Performance of the diamond active target prototype for the PADME experiment at the DA$\hat{I}¦$NE BTF

Abstract

The PADME experiment at the DA$\hat{I}¦$NE Beam-Test Facility (BTF) is designed to search for the gauge boson of a new $\mathrm{U}(1)$ interaction in the process e${}^{+}$e${}^{-}\to {\hat{I}}^3$+${\mathrm{A}}^{\prime }$, using the intense positron beam hitting a light target. The ${\mathrm{A}}^{\prime }$, usually referred as dark photon, is assumed to decay into invisible particles of a secluded sector and it can be observed by searching for an anomalous peak in the spectrum of the missing mass measured in events with a single photon in the final state. The measurement requires the determination of the 4-momentum of the recoil photon, performed by a homogeneous, highly segmented BGO crystals calorimeter. A significant improvement of the missing mass resolution is possible using an active target capable to determine the average position of the positron bunch with a resolution of less than 1 mm. This report presents the performance of a real size $(2x2c{\mathrm{m}}^2)$ PADME active target made of a thin (50 $\hat{I}¼$m) diamond sensor, with graphitic strips produced via laser irradiation on both sides. The measurements are based on data collected in a beam test at the BTF in November 2015.

7 pages, 10 figures