Karl Berkelman, the Goldwin Smith Professor Emeritus of Physics and a leader in experimental particle physics at Cornell, died Feb. 26 in Sayre, Pa., following a heart attack. He was 75.

Berkelman was director of the Laboratory of Nuclear Studies from 1985 to 2000, during which time he led the development of the Cornell Electron Storage Ring (CESR) and versions of CLEO, its associated detector. (CESR and CLEO are now part of CLASSE, the Cornell Laboratory for Accelerator-based Sciences and Education.)

His leadership marked one of the most productive periods of research in experimental particle physics on campus, with CESR operating for 10 years at the world's highest colliding beam luminosity. He led the construction of the CLEO II detector, key features of which have been adopted by other collaborations in the field. During this period the CLEO collaboration led the field of heavy quark and lepton physics.

An experimentalist who measured the properties of nature's smallest particles, Berkelman was widely recognized for his ability to design and conduct experiments that tested complex theoretical concepts to the highest precision possible. He was also known for his hands-on leadership style, his mastery of subspecialties across the field, his skill as a communicator and his interest in his students and colleagues.

"He saw the big picture, but he was quite familiar with the details," said Maury Tigner, the Hans A. Bethe Professor Emeritus of Physics and director of CLASSE. "He understood enough about everything that was going on in the lab that he was able to make very difficult decisions about priorities. That's what stood the lab in such very good stead over all those years."

Born June 7, 1933, in Lewiston, Maine, Berkelman earned his bachelor's degree in physics from the University of Rochester in 1955 and Ph.D. in physics at Cornell in 1959. He joined the Cornell faculty in 1961.

In the 1960s he worked with then director Robert Wilson and others on groundbreaking measurements of the structure of the proton. Later he led a group of graduate students in the first successful measurement of the size of the pi meson, a charged particle produced when electrons and protons collide.

Throughout his career, Berkelman was an active member in the small faculty core who worked on Cornell's evolving series of particle accelerators. In the 1970s Berkelman and collaborators studied so-called inelastic electron scattering, in which electrons colliding with protons break them apart to produce other particles.

When CESR and CLEO were constructed in the late 1970s, Berkelman led the design and construction of the injection system, which transfers electrons from the synchrotron into the storage ring. He also wrote the first track finding program for CLEO -- and many refined versions in later years -- enabling researchers to reconstruct the path and momentum of charged particles following a collision.

During leaves from Cornell, Berkelman worked as a visiting scientist at the CERN laboratory in Geneva and the DESY laboratory in Hamburg. He was named Cornell's Goldwin Smith Professor of Physics in 1995; and despite retiring in 2006, he remained active in the CLEO collaboration for many years.

In 2004 Berkelman published "A Personal History of CESR and CLEO: The Cornell Electron Storage Ring and Its Main Particle Detector Facility," which describes the evolution of experimental particle physics at Cornell throughout his four-decade tenure and his thoughts on the benefits of a democratic leadership style.

Berkelman is survived by his wife, Mary, three sons and extended family. A memorial service is planned for 3 p.m. Saturday, April 18, at the First Presbyterian Church in Ithaca.