secondaries to very high accuracy. Clearly this procedure is very expensive (although necessary for final states of high multiplicity) general plan view of the experiment is shown in Fig. 1. The pion beam, after passing through a beam counter system, is incident on a liquid hydrogen target almost completely surrounded by y-ray detectors. Slow recoil protons emerge through a side slot in these counters, pass through direction-determining wire planes, through dE/dx counters, and into a total-absorption en~rgy detector. Fast decay secondaries (and the incident beam) pass through a downstream slot, and through a series of spark chamber planes and an analyzing magnet. A large y detector is located about 12 meters downstream of the target. An on-line computer is used to record data and to pe~form preliminary calculations. The NAL Medium Energy High Resolution (MEHR) beam encompasses the desired incident pion momentum range of' 40 to 80 GeV/c. Hopefully, this range is below the pre­ -dieted disappearance of the p p, etc. cross sections into the undergrowth. Somewhat lower energies might be studied by compressing the experimental arrangement longitudinally. The momentum transfer range to be studied,·0.04 < It I < 0.55 (GeV/c)

ex~ra rrO to ~ 1 - 2 GeV!c in the laboratory, as well as to ±25 milliradians of forward, as described above. Such a situation can easily arise from e.g., N* rr-rro production aecaying to (prrO) rr-rro. However, fewer than 1/10% of these events give a rro in the kinematically allowed solid angle, and, furthermore, a rro this slow is nearly certain to be vetoed by the gamma detectors surrounding the target since the minimum opening angle is larger than the aperture left open for the desired fast particles. The result of all this is that we expect a mass resolu­ tion of about ±10 MeV/c 2 on 3rr decays, and about ±10 to ±50 MeV/c2 on rr-rro, etc., decays, depending on the resolu­ tion ~n y-ray angle (conversion point location) that can be obtained. It is easy to show that the insertion of a magnet does not spoil the resolution based on a ful·l lever arm of 12 meters. Thus, it should be possible to separate the produced.resonances. Experimental A lan view of the apparatus is shown in Fig. 1, and a detail of the target region in Fig. 2. We propose to use the MEHR beam (80 GeV/c maximum) brought tQ a focus about

identification are assumed to be available. The 15 - em­ long X 5-mm - diameter hydrogen target f9llows an array, of beam counters and a multiwire proportional plane. The target is almost completely surrounded by a box of lead­ scintillator y-ray and charged-particle veto counters. The proton detector is an array of E and dE/dx counters. Three thin counters are followed by a liquid scintillator tank 50 cm Xi 79 cm X 40 cm deep for stopping more energetic protons (up to 800 MeV/c). All pulse heights are digitized, as is the proton time-of-flight over the 2 meter flight path. The proton energy is deter­ "mined by the total light and the other data aid in its identification. The resolution of this technique is claimed to be excellent,4 being < 2% in kinetic energy at 150 MeV. Even at 800 MeV/c, it promises to work better than might be expected because of the detection of absorbed products which would otherwise smear the resolution. (We have started developing this technique. The liquid scintillator detector has already be~n built, and is currently being tested in light collection studies.) The proton angle is measured ick (Brookhaven & Nbrtheastern),private communication see also NAL Summer Study SS-38

system" to be described below, at least 5 gaps (10 planes) conventional wire planes and at least two wire proportional chambers. Deadening of conventional wire planes near the target in the moderately high flux beam would obscure too many tracks we wish to detect. Gap-transfer proportional planes 5 with magnetostrictive readout may be the solution most compatible with our present electronics. A thin counter is placed downstream of ~he target as shown. We assume that chambers, etc. are thin enough that mUltiple scattering is negligible for the downstream particles. The magnet suggested is 1 meter long X 0.8 meter wide with a 0.4 m gap, and has a 15 kg field. This gives ~p/p ~ 4% at 40 Gev/c. The high energy gamma analyzer at the end of the system requires further study: first thoughts are des­ cribed below. The main concern is accurate location of the shower to determine the y-ray direction. Strip chambers, as,used in a recent ~ochester-Cornell collabora­ tion6, appear to work but lack the desired resolution. We wish to study means for determining the centroid of the multiple tracks of a high-energy shower, e.g.,by electronically processing the magnetostriction signals. High mUltiple 5. As developed er at Brookhaven. 6. Behrendetal., Physical Review Letters ~,1246 (1970)

time as possible prior~o serious data taking. Possible modes of tune up and testing would be discussed with'NAL staff when appropriate. operation in tandem with other experiments using a defocussed beam (up to 2 cm dia.) and a very thin target would be a very useful parasitic operation (our apparatus cqntains very little material in the beam). Apparatus We believe we already possess a large fraction of the necessary apparatus, but obviously major components remain to be built.· As mentioned previously.we have constructed a prototype proton detector which is now being tested. We have on order eight wire-spark chambers from Science Accessories Corporation design) with dimensions up to 1m x 1m active area, but will need to construct (or purchase) additional chambers about 0.6m x 1.2m in area. The exact number depends on our experience with chamber efficiency, determin~ng the number of chambers necessary to reconstruct three trucks. All counters will have to be constructed. We plan to use liqui~ scintillator for several of the detectors, including the downstream shower detectors, to reduce costs. (We are experimenting with techn~ques to allow total internal reflection ""

because of the mUltiple registers. A single 37 ips, 9 track tape unit, a teletype, a card reader, a line printer, and a display scope are included. The general software available is extensive, including Fortran IV. In addition, we expect to benefit by cooperation with a University of Chicago group, which is purchasing similar computers, on spark chamber software development. Event filtering and some analysis will be done on-line. The computer will also be employed for co~siderable off-li.ne analysis. We also have access to an IBM 360/50 at UICC, due to be replaced by an IBM 60/65 or a XDS Sigma 7 this fall. The biggest item required from NAL is, of Gourse, the magnet. At 15 Kg, the 1 meter length assumed gives a conservative momentum resolution of 4% at 40 GeV/c. Thus, greater length (and a wider aperture) would be preferred. Possibilities might be other accelerator transport magnets with enlarged gaps. The pniformity of field need not be high. 10 University of Chicago, priv~te communication..., - - - - _. _.__. ---~ --------~