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Register a new userInvestigation of the Lambda(1405) line shape observed in pp collisions
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In this work we investigate different possible explanations for the observed low mass {Lambda}(1405) signal associated to the production of the {Lambda}(1405) in p+p reactions at 3.5 GeV beam kinetic energy measured by the HADES collaboration. We study the influence of interference effects between the {Lambda}(1405) resonance and the non-resonant background. Furthermore, we present a phenomenological method to use the HADES data for determining the relative contribution of the two {Lambda}(1405) poles and discuss to which extent the data can constrain the position of these poles in the complex energy plane.
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We present an analysis of the Lambda(1405) resonance produced in the reaction p+p->Sigma^{pm}+pi^{mp}+K+p at 3.5 GeV kinetic beam energy measured with HADES at GSI. The two charged decay channels Lambda(1405) -> Sigma^{pm}+pi^{mp} have been reconstructed for the first time in p+p collisions. The efficiency and acceptance-corrected spectral shapes show a peak position clearly below 1400 MeV/c^2. We find a total production cross section of sigma_{Lambda(1405)}=9.2 +- 0.9 +- 0.7 +3.3-1.0 mub. The analysis of its polar angle distribution suggests that the Lambda(1405) is produced isotropically in the p-p center of mass system.
The reaction pp->p K0 pi+ Lambda has been studied with the ANKE spectrometer at COSY-Juelich at a beam momentum of 3.65 GeV/c in order to search for a possible signal of the pentaquark Theta+(1540), decaying into the p K0 system. By detecting four charged particles in the final state, the K0 and the Lambda have been reconstructed to tag strangeness production. It has been found that the pi+ Lambda missing-mass spectrum displays no significant signal expected from the Theta+(1540) excitation. The total cross section for the reaction pp->p K0 pi+ Lambda has been deduced, as well as an upper limit for the Theta+ production cross section. The intermediate Delta++ K0 Lambda state is found to provide a significant contribution to the reaction.
Low-energy data on the three charge states in $gamma p to K^+(Sigmapi)$ from CLAS at JLab, on $K^-pto pi^0pi^0Lambda$ and $pi^0pi^0Sigma$ from the Crystal Ball at BNL, bubble chamber data on $K^-ptopi^-pi^+pi^{pm}Sigma^{mp}$, low-energy total cross sections on $K^-$ induced reactions, and data on the $K^-p$ atom are fitted with the BnGa partial-wave-analysis program. We find that the data can be fitted well with just one isoscalar spin-1/2 negative-parity pole, the $Lambda(1405)$, and background contributions.
The aim of the present analysis is to determine the relative production cross sections of the $Lambda$(1405) and $Sigma(1385)^{0}$ resonances in p+p collisions at E$_{kin}$=3.5 GeV measured with HADES. Upper and lower limits have been determined for the ratio $sigma_{(Sigma(1385)^{0}+p+K^{+})}/sigma_{(Lambda(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$. The knowledge of this ratio is an essential input for the analysis of the decay $Lambda(1405)rightarrowSigma^{pm}pi^{mp}$, where an unambiguous separation of the $Lambda$(1405) and $Sigma(1385)^{0}$ signals is not possible.
Since the discovery of the $Lambda(1405)$, it remains poorly described by conventional constituent quark models, and it is a candidate for having an exotic meson-baryon or penta-quark structure, similar to states recently reported in the hidden charm sector. The $Lambda(1405)$ can be produced in the reaction $gamma p rightarrow K^+Lambda(1405)$. The pure I=0 decay mode into $Sigma^0pi^0$ is prohibited for the mass-overlapping $Sigma(1385)$. Combining a large aperture forward magnetic spectrometer and a central BGO crystal calorimeter, the BGO-OD experiment is ideally suited to measure this decay with the $K^+$ in the forward direction. Preliminary results are presented. *Supported by DFG (PN 388979758, 405882627).
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