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 present measurements of the differential cross section and Lambda recoil polarization for the gamma p to K+ Lambda reaction made using the CLAS detector at Jefferson Lab. These measurements cover the center-of-mass energy range from 1.62 to 2.84 GeV and a wide range of center-of-mass K+ production angles. Independent analyses were performed using the K+ p pi- and K+ p (missing pi -) final-state topologies/ results from these analyses were found to exhibit good agreement. These differential cross section measurements show excellent agreement with previous CLAS and LEPS results and offer increased precision and a 300 MeV increase in energy coverage. The recoil polarization data agree well with previous results and offer a large increase in precision and a 500 MeV extension in energy range. The increased center-of-mass energy range that these data represent will allow for independent study of non-resonant K+ Lambda photoproduction mechanisms at all production angles.
Differential cross section as a function of COS(THETA(K)) for the centre-of-mass range 1.62-1.63 GeV.
Differential cross section as a function of COS(THETA(K)) for the centre-of-mass range 1.63-1.64 GeV.
Differential cross section as a function of COS(THETA(K)) for the centre-of-mass range 1.64-1.65 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.
The cross section for the reaction $ e p \to e^{\prime} p \pi^{+} \pi^{-}$ was measured in the resonance region for 1.4$<$W$<$2.1 GeV and 0.5$<Q^{2}<$1.5 GeV$^{2}$/c$^{2}$ using the CLAS detector at Jefferson Laboratory. The data shows resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on $N^{*}$ and $\Delta$ states shows an evident discrepancy. A better description of the data is obtained either by a sizeable change of the properties of the $P_{13}$(1720) resonance or by introducing a new baryon state, not reported in published analyses.
Measured cross section DSIG/DM(PI+PI-) for the W range 1400 to 1425GeV.
Measured cross section DSIG/DM(PI+PI-) for the W range 1425 to 1450GeV.
Measured cross section DSIG/DM(PI+PI-) for the W range 1450 to 1475GeV.
Results are presented on the charge exchange reaction\(\bar pp \to \bar nn\) and\(\bar np\) annihilations from bubble chamber exposures to antiproton beam of momenta 700 and 760 MeV/c. The differential cross section of\(\bar pp \to \bar nn\) shows a forward spike followed by a clear dip bump structure. Total annihilation cross section of\(\bar np\) for average\(\bar n\) momentum of 700 MeV/c has been evaluated to be 55.4±2.2 mb. The multiplicity, Feynmanx andpT2 distributions for inclusive charged pions in\(\bar pp\) and\(\bar np\) annihilations are found to be similar. The emission of charged pions from\(\bar np\) annihilations are found to be consistent with thermodynamic models with temperature ∼110 MeV.
No description provided.
No description provided.
No description provided.
Differential cross sections and photon beam asymmetries have been measured for the gamma n -> K+ Sigma- and gamma p -> K+ Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of Egamma=1.5-2.4 GeV at 0.6<cosTheta<1. The cross section ratio of sigma(K+Sigma-)/sigma(K+Sigma0), expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+Sigma- reaction, large positive asymmetries are observed indicating the dominance of the K*-exchange. A large difference between the asymmetries for the K+Sigma- and K+Sigma0 reactions can not be explained by simple theoretical considerations.
Differential cross section for GAMMA P --> K+ SIGMA0.. Errors are statistical only.
Photon beam asymmetry for GAMMA N --> K+ SIGMA-.. Errors are statistical only.
Photon beam asymmetry for GAMMA P --> K+ SIGMA0.. Errors are statistical only.
Differential cross sections and photon beam asymmetries for the gamma p rightarrow K+ Lambda and gamma p rightarrow K+ Sigma0 reactions have been measured in the photon energy range from 1.5 GeV to 2.4 GeV and in the angular range from Theta_{cm} = 0 to 60 of the K+ scattering angle in the center of mass system at the SPring-8/LEPS facility. The photon beam asymmetries for both the reactions have been found to be positive and to increase with the photon energy. The measured differential cross sections agree with the data measured by the CLAS collaboration at cosTheta_{cm}<0.9 within the experimental uncertainties, but the discrepancy with the SAPHIR data for the K+Lambda reaction is large at cosTheta_{cm}>0.9. In the K+Lambda reaction, the resonance-like structure found in the CLAS and SAPHIR data at W=1.96 GeV is confirmed. The differential cross sections at forward angles suggest a strong K-exchange contribution in the t-channel for the K+Lambda reaction, but not for the K+Sigma0 reaction.
Photon beam asymmetries for the two reactions as a function of CM angle for photon beam energy 1.55 GeV (W=1.947 GeV).
Photon beam asymmetries for the two reactions as a function of CM angle for photon beam energy 1.65 GeV (W=1.994 GeV).
Photon beam asymmetries for the two reactions as a function of CM angle for photon beam energy 1.75 GeV (W=2.041 GeV).
Cross sections for the $\gamma p \to K^+ \Lambda$ have been measured at backward angles using linearly polarized photons in the range 1.50 to 2.37 GeV. In addition, the beam asymmetry for this reaction has been measured for the first time at backward angles. The $\Lambda$ was detected at forward angles in the LEPS spectrometer via its decay to $p\pi^-$ and the K^+ was inferred using the technique of missing mass. These measurements, corresponding to kaons at far backward angles in the center-of-mass frame, complement similar CLAS data at other angles. Comparison with theoretical models shows that the reactions in these kinematics provide further opportunities to investigate the reaction mechanisms of hadron dynamics.
Differential cross sections as a function of the Mandelstam variable U for photon beam energy 1.5 to 1.8 GeV.
Differential cross sections as a function of the Mandelstam variable U for photon beam energy 1.8 to 2.1 GeV.
Differential cross sections as a function of the Mandelstam variable U for photon beam energy 2.1 to 2.4 GeV.
The production of thef0 in two photon collisions, with the subsequent decayf0→π+π− has been observed in the CELLO detector at PETRA. Thef0 peak was found to lie on a dipion continuum and to be shifted downwards in mass by ≃50 MeV/c2. The ππ mass spectrum from 0.8 to 1.5 GeV/c2 was well fitted by the model of Mennessier using only a unitarised Born amplitude and helicity 2f0 amplitude. The previously observed mass shift and distortion of thef0 peak are explained by strong interference between the Born andf0 amplitudes. The only free parameter in the fit of the data to the model is the radiative widthΓγγ(f0). It was found that:Γγγ(f0)=2.5±0.1±0.5 keV where the first (second) quoted errors are statistical (systematic).
Data read from graph.
Data read from graph.
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.
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