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).
The exclusive production of proton-antiproton pairs in the collisions of two quasi-real photons had been studied using data taken at sqrt(s)_ee=183 GeV and 189 GeV with the OPAL detector at LEP. Results are presented for Ppbar invariant masses, W, in the range 2.15 W< <3.95 GeV. The cross-section measurements are compared with previous data and with recent analytic calculations based on the quark-diquark model.
Cross section as a function of the invariant mass of the pbar-p pair.
Cross section for two photon production of the pbar-p pair.
Angular distributions in 3 W ranges.
We present results of searches for diphoton resonances produced both inclusively and also in association with a vector boson (W or Z) using 100 $pb^{-1}$ of $p\bar{p}$ collisions using the CDF detector. We set upper limits on the product of cross section times branching ratio for both $p\bar{p} \to \gamma \gamma + X$ and $p \bar{p} \to \gamma \gamma + W/Z$. Comparing the inclusive production to the expectations from heavy sgoldstinos we derive limits on the supersymmetry-breaking scale $\sqrt{F}$ in the TeV range, depending on the sgoldstino mass and the choice of other parameters. Also, using a NLO prediction for the associated production of a Higgs boson with a W or Z boson, we set an upper limit on the branching ratio for $H \to \gamma \gamma$. Finally, we set a lower limit on the mass of a 'bosophilic' Higgs boson (e.g. one which couples only to $\gamma, W,$ and $Z$ bosons with standard model couplings) of 82 GeV/$c^2$ at 95% confidence level.
No description provided.
No description provided.
The inclusive one- and two-jet production cross-sections are measured in collisions of quasi-real photons radiated from the LEP beams at e+e− centre-of-mass energies \(\sqrt{s}_{\rm ee}=130\) and 136 GeV using the OPAL detector at LEP. Hard jets are reconstructed using a cone jet finding algorithm. The differential jet cross-sections \({\rm d}\sigma /{\rm d}E_{T}^{\rm jet}\) are compared to next-to-leading order perturbative QCD calculations. Transverse energy flows in jets are studied separately for direct and resolved two-photon events.
Inclusive one-jet cross section.
One-jet rapidity distribution.
Inclusive two-jet cross section.
None
NAME=THEORY DENOTES THE MONTE-CARLO GENERATED CROSS SECTIONS.
We report cross sections for the process γγ→pp¯ at center-of-mass energies W from 2.0 to 2.8 GeV. These results have been extracted from measurements of e+e−→e+e−pp¯ at an overall center-of-mass energy of 29 GeV, using the TPC/Two-Gamma facility at the SLAC storage ring PEP. Cross sections for the untagged mode [both photons nearly real] are shown to lie well above QCD predictions. Results are also presented for the single-tagged mode [one photon in the range 0.16<Q2<1.6 (GeV/c)2].
Data read from graph in preprint. Statistical errors only.
Data read from graph. Statistical errors only.
Data read from graph. Statistical errors only.
We report measurements of the two-photon processes e+e−→e+e−π+π− and e+e−→e+e−K+K−, at an e+e− center-of-mass energy of 29 GeV. In the π+π− data a high-statistics analysis of the f(1270) results in a γγ width Γ(γγ→f)=3.2±0.4 keV. The π+π− continuum below the f mass is well described by a QED Born approximation, whereas above the f mass it is consistent with a QCD-model calculation if a large contribution from the f is assumed. For the K+K− data we find agreement of the high-mass continuum with the QCD prediction; limits on f′(1520) and θ(1720) formation are presented.
Data read from graph. Additional overall systematic error 20% not included.
Data read from graph.. Additional overall systematic error 20% not included.
Data read from graph.. Additional overall systematic error 20% not included.. The Q**2 dependence is normalized to unity for the bin centred on Q**2 = 0.
We measured dσdt for p↑+p↑→p+p from P⊥2=4.50 to 5.09 (GeV/c)2 at 11.75 GeV/c. We used a 59%-polarized proton beam and a 71%-polarized proton target with both spins oriented perpendicular to the scattering plane. In these large-P⊥2 hard-scattering events, spin effects are very large and the ratio (dσdt)↑↑:(dσdt)↑↓ grows rapidly with increasing P⊥2, reaching a value of 4 at 90° (c.m.). Thus, hard elastic scattering, which is presumably due to the direct scattering of the protons' constituents, may only occur when the two incident protons' spins are parallel.
THE ERRORS INCLUDE STATISTICAL AND SYSTEMATIC ERRORS ADDED IN QUADRATURE. THE PARALLEL/ANTIPARALLEL SPIN CROSS SECTION RATIO IS (1+CNN)/(1-CNN).
The differential elastic p−p scattering cross section was measured at 6 GeV/c at the Argonne Zero Gradient Synchrotron in the range P⊥2=0.60−1.0 (GeV/c)2 using a 65% polarized target and a 75% polarized proton beam of intensity 3 × 109 protons/pulse. The polarization of the recoil proton was simultaneously measured with a well calibrated carbon-target polarimeter. All three polarizations were measured perpendicular to the horizontal scattering plane. Our results indicate that P and T invariance are both obeyed to good precision even at our largest P⊥2. Parity invariance implies that the eight single-flip transversity cross sections are zero, so our data gives the magnitudes of the eight remaining pure spin cross sections where all spins are measured. We find that the four double-flip transversity cross sections are nonzero.
No description provided.
THE FIVE INDEPENDENT PURE FOUR-SPIN CROSS SECTIONS AS DERIVED FROM THE EIGHT MEASURED THREE-SPIN CROSS SECTIONS ASSUMING P AND T INVARIANCE. THE ABSOLUTE DIFFERENTIAL CROSS SECTION VALUES ASSUME THAT THE SPIN-AVERAGED D(SIG)/DT IS 2.25, 1.17, 0.365 AND 0.167 MB/GEV**2 FOR EACH VALUE OF PT**2 RESPECTIVELY.
WOLFENSTEIN PARAMETERS. POL(NAME=A) IS (N000) OR (0N00), THE ANALYZING POWER AVERAGED OVER TARGET OR BEAM POLARIZATION. POL(NAME=P) IS (00N0), THE POLARIZATION PARAMETER. TIME-REVERSAL INVARIANCE REQUIRES THAT P = A. POL.POL(NAME=CNN) IS (NN00) USING T-INVARIANCE. POL.POL(NAME=DNN) IS (0N0N). POL.POL(NAME=KNN) IS (N00N). POL.POL(NAME=C3N) IS A COMPONENT OF THE TRIPLE SPIN CORRELATION TENSOR. PARITY INVARIANCE REQUIRES THAT C3N = P.
An experiment is described to measure the differential cross section for the charge-exchange reaction K 0 p → K + n from 0.6 to 1.5 GeV/ c incident kaon momentum in the angular range −0.65 < cos θ ∗ < 0.85 The calibration of the kaon beam by observation of K S 0 regeneration is also described. The differential cross sections are fitted with Legendre polynomials and compared with those from the time-reversed reaction using deuterium targets. Qualitative conclusions are drawn on the behaviour of particular charge-exchange amplitudes.
No description provided.
FITTED VALUES OF DIFFERENTIAL CROSS SECTION LEGENDRE COEFFICIENTS (4 TIMES USUAL DEFINITION).
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