The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The differential cross section DSIG/DT for the LRG and the LPS data samples.
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
Results on charged pion and kaon production in central Pb+Pb collisions at 20A and 30A GeV are presented and compared to data at lower and higher energies. A rapid change of the energy dependence is observed around 30A GeV for the yields of pions and kaons as well as for the shape of the transverse mass spectra. The change is compatible with the prediction that the threshold for production of a state of deconfined matter at the early stage of the collisions is located at low SPS energies.
Transverse mass spectra for pion production in the central rapidity region for collisions at 20 GeV per nucleon.
Transverse mass spectra for pion production in the central rapidity region for collisions at 30 GeV per nucleon.
Transverse mass spectra for kaon production in the central rapidity region for collisions at 20 GeV per nucleon.
Data on the reactions π − p → p π − , p p → π + π − , K − p → pK and p p → p p at 8 and 12 GeV/ c are presented. Our results agree with line reversal symmetry (between π − p → p π − and p p → π + π − ), Regge pole behaviour for non-exotic reactions ( π − p → p π − , p p → π + π − ), and universal behaviour for exotic reactions ( p p → p p , K − p → pK − ) with d σ /d u | u =0 ∼ s −10 excluding the existence of a “glory” mechanism in p p elastic backward scattering in our energy range.
No description provided.
No description provided.
No description provided.
We have analysed about 85 000 fast Λ 0 events, obtained in a fast proton triggered experiment performed at the CERN-Ω spectrometer at 9 and 12 GeV/ c incident π − beam. Nearly 2500 Λ 0 K + π − events have been isolated. We find strong production of quasi-two-body processes Λ 0 K ∗0 and ∑ ∗− K + consistent with u -channel hyperon exchange. Results on Λ 0 polarization, K ∗0 decay parameters and differential cross sections are given for Λ 0 K ∗0 (892) and Λ 0 K ∗0 (1430) final states. A comparison is made with the associated backward Λ 0 (1520) K ∗0 production seen in the four-prong reaction π − p→pK − K + π − obtained in the same experiment.
No description provided.
No description provided.
EXPONENTIAL FIT TO DN/DU.
The construction of a K L 0 beam for the CERN 2 m hydrogen bubble chamber and the derivation of the beam momentum spectrum are described. Cross sections are presented for the reaction K L 0 +p → K S 0 + π + + π − +p for K L 0 momenta up to 17 GeV/ c . The reacti is seen to be dominated, particularly at the highest momenta, where there are no previous data, by the production of the Q 0 - Q 0 system. The shapes of the t -distributions for Q 0 and Q 0 prodcution are found to be different in a sense opposite to that expected from the pion-exchange Deck model. A model in which the observed effect is ascribed to the addition of a K ∗ exchange Deck graph is found to be incompatible with the data. The data are, however, consistent with a model in which the Q 0 - Q 0 system is largely resonant and the sense of the cross-over is determined by the s -channel quantum numbers.
No description provided.
ABSOLUTE SCALE IS APPROXIMATE DUE TO THE CUTS FOR Q SELECTION.
ABSOLUTE SCALE IS APPROXIMATE DUE TO THE CUTS FOR Q SELECTION.
We have studied the backward production of ω 0 mesons in the u -channel I u = 1 2 exchange reaction π − p → N 0 (1680) ω 0 at 9 GeV/ c and 12 GeV/ c incident momenta. The data come from an experiment performed at the CERN Omega Spectrometer using a fast proton trigger device. The backward production of the η 0 meson has also been observed and the coupling constant ratio g η NN / g π NN has been estimated.
No description provided.
No description provided.
JACKSON FRAME (U-CHANNEL HELICITY SYSTEM).
From a muon-proton scattering experiment with a streamer chamber at the Stanford Linear Accelerator we present results in the ranges 0.3<Q2<4.7 GeV2 and 1.7<W<4.7 GeV for the reactions μ+p→μpV where V is a vector meson (ρ0, ω, or φ). It is shown that in ρ production the skewing parameter and the longitudinal-transverse ratio change significantly as Q2 increases above 1 GeV2. The cross section for ρ0 production as a function of Q2 falls below the vector-meson-dominance prediction. The ratio of the cross section for exclusive vector-meson production to the total cross section falls by a factor of 10 between photoproduction and a Q2 of 2 GeV2, yet the ratio of ω to ρ production remains constant at the photoproduction value out to Q2>2 GeV2.
THE ABSOLUTE TOTAL CROSS SECTION IS FROM A FIT TO THE MIT-SLAC ELECTRON SCATTERING DATA BY W. ATWOOD AND S. STEIN.
No description provided.
FOR 0.6 < M(PI+ PI-) < 0.9 GEV, USING THE METHOD OF MOMENTS.
We have analyzed backward meson production in the reaction π − p → p f π + π − π − at 9 GeV/ c and 12 GeV/ c incident π − momenta, from an experiment performed at the CERN Ω Spectrometer using a fast proton (p f ) trigger device. We find strong production of quasi-two-body processes N ∗ ϱ and N ∗ f with a production mechanism consistent with u -channel nucleon exchange. At a lower level, we observe N ∗ π processes with a 3-body baryon decay through Δ(1232)π. In the (3π) − system, we find evidence for A 1 − and clear A 2 − backward production with similar cross sections (≈0.5 μb).
No description provided.
U-HELICITY JACKSON FRAME.
U-HELICITY JACKSON FRAME.
Results on backward (3 π ) - system produced in π - p→p f π + π - π - reaction at 9 and 12 GeV/ c are given. The ϱ 0 π - mass spectra show two clear signals at 1050 MeV (A 1 region) and 1303 MeV (A - 2 ). The width of the enhancement in the A 1 region (195±32 MeV) is narrower than found in diffractive experiments. Total backward cross sections for those signals are of the same order of magnitude (∼0.5 μb).
No description provided.
The cross sections for the line-reversed reaction pairs K+n→K0p and K−p→K¯0n, and K+p→K0Δ++ and K−n→K¯0Δ− have been determined with high statistics and good relative normalization at 8.36 and 12.8 GeV/c in a spectrometer experiment at Stanford Linear Accelerator Center. The cross sections for the K+-induced reactions are larger than for the K−, contrary to the expectations of weakly-exchange-degenerate Regge-pole models. The ratio of the reaction cross sections is about the same as at lower energies and shows little change with momentum transfer.
Axis error includes +- 11/11 contribution.
Axis error includes +- 11/11 contribution.
Axis error includes +- 11/11 contribution.
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