Since its foundation in 1967, creeping urbanization has taken away some of Fermilab’s remoteness, but the famous buffalo still roam, and farm buildings evocative of frontier America dot the landscape – appropriately for a laboratory at the high-energy frontier of modern research.
The US National Accelerator Laboratory formally saw the light of day on 21 November 1967, when President Johnson signed the bill that brought it into existence. Robert R Wilson moved from Cornell to become its founding director, and two years later he famously told Congress that the laboratory’s contribution was not to the defence of America, but rather to what made the nation worth defending. In 1974, the National Accelerator Laboratory became the Fermi National Accelerator Laboratory – Fermilab – at a dedication ceremony attended by Enrico Fermi’s widow, Laura.
Fermilab has since gone on to gain an enviable reputation as a place where discoveries are made. The bottom quark made its first appearance there in 1977, and the top quark joined it in 1995. In 2000, Fermilab researchers announced the first direct observation of the tau neutrino, filling the final slot in the Standard Model’s three families of matter particles. The laboratory is justifiably proud of these achievements, and quietly reminds the world of them in its generic email address of topquark@fnal.gov.
Fermilab today
Today, all eyes are on run II of Fermilab’s Tevatron proton-proton collider, but that is just one part of a broad research programme. The laboratory is also a focus for US involvement in CERN’s Large Hadron Collider (LHC), and the Compact Muon Solenoid (CMS) experiment preparing for physics at the LHC. A two-pronged neutrino programme is just getting under way (MiniBOONE goes live at Fermilab), and with leading roles in the Pierre Auger project, the Cryogenic Dark Matter Search (CDMS) and the ambitious Sloan Digital Sky Survey, Fermilab is increasingly involved in non-accelerator research.
Tevatron’s run II started in April 2001 and is scheduled to last six years. After a slow start, the collider’s luminosity is steadily climbing. Run II makes the two collider experiments CDF and D0 the main focus of Fermilab’s research in the short term. With the Tevatron being the world’s highest-energy particle collider until the LHC assumes that mantle in 2007, they represent Fermilab’s best immediate hope of adding new discoveries to its already impressive tally in the coming years.
Both CDF and D0 have undergone major upgrades for run II, and the collaborations have also experienced important demographic changes, reflecting the increasing globalization of particle physics. The CDF experiment began as a collaboration of physicists from the US, Italy and Japan. Today, it has 600 members from 11 countries. At D0, the change has been even more dramatic. Since 1996, when the French Saclay laboratory was the collaboration’s sole non-US institution, the number has grown to 30. D0’s upgrade has seen an order-of-magnitude jump in the number of detector readout channels, and the establishment of a computing grid structure for data analysis connecting data farms at Fermilab, Lyons in France, Lancaster in the UK, and Amsterdam in the Netherlands. Both experiments list their priorities for run II as top quark studies and the search for Higgs bosons.
Looking towards the medium term, Fermilab is developing a broad neutrino programme based on two complementary new neutrino beams. One uses a short baseline and a low-energy beam, while the other has a long-baseline, high-energy beam configuration. The Mini Booster Neutrino Experiment (MiniBOONE) is the first experiment to begin data-taking. It is a 500 m baseline experiment that started up in September. Using a proton beam from Fermilab’s 8 GeV booster ring, the MiniBOONE collaboration has optimized the energy-to-baseline ratio to test the contested oscillation result announced by the Los Alamos laboratory’s LSND experiment in 1996. By looking for electron-neutrinos in the essentially pure muon-neutrino beam from the booster, MiniBOONE aims to provide the first unambiguous accelerator-based observation of neutrino oscillations. If oscillations are observed, the “Mini” prefix will be dropped and a second detector will be added further downstream. This will allow the collaboration to make precision measurements of oscillation parameters, and to search for violation of charge-parity (CP) and time-reversal (T) symmetry in the neutrino system.
Fermilab’s second neutrino experiment, the Main Injector Neutrino Oscillation Search (MINOS), is scheduled to start data-taking in 2005. MINOS will have a near detector on the Fermilab site and a far detector some 735 km away in Minnesota’s Soudan mine. It takes its primary beam from the 120 GeV main injector, providing a very different energy-to-baseline ratio from MiniBOONE. Fermilab neutrino physicists are also enthusiastic about developing the neutrino programme to include experiments that will probe the strange quark content of the proton through neutrino-proton elastic scattering.
Completing the accelerator research picture are two more fixed-target experiments foreseen for the main injector. The CKM experiment received scientific approval in 2001. Starting in 2006, it will study the decay of positive kaons into pions accompanied by a neutrino-antineutrino pair. This rare decay, forbidden in the Standard Model at tree level but possible through quark loops, gives a direct measure of the Cabbibo-Kobayashi-Maskawa (CKM) quark mixing matrix element Vtd that describes transitions between top and down quarks. Two years later, CKM is scheduled to be joined by BTeV, an experiment dedicated to advancing the study of CP violation in B mesons, recently begun at SLAC’s BaBar experiment in California and the Belle experiment at Japan’s KEK laboratory.
With a $167 million (€167 million) share of the total US contribution of $531 million to the LHC project, Fermilab has a major stake in what will soon be the world’s flagship particle physics research facility. Fermilab coordinates both the US-LHC accelerator project and US participation in the CMS experiment.
The US LHC accelerator project involves Fermilab, Brookhaven and the Lawrence Berkeley National Laboratory (LBNL). It is responsible for the four interaction regions and the radiofrequency straight section of the LHC, for testing superconducting cable for the main magnets, and for accelerator physics calculations. Integrated “inner-triplet” magnet systems will bring the LHC’s proton beams into collision. They are being built at Fermilab using high-gradient quadrupoles produced by Fermilab and KEK, corrector coils provided by CERN, dipoles from Brookhaven, cryogenic feedboxes from LBNL, and absorbers provided by LBNL to protect the superconducting magnets from collision debris. The inner triplets have now entered the production phase, and are on schedule to be delivered to CERN by the end of 2004.
The US contribution to CMS is also coordinated from Fermilab. US CMS researchers account for around 20% of the collaboration’s total, and are involved in many of the detector’s subsystems. There are plans to establish a virtual CMS control room at the laboratory, so that US physicists don’t have to cross the Atlantic to run shifts.
Non-accelerator programme
With the growing convergence between astrophysics and particle physics, Fermilab is playing an increasingly important role in non-accelerator-based studies. The laboratory has responsibility for data handling for the ambitious Sloan Digital Sky Survey. Using an observatory at Apache Point in New Mexico, the survey aims to map in detail over a quarter of the entire sky, determining the distance and brightness of more than 100 million celestial objects over a period of five years. The data amassed by the survey will provide invaluable information about the large-scale structure of the universe, allowing discrimination between models of the universe’s evolution.
Fermilab also plays a managerial role in the Pierre Auger Project. With two giant detector arrays each covering an area of 3000 km2, the Auger observatory will study the direction and composition of the cosmic ray showers above 1019 eV that arrive at the Earth in apparent defiance of the Greisen-Zatsepin-Kuzmin (GKZ) cut-off. According to this, space should be opaque to cosmic rays of such high energy, making their origin something of a mystery.
Completing Fermilab’s triplet of non-accelerator experiments is CDMS, currently installed at an underground facility at Stanford, California. For its second stage, the detector will move to the Soudan mine to carry out its search for weakly interacting massive particle (WIMP) candidates for dark matter.
Accelerators for the future
Fermilab’s 2001-2006 institutional plan states that the post-LHC energy frontier is the challenge of the future, and outlines its plans to meet that challenge. The laboratory is engaged in research and development projects for a possible muon collider, with work concentrating on the cavities embedded in a solenoidal field that would form part of the cooling scheme for a muon beam. A small study group has also investigated the possibility of a Very Large Hadron Collider with energies up to 100 TeV. Research continues on next-generation accelerator magnets, both superconducting and superferric.
Top priority, however, is a linear collider. Fermilab is involved in the Next Linear Collider and TESLA projects; it built the photoinjector for the TESLA Test Facility at Hamburg’s DESY laboratory, and retains an identical device that is being used with teams from UCLA to study plasma acceleration. Most particle physicists agree that a linear collider is the logical next step for high-energy physics, and many laboratories are involved in preparatory work for such a machine. When it comes to choosing a location, Fermilab’s director Mike Witherell believes his laboratory has much to offer. Keeping a major regional facility for particle physics in the US remains a priority for Fermilab.
