Search

Data taken by the Mark II detector at the SLAC {ital e}{sup +}{ital e}{sup {minus}} storage ring PEP was used to search for exclusive decays of {ital D}{sup {plus minus}} and {ital B}{sup {plus minus}} mesons into two charged leptons plus a charged pion or kaon. All possible charge and lepton combinations consistent with charge conservation were considered and no evidence for any signals was found. We obtain upper limits for the various branching ratios ranging from 2.5{times}10{sup {minus}3} to 9.2{times}10{sup {minus}3}, at a 90% confidence level. Some of these limits can be used to constrain leptoquark masses in various models.

This talk deals with my recollections about the discoveries of the J/ψ and ψ′ as well as psion spectroscopy and charmed mesons. I give a chronology for the ψ and ψ′ discoveries. I also discuss the events which led to the charmed meson discovery as well as detailed discussions on the proof that the resonance we observed in the K - π + system, at 1865 MeV, was indeed the predicted charmed meson.

We present a new high-statistics measurement of the cross section for the process {ital e}{sup +}{ital e}{sup {minus}}{r arrow}{ital e}{sup +}{ital e}{sup {minus}}{pi}{sup +}{pi}{sup {minus}} at a center-of-mass energy of 29 GeV for invariant pion-pair masses {ital M}({pi}{sup +}{pi}{sup {minus}}) between 350 MeV/{ital c}{sup 2} and 1.6 GeV/{ital c}{sup 2}. We observe the {ital f}{sub 2}(1270) and measure its radiative width to be 3.15{plus minus}0.04{plus minus}0.39 keV. We also observe an enhancement in the {pi}{sup +}{pi}{sup {minus}} spectrum near 1 GeV. General agreement is found with unitarized models of the {gamma}{gamma}{r arrow}{pi}{sup +}{pi}{sup {minus}} reaction that include final-state interactions.

We have studied several features of the production of charged-hadron pairs by ..gamma gamma.. collisions. We have measured the f/sup 0/ partial width GAMMA/sub f//sup 0/..--> gamma gamma..(Q/sup 2/) for Q/sup 2/ in the range 0 gamma gamma.. = 2.52 +- 0.13 +- 0.38 keV at Q/sup 2/roughly-equal0. The measured Q/sup 2/ dependence is in agreement with the generalized vector-dominance model. The cross section for ..gamma gamma -->..(..pi../sup +/..pi../sup -/+K/sup +/K/sup -/) in the mass region 1.6< or =M/sub pipi/< or =2.5 GeV/c/sup 2/ has also been measured and the result compared with that expected from the QCD continuum.

In a 48 000-picture exposure of the Fermilab 30-inch hydrogen bubble chamber to a 205 GeV/ c π − beam, we have measured 169 events of the reaction, π − p → π − π + π − p, with a cross section of 635 ± 61 μ b. This reaction proceeds almost entirely via low mass π − → 3 π and p → p ππ dissociation. Factorization is satisfied for p → pππ dissociation in πp and pp interactions.

The inclusive ϱ ° production cross section has been measured in the reaction π − p → π + π − X at 205 GeV/ c . We find σ ( ϱ ° ) = 13.5 ± 3.4 mb, with most of the production occuring in the central region. Assuming σ ( ϱ + ) ≈ σ ( ϱ − ) ≈ σ ( ϱ ° ), it is concluded that approximately one-third of the pions at this energy come from ϱ -decay.

Evidence for a bound ${\ensuremath{\Delta}}_{33}(1236)\ensuremath{-}{\ensuremath{\Delta}}_{33}(1236)$ component of the deuteron is sought by using ${\ensuremath{\pi}}^{+}$, ${\ensuremath{\pi}}^{\ensuremath{-}}$, and ${K}^{+}$ mesons as probes of nuclear structure. Events are observed which might contain $\ensuremath{\Delta}(1236)$ "spectators" in the breakup of a deuteron in a $\ensuremath{\Delta}\ensuremath{\Delta}$ state. However, other mechanisms may contribute to the signal, and we cannot unambiguously ascribe our events to a $\ensuremath{\Delta}\ensuremath{\Delta}$ contribution in the deuteron. With certain assumptions we obtain an upper limit of \ensuremath{\sim}0.7% for the $\ensuremath{\Delta}\ensuremath{\Delta}$ component of the deuteron.

A beam of \ensuremath{\sim}200-Mev ${\ensuremath{\pi}}^{+}$ mesons was defined inside the vacuum chamber of the Nevis Cyclotron. Nuclear emulsions were exposed to a flux of about ${10}^{4}$ mesons/${\mathrm{cm}}^{2}$. The plates were scanned for pion-hydrogen scatterings and 103 such events were observed in two interaction energies, 151\ifmmode\pm\else\textpm\fi{}7 Mev and 188\ifmmode\pm\else\textpm\fi{}8 Mev. We obtain total cross sections of 152\ifmmode\pm\else\textpm\fi{}31 and 159\ifmmode\pm\else\textpm\fi{}34\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}27}$ ${\mathrm{cm}}^{2}$, respectively. The data suggest that the angular distribution changes from backwards peaked to almost symmetric over this energy interval. Our observations are not in agreement with the hypothesis of a ${P}_{\frac{3}{2}}$-wave resonance in this energy region. The best fit to the combined results includes a $D$-wave contribution of -5.4\ifmmode^\circ\else\textdegree\fi{}, although satisfactory agreement may be obtained with only $S$ and $P$ waves.

Recent observations of angular distributions of $\ensuremath{\pi}$ mesons in $\overline{p}\ensuremath{-}p$ annihilation indicate a deviation from the predictions of the usual Fermi statistical model. In order to shed light on these phenomena, a modification of the statistical model is studied. We retain the assumption that the transition rate into a given final state is proportional to the probability of finding $N$ free $\ensuremath{\pi}$ mesons in the reaction volume, but express this probability in terms of wave functions symmetrized with respect to particles of like charge. The justification of this assumption is discussed. The model reproduces the experimental results qualitatively, provided the radius of the interaction volume is between one-half and three-fourths of the pion Compton wavelength; the dependence of angular correlation effects on the value of the radius is rather sensitive. Quantitatively, there seems to remain some discrepancy, but we cannot say whether this is due to experimental uncertainties or to some other dynamic effects. In the absence of information on $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ interactions and of a fully satisfactory explanation of the mean pion multiplicity for annihilation, we wish to emphasize the preliminary nature of our results. We consider them, however, as an indication that the symmetrization effects discussed here may well play a major role in the analysis of angular distributions. It is pointed out that in this respect the energy dependence of the angular correlations may provide valuable clues for the validity of our model.

Thirty-five antiproton stars have been found in an emulsion stack exposed to a 700-Mev/c negative particle beam. Of these antiprotons, 21 annihilate in flight and three give large-angle scatters ($\ensuremath{\theta}g15\ifmmode^\circ\else\textdegree\fi{}$, ${T}_{\overline{p}}g50$ Mev), while 14 annihilate at rest. From the interactions in flight we obtain the total cross section for antiproton interaction: $\frac{{\ensuremath{\sigma}}_{\overline{p}}}{{\ensuremath{\sigma}}_{0}}=2.9\ifmmode\pm\else\textpm\fi{}0.7$, where ${\ensuremath{\sigma}}_{0}=\ensuremath{\pi}{{R}_{0}}^{2}$ and ${R}_{0}=1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{A}^{\frac{1}{3}}$ cm. This cross section was measured at an average antiproton energy of ${\overline{T}}_{\overline{p}}=140$ Mev.We also find that the antiproton-nucleon annihilation proceeds primarily through pion production with occasional emission of $K$ particles. On the average 5.3\ifmmode\pm\else\textpm\fi{}0.4 pions are produced in the primary process; of these, 1 pion is absorbed and 0.3 inelastically scattered. From the small fraction of pions absorbed, we conclude that the annihilation occurs mainly at the surface of the nucleus at a distance larger than the conventional radius.A total energy balance of particles emitted in the annihilation gives a ratio of charged to neutral pions consistent with charge independence. Conversely, assuming charge independence, we conclude that the energy going into electromagnetic radiation or neutrinos is small.Comparisons with the Fermi statistical model and the Lepore-Neuman statistical model have been made. Good agreement with the experimental results on the annihilation process can be obtained through appropriate choice of the interaction volume parameters.Several different estimates of the antiproton mass are in good agreement and suggest strongly that the antiproton mass is the same as the proton mass within an accuracy of 2\textonehalf{}%.A study of the elastic scattering of the antiprotons down to angles of 2\ifmmode^\circ\else\textdegree\fi{} suggests a possible destructive interference between nuclear and Coulomb scattering.

Author(s): Goldhaber, Gerson; Brown, John L.; Butterworth, Ian; Goldhaber, Sulamith; Hirata, Allan A.; Kadyk, John A.; Shen, Benjamin C.; Trilling, George H.

The study of the Kπ system in the channel K+π−Δ++ is complicated by the presence of the broad low-mass Δ++π− enhancement centered near 1580 MeV. A cut which removes this effect reveals a break in the t′ distribution at |t′| ≈ 0.05 (GeV/c)2, with a very steep forward peak of slope a = 23.6±5.2 (GeV/c)−2 for 2. |t′| ;.sfnc;t′| ⩾ 0.05 (GeV/c) We associate this forward peak with a single-pion-exchange mechanism. A small enhancement at M(K+π−) ≈ 1100 MeV is observed in a t′ region dominated by non-pion-exchange mechanisms.

We present evidence for structure in the Kπ system at a mass near 1.85 GeV in the reaction K+n→K+π−p at 12 GeV/c. One interpretation of the observations is the production by pion exchange of a J P = 3 − K ∗ resonance at about this mass, which interferes strongly with other processes.

We have continued work on antiproton interactions in photographic emulsions. Most of the data come from an exposure at the Bevatron to an enriched antiproton beam of 700 Mev/c momentum. In this paper we present the analysis of 221 antiproton stars, 95 of which occurred in flight. We find an average antiproton cross section of $(1.9\ifmmode\pm\else\textpm\fi{}0.2){\ensuremath{\sigma}}_{0}$, where ${\ensuremath{\sigma}}_{0}=\ensuremath{\pi}{(1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{A}^{\frac{1}{3}})}^{2}$ ${\mathrm{cm}}^{2}$, for all the elements in emulsion, excluding hydrogen. The primary antiproton annihilation gives rise to 5.36\ifmmode\pm\else\textpm\fi{}0.3 pions on the average. In annihilations at rest, 1.3 of the pions formed interact with the parent nucleus; in reactions in flight, 1.9 of the pions. For stars at rest the energy available in the annihilation in complex nuclei is divided up among the products as follows: charged pions, 48\ifmmode\pm\else\textpm\fi{}6%, neutral particles (other than neutrons and ${K}^{0}$ mesons) 28\ifmmode\pm\else\textpm\fi{}7%; $K$ mesons 3\ifmmode\pm\else\textpm\fi{}1.5%; and cascade nucleons and nuclear excitation 21\ifmmode\pm\else\textpm\fi{}2%. For the stars in flight the corresponding percentages are: 45\ifmmode\pm\else\textpm\fi{}7%, 22\ifmmode\pm\else\textpm\fi{}7%, 3\ifmmode\pm\else\textpm\fi{}1.5%, and 30\ifmmode\pm\else\textpm\fi{}2%. To fit the average pion multiplicity, the interaction radius of the Fermi statistical model must be taken as $\frac{2.5\ensuremath{\hbar}}{{m}_{\ensuremath{\pi}}c}$. Other proposals to explain the large multiplicity are discussed. We deduce from the fraction of pions interacting in the same nucleus that the annihilation takes place at the outer fringes of the nucleus.

Author(s): Goldhaber, Gerson; Brown, John L.; Goldhaber, Sulamith; Kadyk, John A.; Shen, Benjamin C.; Trilling, George H.

The four-particle final states of the K/sup +/-p interaction at 1.96 Bev/ c were investigated. It is found that these states are predominantly produced via the double resonance production K/sup +/ + p yields K/sup */ + N/sup */. The experimental data support a spin-zero meson exchange, presumably a meson( pi ), for small four-momentum transfers. The four particles produced in the reaction are in the isotopic spin T = 1 state and occur in five possible charge combinations. The observed cross sections of these reactions and the branching ratios expected on the assumption that the nucleon and meson( pi ) are always produced in the T = 3/2 state and that the meson (K) and ( pi ) are always produced in the T = 1/2 state are presented. (C.E.S.)

Results obtained in studies of elastic and inelastic K/sup +/-p interaction at 455 Mev are presented. Tables are included that show the phase shifts for K/sup +/-N scattering in the T = 1 state and the modes of pi prcduction. A mass resolution curve and a differential cross section plot are also included. (L.N.N.)

The P-p aminilation process leading to pure pion production affords an oppcrtunity to examine possible pionpion interactions. An analysis of annhilation events inpropane was made. The events chosen were "hydrogen like," i.e., events showing no visible evaporation prongs and with N/sub pi /i+ = N/sub approximately /-. The distribution of angles be tween pions of like and unlike charge in the P-p c.m. system as well as the distribution of total energy of pion paris of like and unlike charge in thier c.m. system was examined. (L.T.W.)

The branching fractions for the major decay modes of the lepton are measured from a sample of tagged decays selected from +- pairs produced in e+e- annihilation. The decay products of one member of the +- pair are used to identify the event. The opposite member of the pair is then included in the sample if it satisfies an invariant-mass cut and a charged-multiplicity cut. In this way, we attempt to select an unbiased sample of decays. The sample is divided into categories based on charged- and neutral-particle multiplicities, and charged-particle identification. The branching fractions are measured simultaneously, with an unfold technique and a maximum-likelihood fit, with the sum of the branching fractions constrained to be unity. The branching fractions for the decay modes - K- and - K*- are fixed at the world averages in the fit. The following branching fractions are measured: B(-e) =(19.10.81.1)%, B(-' - )=(18.30.90.8)%, B(-) =(10.01.1 *1,4)%, B(-0) =(25.81.72.5)%, B(-(n0, n>1))=(12.01.42.5)%, B(-+-) =(6.7 0.80.9)%, and B(-+- (n0,n>0)) =(6.10.80.9)%. The total branching fraction to one charged pion plus at least one neutral hadron is measured to be (37.81.21.0)%. Limits on allowed decay modes involving the meson are discussed. © 1987 The American Physical Society.

An experiment to study the $\overline{p}$ annihilation process at 1.05 Bev/c was performed with the Lawrence Radiation Laboratory 30-in. propane bubble chamber. It was observed that the $K$-meson production in annihilation events rises sharply with the increase in energy, namely from 4\ifmmode\pm\else\textpm\fi{}1% for annihilations at or near "rest" to 8\ifmmode\pm\else\textpm\fi{}1%. On the other hand, the pion multiplicity was not observed to increase appreciably with the increase of available energy. We have found a pion multiplicity of 5.0\ifmmode\pm\else\textpm\fi{}0.2. These numbers are discussed in this paper and compared with existing models for the $\overline{p}$ annihilation process. It is pointed out that with further increase in bombarding energy different models may differ appreciably in the above quantities.We have observed a $\overline{p}$-H annihilation cross section of 51\ifmmode\pm\else\textpm\fi{}10 mb and a $\overline{p}$-C annihilation cross section of 368\ifmmode\pm\else\textpm\fi{}60 mb at a $\overline{p}$ momentum of 1.05 Bev/c. Crude determinations of the $\overline{p}$ charge-exchange process---which turns out to be forward peaked--- and of $\overline{p}$ inelastic-scattering events leading to pion production are also discussed.

Author(s): Goldhaber, Gerson; Fowler, William B.; Goldhaber, Sulamith; Hoang, T.F.; Kalogeropoulos, Theodore E.; Powell, Wilson M.

Pion and proton diffraction dissociation are observed in π−p interactions at 205 GeV/c. The 2‐ and 4‐prong final states show evidence for N* and A1 production. Pion diffraction into masses up to ∼ 6 GeV is observed in the inclusive reaction π−p ⇒ p + X.

We present experimental results on K + d interactions from 865 to 1585 MeV/ c incident beam momentum. We report measurements of several K + d partial cross sections and calculate most of the others using relations derived from isospin conservation and data from other experiments. The most striking feature of the cross section data is the abrupt rise of the total single-pion-production cross section near 1000 MeV/ c . We extract isospin-0 KN partial cross sections and find a rapid quasi-two-body reaction KN → K ∗ N . As in the case of the isospin-1 K + N system, it appears that the structure around 1200 MeV/ c in the total cross section for the isospin-0 K ∗ N system is well reconstructed by the sum of three smoothly varying channel cross sections σ 0 (KN), σ 0 (KN π ) and σ 0 (KN ππ ). We study thereaction KN → K ∗ N near threshold and find that the production and decay angular distributions can be interpreted in terms of t -channel phenomena, specifically a superposition of ω, ϱ, and π exchange. As is true of the isospin-1 KΔ and K ∗ N final states, the isospin-0 K ∗ N state has a behavior near threshold which is not very different from its behavior at much higher energy.