The differential cross section $d\sigma/dt$ for elastic $\rho~0$ photoproduction, $\gamma p \rightarrow \rho~0 p (\rho~0 \rightarrow \pi~+ \pi~-)$, has been measured in $ep$ interactions at HERA. The squared four-momentum exchanged at the proton vertex, $t$, has been determined directly by measuring the momentum of the scattered proton using the ZEUS Leading Proton Spectrometer (LPS), a large scale system of silicon micro-strip detectors operating close to the HERA proton beam. The LPS allows the measurement of the momentum of high energy protons scattered at small angles with accuracies of 0.4% for the longitudinal momentum and 5 MeV for the transverse momentum. Photoproduction of $\rho~0$ mesons has been investigated in the interval $0.073< |t| <0.40 GeV~2$, for photon virtualities $Q~2<1 GeV~2$ and photon-proton centre-of-mass energies $W$ between 50 and 100 GeV. In the measured range, the $t$ distribution exhibits an exponential shape with a slope parameter $b = 9.8 \pm 0.8 (stat.) \pm 1.1 (syst.) GeV~{-2}$. The use of the LPS eliminates the contamination from events with diffractive dissociation of the proton into low mass states.
SLOPE OF THE DSIG/DT distribution.
Total cross section integrated over t region.
Additional cross section, SIG, not given in the paper.
The reaction $\gamma p \rightarrow \omega p$ $(\omega \rightarrow \pi~+\pi~-\pi~0$ and $\pi~0\rightarrow\gamma\gamma)$ has been studied in $ep$ interactions using the \mbox{ZEUS} detector at photon-proton centre-of-mass energies between $70$ and $90\uni{GeV}$ and $|t| < 0.6\uni{GeV}~2$, where $t$ is the squared four momentum transferred at the proton vertex. The elastic \ome photoproduction cross section has been measured to be $\sigma_{\gamma p\rightarrow \omega p} = 1.21\pm 0.12\pm 0.23 \mu\mbox{b}$. The differential cross section $d\sigma_{\gamma p\rightarrow \omega p} /d|t|$ has an exponential shape $\mbox{e}~{-b |t|}$ with a slope $b = 10.0\pm 1.2\pm 1.3\uni{GeV}~{-2}$. The angular distributions of the decay pions are consistent with {\it s}-channel helicity conservation. When compared to low energy data, the features of $\omega$ photoproduction as measured at HERA energies are in agreement with those of a soft diffractive process. Previous measurements of the $\rho~0$ and $\phi$ photoproduction cross sections at HERA show a similar behaviour.
Total Elastic Cross Section.
No description provided.
SLOPE OF DSIG/DT distribution.
We measure the differential cross sections with respect to Feynman x ( xF) and transverse momentum ( pT) for π, K, and p-induced charm meson production using fully reconstructed D+, D0, and Ds decays. The shapes of these cross sections are compared to the theoretical predictions for charm quark production of next-to-leading order perturbative QCD using modern parametrizations of the pion and nucleon parton distributions. We observe the differences expected in production induced by projectiles with different gluon distributions, harder distributions being indicated for mesons than for protons.
Additional systematic errors of 6 pct, 6 pct and 9 pct respectively for pi, K and p beams.
Additional systematic errors of 6 pct, 6 pct and 9 pct respectively for pi, K and p beams.
Result of fitting DSIG/dXL spectra with form (1-XL)**POWER.
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.
The production of $\phi$ mesons in the reaction $e~{+}p \rightarrow e~{+} \phi p$ ($\phi \rightarrow K~{+}K~{-}$) at a median $Q~{2}$ of $10~{-4} \ \rm{GeV~2}$ has been studied with the ZEUS detector at HERA. The differential $\phi$ photoproduction cross section $d\sigma/dt$ has an exponential shape and has been determined in the kinematic range $0.1<|t|<0.5 \ \rm{GeV~2}$ and $60 < W < 80 \ \rm{GeV}$. An integrated cross section of $\sigma_{\gamma p \rightarrow \phi p} = 0.96 \pm 0.19~{+0.21}_{-0.18}$ $\rm{\mu b}$ has been obtained by extrapolating to {\it t} = 0. When compared to lower energy data, the results show a weak energy dependence of both $\sigma_{\gamma p \rightarrow \phi p}$ and the slope of the $t$ distribution. The $\phi$ decay angular distributions are consistent with $s$-channel helicity conservation. From lower energies to HERA energies, the features of $\phi$ photoproduction are compatible with those of a soft diffractive process.
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Numerical values of dsig/dt distribution requested from authors.
Numerical values of dsig/dt distribution read from plot.
The nuclear dependence for 800 GeV/c proton production of neutron D mesons has been measured near xF=0 in Experiment 789 at Fermilab. D mesons from beryllium and gold targets were detected with a pair spectrometer and a silicon vertex detector via their decay D→Kπ. No nuclear dependence is found, with a measured α=1.02±0.03±0.02. The measured differential cross section, dσ/dxF, for neutral-D-meson production at 〈xF〉=0.031 is 58±3±7 μb/nucleon. The integrated cross section obtained by extrapolation of the measured cross section to all xF is 17.7±0.9±3.4 μb/nucleon and is consistent with previous measurements.
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The reaction π−p→η′η′n has been studied atpπ=37 GeV/c. Total of 14 events of this reaction have been selected. It has been shown that in the effective mass spectrum of the η′η′ system the events are concentrated mainly near the reaction threshold, which might be caused by the decayX(1910)→η′η′. The reaction cross-section has been evaluated: σ(π−p→η′η′n)=110±40 nb.
No description provided.
No description provided.
Results of fitting the differential distributions in x F and p T 2 of D mesons produced in 400 GeV/ c p-p interactions to the form d 2 σ d x F d p T 2 ∝(1−x F ) n exp [−(p T 2 /〈p T 2 〉)] are discussed. The D + distribution is found to be relatively hard [ n =3.1±0.8〈 P t 2 〉=1.32±0.27 (GeV/ c ) 2 ] and the D̄ 0 distribution relatively soft [ n =8.1±1.9,〈 p T 2 〉=0.62±0.14 (GeV/ c ) 2 ] compared to the average for all D's [ n =4.9±0.5,〈 p T 2 〉=0.99±0.10 (GeV/ c ) 2 ]. It is suggested that these distributions could reflect contribution of leading di-quarks in pp collisions. Comparison is made with evidence for leading quarks in charm production in 360 GeV/ cπ − p interactions.
The invariant (C=INV) and non-invariant (C=NON-INV) distributions are fitted to (1-XL)**POWER. Pt distribution is fitted to EXP(-PT**2/SLOPE).
We have measured the inclusive production properties of D and D messons produced from pp interactions at s =27.4 GeV . The differential production cross section is well represented by the empirical form d 2 σ d x F d P 2 T = 1 2 [σ ( D / D )(n+1)b](1−|x F |) n exp (−bp 2 T ) with n=4.9 ± 0.5, b=(1.0±0.1)( GeV /c) −2 , and the inclusive D / D cross section σ ( D / D ) is (30.2±3.3) ωb. The QCD fusion model predicts D / D production which is in good agreement with our data except for the magnitude of the cross section which depends sensitively on the assumed mass of the charm quark.
No description provided.
No description provided.
No description provided.
We have measured the ratio of the real to the imaginary parts of the p¯p forward-scattering amplitude in the incident-momentum range 360 to 650 MeV/c. These results are in good agreement with predictions of the Paris nucleon-antinucleon potential model which include spin-flip effects.
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RESULTS OF FITS TO THE FORWARD-SCATTERING DIFFERENTIAL CROSS SECTIONS ASSUMING THE RATIO OF THE SPIN-FLIP TO NON-SPIN-FLIP PARTS OF THE FORWARD AMPLITUDE IS ZERO.
RESULTS OF FITS TO THE FORWARD-SCATTERING DIFFERENTIAL CROSS SECTIONS ASSUMING THE RATIO OF THE SPIN-FLIP TO NON-SPIN-FLIP PARTS OF THE FORWARD AMPLITUDE IS PARAMATERISED AS 0.3698-0.1384*PLAB(IN GEV).
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