Air Showers in a Self-Triggered Neutron Monitor

1. Air Showers in a Self-Triggered Neutron Monitor Alejandro Sáiz, David Ruffolo, WaritMitthumsiri, ChanoknanBanglieng, Pierre-Simon Mangeard, Waraporn Nuntiyakul, Paul Evenson April 10, 2018

2. Asking for Help: What this is about … • I have always been interested in detecting air showers with a neutron monitor, but it has been mostly a curiosity • I have never thought seriously about what science may be possible • Our recent work has focused on very tiny showers, but larger ones have proved to be easily detectable • So … I would like to get some help to see whether there might be some scientific value in looking into the larger showers with more detail • Comments and suggestions are therefore greatly appreciated!!

3. Neutron Monitors • High energy cosmic rays are rare. Observing them at high time resolution requires a large detector. • Ground based instruments remain the state-of-the-art method for studying these elusive particles. • Neutron monitors and muon detectors on the surface record the byproducts of nuclear interactions primary cosmic rays with Earth's atmosphere.

4. Solar Modulation We look for tiny air showers resulting from particles that are influenced by solar activity.

5. Neutron Monitor Principle • An incoming hadron interacts with a nucleus of lead to produce several low energy neutrons. • These neutrons thermalize in polyethylene or other material containing a lot of hydrogen. • Thermal neutrons cause fission reaction in a 10B (7Li + 4He) or 3He (3H + p) gas proportional counter. • The large amount of energy released in the fission process dominates that of all penetrating charged particles. There is essentially no background.

6. Simulated Interaction In a Neutron Monitor

7. Monitor Counting Rate • Mostly we just use the counting rate of the monitor

8. Pierre-Simon’s Recent Project Just Accepted by ApJ!

9. Measuring Particle Spectra • Variable geomagnetic cutoff can be used to investigate spectra – but what about the region near and above the highest available cutoff.

10. Interaction in the Lead Shows Some Dependence on Energy of Incoming Particle

11. For Several Years We Have Looked at the Time Distribution of Neutrons in Individual Detectors

12. Recently We Have Expanded to Correlations Among Detectors For adjacent detectors the neutrons can propagate, but for larger separations the correlations must result from distinct secondary particles from the same primary. It is more or less obvious that these must (on average) be higher energy primaries

13. To Make A Long Story Short … • We are now working on getting time histories of these multiple events to go beyond simple two-fold correlations. We know how to proceed with the small events – or at least think we do. • But we also (surprisingly) trigger nicely on much bigger events, and have no real idea how interesting these might be. • Do we try to publish this as a new result or just continue with our program as planned?

14. Trigger Where All Detectors Fire

15. We are working on improved electronics to get better resolution near the main interaction – but that is years away. Is it worth proposing?

16. Possible Applications • The main objective – study of modulation near 18 GeV with the monitor in Thailand. • Addition of energy resolution to other monitors, specifically South Pole • Study of air showers using the muon information from Syowa (next slide) • Coincidences with the IceCube detector at South Pole

17. Combination Neutron Monitor and Directional Muon Detector Now Operating at Syowa Station Antarctica