BNL-49921 Submitted to JSPS-NSF Seminar: The Hyperon-Nucleon Interaction October 24-28,1993, Maui, Hawaii
BNL POSSIBILITIES*
PHILIP H. PILE Brookhaven National Laboratory \' • •••• 0 d ••"••"v'i Building 91 IB r,. - Upton, New York 11973-5000, U.S.A. ^ » J
ABSTRACT
The Brookhaven National Laboratory AGS facility provides the intense kaon and pion beams necessary for detailed studies of the hyperon-nucleon interaction. A description of available beams is provided along with a summary °f me current and future physics program.
1. The BNL Facility for High Energy and Nuclear Physics
1.1 The Panicle Accelerators The Brookhaven National Laboratory High Energy and Nuclear Physics experimental programs are based on a 30 GeV Alternating Gradient Synchrotron (AGS). Particles are injected into the AGS using a 1.5 GeV, 7.5 Hz Booster Synchrotron. All ion species from protons (including polarized protons) to gold can be accelerated; however, only protons and gold ions are currently in use. Injectors into the Booster include a 200 MeV proton Linac and two 15 MeV MP tandem accelerators for heavy tons. Toward the end of the decade beams from the AGS will be injected into the Relativistic Heavy Ion Collider (RHIC). The RHIC facility, currently under construction, will allow beam-beam collisions with energies up to 250 GeV/c x Z/A for each beam. Initial experiments with RHIC will search for the quark gluon plasma using 100 GeV/c/nucleon gold on gold--'") TeV in the center-of-mass. In addition to the heavy ion program at RHIC, programs are being developed that make use of proton-proton collisions, including polarized protons. The RHIC physics program is expected to run concurrently with the AGS fixed target program described in this paper. For example, a ten hour lifetime is expected for gold on gold collisions with RHIC fill times on the order of minutes. So except for filling times the AGS machine will be available for acceleration of other ions.
1.2 The AGS Fixed Target Program During the past few years the AGS physics program has remained diverse. The experiments have used a variety of ion beams, including protons, polarized protons, 16O, 28Si, and 197Au. The range of physics topics has included experiments such as rare K decays, neutrino oscillations, dibaryon searches, strangelet searches, exotic meson searches, hypernuclear physics, fractional charge and quark gluon-plasma searches. $ Work performed under the auspices of the U.S. Dept. of Energy.
OF THIS DOCUMENT IS unumm The 1993 experiment program ran for a total of 14 weeks~8 weeks with 24 GeV/c protons and 6 weeks with an 11 GeV/c/nucleon Au beam. The proton program was shortened in 1993 to allow the upgrade of three major experiments to be sufficiently complete for meaningful engineering runs. These experiments included two rare kaon decay experiments (E8651 and E8712) and an exotic meson search experiment (E852)3. Other experiments included an H dibaryon search (E813),4 a color transparency experiment (E850),5 a K+ elastic scattering experiment (E874),6 and a rare r\ decay test (E890). In addition 21 test beam user groups were given beam time for detector tests for AGS experiments and for planned experiments at RHIC, SSC, and FNL. Two new AGS beam lines were commissioned in 1993. These included a 6GeV/c un- separated beam line for the K+ - n+u.+e* rare K decay experiment (E865) and a new 1-9 GeV/c test beam facility. Table I lists all the currently available secondary beam lines at the AGS.
Table I. AGS beam line parameters. See Fig. 1 for location on the AGS floor.
AGS BEAMS October 1083
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Stpantad Chur|«i PurtloJ« Bauu jO63 4 oo ii 4.6X10* J.SllO* 1.9110* 1.0x10* 6.0X1Q* e.OzlO* O.BO n'/f • 0.4 L-lta. IX3IO Ct.Ct jo 75 5 60 |0. 3.0x10* 1.0x10* 1.0x10* 1.4X10* 6.0x10*6.0x10* 0.70 irvx~ - e L-ISO, ram »•/«[•- i 63x10* 8.3x10* 3 0H0* 1.1x10* *»»10* 4.1x10* 1.60 n"/T - 0 8 Viltt, Kit 1MB Un 1.60 n-/» - •« Unseparated Charged Particle Beams
5-26 3 0 0.2 l.ftzIO* Z.txlO* 9.0x10* 2.3x10* 3.OZI011.0X10T 16
HUSO O«BMl 0H-.» •(«) Wn) la • (.9110* Klutrlno Baun )tol (Hwllr mltoku * 114. h>l FII flux «Tt. « 11 1 HM- IBlO'/a T14» U«4 i icr/' im t—4 g-2 rt-/t Transfer line »* a» - 1.6x10* Tl •at 06 0 f«r IBJ«CU«B U (-1 rti M* fl«» - 7,110* i i im, im »»ai ui/or A schematic of the AGS experimental floor as it is being configured for the 1994 run is shown in Fig. 1. Ten proton beam experiments are currently scheduled to run in 1994. All three rare K decay experiments, as well as the MPS exotic meson search experiment, are expected to begin serious data taking during this run. Additional experiments include a new H particle search experiment (E836),° the continuation of color transparency studies (E850),5 a S hypernuclei search (E887),9 and continued t\ production studies (E890, aimed toward future rare rj decay experiments). Finally an experiment will begin that will test the feasibility of using a partial snake (solenoid) in the AGS ring to cir- cumvent the many depolarizing resonances associated with the acceleration of polarized protons - E880.10 AGS Experimental Area FY1994 Physics Program V-K»fSUt H Sunk: IMS AA H^wmvaM M-te«rjn«s, x* » »v A3-MM, StrUf«l«t« (») KlMt Bl-IM*. QGP (HI) C0-I877. QGP (H) C8-1XSBD. UtO C8-IXS8M887 I Hrp«niuc]d v fhjwka HyptrnuelMr SpvctrfiswUr Fig. I. The AGS experimental floor as expected to be configured for the 1994 proton and heavy ion physics program. The AGS proton beam intensity reached a record 2.5 x 1013 protons per pulse in 1993. This was made possible by the addition of a 1.5 GeV/c booster synchrotron commissioned in 1992 that now serves as the beam injector for the AGS. With the completion of the AGS RF upgrade over the next two years, the beam intensity is expected to reach 6 x 1013 protons per pulse-a factor of four increase over the pre-Booster beam intensity. The increased beam intensity will allow experiments that search for rare processes, such as rare kaon decays, to proceed without being limited by lack of proton intensity. 1.3 New Secondary Beam Lines A new generation of beam lines designed to allow the exploitation of rare processes has been constructed at the AGS. These beam lines are designed to deliver intense clean beams of kaons, thus allowing full utilization of the intense proton beam now available from the AGS. The first of these beam lines, the 2 GeV beam line, was commissioned in 1991.11 The 2 GeV beam line was designed to deliver an intense, clean beam of 1.8 GeV/c kaons to two H particle search experiments, E813 and E836. The beam line incorporates two ExB separator stages together with two mass slits, specialized collimators, optics corrected to third order, and a radiation resistant front end magnet. E813 reached its goal of 1012 integrated negative kaons by the end of the 1993 run. During the 1993 run the proton beam intensity delivered to the 2GeV kaon production target reached a record 1.5 x 1013 proton per AGS spill. With this proton intensity the 1.8 GeV/c K" flux was typically 3.5 x 106 with less than 3 x 106 pions per spill contamination. The performance of this beam line has exceeded its original design goals and has allowed this sensitive H search experiment to run without being seriously limited by lack of kaon flux or by beam purity. Figure 2 shows the K~ and p flux and purity as a function of momentum. As can be seen the nominal full acceptance antiproton beam is between 90-99% pure. Furthermore, with some sacrifice in kaon beam intensity, the kaon beam purity can be made considerably better than 1:1 jt/K. Note that at the most restrictive mass slit opening the K" beam at 1.8 GeV/c is 80% pure and still delivers about 106 K' per 10" protons. This is an important consideration for experiments that are limited by in-beam detector rates or by beam interactions in target material such as nuclear emulsions or scintillating fiber targets. :' ' ' ' 1 1 1 ' ': X . K" \ 1992 El/E8-750/375kV § *-'P ) o • x o o • - K" 1BB3 El/I8-750/«50kV ^— a 6 10 — y 5 10 - Fig. 2. The 2GeV beam line K" and p flux and purity as a function of .... i . ... 1 .... 1 .... 1 , . . 1.2 1.4 1.6 momentum. Note that the Momentum (GeV/c) 1992 data was taken with the second electrostatic ' I ' ' ' ' I ' ' ' • I ' separator running at one mTi 18»Z K/lE2-7'50/3?SkV " P ' half its designed voltage, 1083 El/E2-750/850kV ""he various 1993 data points at 1.8 GeV/c were 10° I p. taken with various mass o slit #1 and Wl openings. Except as noted the fits are to guide the eye. 101-2 - 1.2 1.4 1.0 Momentum (GeV/c) A second new beam line, LESBIII, was commissioned in 1992. This beam line was built in support of one of the rare kaon decay experiments, E787.n This experiment is attempting to measure theK+ -«+vv decay which is allowed by Standard Model at about the 10"10 level. Phase I of this experiment was limited by the presence of a 2:1 pion contamination accompanying their 800 MeV/c K+ beam and by detector limitations. The design of this new beam line for E787 was the result of a joint effort between BNL and TRIUMF which began in late 1989. The resulting design incorporates many of the features found in the 2GeV beam line just discussed, including two-stage separation, optics corrected to third order and radiation resistant front end elements. This beam line design, however, allows for an additional small opening horizontal collimator, located at an achromatic focus about 5 meters upstream of the final focus. A schematic of this beam line is shown in Fig. 3. The added collimator (HS2 in Fig. 3) was predicted to virtually eliminate pions from extended sources (hyperon and meson decays, pole tip scattering, etc.). The beam line was predicted to deliver a very pure positive kaon beam to E787 (JI +/K+ z 0.5:1), with a factor of 2 improvement in K+ flux over LESBI, the beam line it replaced. These expectations were realized during the commissioning run. The measured 800 MeV/c K+ flux was 4.8 x 106 per 1013 protons with a 0.4:1 (it + \i +e+) to K+ ratio and negligible protons. With more restrictive slits the K+ flux was 3.7 x 106 per 1013 protons and 0.2:1 purity. This beam line will allow E787 to proceed without being limited by either K+ flux or beam purity. SVIC3 HS2 Fig. 3. A schematic of the AGS Low Energy Separated Beam III (LESBIII) that is used to deliver an 800 MeV/c K+ beam to E787, a rare kaon decay experiment. A third beam line, 6GeV, was commissioned in 1993 in support of another rare kaon decay experiment, E865.' This experiment is a search for the K+ - n + *i+e' kaon decay which is forbidden in the Standard Model (violates lepton family number conservation). This experiment is the successor to E777" which established a 2 x 10'10 limit for the decay but was limited by an intense beam halo accompanying the K+ beam. This unseparated beam line design was a result of a joint AGS-Yale collaboration and follows the design features of the 2GeV and LESBIII beam line previously discussed. The production target is first imaged (horizontal and vertical focus) on a narrow vertical slit where the beam momentum is defined with horizontal collimators. The vertical col- limator was predicted to eliminate a large fraction of the beam halo due to front end magnet scattering and particle decay. The beam is then refocussed on a clean-up collimator at an achromatic focus. This final collimator was predicted to eliminate most of the remaining beam halo. The beam is then transported to the vacuum tank where K+ decays are observed. During the 1993 run it was determined that the beam flux was as predicted and the associated beam halo was about a factor of S less per incident kaon compared to the old E777 beam line. The measured beam halo background was considerably better than the old E777 beam line, but was still about a factor of two greater than predicted by beam line Monte Carlo simulations. Although studies are planned in 1994 aimed at a further reduction in this background, the present levels are deemed low enough for E86S to proceed and make a significant improvement in sensitivity. These three new state of the art beam lines coupled with the increased AGS beam intensity will allow three major experiments to proceed without being seriously limited either by lack of primary proton beam intensity or kaon beam intensity. 2.1 The Long Range AGS Schedule The AGS proton beam running time is expected to increase to about 25 weeks per year as the second generation rare kaon decay experiments begin serious data taking. These three rare kaon decay experiments are expected to require a total of about 6 x 1013 protons per spill once fully operational. The full booster potential will therefore be required if the experiments operate up to expectations. The major high energy experiments expected to run through 1997 are shown in Fig. 4. The experiments are grouped according to the primary beam line. Note that most beam lines support more than one experiment. For example: the C-line can serve up to three simultaneous experiments. Future experiments will continue to investigate rare processes. Rare K decay experiments are expected to continue and rare eta decay experiments should begin. Other experiments include a precision measure of the muon g-2 factor, E821.14 This experiment will provide a measurement of the hadronic contribution to g-2 and will provide another test of physics beyond the Standard Model. An important new long baseline neutrino oscillation experiment, E889,15 is also planned at the AGS. If E889 is funded according to its plan, this experiment could begin before the end of this decade. AGS MAJOR HEP EXPERIMENTS SCHEDULE PROJECTION Target Station FY93 FY94 FY95 FY96 FY97 Exotics A (E852) > (E865) Strangelets (Au Beam) (E864) B (E871) K+ - »i+vv C (E787) Color Transparency (E850) > Rare r\ decays *(E897) D (E813)l H Searches (E836)/ > AA hypernuclei (E885) > v Oscillations U *(E889) > Muon g-2 V (E821) > * Not fully approved. Figure 4. The AGS schedule of major experiments projected through 1997. The experiments planned for the D-line are of particular interest to this conference. The performance of the 2GeV beam line was discussed earlier and experiments are scheduled into 1996. The intense kaon beam available with this beam line will allow double lambda hypernuclear experiments to be performed with the hope of seeing many such events using counter techniques. Previously, only emulsion experiments have been able to isolate double lambda hypernuclei events and in fact only three have been identified to date. Double lambda hypemuclei offer a unique opportunity to study the AA interaction. The 2GeV beam line may also be the site of future A, £ or S scattering experiment at the AGS. Such experiments have started at KEK (see elsewhere in these proceedings) but the lack of sufficient kaon flux at KEK will not allow detailed systematic studies to be performed. Ransome (elsewhere in these proceedings) has presented results of a study that suggest the feasibility of staging a precision Ap scattering experiment at the AGS using this beam line. Other experiments expected to be proposed that use the 2GeV beam include 3" hypernuclei spectroscopy studies that use either the existing E813 K+ spectrometer system or the Medium Energy Spectrometer (MRS) that may become available from LANL. Furthermore, a letter of intent16 from Nefkens and Chrien has been submitted to the AGS Program Committee that proposes to use the SLAC Crystal Ball detector to study baryon spectroscopy using pion and kaon beams. Another experiment that would use the Crystal Ball has been proposed by the same collaboration. This experiment, E897,17 plans to site the crystal ball in the C8 branch (see Table I and Fig. 1) of LESBH and will investigate rare decay modes of the eta meson. Once E897 is finished the baryon spectroscopy studies could begin in LESBII and then continued using the 2 GeV beam line for those resonances that require a beam momentum greater that 750 MeV/c. 3. Concluding Remarks The AGS is one of the world's forefront High Energy physics machines. The available low energy kaon beam intensities are unmatched by any other machine in the world. Furthermore, as a result of innovative kaon beam line designs, the kaon beams can be made with little contamination from other particles. These intense, clean kaon beams will allow experiment investigating rare processes to proceed without serious beam limitations. The present rare kaon decay experiments are testing the limits of the Standard Model either through the observation of very rare decays or through searches for rare decays that could only be mediated by new gauge bosons with masses beyond the reach of even the SSC. Other experiments search for exotic particles such as the H particle, strangelets and mesons with unusual quantum numbers. New proposals are welcomed at the AGS. The AGS fixed target program should continue well into the RHIC era. The AGS experimental floor will continue to evolve as dictated by new, yet to be proposed experiments. As in the past, AGS machine upgrades will continue to be driven by the needs of experiments. There are possible paths (post Booster, Stretcher) to even higher beam intensities than are presently available. Although such upgrades have not been formally proposed, we expect with sufficient physics motivation a case could be made for such upgrades. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States United Stales Government or any agency thereof. References 1. AGS Experiment E865, Proposal to perform an improved search for the decay K+ - 7r+ n+e". BNL, Connecticut, INR-Moscow, JINR-Dubna, New Mexico, PSI, Basel, Pittsburgh, Tbilisi, Yale, Zurich, M. Zeller, spokesman. 2. AGS Experiment E871, A new search for very rare KL Decays. UC-Irvine, Temple, Stanford, Texas-Austin, William and Mary, W.R. Molzon, J.L. Ritchie, and S.G. Wojcicki, spokesmen. 3. AGS Exp. 852, Search for mesons with unusual quantum numbers. BNL, Indiana, Louisville, UMassachusetts-Dartmouth, Notre Dame, Moscow, S.U. Chung and A.R. Dzierba, spokesmen. 4. AGS E813, Search for a strangeness -2 dibaryon. Carnegie-Mellon, Alberta, Birmingham, BNL, Freiburg, IUCF, Kyoto, Kyoto-Sangyo, LAMPF, Manitoba, New Mexico, TRIUMF, Vassar, Yale, G.B. Franklin and P.D. Barnes, spokesmen. 5. AGS Experiment E8S0, EVA, a solenoida! detector for large angle exclusive reactions-Experiment 850 - Determining color transparency to 22 GeV/c. BNL, Minnesota, Mt. Holyoke, Penn St, UMass-Dartmouth, Tel-Aviv, A.S. Carroll and S. Heppelmann, spokesmen. 6. AGS Experiment 874, Kaon -nucleus quasielastic and elastic scattering at 720 MeV/c. Colorado, Houston, BNL, R.E. Chrien, E. Hungerford, R.J. Peterson, spokesmen. 7. AGS Experiment E890, A new test of charged symmetry in eta production on deuterium. UCLA, BNL, LANL, Jiilich, Ruder Boskovic Inst., B.M.K. Nefkens, R.E. Chrien, J.C. Peng, spokesmen. 8. AGS Experiment E836, Search for a strangeness -2 dibaryon using a 3He target. Carnegie-Mellon, Alberta, Birmingham, BNL, Freiburg, IUCF, Kyoto, Kyoto- Sangyo, LAMPF, Manitoba, New Mexico, TRIUMF, Vassar, Yale, G.B. Franklin and P.D. Barnes, spokesmen. 9. AGS Experiment E887, Do Narrow 2 hyprnuclear states exist? BNL/CEBAF, Houston, Indiana, INS-Tokyo, Ohio Univ., Tokyo, R. Sawafta and K. Hicks, spokesmen. 10. AGS Experiment E880, The effects of a partial Siberian Snake on polarization at the AGS. IUCF, BNL, ANL. TRIUMF, KEK, S.Y. Lee and L. Ratner, spokesmen. 11. P.H. Pile, D. Beavis, R.L. Brown, R. Chrien, G. Danby, J. Jackson, D.M. Lazarus, W. Leonhardt, C. Pearson, A. Pendzick, P. Montemurro, T. Russo, J. Sandberg, R. Sawafta, C. Spataro, J. Walker, H.A. Enge. A new 1-2 GeV/c separated beam for BNL. Nucl. Instrum. & Methods in Phys. Res. A321.48-58 (1992). 12. AGS Exp. 787, BNL, Princeton, TRIUMF,INS-Tokyo, KEK collaboration, D. Bryman, L. Littenberg, and S. Smith, spokesmen. 13. AGS Experiment 777, A search for the rare decays K+ - ir+u+e*. BNL, Swiss Institute for Nuclear Research, Washington, Yale, M. Zeller, spokesman. 14. ACS E821, A new precision measurement of the muon g-2 value at the level of 0.35 PPM. Boston, BNL, Cornell, Fairfield, Heidelberg, Illinois, LANL, Max Planck Inst., Tokyo, KEK, Riken, INP-Novosibirsk, Yale, V.W. Hughes, W.M. Morse, B.L. Roberts, spokesmen. 15. AGS E889, Long baseline neutrino oscillation search. BNL, UC-Riverside, UC- Santa Barbara, Linfield, LANL, Louisiana Tech., New Mexico, Penn, Southern Univ. and A&M College, Temple, Texas, TRIUMF, Valparaiso, A. Mann, spokesman. 16. AGS LOI, Baryon Spectroscopy with the Crystal Ball, August 1993, BNL, UCLA, CMU, Abilene, George Washington, Jiilich, Zagred, Dubna. R.E. Chrien and B.M.K. Nefken, spokesmen. 17. AGS Experiment E897, Tests of C and CP in Rare Eta Decays with the Crystal Ball Detector. UCLA, BNL, Carnegie-Mellon, Abilene, George Washington, Jiilich, Zagreb, Dubna, B.M.K. Nefkens and R.E. Chrien, spokesmen.