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 = 1.33, 1.35 and 1.37 GeV.
Total cross section for the cos(theta*) ranges 0.0 to 0.6 and 0.0 to 0.8.
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.
The reactione+e−→e+e− A2 (1320) has been observed by detecting the decayA2→π+,π-π0. The two-photon width of theA2 has been measured to be Г(A2→γγ)=(0.09±0.27 (stat)±0.16 (syst)) keV. The cross section σ(γγ→π+,π-π0 has been determined outside theA2 resonance region.
Data read off a graph.
An analysis of the production ofKS0KS0 andK±Ks0π∓ by two quasi-real photons is presented. The cross section forγγ→K0\(\overline {K^0 } \), which is given for the γγ invariant mass range fromK\(\bar K\) threshold to 2.5 GeV, is dominated by thef′(1525) resonance and an enhancement near theK\(\bar K\) threshold. Upper limits on the product of the two-photon width times the branching ratio intoK\(\bar K\) pairs are given forΘ(1700),h(2030), and ξ(2220). For exclusive two-photon production ofK±Ks0π∓ no significant signal was observed. Upper limits are given on the cross section ofγγ→K+\(\overline {K^0 } \)π− orK−K0π+ between 1.4 and 3.2 GeV and on the product of the γγ width times the branching ratio into theK\(\bar K\)π final states for theηc(2980) and the ι(1440), yieldingΓ(γγ)→i(1440))·BR(i(1440)→K\(\bar K\)π<2.2 keV at 95% C.L.
Data read from graph.. Corrected for the angular distribution, which is assumed to be sin(theta)**4 for W > 1.14 GeV and isotropic in the first bin.
The π+ photoproduction cross section in hydrogen has been measured at 180° for photon energies from 0.22 to 3.1 GeV by detecting the pion in the backward direction. The statistical accuracy of the measurements varies typically from 3 to 10% depending on the energy. The data are compared with other recent experimental results and predictions of phenomenological theories.
No description provided.
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.
Single pi0 photoproduction has been studied with the CB-ELSA experiment at Bonn using tagged photon energies between 0.3 and 3.0 GeV. The experimental setup covers a very large solid angle of about 98% of 4 pi. Differential cross sections (d sigma)/(d Omega) have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gamma p --> N* (Delta*) --> p pi0. A combined analysis including the data presented in this letter along with other data sets reveals contributions from known resonances and evidence for a new resonance N(2070)D15.
Total cross section for GAMMA P --> P PI0 obtained by integration of the angular distributions and extrapolation into the forward and backward regions using the PWA result.
Differential cross section as a function of c.m. angle for the photon energy range 425 to 550 GeV.
We report the first measurement of the neutron electric form factor $G_E^n$ via $\vec{d}(\vec{e},e'n)p$ using a solid polarized target. $G_E^n$ was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia, $^{15}$ND$_3$. The measurement was performed in Hall C at Thomas Jefferson National Accelerator Facility (TJNAF) in quasi free kinematics with the target polarization perpendicular to the momentum transfer. The electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle segmented detector. We find $G_E^n = 0.04632\pm0.00616 (stat.) \pm0.00341 (syst.)$ at $Q^2 = 0.495$ (GeV/c)$^2$.
No description provided.
At the Bonn 2.5 GeV electron synchrotron the first measurements of the target asymmetry for the reaction γ + n ↑ → π − + p have been performed. The negative pions were detected in a magnetic spectrometer at a constant pion c.m. angle of 40° and photon energies between 0.45 GeV and 2.0 GeV. Deuterated butanol was used as target material. The polarization of the deuterons was about 16%. The results show a significant difference from the previously measured π + asymmetry.
No description provided.
Resonance production in the γγ reactionse+e−→e+e+e−π0π0 ande+e−π0η has been studied with the JADE detector at PETRA. The decay widths into γγ of thef2(1270),a0(980) anda2(1320) were measured to be\(\Gamma _{\gamma \gamma } (f_2 (1270)) = 3.19 \pm 0.09_{ - 0.38}^{ + 0.22} \) Kev,Γλλ(a0(980))=0.28±0.04±0.10 KeV/BR(a0(980)→π0η) andΓλλ(a2(1320))=1.01±0.14±0.22KeV. For thef0(975) andf4(2050) upper limits of the widths were obtained,Γλλ(f0(975))<0.6 KeV, andΓλλ(f4(2050))<1.1 KeV, both at the 95% C.L. Assuming that the spin 0 background under thef2(1270) is small, thef2(1270) was found to be produced exclusively in a helicity 2 state. The helicity 0 contribution is <15% at the 95% C.L. The cross section forλλ→π0π0 in the mass range 2.0–3.5 GeV/c2 was measured for the first time. Since the cross section forλλ→π+π− is a factor ∼2 larger, ππ production in this range can be interpreted as taking place via isospin 0 production.
Data read from graph.. Event distributions uncorrected for angular acceptance and the efficiency with energy of the detector RE = GAMMA GAMMA --> PI0 PI0.
Data read from graph.
Data read from graph.. Event distributions uncorrected for angular acceptance and the efficiency with energy of the detector RE = GAMMA GAMMA --> PI0 PI0.