Total and differential cross sections for exclusive production of proton-antiproton pairs in photon-photon collisions have been measured using the JADE detector at PETRA. The total cross section in the CM angular |cos θ ∗ | < 0.6 reaches a maximum value of 3.8 nb for a γγ invariant mass of W γγ = 2.25 GeV, and decreases rapidly for higher values of W γγ . In the range 2.0 GeV < W γγ < 2.6 GeV the angular distribution is not isotopic. The nucleons are preferentially emitted at large angles to the collision axis.
Data read off graph.
Data read off graph.
The SATURNE II polarized proton beam and the Saclay frozen spin polarized proton target were used to measure the total cross section difference Δσ T = −2 σ 1 tot at 26 energies between 0.43 and 2.4 GeV. Here Δσ T is the total cross section difference for transverse beam and target spins parallel and antiparallel, respectively, and σ 1tot is one of spin-dependent terms in the total cross section σ tot . The energy dependence of Δσ T below 1 GeV shows similar structures as for Δσ L . An additional minimum appears at about 1.3 GeV, which involves a structure in singlet spin partial waves.
Errors contain both statistics and systematics.
We have performed absolute measurements of the differential cross section for elastic e−p scattering in the range of momentum transfer from Q2=2.9 to 31.3 (GeV/c)2. Combined statistical and systematic uncertainties in the cross-section measurements ranged from 3% at low Q2 to 19% at high Q2. These data have been used to extract the proton magnetic form factor GMp(Q2). The results show a smooth decrease of Q4GMp with momentum transfer above Q2=10 (GeV/c)2. These results are compared with recent predictions of perturbative QCD.
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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 evidence for inclusive F-meson production in B-meson decay. The product branching fraction B(B→FX)B(F+→φπ+) is measured to be 0.0038±0.010. The F momentum spectrum indicates the presence of a large component of two-body final states in the decay B→FX.
No description provided.
DATA SAMPLE CONSISTED OF 77 1/PB. DATA TAKEN ON THE PEAK OF THE UPSI(10575).
CONTINUUM DATA SAMPLE CONSISTED OF 36 1/PB. ENERGY JUST BELOW THE UPSI(10575).
We have studied the processpp→γγ+X at\(\sqrt s= 63 GeV\) GeV in the central rapidity region. We report a positive signal at 96% C.L., a ratio γγ/e+e−=4.0±3.0 when the transverse momentum of each photon is above 2 GeV/c, and a cross-sectiondσ/dydMγγ=(5.5±2.7)×10−34 cm2/GeV when |y|<0.5,4<Mγγ<6 GeV.
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We have measured the processe+e−→e+e−+hadrons, where one of the scattered electrons was detected at large angles, withQ2 ranging from 7 to 70 (VeV/c)2. The photon structure functionF2γ(x, Q2) was determined at an averageQ2 of 23 (GeV/c)2. The measurements were compared to theoretical predictions of the Quark Parton Model and Quantum Chromodynamics. In both models a hadronic part was added. Within the errors the data are in agreement with the QPM using quark masses of 300 MeV/c2 for the light quarks. The data also agree with a QCD calculation including higher order corrections. A fit yielded a\(\Lambda _{\overline {MS} } \) value of 140−65+190 MeV, where the errors include statistical and systematic uncertainties.
No description provided.
The experimental results are presented for ratios of ν-meson inclusive differential cross sections in 10.5 GeV/ c π + p, π + D and π + A collisions, R D/p =(d σ /d x F )( π + D → η X)/ (d σ /d x F ) π + p→ η X), R A =(d σ /d x F )( π + D→ η X) in the beam fragmentation region. The results are based on the statistics of ≈ 5 × 10 4 detected η → 2 γ decays. It is shown that the power α in the parametrisation R A ≈ A α ( xf ) does not change significantly with x F and its mean value is 0.50±0.02. The lower limit is obtained for the effective coefficient with string tension in the colour string model, κ ⩾ 3 GeV/fm. The observed growth of R A with x F can be explained by an assumption of a neutron halo with the factor H ≈ 4 in the nuclei.
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BEBC filled in turn with hydrogen, and with a neon-hydrogen mixture, was exposed to the CERN SPS wide band neutrino and antineutrino beams. The ratios of the charged-current cross sections per nucleon, σ(νH 2 ) σ(ν Ne ) and σ( ν H 2 ) σ( ν Ne ) , between 20 and 300 GeV were found to be 0.656 ± 0.020 and 1.425 ± 0.052, respectively. Multiplying these ratios by the revised cross sections in neon, σ(ν Ne ) E = (0.723 ± 0.038) × 10 −38 cm 2 / GeV per nucleon and σ( ν Ne ) E = (0.351 ± 0.019) × 10 −38 cm 2 / GeV per nucleon, and their ratio, σ( ν Ne ) σ(ν Ne ) = 0.485 ± 0.020 ,, yields values for the total charged-current cross sections on protons, σ(νp)/ E and σ( ν p ) E , of (0.474 ± 0.029) × 10 −38 cm 2 /GeV and (0.500 ± 0.032) × 10 −38 cm 2 /GeV. respectively, and a value for the ratio σ( ν p ) σ(ν p ) of 1.053 ± 0.066.
No description provided.
The pion form factor has been measured in the space-like q 2 region 0.014 to 0.26 (GeV/ c ) 2 by scattering 300 GeV pions from the electrons of a liquid hydrogen target. A detailed description is given of the apparatus, data analysis and corrections to the data. The mean square charge radius extracted from the data is model-dependent. We find that a form which includes a realistic description of the form factor phase gives a similar results to the naive pole form, and conclude 〈r 2 π 〉 = 0.438±0.008 fm 2 .
No description provided.
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