Uriel Nauenberg

Uriel Nauenberg, Professor Emeritus at the University of Colorado Boulder, died on 31 December 2019. He was an experimental particle physicist who cared deeply about the physics his experiments would illuminate and the potential for discoveries from facilities beyond the horizon.

Born on 16 December 1938 in Berlin, Uriel completed his PhD at Columbia University in 1963 under the supervision of Jack Steinberger. His doctoral thesis contained a determination of the spin and parity of the Y₁* hyperon resonance (Σ(1385) in modern notation) in pion–proton interactions in the 30-inch bubble chamber at the Cosmotron.

Uriel joined the faculty at Princeton University in 1963, first as an instructor, later as an assistant professor. His research at that time emphasized the study of hyperon production and decay, notably a test of the ΔS/ΔQ rule in Σ^± beta decay. The discovery of CP violation by Fitch, Cronin et al. shortly after Uriel’s arrival motivated his tests of CPT symmetry in neutral and charged kaon decays.

In 1969 Uriel became an associate professor at the University of Colorado Boulder, advancing to professor in 1973. By then he found himself the senior experimental particle physicist in the department, and he worked tirelessly, and successfully, to build a healthy program in both experimental and theoretical particle physics. He was also named a Fellow of the APS.

With a collaboration at SLAC, Uriel produced measurements of long-lived kaon decays to two- and three-pion final states, significantly advancing the characterization of CP violation. New insight into the parton picture of hadrons was gained with his comprehensive study, in collaboration with a multihadron spectrometer group at Fermilab, of the production of neutral hadrons. The results gave support to quark-counting rules predicted by the constituent-interchange model.

As members of the Tagged Photon Spectrometer collaboration at Fermilab, Uriel and his group contributed to multiple papers on the photoproduction and decay of charmed hadrons. A large-volume Cerenkov detector was built at Colorado and served for particle identification in the spectrometer.

In the mid 1980s, Uriel and junior colleague John Carr joined the SLD collaboration at SLAC. They built the endcap tracking detectors for that facility. The collaboration, exploiting the polarized electron feature of the SLC electron–positron collider and a unique vertex detector extremely close to the interaction point, produced measurements from Z boson decay data, complementary to those from LEP, that greatly advanced our understanding of the electroweak standard model.

As the competition for siting the Superconducting Super Collider (SSC) heated up, Uriel played a central role in developing the State of Colorado’s bid. Once the project was under way at the winning Texas site, he conceived of a regional laboratory to facilitate participation in the project by institutions in the Rocky Mountain and plains region. While no physical facility emerged from that effort, the Rocky Mountain Consortium for High Energy Physics did succeed in attracting funding that helped seed new or rejuvenated programs at some of the member institutions. These programs continue to flourish, the benefits of Uriel’s vision outlasting the SSC project. Uriel also participated in the development of plans for the experiments that would have run at the SSC.

He also revisited the study of long-lived kaon decays with the KTeV Collaboration at Fermilab, joining that effort alongside the late Tony Barker in 1992. This experiment discovered direct CP violation and resolved an apparent longstanding tension between previous results at Fermilab and CERN.

The violation of CP symmetry in the decay of mesons containing b quarks was the focus of the BABAR Collaboration, which with Uriel’s participation collected data over most of the first decade of the 2000s. That experiment and its Japanese competitor, Belle, along with the prior neutral kaon results, firmly established the CP-violating effect formulated in the CKM mechanism, leading to a Nobel Prize for two of that theory’s authors.

A particular passion of Uriel in his later career was the prospect of discovering manifestations of the hypothetical supersymmetry theory. He pursued this goal both with data from the CMS experiment at CERN’s Large Hadron Collider and with studies toward an eventual linear electron–positron collider. As a CMS collaborator, he was a coauthor of the 2012 Higgs boson discovery.

Uriel was an exceptionally effective and appreciated teacher, especially of upper-division physics students, a remarkable number of whom he engaged also in his research efforts. About a dozen graduate students earned their PhDs under his supervision. His colleagues owe a debt of gratitude for his dedication to the department and campus, and for the opportunities he created for a thriving HEP research program.