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Based on $334{\mathrm{pb}}^{-1}$ of photoproduction data collected with the GlueX detector at Jefferson Lab, we have measured for the first time the cross section of the exclusive reaction $\gamma +p\to \varphi \left(1020\right){\pi }^{+}{\pi }^{-}p$ by reconstructing the final state $K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}p$ produced with a photon beam of energies between 8.0 and 11.6 GeV. Based on the measured differential cross section, we have performed a search for the strangeoniumlike exotic candidate $Y\left(2175\right)$ , recently renamed to $\varphi \left(2170\right)$ . This state has been reported by different $e^{+}{e}^{-}$ annihilation experiments and it is addressed here for the first time in a photoproduction experiment. We do not find evidence for this state when using the resonance parameters quoted by the Particle Data Group and provide upper limits on the photoproduction cross section. Instead, we find a structure at a mass of $m\left(\varphi {\pi }^{+}{\pi }^{-}\right)=2.24\mathrm{GeV}/c^2$ with a statistical significance of about $5\sigma$ . The parameters of this structure differ from those quoted by the Particle Data Group for the $\varphi \left(2170\right)$ and are consistent with a previous observation in $e^{+}{e}^{-}$ annihilation. In addition, there is evidence for a second structure at $1.82\mathrm{GeV}/c^2$ . 

The experiment at Jefferson Lab has observed $p\overline{p}$ and, for the first time, $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ and $p\overline{\mathrm{\Lambda }}$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like $t$ -channel exchange. Asymmetric wide-angle antibaryon distributions show the presence of additional processes. In a phenomenological model, we find consistency with a double- $t$ -channel exchange process where antibaryons are created only at the middle vertex. The model matches all observed distributions with a small number of free parameters. In the hyperon channels, we observe a clear distinction between photoproduction of the $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ and $p\overline{\mathrm{\Lambda }}$ systems but general similarity to the $p\overline{p}$ system. We report both total cross sections and cross sections differential with respect to momentum transfer and the invariant masses of the created particle pairs. No narrow resonant structures were found in these reaction channels. The suppression of $s\overline{s}$ quark pairs relative to $d\overline{d}$ quark pairs is similar to what has been seen in other reactions. 

American Physics Society 

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized 8.5GeV photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson 𝜌(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of 𝑠-channel helicity conservation at small squared four-momentum transfer 𝑡 and are able to extract the 𝑡 dependence of natural- and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full 𝑡 range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced 𝜌⁡(770) differ by two units are negligible for −𝑡<0.5GeV2/𝑐2.