Journal ArticleThis paper presents results of a beam-dump experiment performed at the Brookhaven alternating-gradient synchrotron to search for prompt sources of neutrinos and axionlike particles. We observe no excess of vµ or events, and no excess in neutral-current events over that expected from neutrinos from ir and K decays. We report on limits of prompt particle-production cross sections and lifetimes

Coteus, P.

Sokolsky, Pierre

English

The University of Utah: J. Willard Marriott Digital Library

Search for New Particles at the Alternating-Gradient - Synchrotron Beam Dump P. Coteus, M. Diesburg, R. Fine, W. Lee, and P. Sokolsky Columbia University, New York, New York 10027 and R. Brown, S. Fuess, P. Nienaber, and T. Q'Halloran University of Illinois, Urbana, Illinois 61801 and Y. Y. Lee Brookhaven National Laboratory, Upton, New York 11973 (Received 7 February 1979) This paper presents results of a beam-dump experiment performed at the Brookhaven alternating-gradient synchrotron to search for prompt sources of neutrinos and axionlike particles. We observe no excess of Ve or v~ events, and no excess in neutral-current events over that expected from neutrinos from 7r and K decays. We report on limits of prompt particle-production cross sections and lifetimes. We report on a beam-dump experiment per-formed at the Brookhaven National Laboratory (BNL) alternating-gradient synchrotron (AGS) neutrino beam to search for prompt sources of neutrinos and new penetrating neutral particles. Prompt sources of electron neutrinos have been observed at the CERN Super Proton Synchrotron.1 The detector consisted of 22 6-ftx 6-ft thin-plate optical spark chambers interspersed with twenty planes of plastic scintillator (Fig. 1). The fiducial volume was five tons. The fiducial vol-ume was followed by a muon identifier consisting of magnetized toroids and 8-ftx 8-ft aluminum spark chambers. The BNL neutrino beam was run in two configu-rations. In the first (bare target) configuration, protons impinged on a 6-in. x 12-in. x 12-in. cop-per target. Pions and kaons produced in the tar-get decayed in a 200-ft drift space behind the tar-get. Remaining charged particles were then at-tenuated by a 100-ft iron shield. In the second (beam dump) configuration, protons were trans-ported to a 24-in. x 12-in. x 12-in. copper target immediately in front of the iron shield. The strong suppression of neutrinos from 7T and K de-cays in this configuration increases sensitivity to new sources of neutrinos or other neutral pene-trating particles. The bare-target run allows a direct comparison of interactions observed in the beam-dump run with neutrino interactions from 7T and K decays. We report on data for 1.9x 1017 protons on target in the bare-target configuration and 4.7x1018 protons on target in the beam-dump configuration. The two exposures were adjusted to yield approximately equal numbers of charged-current neutrino interactions from 7T and K de-cays. The calculated energy spectra of neutrinos was similar in the two configurations. We com-pare the beam-dump data to the bare-target data for anomalous v il and vil charged-current rate, 1438 © 1979 The American Physical Society VOLUME 42, NUMBER 22 PHYSICAL REVIEW LETTERS 28 MAY 1979 WIDE ANGLE /COUNTERS I II II [[[[[IIf"illOi~1 S'CHAMBERS S'CHAMBERS S'CHAMBERS SCINTILLATION COUNTERS o 5 I, I . FEET 10 ! I 72 DIS FIG. 1. Detector configuration. neutral-current rate, and electron-neutrino rate. We also examine the beam-dump data for evi-dence of the axion decay a - YY / in a 50-ft drift space in front of the apparatus. We first examine the charged-current and neu-tral-current rates. Events were selected with three of any five adjacent counters firing in co-incidence. These events were scanned by physi-cists for vertex events. The minimum track length was 1 in. of AI; the minimum shower en-ergy was 100 MeV. Events with a muon were called charged current (CC); events without, neu-tral current (NC). A muon was defined as a track either exiting from the detector or stopping with a minimum range of 18 in. of AI. The time of each event was measured by the counters rela-tive to the beam arrival at the iron shield. Pro-tons from the AGS were delivered in 50-ns buck-ets separated by 220 ns. The times for NC and CC events in the beam dump are shown in Figs. 2(a) and 2(b) (modulo 220 ns). The 50-ns bucket is clearly seen, along with some out-of-time background. We attribute this background to neu-trons. After a flat neutron subtraction, the num-ber of events we find is, for bare target, 53 CC and 9 NC; for beam dump, 49 CC and 14 NC. We have not selected single-track NC topologies (vp, Vn1T+, etc.). Limiting ourselves to NC with ~ 2 ,,20 ., '" ~IO "-(J) I-z ~ 5 w o nsec BARE TARGET C.C. N.C. 200 FIG. 2. Folded time of flight of CC and NC events for absorption-target and bare-target configurations. tracks and CC with ~ 3 tracks (where one is the muon), we find for bare target, 24 CC and 9 NC; for beam dump, 29 CC and 14 NC. We also se-lect 1TD events with at least one shower with E sholler ~ 100 MeV. We then find for bare target, 14 CC (1TD) and 7 NC (1TD); for beam dump, 14 CC (1TD) and 7 NC (1TD). There is no evidence for a significant increase of NC events in the beam dump for these topologies. The multiplicity, an-gle, and range distributions of NC and CC events are similar in the two configurations. To examine the inclusive electron-neutrino rates, ve +N -e + anything, we define an electron as a shower starting at the vertex with Eelectron > 500 MeV. We observe one candidate in the bare-target data and one candidate in the beam-dump data. We conclude that there is no excess of elec-tron candidates in the beam-dump run. The film was also scanned for events originat-ing in the 6-ft chambers with muons entering the magnetized toroids. The sign of the curvature of muons traversing at least two toroids was deter-mined. We then find for bare target, four J1. + and nineteen J1. - ; for beam dump, six J1. + and nineteen J1. -. There is no evidence for an increase in the vJ.l/vJ.l ratio for the beam-dump configuration. We finally examine single-shower events. Axi-ons decaying in a 50-ft drift space in front of the detector could result in an in-time signal for sin-gle showers observed in the detector. We select ~IOCJ  Iy ;;; 5 I-Z w ~ 0 100 200 nsec FIG. 3. Folded time of flight for single showers en-tering the detector in the absorption-target run. 1439 VOLUME 42, NUMBER 22 PHYSICAL REVIEW LETTERS 28 MAY 1979 single-shower events with E sho\\er > 250 MeV. The time-of-flight distribution is shown in Fig. 3. We observe nO clear in-time signal. We have performed a Monte Carlo calculation using the Sanford-Wang formula to compare CC rates for the beam dump and bare target. Since 1T and K secondary interactions in targets may be important, we calculate rates using an effective 1T ,K absorption length of 30 cm for the beam dump. We assume two cases for the bare target. First, all inelastic pion scatterings remove pions from the beam; and second, there are no pion interactions. In the first case, we are in reason-able agreement with measured yields. In the sec-ond case we calculate a beam-dump-to-bare-target event ratio a factor of 2 below what we ob-serve. However, even if one assumes that that discrepancy is due to prompt sources, we can rule out two possibilities. Prompt sources such as charm are expected to yield equal excess of 1111 (V1l) and lie (Ve) events. We observe no excess II e (ve) events over those expected from K decays and no excess V 11 events over those observed in the bare-target configuration. Neutral penetrat-ing particles interacting in the detector would yield muonless events. We observe no excess NC events for any of the topologies studied. We use our electron-neutrino rate to set a 90%-confidence-level limit on charm production. As-suming that the invariant cross section for DD production is proportional to (1 -Ix F i)Ne - bP.t, we calculate an upper limit for the product (J PP ~ nrfi (cross section times branching ratio to II e) of 20 JJ.b for N =3 and b =0.5; and 12 JJ.b for N =3 and b = 2. Here we assume the A dependence for D pro-duction and 1T production to be the same. The lim-it is quite independent of the value of N, since we are sensitive to the low-lxFI region. We have used our observed NC rate to set an upper limit on new penetrating particles interact-ing in our detector. Assuming a production spec-trum given by that of the 1T, we set an upper limit of (J prod aint ~ 5 X 10- 68 cm4 at the 90% confidence level. If we assume ainta =(J prod a = 2.2 X 10- 34 cm2 , we find that R =(J prod a/a If = 1 X 10- 8. Using this limit we can calculate the number of in-time single showers expected from the axion decay a -yy in the 50-ft decay space in front of our apparatus as a function of CyT. Assuming an upper limit of three in- time events, we set the limits CYT> 1 X 109 ft or CyT < 12 ft. We would like to thank Lou Repeta for construc-tion of the targets and the staff of the AGS for a successful run. S. Marino, E. Druik, and J. Zuck-er were of great help at various stages of the ex-periment and the scanning staffs of the University of Illinois and Columbia University did their usual excellent job. This research was supported by the National Science Foundation and the Depart-ment of Energy. One of us (P.S.) wishes to thank the Alfred P. Sloan Foundation for support. Ip. Alibran et ai., Phys. Lett. 74B, 134 (1978). T. Hansl etai., Phys. Lett. 74B,""'i39 (1978); P. C. Bosetti et ai., Phys. Lett. 74B, 143 (1978). 28. Weinberg. Phys. Rev. Lett. 40, 223 (1978); F. Wil-czek, Phys. Rev. Lett. 40, 279 (1978). 

Search for new particles at the alternating-gradient-synchrotron beam dump

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Search for new particles at the alternating-gradient-synchrotron beam dump

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