WJP, PHY381 (2015) Wabash Journal of Physics v4.2, p.1 Cosmic Muon Shower Study with QuarkNet Brian Hayhurst, Jia Qi, and James Brown Department of Physics, Wabash College, Crawfordsville, IN 47933 (Dated: May 7, 2015) The purpose for this experiment is to study the properties of cosmic ray muon shower using the QuarkNet equipment. Using the QuarkNet set from Notre Dame University, which consists of four separate scintillation panels, we measure the rate of cosmic muon shower events. We collected 18 individual coincidence level four shower events in 5 hours of collection, which is significantly higher than the expected random rate. By studying individual events, we can get some information about the amount of energy deposited to each channel by muons they detected. However, this does not tell us the direction of the cosmic muon shower.
WJP, PHY381 (2015) Wabash Journal of Physics v4.2, p.2 I. INTRODUCTION The earth receives cosmic rays from outer space everyday. Some of those cosmic rays carries extremely high energies, sometimes higher than the LHC particle energy. Thus, the study of cosmic ray is crucial to the development of particle physics. Most research projects about cosmic rays are very complicated and expensive. However, for there are many simpler experiments designed for accessible and affordable studies about cosmic ray to undergraduate or event high school students. Using scintillation detector, on can study properties about muons such as their flux angular distribution, decay constant, and cosmic showers[2][4][6]. QuarkNet is a long-term teaching program funded by National Science Foundation. With the collaboration of mentor physicists and physics teachers, the program tries to bring frontier research in particle physics to high school classroom and offers research experience to high school teachers and students[5]. Using the QuarkNet equipment set from the University of Notre Dame, we can detect cosmic muon events and conduct may interesting experiments for high school students. One thing we think can be interesting to high school students is to visually study cosmic muon showers. Earth constantly receives cosmic muons that are not sensible to humans. However, with the help of separate scintillation detector, one can catch cosmic shower events on his computer. The cosmic ray shower data acquired from one site can also be compared with that from other sites[7]. II. THEORETICAL MODEL A cosmic ray shower begins with a collision and resulting interaction between a cosmic ray and nucleus in the air. Many particles, including charged pions and gamma rays, are created which in turn may strike nuclei in the air. As this process continues, the number of particles cascades into a large group of particles moving near the same path as the original particle; once the particles lose enough energy from each of their interactions, they will be unable to interact and add new particles to the shower. As a result of many of the particles having expended their energy and some beginning to decay, the shower reaches a maximum. Eventually, additional particles decay and the scope of the shower is reduced; the level of reduction depends on particle energy and whether the showers is hitting at sea level or high in the mountains [3].
WJP, PHY381 (2015) Wabash Journal of Physics v4.2, p.3 The primary cosmic rays are mainly high energized protons. protons in the air, it produces muons through interactions While interacting with p + p p + p + π + + π 0 + π (1) and p + p p + p + π + + π 0 + π (2) And those resulting muons can be detected by our detector panels in the QuarkNet equipment. The panels in the QuarkNet equipment are made of scintillator, which absorbs energy from cosmic muons while muons hit it. Muons energize molecules in the scintillation material and, consequently, emit photons, which can be detected by photon multipliers attached to the scintillation panel[7]. Thus, if we can detect several muons simultaneously in four separate panels of our muon detectors more than a random rate, we probably catch air shower events. FIG. 1. When an incoming cosmic muon hits the scintillation panel, it interacts with molecules in the scintillation material, which produces photons within the panel traveling in opposite directions. These photons can be detected by the photomultiplier tube attached onto the scintillation panel. III. EXPERIMENT SETUP In this experiment, we use the QuarkNet muon detector equipment set from University of Notre Dame. The detector consists of four separable detecting panels. For each panel, it is made up with a scintillation panel and a photomultiplier tube attached to it. Four detecting
WJP, PHY381 (2015) Wabash Journal of Physics v4.2, p.4 panels are connected into a series 6000 DAQ board. Four panels are labeled with different colors as shown in Fig. 2. From channel 1 to 4, they are labeled with red, green, yellow, and blue respectively. The power input voltages for each channel is different, which are set to be 0.75V, 0.75V, 0.85V, and 0.90V from channel 1 to 4, due to their different working voltages. This different power input is achieved by the power distribution box attached to the DAQ board. In the end, the DAQ board is connected to the computer to output cosmic muon data. FIG. 2. To perform the shower study for the QuarkNet equipment, the four color-labeled scintillation panels are placed on the four corners of a table where w = 157cm and l = 212cm. The muon rates on the four panels are measured and compared, which can confirm that all panels are capturing consistent muon events. Four the cosmic rays shower studies, the four panels are put separately in four different positions (Fig. 2). For a shower event, multiple panels should detected muons simultaneously. To muon shower events from different coincidence level, we set the coincidence level for detectors as 2. Thus, we can get data for coincidence level 2, 3, and 4 data. The gate width of coincidence is set to be 100ns in our experiments. Since four detecting panels are all covered by thick black electric tape, we do not need to concern about light from the environment. After setting this, we run the data collection for 5 hours and analyze our data. Since the power distribution box got broken after this run, we are not able to acquire more data.
WJP, PHY381 (2015) Wabash Journal of Physics v4.2, p.5 FIG. 3. This table shows the number of events we get for coincidence level 2, 3, and 4 during our 5 horus data collection. Compared with the expected number of events for random coincidence, the amount of events we get is much higher. IV. DATA AND ANALYSIS Since we do not have access to the online data analysis tool for QuarkNet, we developed excel and python programs to extract and analyze our data. For our 5 hours of data, we detect several level 2, 3, and 4 data, and we put this in a table (Fig 3). To distinguish this with the random coincidence, we also calculate random rate for level 2, 3, and 4 event. The formula for the random rate is, τ = τranw n n 1 (3) where τ r an is the random event rate for one panel, n is the level of coincidence, and w is the gate width for coincidence. Compared with the random value, we can see that the number of events we get is much higher than the expected random value. Thus, we can safely say that most of events we get are actually cosmic shower events, instead of random coincidence. Also, we notice that, for coincidence level 4, the chance for a random coincidence to happen is negligible. Thus, all 18 single events we get for the level 4 events are shower events, probably. Because the original voltage inputs are different for the four channels in our setup, we need to renormalize our signal using the average of each channel. For our data, the average length of signal in each channel are calculated and listed (Fig. 4). Using this, we renormalize our single shower events for coincidence level 4. Here is an example of single level 4 shower event (Event 13) we get. Because the duration of a signal in the photomultiplier tube is proportional to the energy of the detected muon, we can see that the muon in channel 1 deposits more energy into the panel than the other channels. This indicates that channel 1 may detect two muons during this trigger. However, this does not tell us anything about the direction of cosmic shower, because this can happen for cosmic shower from any direction.
WJP, PHY381 (2015) Wabash Journal of Physics v4.2, p.6 FIG. 4. This histogram gives the average signal lengths in four channels. We need to use this data to renormalize the signal lengths in four channels for each individual shower events. FIG. 5. This histogram illustrates the signal lengths on four channels for a single shower events. We can see that signal length for channel 1 is higher than the other three channels. V. CONCLUSION AND FUTURE WORK As a conclusion, we collected 18 coincidence level 4 events in our detector over a 5 hours duration. This rate of events is much higher than the random event rate for coincidence level four, which is almost negligible. Thus, we can safely say that we acquired 18 cosmic ray shower events. This proves that our QuarkNet detector can successfully catch cosmic shower events. Unfortunately, we cannot get the direction of each individual muon shower using the data we have. For the future work, the power distribution box in our equipment set broken in the end, the next group could start with fixing that problem. During our experiments, we also failed to get the permission to access the associated online data analysis tools from cosmic e-lab. With the help of that, the data analysis process will be simpler and accessible by real high
WJP, PHY381 (2015) Wabash Journal of Physics v4.2, p.7 school classes. The GPS units in our equipment set was absent since it first came, the future group could add the GPS units to the setup, because a GPS unit will probably help us to understand the direction of muon showers. With this QuarkNet set, the future group could also work on other experiments such as muon decay constant determination and angular distribution of cosmic muons [1] Blasi, B. Recent Developments in Cosmic Ray Physics. Nuclear Physics B, (2014): 36-47. [2] Damazio, Denis O., T. Falcone, N. L. Mehta, and Helio Takai. A Simple and Cost-Effective Passive Radar Technique for Ultra High Energy Cosmic Ray Detection. Nuclear Physics B (2004): 217-19. [3] Greisen, K. Cosmic Ray Showers. Annual Review of Nuclear Science 10.1 (1960): 63-108 [4] H. Sten, et. al., Low-Cost Data Acquisition Card for School-Network Cosmic Ray Detectors, IEEE TRANS NUCL SCI, vol. 51, no. 3, pp. 926-930, 2004 [5] M. Bardeen, et. al., The QuarkNet/Grid Collaborative Learning e-lab, Future Generation Computer Systems, Volume. 22, Issue 6, May 2006. [6] R. Franke, et. al., CosMO A Cosmic Muon Observer Experiments for Students. arxiv: 1309. 3391, September 2013. [7] J. Rylander, T. Jordan, J. Paschke, H. G. Berns, QuarkNet Cosmic Ray Muon Detector User s Manual Series 6000 DAQ