SA

S.P. Ahlen

Also known as: Steven P. Ahlen, S. Ahlen, Steve Ahlen

Boston University, University of California System

Research areas: Physics and Astronomy · Nuclear and High Energy Physics · Particle physics theoretical and experimental studies · Particle Detector Development and Performance · Quantum Chromodynamics and Particle Interactions

ORCID iD 0000-0001-6098-7247
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About

Steve Ahlen got BS (MS) degrees in Physics from the University of Illinois at Chicago in 1970 (1971). He was a graduate student at the University of California at Berkeley from 1972 to 1976 and got a PhD in Physics from Berkeley in 1976. He was employed in various research positions at Berkeley from 1976 to 1983. In 1983 he became Assistant Professor of Physics at Indiana University in Bloomington and he moved to Boston University (BU) in 1985 as a Professor of Physics. He has been at BU ever since and became Professor Emeritus in 2020. Over his career, Ahlen has done research in various areas of physics, including nuclear physics, high-energy physics, astrophysics, and cosmology. Research activities include:

1) Several balloon experiments flown from South Dakota and Canada to measure the abundance of cosmic ray isotopes,
2) A high-energy heavy-ion accelerator search at Berkeley for fractional charge,
3) Two searches deep underground (MACRO in Italy, and a search using the naturally occurring mineral mica) for magnetic monopoles,
4) A balloon experiment in Canada (PBAR) and an experiment on the International Space Station (AMS) to search for cosmic ray antimatter and dark matter,
5) Searches for dark matter in two mines and at the Large Hadron Collider (LHC). One of the experiments was done in the Homestake mine in 1987 in South Dakota and was the first search for Weakly Interacting Massive Particles. This experiment set limits that excluded the dark matter from being due to heavy Dirac-type neutrinos.

Ahlen worked on MACRO from its creation in 1983 until 1995. He directed the installation, commissioning and operation of the U.S. part of the first Supermodule of MACRO in 1988-1989. By 1995 MACRO had acquired evidence for a deficit of upgoing muons that were produced by upgoing neutrinos (the neutrinos having been made in the Earth's atmosphere by the decays of products of collisions of cosmic rays in the atmosphere). This deficit was shown in 1998 to be due to neutrino oscillations. This phenomenon had been discovered that year by the Super-Kamiokande Collaboration which won a Nobel Prize in Physics for Takaaki Kajita in 2015. In 1998 MACRO was the first experiment to confirm the discovery of neutrino oscillations.

Ahlen was a member of the ATLAS Collaboration at the LHC in France/Switzerland from 1997 to 2016. He was a participant in the search for and co-discovery of the Higgs boson with ATLAS in 2012 (co-discovered at the same time by CMS). Ahlen's contributions included supervising the construction of the engineering prototype Monitored Drift Tube (MDT) precision muon chamber for the ATLAS endcaps, and direction of the production of 80 endcap MDT chambers for ATLAS. The MDT chambers were based essentially on the same technology that Ahlen had proposed for the SSC in 1991. The 2013 Nobel Prize in Physics was awarded to Peter Higgs and Francois Englert "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider."

Ahlen joined the Dark Energy Spectroscopic Instrument Collaboration (DESI) in 2016. He supervised the machining and metrology of the focal plane petals for DESI. The petals, which required very stringent mechanical tolerances, were made in the Scientific Instrument Facility at Boston University and the metrology was done by Zeiss. He also supervised the production of jigging components at Boston University for several assembly lines of 5000 robotic fiber optic positioners that were put together at the University of Michigan. DESI is now mounted in the focal plane of the 4-meter Mayall telescope and is taking data at Kitt Peak National Observatory in Arizona. DESI will measure the Hubble parameter as a function of the age of the Universe by using the baryon-acoustic-oscillation feature for galaxies and quasars out to a redshift of 4, which will greatly increase our understanding of dark energy.

In addition, Ahlen has helped develop three different kinds of neutron detectors for Homeland Security, one of which has been further developed commercially and will be used in large numbers of radiation portal monitors, and another that can be converted into a direction-sensitive dark matter detector. He has also written a number of papers on the energy loss and detection mechanisms of magnetic monopoles, dark matter, antimatter, fractional charge and relativistic heavy ions. This work has contributed to his participation in the invention of several novel particle detection systems.

Ahlen has received funding from NASA, NSF, DOE and the Department of Homeland Security to support the activities described above.

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Publications (1229)