# New Inorganic Scintillators' Application in the Electromagnetic Calorimetry in High-Energy Physics
## 1 Introduction  
Homogeneous calorimeters based on scintillation monocrystals are widely used in high-energy physics and related fields due to their excellent energy, spatial and time resolutions. The high-granular photon spectrometer PHOS [1] of the ALICE experiment [2] at the Large Hadron Collider is one example of how such crystals, namely, lead tungstate crystals, PbWO\({}_{4}\) (PWO), are used. These crystals are also employed in the CMS experiment [3], as well as in a variety of other experiments in high-energy physics and related fields, such as those conducted on the ISS (the CALET experiment [4]). As shown in [5], such a calorimeter enables one to acquire the resolution of the \(\pi^{0}\)-meson peak with a value of \(\sigma_{m}^{\pi^{0}}=4.56\pm 0.03\) MeV/\(c\) for \(p_{\mathrm{t}}>1.7\) GeV/\(c\). The good energy and spatial resolution of PWO-based calorimeter allows one to measure experimentally difficult quantities, such as direct photons [6]. However, because of the limited light yield, these measurements are restricted to a relatively high \(p_{\mathrm{t}}\geq 1\) GeV/\(c\). Extending measurements to lower energies will allow for the exploration of direct photons in new regions, and even access to new directions, such as tests of the Low theorem [7; 8; 9]. For a precise measurement of soft photon energy, crystals with a high scintillation light yield, such as the new promising material Gd\({}_{3}\)Al\({}_{2}\)Ga\({}_{3}\)O\({}_{12}\):Ce (GAGG), can be employed. The GAGG crystals of different lengths of 0.5, 1.5, and 3 cm (Figure 1) examined in this work were produced by Fomos Materials Company [10]. In comparison to other scintillation monocrystals, GAGG crystals have a relatively good radiation resistance, density, and light yield ([11; 12; 13], see Table 1). GAGG crystals are considered for use in experiments on hadron colliders; for example, in the LHCb calorimeter system after the Phase II upgrade [14]. An operating shashlik calorimeter consists of non-radiation hard scintillator and plastic light guides. It provides an excellent energy resolution; however, in its current form, it cannot be operated afterthe High-Luminosity LHC Upgrade due to material not being able to sustain such a high level of radiation. The other reasons for the upgrade are the wish to improve the timing resolution and the need to increase granularity while keeping energy resolution at the present level. Possible variants to the upgrade are homogeneous crystals, shashlik module or spaghetti module (SpaCal). However, homogeneous crystals require a long length to contain 25 \(X_{0}\) and have a high cost. Furthermore, no radiation-hard WLS fibers to transport light have been constructed to date for a shashlik-type calorimeter. A spaghetti module can be made very compact and the fibers of the module scintillate and transport light. As GAGG crystals have superb radiation-hardness and a high light yield, they make a perfect candidate for application in SpaCal technology. The idea of creating a calorimeter with more than one crystal per cell is discussed regarding some future experiments in high-energy physics. For example, the Novel High-Granularity Crystal Electromagnetic Calorimeter for CEPC considers an option of several short crystal bars arranged in both longitudinal and transverse directions with a single-ended readout. The BGO material is considered for a calorimeter that provides a great performance in terms of particle flow analysis, achieving an energy resolution of about 2-3%/\(\sqrt{E(GeV)}\)[15]. A similar approach is discussed for space-based experiments, introducing the concept of the CaloCube 3D highly-segmented calorimeter [16]. In this calorimeter, an array of \(20\times 20\times 20\) CsI(Tl) crystals of 3.6 cm side are arranged in a cube; each crystal is equipped with two photodiodes: one for small signals and the other for large signals. This detector is expected to measure cosmic rays in a wide range, from \(\sim\)10 MeV up to \(\sim\)100 TeV.