$\varphi$ photoproduction on the proton at $E_{\gamma }=1.5–2.9\mathrm{GeV}$

Differential cross sections at $t=t_{\text{min}}$ and decay asymmetries for the $\gamma p\to \varphi p$ reaction have been measured using linearly polarized photons in the range 1.5 to 2.9 GeV. These cross sections were used to determine the Pomeron strength factor. The cross sections and decay asymmetries are consistently described by the $t$-channel Pomeron and pseudoscalar exchange model in the $E_{\gamma }$ region above 2.37 GeV. In the lower energy region, an excess over the model prediction is observed in the energy dependence of the differential cross sections at $t=t_{\text{min}}$. This observation suggests that additional processes or interference effects between Pomeron exchange and other processes appear near the threshold region.

Figure 1

(a) Missing mass distribution for the $p(\gamma ,K^{+}{K}^{-})X$ reaction. (b) The $K^{+}{K}^{-}$ invariant mass distribution after the proton selection cut on the $MM(\gamma ,K^{+}{K}^{-})$ distribution. The hatched histogram is the background distribution obtained by Monte Carlo simulations.

Figure 2

The $t$ dependences of differential cross sections. The green dashed curves are the results of the fit using Eq. (1), with ${(d\sigma /dt)}_{t=t_{\text{min}}}$ and $B$ as floating parameters. The red solid curves are the results of the fit with fixing $B$ to $3.57{\text{GeV}}^{-2}$. The error bars represent statistical errors. The hatched histograms represent systematic errors. The open squares (cyan) are the CLAS [8] data for the neutral decay mode of the $\varphi$.

Figure 3

Energy dependence of $t$-slope factor $B$, compared to previous data. The open squares represent the CLAS results for the charged mode with ${\mathrm{\Lambda }}^{*}$ cuts included [7]. The hatched histogram represents systematic errors for this work.

Figure 4

Energy dependence of ${(d\sigma /dt)}_{t=t_{\text{min}}}$. The red solid circles are the results of the present work. The error bars represent statistical errors. The hatched histogram represents systematic errors. The open squares represent the CLAS results for the charged mode with ${\mathrm{\Lambda }}^{*}$ cuts included [7]. The green solid curve represents the theoretical calculation with the Pomeron strength factor determined by the present measurements. See text for details.

Figure 5

The integrated one-dimensional decay angular distributions in the Gottfried-Jackson frame. The energy and $t$ ranges are $2.37<E_{\gamma }<2.77\text{GeV}$ and $t-t_{\text{min}}>-0.05{\text{GeV}}^2$. The red curves represent the fitting results. The hatched histograms represent systematic errors.

Figure 6

$t$ dependences of the spin-density matrix elements in the Gottfried-Jackson frame. The energy range is $2.37<E_{\gamma }<2.77\text{GeV}$. The red solid curves represent the theoretical calculations at $E_{\gamma }=2.57\text{GeV}$ with the Pomeron strength factor $C_{\mathbb{P}}$ determined by the cross sections ($C_{\mathbb{P}}=0.649{\text{GeV}}^{-2}$). The green dashed curves represent the same model with $C_{\mathbb{P}}=0.7566{\text{GeV}}^{-2}$ [12].

Figure 7

$E_{\gamma }$ dependences of the spin-density matrix elements in the Gottfried-Jackson frame. The $t$ range is $t-t_{\text{min}}>-0.05{\text{GeV}}^2$. The open circles represent the previous LEPS results [27]. The red solid curves represent the theoretical calculations at zero degrees ($t=t_{\text{min}}$) with the Pomeron strength factor $C_{\mathbb{P}}$ determined by the cross sections ($C_{\mathbb{P}}=0.649{\text{GeV}}^{-2}$). The green dashed curves represent the same model with $C_{\mathbb{P}}=0.7566{\text{GeV}}^{-2}$ [12].