PoS(PhotoDet2015)039 http://pos.sissa.it/ for the MuSEUM collaboration ∗ kanda@post.kek.jp Speaker. Muon spin spectroscopy has beenPARC utilized (Japan for Proton Accelerator both Research particle Complex), physics thebeam and world’s has highest-intensity been material realized. pulsed science. muon With the increase Athigh-rate of J- capability the beam becomes intensity, essential. the Spectroscopy requirement of for the muonof detector’s spin positron is angular performed asymmetry by measurement fromphotomultiplier muon decays. (SiPM) readout A new is muon underhyperfine spin splitting. development spectrometer for with The precision silicon positron measurementreadout-circuits detector of with consists muonium ASIC of based tiled ASD plasticthe and scintillators, detector FPGA was SiPMs, implemented developed and and multi-hit its fast TDC. performancebeam A was at prototype evaluated with of J-PARC. a Based high intensity onsponse, pulsed an a muon understanding realistic event of generator SiPM’sthe measurement. was characteristics developed Several and methods for analog of evaluation pileup circuituncertainty. of correction re- were systematic In studied uncertainties this to of paper, minimizediscussed. the overview systematic of the project and details of the detector development are ∗ Copyright owned by the author(s) under the terms of the Creative Commons c ⃝ Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). International Conference on New Photo-detectors, PhotoDet2015 6-9 July 2015 Moscow, Troitsk,Russia Sohtaro Kanda Department of Physics, University of Tokyo,E-mail: 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan Development of a new positron countingwith system SiPM readout for muon spin spectrometers PoS(PhotoDet2015)039 B N and F N where B B N N SR), which is known + − lifetime and a positron F F µ N N s µ = A 2 Schematic of a muon spin spectrometer Figure 1: Figure 1 shows a schematic view of a muon spin spectrometer for the measurements of muon Muon spin spectroscopy can be performed with both continuous and pulsed muon beam. A In the presence of a magnetic field, the muon spin undergoes precession with a frequency Muons are obtained from parity violating decay of pion with spin polarized along the direction 1.2 Requirements for a muon spin spectrometer are the number of positron detected by the forward/backward counter. proportional to the magnetic field strength.causes A muon non-uniformity spin or relaxation. a The distribution muon in stoppedexperimental the in technique magnetic matter is field is utilized called as a muon local spin magnetic probe. rotation/relaxation/resonance This ( of its momentum. Thecan muon be decay obtained is by also the a measurement of parity the violating decay process, positron so angular asymmetry. the averaged muon spin Development of a newSohtaro positron Kanda counting system with SiPM readout for muon spin spectrometers 1. Introduction 1.1 Muon spin spectroscopy as an unique method tomagnetism investigate in the micro-second magnetic time properties scale. of Furthermore,and test a search of for material the physics and beyond standard the the model standard dynamicsor of model its particle of can bound physics the be state. performed via spin spectroscopy of muon decay timing and positron emissionthe angle. upstream direction. The incident A positive muonenergy muon is via beam the implanted electromagnetic is into interaction. spin a Theis target polarized muon material in emitted decays and with with the a an muon 2.2 positron loses angular is its asymmetry detected kinetic as by a aphoto multiplier positron function tube counter, (PMT). of The which time the typically dependentthe positron angular consists information asymmetry kinetic of of of positron a energy. time counting plastic contains evolutiondownstream The scintillator of of the and muon decay muon spin. a decay volume. The The positron asymmetry is counters defined are as located upstream and PoS(PhotoDet2015)039 ]. It consists of an analog signal 1 pixel pitch). m µ 3 1.3 mm active area (50 × at 500 kW accelerator beam power. The beam is double pulsed in 600 ns s / + µ 7 10 × 1 The ASIC contains two steps of voltage amplifier. Slow control parameters are described in As a series of readout electronics for SiPM, Kalliope (KEK Advanced Liner and Logic board Instead of a PMT, a silicon photomultiplier developed by Hamamatsu Photonics K.K. was A plastic scintillator with a fast decay time constant and an emission wavelength around 450 A traditional muon spin spectrometer is the combination of plastic scintillator, PMT, and dis- 20 bits of register pattern fordiscriminator threshold, amplifier and gain, fine signal tuning shaping of parameters thethe bias implementation related voltage of to for a amplifier SiPM. multi-hit biases, The TDC FPGArotating with firmware 250 1 contains MHz ns timing clocks. resolution, which is realized by four phase circuit with an ASIC named VOLUME2012 and a digital circuit with a FPGA. Integrated Optical detector for Positron and Electron)and has Institute been developed of by the Materials Electronics Structure Group Science (IMSS) of KEK[ adopted as a photo sensor.which A has MPPC 667 (Multi pixels in Pixel 1.3 Photon mm Counter) S12825-050P-01 was utilized, 2.1.3 Readout electronics nm is suitable for aThe new dimension positron of counter. a EJ212 segment produced was by decided ELGEN based on technologies simulation was study adopted. 2.1.2 as hereinafter SiPM described. crete signal processing electronics.beam at To deal J-PARC, a with new the positronsists unprecedented counting of system high a for intensity small a segment pulsedelectronics muon of with muon spectrometer ASIC plastic was based scintillator, designed. amplifier, a shaper, Itmented and silicon in con- discriminator photomultiplier FPGA. (ASD) (SiPM), and multi-hit and TDC fast imple- readout 2.1.1 Plastic scintillator 2.1 Detector components interval with a repetition cycleeffect on of the 25 accumulation Hz. of statistics infor The a a high limited positron intensity beam counter time. is pulsed more On muonare severe the beam than detected other in hand, has by the the a a case requirements muon of beneficial order a spin continuous to spectrometer beam. at achieve A short a number intervals ofsegmentation large and positrons of solid the signal detector angle pileup with becomes and an severe. integrated the readout In suppression electronics of is essential. signal pileup at2. the Detector same design time, fine Development of a newSohtaro positron Kanda counting system with SiPM readout for muon spin spectrometers pulsed muon beam is suitable forhighest high intensity statistical pulsed precision muon in beam a was short established(MLF) measurement at Muon time. J-PARC Materials The Science and world Life Establishment Science (MUSE).D-Line Facility is The typical muon beam intensity at MLF MUSE PoS(PhotoDet2015)039 ]. 1 4 Simulation setup with an accumulated event display Figure 2: ]. Following chapters describe in more details the positron counting system devel- 3 , 2 The event loss due to the signal pileup was evaluated as a function of the maximum event rate. Figure 3 shows a typical hit map on the detector. Figure 4 shows a simulated positron time Figure 2 shows a geometrical simulation setup with an accumulated event display. The red In order to estimate the positron counting rate and systematic uncertainties of the positron de- At J-PARC MLF MUSE, there were several proposals of muon spin spectrometer develop- Figure 5 shows aevents simulated per result total of events. event Polynomial loss.Pileup fitting correction was was The performed applied and ordinate to a the axisure correction time indicates 6 function spectrum presents the was for a obtained. suppression number result of ofnormalized systematic of by lost uncertainty. pileup the total Fig- correction number where of events. theThe The abscissa red black axis histogram histogram is indicates corresponds a the to result without a relative pileup statistics corrected correction. result according to the correction function obtained spectrum. The blue line representsspectrum with the signal ideal pileup. time spectrum while the red line represents the time lines correspond to the muon trajectoriesThree and layers the of blue positron lines counter correspondA to were the three-dimensional placed positron downstream magnetic trajectories. of field themented. distribution gas calculated chamber Detector filled by response with finite was krypton. waveform implemented element and based photon method yield. on was Individual the fluctuation imple- measurement ofconsidered. SiPM’s results photo of detection efficiency a (PDE) signal was pulse tector performance, a Monte-Carlo simulationportation framework and was the developed. particle tracking The were muon simulated beam by trans- a GEANT4-based event generator. 3. Simulation study ment for each specific purposes.Helmholtz coil and For a material variation science, for the general measurement purpose in high detectors magnetic with field have three-axis been developed[ opment for the MuSEUM experiment. Development of a newSohtaro positron Kanda counting system with SiPM readout for muon spin spectrometers 2.2 Muon spin spectrometer at J-PARC MUSE For particle physics, a new muontroscopy spin of spectrometer muonium was atom proposed called for MuSEUM aexperiment[ precision (Muon microwave Spectroscopy spec- Experiment Using Microwave) PoS(PhotoDet2015)039 ]. A new 4 Normalized statistics 839 839 0.008513 0.008513 h2h2 Simulated pileup correction Entries Entries Mean Mean 839 839 0.9965 0.9965 RMS RMS Integral Integral 839 839 3 mm plastic scintillator with a SiPM Simulated positron detection time spectrum h1h1 × Figure 6: Entries Entries Mean Mean 839 839 0.9599 0.9599 RMS RMS 0.03418 0.03418 Integral Integral 0.8 0.85 0.9 0.95 1 1.05 1.1 0 50 300 250 200 150 100 Figure 4: 10 mm 5 × Maximum event rate (MHz) Simulated event loss 0.001951 0.001951 0.001799 0.001799 ±± 0.0004383 0.0004383 0.0004409 0.0004409 ±± 829.1 / 835 829.1 / 835 ±± ±± 0.04618 0.04618 0.001431 0.001431 −− 0.006667 0.006667

−− 0.0001331 0.0001331

Simulated hit map on the detector plane Figure 5: 0.5 1 1.5 2 2.5 3 3.5 / ndf / ndf 22 p3 p3 p1 p1 p2 p2 Prob Prob p0 p0 0.5512 0.5512 χχ With the objective of high-rate data processing, Kalliope readout system has no ADC for For the proof of principle and the specification evaluation of a detector with plastic scintilla- 0 0.1

0.16 0.14 0.12 0.08 0.06 0.04 0.02 Normalized event loss event Normalized Figure 3: muon spin spectrometer for thetype MuSEUM evaluation experiment and was simulation developed study. on Figureof the 7 ground the is of positron a t counter conceptual heproto- consists designdirectly of attached of the to a detector. the 10 An center mm detector unit of plane cell the with detector scintillator segment. segments. The FigureCircuit SiPMs 8 Board) were plane. is arranged a in photograph a of matrix the on a developed PCB (Printed pulse height or charge measurement. In order to perform gain tuning and operation monitoring, 4.2 Operation and tuning of the detector tor and SiPM, a detector prototype was developed and evaluation tests were performed[ 4. Development of a positron counter 4.1 Designing and production of the detector from Figure 5. After pileupacceptable correction, level. systematic uncertainty due to pileup was suppressed to an Development of a newSohtaro positron Kanda counting system with SiPM readout for muon spin spectrometers PoS(PhotoDet2015)039 2467 2467 hh Entries Entries Mean Mean 3014 3014 31.62 31.62 RMS RMS 11.18 11.18 Integral Integral Time over threshold (ns) Measured TOT spectrum 10 20 30 40 50 60 70 80 90 100 0 80 60 40 20 200 180 160 140 120 100 Figure 9: 6 Conceptual design of the detector Figure 7: ., J. Phys. Conf. Ser. 551, 012063 (2014). Developed detector plane ., PoS(NUFACT2014)087 (2015). et al ., JPS Conf. Proc. 8, 025006 (2015). et al et al Figure 8: S. Kanda K. Shimomura, AIP Conf. Proc. 1382, 245 (2011). P. Strasser K. M. Kojima Muon spin spectroscopy is an unique technique for both material science and particle [3] [4] [1] [2] physics. For muon spin spectroscopynew with type high of intensity highly pulsed segmented muonrequirements positron beam, for counter development positron was of proposed. counting a system, AsSiPM, a a and positron solution fast counter that readout with meets electronics segmented the study, was plastic a designed. scintillator, high After rate prototype capable development positrondetector and counter system simulation for was the assembled MuSEUM andMUSE. experiment a This was beam developed. work test was The is supported scheduled by in JSPS November Grant-in-Aid 2015 for at JSPS J-PARC MLF Fellows NumberReferences 26-11374. 5. Summary time over threshold (TOT) samplingtypical was measured implemented TOT spectrum in with the discretethe structure FPGA derived SiPM. firmware. from Due the to Figure Geiger a 9 mode correlationdetector operation shows is between of a ensured TOT and by tuning signal the pulse operation height, voltages uniform for performance each of SiPMs. the Development of a newSohtaro positron Kanda counting system with SiPM readout for muon spin spectrometers