Recently, the particle physics community has put an increasing effort in developing radiation detectors and equipment based on oriented crystals. A key feature that distinguishes an oriented crystal from the ordinary matter is the reduction of the radiation length (X0) seen by electrons, positrons and photons crossing the lattice along one of its symmetry axes. This effect has been experimentally observed only in the last few decades and with samples limited in number, composition and length. In order to characterize a variety of oriented crystals with a standardized procedure, the STORM Collaboration has developed an advanced modular setup, which allows to study the features of any crystal sample with both electron (or

positron) and photon beams. This contribution describes the key elements of this setup, namely silicon strip tracking detectors, plastic scintillators, Silicon PhotoMultipliers (SiPMs) coupled to the crystal under test, a photon calorimeter and an electromagnetic spectrometer

Bandiera, L.

Bomben, L.

Carsi, S.

Monti-Guarnieri, P.

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DOI 10.1393/ncc/i2023-23098-5Communications: SIF Congress 2022IL NUOVO CIMENTO 46 C (2023) 98Development of an advanced modular setup for the on beamcharacterization of oriented crystalsP. Monti-Guarnieri(1)(2)(∗), L. Bandiera(3), L. Bomben(1)(2), S. Carsi(1)(2),D. De Salvador(4)(5), V. Guidi(3)(6), V. Haurylavets(7), M. Korjik(7),G. Lezzani(1), A. Lobko(7), V. Mascagna(8)(9), A. Mazzolari(3),M. Moulson(10), L. Perna(1) M. Prest(1)(2), M. Romagnoni(3),F. Ronchetti(1)(2), A. Selmi(1)(2), F. Sgarbossa(4)(5), M. Soldani(3)(6),A. Sytov(3), V. Tikhomirov(7) and E. Vallazza(2)(1) Università degli Studi dell’Insubria - Como, Italy(2) INFN, Sezione di Milano Bicocca - Milano, Italy(3) INFN, Sezione di Ferrara - Ferrara, Italy(4) Università degli Studi di Padova - Padova, Italy(5) INFN, Laboratori Nazionali di Legnaro - Legnaro, Italy(6) Università degli Studi di Ferrara - Ferrara, Italy(7) Institute for Nuclear Problems of Belarusian State University - Minsk, Belarus(8) Università degli Studi di Brescia - Brescia, Italy(9) INFN, Sezione di Pavia - Pavia, Italy(10) INFN, Laboratori Nazionali di Frascati - Frascati, Italyreceived 26 January 2023Summary. — Recently, the particle physics community has put an increasing effortin developing radiation detectors and equipment based on oriented crystals. A keyfeature that distinguishes an oriented crystal from the ordinary matter is the reduc-tion of the radiation length (X0) seen by electrons, positrons and photons crossingthe lattice along one of its symmetry axes. This effect has been experimentally ob-served only in the last few decades and with samples limited in number, compositionand length. In order to characterize a variety of oriented crystals with a standardizedprocedure, the STORM Collaboration has developed an advanced modular setup,which allows to study the features of any crystal sample with both electron (orpositron) and photon beams. This contribution describes the key elements of thissetup, namely silicon strip tracking detectors, plastic scintillators, Silicon Photo-Multipliers (SiPMs) coupled to the crystal under test, a photon calorimeter and anelectromagnetic spectrometer.(∗) Corresponding author. E-mail: pmontiguarnieri@studenti.uninsubria.itCreative Commons Attribution 4.0 License (https://creativecommons.org/licenses/by/4.0) 12 P. MONTI-GUARNIERI et al.Fig. 1. – The STORM experimental setup for the beamtest characterization of oriented crystalsin SF conditions. Top: “electron” mode. Bottom: “photon” mode.1. – IntroductionIt is known since the 1970s that the bremsstrahlung cross-section differs from the re-sult of the Bethe-Heitler calculation, if the medium in which the process takes place is anordered structure, such as an oriented single crystal. If the radiating particle features anenergy larger than ∼10GeV and a small enough incidence angle with respect to a crys-talline axis or plane, the Strong Field (SF) regime is attained [1]. In this condition, theintensity of the emitted radiation is enhanced by a factor 10− 100. For incidence angleslarger than a critical value (Θ0∼1mrad), which depends only on the properties of thetarget crystal, the Strong Field regime breaks down and the coherent bremsstrahlungphenomenon takes place. A similar enhancement has been observed for the electron-positron pair production [1]. Due to these effects, the electromagnetic shower developsin a much more compact space, when it is produced inside an oriented crystal in SFcondition [2]. This phenomenon could be exploited in a number of particle physics ap-plications, such as a compact and hadron-blind electromagnetic calorimeter [3]; however,in order to account for the SF regime in an arbitrary material, it would be necessary tohave access to a large amount of experimental data. Unfortunately, these data are notavailable yet, since the SF regime has been experimentally observed only in the past fewdecades and with crystal samples severely limited in terms of number, composition andlength (i.e.,  1X0) [1, 4]. For these reasons, in the last few years, the STORM collabo-ration has investigated the Strong Field effects in a variety of crystals (e.g., W, PbWO4and PbF2), with a thickness of ∼0.5–3X0 [3, 5, 6]. This study required the developmentof a standardized experimental setup, which allows the beamtest characterization of ori-ented crystals in the SF regime with high-energy electrons, positrons and photons. Thiscontribution aims at briefly describing this setup and its key elements.2. – The standard STORM experimental setupThe STORM experimental setup can be installed on any beamline capable of provid-ing an e± beam, with a high energy ( 20GeV) and a low divergence ( 100μrad). TheA MODULAR SETUP FOR THE CHARACTERIZATION OF ORIENTED CRYSTALS 3Fig. 2. – Correlation between the energies of the photons incident on a 1 X0 PbWO4 crystal andthe PH of the MC. Left: photon beam incident on the crystal, in random alignment condition.Right: photon beam incident on the 〈100〉 axis of the crystal. The entries in both histograms arenormalized. Data were selected requiring the detection of at least 5 clusters in both planes ofa silicon tracker placed downstream of the MC. It was also required that the photons crossed afiducial region in the center of the crystal. The increase of the average PH of the MC of a factor∼1.5, for a large enough photon energy, is due to the SF enhancement of the pair productioncross-section.beam intensity should allow to maximize the number of acquired single-track events(1),since these are the only ones useful for the data analysis. This setup is modular, mean-ing that its elements may be rearranged with minimal effort, in order to test a crystalsample using either the primary charged beam (“electron” mode, fig. 1) or a secondarytagged photon beam (“photon” mode). In “electron” mode, the primary beam particlesimpinge on a plastic scintillator trigger (PST) and their trajectories are reconstructedby several double sided silicon microstrip telescopes (T1, T2, T3), which feature a smallactive area (2 cm× 2 cm) and a spatial resolution of ∼5μm on the junction side [7]. Thecrystal sample under test is mounted on a high-precision goniometer, composed of twotranslational and two rotational stages, with a 5μm and a 0.25μrad resolution [8]. Ifthe crystal is a scintillator or a Cherenkov radiator, Silicon PhotoMultipliers (SiPMs)are used to directly measure the energy deposited by the beam particles in the activematerial [6]. The multiplicity of the charged particles exiting from the crystal is evalu-ated by measuring the signal of the Multiplicity Counter (MC), a ∼ 5 cm thick plasticscintillator, and comparing it with the signal given by a Minimum Ionizing Particle(MIP). The charged particles are then deflected by a dipole magnet. A homogeneouselectromagnetic calorimeter composed of BGO crystals (γCAL) measures the energy ofthe photons produced inside the crystal, with an energy resolution of ∼ 3%√E⊕ 2%E ⊕ 2%,where E is the energy in GeV. This measurement is a fundamental step in the charac-terization of the SF effects, since the radiation spectrum is one of the few observables(1) For instance, in the beamtests performed on the H2 beamline (CERN SPS), the beamintensity was of ∼104–105 particles/spill (with a spill length of 4.8 s), corresponding to∼103–104 single-track events/spill.4 P. MONTI-GUARNIERI et al.which can be easily compared with the predictions of the theory [1]. All these detectorsare readout by commercial digitizers, such as the CAEN V1742 and DT5730 modules.The Data AcQuisition system (DAQ) is based on custom VME readout/memory boards.The maximum acquisition rate allowed by the DAQ, due to the irreducible time requiredfor the initialization of the boards and the readout of the data, is ∼ 6 kHz [7].When the setup is used in the “photon” mode, a tagged photon beam is producedby replacing the crystal with a non-oriented copper converter (BS, ∼ 0.1X0). The pri-mary electron beam, which exits from the converter, is deflected by the bending magnetand then absorbed by a spectrometer (eCAL), which is composed of several lead glasscalorimeters, which feature an energy resolution of ∼ 9%√E⊕ 1% [3]. The differencebetween the energy of the primary beam and the one measured by eCAL gives the en-ergy of the photons which impinge on the crystal. The efficiency and spatial coverage ofthe spectrometer can be estimated with a Geant4 simulation: typically, the maximumefficiency (∼ 100%) is achieved in the 20–90GeV energy range. The multiplicity of thecharged particles produced in the sample is measured by the Multiplicity Counter, whilethe energy of all the exiting particles is measured by γCAL. Figure 2 presents a typicalplot obtained during the data taking stage.3. – ConclusionsIn the last few years, the STORM collaboration has studied the Strong Field regimein oriented single crystals. To perform this study, a standardized experimental setupand a custom DAQ system have been developed and optimized. Using this setup, ithas been possible to measure the energy deposited in several oriented crystals by highenergy electron and photon beams and the multiplicity of the charged particles exitingfrom the crystals. The data acquired in these years will be fundamental for the futuredevelopment of the first electromagnetic calorimeter based on oriented crystals.∗ ∗ ∗The authors acknowledge the support of the CERN PS/SPS physics coordinator andof the CERN SPS and EN-EA group technical staff. This work has been partially sup-ported by INFN CSN1 (NA62 experiment/KLEVER project) and CSN5 (STORM ex-periment).REFERENCES[1] Uggerhoj U. I., Rev. Mod. Phys., 77 (2005) 12.[2] Baier V. N. et al., Nucl. Instrum. Methods Phys. Res. B, 119 (1996) 1.[3] Soldani M. et al., Eur. Phys. J. C, 83 (2023) 101.[4] Moore R. et al., Nucl. Instrum. Methods Phys. Res. B, 119 (1996) 1.[5] Bandiera L. et al., Phys. Rev. Lett., 121 (2018) 2.[6] Selmi A. et al., Nucl. Instrum. Methods Phys. Res. A, 1048 (2023) 167948.[7] Lietti D. et al., Nucl. Instrum. Methods Phys. Res. A, 729 (2013) 527.[8] Scandale W. et al., Rev. Sci. Instruments, 79 (2008) 023303.

Development of an advanced modular setup for the on beam

characterization of oriented crystals

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Development of an advanced modular setup for the on beam characterization of oriented crystals

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