Search

We have constructed and operated a high-speed parallel-pipelined track and vertex processor and used it to trigger data acquisition in a high-rate charm and beauty experiment at Fermilab. The processor uses information from hodoscopes and wire chambers to reconstruct tracks in the bend view of a magnetic spectrometer, and uses these tracks to find the corresponding tracks in a set of silicon-strip detectors. The processor then forms vertices and triggers the experiment if at least one vertex is downstream of the target. Under typical charm running conditions, with an interaction rate of ≈5 MHz, the processor rejects 80–90% of lower-level triggers while maintaining efficiency of ≈70% for two-prong D-meson decays.

Using a silicon-microstrip detector array to identify secondary vertices, we have observed {ital b}{r_arrow}{ital J}/{psi}{r_arrow}{mu}{sup +}{mu}{sup {minus}} decays in 800 GeV/{ital c} proton-gold interactions. The doubly differential cross section for {ital J}/{psi} mesons originating from {ital b}-quark decays, assuming linear dependence on nucleon number, is {ital d}{sup 2}{sigma}/{ital dx}{sub {ital Fdp}}{sup 2}{sub {ital T}}=107{plus_minus}28{plus_minus}19/nucleon at {ital x}{sub {ital F}}=0.05 and {ital p}{sub {ital T}}=1GeV/{ital c}. This measurement is compared to next-to-leading-order QCD predictions. The integrated {ital b}-quark production cross section, obtained by extrapolation over all {ital x}{sub {ital F}} and {ital p}{sub {ital T}}, is {sigma}({ital pN}{r_arrow}{ital bb}{ovr bar}+{ital X})=5.7{plus_minus}1.5{plus_minus}1.3 nb/nucleon.

The differential cross sections do/dxF for J/G produced inclusively in 800 GeV/c p-Cn and pBe collisions have been measured in the kinematic range 0.30 5 IF < 0.95 through the decay mode J/G + p+p-. They are compared with the predictions of the semilocal duality model for several sets of parton density functions. No evidence for a suggested intrinsic charm contribution to the cross section is observed. The ratio of the differential cross sections for Cu and Be targets confirms the suppression of J/$ production in heavy nuclei at large ZF.

A Silicon Microstrip Spectrometer has been installed and successfully operated in experiment E789 at Fermilab. The main physics goal of the experiment is to search for charged particle decays of B and D Mesons. Damage effects due to ionizing radiation exposure to the silicon during the experiment are reported.

The {sup 70,72}Ge({ital n},{ital p}){sup 70,72}Ga reactions have been measured at a beam energy of 200 MeV in order to study the behavior of Gamow-Teller (GT) strength near the {ital N}=40 subshell closure. The GT quenching factor extracted for {sup 70}Ge is consistent with results for {sup 54}Fe and with calculations done on the quasiparticle random-phase-approximation model if they are renormalized by a factor of about 0.6. The quasiparticle random-phase approximation predicts a drastic reduction in concentrated GT strength from {sup 70}Ge to {sup 72}Ge which is also seen in the data. These results are relevant to models of supernovae.

Cross sections for the 48 Ti(n, p) reaction have been measured at angles of 0°, 6°, and 12° at an energy of 200 MeV. The measurements are compared with results of DWIA calculations to obtain estimates of transition strengths for L = 0, 1, and ⩾2 up to an excitation energy of 25 MeV. Gamow-Teller strength ( L = 0) is peaked between 3 and 4 MeV excitation energy, with a significant distribution extending to about 12 MeV. The L = 1 strength is found mainly between 6 and 20 MeV while the cross section for transitions with L ⩾2 increases from 10 MeV to the upper limit of the measurements. The distribution of Gamow-Teller strength is in poor agreement with theoretical distributions used to calculate the lifetime for double beta decay of 48 Ca.

A parallel pipelined dataflow trigger processor which is used in Fermilab E789 is described. E789 is an experiment designed to study low-multiplicity decays of particles containing b or c quarks. The processor consists of an upstream vertex processor and a downstream track processor. The algorithms which reconstruct the postulated particle paths and calculate particle origin are implemented via interconnected function-specific hardware modules. The algorithm is directly dependent upon the organization of the modules, the specific arrangement of the intermodule cabling, the on-board wire patch patterns, and, where appropriate, the on-board memory data. The uniqueness of this particular dataflow processor lies in the inclusion of the particle origin calculation. The vertex processor utilizes silicon detector hits to calculate the particle origin and to verify consistency with the downstream track. The downstream tracks are reconstructed by the track processor. The processor provides an indication of the presence of at least one interesting particle pair in the current event by asserting read on its read/skip output. The read assertion is then used as a trigger to capture all of the event's data for subsequent extensive offline analysis. >

Results of a search for the three neutral charm decays, D0 -> mu e, D0 -> mu mu, and D0 -> e e, are presented. This study was based on data collected in Experiment 789 at the Fermi National Accelerator Laboratory using 800 GeV/c proton-Au and proton-Be interactions. No evidence is found for any of the decays. Upper limits on the branching ratios, at the 90% confidence level, are obtained., 28 pages, 18 figures. Submitted to Physical Review D

With a data sample containing 1.1{times}10{sup 5} {ital J}/{psi}{r_arrow}{mu}{sup +}{mu}{sup {minus}} decays reconstructed with 16 MeV/{ital c}{sup 2} rms mass resolution, we have measured the differential cross sections versus Feynman-{ital x}, rapidity, and {ital p}{sub {ital T}} for the production of {ital J}/{psi} and {psi}{prime} in 800 GeV/{ital c} {ital p}-Au collisions. Our results are compared with leading-order QCD predictions and with previous measurements. While the shapes of the cross sections are in qualitative agreement with QCD predictions, the magnitudes disagree by factors of 7 ({ital J}/{psi}) and 25 ({psi}{prime}). Assuming an appropriate form for the differential cross sections in regions not measured we derive a total {ital J}/{psi} production cross section {sigma}({ital p}+{ital N}{r_arrow}{ital J}/{psi}+{ital X})=442{plus_minus}2{plus_minus}88 nb/nucleon and a (model-dependent) total {psi}{prime} cross secton {sigma}({ital p}+{ital N}{r_arrow}{psi}{prime}+{ital X})=75{plus_minus}5{plus_minus}22 nb/nucleon. For {ital J}/{psi} produced at central rapidity, {ital d}{sigma}({ital p}+{ital N}{r_arrow}{ital J}/{psi}+{ital X})/{ital dy}{vert_bar}{sub {ital y}=0}=230{plus_minus}5{plus_minus}46 nb/nucleon.

The nuclear dependence for 800 GeV/[ital c] proton production of neutron [ital D] mesons has been measured near [ital x][sub [ital F]]=0 in Experiment 789 at Fermilab. [ital D] mesons from beryllium and gold targets were detected with a pair spectrometer and a silicon vertex detector via their decay [ital D][r arrow][ital K][pi]. No nuclear dependence is found, with a measured [alpha]=1.02[plus minus]0.03[plus minus]0.02. The measured differential cross section, [ital d][sigma]/[ital dx][sub [ital F]], for neutral-[ital D]-meson production at [l angle][ital x][sub [ital F]][r angle]=0.031 is 58[plus minus]3[plus minus]7 [mu]b/nucleon. The integrated cross section obtained by extrapolation of the measured cross section to all [ital x][sub [ital F]] is 17.7[plus minus]0.9[plus minus]3.4 [mu]b/nucleon and is consistent with previous measurements.

Fermilab experiment 789 studies low‐multiplicity decays of neutral D and B mesons in a high‐rate fixed‐target environment. Preliminary results from the 1991 run are presented.

Forward-angle cross sections for 1/sup +/, T = 1 and 1/sup +/, T = 0 states in /sup 28/Si excited by the (p,p') reaction have been measured to determine the energy dependence of important pieces of the effective nucleon-nucleus interaction. The isovector spin-transfer transitions depend on energy as expected from distorted-wave impulse approximation calculations based on the dominant V/sub ..sigma..//sub tau/ part of the Franey-Love interaction. The parts of this interaction responsible for exciting the 9.5 MeV isosca- lar spin-flip transition predict a weaker energy dependence than is observed experimentally. The summed Gamow-Teller strength for isovector transitions below 14.5 MeV is found to be (0.89 +- 0.09) times the result of large-scale shell model calculations

Cross sections and a complete set of seven independent spin observables have been measured for inclusive quasielastic scattering of 290-MEV protons from /sup 54/Fe at a quasifree momentum transfer of 1.36 fm/sup -1/ and energy transfers varying from 0--90 MeV. Comparison of the results with relativistic and nonrelativistic impulse-approximation models shows that Fermi-motion averaging, a realistic nuclear response function, and medium modifications of the NN interaction are essential ingredients of a successful theory.

Protons scattered inelastically from /sup 12/C were detected at laboratory angles between 6/sup 0/ and 13/sup 0/ in coincidence with ..gamma.. rays from deexcitation of the 1/sup +/ T = 1 state in the recoil nucleus. Coincident cross sections for ..gamma.. rays emitted normal to the reaction plane and angular correlations for ..gamma.. rays emitted in the proton scattering plane at angles between 90/sup 0/ and 270/sup 0/ are presented and compared with predictions from both nonrelativistic and relativistic models of proton-nucleus scattering calculated in the impulse approximation. These data display a clear preference for the relativistic-model prediction.