Abstract
The nucleon-like memberN(1685) of the speculative baryon antidecuplet denotes one possible explanation for the narrow peak-structure aroundW= 1.68 GeV observed in the total cross section ofη- photoproduction off the neutron. If this baryon existed, it would likely to be seen in other reactions as well. While the aforementioned peak, whatever its nature is, was confirmed by several experiments, claims for signa tures of theN(1685) in other reactions and observables are mainly made by V. Kuznetsov etal.using GRAAL data. Their latest work suggests signals of bothN(1685) charge states in all isospin channels ofηπ- photopro duction off the proton and neutron. This contribution reports on challenging these claims with data from the A2 at MAMI experiment employing photon beam energies from Ey=1.43-1.58 GeV. Theηπ0pandηπ+nfinal states produced from a hydrogen target were studied and new analysis cuts were tested in order to enhance a possible signal.
Highlights
The search for exotic states denotes a major focus of contemporary hadron physics
In case of the γp → ηπ0 p reaction, the results shown in figure 5 are compared to the distributions obtained from phase-space MC simulations using event weights from the
The η → 2γ decay has been analyzed so far, as the η → 3π0 decay leads to a total number of nine particles in the final state, which will degrade the detection efficiency resulting in a smaller data set
Summary
The search for exotic states denotes a major focus of contemporary hadron physics. Such bound states of the strong interaction are not built from ordinary qq (for mesons) and qqq (for baryons) configurations in terms of the quark model but involve qqqq (tetraquark), qqqqq (pentaquark), etc. as well as gluonic degrees of freedom to constitute a color singlet.1.1 Exotic PentaquarksThe most recent experimental evidence for pentaquark states was claimed in 2015 by the LHCb collaboration in the J/ψp final state of Λ0b decays hinting at an uudccquark content [1]. The search for exotic states denotes a major focus of contemporary hadron physics. Such bound states of the strong interaction are not built from ordinary qq (for mesons) and qqq (for baryons) configurations in terms of the quark model but involve qqqq (tetraquark), qqqqq (pentaquark), etc. GlueX, a first independent experiment using J/ψ-photoproduction as an alternative production mechanism could not see any evidence of these pentaquark states [3]. More data from GlueX and other experiments are being taken and analyzed, and theoretical efforts to understand the production mechanisms are ongoing [4]. Large statistics measurements, mainly from the CLAS experiment, could not confirm the initial findings (see [6] for an overview). As the detector acceptances of CLAS and LEPS are quite different, new LEPS results using an improved setup and analysis
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