GSI Helmholtzzentrum für Schwerionenforschung GmbH, D-64291 Darmstadt, Germany.
Old Dominion University, Norfolk, Virginia 23529, USA.
Phys Rev Lett. 2019 Aug 16;123(7):072001. doi: 10.1103/PhysRevLett.123.072001.
We report on the measurement of the γp→J/ψp cross section from E_{γ}=11.8 GeV down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment. We find that the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section dσ/dt has an exponential slope of 1.67±0.39 GeV^{-2} at 10.7 GeV average energy. The LHCb pentaquark candidates P_{c}^{+} can be produced in the s channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions B(P_{c}^{+}→J/ψp) and cross sections σ(γp→P_{c}^{+})×B(P_{c}^{+}→J/ψp).
我们报告了使用 GlueX 实验的标记光子束，从 E_{γ}=11.8 GeV 测量到 8.2 GeV 的阈值的 γp→J/ψp 截面。我们发现总截面在阈值处的下降速度比双胶子交换模型所预期的要慢。在 10.7 GeV 的平均能量下，微分截面 dσ/dt 的斜率为 1.67±0.39 GeV^{-2}。LHCb 五夸克候选体 P_{c}^{+}可以在这个反应的 s 通道中产生。我们没有看到它们的证据，并对它们的分支比 B(P_{c}^{+}→J/ψp)和截面 σ(γp→P_{c}^{+})×B(P_{c}^{+}→J/ψp)设置了模型依赖的上限。
