← Research

E260 — Hadron Jets from Quark Scattering

Fermilab · 1977–1980

If hadrons are made of quarks, then when two hadrons collide hard enough, the quarks inside them should scatter off one another like billiard balls — and each scattered quark should announce itself as a narrow spray of particles carrying its momentum. E260 set out to find those sprays.

E260 was the first experiment to trigger on hadron jets with a calorimeter — to decide, in hardware and in real time, that a jet had just happened and this event was worth recording. Without that, jet events are needles in a haystack of ordinary collisions.

The experiment fired 200 GeV beams of pions and protons at hydrogen, beryllium and aluminium targets at Fermilab, and looked at the rare events in which a large amount of momentum came out sideways. At high transverse momentum the debris was not spread uniformly. It arrived in jets: collimated groups of hadrons, back to back, exactly as expected if a single constituent had been struck and knocked out.

The decisive point was which jets they were. Electron–positron annihilation experiments had already seen jets, produced there by a quark and antiquark created cleanly out of the vacuum. The jets E260 found in hadron collisions had the same character. Two hadrons were therefore interacting through their constituents, and a struck quark turned into hadrons the same way whatever had produced it — the same process, reached by a completely different route. That universality is what made the quark picture a description of nature rather than a bookkeeping device.

That first paper was followed by a programme of measurement rather than a single sighting: how often jets are produced, how their rate falls with transverse momentum, how the pattern differs between pion and proton beams, and whether the details match the predictions of the then-new theory of the strong force. By 1979 the collaboration was using jets as a quantitative test of quantum chromodynamics — treating the quark-scattering picture as established well enough to probe.

The thesis

Rohlf's doctoral thesis, Observation of Jets and Tests of Quantum Chromodynamics, was completed at the California Institute of Technology in 1980. It used the Field–Feynman model to compare the jets seen in hadron collisions with those from electron–positron annihilation, and — after detailed acceptance corrections — produced the first measurement of quark–quark scattering cross sections.

Thesis and paper are the same document — an arrangement agreed with Fox after the fact. Rohlf had already written the collaboration's paper and seen it published; rather than spend several months restating the same work in thesis form, the two of them settled on putting a title page on the paper and submitting that. Caltech accepted it. The thesis on the shelf at Pasadena and the article in Nuclear Physics B are one and the same piece of work.

Thesis committee: G. C. Fox (advisor), C. Barnes, R. P. Feynman, R. Gomez.

Jets have since become the basic language of hadron collider physics. Every result on the CMS page downstream of this one is stated in terms of them, and the angular distribution of jet pairs went on to establish the spin of the gluon.

Papers

Fermilab experiments E-260 and E-110. Citation counts from INSPIRE-HEP, August 2026.