We present results on the photoproduction of 10 000 charmed particles from the 108 recorded triggers of Fermilab experiment E691. The total cross section for the photoproduction of D0 and D+ particles (and antiparticles) for xF>0.2 is measured to be 3.88±0.06±0.40 μb/Be nucleus at 〈Eγ〉=145 GeV. We have also measured the relative production of different charmed particles, their pT2 and xF distributions, and the energy dependence of the total charm cross section. The mean pT2 is 1.16±0.04 GeV2/c2 and the ratio of charm cross sections at 200 and 100 GeV is 1.96±0.24. Results of fits to the xF distribution are also reported.
D0/AD0 cross section from K-PI+/K+PI- decay mode.
D+/D- cross section from K-2PI+/K+2PI- decay mode.
D*+/D*- cross section from D0<K-PI+>PI+ + CC decay mode.
Data are presented on inclusive π0 production in the forward c.m. hemisphere (xF>0.025) in π+p,K+p andpp interactions at 250 GeV/c. These data are compared to results at other energies and interpreted in terms of quark-parton models.
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The experimental results are presented for ratios of ν-meson inclusive differential cross sections in 10.5 GeV/ c π + p, π + D and π + A collisions, R D/p =(d σ /d x F )( π + D → η X)/ (d σ /d x F ) π + p→ η X), R A =(d σ /d x F )( π + D→ η X) in the beam fragmentation region. The results are based on the statistics of ≈ 5 × 10 4 detected η → 2 γ decays. It is shown that the power α in the parametrisation R A ≈ A α ( xf ) does not change significantly with x F and its mean value is 0.50±0.02. The lower limit is obtained for the effective coefficient with string tension in the colour string model, κ ⩾ 3 GeV/fm. The observed growth of R A with x F can be explained by an assumption of a neutron halo with the factor H ≈ 4 in the nuclei.
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Axis error includes +- 0.0/0.0 contribution (?////RES-DEF(RES=DEL++,BACK=CORRECTED,DEF=1.08 < M(P PI+) < 1.8 GEV)//RES-DEF(RES=SIG(1385P13)+-,BACK=CORRECTED,DEF=1.26 < M(LAMDA PI+-) <2.0 GEV)//RES-DEF(RES=ASIG(1385P13)+-,BACK=CORRECTED,DEF=1.26 < M(ALAMDA PI+-) < 2.0< GEV)).
Axis error includes +- 0.0/0.0 contribution (?////RES-DEF(RES=DEL++,BACK=CORRECTED,DEF=1.08 < M(P PI+) < 1.8 GEV)//RES-DEF(RES=SIG(1385P13)+-,BACK=CORRECTED,DEF=1.26 < M(LAMDA PI+-) <2.0 GEV)//RES-DEF(RES=ASIG(1385P13)+-,BACK=CORRECTED,DEF=1.26 < M(ALAMDA PI+-) < 2.0< GEV)).
Axis error includes +- 0.0/0.0 contribution (?////RES-DEF(RES=DEL++,BACK=CORRECTED,DEF=1.08 < M(P PI+) < 1.8 GEV)//RES-DEF(RES=SIG(1385P13)+-,BACK=CORRECTED,DEF=1.26 < M(LAMDA PI+-) <2.0 GEV)//RES-DEF(RES=ASIG(1385P13)+-,BACK=CORRECTED,DEF=1.26 < M(ALAMDA PI+-) < 2.0< GEV)).
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We present results on inclusive φ meson production in K + p interactions at 70 GeV/ c in the kaon fragmentation x >0.2 region. Comparison with other data on φ meson production in K ± and p induced reactions provides evidence that the strange valence-quark fragmentation or recombination processes play the dominant role in the K ± → φ transitions. Arguments are presented that the kaon valence strange s -quark carries a much higher momentum fraction than the u-quark. Evidence for the previously observed narrow φπ + state at mass ∼2.1 GeV is discussed.
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We present results on the inclusive polarization of Λ hyperons produced in K + p interactions at 32 and 70 GeV/ c . A large positive Λ polarization is observed in the kaon fragmentation region. The polarization is energy independent, increases strongly with increasing x , but shows essentially no p T -dependence.
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