WLS Fibers Research Articles

Large area scintillation muon hodoscope for monitoring of atmospheric and heliospheric processes

A new muon hodoscope for investigations of the processes in heliosphere and terrestrial atmosphere by means of cosmic ray muons is described. The setup design is based on multi-layer assemblies of narrow long scintillation strips with WLS fiber readout. Features of the hodoscope design are described and results of tests of a full-scale prototype of the basic unit of the hodoscope detection system - the mod- ule - are discussed.

Large-area sandwich veto detector with WLS fibre readout for hadron spectroscopy at COMPASS

A sandwich detector composed of scintillator and steel-covered lead layers was introduced in the fixed-target COMPASS experiment at CERN for vetoing events not completely covered by the two-stage magnetic spectrometer. Wavelength shifting fibres glued into grooves in the scintillator tiles serve for fast readout. Minimum ionising particles impinging on the 2 m ×2 m detector outside of a central hole, sparing the spectrometer's entry, are detected with a probability of 98%. The response to charged particles and photons is modelled in detail in Monte Carlo calculations. Figures of merit of the veto trigger in 190 GeV/ c π − + p (or nucleus) experiments are an enrichment of exclusive events in the recorded data by a factor of 3.5 and a false-veto probability of 1%.

Tests of the MICE Electron Muon Ranger frontend electronics with a small scale prototype

The MICE experiment is being commissioned at RAL to demonstrate the feasibility of the muon ionization cooling technique for future applications such as the Neutrino Factory and the Muon Collider. The cooling will be evaluated by measuring the emittance before and after the cooling channel with two 4 T spectrometers; to distinguish muons from the background, a multi-detector particle identification system is foreseen: three Time of Flight stations, two Cherenkov counters and a calorimetric system consisting of a pre-shower layer and a fully active scintillator detector (EMR) are used to discriminate muons from pions and electrons. EMR consists of 48 planes of triangular scintillating bars coupled to WLS fibers readout by single PMTs on one side and MAPMTs on the other; each plane sensible area is 1 m 2. This article deals with a small scale prototype of the EMR detector which has been used to test the MAPMT frontend electronics based on the MAROC ASIC; the tests with cosmic rays using both an analog mode and a digital readout mode are presented. A very preliminary study on the cross talk problem is also shown.

The MU-RAY project: Volcano radiography with cosmic-ray muons

Cosmic-ray muon radiography is a technique for imaging the variation of density inside the top few 100 m of a volcanic cone. With resolutions up to 10s of meters in optimal detection conditions, muon radiography can provide images of the top region of a volcano edifice with a resolution that is considerably better than that typically achieved with conventional methods. Such precise measurements are expected to provide us with information on anomalies in the rock density distribution, like those expected from dense lava conduits, low density magma supply paths or the compression with depth of the overlying soil. The MU-RAY project aims at the construction of muon telescopes and the development of new analysis tools for muon radiography. The telescopes are required to be able to work in harsh environment and to have low power consumption, good angular and time resolutions, large active area and modularity. The telescope consists of two X– Y planes of 2×2 square meters area made by plastic scintillator strips of triangular shape. Each strip is read by a fast WLS fiber coupled to a silicon photomultiplier. The readout electronics is based on the SPIROC chip.

Performance of a scintillating strip detector with G-APD readout

The upgraded KLM detector end cap of Belle II experiment will consist of more than 16 000 scintillating detectors of 0.5–2.8 m long strips. One of possible solutions is presented: a detector of 2800×40×10 mm 3 with light readout via WLS fiber and new solid state photo-detector multi-pixel avalanche photo-diode working in Geiger mode. Concept of the mechanical structure of upgraded KLM detector is given. Properties demonstrating the operation capabilities of such a scintillating detector: MIP registration efficiency, noise pulse rate with respect to expected background rate are demonstrated as well as response distributions in longitudinal and transverse directions. Study of radiation damage of photo-detectors shows that Hamamatsu MPPC can be used in Belle II environment during at least 10 years.

Modeling scintillator and WLS fiber signals for fast Monte Carlo simulations

In this work we present a fast, robust and flexible procedure to simulate electronic signals of scintillator units: plastic scintillator material embedded with a wavelength shifter optical fiber coupled to a photo-multiplier tube which, in turn, is plugged to a front-end electronic board. The simple rationale behind the simulation chain allows to adapt the procedure to a broad range of detectors based on that kind of units. We show that, in order to produce realistic results, the simulation parameters can be properly calibrated against laboratory measurements and used thereafter as input of the simulations. Simulated signals of atmospheric background cosmic ray muons are presented and their main features analyzed and validated using actual measured data. Conversely, for any given practical application, the present simulation scheme can be used to find an adequate combination of photo-multiplier tube and optical fiber at the prototyping stage.

Scintillator counters with WLS fiber/MPPC readout for the side muon range detector (SMRD) of the T2K experiment

The T2K neutrino experiment at J-PARC uses a set of near detectors to measure the properties of an unoscillated neutrino beam and neutrino interaction cross-sections. One of the sub-detectors of the near-detector complex, the side muon range detector (SMRD), is described in the paper. The detector is designed to help measure the neutrino energy spectrum, to identify background and to calibrate the other detectors. The active elements of the SMRD consist of 0.7cm thick extruded scintillator slabs inserted into air gaps of the UA1 magnet yokes. The readout of each scintillator slab is provided through a single WLS fiber embedded into a serpentine-shaped groove. Two Hamamatsu multi–pixel avalanche photodiodes (MPPC's) are coupled to both ends of the WLS fiber. This design allows us to achieve a high MIP detection efficiency of greater than 99%. A light yield of 25–50p.e./MIP, a time resolution of about 1ns and a spatial resolution along the slab better than 10cm were obtained for the SMRD counters.

Use of micro-pixel avalanche photodiodes for the readout of a lead/scintillator hadron calorimeter

The application of micro-pixel Avalanche photodiodes (MAPD) for the readout of hadron calorimeters is discussed. A prototype calorimeter was constructed consisting of individual lead/scintillator sandwich modules with a sampling satisfying the compensating condition. The light from each scintillator tile is captured and transported with WLS fibers embedded in the scintillator and extended to the rear end of the module. A set of 6 WLS fibers from neighboring tiles is grouped in one bundle and viewed by a 3×3 mm 2 avalanche micro-pixel photodiode. The design provides a longitudinal segmentation of the module into 10 sections with independent MAPD readout. Use of MAPDs with pixel density 10 4/mm 2 ensures good linearity of calorimeter response over a wide dynamical range. The performance of the calorimeter prototype in beam tests is reported.

Application of multi-pixel avalanche photodiodes operating in Geiger mode for scintillator pad detector read-out

Details of application of Si avalanche photodiode read-out for scintillator pad detector are discussed. The detection of charged particles using scintillator pads read-out with embedded WLS fiber is explored in many HEP experiments. The 12 cm×12 cm and 4 cm×4 cm scintillator counter design developed for LHC-b experiment [LHC-b Calorimeters Technical Design Report, CERN/LHCC/, 2000-0036] is being explored for the “OKA” experiment (Protvino) [V.F. Obraztsov, OKA: the experimental program with RF-separated K+-beam, KAON-05, Evanston, 2005, 〈 http://www.oka.ihep.su〉] aimed to K-meson rare decays study. Recently developed multi-pixel avalanche photodiodes operating in Geiger mode have definitive advantages with respect to conventional multi-anode PMT, i.e. larger quantum efficiency, compact detector design and small light losses, lower supply voltage. All this allows one to achieve a high light response of more than 100 photo-electrons per MIP with a simple and economical detector design. In this paper we describe characteristics of 3 batches of MRS APD, produced by the CPTA, Moscow [Center of Perspective Technologies and Apparatus (CPTA), Moscow; Photonique SA, Geneva 〈 http://www.photonique.ch〉]. We tested 3 types of photodiodes with a sensitive area of 1 mm 2 with 556 pixels, defining the noise counting rate and detection efficiency as a function of electronics threshold.

The LHCb Hadron Calorimeter

The Hadron Calorimeter of LHCb is a sampling iron-scintillator calorimeter of 5.6 δ1 thickness with structure arranged along the collider beam direction. The light readout is performed with WLS fibers running along the scintillator tile edges. The fast front end electronics allows to digitize events at 40 MHz without dead time. The self-calibration system based on 137Cs radioactive source embedded into the calorimeter structure allows to obtain absolute calibration with precision of about 2It is also equipped with a LED monitoring system, which allows to follow the PMT response variations during physics data taking.

The prototype of the MICE Electron–Muon Ranger: Design, construction and test

Muon Ionization Cooling Experiment (MICE) and its goal to demonstrate the feasibility of ionization cooling represent the first step toward a neutrino factory. Muons in MICE are produced by pions which derive from the interaction of protons with a target. Muons being short lived particles, a special cooling procedure has to be developed, to be able to reduce the emittance quickly. MICE intends to measure the emittance value with a 0.1% accuracy before and after the cooling element; thus a detector able to reconstruct and identify individual particles is required. The presence of electrons due to muon decay introduces a systematic error on the emittance and cooling measurements. For this reason a particle identification system is being developed based on a totally active scintillator tracker/calorimeter (Electron–Muon Ranger (EMR)). The detector consists of 40 planes of extruded scintillator bars 1 m long; the bars are read out with 0.8 mm WLS fibers coupled to multianode photomultipliers. The readout segmentation will be chosen accordingly to the rate (600 good muons per 1 ms spill every 1 s). This paper describes the design, construction and test at the CERN PS T9-line of the first small size prototype of the EMR with full analog readout, consisting of eight layers (4 x and 4 y ) with 10 bars 19 cm long each.

Wavelength-shifting-fibre-based neutron image detector with a fibre-optic taper to increase the spatial resolution

The effective pixel size of a two-dimensional wavelength-shifting-fibre (WLS-fibre)-based neutron image detector was improved from 0.5 to 0.16 mm by including a fibre-optic taper (FOT) between the scintillator screen and the WLS fibre. The WLS-fibre-based detector consisted of a thin ZnS/ 6LiF screen, a FOT and WLS ribbons crossed in the x and y directions. The demonstrator detector had 16 fibre channels in each direction, and the light signals in each fibre were read out individually. The FOT was constructed from fine glass fibres with a taper ratio of 3.1 and served as an image magnifier. The prototype detector equipped with the FOT exhibited a spatial resolution of 0.3 mm, compared to the spatial resolution of 0.8 mm of the original detector without the FOT.

The NOνA experiment

The NOνA Project will construct a 15 kt Far Detector 835 km from Fermilab at Ash River Minnesota, a 220 ton Near Detector on the Fermilab site and upgrade the existing NuMI beamline from 400 kW to 700 kW. The detector technology is liquid scintillator captured in reflective rigid PVC cells. The light is captured using WLS fibre and routed to avalanche photo diodes. NOνA is designed to observe the appearance of electron neutrinos, determine the value of sin2(2θ13) and begin the study of CP violation in the neutrino sector. NOνA is the only currently approved experiment with the ability to determine the neutrino mass ordering. The NOvA physics program and projected sensitivities are described in this report.

Scintillator tile hadron calorimeter with novel SiPM readout

The CALICE collaboration is presently constructing a test hadron calorimeter (HCAL) with 7620 scintillator tiles readout by novel photo-detectors—Silicon Photomultipliers (SiPMs). This prototype is the first device which uses SiPMs on a large scale. We present the design of the HCAL and report on measured properties of more than 10 000 SiPMs. We discuss the SiPM efficiency, gain, cross-talk, and noise rate dependence on bias voltage and temperature, including the spread in these parameters. We analyze the reasons for SiPM rejection and present the results of the long-term stability studies. The first measurements of the SiPM radiation hardness are presented. We compare properties of SiPM with the properties of similar devices, MRS APD and MPPC. A possibility to make the tiles thinner and to read them out without WLS fibers has been studied.

Scintillator counters with multi-pixel avalanche photodiode readout for the ND280 detector of the T2K experiment

The Tokai-to-Kamioka (T2K) experiment is a second generation long baseline neutrino oscillation experiment which aims at a sensitive search for ν e appearance. The main design features of the T2K near neutrino detectors located at 280 m from the target are presented, and the scintillator counters are described. The counters are readout via WLS fibers embedded into S-shaped grooves in the scintillator from both ends by multi-pixel avalanche photodiodes operating in a limited Geiger mode. Operating principles and results of tests of photosensors with a sensitive area of 1 mm 2 are presented. A time resolution of 1.75 ns, a spatial resolution of 9.9 – 12.4 cm , and a detection efficiency for minimum ionizing particles of more than 99% were obtained for scintillator detectors in a beam test.

The NOνA Experiment

The NOvA Project will construct a 15 kt Far Detector 835 km from Fermilab at Ash River Minnesota, a 220 ton Near Detector on the Fermilab site and upgrade the existing NuMI beamline from 400 kW to 700 kW. The detector technology is liquid scintillator captured in reflective rigid PVC cells. The light is captured using WLS fibre and routed to avalanche photo diodes. NO?A is designed to observe the appearance of electron neutrinos, determine the value of sin{sup 2}(2{theta}{sub 13}) and begin the study of CP violation in the neutrino sector. NO?A is the only currently approved experiment with the ability to determine the neutrino mass ordering. The NOvA physics program and projected sensitivities are described in this report.

A scintillator tile-fiber preshower detector for the CDF central calorimeter

The front face of the CDF central calorimeter is being equipped with a new Preshower detector, based on scintillator tiles read out by WLS fibers, in order to cope with the luminosity increase provided by the Main Injector during the Tevatron's Run II data taking. A light yield of about 40 pe/MIP at the tile exit was obtained, exceeding the design requirements.

Effects of the strong magnetic field on LED, extruded scintillator and MRS photodiode

The experimental results on the performance of the Metal/Resistor/Semiconductor (MRS) photodiode in the strong magnetic field of 4.4 T, and the possible impact of the quench of the magnet at 4.5 T on sensor's operation are reported. In addition, the experimental results on the performance of the extruded scintillator and WLS fiber, and various LEDs in the magnetic fields of 1.8 and 2.3 T, respectively, are detailed. The measurement method used is being described. The results of the work agree with the expectations that the LED, MRS and scintillator are not exhibiting sensitivity to the magnetic field presence. This result is essential for the design of the future electron–positron linear collider detector.

Long sandwich modules for photon veto detectors

Long lead-scintillator sandwich modules developed for the BNL experiment KOPIO are described. The individual 4 m long module consists of 15 layers of 7 mm thick extruded scintillator and 15 layers of 1 mm lead absorber. Readout is implemented via WLS fibers glued into grooves in a scintillator with 7 mm spacing and viewed from both ends by the phototubes. Time resolution of 300 ps for cosmic MIPs was obtained. Light output stability monitored for 2 years shows no degradation beyond the measurement errors. A 4 m long C-bent sandwich module was also manufactured and tested.

Measurement of light attenuation angular dependence in a double-clad wavelength shifting fibre Y11(200)MS

Measurements of attenuation in double-clad WLS fibre Y11(200)MS were carried out using a blue LED source and angular positioning of the photodetector. Data obtained for the external polar angle range up to 60 ∘ allowed the separation of the bulk attenuation and reflection inefficiencies for the fibre core and core–clad1 interface as well as for the clad1–clad2 interface. Fibres of this type have been used for the optical instrumentation of the Tile Hadron Calorimeter of the ATLAS detector.