We report measurements of the exclusive electroproduction of $K^+\Lambda$ and $K^+\Sigma^0$ final states from a proton target using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions $\sigma_T$, $\sigma_L$, $\sigma_{TT}$, and $\sigma_{LT}$ were extracted from the $\Phi$- and $\epsilon$-dependent differential cross sections taken with electron beam energies of 2.567, 4.056, and 4.247 GeV. This analysis represents the first $\sigma_L/\sigma_T$ separation with the CLAS detector, and the first measurement of the kaon electroproduction structure functions away from parallel kinematics. The data span a broad range of momentum transfers from $0.5\leq Q^2\leq 2.8$ GeV$^2$ and invariant energy from $1.6\leq W\leq 2.4$ GeV, while spanning nearly the full center-of-mass angular range of the kaon. The separated structure functions reveal clear differences between the production dynamics for the $\Lambda$ and $\Sigma^0$ hyperons. These results provide an unprecedented data sample with which to constrain current and future models for the associated production of strangeness, which will allow for a better understanding of the underlying resonant and non-resonant contributions to hyperon production.
Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.6 to 1.7 GeV.
Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.70 to 1.75 GeV.
Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.75 to 1.80 GeV.
Measurements of the analysing power for the p(pol)p --> ppeta reaction have been performed in the close-to-threshold energy region at beam momenta of p_{beam}=2.010 and 2.085 GeV/c, corresponding to excess energies of Q=10 and 36 MeV, respectively. The determined analysing power is essentially consistent with zero implying that the eta meson is produced predominantly in the s-wave at both excess energies. The angular dependence of the analysing power, combined with the hitherto determined isospin dependence of the total cross section for the eta meson production in nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S_{11}(1535) resonance, the process which intermediates the production of the eta meson, is predominantly due to the exchange of the pi meson between the colliding nucleons.
Analysing power measurements for excess energy 10 MeV.
Analysing power measurements for excess energy 36 MeV.
Differential cross sections for the exclusive reaction p⃗p→ppη observed via the η→π+π−π0 decay channel have been measured at Tbeam=2.15GeV, 2.50GeV, and 2.85GeV (excess energies 324MeV, 412MeV, and 554MeV). The influence of the N(1535)S11 resonance is clearly seen in the invariant mass and momentum dependent differential cross sections. The extracted resonance parameters are compatible with existing data. No significant evidence for further resonance contributions has been found. In addition, angular distributions of the ppη final state have been measured. The polar angle distribution of the η shows an anisotropy with respect to the beam axis for the lowest beam energy, which vanishes for the higher energies. The sign of this anisotropy is negative and expected to be sensitive to the dominant production mechanism. In contrast, the proton polar angle in the pp rest frame tends to be more strongly aligned along the beam axis with increasing beam energy. The analyzing power Ay is compatible with zero for all beam energies.
Differential cross section for incident kinetic energy 2.15 GeV, divided by the phase space as a function of the invariant mass of the ETA and the final state proton with the lower value of ABS(T). This is proportional to the square of the decay matrix element ABS(M)**2 of the P-ETA system.
Differential cross section for incident kinetic energy 2.50 GeV, divided by the phase space as a function of the invariant mass of the ETA and the final state proton with the lower value of ABS(T). This is proportional to the square of the decay matrix element ABS(M)**2 of the P-ETA system.
Differential cross section for incident kinetic energy 2.85 GeV, divided by the phase space as a function of the invariant mass of the ETA and the final state proton with the lower value of ABS(T). This is proportional to the square of the decay matrix element ABS(M)**2 of the P-ETA system.
Measurements of the eta meson production with a polarised proton beam in the reaction p(pol) p --> p p eta have been carried out at an excess energy of Q = 40 MeV. The dependence of the analysing power A_y on the polar angle theta^*_q of the eta meson in the center of mass system (CMS) has been studied. The data indicate the possibility of an influence of p- and d-waves to the close to threshold eta production.
Averaged value of the analyzing power and cross section as a function of the emmission angle of the ETA meson is the CM system.
The result of a feasibility study to measure the Λ polarization in associated K + – Λ electro-production is presented. This measurement was performed in the experimental Hall C at Jefferson Lab. The scattered electron was detected in the HMS spectrometer, and the electro-produced kaon and the proton from the Λ → pπ − decay were both detected in the SOS spectrometer. This quantity is very sensitive to the elementary p ( e , e ′ K ) Λ process and gives information on resonance production, and Regge exchange, among others. The result presented was measured at Q 2 =1.50 (GeV/c) 2 and cos θ Kγ CM =14°. The limits of the Λ polarization, with respect to the p γ × p K axis, were found to be −0.21 and +0.89 with a confidence level of 68%. The result is compared to theoretical predictions based on an effective hadronic field Lagrangian model and a Regge framework model.
LAMBDA polarization, with respect to the p_gamma x p_k axis.
The polarization in pion-nucleon charge exchange was measured at 6 GeV/c incident momentum for 0.1 (GeV/c)2 < |t| < 1.6 (GeV/c)2. Using the channel π+ n ↑ → π0p allowed precise measurement of the recoil proton for good rejection of inelastic events. The results are compared with previous experiments using channel π−p ↑ with or without detection of the recoil neutron.
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Differential cross sections and polarizations are presented for the reactions K − p → Λπ 0 , Λη , Λη ′ at 8.25 GeV/ c incident K − momentum. The data, which come from a high statistics experiment in the CERN 2 m bubble chamber, are compared with previous experimental results on the same reactions and with current theoretical ideas.
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The reactions K − p → Ξ 0 − (1320) K 0 + , Ξ − (1320) K + (890), Ξ 0 − (1530) K 0 − and Ξ 0 − (1530) K 0 + (890) are studied at 4.2 GeV/ c incident momentum. The data come from a high-statistics bubble chamber experiment with a sensitivity of ∼ 133 events/ μ b. Total anddifferential cross sections are presented. The results are compared to the SU(3)-related processes K + p → pK + and K + p → pK + (890) in the backward hemisphere. In the forward hemisphere “forbidden” peaks are observed and current ideas about them are discussed.
FULLY CORRECTED FOR ALL CUTS AND UNSEEN DECAY MODES.
TOTAL, FORWARD AND BACKWARD CROSS SECTIONS. FULLY CORRECTED FOR CUTS, K0 AND LAMBDA UNSEEN DECAY MODES AND OTHER K*(892) AND XI(1530P13) DECAYS. IN 3-BODY FINAL STATES, THETA REFERS TO THE PI-K SYSTEM.
No description provided.
In order to determine the ηNN coupling constant we have measured the two reactions K − p→ Λη and K − p→ Λπ 0 with a magnetic wire chamber spectrometer which contained a gamma counter for the γγ decays of π 0 and η. The Λ polarization and the differential cross sections are given. The latter have quite different u dependences. Their ratio is interpreted, in terms of a nucleon-Regge exchange model, as the effect of a small ηNN coupling constant for which we obtain G η NN 2 = G π NN 2 · (0.26 ± 0.10) as allowed by SU(3). The large value given by Heisenberg's non-linear field theory, G η NN 2 = G π NN 2 · 0.9, is excluded by this measurement if the characteristic u dependence of the Λπ 0 channel is attributed to N α Regge exchange.
Axis error includes +- 10/10 contribution.
No description provided.
Axis error includes +- 10/10 contribution.
Polarized cross sections for the reaction π − p → η n have been measured at 12 incident momenta between 1171 and 2267 MeV/ c . The data show that the polarization is small in the forward direction and there is a general trend for it to be large and positive near cos θ ∗ = 0.2 . These are the first published results on polarization effects in this channel in the resonance region. An energy-dependent partial-wave analysis has been performed and the couplings and branching fractions for decays of nucleon resonances to this channel are presented.
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