Status of the CALIFA/R3B calorimeter∗

D. Cortina-Gil † 1, H. Álvarez-Pol1, T. Aumann2,5, V. Avdeichikov3, M. Bendel4, J. Benlliure1, D.Bertini5, A. Bezbakh6, T. Bloch2, M. Böhmer4, M.J.G. Borge7, J.A. Briz7, P. Cabanelas1, E.

Casarejos8, M. Carmona Gallardo7, J. Cederkäll3, L. Chulkov9, M. Dierigl4, D. Di Julio3, I. Durán1,E. Fiori10, A. Fomichev6, D. Galaviz11, M. Gascón1, R. Gernhäuser4, J. Gerl5, P. Golubev3, M.

Golovkov6, D. González1, A. Gorshkov6, A. Heinz12, M. Heil5, W. Henning4, G. Ickert5, A. Ignatov2,B. Jakobsson3, H.T. Johansson12, Th. Kröll2, R. Krücken ‡ 4, S. Krupko6, F. Kurz4, T. Le Bleis4, B.Löher10, N. Montes1, E. Nacher7, T. Nilsson12, C. Parrilla8, A. Perea7, N. Pietralla2, B. Pietras1, R.Reifarth13, J. Sanchez del Rio7, D. Savran10, S. Sidorchuk6, H. Simon5, L. Schnorrenberger2, O.

Tengblad7, P. Teubig11, R. Thies12, J.A. Vilán8, M. von Schmid2, M. Winkel4, S. Winkler4, F. Wamers2,and P. Yañez8

1Universidad de Santiago de Compostela; 2Technische Universität Darmstadt; 3Lund University; 4TechnischeUniversität München; 5Helmholtzzentrum für Schwerionenforschung, Darmstadt; 6Joint Institute for Nuclear Research,

Dubna; 7Instituto Estructura de la Materia, CSIC Madrid; 8Universidad de Vigo; 9National Research Centre,Kurchatov Institute Moscow; 10Extreme Matter Institute and Research Division, GSI; 11Centro de Física Nuclear daUniversidade de Lisboa; 12Chalmers University of Technology, Göteborg; 13Goethe University Frankfurt am Main

CALIFA (the CALorimeter for In Flight detection of γrays and light charged pArticles) is one of the key detectorsof the R3B experiment. It surrounds the reaction target andis optimised according to the exacting requirements givenby the ambitious physics program proposed for the R3Bfacility [1]. CALIFA is a versatile detector and will be usedin a wide spectrum of experiments. In certain spectroscopyexperiments, high γ-ray energy resolution ( 5% at 1 MeV)as well as multiplicity determination is required. In otherexperiments the goal is to attain calorimetric response withhigh efficiency. Part of the complexity arises from thereaction kinematics which leads to large Lorentz boostsand broadening of the detected γ rays peaks, i.e. effectsthat the detector should be able to account for. Chargedparticles of moderate energy, e.g. protons up to 300 MeV,should also be identified with an energy resolution betterthan 1%.In order to meet these targets the detector is dividedinto two sections, a "Forward EndCap" covering po-lar angles between 7-43.2o and a cylindrical "Barrel"section that provides angular coverage up to 140.3o.The Technical Design Report (TDR) [2] of the Barrelsection was recently approved (January 2013) by FAIR,following the recommendation of the Expert Committeefor Experiments (ECE)1. The adopted technical solutionconsists of 1952 CsI(Tl) crystals, readout by Large AreaAvalanche Photodiodes (LAAPDs), and a very compactgeometry (internal radius 30 cm) in order to maximise thecalorimetric properties. To optimize the detector efficiencyand to minimize energy straggling for inter-crystal protonscattering, the passive material must be kept at an absolute

∗Work performed in the CALIFA/R3B Working group and supportedby the Helmholtz International Centre for FAIR

†Convener of the CALIFA Working group‡Also affiliated to TRIUMF1Decision adopted in the ECE first meeting in November 2012

minimum. These demands have lead to an in-depthinvestigation of the best crystal housing, support structuresand overall mechanical design.The coupling of LAAPDs to CsI crystals was found tofulfil many of the R3B programme’s most challengingdemands. Their ability to meet the energy resolution re-quirement has been proven via an extensive R&D programusing standard radioactive sources. The performance overa wide dynamic range has been investigated via irradiationof smaller size prototypes with proton beams at 25 (MLL,2011), 180 (TSL, 2009), 200 and 400 MeV (GSI, 2012).Readout support for the photosensors is provided byMesytec MPC-16B preamplifiers, which feature an onlinetemperature-gain correction. A custom digital FEBEXelectronic support system, envisaged for use in the finalCALIFA setup is currently undergoing tests. In addition tothe compact, high performance design, this approach takesadvantage of the different CsI decay times for pulse shapeanalysis for particle identification. The FEBEX setup ishighly flexible and allows for easy reprogramming of theFPGA online processing to suit individual experimentalrequirements [3].Detailed simulations of the response of the CALIFABarrel have been performed within the R3BROOT analysisframework in order to guide the progression through eachstage of the development process. These simulations havebeen validated by comparison to experimental data fora number of smaller scale prototypes for both γ-ray andproton irradiation over a wide range in energy.The next milestone as described in the TDR is the construc-tion of the CALIFA Demonstrator. The Demonstrator willhave a modular configuration of 8 petals each comprising20 alveoli. The Demonstrator will cover a polar range of32.5 – 65◦, with 4 types of alveoli/crystals and 3 segmentsof 2 alveoli in the azimuthal direction and 10 alveoli in

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polar direction. The design provides a significant sectionof the final calorimeter and will ultimately be incorporatedinto CALIFA [4]. In addition to detector characterisation,the Demonstrator is intended for use in a real experimentalcampaign. In Figure 1 an artistic view of the CALIFADemonstrator is shown.

Figure 1: An artistic impression of the CALIFA Demon-strator.

We are in parallel working on the R&D towards an op-timal solution for the "Forward EndCap" section. This po-lar region will be subject to high energy charged particlesin addition to γ rays boosted to several times their energyin the projectile rest frame. The long CsI(Tl) crystals em-ployed for the CALIFA Barrel section would fulfil the R3Bphysics requirements for the EndCap section, however thisoption would suffer from incident charged particles under-going a large number of inelastic reactions, significantlyreducing the full energy peak efficiency. This restrictionmay be overcome by the use of a phoswich concept withtwo, relatively short, high performance scintillator layerswhich provide two ΔE measurements as charged particlespass through them. From these measurements the particle’sincident energy can be determined. This approach reducesthe detector volume significantly and several phoswich op-tions are currently under investigation.One such concept proposes a combination of two novelscintillation materials: 4 cm of LaBr3(Ce) followed by6 cm LaCl3(Ce). This configuration works as a telescope,the first section (LaBr3(Ce)) provides a ΔE measurementwhereas the total E is obtained by the two consecutive en-ergy loss measurements (ΔE LaBr3+ΔE LaCl3). An initialsmall size prototype consisting of an array of 2x2 phoswichLaBr3+LaCl3 elements, formed by rectangular crystals,was recently irradiated with high energy protons (GSI, 200-1000 MeV). Data analysis is currently under way.We have also progressed towards the final design of the

segmentation of the Forward EndCap. The large segmen-tation present in the Barrel must be preserved in order toretain the spectrometric capabilities. A dedicated design

Figure 2: An artistic representation of the complete CAL-IFA calorimeter.

places frustum shaped crystals into 10 branches, each onecontaining 5 alveoli. The alveoli are sub-divided into 15sectors holding individual crystals which results in a totalof 750 crystals. The performance of this system has beenstudied by means of Monte Carlo simulations [5].Figure 2 shows an artistic conception of CALIFA whereboth sections: Barrel and Forward EndCap, are mounted ona common platform. CALIFA is currently entering a veryexciting period, with the full implementation and commis-sioning of the CALIFA Demonstrator expected in the firstquarter of 2014. The submission of the TDR for the for-ward section is foreseen by the end of 2014. Accordingto our plans the complete CALIFA should be installed andoperational in the R3B cave by the end of 2016.

This work was supported by Mineco (FPA2009-14604-C02-01, FPA2009-14604-C02-02, FPA2009-07387), HIC/FAIR, BMBF (06DA9040I, 05P12RDFN8, 06MT9156,05P12WOFNF), DFG (EXC153), GSI-TU Darmstadt co-operationn and the EraNet NupNet GANAS.

References[1] T. Aumann et al., Technical Proposal for the design, con-

struction, commissioning and operation of R3B, A universalsetup for kinematical complete measurements of Reactionswith Relativistic Radioactive Beams (2005).

[2] T. Aumann et al., Technical report for the Design, Construc-tion and Commissioning of the CALIFA Barrel: The R3BCALorimeter for In Flight detection of γ-rays and high en-ergy charged particles (2011)

[3] T. le Bleis et al., Test of Integration of CALIFA into R3B,GSI SCIENTIFIC REPORT 2012

[4] E. Casarejos et al., Mechanics of CALIFA Barrel, GSI SCI-ENTIFIC REPORT 2012

[5] J. Sanchez del Rio et al., CEPA: A LaBr3(Ce)/LaCl3(Ce)phoswich array for detection of high energy protons andgamma radiation, GSI SCIENTIFIC REPORT 2012

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