CERN Accelerating science

(left) Design drawing and (right) photo of the final construction of the \epical prototype. Layers are oriented such that the most upstream layer (0) has no tungsten absorber in front of the ALPIDE sensors.\protect\label{fig:design}

(left) Exploded view of the design of a single \epical prototype layer and (right) photo of an assembled layer. See text for details.

Schematic view of the readout system of the \epical detector.

The \epical setup at the DESY II Test Beam Facility \cite{DESY} (not to scale).

(left) Implementation of an \epical layer in the \Allpixtwo simulation, with local coordinate system defined (right) Magnitude of the electric field within a single pixel, in the ($y-z$) plane (sensor local coordinate system).

(left) Implementation of an \epical layer in the \Allpixtwo simulation. (right) $z$-component of the electric field strength for a single pixel.

(left) Implementation of an \epical layer in the \Allpixtwo simulation, with local coordinate system defined (right) Magnitude of the electric field within a single pixel, in the ($y-z$) plane (sensor local coordinate system).

Comparison of data and simulation for distributions of (left) \Nhits and (right) \Nclus for all energies.

Comparison of data and simulation for distributions of (left) \Nhits and (right) \Nclus for all energies.

Comparison of data and simulation as a function of electron beam energy for (upper) Energy response in terms of \Nhits and \Nclus, including pedestal measurements at $E=0$. For \Nhits, data from the \mimosa prototype are also shown. (lower) Difference relative to the linear fit, displaced horizontally for clarity. In these ratios, a one-sided systematic uncertainty is included for the experimental data for \epical, as discussed in the text (a corresponding uncertainty is not shown for \mimosa data).

Energy resolution as a function of electron beam energy. Parametrisations are according to equation~\ref{eq:resolution}. (left) Data are compared to simulations in which electron energy spreads of $\Delta E = 158 \mev$ and $\Delta E = 0\mev$ are used. (right) Comparison to data from the \mimosa prototype \cite{deHaas:2017fkf} and to the resolution of the CALICE silicon-tungsten ECAL physics prototype \cite{CALICE:2008kht}.

Energy resolution as a function of electron beam energy. Parametrisations are according to equation~\ref{eq:resolution}. (left) Data are compared to simulations in which electron energy spreads of $\Delta E = 158 \mev$ and $\Delta E = 0\mev$ are used. (right) Comparison to data from the \mimosa prototype \cite{deHaas:2017fkf} and to the resolution of the CALICE silicon-tungsten ECAL physics prototype \cite{CALICE:2008kht}.

Longitudinal profile for the electron beam energies for the total number of (left) hits and (right) clusters per layer, averaged over all events. The predictions of detailed simulations are overlaid, see text for details.

Longitudinal profile for the electron beam energies for the total number of (left) hits and (right) clusters per layer, averaged over all events. The predictions of detailed simulations are overlaid, see text for details.