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.

This article describes BabyIAXO, an intermediate experimental stage of the International Axion Observatory (IAXO), proposed to be sited at DESY. IAXO is a large-scale axion helioscope that will look for axions and axion-like particles (ALPs), produced in the Sun, with unprecedented sensitivity. BabyIAXO is conceived to test all IAXO subsystems (magnet, optics and detectors) at a relevant scale for the final system and thus serve as prototype for IAXO, but at the same time as a fully-fledged helioscope with relevant physics reach itself, and with potential for discovery. The BabyIAXO magnet will feature two 10 m long, 70 cm diameter bores, and will host two detection lines (optics and detector) of dimensions similar to the final ones foreseen for IAXO. BabyIAXO will detect or reject solar axions or ALPs with axion-photon couplings down to gaγ ∼ 1.5 × 10−11 GeV−1, and masses up to ma ∼ 0.25 eV. BabyIAXO will offer additional opportunities for axion research in view of IAXO, like the development of precision x-ray detectors to identify particular spectral features in the solar axion spectrum, and the implementation of radiofrequency-cavity-based axion dark matter setups.

We discuss the physics case for and the concept of a medium-scale axion helioscope with sensitivities in the axion-photon coupling a few times better than CERN Axion Solar Telescope (CAST). Search for an axion-like particle with these couplings is motivated by several persistent astrophysical anomalies. We present early conceptual design, existing infrastructure, projected sensitivity and timeline of such a helioscope (Troitsk Axion Solar Telescope Experiment, TASTE) to be constructed in the Institute for Nuclear Research, Troitsk, Russia. The proposed instrument may be also used for the search of dark-matter halo axions.Keywords: Large detector systems for particle and astroparticle physics; Dark Matter detectors (WIMPs, axions, etc.); X-ray detectorsRecently ADMX-HF [46] has put strong limits g aγγ < 2 × 10 −14 GeV −1 over the mass

1 nuclear collisions of p+Al, p+Au, d+Au, and 3 He+Au at √ s N N = 200 GeV 2 121 4Asymmetric nuclear collisions with a light projectile nucleus striking a heavier target nucleus have proven to be an 123 excellent testing ground for particle production models and the longitudinal dynamics following the initial collision -124 for an early review see Ref. [1]. Many calculations have successfully described the longitudinal (or rapidity) distribution 125 of produced particles in proton-nucleus (p+A) collisions via the fragmentation of color strings and with counting rules 126 based on the number of "wounded" or struck nucleons or quarks in the projectile and target. Recently, a proposal 127 for testing the wounded-quark model [2] was put forth that specifically called for the measurement of dN ch /dη over a 128 broad range of pseudorapidity in p+Au, d+Au, and 3 He+Au collisions [3]. Fully three-dimensional hydrodynamical 129 models also require input on the longitudinal distribution of initial deposited energy and gradients thereof [4]. Once 130 the initial partons or fluid elements are populated, the models evolve the system dynamically. Measurements of elliptic 131 flow as a function of pseudorapidity provide constraints on the longitudinal dynamics of the evolution. 132As the incoming hadrons or nuclei break up, the rapidity distribution of liberated partons may be determined by 133 the longitudinal parton distribution functions [5, 6] or via a universal color field breakup for each struck nucleon 134 or quark [7]. For that reason, calculations based on Monte Carlo Glauber models have been developed to calculate 135 the number of struck nucleons and struck quarks (see for example Refs. [8-10]). The PHOBOS collaboration has 136 previously published charged hadron dN ch /dη measurements over |η| < 5.4 in d+Au collisions at √ s N N = 200 GeV [11]. 137 PHENIX has also published dN ch /dη measurements in high-multiplicity d+Au collisions at √ s N N = 200, 62, 39, and 138 19.6 GeV [12]. The wounded-quark model has been constrained by the d+Au data and found to be in reasonable 139 agreement with the centrality dependence, while the wounded-nucleon model cannot describe the data [3]. A crucial 140 test of the wounded-quark model is to see if it is universal across different colliding systems. Additional measurements 141 in light and heavy systems at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) can 142 also be tested in this context-see for example different geometry tests in Refs. [13-15]. 143 157 section of 2.30, 2.26, 1.76, 0.54 barns for 3 He+Au, d+Au, p+Au, and p+Al respectively. The dN ch /dη analysis has 158 negligible statistical uncertainties and thus a subset of runs with the most stable detector configuration are utilized 159and the run-to-run variation is used in the determination of systematic uncertainties. For the elliptic flow v 2 analysis 160 in high-multiplicity events, also referred to as central events, an additional trigger was used that required the number 161 of fi...

Sterile neutrinos are a minimal extension of the standard model of particle physics. A promising model-independent way to search for sterile neutrinos is via high-precision β-spectroscopy. The Karlsruhe tritium neutrino (KATRIN) experiment, equipped with a novel multi-pixel silicon drift detector focal plane array and read-out system, named the TRISTAN detector, has the potential to supersede the sensitivity of previous laboratory-based searches. In this work we present the characterization of the first silicon drift detector prototypes with electrons and we investigate the impact of uncertainties of the detector’s response to electrons on the final sterile neutrino sensitivity.