Using thin scintillating fibers with Silicon Photomultiplier (SiPM) readout a
mo dular high-resolution charged-particle tracking detector has been designed.
The fiber modules consist of 2 x 5 layers of 128 round multiclad scintillating
fiber s of 0.250mm diameter. The fibers are read out by four SiPM arrays (8mm x
1mm) e ach on either end of the module.Comment: 6 pages, 5 figures, presented at the ICATPP 1

Gast, H.

Greim, R.

Kirn, T.

Schael, S.

Yearwood, G. Roper

English

arXiv

A novel modular high-resolution charged-particle tracking detector design using $250\mu m$ diameter, round, scintillating fibers and SiPM arrays for readout is presented. The fiber modules consist of 8 layers of 128 fibers, mechanically sta bilized by a carbon fiber / Rohacell foam structure. A prototype using scintillating fibers with a diameter of $300\mu m$ and two typ es of silicon photomultipliers has been tested in a $10GeV$ proton beam in late October 2006 at the T9 PS-beamline, CERN. We present the measured spatial resolu tion, efficiency and signal-over-noise for this setup. The advantage of this tra cker concept is a compact and modular design with low material budget and only little or no cooling requirements depending on the quality of the silicon photomultiplieres

Gast, Henning

Kirn, Thomas

Roper Yearwood, Gregorio

Schael, Stefan

CERN Document Server

arXiv:physics/0703158v1   15 Mar 2007 Ahigh resolution scintillating fiber tracker with SiPM readoutHenning Gast, Thomas Kirn, Gregorio Roper Yearwood, Stefan SchaelRheinisch-Westfa¨lische Technische Hochschule, Aachen, GermanyAbstractA novel modular high-resolution charged-particle tracking detector design using 250µm diameter, round, scintillatingfibers and SiPM arrays for readout is presented. The fiber modules consist of 8 layers of 128 fibers, mechanicallystabilized by a carbon fiber / Rohacell foam structure. A prototype using scintillating fibers with a diameter of 300µmand two types of silicon photomultipliers has been tested in a 10GeV proton beam in late October 2006 at the T9PS-beamline, CERN. We present the measured spatial resolution, efficiency and signal-over-noise for this setup. Theadvantage of this tracker concept is a compact and modular design with low material budget and only little or nocooling requirements depending on the quality of the silicon photomultiplieres.1. IntroductionThe idea to use scintillating fibers for charged-particle tracking is not new. Several experimentshave already successfully built and used scintillat-ing fiber trackers in high-energy and astro-particlephysics. The DØ experiment [1] for example choseto use a scintillating fiber tracker built from 835µmthick, multi-clad scintillating fibers, read out byVisible-Light Photon Counters (VLPC). The MICEexperiment took the idea of a scintillating fibertracker one step further, using 350µm thin mul-ticlad fibers, also read out by VLPCs. The use ofVLPCs requires a significant overhead, becausethey have to be operated in cryostats at temper-atures of around 7K. We therefore propose a newdetector design, using 250µm thin fibers, read outby Silicon Photomultipliers (SiPM) that can beused very effectively with only moderate cooling.2. Silicon PhotomultipliersA SiPM is a relatively new kind of multipixelsemiconductor photodiode that achieves a high in-trinsic gain by being operated above its breakdownvoltage[3]. SiPMs have a high photodetection effi-Fig. 1. Emission spectrum of a BCF-20 fiber [6] in compar-ison to the wavelength dependant response functions of aHamamatsu SiPM (model MPPC S10361-025U) and a Pho-tonique SiPM (model SSPM-0606EXP) [8]ciency of up to 65%, exceeding that of regular pho-tomultiplier tubes. In addition, they scale to smalldimensions, allowing for a compact readout of thinscintillating fibers.Major distributors of SiPM are Hamamatsu[4],Japan and Photonique[5], Switzerland. Pho-tonique SiPM of type SSPM-0606EXP and SSPM-050701GR were used during the beamtest of aSciFi/SiPM tracker prototype.Preprint submitted to Elsevier 16 March 2007Fig. 2. The photodetection efficiency of various SiPM typesdepending on the bias voltageSiPM from Photonique reach the peak sensitivityat around 600nm (see fig. 1). The type SSPM-050701GR has a very high internal gain greaterthan 106 while showing a dark count rate of around1MHz at room temperature and about 200kHzat −10◦C at the recommended operating voltageof typically 41V . Its photodetection efficiency at494nm is 25% (see fig. 2). The type PhotoniqueSSPM-0606EXP, which does not have any protec-tive epoxy layers on top of the device, exhibits aphotodetection efficiency of about 40% at a pixeldensity of 556 pixels per mm2. The gain of theSSPM-0606EXP device is about 3 · 105. The noiseof this device is about 5 times higher than that ofthe SSPM-050701GR device.The Hamamatsu model MPPC S10361-025U hasan extremely high pixel density of 1600/mm2. Theresulting low geometrical fill factor of 37% signifi-cantly limits the photodetection efficiency to about25% at 494nm. Hamamatsu also offers a modelS10361-100U with only 100 pixels per mm2 anda geometrical fill factor close to 80% that offers aphotodetection efficiency of 65%[4]. The dark noiserate of the tested Hamamatsu MPPC S10361-025Uis 300kHz at 21◦C and around 20kHz at −20◦C.3. Beamtest of the first PrototypeThe prototype (see fig. 3) consisted of 300µm ×300µm square, multiclad fibers of type Bicron[6]BCF-20 with white EMA coating and PhotoniqueSiPMs of type SSPM-050701GR and of type SSPM-Fig. 3. A drawing of the beamtest setup shows the triggers,the beam telescope and the actual prototype consisting oftwo fiber ribbons and 19 SiPM to read out the fibers.0606EXP. The peak emission wavelength of BCF-20fibers is at 492nm, matching the peak sensitivity ofPhotonique SSPM-0606EXP SiPM (see fig. 1).The scintillating fibers were arranged in two rib-bons of 3 × 10 fibers. The fiber ribbons were sta-bilized using glue as an adhesive. Both ends of the3-fiber ribbons were glued into a plastic connectorand polished. One end was connected to a SiPM bymounting it into a copper block and held in place bya aluminum frame and a spring. The SiPM’S weremounted into the copper-block to allow for a tem-perature control. Part of the beam test the opposingend of the fibers was covered by a reflective foil toincrease the light output for the SiPMs.A beam telescope with four silicon strip modulesfrom the CMS tracker project was used to measurethe position of the incident particles. The siliconmodules had a strip pitch of 113..139µm and an in-trinsic resolution of about 40µm [7].Four scintillator counters, two in front of and twobehind the prototype provided the trigger with ahalo counter as a veto.The beamtest of the prototype took place in a10GeV proton beam at PS, CERN. During the2Fig. 4. The signal spectrum and the dark spectrum of aSSPM-0606EXP device during the beamtest with reflectivefoil. Both spectra are normalized to 1.Fig. 5. A plot of the measured efficiency of the particle de-tection vs. the measured average number of photoelectronsfor new and old Photonique SiPM. The efficiency was de-termined for the lowest possible cut of 0.5p.e. for the SiPMsignal.beamtest, 1.5 million events were recorded andabout 800,000 particle tracks were reconstructedwith the beam telescope. The position of each fibercolumn was determined by reconstructing the posi-tion of particles that produced a high signal withinthe fiber (see fig. 4). The average measured distancebetween two fiber columns was 309µm with a preci-sion of 10µm. The spatial resolution for particles ofperpendicular incidence that pass through all threefibers of one fiber column was about 90µm whichmatches the expected intrinsic resolution of d√12where d is the fiber pitch.Knowing the positions of the fibers, we deter-mined the average photoelectron yield for particlesFig. 6. Drawing of the geometry of a single tracker mod-ule, showing the fiber placement on the mechanical supportstructure and the frontend hybrids mounted on the fibermodule.that passed through one of the fiber columns. Forparticles with perpendicular incidence the averagephotoelectron yield for both types of SiPMwith andwithout reflective foil on the opposing fiber end wasmeasured. The SSPM-050701GR signal was about2.2 photoelectrons without and 3.5 photoelectronswith reflective foil (see fig. 5). The SSPM-0606EXPachieved an average photoelectron yield of 3.8 with-out reflective foil and 5.8 with reflective foil (omit-ting one SiPM that actually showed a reduced pho-toelectron yield after adding the reflective foil).The measured signal-to-noise ratio was about20 for the SSPM-0606EXP with reflective foil andabout 100 for the SSPM-050701GR with reflectivefoil. The mean efficiency for perpendicular inci-dence, setting a cut at 0.5 photoelectrons, was 96%for the ribbon read out by the SSPM 0606EXP and91% for the SSPM 050701GR.4. Tracker Module DesignThe tracker design is modular. It consists of sev-eral layers of tracker modules, each module consist-ing of 8 layers of scintillating fibers with 128 fibersin every layer. 4 layers of fibers are glued to each sideof a module core that consists of 5mm thick Roha-cell foam covered by 100µm thin carbon fiber skinson either side of the module (see fig. 6). Neighboringlayers are shifted by one half of the fiber pitch withrespect to each other to improve the spatial resolu-tion.3Fig. 7. Spatial resolution for a bundle of fibers of 300µmwidth from testbeam data and Monte Carlo simulations.Testbeam data obtained with a fiber bundle without reflec-tive foil and Photonique SSPM-050701GR SiPM readout areplotted using square markers. Results fromMonte Carlo sim-ulations are added to study the behavior for improved photoelectron yields. A yield of 5.8 photo electrons was reachedin the testbeam with SSPM-0606EXP SiPMs and reflectivefoil, but only data at 0◦ were taken in this configuration.SiPM arrays with a sensitive area of 8mm×1mmand 32 readout channels, each channel covering anarea of 0.25mm × 1mm are used for column-wisefiber readout. The SiPM arrays are mounted on al-ternating ends of the fiber modules along with an in-tegrated preamplifier and digitization solution. Theopposing ends of the fibers are covered by a reflec-tive coating.A dedicated Monte Carlo simulation, again usingthe Geant4 package, has been developed for compar-ison to and generalization of the testbeam results.A key question to be answered was the spatial res-olution obtained with a fiber module as a functionof the mean photo electron yield np.e. of the fibre-SiPM chain. Figure 7 shows the result. The spatialresolution σy′ is plotted for different values of np.e.and depending on the angle α of incidence of a par-ticle, projected into the bending plane of the mag-net. σy′ is the resolution along the axis perpendic-ular to the fibers. Since the beam telescope used inthe testbeam measured the coordinate y perpendic-ular the direction of incidence z, σy′ is calculatedfrom the measured σy and the positioning accuracyσz = 10µm as follows:σy′ = σy cosα⊕ σz sinα (1)For the photo electron yield achieved in the test-beam, a spatial resolution of 72µm is obtained atthe mean projected angle of incidence, which is α¯ =11◦ for the PEBS geometry.5. ConclusionThe testbeam results indicate that this conceptfor a high-resolution SciFi/SiPM tracker is techni-cal feasible. The average yield of 6 photoelectronswith a reflective foil on one fiber end and the SSPM-0606EXP SiPM matched our requirements. SiPMswith a reduced pixel density and a 50% higher PDEare already commercially available from Hama-matsu. Furthermore the light output from scintil-lating fibers can be improved by 20% − 40% usingfibers without white coating as measurements withdifferent fiber coatings conducted for the CREAMexperiment have shown[9]. Up to now we have notengineered the optical coupling between fibers andSiPM’s at all.A spatial resolution as good as 40µm is in prin-ciple possible, depending on the granularity of thereadout, the quality of the SiPM’s, the qualtity ofthe optical coupling of the fibers to the SiPM’s andthe type of fibers used. With the understanding andtechnology we have today, an average spatial reso-lution of 60µm is expected.References[1] DØ Collaboration, NIM A565, p. 463-537, 2006[2] Yoshida, M., MICE Overview - Physics Goals AndProspects, Proceedings of EPAC 2006, Edinburgh,Scotland[3] Dolgoshein, B. et al., NIM A504, p. 48-52, 2003[4] Hamamatsu Photonics, K.K., Japan URL:http://sales.hamamatsu.com[5] Photonique SA, Switzerland URL:http://www.photonique.ch[6] Saint-Gobain Crystals, Paris, France URL:http://www.bicron.com[7] The CMS Collaboration, NIM A517, p. 7793, 2004[8] Musienko, Y., Unpublished Measurements for the PEBSproject at APDlab, CERN, Switzerland, 2007[9] Young Soo Yoon et al., 29th ICRC Pune, p. 101-104,20054

A high resolution scintillating fiber tracker with SiPM readout

RWTH Publications

Publikationsserver der RWTH Aachen University

A high resolution scintillating fiber tracker with SiPM readout for the
  PEBS experiment

A high resolution scintillating fiber tracker with SiPM readout for the PEBS experiment

Abstract

Similar works

Full text

Available Versions

CERN Document Server

RWTH Publications

Publikationsserver der RWTH Aachen University