Speaker
Description
Exclusive photoproduction of Ï0(770) mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900000 events is used to measure single- and double-differential cross sections for the reaction $\gamma p\to\pi^{+}\pi^{-}Y$. Reactions where the proton
stays intact ($m_Y=m_p$) are statistically separated from those where the proton dissociates to a low-mass hadronic system ($m_p< m_y< 10$ GeV). The double-differential cross sections are measured as a function of the invariant mass $0.5
The Regge trajectory $\alpha(t)$ is extracted from these H1 data alone.
Measurements of two- and multi-particle angular correlations are presented in both $ep$ deep-inelastic scattering at $\sqrt{s}=319$ GeV and in photoproduction off protons at energies $W_{\gamma p}=270$ GeV, as a function of charged-particle multiplicity. No long-range ridge structure is observed in the correlation functions. The second-order ($V_{2∆}$) and third-order ($V_{3∆}$) azimuthal anisotropy
Fourier harmonics are extracted. Further, $C_2\{4\}$ signals are extracted from four-particle correlations for the first time in $ep$ collisions and are found to be positive or consistent with 0. In summary, collective behavior has not been observed in collisions of protons with virtual or quasi-real photons at HERA energies.
