3C41 Project
Cosmic Ray Flux Measurements With A Portable 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 provides some understanding of the primary cosmic ray flux.

Though muons are long lived, some fraction of muons will decay into an electron and two additional neutrinos before they collide with the earth's surface. These neutrinos, as well as those produced in $\pi$ decay, are the major component of the cosmic ray neutrino spectrum. Because neutrinos are produced either with muons or in their decay, measurements of the cosmic ray muon flux provide information on the neutrino flux. That's important to experiments such as Super-Kamiokande and MINOS, which were designed to study the fabulously exciting subject of neutrino oscillations¹.

Project Goals

Figure 2: The existing cosmic ray detector.

You will complete the construction of a portable cosmic ray detector and use it to measure the cosmic ray flux at the earth's surface. The existing detector, shown in Figure 2, is made of plastic scintillator read out by a multi-anode photomultiplier tube and was (incompletely) constructed by a previous group. It most likely still works and your initial task will be to verify that this is indeed the case. The detector must be equipped with electronics which will allow you to efficiently collect cosmic ray data in a form which may be analyzed by computer. Ideally the finished detector will be portable (e.g., in a regular car) and will include a facility to display it's measurements in real time (e.g., for public outreach purposes).

The cosmic ray measurements may require you to build or borrow additional, but much simpler, scintillator detectors. Analysis and presentation of the data will require you to learn to use a standard histogramming package, such as PAW or ROOT. It is possible you will want to simulate the detector with a program such as GEANT.

Resources Available

Your board member is Mike Kordosky, phone 3775, kordosky@hep.ucl.ac.uk. You will be allocated about 4 hours of consultation time to be used with local experts, a list of which will be derived during the first meeting with your board member.

Suggested Reading

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

1. The Particle Data Book, specifically the reviews on cosmic rays, particle detectors and the passage of particles through matter.
2. Detectors for Particle Radiation by Konrad Kleinknecht (ISBN 0521640326). He provides a nice overview of scintillator detectors.
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 Experimental Foundations of Particle Physics by Robert N. Cahn and Gerson Goldhaber (ISBN 0521424259). High energy physics began with the study of cosmic rays, so you ought to look at the first two chapters.
5. The Particle Detector BriefBook. A mini-encyclopedia of useful particle detector terms.
6. The Data Analysis BriefBook. A mini-encyclopedia of data analysis concepts and words.

Footnotes

... oscillations¹

The author, being a member of one of these experiments, could be accused of holding a biased opinion.