Development and performance of a compact LumiCal prototype calorimeter for future linear collider experiments
DDevelopment and performance of a compact LumiCalprototype calorimeter for future linear colliderexperiments
Maryna Borysova 𝑎, , ∗ 𝑎 Institute for Nuclear Research,47, prospekt Nauky, Kiev, Ukraine
E-mail: [email protected]
The FCAL collaboration is preparing large-scale prototypes of special calorimeters to be usedin the very forward region at future electron-positron colliders for a precise measurement ofintegrated luminosity and for instant luminosity measurement and assisting beam-tuning. LumiCalis designed as a silicon-tungsten sandwich calorimeter with very thin sensor planes to keep theMolière radius small, facilitating such the measurement of electron showers in the presence ofbackground. Dedicated front-end electronics has been developed to match the timing and dynamicrange requirements. A partially instrumented prototype was investigated in a 1 to 5 GeV electronbeam at the DESY II synchrotron. In the recent beam tests, a multi-plane compact prototype wasequipped with thin detector planes fully assembled with readout electronics and installed in 1 mmgaps between tungsten plates of one radiation length thickness. High statistics data were used toperform sensor alignment, and to measure the longitudinal and transversal shower developmentin the sandwich. This talk covers the latest status of the calorimeter prototype development andselected performance results, obtained in test beam measurements, the prospects for the upcomingDESY test beam, as well as the expected simulation performance. For the FCAL collaboration ∗ Speaker © Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/ a r X i v : . [ phy s i c s . i n s - d e t ] J a n evelopment and performance of compact LumiCal Maryna Borysova
1. Introduction
Forward calorimeters for future electron-positron linear collider experiments have challengingrequirements on geometrical compactness and high precision measurements of integrated luminos-ity [1] resulting in the design of highly compact calorimeters. The FCAL Collaboration is designingtwo such calorimeters that would cover the far-forward region of proposed future electron-positronlinear colliders [2–4]. Precise measurement of integrated luminosity is provided by the LumiCaldetector. Another detector, BeamCal, is designed for instant luminosity measurement and assistingbeam tuning when included in a fast feedback system. Both detectors extend the capabilities of theexperiments for physics study in the high rapidity region.Luminosity in e + e − collider experiments can be measured using Bhabha scattering, as a gaugeprocess (e + e − → e + e − ( 𝛾 )). In this case the luminosity is obtained as a ratio of the number of Bhabhaevents in a certain polar angle range to the integral of differential cross section 𝐿 = 𝑁 𝐵 / 𝜎 𝐵 . Thecross section can be accurately calculated in QED [5]. The range in the polar angle for the LumiCalbaseline design was optimised in a simulation [1]. The statistical uncertainty of the luminositymeasurement is defined by the number of Bhabha events identified by LumiCal. The fiducialvolume in a polar angle range considered is the part of the polar angle range where electron showersare fully contained. Keeping it as large as possible allows reducing the statistical uncertaintyof luminosity measurement. This is achieved by designing a calorimeter with a small Molièreradius. A small Molière radius is also important for BeamCal to improve high energy electronsreconstruction on top of background.
2. Compact LumiCal prototype
L 2 L1 R R pad s : - Outer active radiusR = 195.2 mm3 x 100 μm guard ringsInner active radius R = 80.0 mm
Figure 1:
The LumiCal silicon sen-sor prototype.
Figure 2:
The LumiCal detector module assembly.
The design of a LumiCal sensor was optimized in simulations to provide the required resolutionof the polar angle reconstruction. Tungsten absorber plates of one radiation lenght thickness areinterspersed with silicon detector planes. A silicon sensor prototype is shown in Fig.1. It is shapedas a ring segment of 30 degrees, subdivided into four sectors of 7.5 degrees each. There are 64 radialp-type pads in each sector with a pitch of 1.8 mm. The sensor is about 11 cm long with an innerradius of 80 mm. It is made of n-type silicon with the thickness of 320 𝜇𝑚 . The compactness of the2 evelopment and performance of compact LumiCal Maryna Borysovacalorimeter is achieved by a thin detector module design as shown in Fig.2. In the current prototypethe space between tungsten plates is 1 mm. Fig. 2 shows a detector module of about 650 𝜇𝑚 thickness to be installed in the 1 mm gap. Two thin Kapton PCBs are used to supply high voltageand to connect read-out electronics to the sensor. The first one is connected by conductive glue andthe second by ultrasonic wire bonding. A carbon fiber support provides mechanical stiffness andfacilitates handling and mounting between tungsten plates.To allow the insertion of the detector planes without damage, exceptionally flat tungsten platesare needed. To facilitate machining, tungsten plates are made of an alloy with 93 % tungsten, 5 %nickel and 2 % copper. The measurements showed that the flatness of the tungsten plates is betterthan 30 𝜇𝑚 . They are glued to permaglass frames that accurately determine their positions in thecalorimeter stack.
3. The dedicated readout ASIC
A dedicated readout ASIC for LumiCal - FLAME - is being developed. This is a completereadout ASIC with a full functionality, including front-end readout, ADC, biasing and calibrationfabricated in 130 nm CMOS technology. The FLAME layout with dimensions of 3.7 mm x 4.3 mmis shown in Fig. 3. It has 32 mix-mode channels. Each channel comprises variable gain front-end;10 bit ADC with sampling rate up to 50 mega samples per second with power consumption, below2 mW/channel. FLAME also contains a fast serializer with transmission rate up to 8 Gbps.
Figure 3:
The FLAME layout, the size is 3.7mm x 4.3mm evelopment and performance of compact LumiCal Maryna Borysova
4. The performance tests
Measurements were perfomed in two beam test campaigns in 2016 and 2020 at the DESY-IISynchrotron using electrons with energies between 1 GeV and 5 GeV. A sketch of the experimentalsetup is shown in Fig. 4. The main goal of the 2016 test beam was to study the performance of theultra compact design. e Sc1 Sc2 Sc3
Magnet
TgT1 T2
LumiCalTracker e
30 58 212 31410
Figure 4:
Geometry of the beam test setup (not to scale). Sc1, Sc2 and Sc3 are scintillator counters; T1 andT2 the arms of three-planes pixel telescope, Tg the copper target for bremsstrahlung photon production andLumiCal, the calorimeter prototype under test. Distances, rounded to integer numbers in centimetres, areshown in the upper part of the figure.
The average transverse shower profile as a function of the distance from the core, in units ofthe pad dimension (1.8 mm) is shown in Fig. 5. The lower part of the figure shows the ratio of thedistributions to the fitted function, for the data (blue) and simulation (red). The segmentation of theLumiCal sensor is rather specific and a method was developed [6] to take into account its circularshape to measure the Molière radius. The effective Molière radius is found to be: (8.1 +/- 0.1(stat.)+/-0.3(syst.)) mm [7].The resolution of the shower position reconstruction in the calorimeter is estimated using thetracker planes in front of the calorimeter denoted as ‘Tracker’ in Fig. 4. Fig. 6 shows the distributionof the residuals of the reconstructed radial position of the shower in the calorimeter and in the twoplanes of the tracker. The position resolution amounts to (440+/-20) 𝜇𝑚 for 5 GeV electrons. It isin agreement with the simulation and the design for ILC energies.In addition, the data taken for an electron beam of 5 GeV are used to measure the efficiency ofelectron/gamma identification using two tracking planes in front of the calorimeter. The geometryof the setup for this study is optimized in a simulation. Bremsstrahlung photons are produced by theelectron beam hitting the copper target installed upstream close to the dipole magnet. The magneticfield is chosen to allow both photons and electrons to travel within the acceptance of the secondtelescope T2 and arrive to LumiCal at a distance between them large enough to be resolved in thecalorimeter. The efficiency of electron/gamma identification is estimated to be more than 90% at2.5 mm matching distance.The most recent test beam 2020 campaign was dedicated to studies of the performance of deepLumiCal prototype with 15 sensitive layers. In these tests, 3 planes were equipped with FLAMEand the others - with double-gain readout using APV25 as seen in Fig. 7. In addition, edge-scans4 evelopment and performance of compact LumiCal Maryna Borysova , Pads core d10 - - , M I P æ n E Æ Electron beam 5 GeV DataData - fitMCMC - fit , Pads core d10 - - R a t i o Figure 5:
The average transverse shower pro-file as a function of the distance from the core, 𝑑 𝑐𝑜𝑟𝑒 , in units of the pad dimension (1.8 mm),for data (blue triangles) and MC simulation (redcircles). The distributions are obtained with a 5GeV electron beam. Radial residuals, mm4 - - N u m be r o f c l u s t e r s · First planeFirst plane fitSecond planeSecond plane fitElectron beam 5 GeV
Figure 6:
Distribution of residuals of the radialposition measurements in the tracking planes andthe calorimeter, obtained with a 5 GeV electronbeam.
Figure 7:
The sketch of experiment layout for a fiducial volume study were carried out, electron/gamma response was tested and data with atilted calorimeter were collected to study the reconstruction of showers in ILC-like geometry. Thedata analysis is in progress.
5. Summary
FCAL has developed a design for the very forward region for experiments at e + e − colliders.The LumiCal calorimeter is foreseen for the precise measurement of the integrated luminosityand BeamCal - for bunch-by-bunch luminosity measurement and high-energy electron tagging.Silicon sensors for prototype of LumiCal are designed and fabricated. Dedicated front-end ASICsare designed and fabricated in 130 nm CMOS technology. Prototypes of fully instrumented5 evelopment and performance of compact LumiCal Maryna Borysovadetector planes are built and tested. A prototype of a highly compact calorimeter was studied intest-beams at DESY resulting in an effective Molière radius of 8 mm at 5 GeV and the showerposition reconstruction of 440 𝜇𝑚 resolution at 5 GeV. The simulations are in agreement with thedata. Technologies developed in FCAL are applied in other experiments, e.g. CMS, XFEL andconsidered for LUXE at DESY. Acknowledgments
This study was partly supported by the Israel Science Foundation (ISF), Israel German Founda-tion (GIF), the I-CORE program of the Israel Planning and Budgeting Committee, Israel Academyof Sciences and Humanities, by the National Commission for Scientific and Technological Re-search (CONICYT - Chile) under grant FONDECYT1170345, by the Polish Ministry of Scienceand Higher Education under contract nrs 3585/H2020/2016/2 and 3501/H2020/2016/2, the Roma-nian UEFISCDI agency under 18PCCDI/2018 project and grant no. 16N/2020, by the Ministry ofEducation, Science and Technological Development of the Republic of Serbia within the projectOl171012, by the United States Department of Energy, grant de-sc0010107, and by the Euro-pean Union Horizon 2020 Research and Innovation programme under Grant Agreement no.654168(AIDA-2020). The measurements leading to these results have been performed at the Test BeamFacility at DESY Hamburg (Germany), a member of the Helmholtz Association (HGF).
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