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No description provided.
Photon diffractive dissociation, $\gamma p \to Xp$, has been studied at HERA with the ZEUS detector using $ep$ interactions where the virtuality $Q^2$ of the exchanged photon is smaller than 0.02 GeV$^2$. The squared four-momentum $t$ exchanged at the proton vertex was determined in the range $0.073<|t|<0.40$ GeV$^2$ by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photon-proton centre-of-mass energy interval $176<W<225$ GeV and for masses of the dissociated photon system $4<M_X<32$ GeV, the $t$ distribution has an exponential shape, $dN/d|t| \propto \exp{(-b|t|)}$, with a slope parameter $b=6.8 \pm 0.9$~(stat.)~$ ^{+1.2}_{-1.1}$~(syst.)~GeV$^{-2}$.
T is the squared four momentum transfer at the proton vertex.
SLOPE of the DN/DT distribution.
We discuss the structure of the momentum transfer distributions for the diffractive dissociation processes p → n π + , p → Δ ++ π − and K − → K 890 ∗0 π − . In the near-threshold mass region a clear break of slope is found around t ′KK ∼ 0.25 GeV 2 for the two baryonic channels, whereas no comparable structure is seen for the mesonic system. The K → K ∗ π differential cross section exhibits a nearly exponential behaviour up to t ′ pp ∼ 0.6 GeV 2 , falling over three orders of magnitude. The slope variations and breaks are strongly correlated both to the mass region considered and to the decay angle of the fragmentation system.
No description provided.
We study the internal structure of a forward-going pπ + π − π + π − system, with invariant mass in the range 2.5-4 GeV, produced through diffractive dissociation of a beam proton at the ISR. The shape of the system, as seen in its center-of-mass, deviates strongly from isotropic phase space and possesses, rather, a longitudinal structure with a major axis along the incoming proton direction. The final state proton momentum is aligned in the direction of the incoming proton, an effect which becomes more pronounced with increasing diffractive mass.
Acceptance corrected distribution of momentum transfer to the diffractive (p-4pi) system. Data requested from authors.
No description provided.
Neutron diffraction dissociation has been measured at the ISR in proton-neutron interactions at 37 GeV c.m. energy. The data were taken with the Split Field Magnet detector, during a short deuteron storage test run with colliding p-d beams. Differential mass and momentum transfer distributions are reported; the value of the total cross-section shows a weak s -dependence when compared to lower energy data.
ERROR IS MOSTLY SYSTEMATIC.
Neutron-neutron interactions have been observed at the CERN ISR with deutron colliding beams. The double - diffraction dissociation process →(p π p − )( pπ − ) has been measured with the Split Field Magnet at √ s = 26 GeV detecting all final state particles, including the two spectator protons. Mass and t distributions are presented and compared with corresponding spectra observed in single neutron diffraction in the same energy range with supporting evidence for factorization. The cross-section of the process is 11.5±2.8 μ b and can be directly related to the corresponding value for double diffraction dissociation of protons in the same energy range.
ERROR IS MOSTLY SYSTEMATIC. DEUTERON CORRECTIONS APPLIED.
No description provided.
This paper analyzes π−N→π−π−π+N events from Fermilab experiment E-580, using 200-GeV/c particles on a segmented target of plastic scintillator. Starting with 48 657 triggers, data-quality cuts and a cut on missing mass squared of M2<16 GeV2 lead to a final sample of 7205 events. The xF distribution of the 3π system shows almost all events in a sharp peak at xF=1, suggesting the presence of beam diffraction into three pions. The overall t’ distribution is fit to the sum of three exponential terms corresponding to coherent diffraction from carbon nuclei, diffraction from individual nucleons, and background. Cross sections per nucleon and exponential slopes are reported for each of the three components as a function of 3π effective mass. The cross section for diffraction from the nucleons in the target is 0.34±0.04 mb/nucleon. The cross section for coherent diffraction from carbon is 1.08±0.12 mb/nucleus. The exponential slope for diffraction is observed to decrease with increasing 3π effective mass. The fraction of coherent carbon diffraction in the total cross section is observed to decrease with increasing 3π effective mass. In the π−π+ effective-mass spectrum the ρ0(770) and f0(1270) are observed and their cross sections per nucleon are calculated. In the π−π−π+ effective-mass spectrum the A1−/A2− and A3− enhancements are observed and a cross section for the A3− is calculated.
No description provided.
Diffraction from coherent carbon nucleus.
Diffraction from individual nucleon.
The reaction K − n → K − π + π − n has been studied in the SLAC 82″ liquid deuterium bubble chamber with a beam momentum of 12 GeV/ c . Although the kinematic fit for this final state has only one constraint, nonetheless a reasonably pure sample has been obtained. The cross section for the reaction is 1.02 ± 0.10 mb. The process K − n → K ∗0 890 Δ − is observed with cross section 36 ± 9 μ b and t -slope of 10 ± 2 (GeV/ c ) −2 . A kaon diffraction dissociation sample has been obtained, although the Q-signal is not so strong as in experiments with proton targets. Neutron dissociation into n π + π − is also observed with similar properties to those of proton dissociation into p π + π − , but with a broader t -distribution.
BEAM AND TARGET DIFFRACTION DISSOCIATION DATA ARE REPORTED.
The diffractive dissociation of a 200-GeV/c π− beam into KS0KS0π+π−π− has been observed. The diffractive KS0KS0π+π−π− cross section is 1.59±0.78 μb. The ratio of the diffractive KS0KS0π+π−π− cross section to the diffractive KS0KS0π− cross section is 0.40±0.13, which is in good agreement with a diffractive-fragmentation-model prediction of 0.36. There is evidence for simultaneous production of K*− and K*+ in the diffractive KS0KS0π+π−π− sample. The K*+−KS0π−+ mass distribution shows an enhancement near 1.95 GeV.
No description provided.
No description provided.
No description provided.
A partial-wave analysis has been performed on the (K − π − π + ) system produced in the reaction K − p → K − π − π + p at 10 and 16 GeV/ c . In the Q mass region it is found that the two dominant states, K ∗ π and Kπ, both in 1 + S wave, are produced with different polarisations, helicity being approximately conserved in the t -channel for K ∗ π and in the s -channel for Kπ. This is in contradiction with the assumption that the amplitude can be factorised into “production” and “decay” parts, and hence that the two amplitudes are fully coherent. The phase variation of the two states do not indicate simple resonance behaviour. It is concluded that the Q-mass enhancement is composite.
No description provided.