The IceCube Collaboration foresees to upgrade IceTop, the present surface
array, with scintillator detectors augmented by radio antennas. As one of
several goals the scintillator detectors will be used to measure and mitigate
the effects of snow accumulation on the IceTop tanks: the increasing energy
threshold and efficiency loss are nowadays the sources of the largest
systematic uncertainties in shower reconstruction and mass composition
analysis. In addition, the upgrade will provide useful experience for the
development of next generation neutrino detectors proposed for the South Pole.
In the Austral summer season, 2017-2018 two full "stations" were installed near
the center of the IceTop array. Each station features custom-designed
electronics and consists of seven detectors, each having an active area of
1.5m$^{2}$ plastic scintillator and wavelength shifting fibers read out by a
Silicon Photomultiplier. In this contribution we review the detector design and
performance, and show results from more than one year of operation of the
prototype stations. During that year several thousand air shower events have
been measured in coincidence with IceTop.Comment: Presented at the 36th International Cosmic Ray Conference (ICRC
  2019). See arXiv:1907.11699 for all IceCube contribution

Huber, Thomas

Kauer, Matt

Tosi, Delia

Wendt, Chris

English

arXiv

DESY

The Scintillator Upgrade of IceTop: Performance of the Prototype Array

IceCube Collaboration

KITopen

PoS(ICRC2019)309The Scintillator Upgrade of IceTop: Performance ofthe prototype arrayThe IceCube Collaboration∗http://icecube.wisc.edu/collaboration/authors/icrc19_icecubeE-mail: mkauer@icecube.wisc.eduThe IceCube Collaboration foresees to upgrade IceTop, the present surface array, with scintillatordetectors augmented by radio antennas. As one of several goals the scintillator detectorswill be used to measure and mitigate the effects of snow accumulation on the IceTop tanks:the increasing energy threshold and efficiency loss are nowadays the sources of the largestsystematic uncertainties in shower reconstruction and mass composition analysis. In addition, theupgrade will provide useful experience for the development of next generation neutrino detectorsproposed for the South Pole. In the Austral summer season, 2017-2018 two full “stations” wereinstalled near the center of the IceTop array. Each station features custom-designed electronicsand consists of seven detectors, each having an active area of 1.5m2 plastic scintillator andwavelength shifting fibers read out by a Silicon Photomultiplier. In this contribution we reviewthe detector design and performance, and show results from more than one year of operation ofthe prototype stations. During that year several thousand air shower events have been measuredin coincidence with IceTop.Corresponding authors: Matt Kauer†1, Thomas Huber2,3, Delia Tosi1, Chris Wendt11 Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin,Madison, WI 53706, USA2 Institut für Kernphysik, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany3 DESY, D-15738 Zeuthen, Germany36th International Cosmic Ray Conference -ICRC2019-July 24th - August 1st, 2019Madison, WI, U.S.A.∗For collaboration list, see PoS(ICRC2019) 1177.†Speaker.c© 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). http://pos.sissa.it/PoS(ICRC2019)309Scintillator Performance Matt Kauer1. IntroductionIceCube is a cubic-kilometer neutrino detector installed in the ice at the geographic SouthPole [1] between depths of 1450 m and 2450 m, which was completed in 2010. Reconstructionof the direction, energy, and flavor of the neutrinos relies on the optical detection of Cherenkovradiation emitted by charged particles produced in the interactions of neutrinos in the surroundingice. Additionally, an array of surface detectors, IceTop, has also been deployed for cosmic raystudies in the PeV energy range [2] and to provide a partial veto of the down-going background ofpenetrating muons.Accumulating snow cover over the IceTop tanks is continuously increasing the energy thresh-old for the detection of cosmic ray air showers [3]. The complex attenuation effects of the snow addsystematic uncertainties to air shower measurements, particularly in the mass composition analy-sis. We have designed and proposed an upgrade to IceTop consisting of homogeneously-spacedscintillator stations with an areal coverage similar to IceTop. We plan on deploying up to 32 scin-tillator stations over a few years [4, 5]. Two prototype stations with seven scintillator panels eachwere deployed in 2018 shown in Fig. 1. Each station consists of a different data acquisition (DAQ)architecture and is further discussed in Sec. 3. These two stations provide a proof of design andconcept for not only the surface array upgrade but also for the surface field hub concept and WhiteRabbit timing to be used for IceCube-Gen2.Figure 1: Deployment of the 14 scintillator panels at the South Pole. There are 2 scintillator panels deployedat each location A-G. The nearby IceTop tank positions are shown in circles. The overlapping of the circleswith the scintillator locations indicates where the panels are placed on top of an IceTop tank.2PoS(ICRC2019)309Scintillator Performance Matt Kauer2. The Scintillator PanelEach scintillator detector is designed to have a total sensitive area of 1.5 m2 and a total weightof less than 50 kg, to be easily transportable by two people. Each panel comprises 16 extrudedplastic scintillator bars (produced by FNAL-NICADD [6]), made of polystyrene with doping of1% PPO and 0.03% POPOP and coated with a 0.25± 0.13 mm thick layer of TiO2 reflector. Eachbar is 1 cm thick, 5 cm wide and 1.875 m long and has two holes with a diameter of 2.5± 0.2 mm.Y-11(300) wavelength shifting fibers (produced by Kuraray 1) are routed and looped back throughthe holes of the bars, resulting in a bundle of 32 fiber ends which is then readout by a 6×6 mm2Silicon PhotoMultiplier (SiPM "13360-6025PE", produced by Hamamatsu). More information canbe found in [7].3. The Data AcquisitionFigure 2: Timing difference between coincident scintillatorand IceTop events.Each of the two prototype stationshas a different DAQ concept. One sta-tion’s DAQ was developed by the Wis-consin IceCube Particle AstrophysicsCenter (WIPAC) and utilizes digitalcommunications between the scintilla-tor and surface field hub for increasedbandwidth. This is known as the mi-croDAQ station. The other station’sDAQ was developed by the DeutschesElektronen-Synchrotron (DESY) andthe Karlsruhe Institute of Technology(KIT) and is capable of sending fullwaveforms back to the surface field hub.This is known as the TAXI station [8].Each surface field hub houses WhiteRabbit GPS timing distribution and communications via fiber link to the IceCube Computing Lab(ICL). Further detailed information about the two DAQs can be found in [9].4. Scintillator Characterization and Stability4.1 White Rabbit TimingVerification of GPS timing distribution via White Rabbit was realized using coincident eventsbetween IceTop and the scintillators. There are two locations where a scintillator panel is positioneddirectly above an IceTop tank. The scintillator time delay relative to IceTop of ∼335 ns is measuredand shown in Fig. 2 and is consistent with 60 m copper cable delay which is not corrected for onlineas is with IceTop.1http://kuraraypsf.jp/pdf/all.pdf3PoS(ICRC2019)309Scintillator Performance Matt Kauer4.2 Temperature CompensationFigure 3: An example plane fit to the temperature vs volt-age vs measured gain of the SiPM.The gain and photo-detection ef-ficiency (PDE) of SiPMs is tempera-ture dependent. The on-board scintil-lator microDAQ mitigates this effect atthe software level by periodically mea-suring the temperature of the SiPM andadjusting the bias voltage to maintaina constant gain. The temperature de-pendence of each individual scintilla-tor was mapped out prior to deploy-ment and a plane fit to the temperature-vs-voltage-vs-gain surface is sufficientfor the operating range of interest asshown in Fig. 3. The gain is set to30 ADC/PE (Analog-to-Digital Conver-sion units per Photo-Electron) to opti-mize the dynamic range of the microDAQ.4.3 Gain and MIP Light YieldThe gain of the SiPM is measured and monitored in units of ADC counts vs PE by taking theFast Fourier Transform (FFT) of the “finger plot” charge histogram shown in Fig. 4. This proves tobe a precise and computationally quick method as the finger spectrum is analogous to a sine wavein frequency space as shown in Fig. 5. Comparing the PE separation measured from Gaussian fitsin Fig. 4 to the FFT result in Fig. 5, the measurements are consistent. The Gaussian fits give anaverage gain of 29.3± 0.4 ADC/PE and the FFT of the charge histogram gives a gain of 29.4± 0.1ADC/PE proving to be a quick and robust method for determining the gain of the SiPM in units ofADC/PE.Figure 4: Gaussian fits to the finger spectrum give an average PE separation of 29.3± 0.4 ADC/PE whichis consistent with the FFT result shown in Fig. 5.4PoS(ICRC2019)309Scintillator Performance Matt KauerFigure 5: The FFT of charge histogram returns a gain of 29.4± 0.1 ADC/PE which is consistent with theGaussian fit method shown in Fig. 4 proving to be a quicker and more robust method for determining thegain of the SiPM.A gain of 30 ADC/PE was chosen to optimize the dynamic range of the microDAQ and 30ADC/PE is the setpoint for the SiPM gain temperature compensation and is stable within 2 % asshown in Fig. 6.Figure 6: Example temperature-compensated gain stability of one scintillator panel over a broad range ofoperating temperatures.The estimated light yield from minimally ionizing particles (MIPs) is determined by an expo-nential plus Gaussian fit to the spectra after pedestal subtraction and gain correction. An exampleis shown in Fig. 7. The MIP peak light yield from the scintillators ranges from 39-44 PE/MIP andis consistent with GEANT4 optical simulations [5].4.4 Energy LinearityThe scintillator charge linearity is evaluated using coincident events with IceTop. We observea linear charge correlation between IceTop and the scintillators down to IceTop’s charge threshold(∼ 0.16 VEM) as shown in Fig. 8. Charge threshold effects in IceTop due to snow coverage areevident and will be significantly improved with the addition of the scintillator surface array [5].5. Performance of the ArrayThe scintillator data is acquired when one or more scintillator signals cross the discriminatorthreshold (∼ 0.2 MIP). The results shown here require three or more scintillators to have triggeredin coincidence (± 200 ns).5PoS(ICRC2019)309Scintillator Performance Matt KauerFigure 7: An example fit to the MIP peak. The pedestal is in purple, the exponential dark noise componentis green, the MIP component estimated with a Gaussian is in blue, and the fit total is in red. In this examplethe gain was measured to be 29.4 ADC/PE and the MIP was fit to 39.2 PE/MIP.Figure 8: Coincident events are found between IceTop station 33 (tank A) and scintillator location B andIceTop station 43 (tank B) and scintillator location F as shown in Fig.1. Plots show the charge of scintillatorevents in ADC counts vs charge of coincident IceTop events in VEM (vertical equivalent muon).5.1 Reconstruction of Air ShowersThe incidence direction of the shower was reconstructed by a plane-front-fit for the scintillatorarray. The IceCube Laputop algorithm is used for IceTop, whereby the plane-front is calculatedand then used as a seed for a fit to the lateral distribution of the signals and shower front curvature.Fig. 9 shows the distributions of the reconstructed zenith and azimuth values of the scintillators forevents in coincidence with IceTop.The accuracy of the scintillator air-shower reconstruction is estimated by comparing the recon-structed shower plane values with the ones obtained from IceTop data. In Fig. 10 the differences inthe zenith and azimuth angle of the plane front between the scintillator array and IceTop Laputopreconstruction are shown. A good correspondence between the results of the reconstructions isobtained, therefore the quality of the timing information is rather good and sufficient for air showerdetection.6PoS(ICRC2019)309Scintillator Performance Matt KauerFigure 9: Distributions of the reconstructed zenith and azimuth angles of events detected by the TAXIscintillator station (Sec. 3) which are coincident with IceTop events.Figure 10: Histograms of the differences between the TAXI scintillator station (Sec. 3) event reconstructionangles and IceTop Laputop reconstructions. Only IceTop events with Laputop reconstructed core positionswithin the scintillator area are considered. The Gaussian fits are in red with fit results shown in the top-left.6. SummaryThe scintillator upgrade of IceTop is in part a test of the scintillator surface array and in part atest of the infrastructure for the IceCube upgrade. We have demonstrated the stability of the WhiteRabbit timing distribution and the feasibility of surface field hubs for the upgrade. The scintillatorsurface array is performing as expected with light yields around 40-45 PE/MIP as predicted byGEANT4 optical simulations. The charge thresholds of the scintillator surface array are around afactor of five lower than that of IceTop and mitigate the snow accumulation effects observed fromIceTop detectors. The direction of incident air showers are reconstructed accurately, taking intoaccount the small number and area of the detectors. The deployed scintillator stations are a proofof concept of the feasibility of the detector design and shows it fulfills the requirements of a surfaceinstrumentation upgrade of IceTop.7PoS(ICRC2019)309Scintillator Performance Matt KauerReferences[1] IceCube Collaboration, M. G. Aartsen et al., JINST 12 (2017) P03012.[2] IceCube Collaboration, R. Abbasi et al., Nucl. Instrum. Meth. A700 (2013) 188–220.[3] IceCube Collaboration, K. Rawlins, PoS(ICRC2015)628 (2016).[4] IceCube Collaboration, F. G. Schröder, PoS(ICRC2019)418 (these proceedings).[5] IceCube Collaboration, A. Leszczyńska and M. Plum, PoS(ICRC2019)332 (these proceedings).[6] D. Beznosko, A. Bross, A. Dyshkant, A. Pla-Dalmau, and V. Rykalin.[7] IceCube Collaboration, A. Haungs, EPJ Web Conf. 210 (2019) 06009.[8] T. Karg, A. Haungs, M. Kleifges, R. Nahnhauer, and K. H. Sulanke, Introducing TAXI: a TransportableArray for eXtremely large area Instrumentation studies, in 6th International Workshop on Acoustic andRadio EeV Neutrino Detection Activities (ARENA 2014) Annapolis, MD, June 9-12, 2014, 2014.arXiv:1410.4685.[9] IceCube-Gen2 Collaboration, S. Kunwar, T. Huber, J. Kelley, and D. Tosi, PoS(ICRC2017)401(2018).8

The Scintillator Upgrade of IceTop: Performance ofthe prototype array

The Scintillator Upgrade of IceTop: Performance of the prototype array

The Scintillator Upgrade of IceTop: Performance of the prototype array

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