Wide and Narrow Bands FERMILAB
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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,