Rutgers), ran for a total of 6,650 hours from 1972 through 1978. FERMILAB Contemporary with these experi­ Wide and narrow ments was another large counter bands Neutrino experimentation at higher experiment by CalTech and energies was among the justifica­ Fermilab, designated originally as Getting neutrino beams is all tions for the construction of Fermilab E21 A. Along with its successors, about getting enough parent and the earliest studies utilized these E262, E320, and E356 (which particles. The pioneer neutrino new beams produced with 350-400 collected data* over some 4,600h) experiments at Brookhaven in GeV protons. This pre-Tevatron it took part in the first generation 1962 used no focusing tricks, period used both electronic counters programme, and subsequently however the invention of the and the new 15-foot cryogenic spearheaded the second generation magnetic horn by Simon van der bubble chamber. with precision measurements of both Meer at CERN enabled a wide The counter experimental pro­ charged current structure functions range of parent kaon or pion gramme was basically divided into and the weak mixing angle. Finally, momenta to be concentrated into two generations. The first covered this latter collaboration extended its a cone, boosting the subsequent the discovery of new phenomena and participation into the early Tevatron neutrino yield in a 'wide band confirmation of the parton model era, and will continue through the beam'. The focusing horn also using high rate wide-band and the 1990s. selects the electric charge of the first dichromatic narrow-band neu­ The E1A-inspired programme pions and kaons, thereby deter­ trino beams. The second concen­ ended with E310 and a dedicated mining whether neutrinos or anti- trated on precision measurements low-mass, highly visible counter neutrinos are obtained. However with dichromatic beams. neutrino experiment, E594 took its there is little indication of what One flagship experiment, desig­ place. E616 plus E594 constituted the energies of these neutrinos nated "E1 A", was originally a collabo­ the second generation of pre- (or antineutrinos) are. ration of Harvard, Pennsylvania and Tevatron Fermilab experiments. Another approach is the 'narrow Wisconsin, and was the prototype of The Fermilab "15-foot" bubble band beam', where a limited large neutrino calorimeters: a target/ chamber (actually, a 12 foot diameter range of parent pion or kaon calorimeter followed by a large set of sphere with a 3 foot upstream nose), momenta is selected, giving a iron toroidal magnets. E1A and its began operation in 1973, with a forward peak. Here the offset of successor, E310 (which included neon-hydrogen mixture exposed to the neutrinos from the forward direction gives an indication of their energy. However as pions and kaons decay in different ways, the resultant neutrino beam covers two (narrow) momentum bands, and is 'dichromatic'. The first such beams were used at Fermilab in the early 1970s.

The Fermilab 'flagship' E1A neutrino experi­ ment pioneered the use of large neutrino calorimeters. In this 1973 photo are, left to right, standing, Alfred Mann, Richard Imley, David Cline, T.Y. Ling, Don Reeder, Jim Pitcher and Bernard Aubert; seated, Carlo Rubbia, Karen Mattison and Fred Messing.

22 CERN Courier, November 1993 The E21A counter neutrino experiment by CaiTech and Fermilab, here tended by Frank Sciulii (left) and Barry Barish.

There were three "other" experi­ ments of note during the pre- Tevatron era which deserve mention. The first was E253, a 1978 experi­ ment designed to observe and measure neutrino-electron scattering, with an early determination of the weak mixing angle. The second was the first major emulsion neutrino experiment, E531. This was highly successful, establish­ ing a detailed understanding of charmed particle production and the properties of charmed particles. Interestingly the limits set on the oscillation of muon to tau neutrinos through a search for the appearance of the latter still stand today. Also of note was E701 (the original E616 apparatus with an upstream detector) - a true 'disappearance' oscillation experiment in the dichromatic beam in 1982. The advent of the Tevatron with its higher energies boosted Fermilab's programme, with neutrinos produced (indirectly) from 800 GeV protons. This era saw the continuation of the CalTech/Fermilab programme, the wide-band beam in conjunction (dimuon final states) while precision augmented by Columbia, Chicago, with E28, a collaboration of CERN, measurements of the accompanying Rochester, Rockefeller, and subse­ Hawaii, LBL, and Wisconsin. This strange particle content of those quently Wisconsin (CCFRW), the was followed by a series of 15 other events were carried out by the continuation of the flash-chamber experiments using wide- and narrow­ bubble chamber experiments (muon- programme (E733), and the introduc­ band beams focused for both neutri­ electron final states). tion of holography in bubble cham­ nos and antineutrinos. Observation of trileptons and same- bers with the 15-foot (E632) and The 15-foot chamber was later sign dimuons led to a decade of hybrid (E745) chambers. These modified to include an external muon further experimentation and subse­ studies have extended the precision identifier and an internal "picket quent verification of the Standard of many Standard Model tests and fence". Model. form the basis for the second genera­ The first generation experiments at The nucleon structure functions tion of Tevatron neutrino experiments Fermilab were responsible for meas­ were determined through both scheduled for 1995. uring the ratio of neutral to charged charged current and neutral current current interactions with high statis­ scattering during this period. By the tics, although the priority on the early 1980s, the total neutrino experi­ Future neutrino experiments actual discovery of neutral currents mental programme at Fermilab had was somewhat controversial. The contributed greatly to our under­ As Fermilab moves into its third first observation of opposite sign standing of the parton model and decade of operation, much of the dilepton final states and their deter­ particle production in charged current experimental programme, particularly mination occurred at Fermilab in E1A events. in the fixed target area, emphasizes

CERN Courier, November 1993 23 Limits on neutrino oscillation parameters expected from several future experiments, compared with the historical results from CDHSW (WA1) at CERN.

running in each beam will open up the two vital parameters. To date such an analysis has not been worthwhile due to the paucity of antineutrino data. E815 anticipates normal operation of 1013 protons per cycle, for a total of 2 x 1018 integrated protons after an eight-month run. This should yfeld approximately 1.2 million neutrino charged current, 400,000 neutrino neutral current, 220,000 antineutrino charged current and 84,000 antineutrino neutral current events. As the end of the decade ap­ proaches, Fermilab's new Main Injector (May, page 10) will provide new opportunities for fixed target experiments using either the in­ creased intensity Tevatron beam, or the high intensity 120 GeV beam extracted directly from the Main Injector, and available during collider operation. One of the most exciting of these precision experiments to probe deep violation. Measuring this parameter in opportunities is a search for neutrino inside the Standard Model and several processes provides insight oscillations and the concomitant hopefully get a glimpse of what lies into small effects due to higher order evidence for neutrino mass. beyond it. corrections to the Standard Model as The 120 GeV Fermilab Main Injec­ Neutrinos are penetrating probes well as possible deviations from it. tor beam will deliver more than 4 x and will make up an important part of The other parameter - Greek rho - 1013 protons per two-second cycle, this ongoing programme. dictates the strength of the neutral producing an unprecedented flux of After more than a five-year hiatus, current interaction, and in the basic high intensity, high energy neutrinos. the detector used for the CCFRW Standard Model is equal to 1. A preliminary beam design foresees (Chicago/Columbia/Fermilab/ Small effects can creep in due to a muon-neutrino beam with an Rochester/Wisconsin) collaboration's various electroweak corrections, average energy of 15 GeV. experiments (E770/774) will be such as those depending on the One proposal wants to use this reincarnated as E815, an experiment mass of the long-awaited sixth ('top') beam with a hybrid emulsion spec­ designed to make precision meas­ quark. Present values of the Stand­ trometer for a short baseline experi­ urements of the basic electroweak ard Model parameters predict rho to ment to search for muon/tau-neutrino parameters. be 1.0026 ± 0.0038, along with a top oscillations. This follows the philoso­ One of these - the electroweak heavier than 113 GeV, and a higgs phy of the Fermilab E531 experiment mixing parameter (Weinberg angle, particle somewhere in the range 60 and CERN's CHORUS experiment linking the two neutral carriers of the to 1000 GeV. currently under construction. theory with the physical photon and Experiment 815 will measure rho to A compelling feature of this idea is Z boson) - can be obtained in a a precision of ± 0.005, and the the possibility to actually detect the number of ways: direct measurement mixing parameter to ± 0.003. The key interaction of a tau neutrino via the of the W and Z masses, left/right feature will be the operation of a new tau-neutrino/tau charged current asymmetry in Z decays, neutrino- charge selected beam to provide interaction. With the tau neutrino yet nucleon scattering, and atomic parity neutrinos or antineutrinos. Separate to be directly observed, this group

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CERN Courier, November 1993 25 An aerial photograph of the LAMPF facility with the experimental areas in the foreground. The tunnel housing the LSND neutrino experiment is visible in the lower centre of the photo behind a service building. LSND is about 11 metres downstream of the LAMPF beam stop.

proposes a tau-neutrino beam dump which could use the 800 GeV proton beam prior to the completion of the Main Injector. This proposal will soon be submitted for formal consideration. Also being developed are plans for a long baseline experiment. One idea is to extract the Main Injector beam in a direction so that the neutrinos travel toward Soudan, Minnesota, 800 kilometres to the northwest of Fermilab, home of a major under­ ground laboratory. In such a scheme, the near and distant detectors would use the same beam and some common modules. Other long baseline options being studied involve using protons ex­ tracted from the existing 120 GeV Main Ring, the 8 GeV Booster, or the Antiproton Debuncher Ring, the idea being to produce a high intensity neutrino beam, albeit of low energy. This gives good sensitivity to oscilla­ tions over a shorter distance, allow­ searched for the forbidden decay of a this physics (as well as oscillations in ing the "far" detector to be much muon into an electron and two other channels) is LSND (July/ nearer, even on the Laboratory site. neutrinos, and measured the reaction August, page 10 and cover). rate of a neutrino interacting with a In addition to searching for these deuteron to give two protons and an oscillations, LSND will measure electron - the inverse of the reaction neutrino-proton elastic scattering at that drives the sun's primary energy low momentum transfer, providing a LOS ALAMOS source. sensitive measure of the strange- The next LAMPF neutrino experi­ quark contribution to the proton spin. Following the historic observation of ment, a UC Irvine/Maryland/Los LSND began taking data in August. neutrinos in the mid-1950s by two Alamos collaboration, ran from 1982 Los Alamos physicists have also Los Alamos scientists, Fred Reines through 1986 and measured the been busy in neutrino physics experi­ and Clyde Cowan, Jr, using inverse elastic scattering rate of electron- ments elsewhere. beta decay, there has been a long neutrinos and protons, where both One such experiment looked at the and distinguished history of experi­ neutral and charged weak currents beta decay of free molecular tritium mental neutrino physics at LAMPF, contribute. to obtain an essentially model- the Los Alamos Meson Physics With its precision of about 15%, independent determination of the Facility. LAMPF is the only meson the experiment provided the first electron-neutrino mass. The present factory to have had an experimental demonstration of (destructive) inter­ result gives an upper limit on the neutrino programme. ference between the charged and electron-neutrino mass of 9.3 eV, In the late 1970s, the first LAMPF neutral currents. showing that electron neutrinos neutrino experiment used a 6-tonne More recent neutrino experiments cannot by themselves 'close' the water Cherenkov detector 7 metres at LAMPF have searched for neutrino universe. from the beam stop. A collaboration oscillations, especially between Pioneer solar neutrino experiments of Yale, Los Alamos and several muon- and electron-neutrinos. (see page 21) suggested that the other institutions, this experiment The newest experiment to pursue observed flux of high-energy neutri-

26 CERN Courier, November 1993