We present asymmetries between the production of D+ and D- mesons in Fermilab experiment E791 as a function of xF and pt**2. The data used here consist of 74,000 fully-reconstructed charmed mesons produced by a 500 GeV/c pi- beam on C and Pt foils. The measurements are compared to results of models which predict differences between the production of heavy-quark mesons that have a light quark in common with the beam (leading particles) and those that do not (non-leading particles). While the default models do not agree with our data, we can reach agreement with one of them, PYTHIA, by making a limited number of changes to parameters used.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of Feynman variable X. 'Nucleus' are PT and C.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of PT**2. 'Nucleus' are PT and C.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of PT**2. 'Nucleus' are PT and C.
Proton distributions at midrapidity have been measured for 158A·GeV Pb+Pb collisions in the focusing spectrometer experiment NA44 at CERN. A high degree of nuclear stopping is found in the truly heavy ion collisions. Systematic results of single particle transverse momentum distributions of pions, kaons, and protons, of 200A·GeV S+S and 158A·GeV Pb+Pb central collisions will be addressed within the context of thermalization. By comparing these data with thermal and transport models, freeze-out parameters such as the temperature parameter T fo and mean collective flow velocity 〈β〉 are extracted. Preliminary results of the particle ratios of K − K + and p p are discussed in the context of cascade models of RQMD and VENUS.
CENTRAL COLLISIONS: SIG(TRIG)/SIG(GEOM)=10%.
A fresh analysis is reported of high statistics Crystal Barrel data on p p → 3π 0 , ηηπ 0 , ηπ 0 π 0 and ηη ′ π 0 at rest. This analysis is made fully consistent with CERN-Munich data on π + π − → π + π − up to a mass of 1900 MeV, with GAMS data on π + π − → π 0 π 0 , and with BNL and ANL data on π + π − → K K , which are fitted simultaneously. There is evidence for an I = 0, J PC = 2 ++ resonance with weak (≤ 7%) coupling to ππ, strong coupling to both ϱϱ and ωω and pole position 1534 - i90 MeV. This resonance agrees qualitatively with GAMS and VES data on ππ → ωω, previously interpreted in terms of a resonance at 1590–1640 MeV. New masses and widths for (A) ƒ 0 (1370) and (B) ƒ 0 (1500) , fitted to all eight data sets, are M A = 1300 ± 15 Mev, Γ A = 230 ± 15 MeV, M B = 1500 ± 8 MeV, Γ B = 132 ± 15 MeV. Branching ratios to ππ and ηη are given, and differ significantly from earlier determinations because of a new procedure.
A fraction of the initial P-state annihilation into F2(1270) cannot be ruled out. Therefore, the ratio magnitudes include the contribution due to this channel. MESON0 denotes A2(1630) state, not present in RPP.
We searched for long-lived strange quark matter particles, so-called strangelets , and studied particle and antiparticle production in Pb + Pb collisions at 158 GeV/ c per nucleon at zero degree production angle. We give upper limits for the production of strangelets covering a mass to charge ratio up to 120 GeV/ c 2 and lifetimes t lab > 1.2 μ s and plot invariant differential production cross sections as a function of rapidity for a variety of particles.
No description provided.
Preliminary results from WA97 measurements on Λ, Ξ and Ω production in lead-lead and proton-lead collisions are presented, along with a comparison of WA97 proton-lead data with previous WA85 proton-tungsten results. The ratio Ω gX seems to be enhanced in lead initiated reactions compared to proton initiated reactions.
No description provided.
No description provided.
PRELIMINARI DATA.
Differential cross sections for p p elastic scattering have been measured for very small momentum transfers at six different incident antiproton momenta in the range 3.7 to 6.2 GeV/c by the detection of recoil protons at scattering angles close to 90°. Forward scattering parameters σ T , b , and ϱ have been determined. For the ϱ-parameter, up to an order of magnitude higher level of precision has been achieved compared to that in earlier experiments. It is found that existing dispersion theory predictions are in disagreement with our results for the ϱ-parameter.
Results of the SIG(T)-free analysis. Errors include systematic uncertainties.
Results of the SIG(T)-fixed analysis. Errors include systematic uncertainties.
CT values of the total cross section from the SIG(T)-free analysis. Errors include systematic uncertainties.
Muon pair production is studied in p - W and S U collisions at 200 GeV per nucleon, as a function of transverse momentum P Tμμ . The inclusive ϱ + ω and Φ differential cross-sections dσ dP T are measured in the dimuon decay channel, for P T ≥ 0.6 GeV/c, in the central rapidity region, 3.0≤ y ≤ 4.0. Assuming the power law A-dependence σ = σ 0 ( A beam · A target ) α , the study of the integrated cross-sections for p - W and S U collisions leads to α ϱ + ω = 1.00±0.02±0.07 and α Φ = 1.23±0.03±0.05, showing clear evidence of Φ enhancement in S U interactions as compared to p - W collisions.
Statistical errors only.
Statistical errors only.
Statistical errors only.
The p̄p total annihilation cross section has been measured, with the Obelix apparatus at LEAR, at ten values of the antiproton incident momentum between 43 and 175 MeV/ c . The values of the cross section show that the well known 1 p behaviour of the annihilation cross section is drastically modified at very low momenta, which demonstrates the important role of the Coulomb force in low energy p̄p interaction. Moreover, they do not present any explicit resonant behaviour. Finally, when compared to potential model calculations, the data suggest that the percentage of P-wave in p̄p interaction around 50 MeV/ c antiproton incident momentum is less than 5%.
No description provided.
The frequency of the protonium annihilation channel p p → K S K L has been measured at three different target densities: liquid hydrogen ( LH ), gaseous hydrogen at NTP conditions and gaseous hydrogen at low pressure (5 mbar). The obtained results are: f( p p → K S K L , LH) = (7.8 ± 0.7 stat ± 0.3 sys ) × 10 −4 , f( p p → K S K L , NTP) = (3.5 ± 0.5 stat ± 0.2 sys ) × 10 −4 and f( p p → K S K L , 5 mbar ) = (1.0 ± 0.3 stat ± 0.1 sys ) × 10 −4 . Since the K S K L final stat and be originated only from the 3 S 1 initial state, these values give direct information on the scaling of the protonium spin-triplet S-wave annihilation probability with the density.
Three different target densities: liquid hydrogen (LH), gaseous hydrogen atstandard temperature and pressure conditions (NTP), and gaseous hydrogen at 5 m bar pressure (LP). The annihilation proceeds only from 3S1 initial state.
Antiproton production near midrapidity has been studied in central collisions of 32 S with sulphur, silver and gold nuclei at 200 GeV per nucleon. The measured transverse mass distributions can be described by an exponential with inverse slope parameters of about 200 MeV, similar to those obtained from Λ spectra. The rapidity density increases weakly with the target mass, ranging from 0.4 to 0.7. The ratio Λ p near midrapidity is approximately 1.4 on average, significantly larger than the corresponding ratio observed in proton-proton and proton-nucleus collisions.
No description provided.
No description provided.
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