Professor
James W. Rohlf (Jim): Professor of Physics at Boston University.
Experimental particle physics and cosmology
Research pages: home · DESI — dark energy · CMS — calorimeter electronics, AMC13, jets · UA1 — W and Z discovery · CLEO — Upsilon(4S) discovery · E260 — first calorimeter jet trigger
Elsewhere: DESI, talks and papers · selected talks, 1979–2026 · honors · INSPIRE · ORCID · BU DESI
My PhD thesis, “Jet Production in High-Energy Hadron-Proton Collisions,” came from Fermilab E260, the first experiment to trigger on hadron jets with a calorimeter and therefore the first to detect quarks scattered directly out of proton collisions. Using the model of Field and Feynman, I compared the jets we observed in hadron collisions with those seen in electron-positron collisions, and made the detailed acceptance corrections needed for the first measurement of quark-quark scattering cross sections. The analysis techniques developed there laid the foundation for simulation methods that later became standard in the field. My thesis committee was G. C. Fox (advisor), C. Barnes, R. P. Feynman, and R. Gomez.
At the Cornell Electron Storage Ring I discovered the Upsilon(4S) resonance, using the event-shape variables newly invented by Stephen Wolfram and my thesis advisor, Geoffrey Fox. I also performed the particle identification of kaons and charmed mesons that established the quark decay sequence b → c, work that set the foundation for subsequent reconstruction of exclusive B meson decays by CLEO.
At CERN I worked on the UA1 experiment and the discovery of the W and Z bosons, playing an integral role in the identification of the first events. The neutrino from a W decay leaves only missing transverse energy, which admits two kinematic solutions; with the help of Lev Okun I recognized that one solution is often kinematically forbidden while the two are otherwise nearly identical, which made the decay angle accessible and allowed the spin of the W to be measured. I reported that result at the 12th International Conference on High-Energy Accelerators (HEACC 83) at Fermilab. I also built readout electronics for the experiment, including the transition from FASTBUS to VME.
Since 1991 I have worked on the Compact Muon Solenoid experiment at the CERN Large Hadron Collider, having come to it by way of the Superconducting Super Collider, where I measured the radiation hardness of small drift tubes for the L* detector. My work on CMS has centered on the hadron calorimeter and its electronics. I led the design, performance and calibration of the HCAL barrel, outer and endcap wedges, and the synchronization and timing of the calorimeter using test beam, cosmic ray and LHC beam data. I designed two generations of the HCAL Data Concentrator Card, then the AMC13, which provides timing, trigger and data acquisition for the experiment, and most recently the Apollo ATCA platform for the High-Luminosity LHC upgrade. I also worked on the silicon photomultiplier readout and the mapping of calorimeter trigger primitives. On the physics side I have measured the angular distributions of high transverse momentum jets, contributed the hadron calorimeter, jets and missing energy sections of the CMS Physics Technical Design Report Volume 1, and participated in the analyses that discovered the Higgs boson and that established the formation of the quark-gluon plasma in heavy-ion collisions, including the sequential suppression of the Upsilon states.
Since 2024 I have worked on the Dark Energy Spectroscopic Instrument at Kitt Peak National Observatory, which has built the largest three-dimensional map of the universe ever made. DESI measures the expansion history of the universe through baryon acoustic oscillations and the Lyman-alpha forest, constraining the equation of state of dark energy and the sum of the neutrino masses. The data favor a dark energy density that evolves with time.
Selected papers
“DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints,” M. Abdul Karim et al. (DESI Collaboration), Phys. Rev. D 112, 083515 (2025).
“Positive Neutrino Masses with DESI DR2 via Matter Conversion to Dark Energy,” S. P. Ahlen et al. (DESI Collaboration), Phys. Rev. Lett. 135, 081003 (2025).
“Combined Measurement of the Higgs Boson Mass in pp Collisions at sqrt(s) = 7 and 8 TeV with the ATLAS and CMS Experiments,” G. Aad et al., Phys. Rev. Lett. 114, 191803 (2015).
“Observation of a New Boson at a Mass of 125 GeV with the CMS Experiment at the LHC,” S. Chatrchyan et al., Phys. Lett. B 716, 30 (2012).
“Experimental Observation of Lepton Pairs of Invariant Mass Around 95 GeV/c^2 at the CERN SPS Collider,” G. Arnison et al., Phys. Lett. B 126, 398 (1983).
“Experimental Observation of Isolated Large Transverse Energy Electrons with Associated Missing Energy at sqrt(s) = 540 GeV,” G. Arnison et al., Phys. Lett. B 122, 103 (1983).
“Observation of the Production of Jets of Particles at High Transverse Momentum and Comparison with Inclusive Single Particle Reactions,” C. Bromberg et al., Phys. Rev. Lett. 38, 1447 (1977).
I received a B.A. in physics and a B.S. in mathematics from the University of Minnesota in 1973, an M.S. from UCLA in 1975, and a Ph.D. from Caltech in 1980, where my advisor was Geoffrey Fox. I worked on Fermilab E260 as a graduate student, then on CLEO at the Cornell Electron Storage Ring (1980–1983) and UA1 at CERN (1983–1991). I joined the Boston University faculty in 1988, and I have been a member of CMS since 1991 and of DESI since 2024. I am the author of several physics texts, including Modern Physics from α to Z0.