REPORT OF THE NEUTRINO AREA STUDY GROUP

Transcription

1 REPORT OF THE NEUTRINO AREA STUDY GROUP J. Allaby, C. Baltay, D. Cline, W. Fowler, F. Huson, W. Ko, P. Limon, S. Loken, A. Melissinos, J. Peoples, R. Singer, A. Skuja, R. Stefanski, D. Theriot, T. Toohig, W. Walker, R. Yamamoto, T. Yamanouchi The future development of the Neutrino Area at Fermilab was discussed in great detail at the 1976 Summer Study, to a large extent from the point of view of the availability of looo-gev protons from the Energy Doubler/Saver. Everyone at the Summer Study was convinced that the Neutrino Area should be upgraded to be able to utilize the looo-gev protons as soon as they are available. The Neutrino Area houses three separate physics programs: neutrino physics in the IS-ft. chamber and the electronic detectors, muon physics in the muon lab, and hadron physics in the bubble chambers. Thus in the detailed considerations on the future development of the area, the group naturally fell into three subgroups concerned with each of these topics. However, the group as a whole paid a great deal of attention to the common problem of the general layout of the Neutrino Area. I. General Layout of the Neutrino Area In the existing configuration of the Neutrino Area, the muon and neutrino programs use the same target and target tube, and the protons for the hadron target must be transported through the neutrino beam target tube, decay pipe, and the hadron shield. This configuration has a number of undesirable features:

2 -2 (a) The front end of the muon beam in incompatible with the wideband horn or the narrowband neutrino beams. Thus major parts of the neutrino or muon programs have to be shut off for long periods of time while the other is running. In principle, it sounds attractive to utilize the muons from the same meson decays that produce the neutrinos. However, this proton economy has been very rarely realized in the past years of operation, not only because of the incompatibility of beams, but because of the more basic reason that ~uon experiments require slow spill, while many of the counter neutrino experiments, to reduce cosmic-ray backgrounds, as well as the IS-ft. chamber, required relatively short spill times (one millisecond or shorter). This situation is likely to continue in the future. (b) Constraints imposed by the physical presence of the three beam lines in the target area. For example, the enclosures and ~agnets of the muon and hadron beams make the muon shield of the neutrino beam sufficiently inhomogeneous so that neutrino flux and spectrum measurements using muon counters in the shield have not been practicable. Flux measurements in Enclosure 100 have been compromised by the muon and hadron beam ports in the hadron shield, which in principle can be plugged but in practice are generally open for one reason or another. (c) Simultaneous operation of the muon and/or hadron beams has in the past been a source of substantial muon backgrounds in various neutrino experiments. (d) The upgrading of the muon beam to utilize 1000-GeV protons is severely constrained by the existing geometry and is made rather

3 expensive by the four large bends in the beam. (el The intensities that can be targeted in Enclosure for the hadron beams are limited to less than 10 due to various radiation problems. protons/pulse In order to alleviate the difficulties described above, proponents of all three programs (neutrinos, muons and hadronsl concur in the recommendation that the targeting for the neutrino, muon and hadron beams are separated. One scheme to do this was worked out in some detail. A new target hall for the muon and hadron beams would be located in the vicinity of Enclosure 100, about 25 feet east of the neutrino beam line. The primary protons to feed these targets would be split off near the upstream end of Neuhall, and would be transported next to the neutrino target tube, and then outside of the decay pipe, at an angle -20 mrad. The new target hall would have two separate targeting stations for muon and hadron beams respectively. The new improved muon beam could then be laid out with no prior constraints, to lead to a muon detector area east of the Neutrino Area north of Wilson Road. The secondary beams from the hadron target would be fed into the existing beam lines N3 and NS to the 30" and the IS' chambers. The scheme is described ~n detail in report v, B, 2 to this Summer Study. II. The Neutrino Program The physics justification for pursuing neutrino interactions to the highest energies possible at Fermilab seemed clear and therefore did not need further discussion. A summary of the major recommendations to allow neutrino experiments to be carried out

4 -4 with 1000-GeV primary protons follows: (a) The muon shield in the neutrino beam should be upgraded to allow the neutrino detectors to operate with 1000-GeV protons on the target. How this might be best done is discussed in detail in report V, B, 6 of this Summer Study. (b) The neutrino target enclosure, which is now 200 feet long, should be extended to at least twice its present length to allow the construction of high quality narrowband beams up to the highest energies feasible. This might be accomplished by adding a "New Neuhall" downstream of the target tube, or even better, by digging up the target tube* and building one long "New Neuhall" downstream of and continuous with the existing Neuhall. A detailed discussion of this proposal can be found in reports V, B, 2; V, B, 5 of this Summer Study. (c) Both wideband and narrowband v and v, as well as v ll 1l e and v ' beams will be important and useful with 1000-GeV protons. e Various possibilities are discussed in detail in report V, B, 5 of this Study. (d) Due to event rate limitations in the wideband neutrino runs and the flux limits on targets and beam dumps with a fast spill, the proton intensity in the Energy Doubler/Saver is best utilized for neutrino experiments if it comes in 1 msec long 13 pulses with a few 10 protons each, spaced 1 second apart. This is discussed in more detail in report V, B, 1 of this Summer study. (*) NOTE: Even if the radiation levels of the sand and gravel at the target location should prove high, use of a clam shell rather than a traxcavator would keep personnel away from the active material. Only the clam shell itself would then have to be cleaned up to remove activity.

5 -5 (e) The importance of adequate instrumentation for reliable measurements of the neutrino fluxes and spectra can hardly be emphasized enough. A basic part of such instrumentation should be a set of counters to ~easure the range and radial distribution of muons in the shield at the same time that data is taken in each experiment. Such measurements would be possible if the shield were made of passive iron and earth, which could be made uniform if the muon and hadron beams had a separate target station. Removing the hadron beam target from Enclosure 100 would also make room for various Cernekov Counters which are needed for K/~ ratio measurements. (f) The present decay pipe is -400 meters long. Extending the decay pipe to -900 meters to the Wonder Building would increase the fluxes in the v and v beams by a factor of 2 to 3. However, V e for narrowband beams the long decay path (and therefore shorter shield) would spoil the energy resolution considerably. Thus, if the decay pipe were extended one would have to maintain the ability to reinsert the hadron beam dump in its present location in Enclosure 100 to keep the decay pipe length to 400 meters for narrowband running. Keeping the detectors in their present location, a longer decay pipe means a shorter shield, which would have to contain more iron than the 1000-meter iron and earth shield with the 400m decay pipe. Thus, while a factor of 2 to 3 sounds extremely attractive, lengthening the decay pi~ sounds expensive, and thus should probably come in priority after the other items listed above. III. The Muon Program

6 The relevance of a high-quality, high-intensity muon beam at the highest possible energy cannot be overemphasized. Muons are necessary for probing the electromagnetic structure of the nucleon at high momentum transfer and at high energy they become competitive and complementary to neutrinos for probing the weak interactions. They offer distinct advantages in the case of neutral current investigations. Furthermore, the polarization of the muon beam can be controlled which is not possible with neutrinos. Similar physics goals can be achieved only with colliding e-p rings in which case much higher Q2 can be achieved but the luminosity is smaller by several orders of magnitude. In the past, the muon program has been severely weakened because {ll it could not be run simultaneously with the neutrino program; {2l the beam quality and intensity WeI ~ow, and (3) no provision for controlling the polarization was available'. Most of these deficiencies can be resolved if the muon beam is targeted independently from the neutrino beam. We also note that, at high energies, use of the present muon laboratory simultaneously with neutrino running is impossible because of the background induced at the neutrino detectors. For these reasons we recommend strongly that {al the muon and neutrino targets be separated; {bl that the new muon laboratory be established such as not to interfere with the neutrino detectors; {cl that the muon beam be designed so as to provide a ~+/p ratio of 10-5 at the highest energy, have a small spot size and <1% halo, and have a controlled polarization. The details of such a design and the physics justification for it

7 -7 are included in the report V, C, 1. IV. The Hadron Program The new targeting scheme proposed for the muon and hadron beams has great advantages for the hadron program. Presently, the hadron beams are limited by operat1ng fluxes of -5xlO -10 protons on target, due to inadequate radiation seepage check in Enclosure 100. With the new target scheme, there will be no interference with the 12 neutrino or muon operations and fluxes of >10 on target will be feasible. This allows for secondary beam enrichment (secondary, tertiary targeting) to enhance K±, p, TI+ yields. The proposed location for the first focus is about the same as at present. Thus, the optics for the transport beyond the first focus could be left virtually untouched and only one surface beam enclosure to house the vertical momentum bend magnets will have to be constructed. (This enclosure will replace Enclosure 101). This minimal beam modification will allow for a variety of physics in the hybrid system with secondary beams up to 500 GeV in momentum. We thus recommend that: (a) A new target hall, separate from the neutrino target area, be constructed, with separate targeting facilities for the hadron and muon beams. (b) Secondary beams up to 500 GeV/c produced in the hadron target should be channeled into the existing hadron beam lines N3 and N5 to the 30" and 15' chambers. A more detailed discussion of these points is given in reports of this Summer Study.