3C41 Project
Cosmic ray measurements with an underground detector.

Board Member

Mike Kordosky (kordosky@hep.ucl.ac.uk)

Introduction

Figure 1: The production chain for atmospheric neutrinos, starting with the interaction of a primary cosmic ray.

Energetic protons, electrons, alpha particles and heavier nuclei constantly bombard the earth. The particles, known as primary cosmic rays, are generally produced and accelerated outside of our solar system and are therefore of interest to astro-physicists. Primary cosmic rays interact hadronically with nuclei (Figure 1) in the earth's atmosphere and produce a number of secondary particles (mostly protons, pions and neutrons) which propagate downward through the atmosphere, sometimes undergoing additional interactions.

Pions (denoted as $\pi$ and belonging to a class of particles, made of two quarks, known as mesons) are unstable and decay (mostly) into a muon ($\mu$) and a neutrino ($\nu$). Muons (similar to electrons but 200 times heavier) are relatively stable and can penetrate a large amount of material, depositing their energy in a well understood way, before coming to rest. This property makes cosmic ray muons an ideal source which can be used to calibrate particle detectors. Since muons are the (eventual) products of primary cosmic rays, measurements of the muon flux at the earth's surface, and even deep below the surface, provides some understanding of the primary cosmic ray flux.

Project Goals

Figure 2: The MINOS Far detector.

In your project you will study cosmic muons observed in the MINOS Far detector. MINOS (see Fig. 2) is a large (5000 ton) detector located in cavern half a mile below the town of Soudan, Minnesota. The detector was built to observe muon neutrinos produced at a particle accelerator complex (called Fermilab) located 735 km away near Chicago, Illinois. The neutrinos travel all the way through the earth to Soudan (they rarely collide with matter) where a very small proportion of them collide with a nucleus in the MINOS detector. When this occurs a muon is produced. The MINOS detector is very good at observing these sort of muons, which means it is also pretty good at observing cosmic ray muons.

Figure 3: The moon's shadowing effect on primary cosmic rays.

Your study will focus on two interesting topics. Because cosmic ray muons are produced by particles (primary cosmic rays) coming from space, we expect that less muons would be observed if some object were to block the primary cosmic rays. You will attempt to test this hypothesis using the nearest handy object: our own moon. To do this you will write (part of) a computer program to calculate the direction of individual muons observed in the MINOS detector. Knowing the time at which the muon was observed you will figure out the moon's location in the sky and determine if the muon points toward the moon. By studying many muons you will try to determine if, in effect, we can see the moon's shadow (see Fig. 3). For your second topic you will use the results of your computer program to study occasions in which multiple muons are simultaneously observed in the detector (see Fig. 4). For example, how often are two muons seen in the detector? Three? More?

Figure 4: A multi-muon event in the MINOS far detector.

As part of this project you will have to clearly present your measurements and compose a talk explaining them to your peers. The data for your project will be provided by your board member who will also advise you on programming and data analysis.

Resources Available

Your board member is Mike Kordosky, phone 3775, kordosky@hep.ucl.ac.uk. You will have the opportunity to consult with other local experts, a list of which will be derived during the first meeting with your board member.

Suggested References

The science library or the HEP library should have most of these books, so don't buy them yourself!

1. The Experimental Foundations of Particle Physics by Robert N. Cahn and Gerson Goldhaber (ISBN 0521424259). Particle physics began with the study of cosmic rays, so you ought to look at the first two chapters.
2. The Particle Data Book, specifically the reviews on cosmic rays, particle detectors and the passage of particles through matter.

3. Introduction to Elementary Particles by David Griffiths (ISBN 0471603864). A beginning text on particle physics from a pretty good writer. You might want to read about pion decay.
4. The Particle Detector BriefBook. A mini-encyclopedia of useful particle detector terms.
5. The Data Analysis BriefBook. A mini-encyclopedia of data analysis concepts and words.
6. An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements by John Taylor (ISBN 093570275X).
7. Data Reduction and Error Analysis for the Physical Sciences by Philip Bevington & Keith Robinson (ISBN 0072472278)
8. An introductory book on C programming. There are many to choose from.
9. Numerical Recipes in C : The Art of Scientific Computing by William H. Press, Brian P. Flannery, Saul A. Teukolsky, William T. Vetterling.