Low Gain Avalanche Detector (LGAD) technology has been used to design and construct prototypes of time-zero detector for experiments utilizing proton and pion beams with High Acceptance Di-Electron Spectrometer (HADES) at GSI Darmstadt, Germany. LGAD properties have been studied with proton beams at the COoler SYnchrotron facility in Jülich, Germany. We have demonstrated that systems based on a prototype LGAD operated at room temperature and equipped with leading-edge discriminators reach a time precision below 50 ps. The application in the HADES, experimental conditions, as well as the test results obtained with proton beams are presented.

Citation for published version: Glorius, J, Langer, C, Slavkovská, Z, Bott, L, Brandau, C, Brückner, B, Blaum, K, Chen, X, Dababneh, S, Davinson, T, Erbacher, P, Fiebiger, S, Gaßner, T, Göbel, K, Groothuis, M, Gumberidze, A, Gyürky, G, Heil, M, Hess, R, Hensch, R, Hillmann, P, Hillenbrand, P-M, Hinrichs, O, Jurado, B, Kausch, T, Khodaparast, A, Kisselbach, T, Klapper, N, Kozhuharov, C, Kurtulgil, D, Lane, G, Lederer-Woods, C, Lestinsky, M, Litvinov, S, Litvinov, YA, Löher, B, Nolden, F, Petridis, N, Popp, U, Rauscher, T, Reed, M, Reifarth, R, Sanjari, MS, Savran, D, Simon, H, Spillmann, U, Steck, M, Stöhlker, T, Stumm, J, Surzhykov, A, Szücs, T, Nguyen, TT, Zadeh, AT, Thomas, B, Torilov, SY, Törnqvist, H, Träger, M, Trageser, C, Trotsenko, S, Varga, L, Volknandt, M, Weick, H, Weigand, M, Wolf, C, Woods, PJ & Xing, YM 2019, 'Approaching the Gamow window with stored ions: Direct measurement of 124}$Xe(p,) in the ESR storage ring' Physical Review Letters, vol. 122, pp. 0902701. DOI: 10.1103/PhysRevLett.122.092701

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.

The pulse-height versus deposited energy response of a single-crystal chemical vapor deposition (scCVD) diamond detector was measured for ions of Ti, Cu, Nb, Ag, Xe, Au, and of fission fragments of 252 Cf at different energies. For the fission fragments, data were also measured at different electric field strengths of the detector. Heavy ions have a significant pulse-height defect in CVD diamond material, which increases with increasing energy of the ions. It also depends on the electrical field strength applied at the detector. The measured pulse-height defects were explained in the framework of recombination models. Calibration methods known from silicon detectors were modified and applied. A comparison with data for the pulse-height defect in silicon detectors was performed.

Diamond detectors are usually produced from the electronic (detector) grade diamond material in a form of thin plate or film. In order to produce diamond detector, the plate has to be equipped with suitable (most often metallic) electrodes. Such metallic electrodes were and still are produced at GSI Target Laboratory by sputtering of one or more thin metal layers on the surface of the diamond. A particular electrode structure in that case is obtained by using stencil masks that are also a limiting factor since the minimal obtainable structure is of about 100 μm. To overcome this limitation the laser lithography system (shown in Fig. 1) was acquired and put into the operation in the GSI Detector Laboratory.

Typical size of the chemical vapor deposition (CVD) homoepitaxially grown diamond material (also known as the single crystal SC) is limited to some 5 x 5 mm due to the availability of growth substrates made from the highpressure high-temperature (HPHT) diamond. Presently, the only material readily available for the production of diamond detectors with larger area (∼10 cm) is polycrystalline (PC) film grown on silicon wafers with electronic characteristics far inferior in comparison to SC material. In order to produce a large-surface high-quality material for diamond detectors different techniques for heteroepitaxial growing of diamond films are being investigated and developed at the University of Augsburg. By using yttriumstabilized zirconium oxide (YSZ) buffer layer to produce iridium terminated substrate on silicon wafers [1] one can grow diamond films (also know as the diamond on iridium DoI) that are far more homogeneous than PC, however, still burdened with defects. In last few years a remarkable improvement in lowering of the level of impurities and defects was achieved so that the presently produced samples while still not comparable to SC material are far superior to any PC material. Most significant structural defect arising in heteroepitaxial growth are dislocations.In a recent study [2] in which the density of threading dislocations was determined by few methods over a large sample thickness, an inverse growth depth behaviour was found. While this at least in principle confirms that films with very low density of dislocations can be grown, presently procedure would not be economically effective therefore different growing techniques e.g. epitaxial lateral overgrowth are being developed. In order to assess the quality i.e. electronic characteristics of new DoI samples a typical measurement of the charge collection efficiency (CCE) is performed by using the transient current technique (TCT). Alpha particles (Am) are used to test the sample with different polarizations and drift fields so that the properties for both types of charge carriers can be evaluated. In Fig. 1 the set of measurements with a recent DoI sample of 190 μm thickness at different drift fields is presented showing the saturation at values above 0.8 V/μm. While the overall triangular shape of wave forms indicate the presence of the charge recombination defects, additional flat-top slope is related to losses due to the charge carrier trapping within the sample. For this sample we have measured an average CCE of about 60% for holes, which is below the level of the best samples ∗This work was supported in part by HadronPhysics3 (grant agreement No 283286 under the EU FP7.) † m.kis@gsi.de Figure 1: Pulse-shapes (waveforms) obtained for the drift of holes across the sample. The CCE is determined by waveform integration. Each waveform is an average from 1000 recorded events.

The development of the silicon particle array for the EXL project has progressed in solving the vacuum issues connected with the use of telescope-like detector systems in the Ultra-High Vacuum (UHV) environment of the storage ring. In order to achieve UHV conditions it is necessary to bake all the components inside the storage ring up to 200◦C for a period of a couple of days which puts constraints on the choice of materials for the whole construction. To fulfill these requirements we developed a differential pumping concept, where the UHV is separated from the Auxiliary Vacuum (AV) using the innermost DSSD sphere as a vacuum barrier. In such a design, the subsequent layers of DSSDs and/or Si(Li) detectors, together with all unbakeable and thus outgassing components are placed in an AV where vacuum of at least three orders of magnitude worse will be sufficient. Since the vacuum barrier serves at the same time the purpose of an active window it also enables the detection of recoil particles varying from protons to al phas with low energy, down to about 100 keV, as a result of a low momentum transfer. The test was realized in a small vacuum chamber divided into two parts and separated by a custom machined CF150 flange with an opening of 4x4 cm in the middle. The PCB was manufactured from aluminum nitride ceramic because of its low outgassing, good dielectric properties, high thermal conductivity and low thermal expansion coefficient close to that of silicon. The DSSD chip with an active area of 19 ×19 mm and 64 strips on each side [1] was glued on a small step of the cut-out in the middle of the PCB. This PCB was installed over the opening in the CF150 flange using a ring made of aluminum wires of 1.5 mm diameter as a vacuum seal. Both sides of the DSSD were read-out on one side of the PCB (AV side) using 16 channels per side (four strips connected together) to monitor the detector’s spectroscopic performance. After the bake-out, the vacuum on the UHV side reached the value of 1.2 ×10−10 mbar (see Fig. 1 and Ref. [2]) and the corresponding vacuum on the AV side was 2.2×10−7 mbar. Using the needle valve we introduced an artificial air leak on the AV side to observe its influence on the UHV side. While the pressure on the AV side increased due to the leak more than four orders of magnitude, the vacuum on the UHV side stayed well within the achieved 10 −10 mbar range. Outgasing spectra were measured on the UHV side with a residual gas analyzer that show the features of a typical air leak and are free of organic compounds. The most pronounced increase was detected in molecular and atomic nitrogen, molecular oxygen as well as argon, which are the basic air constituents. U H V

In the last year, we continued with the development of large-area diamond sensors grown at the University of Augsburg by chemical vapour deposition (CVD) on wafer scale Ir/YSZ/Si(001) substrates. Early results of diamondon-iridium (DoI) sensors [1] were indicating significant defect densities within the detector bulk, which led to reduced charge collection efficiencies CCE = QColl/QGen= 40% (with QGen the particle induced charge and QColl the charge measured by the sensor) and broad spectra of energy resolution δE/E ≈ 30%. These values were obtained with traversing Am-α-particles for the favourable case of a sensor of thickness d = 12μm = α-range in diamond. A remarkable improvement of the crystal-quality has been achieved in 2010 by using ultra-pure H2/CH4 gas mixtures and optimized growth techniques [2]. Two DoI samples D1 and D2 of thicknesses dD1 = 293 μm and dD2 = 320 μm, respectively, were investigated. Ti/Pt/Au quadrant electrodes with common mass potential were applied in order to prove the spatial homogeneity of the detector performance. Almost symmetrical IED characteristics with respect to the bias polarity were obtained for each sector, while the dark current at electric fields ED ≥ ± 2 V/μm were of the order of 10 A, well comparable to homoepitaxial single-crystal (SC) diamond sensors.

For future particle accelerator experiments, e.g. at FAIR, we are developing novel, advanced diamond sensors grown by chemical vapour deposition (CVD), capable on one hand of replacing the commonly used silicon tracking devices and being on the other hand an advantageous alternative to polycrystalline or single-crystal diamond sensors used so far in beam diagnostics and timing applications. By using heteroepitaxial diamond films grown on Ir/YSZ/Si(001) we want to bridge the gap between polycrystalline (which exhibits inhomogeneous incomplete charge collection) and single-crystal CVD diamond (i.e. of small areas), enabling the fabrication of large-area diamond sensors of good homogeneity, high drift velocity of the charge carriers, and of almost complete collection of the particle induced charge.

S. Sciortino, S.Lagomarsino, M. Bellini, C. Corsi, V. Cindro, K. Kanxheri, A. Morozzi, D. Passeri, L. Servoli, E. Berdermann, C. J. Schmidt, M. Kis, M. Träger, R. Visinka, M. Schreck, S. Gsell, M. Fischer Department of Physics, Florence, Italy; 2 INFN, Florence, Italy; INO-CNR Florence, Italy; LENS, Florence, Italy; Jožef Stefan Institute, Ljubljana, Slovenia; University of Perugia, Italy; INFN, Perugia, Italy; GSI, Darmstadt, Germany; University of Augsburg, Germany;

A promising course for large-area ‘quasi’ single-crystal CVD diamond (scCVDD) is the heteroepitaxial growth on the multilayer structure Ir/YSZ/Si(001) [1] as developed at the University of Augsburg on 4inch wafers. Key issue is the similarity of the lattice constants of diamond (dDia = 3.567 Å) and Iridium (dIr = 3.834 Å). Figure 1 shows characterization results of two Diamond-on-Iridium (DoI) samples compared to commercial scCVDD and polycrystalline CVD-diamond (pcCVDD) detectors [2]. DoI549a (topand central-right data) is a polished freestanding film of 230μm thickness, where a 30μm layer has been removed from the nucleation side. The thickness of DoI724b (bottom left and right data) was optimized for Transient-Current Technique (TCT) measurements with Am-α-particles: an iridium mesh was added in the depth of the α-range providing dD ≈ 12μm.