We review the physics potential of a next generation search for solar axions: the International Axion Observatory (IAXO). Endowed with a sensitivity to discover axion-like particles (ALPs) with a coupling to photons as small as g aγ ∼ 10 −12 GeV −1 , or to electrons g ae ∼10 −13 , IAXO has the potential to find the QCD axion in the 1 meV∼1 eV mass range where it solves the strong CP problem, can account for the cold dark matter of the Universe and be responsible for the anomalous cooling observed in a number of stellar systems. At the same time, IAXO will have enough sensitivity to detect lower mass axions invoked to explain: 1) the origin of the anomalous "transparency" of the Universe to gamma-rays, 2) the observed soft X-ray excess from galaxy clusters or 3) some inflationary models. In addition, we review string theory axions with parameters accessible by IAXO and discuss their potential role in cosmology as Dark Matter and Dark Radiation as well as their connections to the above mentioned conundrums.

A 2 metre long prototype of a lead-liquid argon electromagnetic calorimeter with accordionshaped electrodes, conceived as a sector of the barrel calorimeter of the future ATLAS experiment at the LHC, has been tested with electron and pion beams in the energy range 10 to 287 GeV. A sampling term of 10%= p E(GeV) was obtained for electrons in the rapidity range 0 < < 1, while the constant term measured over an area of about 1 m 2 is 0.69%. With a cell size of 2.7 cm the position resolution is about 4 mm= p E(GeV).

Particle detection can be done with many different sensors. In this case, the particle detector is based on avalanche photodiodes (APDs) integrated on standard CMOS technology. The integration of the sensors allows the possibility to integrate also the processing circuitry, reducing the volume of components, the complexity, and also the cost of the total device. The sensor is based on a double sensor detection to discriminate the inherent noise of APDs. An electrical model of the sensor, including noise modeling of dark counts and afterpulsing, based on fabricated component, has been developed to proof the suitability of the proposed detector circuit.

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A Front End ASIC for the readout of Silicon Photo-Multipliers is presented with the following features: wide dynamic range, high speed, multi channel, low input impedance current preamplifier, low power (7mW per channel), DC coupled input with common mode voltage control and separated timing and charge signal output.A detailed description of the SiPM modeling and parameter extraction is also included allowing the emulation of the signal generated by different commercial devices in the design simulation stage. Current prototype is the first step for a more complex mixed signal design including more channels, analog processing and digital outputs, thus reducing power consumption and increasing integration. This prototype includes basic blocks for 3 channels with: preamplifier with two separate signal paths and fast current discriminator with digital output.