K^+K^- production in two-photon collisions has been studied using a large data sample of 67 fb^{-1} accumulated with the Belle detector at the KEKB asymmetric e^+e^- collider. We have measured the cross section for the process gamma gamma -> K^+ K^- for center-of-mass energies between 1.4 and 2.4 GeV, and found three new resonant structures in the energy region between 1.6 and 2.4 GeV. The angular differential cross sections have also been measured.
Cross section for two photon production of K+ K- in the polar angular region ABS(COS(THETA*)) < 0.6.
Differential cross sections DSIG/DCOS(THETA) for the W range 1.40 to 1.56 GeV.. Statistical errors only.
Differential cross sections DSIG/DCOS(THETA) for the W range 1.56 to 1.72 GeV.. Statistical errors only.
Elastic $\rho~0$ photoproduction has been measured using the ZEUS detector at HERA. Untagged photoproduction events from $ep$ interactions were used to measure the reaction $\gamma p \rightarrow \rho~0 p$ ($\rho~0 \rightarrow \pi~+ \pi~-$) at photon-proton centre-of-mass energies between 60 and 80GeV and $|t|<0.5$GeV$~2$, where $t$ is the square of the four-momentum transferred at the proton vertex. The differential cross section $d\sigma/dM_{\pi\pi}$, where $M_{\pi\pi}$ is the invariant mass of the two pions, and the integrated cross section, $\sigma_{\gamma p\rightarrow \rho~0 p}$, are presented; the latter was measured to be $14.7\pm 0.4(\mbox{stat.})\pm2.4(\mbox{syst.})\mu\mbox{b}$. The differential cross section $d\sigma/dt$ has an approximately exponential shape; a fit of the type $A~{\prime}_{t} \exp{(-b~{\prime}_{t}|t| + c~{\prime}_{t} t~2)}$ yields a $t$-slope $b~{\prime}_{t}= 9.9\pm1.2(\mbox{stat.})\pm 1.4(\mbox{syst.})\mu\mbox{b}$. The results, when compared to low energy data, show a weak energy dependence of both $\sigma_{\gamma p\rightarrow \rho~0 p}$ and of the $t$-slope. The $\rho~0$ is produced predominantly with transverse polarisation, demonstrating that $s$-channel helicity conservation holds at these energies.
Integrated cross section for exclusive rho0 <pi+ pi-> production where 2Mpi < Mpi pi < Mrho + 5width0.
No description provided.
Applying the Spital and Yennie method to each t bin. No errors given.
The $f_1(1285)$ meson with mass $1281.0 \pm 0.8$ MeV/$c^2$ and width $18.4 \pm 1.4$ MeV (FWHM) was measured for the first time in photoproduction from a proton target using CLAS at Jefferson Lab. Differential cross sections were obtained via the $\eta\pi^{+}\pi^{-}$, $K^+\bar{K}^0\pi^-$, and $K^-K^0\pi^+$ decay channels from threshold up to a center-of-mass energy of 2.8 GeV. The mass, width, and an amplitude analysis of the $\eta\pi^{+}\pi^{-}$ final-state Dalitz distribution are consistent with the axial-vector $J^P=1^+$ $f_1(1285)$ identity, rather than the pseudoscalar $0^-$ $\eta(1295)$. The production mechanism is more consistent with $s$-channel decay of a high-mass $N^*$ state, and not with $t$-channel meson exchange. Decays to $\eta\pi\pi$ go dominantly via the intermediate $a_0^\pm(980)\pi^\mp$ states, with the branching ratio $\Gamma(a_0\pi \text{ (no} \bar{K} K\text{)}) / \Gamma(\eta\pi\pi \text{(all)}) = 0.74\pm0.09$. The branching ratios $\Gamma(K \bar{K} \pi)/\Gamma(\eta\pi\pi) = 0.216\pm0.033$ and $\Gamma(\gamma\rho^0)/\Gamma(\eta\pi\pi) = 0.047\pm0.018$ were also obtained. The first is in agreement with previous data for the $f_1(1285)$, while the latter is lower than the world average.
Differential cross section for $\gamma p \to f_1(1285) p \to \eta \pi^+ \pi^- p$ in nanobarns/steradian. The point-to-point uncertainties are given in separate statistical and systematic contributions.
We have studied the properties of pion production in the reaction γ →3 π + 3 π − in the energy range 1.6⩽ W γγ ⩽7.5 GeV with the CELLO detector at PETRA. We present the topological cross section both for Q 2 ≈0 (anti-tag) and Q 2 ≈0 (single-tag). The Q 2 dependence of the cross section is flatter than the GVDM prediction. The distribution of the production angle of the pions in the CMS peaks at small angles, indicating a peripheral process. In accordance with the VDM picture the p T distribution of the pions manifests an exponential fall-off. Like sign pion pairs were found to be Bose-Einstein correlated. We use this correlation to estimate the spatial dimensions of the interaction region.
No description provided.
No description provided.
No description provided.
Neutral pion photoproduction has been measured from 550 to 1500 MeV with the GRAAL facility, located at the ESRF in Grenoble. Differential cross-section and beam asymmetry have been measured over a wi
Measured differential angular distribution for incident photon energy 555 Mev.
Measured differential angular distribution for incident photon energy 578 Mev.
Measured differential angular distribution for incident photon energy 597 Mev.
Photoproduction of the cascade resonances has been investigated in the reactions $\gamma p \to K^+ K^+ (X)$ and $\gamma p \to K^+ K^+ \pi^- (X)$. The mass split of the $\Xi$ doublet is measured to be $5.4\pm 1.8$ MeV/c$^2$, consistent with existing measurements. The differential (total) cross sections for the $\Xi^{-}$ have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV, and are consistent with a possible production mechanism of $Y^*\to K^+\Xi^-$ through a $t$-channel process. The reaction $\gamma p \to K^+ K^+ \pi^-[\Xi^0]$ has also been investigated in search of excited cascade resonances. No significant signal of excited cascade states other than the $\Xi^-(1530)$ is observed. The cross section results of the $\Xi^-(1530)$ have also been obtained for photon beam energies from 3.35 to 4.75 GeV.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.79 Gev.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.89 Gev.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.99 Gev.
High-statistics differential cross sections and spin density matrix elements for the reaction $\gamma p \to p \omega$ have been measured using the CLAS at Jefferson Lab for center-of-mass (CM) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide CM energy bins, each subdivided into $\cos{\theta_{CM}^{\omega}}$ bins of width 0.1. These are the most precise and extensive $\omega$ photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.
Differential cross section for the W range 1.72 to 1.73 GeV.
Differential cross section for the W range 1.73 to 1.74 GeV.
Differential cross section for the W range 1.74 to 1.75 GeV.
Differential cross sections for the reaction $\gamma p \to K^{*0} \Sigma^+$ are presented at nine bins in photon energy in the range from 1.7 to 3.0 GeV. The \kstar was detected by its decay products, $K^+\pi^-$, in the CLAS detector at Jefferson Lab. These data are the first \kstar photoproduction cross sections ever published over a broad range of angles. Comparison with a theoretical model based on the vector and tensor $K^*$-quark couplings shows good agreement with the data in general, after adjusting the model's two parameters in a fit to our data. Disagreement between the data at forward angles and the global angle-energy fit to the model suggests that the role of scalar $\kappa$ meson exchange in $t$-channel diagrams should be investigated.
Cross sections with total uncertainties.
Cross sections with total uncertainties.
The reaction e^+e^- -> e^+e^- proton antiproton is studied with the L3 detector at LEP. The analysis is based on data collected at e^+e^- center-of-mass energies from 183 GeV to 209 GeV, corresponding to an integrated luminosity of 667 pb^-1. The gamma gamma -> proton antiproton differential cross section is measured in the range of the two-photon center-of-mass energy from 2.1 GeV to 4.5 GeV. The results are compared to the predictions of the three-quark and quark-diquark models.
Total cross section for P PBAR production at a mean centre-of-mass energy of 197 GeV.
The cross section as a function of W for ABS(COS(THETA)) < 0.6.
The differential cross section as a function of COS(THETA*) for three W ranges.
Differential cross sections of the reaction gamma d to K+ Sigma- (p) have been measured with the CLAS detector at Jefferson Lab using incident photons with energies between 1.1 and 3.6 GeV. This is the first complete set of strangeness photoproduction data on the neutron covering a broad angular range. At energies close to threshold and up to E_gamma ~ 1.8 GeV, the shape of the angular distribution is suggestive of the presence of s-channel production mechanisms. For E_gamma > 1.8 GeV, a clear forward peak appears and becomes more prominent as the photon energy increases, suggesting contributions from t-channel production mechanisms. These data can be used to constrain future analysis of this reaction.
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