We report results from a measurement of the inclusive diffraction dissociation of photons on hydrogen, γp→Xp, in the range 75
EXTRACTED ELASTIC CROSS SECTIONS.
RESULTS OF EXPONENTIAL FITS TO ELASTIC CROSS SECTIONS.
DIFFERENTIAL CROSS SECTIONS FOR INELASTIC EVENTS.
A measurement is presented of the cross section for D* meson production in diffractive deep-inelastic scattering for the first time at HERA. The cross section is given for the process ep -> eXY, where the system X contains at least one D* meson and is separated by a large rapidity gap from a low mass proton remnant system Y. The cross section is presented in the diffractive deep-inelastic region defined by 2< Q^2 < 100 GeV^2, 0.05 < y < 0.7, x_pom < 0.04, M_Y < 1.6 GeV and |t| < 1 GeV^2. The D* mesons are restricted to the range ptD* > 2 GeV and |\eta_D* | < 1.5. The cross section is found to be 246+-54+-56 pb and forms about 6% of the corresponding inclusive D* cross section. The cross section is presented as a function of various kinematic variables, including z_pom^obs which is an estimate of the fraction of the momentum of the diffractive exchange carried by the parton entering the hard-subprocess. The data show a large component of the cross section at low z_pom^obs where the contribution of the Boson-Gluon-Fusion process is expected to dominate. The data are compared with several QCD--based calculations.
The total D*+- production cross section for the given kinematic region. Also given is the ratio to the DIS*+- production cross section in the samekinematic region.
Cross section as a function of X(NAME=POMERON).
Cross section as a function of LOG10(BETA). BETA = X/X(NAME=POMERON).
We report a measurement of the diffraction dissociation differential cross section d2σSD/dM2dt for p¯p→p¯X at √s =546 and 1800 GeV, M2/s<0.2 and 0≤-t≤0.4 GeV2. Our results are compared to theoretical predictions and to extrapolations from experimental results at lower energies.
Single diffraction dissociation cross section.
We present results from a measurement of double diffraction dissociation in $\bar pp$ collisions at the Fermilab Tevatron collider. The production cross section for events with a central pseudorapidity gap of width $\Delta\eta^0>3$ (overlapping $\eta=0$) is found to be $4.43\pm 0.02{(stat)}{\pm 1.18}{(syst) mb}$ [$3.42\pm 0.01{(stat)}{\pm 1.09}{(syst) mb}$] at $\sqrt{s}=1800$ [630] GeV. Our results are compared with previous measurements and with predictions based on Regge theory and factorization.
Cross sections for double diffractive production.
A measurement is reported of charged multiplicity distributions of high-mass diffractive π±, K±, and p± states produced in 100 and 200 GeV/c hadron-proton collisions, h+p→X+p. The distributions are described well by a Gaussian function that depends only on the available mass M=Mx−Mh, has a maximum at n0≅2M12, and a peak-to-width ratio n0D≅2.
MULTIPLICITY VERSUS AVAILABLE MASS MDD-MPI.
MULTIPLICITY VERSUS AVAILABLE MASS (MDD - MK).
MULTIPLICITY VERSUS AVAILABLE MASS (MDD - MP).
Photon proton cross sections for elastic light vector meson production, σelνp, inelastic diffractive production, σndνp, non-diffractive production, σdνp, as well as the total cross section, σtotνp, have been measured at an average υp center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are σelνp = 18 ± 7 μb, σdνp = 33 ± 8 μb, σndνp = 91 ± 11 μb, and σtotνp 143 ± 17 μb, where the errors include statistical and systematic errors added in quadrature.
Errors contain both statistics and systematics.
We have studied the diffractive dissociation into di-jets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t_{min} approaches 0) we find that when the per-nucleus cross-section for this process is parameterized as $ \sigma = \sigma_0 A^{\alpha} $, $ \alpha $ has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.
Cross sections is fitted to A**POWER.
We report the first observation of diffractively produced W bosons. In a sample of W -> e nu events produced in p-barp collisions at sqrt{s}=1.8 TeV, we find an excess of events with a forward rapidity gap, which is attributed to diffraction. The probability that this excess is consistent with non-diffractive production is 1.1 10^{-4} (3.8 sigma). The relatively low fraction of W+Jet events observed within this excess implies that mainly quarks from the pomeron, which mediates diffraction, participate in W production. The diffractive to non-diffractive W production ratio is found to be R_W=(1.15 +/- 0.55)%.
No description provided.
The reaction γp→ρfast0pπ+π− has been studied with the linearly polarized 20-GeV monochromatic photon beam at the SLAC Hybrid Facility to test the prediction of s-channel helicity conservation in inelastic diffraction for t’<0.4 (GeV/c)2. In a sample of 1934 events from this reaction, the ρ0 decay-angular distributions and spin-density-matrix elements are consistent with s-channel helicity conservation, the π+π− mass shape displays the same skewing as seen in the reaction γp→pπ+π−, and the pπ+π− mass distribution compares well and scales according to the vector dominance model with that produced in π±p→πfast±pπ+π−.
No description provided.
We present a new measurement of the total photoproduction cross section performed with the H1 detector at HERA. For an average centre of mass energy of 200GeV a value of $\sigma_{tot}~{\gamma{p}}= 165\pm2\pm11\mu$b has been obtained. A detailed analysis of the data in adequate kinematic regions enabled a decomposition of the total cross section in its elastic, single diffractive dissociation and remaining non-diffractive parts, based on safe assumptions on the double diffractive dissociation contribution.
No description provided.
Forum