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Register a new userRatio between two $Lambda$ and $bar{Lambda}$ production mechanisms in $p$ scattering
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B. Hoeneisen
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We consider $Lambda$ and $bar{Lambda}$ production in a wide range of proton scattering experiments. The produced $Lambda$ and $bar{Lambda}$ may or may not contain a diquark remnant of the beam proton. The ratio of these two production mechanisms is found to be a simple universal function $r = [ kappa/(y_p - y) ]^i$ of the rapidity difference $y_p - y$ of the beam proton and the produced $Lambda$ or $bar{Lambda}$, valid over four orders of magnitude, from $r approx 0.01$ to $r approx 100$, with $kappa = 2.86 pm 0.03 pm 0.07$, and $i = 4.39 pm 0.06 pm 0.15$.
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With the PICR hydrodynamic model, we study the polarization splitting between $Lambda$ and $bar{Lambda}$ at RHIC BES energy range, based on the meson field mechanism. Our results fit to the experimental data fairly well. Besides, two unexpected effect emerges: (1) the baryon density gradient has non-trivial and negative contribution to the polarization splitting; (2) for 7.7 GeV Au+Au collisions within the centrality range of 20%-50%, the polarization splitting surprisingly increases with the centrality decreases. The second effect might help to explain the significant signal of polarization splitting measured in STARs Au+Au 7.7 Gev collisions.
We investigate the photoproduction of Lambda(1405,1/2^-) = Lambda* off the proton target using the effective Lagrangian in the Born approximation. We observed that, depending on the choice of the K* N Lambda* coupling strength, the total cross section becomes 0.1 <~ sigma_Lambda* <~ 0.2 mu b near the threshold and starts to decrease beyond E_gamma ~ 1.6 GeV, and the angular dependence shows a mild enhancement in the forward direction. It turns out that the energy dependence of the total cross section is similar to that shown in the recent LEPS experiment. This suggests that the production mechanism of the Lambda* is dominated by the s-channel contribution.
To understand the nature of two poles for the $Lambda(1405)$ state, we revisit the interactions of $bar{K}N$ and $piSigma$ with their coupled channels, where two-poles structure is found in the second Riemann sheet. We also dynamically generate two poles in the single channel interaction of $bar{K}N$ and $piSigma$, respectively. Moreover, we make a further study of two poles properties by evaluating the couplings, the compositeness, the wave functions, and the radii for the interactions of four coupled channels, two coupled channels and the single channel. Our results show that the nature of two poles is unique. The higher-mass pole is a pure $bar{K} N$ molecule, and the lower-mass one is a compositeness of mainly $pi Sigma$ with tiny component $bar{K} N$. From our results, one can conclude that the $Lambda(1405)$ state would be overlapped with two different states of the same quantum number.
Thermal vorticity in non-central Au+Au collisions at energies $7.7 leq sqrt{s} leq 62.4$ GeV is calculated within the UrQMD transport model. Tracing the $Lambda$ and $bar{Lambda}$ hyperons back to their last interaction point we were able to obtain the temperature and the chemical potentials at the time of emission by fitting the extracted bulk characteristics of hot and dense medium to statistical model of ideal hadron gas. Then the polarization of both hyperons was calculated. The polarization of $Lambda$ and $bar{Lambda}$ increases with decreasing energy of nuclear collisions. The stronger polarization of $bar{Lambda}$ is explained by the different space-time distributions of $Lambda$ and $bar{Lambda}$ and by different freeze-out conditions of both hyperons.
Inclusive production of $Lambda$-hyperons was measured with the large acceptance NA61/SHINE spectrometer at the CERN SPS in inelastic p+p interactions at beam momentum of 158~GeVc. Spectra of transverse momentum and transverse mass as well as distributions of rapidity and x$_{_F}$ are presented. The mean multiplicity was estimated to be $0.120,pm0.006;(stat.),pm 0.010;(sys.)$. The results are compared with previous measurements and predictions of the EPOS, UrQMD and FRITIOF models.
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