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Register a new userSeparation of the Longitudinal and Transverse Cross Sections in the p(eeK)Lambda and p(eeK)Sigma Reactions
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We report measurements of cross sections for the reaction p(e,eK)Y, for both the Lambda and Sigma_0 hyperon states, at an invariant mass of W=1.84 GeV and four-momentum transfers 0.5<Q2<2 (GeV/c)2. Data were taken for three values of virtual photon polarization, allowing the decomposition of the cross sections into longitudinal and transverse components. The Lambda data is a revised analysis of prior work, whereas the Sigma_0 results have not been previously reported.
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The determination of low-energy cross sections and branching ratios of the K$^-$ multi-nucleon absorption processes in $Lambda$p and $Sigma^0$p final states performed by the AMADEUS collaboration is presented. Low momentum K$^-$ ($p_mathrm{K} simeq$ 127 MeV/c) produced at the DA$Phi$NE collider are impinged on a Carbon target within the KLOE detector and the two and three nucleon absorption processes are disentangled by comparing the experimental data to phenomenological calculations. The $Lambda$p spectra are interpreted in terms of K$^-$ multi-nucleon absorption processes; the possible contribution of a K$^-$pp bound state is demonstrated to overlap with the two nucleon capture process, its absolute yield thus resulting indistinguishable.
High-statistics differential cross sections for the reactions gamma p -> p eta and gamma p -> p eta-prime have been measured using the CLAS at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The eta-prime results are the most precise to date and provide the largest energy and angular coverage. The eta measurements extend the energy range of the worlds large-angle results by approximately 300 MeV. These new data, in particular the eta-prime measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.
The $Lambda(1405)$ production in p+p collisions at 3.5 GeV and K$^-$-induced reactions is discussed. The shift of the measured spectral function of the $Lambda(1405)$ in p+p reactions does not match either theoretical calculations for p+p reactions or experimental observation in previous K$^-$-induced reactions. New experiments with stopped and in-flight $K^-$ are needed to study this initial state more in detail. The state of the art of the analysis is discussed.
Polarization properties of strange baryons produced in pp reactions, p + p -> p + Lambda^0 + K^+ and p + p -> p + Sigma^0 + K^$, near thresholds of the final states (p Lambda^0 K^+) and (p Sigma^0 K^+) are analysed relative to polarizations of colliding protons. The cross sections for pp reactions are calculated within the effective Lagrangian approach accounting for strong pp rescattering in the initial state of colliding protons with a dominant contribution of the one-pion exchange and strong final-state interaction of daughter hadrons (Eur. Phys. J. A 9, 425 (2000)).
The longitudinal or transverse spin transfer to Lambda and anti-Lambda hyperons in polarized proton-proton collisions is expected to be sensitive to the helicity or transversity distributions of strange and anti-strange quarks of the proton, and to the corresponding polarized fragmentation function. We report the first measurement of the transverse spin transfer to $Lambda$ and $bar Lambda$ along the polarization direction of the fragmenting quark, $D_{TT}$, in transversely polarized proton-proton collisions at 200 GeV with the STAR experiment at RHIC. The data correspond to an integrated luminosity of 18 pb$^{-1}$, and cover a kinematic range of |$eta$|< 1.2 and transverse momentum $p_T$ up to 8 GeV/c. We also report an improved measurement of the longitudinal spin transfer $D_{LL}$ to $Lambda$ and $bar Lambda$ with $p_T$ up to 6 GeV/c, using data with about twelve times larger figure-of-merit than the previously published STAR results. The prospects of hyperon polarization measurements in the forward pseudo-rapidity region (2.5<$eta$<4) in p+p collision in the year of 2021 and beyond will also be discussed, which is based on the STAR forward detector upgrade plan including a forward tracking system and a forward calorimeter system.
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