We report a high-statistics measurement of differential cross sections for the process gamma gamma -> pi^0 pi^0 in the kinematic range 0.6 GeV <= W <= 4.0 GeV and |cos theta*| <= 0.8, where W and theta* are the energy and pion scattering angle, respectively, in the gamma gamma center-of-mass system. Differential cross sections are fitted to obtain information on S, D_0, D_2, G_0 and G_2 waves. The G waves are important above W ~= 1.6 GeV. For W <= 1.6 GeV the D_2 wave is dominated by the f_2(1270) resonance while the S wave requires at least one additional resonance besides the f_0(980), which may be the f_0(1370) or f_0(1500). The differential cross sections are fitted with a simple parameterization to determine the parameters (the mass, total width and Gamma_{gamma gamma}B(f_0 -> pi^0 pi^0)) of this scalar meson as well as the f_0(980). The helicity 0 fraction of the f_2(1270) meson, taking into account interference for the first time, is also obtained.
Differential cross section for W = 1.27, 1.29 and 1.31 GeV.
Differential cross section for W = 1.33, 1.35 and 1.37 GeV.
Differential cross section for W = 1.39, 1.41 and 1.43 GeV.
We report on a high statistics measurement of the total and differential cross sections of the process gamma gamma -> pi^+ pi^- in the pi^+ pi^- invariant mass range 0.8 GeV/c^2 < W < 1.5 GeV/c^2 with 85.9 fb^{-1} of data collected at sqrt{s}=10.58 GeV and 10.52 GeV with the Belle detector. A clear signal of the f_0(980) resonance is observed in addition to the f_2(1270) resonance. An improved 90% confidence level upper limit Br.(eta'(958) -> pi^+ pi^-) < 2.9 x 10^{-3} is obtained for P- and CP-violating decay of the eta'(958) meson using the most conservative assumption about the interference with the background.
Total cross section.
We study the process $e^+e^-\to\pi^+\pi^-\pi^+\pi^-\gamma$, with a hard photon radiated from the initial state. About 60,000 fully reconstructed events have been selected from 89 $fb^{-1}$ of BaBar data. The invariant mass of the hadronic final state defines the effective \epem center-of-mass energy, so that these data can be compared with the corresponding direct $e^+e^-$ measurements. From the $4\pi$-mass spectrum, the cross section for the process $e^+e^-\to\pi^+\pi^-\pi^+\pi^-$ is measured for center-of-mass energies from 0.6 to 4.5 $GeV/c^2$. The uncertainty in the cross section measurement is typically 5%. We also measure the cross sections for the final states $K^+ K^- \pi^+\pi^-$ and $K^+ K^- K^+ K^-$. We observe the $J/\psi$ in all three final states and measure the corresponding branching fractions. We search for X(3872) in $J/\psi (\to\mu^+\mu^-) \pi^+\pi^-$ and obtain an upper limit on the product of the $e^+e^-$ width of the X(3872) and the branching fraction for $X(3872) \to J/\psi\pi^+\pi^-$.
Measured PI+ PI- PI+ PI- cross sections. The errors are statistical only.
The reaction gamma p --> K0 Sigma+ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross section and the polarization of the Sigma+ as a function of the kaon production angle in the centre-of-mass system, cos(Theta_K^{c.m.}), and the photon energy. The cross section is lower and varies less with photon energy and kaon production angle than that of gamma p --> K+ Sigma0. The Sigma+ is polarized predominantly at cos(Theta_K^{c.m.}) \approx 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.
Polarization parameter of the SIGMA+ as a function of angle in two photon energy ranges.
We measured the inclusive electron-proton cross section in the nucleon resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2 with the CLAS detector. The large acceptance of CLAS allowed for the first time the measurement of the cross section in a large, contiguous two-dimensional range of Q**2 and x, making it possible to perform an integration of the data at fixed Q**2 over the whole significant x-interval. From these data we extracted the structure function F2 and, by including other world data, we studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate higher twist contributions. The small statistical and systematic uncertainties of the CLAS data allow a precise extraction of the higher twists and demand significant improvements in theoretical predictions for a meaningful comparison with new experimental results.
No description provided.
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We report measurements of the asymmetry A_parallel for inclusive hadron production on longitudinally polarized proton and deuteron targets by circularly polarized photons. The photons were produced via internal and external bremsstrahlung from an electron beam of 48.35 GeV. Asymmetries for both positive and negative signed hadrons, and a subset of identified pions, were measured in the momentum range 10<P<30 GeV at 2.75 and 5.5 degrees. Small non-zero asymmetries are observed for the proton, while the deuteron results are consistent with zero. Recent calculations do not describe the data well.
The asymmetry for polarized photoproduction of inclusive hadrons from a polarized proton target. The errors are statistical only.
The asymmetry for polarized photoproduction of inclusive identified pions from a polarized proton target. The errors are statistical only.
Results on the elastic K − π − scattering have been obtained from a study of the K − π − system in 15 000 events of the type K − p→K − π − p π + at a K − beam momentum of 4.25 GeV/ c . The on-mass-shell values of the spherical harmonic moments of the K − π − scattering angular distribution and the K − π − elastic cross section have been obtained by extrapolation to the pion pole. From these values we determined the s- and p-wave phase shifts δ 0 3 and δ 1 3 as a function of the effective mass of the K − π − system between threshold and 1.25 GeV/ c 2 . The value of | δ 0 3 | is smaller than 17° for all mass values and the existence of a p-wave cannot be neglected. At m K − π − = 1.18 GeV/ c 2 there are two solutions for the phase shifts. On the average, the cross section of the K − π − elastic scattering over the region of the effective mass considered amounts to approximately 2.5 mb.
The errors are statistical.
The yields and average transverse momenta of pions, kaons, and antiprotons produced at the Fermilab p¯p collider at s=300, 540, 1000, and 1800 GeV are presented and compared with data from the energies reached at the CERN collider. We also present data on the dependence of average transverse momentum 〈pt〉 and particle ratios as a function of charged particle density dNcdη; data for particle densities as high as six times the average value, corresponding to a Bjorken energy density 6 GeV/fm3, are reported. These data are relevant to the search for quark-gluon phase of QCD.
No description provided.
No description provided.
The process γγ→π+π−π+π− has been investigated in reactions of the typee+e−→e+e−π+π−π+π− in the single tag mode. The range of the four momentum squared of one of the virtual photons was 0.28 GeV2/c2≦Q2≦3.6 GeV2/c2, the average being 〈Q2〉=0.92 GeV2/c2; the other photon was quasi real. The reaction is mainly described by the channels γγ→ρ0ρ0 and γγ→4π (phase space), occuring with about equal probability. TheQ2-dependence of the cross section is in agreement with the ρ form factor.
Data read from graph.. Additional overall systematic error 25%.
We present a measurement of the polarization of Antilambda hyperons produced in nu_mu charged current interactions. The full data sample from the NOMAD experiment has been analyzed using the same V0 identification procedure and analysis method reported in a previous paper for the case of Lambda hyperons. The Antilambda polarization has been measured for the first time in a neutrino experiment. The polarization vector is found to be compatible with zero.
Lambdabar polarization in regions of the Bjorken scaling variable X.
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