A highly granular SiPM-on-tile calorimeter prototype
AA highly granular SiPM-on-tile calorimeter prototype
Felix Sefkow and Frank Simon On behalf of the CALICE Collaboration DESY, Hamburg, Germany Max-Planck-Institut f¨ur Physik, Munich, GermanyE-mail: [email protected]
Abstract.
The Analogue Hadron Calorimeter (AHCAL) developed by the CALICEcollaboration is a scalable engineering prototype for a Linear Collider detector. It is asampling calorimeter of steel absorber plates and plastic scintillator tiles read out by siliconphotomultipliers (SiPMs) as active material (SiPM-on-tile). The front-end chips are integratedinto the active layers of the calorimeter and are designed for minimizing power consumption byrapidly cycling the power according to the beam structure of a linear accelerator. 38 layers of thesampling structure are equipped with cassettes containing 576 single channels each, arrangedon readout boards and grouped according to the 36 channel readout chips. The prototype hasbeen assembled using techniques suitable for mass production, such as injection-moulding andsemi-automatic wrapping of scintillator tiles, assembly of scintillators on electronics using pick-and-place machines and mass testing of detector elements. The calorimeter was commissionedat DESY and was taking data at the CERN SPS at the time of the conference. The contributiondiscusses the construction, commissioning and first test beam results of the CALICE AHCALengineering prototype.
1. Introduction
The physics at future high-energy lepton colliders, with its requirement for a jet energyreconstruction with unprecedented precision, is one of the primary motivations for thedevelopment of highly granular calorimeters by the CALICE collaboration. The detectorconcepts for the International Linear Collider (ILC) and the Compact Linear Collider (CLIC)rely on Particle Flow Algorithms (PFA) [1, 2, 3], which are capable of achieving the requiredresolution. This event reconstruction technique requires highly granular calorimeters to deliveroptimal performance.One of the technologies developed within CALICE is the Analogue Hadron CalorimeterAHCAL. It is based on active elements consisting of 3 × plastic scintillator tiles individuallyread out by silicon photomultipliers (SiPMs) in a steel absorber structure with approximately 20mm of absorber material between each active layer. A cubic-metre sized ”physics prototype” [4],which has been extensively tested in particle beams at DESY, CERN and Fermilab, hasdemonstrated the capabilities of this technology, achieving competitive single hadron energyresolution [5] and the two-particle separation required for good PFA performance [6]. Theprototype was also successfully tested with tungsten absorbers [7, 8]. An overview of the resultscan be found in [9]. a r X i v : . [ phy s i c s . i n s - d e t ] A p r . The CALICE SiPM-on-Tile Hadron Calorimeter Engineering Prototype With the establishment of the principal viability of the AHCAL technology, the focus hasshifted from the study of the physical performance characteristics of such a detector to thedemonstration of the feasibility of the detector concept while satisfying the spatial constraintsand scalability requirements of collider experiments [10, 11]. Such a concept must be basedon a scintillator tile design well-suited for mass production and automatic assembly, originallyproposed in [12] and subsequently varied and optimised in further studies [13, 14].The new AHCAL prototype consists of a non-magnetic stainless steel absorber structure with38 active layers and has 21888 channels. The basic unit of the active elements is the HCAL BaseUnit HBU [15], with a size of 36 ×
36 cm , holding 144 SiPMs controlled by four SPIROC2EASICs [16]. A key element of the electronics is the capability for power-pulsed operation toreduce the power consumption and eliminate the need for active cooling, making use of thelow duty cycle in the linear collider beam time structure. In addition to dual-gain energymeasurement, the electronics also provides a cell-by-cell auto trigger and time stamping on thefew ns level in test beam operations. In operating conditions with shorter data-taking windowscloser to the bunch train structure of linear colliders, sub-ns time resolution is expected.The prototype uses Hamamatsu MPPC S13360-1325PE photon sensors and injection-moulded polystyrene scintillator tiles with a central dimple [14] for optimal light collection,as shown in Figure 1. Figure 1.
CALICE AHCAL scintillator tiles with central dimple, wrapped and unwrapped,mounted on an HBU with SiPMs.The SiPMs were delivered in lots of 600 pieces with a uniform break-down voltage within ±
100 mV. Spot-samples of all SiPM lots, and each one of the ASICs, had undergone semi-automatic testing procedures before soldering the HBUs [17]. The gain of the SiPMs was foundto be uniform within 2.4% when operated at a common over-voltage. Without any further surfacetreatment, the scintillator tiles are wrapped in laser-cut reflective foil by a robotic procedureand mounted on the HBUs using a pick-and-place machine, after glue dispensing with a screenprinter.The HBUs have been integrated into cassettes with interfaces for DAQ [18], LED pulsing andpower distribution, which provide active compensation of temperature variations by automaticadjustments of the common bias voltage of the photon sensors in each layer. Figure 2 shows thetop side of one active layer, with the scintillator tiles visible. All layers have been calibrated inthe DESY test beam, and 99.96% of the total 21888 channels are working.Finally the calibrated layers were assembled into the absorber stack and connected to dataconcentration, power distribution and cooling services. Figure 3 shows the active layers with igure 2.
Active layer side with wrapped tiles on 4 HBUs, with interfaces for DAQ, LEDs andpower.
Figure 3.
SiPM-on-tile AHCAL engineering prototype.connected services inserted in the absorber structure. The full prototype has been commissionedwith cosmic muons, exploiting its self-triggering capabilities; see Figure 4. Two event displaysare shown from cosmic rays interacting in the calorimeter. The top figures is a straight trackfrom a minimum-ionising muon and the bottom is most likely a shower developed from aninelastic interaction of a muon with the absorber material. igure 4.
Event display of cosmic muons. Left: minimum-ionizing track. Right: muon-inducedshower in the calorimeter volume.
Christian Graf Asian Linear Collider Workshop - Fukuoka - May ’18
Beam Composition - Electron Beam Center of Gravity Z [mm]0 100 200 300 400 500 600 700 800 900 1000 N u m be r o f H i t s CALICE work in progress
Figure 5.
Distribution of the number of hits vs. the hit-energy weighted centre-of-gravity (cog);event displays of typical electron, hadron and muon events.
3. Beam test at the CERN SPS
The prototype has been installed in the test beam for data taking at the CERN SPS. Duringtwo periods in May and in June 2018, several 10 events with muon tracks, as well as electronand pion showers in the energy ranges 10 – 100 GeV and 10 – 200 GeV, respectively, have beenrecorded. The data taking rate averaged over the about 5 s long spills was up to 400 events persecond.Figure 5 from the quasi-instantaneous data quality monitoring shows the distribution of thenumber of hits vs. the hit-energy weighted centre-of-gravity (cog) along the beam axis z foran electron run with a beam momentum of 50 GeV/c and admixtures of muons and hadrons.The different particle types populate different regions of the plot, which is illustrated by theassociated event displays.While electron showers are characterised by a relatively narrow distribution of number ofhits and a cog near the front face of the detector, hadrons exhibit a wider distribution of thecog, and a larger number of hits, decreasing as the cog moves towards the rear of the detector,and leakage increases. Muons appear as a narrow band with ∼
38 hits and a cog on z ay aboutalf the depth of the detector. The figure shows how the detailed topological information of theAHCAL can be used for the identification of particle types. The width of the distribution forelectrons, and tails towards lower number of hits, suggest a compromised beam quality for theMay period shown here, which indeed was resolved for the June period.
4. Conclusions
A highly granular hadron calorimeter prototype with 21888 channels, based on 3 × scintillator tiles and SiPMs integrated with the embedded read-out electronics, has beensuccessfully constructed and operated in test beams. The scalable design and automatedconstruction and quality assurance procedures validate the concept for linear collider detectorapplications. This has also inspired the design of the scintillator section of the CMS end-cap calorimeter upgrade for the high luminosity phase of the LHC [19]. The rich data samplecollected in the two test beam periods in 2018 will be used for shower separation studies based on5-dimensional reconstruction algorithms exploiting the high spatial, energy and time resolutionof this novel detector. Acknowledgments
We would like to thank our CALICE colleagues for many enlightening discussions and continuoussupport. This project has received funding from the European Unions Horizon 2020 Researchand Innovation programme under Grant Agreement no. 654168.
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