Looking deep into the proton

3 D ecember 1997

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An electron is turned backwards by its collision deep within a proton in this classic image from the ZEUS detector at the DESY laboratory in Hamburg. ZEUS is one of two major detectors that record head-on collisions between high energy electrons and protons travelling in opposite directions around the Hadron Electron Ring Accelerator (HERA) at DESY. The electrons and protons travel through the beam pipe, across the centre of this image - the electrons from the left, the protons from the right. In this view an electron shoots off backwards and upwards (at about 11 o'clock), having made an almost direct hit with one of the proton's constituents - a quark. The struck quark sets off downwards and immediately transforms into a shower of particles that create the spray of tracks in the lower half of the image. You can see the momentum balance between the electron and the quark more clearly by looking end on at the detector, if you click here.

Credit: DESY / ZEUS

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