Physics colloquium-“The Extreme Universe Space Observatory on a Super Pressure Balloon 2: The Science, the Mission, & Some of the Adventures”

Lawrence Wiencke

Colorado School of Mines, Physics Department

Abstract: Ultra-high energy cosmic rays are the highest energy subatomic particles known to exist. Although much harder to detect, very high-energy neutrinos also carry information about the most extreme environments in the universe. And since they have zero charge, they point back to their creation point. The Extreme Universe Space Observatory on a Super Pressure Balloon II (EUSO-SPB2) was designed to search for PeV energy neutrinos from steady-state and transient astrophysical sources and to measure PeV and EeV cosmic rays using optical techniques from sub-orbital altitude. This exploratory mission of opportunity was a pathfinder for a space observatory such as the Probe of Extreme Multi Messenger Astrophysics (POEMMA). EUSO-SPB2 flew two astroparticle telescopes that featured wide fields of view, 1 meter diameter entrance pupils, and specialized camera systems to measure fast pulses of light from extensive air showers in the atmosphere. A fluorescence telescope was pointed down to measure scintillation light from EeV cosmic ray interactions. A Cherenkov telescope was pointed toward the earth’s limb. This instrument could be tilted a few degrees above the limb to observe Cherenkov emission from PeV energy cosmic rays or tilted below the limb to search for Cherenkov emission from air showers induced through neutrino interactions in the earth’s limb. The gondola could be rotated in azimuth to point the CT to observe sources of interest just before they rise or just after they set. After several years of preparations, lab tests, field tests, reviews, and integrations, the payload was delivered to NASA’s mid-latitude launch site in Wanaka NZ, and launched May 13, 2023. Unfortunately, the balloon developed a bad leak and the entire flight train was terminated into the Pacific Ocean after just two nights aloft. Despite all this, the instruments turned on successfully and worked, with almost 60 GB of data downloaded. Data analysis is in progress with some performance and preliminary results reported at conferences this summer. Planning for a follow-up mission is in progress.

Biography: Grew up in Vermont. AB Dartmouth College, MA, MPhil, PhD Columbia University (I don’t know why they hand out 3 degrees). Did particle physics as a grad student working on an experiment at the historic Alternating Gradient Synchrotron at Brookhaven National Labs. Thesis “Observation of Coulomb Effects in pp and np collisions at 27.5 GeV/c”. By the time I finished my PhD, I needed a change from accelerator laboratories (the uncertainty in accelerator scheduling was interfering with my climbing trips, among other things). Left the NYC area for a postdoc with the High Resolution Fly’s Eye Comic Ray experiment in the Utah West Desert (the HiRes schedule was driven by the moon). Discovered the rewards of working with UV laser systems in the desert, and mountain trail running, and telemark skiing. We made the first observation of high energy cosmic air showers in stereo with the fluorescence technique And made the first observation of the cosmic ray flux suppression around 10^20 eV, explained at that time by energy loss in the cosmic microwave background radiation. While at Utah, I joined the Pierre Auger Observatory project as construction was starting near Malargue, Argentina. I worked with a small team that designed and built a laser system in the middle of nowhere to mimic the optical signatures of high energy cosmic rays, but traveling in the wrong direction. By the time I joined the faculty at Mines in 2007, we had a second of these systems installed in the Pampas. A few months after arriving in Golden it blew up in a massive propane “anomaly”. Despite that, Fred Sarazin and I secured the first NSF grant for astroparticle physics at Mines. Organized a team to replace that system and upgraded the first, (Eric Mayotte who was a grad student at the time can tell you more about that experience). About 2012, we decided to expand the reach of the group by joining the JEM-EUSO collaboration. Although the goal of putting a fluorescence telescope to measure cosmic ray airshows from the ISS didn’t pan out, I participated in three balloon experiments to test techniques and instruments needed to measure high energy cosmic rays from the vantage point of space. I served as international deputy PI and project manager for the last two. Anyway, Mines is now on the map in astroparticle physics. It’s been a team effort including many great graduate and undergraduate students, and tremendous support from administrative and shop staff.

All lectures in Hill Hall 202 unless otherwise specified