1 Very forward calorimeters for future electron-positron colliders Ivan Smiljanica,1 aVinca Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia Presented at the 30th International Symposium on Lepton Photon Interactions at High Energies, hosted by the University of Manchester, 10-14 January 2022. Abstract: Detectors at future e+e- colliders need special calorimeters in the very forward region for a fast estimate and precise measurement of the luminosity, to improve the hermeticity and mask the central tracking detectors from backscattered particles. In our concept, two compact calorimeters are foreseen, LumiCal and BeamCal. Both are designed as sandwich calorimeters with very thin sensor planes to keep the Molière radius small, facilitating such the measurement of electron showers in the presence of background. Silicon sensor prototypes and dedicated FE ASICs have been developed and produced. The ASICs match the timing and dynamic range requirements. In the recent beam tests, a multi-plane compact prototype was equipped with thin sensor planes fully assembled with the new readout electronics and installed in 1 mm gaps between tungsten plates of one radiation length thickness. The latest status of the calorimeter prototype development will be presented, including selected performance results, obtained in a 5 GeV electron beam at DESY, as well as the expected performance obtained from simulation. 1. Introduction In the forward region of future high energy linear e+e- colliders [1, 2], two specialized calorimeters are foreseen: luminosity calorimeter - LumiCal for the integrated luminosity measurement and BeamCal for fast luminosity estimate and the beam parameters control. LumiCal and BeamCal are cylindrical electromagnetic calorimeters designed as sensor-tungsten sandwich; the absorber thickness is 3.5 mm, corresponding to one-radiation length. The longitudinal structure of both calorimeters consists of layers of absorber interspersed with very thin detector planes. Several solid- state sensor materials [3], including GaAs [4], diamond [5] and single-crystal sapphire [6], along with conventional silicon diode sensors, are being assessed for radiation tolerance. The main parameters of the LumiCal and BeamCal in ILD and CLICdet detector concepts are shown in Table 1. In this paper, the latest developments towards the compact LumiCal prototype calorimeter as well as performance highlights from test-beam campaigns will be presented. Table 1. Main parameters of the LumiCal and BeamCal in ILD and CLICdet detector concepts Parameters ILD CLICdet LumiCal geometrical acceptance [mrad] 31-77 38-110 Fiducial acceptance [mrad] 41-67 44-80 z from IP [mm] 2480 2539 number of layers (W+Si) 30 40 BeamCal geometrical acceptance [mrad] 5-40 10-40 z from IP [mm] 3200 3181 number of layers (W+Si) 30 40 2. LumiCal prototype (a) (b) (c) Figure 1. (a) Model of LumiCal; (b) Sector of the LumiCal Si sensor; (c) Detector plane assembly The combination of Si and W for the construction of the detector allows the assembly of a very compact calorimeter made up of compact active layers with small cell size (high granularity) in the transverse and longitudinal directions (Figure 1a). The sensor is made of a 320 μm thick high resistivity n-type silicon wafer. It has the shape of a sector of a 30◦ angle, with inner and outer radii of the sensitive area of 80 mm and 195.2 mm, respectively (Figure 1b). It comprises four sectors with 64 p-type pads of 1.8 mm pitch. The silicon sensor was glued with epoxy to a fan-out made of flexible 1 On behalf of FCAL Collaboration