CERN is known for its collider facilities, yet fixed-target experiments also have a long history at the Laboratory, forming essential building blocks in the physics landscape. Notable among them are experiments fed by the Super Proton Synchrotron (SPS) accelerator, which has provided a steady stream of high-energy proton beams to the North Area at CERN’s Prévessin site. As the North Area marks 40 years since the publication of its first physics, a symposium at CERN on 3 April, broadcast via webcast, celebrates this hub of experiments, which have been exploring many fundamental questions and will continue to enrich the programme of the Laboratory.
In fixed-target experiments, a particle beam collides with a stationary target, in most cases producing secondary particles for specific studies. High-energy machines such as the SPS, which produces proton beams with a momentum of up to 450 GeV/c, give the secondary products a large forward boost, providing intense sources of secondary and tertiary particles such as electrons, muons and hadrons. Compared to collider experiments, fixed-target experiments tend to be more specialised and focus on precision measurements that demand very high statistics, such as those involving ultra-rare decays.
The North Area fixed-target experiments range from the pioneering NA1, which measured the photoproduction of vector and scalar bosons until 1992, to today’s NA64, which studies the dark sector. Among the key results from the NA experiments are first studies of the quark–gluon plasma, the first evidence of direct charge-parity (CP) violation and a detailed understanding of how nucleon spin arises from quarks and gluons. The first muons in CERN’s North Area were reported at the start of the commissioning run in March 1978, and the first physics publication – a measurement of the production rate of muon pairs by quark–antiquark annihilation – was published in 1979 by the NA3 experiment.
Today, the North Area’s physics programme is as vibrant as ever,and this looks set to remain true, with many proposals for new experiments appearing on the horizon, ranging from the study of very rare decays and light dark matter to the study of quantum chromodynamics (QCD) with hadron and heavy-ion beams. There is even a study under way to possibly extend the North Area with an additional very-high-intensity proton beam serving a so-called beam dump facility. Read more about the physics research in the North Area in this CERN Courier feature, from which this text was extracted.
Follow the webcast of the event here.