SeaQuest experiment

SeaQuest experiment. The SeaQuest experiment, designated E906 at Fermilab, was a high-energy physics investigation conducted in the Main Injector beamline. It precisely measured the antiquark structure of protons and nuclei using the Drell-Yan process. The data significantly advanced understanding of quantum chromodynamics and the origins of nucleon spin.

Overview

The experiment was a successor to the earlier Fermilab E866/NuSea experiment, aiming to probe deeper into the asymmetry between up and down antiquarks within the nucleon sea. It utilized a high-intensity proton beam from the Main Injector colliding with stationary liquid hydrogen and deuterium targets, as well as solid nuclear targets like carbon, iron, and tungsten. By analyzing the resulting muon pairs from the Drell-Yan process, researchers could map the momentum distributions of these fundamental sea quarks. The collaboration involved scientists from numerous international institutions, with primary operations based at Fermilab in the United States.

Experimental setup

The core apparatus was situated in the Neutrino Area of Fermilab's Main Injector complex. A 120 GeV primary proton beam was extracted and directed onto one of several interchangeable targets housed within a target station. The resulting collisions produced dimuon pairs, which were detected by a sophisticated spectrometer featuring a large-aperture magnet from the former Fermilab E605 experiment. Key detector components included a series of proportional wire chambers and drift chambers for precise tracking, followed by a muon identifier constructed from thick iron absorbers and scintillation counters. This design allowed for efficient triggering and high-precision measurement of the muons' momenta and trajectories.

Physics goals and results

A primary objective was to determine the ratio of antidown to antiup quark distributions over a broad range of Bjorken x, testing predictions from various quantum chromodynamics models and lattice calculations. The experiment confirmed the significant asymmetry first observed by Fermilab E866/NuSea, ruling out symmetric sea models. Furthermore, by comparing yields from deuterium and hydrogen targets, SeaQuest provided stringent constraints on the flavor structure of the nucleon sea. Measurements with heavy nuclear targets like tungsten and iron offered crucial insights into the modification of antiquark distributions in nuclei, a phenomenon linked to the EMC effect discovered at CERN. These results are vital for interpreting data from ultra-relativistic heavy-ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider.

Collaboration and institutions

The SeaQuest collaboration was a multinational team led by principal investigators from Argonne National Laboratory, University of Michigan, and University of Illinois at Urbana-Champaign. Other major participating institutions included Academia Sinica in Taiwan, Kyoto University, University of Glasgow, University of Bonn, and University of Science and Technology of China. Key funding and support were provided by the United States Department of Energy and the National Science Foundation. The collaboration managed all aspects from detector design and construction at Fermilab to data analysis and publication of results in journals like Physical Review Letters.

Legacy and future experiments

SeaQuest completed its data-taking in 2017, leaving a legacy of high-precision data on nucleon structure. Its findings directly inform the design and physics case for next-generation facilities. The proposed Electron-Ion Collider, planned for construction at Brookhaven National Laboratory, will use SeaQuest results as a benchmark for its detailed imaging of sea quarks and gluons. Furthermore, the experimental apparatus and expertise are being leveraged for the follow-on SpinQuest experiment, which will use a polarized target to directly measure the contribution of antiquarks to the proton spin, a major open question in nuclear physics.

Category:Particle physics experiments Category:Fermilab