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Register a new userK$^-$ multi-nucleon absorption cross sections and branching ratios in $Lambda$p and $Sigma^0$p final states
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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.
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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)).
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.
Differential cross sections for the reaction $gamma p to K^{*0} Sigma^+$ are presented at nine bins in photon energy in the range from 1.7 to 3.0 GeV. The kstar was detected by its decay products, $K^+pi^-$, in the CLAS detector at Jefferson Lab. These data are the first kstar photoproduction cross sections ever published over a broad range of angles. Comparison with a theoretical model based on the vector and tensor $K^*$-quark couplings shows good agreement with the data in general, after adjusting the models two parameters in a fit to our data. Disagreement between the data at forward angles and the global angle-energy fit to the model suggests that the role of scalar $kappa$ meson exchange in $t$-channel diagrams should be investigated.
The reaction pp -> K+ + (Lambda p) was measured at Tp=1.953 GeV and Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. The large final state enhancement near the Lambda p threshold can be described using the standard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously the Lambda p invariant mass spectrum and the total cross section data of the free Lambda p scattering.
We report on the $W$ and $Z/gamma^*$ differential and total cross sections as well as the $W^+$/$W^-$ and $(W^+ + W^-)$/$(Z/gamma^*)$ cross-section ratios measured by the STAR experiment at RHIC in $p+p$ collisions at $sqrt{s} = 500$ GeV and $510$ GeV. The cross sections and their ratios are sensitive to quark and antiquark parton distribution functions. In particular, at leading order, the $W$ cross-section ratio is sensitive to the $bar{d}/bar{u}$ ratio. These measurements were taken at high $Q^2 sim M_W^2,M_Z^2$ and can serve as input into global analyses to provide constraints on the sea quark distributions. The results presented here combine three STAR data sets from 2011, 2012, and 2013, accumulating an integrated luminosity of 350 pb$^{-1}$. We also assess the expected impact that our $W^+/W^-$ cross-section ratios will have on various quark distributions, and find sensitivity to the $bar{u}-bar{d}$ and $bar{d}/bar{u}$ distributions.
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