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A strangelet search in Si+Pt and Au+Pt collisions at alternating-gradient synchrotron (AGS) energies, using a focusing spectrometer, sensitive to mass per charge of 3-14 GeV/c2 was conducted during the 1992 and 1993 heavy ion runs at the AGS. The null results thereof are presented as upper limits on the invariant production cross section, in the range of 10−5-10−4 mb c3/GeV2, and model dependent sensitivity limits in the range of 10−7-10−5 per collision. Measurements of the production cross sections of several nonstrange nuclear systems, from p to Be7 and Li8, the background of the strangelet search, are also presented.
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Recently, highly relativistic Au beams have become available at the Brookhaven National Laboratory, Alternating Gradient Synchrotron. Inclusive production cross sections for composite particles, d, t, He3, and He4, in 11.5A GeV/c Au+Pt collisions have been measured using a beam line spectrometer. For comparison, composite particle production was also measured in Si+Pt and p+Pt collisions at similar beam momenta per nucleon (14.6A GeV/c and 12.9 GeV/c, respectively). The projectile dependence of the production cross section for each composite particle has been fitted to Aprojα. The parameter α can be described by a single function of the mass number and the momentum per nucleon of the produced particle. Additionally, the data are well described by momentum-space coalescence. Comparisons with similar analysis of Bevalac A+A data are made. The coalescence radii extracted from momentum-space coalescence fits are used to determine reaction volumes (‘‘source size’’) within the context of the Sato-Yazaki model.
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During the recent commissioning of Au beams at the Brookhaven Alternating Gradient Synchrotron facility, experiment 886 measured production cross sections for π±, K±, p, and p¯ in minimum bias Au+Pt collisions at 11.5A GeV/c. Invariant differential cross sections, Ed3σ/dp3, were measured at several rigidities (p/Z≤1.8 GeV/c) using a 5.7° (fixed-angle) focusing spectrometer. For comparison, particle production was measured in minimum bias Si+Pt collisions at 14.6A GeV/c using the same apparatus and in p+Pt collisions at 12.9 GeV/c using a similar spectrometer at KEK. When normalized to projectile mass, Aproj, the measured π± and K± cross sections are nearly equal for the p+Pt and Si+Pt reactions. In contrast to this behavior, the π− cross section measured in Au+Pt shows a significant excess beyond Aproj scaling of the p+Pt measurement. This enhancement suggests collective phenomena contribute significantly to π− production in the larger Au+Pt colliding system. For the Au+Pt reaction, the π+ and K+ yields also exceed Aproj scaling of p+Pt collisions. However, little significance can be attributed to these excesses due to larger experimental uncertainties for the positive rigidity Au beam measurements. For antiprotons, the Si+Pt and Au+Pt cross sections fall well below Aproj scaling of the p+Pt yields indicating a substantial fraction of the nuclear projectile is ineffective for p¯ production. Comparing with p+Pt multiplicities, the Si+Pt and Au+Pt antiproton yields agree with that expected solely from ‘‘first’’ nucleon-nucleon collisions (i.e., collisions between previously unstruck nucleons). In light of expected p¯ annihilation in the colliding system, such projectile independence is unexpected without additional (projectile dependent) sources of p¯ production. In this case, the data indicate an approximate balance exists between absorption and additional sources of antiprotons. This balance is remarkable given the wide range of projectile mass spanned by these measurements.
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Total cross sections have been measured for H, He, 6 Li, C, O and Pb targets for 1 GeV incident energy protons. From the differential elastic scattering data published elsewhere, we also obtain the total elastic scattering and reaction cross sections for H, He, C and O. When our data are combined with other measurements in the same energy region, it is found that the total and reaction cross sections can be fit by the formulae σ T = 47 A 0.82 and σ R = 42 A 0.67 mb. It is also observed that the total and reaction cross sections for negative pions on nuclei can also be fit with these same A -dependencies.
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The study of the K + total cross sections on a wide range of nuclei has revealed important modifications of the free-space K + -nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on 6 Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.
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The emission of protons from targets of Li6, Li, C12, Al27, Ca40, V51, Zr90, and Pb under bombardment from 800 MeV protons has been studied using a high resolution proton spectrometer. Spectra were measured at laboratory scattering angles of 5°, 7°, 9°, 11°, 13°, 15°, 20°, 25°, and 30° with special emphasis on the quasifree region. Outgoing momenta corresponding to the region of pion production were examined at 11° and 15°. Absolute cross sections have been derived by reference to known (p,p) scattering data at 800 MeV. The quasifree scattering has been compared to a distorted-wave impulse approximation analysis by summing over the unobserved (struck) nucleon. The systematics of proton production and the applicability of the distorted-wave impulse approximation analyses are discussed. NUCLEAR REACTIONS (p,p′) on Li6, Li, C12, Al27, Ca40, V51, Zr90, Pb; Ep=800 MeV, θL=5° to 30°; quasielastic scattering, DWIA analysis.
APPROXIMATE SYSTEMATIC CROSS SECTION ERROR IS EQUAL TO +-6.5%.
APPROXIMATE SYSTEMATIC CROSS SECTION ERROR IS EQUAL TO +-6.5%.
APPROXIMATE SYSTEMATIC CROSS SECTION ERROR IS EQUAL TO +-6.2%.
We employ data taken by the JADE and OPAL experiments for an integrated QCD study in hadronic e+e- annihilations at c.m.s. energies ranging from 35 GeV through 189 GeV. The study is based on jet-multiplicity related observables. The observables are obtained to high jet resolution scales with the JADE, Durham, Cambridge and cone jet finders, and compared with the predictions of various QCD and Monte Carlo models. The strong coupling strength, alpha_s, is determined at each energy by fits of O(alpha_s^2) calculations, as well as matched O(alpha_s^2) and NLLA predictions, to the data. Matching schemes are compared, and the dependence of the results on the choice of the renormalization scale is investigated. The combination of the results using matched predictions gives alpha_s(MZ)=0.1187+{0.0034}-{0.0019}. The strong coupling is also obtained, at lower precision, from O(alpha_s^2) fits of the c.m.s. energy evolution of some of the observables. A qualitative comparison is made between the data and a recent MLLA prediction for mean jet multiplicities.
Overall result for ALPHAS at the Z0 mass from the combination of the ln R-matching results from the observables evolved using a three-loop running expression. The errors shown are total errors and contain all the statistics and systematics.
Weighted mean for ALPHAS at the Z0 mass determined from the energy evolutions of the mean values of the 2-jet cross sections obtained with the JADE and DURHAMschemes and the 3-jet fraction for the JADE, DURHAM and CAMBRIDGE schemes evaluted at a fixed YCUT.. The errors shown are total errors and contain all the statistics and systematics.
Combined results for ALPHA_S from fits of matched predicitions. The first systematic (DSYS) error is the experimental systematic, the second DSYS error isthe hadronization systematic and the third is the QCD scale error. The values of ALPHAS evolved to the Z0 mass using a three-loop evolution are also given.
Measurements are presented of the recoil-proton polarization for π0 photoproduction angles near 64° in the c.m. system. The steep angular dependence observed by others at lower energies persists to at least 1500 MeV, and the polarization crosses through zero near 63° over the entire 900-1600-MeV energy interval. Summary fits are made to available recoil-proton polarization data, 950-1250 MeV, and are found to require terms of order cos3θ, but no higher.
Axis error includes +- 0.0/0.0 contribution (?////).
The production of π∘ mesons in the reaction γ+p→π∘+p is investigated as a function of the incident γ-ray energy in the region from 200 Mev to 300 Mev. For the π∘ emitted at approximately 90° laboratory angle, the differential cross section can be represented by (dσπ∘dΩ)π2=C(K−145)1.9±0.4, where K= energy of incident γ-ray in Mev. The approximate threshold for the reaction is 145 Mev. The ratio of the cross section at 60° laboratory angle to that at 90° laboratory angle, for γ-rays between 250 Mev and 300 Mev, is 1.45±0.25.
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