Results from the HELIOS External Spectrometer on kaon production in 200 GeV/ A S + W and p + W collisions are presented. The K π ratios are compared with results from a lower beam energy and are found to be remarkably similar. Evidence for secondary production of K + by meson-baryon rescattering is reviewed. Our results at y = 1.0–1.5 are compared with neutral strange particle results at midrapidity.
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Cross sections are presented for the inclusive production of Λ hyperons in electron-positron annihilations at s=29 GeV based on the full 291-pb−1 sample of data taken in the High Resolution Spectrometer experiment at the SLAC e+e− storage ring PEP. These results, and the associated correlation analyses, are consistent with the Lund model predictions with the strange diquark suppression ratio δ fixed at 0.59±0.10±0.18, as compared to the standard Lund value of 0.32. The Λ multiplicity has been found to be 0.182±0.020 per event. The opposite-strangeness multiplicity 〈nΛΛ¯〉 has been measured to be 0.046±0.020, whereas the like-strangeness multiplicity 〈nΛΛ+Λ¯Λ¯〉 is 0.009±0.028. A strong correlation is found between Λ's and Λ¯'s; when one is found in an event, the other is found in the same event with a probability that exceeds 50%.
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Extrapolate to full z interval using Lund fit.
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The doubly differential cross section for the production of He3 and He4 by 800 MeV protons from C12, Ti, and Pb has been measured at laboratory angles of 6° and 15°. The momentum of the detected helium nuclei varied from 1 to 2 GeV/c, the maximum being well above the incident proton momentum of 1.46 GeV/c. The cross sections were found to increase with increasing target mass and decrease with increasing momentum and scattering angle. In our momentum region, the He3 production cross section is 1.5–10 times larger than He4 depending on the target and the momentum. The data are consistent with the hypothesis that the dominant reaction mechanism is a direct process where the initial nucleon-nucleon scattering is followed by a sequential pickup of neutrons.
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We used nuclear track detectors to construct the trajectories of interactions and to measure with high resolution the charge of the beam and of heavy nuclear fragments produced in interactions. A null result of our search for fractional charge states in high-energy fragments with charges 8≤Z≤13 produced in collisions of 14.5A GeV Si28 nuclei with Pb and Cu targets leads us to conclude that the upper limits for the probability of production of a fragment with charge 23/3, 25/3, 26/3 28/3 29/3, 31/3 32/3, 34/3, 35/3, 37/3, or 38/3 charge unit in Pb and Cu at 90% confidence level are 1.9×10−4 and 3.9×10−4, respectively. We set a similar limit on the relative number of particle-stable fragments with 8≤Z≤14 created in the central rapidity region.
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The analyzing power Ay for p+p elastic scattering at θlab=8.64°±0.07° (θcms=18.1°) and at a bombarding energy of 183.1±0.4 MeV has been determined to be Ay=0.2122±0.0017. The error includes statistics, systematic uncertainties, and the uncertainty in bombarding energy and angle. This measurement represents a calibration standard for polarized beams in this energy range. The absolute scale for the measurement has been obtained by comparison with p+C elastic scattering at the same energy at an angle where Ay is very nearly unity.
Axis error includes +- 0.0/0.0 contribution (?////).
We present measurements of the rapidity and transverse-momentum distributions of the protons emitted in S+W, O+W, andp+W reactions at 200 GeV/A around the target rapidity (y=1). The rapidity density rises linearly with the transverse energy for all three systems, but the slope forp+W is much steeper than for O+W and S+W. The rapidity density forp+W is much higher than predicted by summing single nucleonnucleon collisions without any nuclear effects, indicating substantial rescattering of the produced particles. The predictions of the VENUS 3 model, including rescattering, show reasonable agreement with the data for all three systems. We do not have evidence for a strong collective flow of the outgoing particles.
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We have measured the polarization of D*, the energy dependence of the polarization, and the spin-density matrix of D* in e+e− annihilation at a center-of-mass energy of 29 GeV using the Time Projection Chamber detector at the SLAC storage ring PEP. In 147 pb−1 of data we see no strong evidence for polarization, alignment, or final-state interactions in this fragmentation process.
Polarization is the factor alpha(z) in the expression d width (D*-->D pi)/domega = C(1+alpha(z)cos(theta)**2).
Spin density matrices for D* --> D0 pi+.
Total reaction cross sections of 20 MeV π − and 30 MeV π + and π − have been measured for carbon and nickel targets. The experimental results are in very good agreement with calculations based on commonly accepted pion-nucleus potentials but disagree with calculations based on the potentials associated with the so-called pionic atom anomaly.
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Integral cross sections for π + p interaction have been measured between 125.9 and 201.7 MeV using the transmission method. Over this energy range the results are in very good agreement with predictions made with currently accepted phase shifts. These results are also consistent with similar measurements at lower energies when the dispersion relation constrained Karlsruhe phase shifts are used.
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We present a new high-statistics measurement of the cross section for the process e+e−→e+e−π+π− at a center-of-mass energy of 29 GeV for invariant pion-pair masses M(π+π−) between 350 MeV/c2 and 1.6 GeV/c2. We observe the f2(1270) and measure its radiative width to be 3.15±0.04±0.39 keV. We also observe an enhancement in the π+π− spectrum near 1 GeV. General agreement is found with unitarized models of the γγ→π+π− reaction that include final-state interactions.
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Statistical errors only.
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