Number 175 (Story #1), April 25, 1994 by Phillip F. Schewe and Ben Stein EXPLORING MATTER ON A SCALE OF 10**-16 CM , 1000 times smaller than the size of the proton, is possible at the HERA electron-proton collider at Hamburg, Germany. In some of the HERA interactions ("diffraction scattering") the electron merely grazes the proton, but in other interactions the electron, which is immune to the strong nuclear force, burrows deep inside the proton and scatters from individual constituent quarks or even from short-lived virtual quarks popping into existence out of the vacuum. In these violent "deep inelastic scattering" events the proton is usually shattered. Speaking at last week's American Physical Society meeting in Virginia, Allen Caldwell of Columbia University reported on a mysterious class of events recorded at the ZEUS detector at HERA that seem to be both diffractive and deep-inelastic in nature. In these events, a single high-energy quark is ejected from the target proton, indicative of deep-inelastic scattering. But the debris from what should have been a broken-up proton was nowhere to be found. Caldwell had no solid explanation for this odd behavior, but speculated that the electron might in this case be scattering from some combination of quarks or gluons within the proton.