pass from the earth into the ocean (or into the ice caps) • This light can be picked up by Photomultiplier Tubes (PMTs) and used to determine the speed and direction of the original neutrino • Extremely high energy particles (10^19 eV) only arrive once per sq Km per year. • The Auger Observatory in Argentina has covered an area the size of the state of Rhode Island with a hybrid detection system looking specifically for high energy particles • We took the testing of the scintillator detectors a step further and used them to find the angular distribution of the cosmic rays • Two rows of three bars were stacked on top of one another,, then one bar was placed laying down on top to act as a trigger for our data acquisition system • We used the time it took each signal to reach each PMT to calculate exactly where each particle had passed • We wrote a basic program in ROOT, a data analysis system, that we used to analyze a run containing over 1 million events • The result of that analysis was this histogram illustrating the angular distribution of cosmic rays. ANTARES, a neutrino telescope off the coast of France I would like to thank: Douglas Higinbotham, Or Chen, Dominik Wermus, David Abbott, Eliazer Piasetzky, Moshe Zilka, Brad Sawatzky as well as my fellow interns for all their help, instruction and for making my experience here at Jefferson Lab very enjoyable. The Hybrid Detection System Conclusion Cosmic rays can be extremely useful and are the focus of many cutting edge experiments. There is still much we can learn about these particles, their effects, and where they come from.