- Email: [email protected]
Tests of FARICH prototype with precise photon position detection
Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Tests of FARICH prototype with precise photon position detection A.Yu. Barnyakov a, M.Yu. Barnyakov a,c, I.Yu. Basok a, V.E. Blinov a,c, V.S. Bobrovnikov a, A.A. Borodenko a, A.R. Buzykaev a, A.F. Danilyuk d, C. Degenhardt f, R. Dorscheid f, D.A. Finogeev e, T. Frach f, V.V. Gulevich a, T.L. Karavicheva e, P.V. Kasyanenko a, S.A. Kononov a,b, D.V. Korda a,c, E.A. Kravchenko a,b,n, V.N. Kudryavtsev a, A.B. Kurepin e, I.A. Kuyanov a, O. Muelhens f, A.P. Onuchin a,c, I.V. Ovtin a,c, N.A. Podgornov a,c, A.Yu. Predein d, V.G. Prisekin a, R.S. Protsenko d, V.I. Razin e, A.I. Reshetin e, R. Schulze f, L.I. Shekhtman a,b, A.A. Talyshev a,b, E.A. Usenko e, B. Zwaans f a
Budker Institute of Nuclear Physics SB RAS, Novosibirsk, Russia Novosibirsk State University, Novosibirsk, Russia c Novosibirsk State Technical University, Novosibirsk, Russia d Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia e Institute of Nuclear Research RAS, Moscow, Russia f Philips Digital Photon Counting, Aachen, Germany b
art ic l e i nf o
Keywords: Aerogel Ring imaging Cherenkov counter Particle identification
a b s t r a c t In June 2012 a FARICH prototype from Philips Digital Photon Counting (PDPC) based on a photon camera with dimensions of 200 200 mm has been tested at CERN. Remarkable particle separation has been achieved with a 4-layer aerogel sample: the π/K separation at a 6 GeV/c momentum is 3.5s, the μ=π separation is 5.3s at 1 GeV/c. The analysis of the data has shown that the main contribution to the accuracy of the ring radius measurement comes from aerogel. The development of focusing aerogels is proceeding in two main directions: tuning of production technology of multilayer blocks and development of a new production method with continuous density (refractive index) gradient along the block depth. The beam test was carried out in December 2012–January 2013 at the electron beam test facility at the VEPP-4 M e þ e collider. The goal of this test was to measure different single layer and focusing aerogel samples, both multilayer and gradient. Aerogel samples were tested with a PDPC FARICH prototype. A part of DPC SPADs in each pixel was disabled to form an active area of 1 1 mm2. The collected data proved that gradient aerogel samples focus Cherenkov light. & 2014 Published by Elsevier B.V.
1. Introduction Focusing Aerogel Ring Imaging Cherenkov (FARICH) detector is suggested for particle identification at a Super-cτ-factory (SCTF) in Novosibirsk [1]. The ’focusing aerogel’ refers to aerogel radiators for proximity focusing RICH detectors with a nonuniform refractive index. Basically, we distinguish two types of such radiators: multilayer and gradient aerogel radiators. The first one is done in such a way that rings from different layers having particular refractive indices overlap on the photon detection surface. Such radiators could consist of separate aerogel samples [2] or this could be a monolith aerogel sample with several (2–4) layers [3]. n Corresponding author at: Budker Institute of Nuclear Physics SB RAS, Novosibirsk, Russia. E-mail address: [email protected] (E.A. Kravchenko).
This concept was first proposed in 2004 to minimize the contribution of the finite radiator thickness to the Cherenkov angle error [2,3]. The second one is a monolithic aerogel sample, where refractive index inside the sample gradually changes in such a way that generated Cherenkov photons are projected to a ring with zero width on the photon detection surface. In a sense, a gradient radiator is a multilayer radiator with the infinite number of layers. One of the important physics cases of the SCTF is a search of τ-μγ lepton-flavor-violating decay. The ability of FARICH to separate muons and pions up to 1.7 GeV/c a 3s level combined with precise calorimetry and kinematic analysis should help to set an upper limit of the order of 10 9 on the corresponding branching fraction [4]. The main parameters of the FARICH for the SCTF detector are
4π geometry; 17 m2 of the radiator and 20 m2 of photon detectors;
http://dx.doi.org/10.1016/j.nima.2014.04.086 0168-9002/& 2014 Published by Elsevier B.V.
Please cite this article as: A.Yu. Barnyakov, et al., Nuclear Instruments & Methods in Physics Research A (2014), http://dx.doi.org/ 10.1016/j.nima.2014.04.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87
A.Yu. Barnyakov et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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silicon photomultipliers (SiPM) for photon detection, 3
3 mm2 , pitch 4 mm; 4-layer ‘focusing’ aerogel, nmax ¼ 1:07, total thickness 35 mm; and the expansion gap 200 mm.
SiPMs are promising candidates to be used as photon sensors in FARICH detectors due to their high gain, photon detection efficiency, immunity to magnetic field, compactness and potentially low cost. However, a high dark count rate of the order of 1 MHz/mm2 at room temperature of present SiPMs requires some challenging technical solutions such as cooling the detector and/or achieving a high photon timing resolution ( 100 ps) combined with a fast data acquisition. Several years ago the PDPC has developed a digital silicon photomultiplier called Digital Photon Counter (DPC) by integrating readout electronics on the same chip as the array of single pixel Avalanche diodes (SPAD) using conventional CMOS process technology [5]. Each cell (one SPAD), when it is hit, generates a logical signal that enables counting the number of fired cells and constructing coincidences of cell groups to produce the trigger signal and measure its timing. The DPC cardinally solves the problem of front-end electronics integration, offering an easily scalable solution for a high channel number and density. It has much lower dark counting rate and superior timing resolution than the conventional ’analogue’ SiPM. In 2012 a Focusing Aerogel RICH detector prototype based on DPC by Philips was tested at the CERN PS T10 beam line. The measured π =K separation at 6 GeV/c momentum was 3:5s, the μ=π separation was 5:3s at 1 GeV/c. We would like to note that these numbers for particle separation are 2.6 times worse than in the initial Monte Carlo simulation. One of the main reasons of such discrepancy is the difference of the actual parameters of focusing aerogel sample from the ideal design values [6].
Cherenkov photon timing for each channel. The timing resolution of channels st varies from 300 to 900 ps. The distance between the downstream face of the aerogel block and SiPMs (expansion gap) could be varied. According to calculations the minimum width (sr) of the Cherenkov ring should be observed for the expansion gap of about 62 mm. This value could be defined as a ‘focal’ length of the aerogel sample. The density of photoelectrons on radius measured at the 62 mm expansion gap for one SiPM is presented in Fig. 2. The measured spatial resolution for Cherenkov photons is equal to 1.1 mm which is comparable with a photon position resolution of about 0.7 mm. The measured sr is dominated by photon position resolution and track resolution. This restricts precise examination of uncertainty due to parameters aerogel samples. Based on the results from the FARICH prototype #1 and the PDPC FARICH prototype we made the conclusion that to investigate parameters of focusing aerogel samples and tune the production technology, we need to improve the coordinate resolution of the photon detection.
3. Focusing aerogel radiator development The development of focusing aerogels is going in two main directions: tuning of the production technology of multilayer blocks and developing a new production method with continuous Table 1 The refractive index and thickness of the layers of tested focusing aerogel sample. Layer number
1
2
3
4
Index of refraction Thickness (mm)
1.050 6.2
1.041 7.0
1.035 7.7
1.030 9.7
2. Test of FARICH prototype #1 A beam test with the first FARICH prototype was done in 2011 at the electron beam test facility at VEPP-4 M collider (Budker INP, Novosibirsk) (Fig. 1). The 4-layer focusing aerogel block was tested. The dimensions of the block were 100 100 31 mm3. The light scattering length in the sample was 43 mm at 400 nm wavelength. The index of refraction and thickness of the layers is presented in Table 1. The FARICH prototype used 32 SiPMs from the CPTA company (Moscow, Russia) as photon detectors. The SiPMs pixel size was 2.1 2.1 mm2. The custom made discriminator boards and the CAEN V1190B multihit TDC were used for the signal readout. The test beam apparatus also comprised the trigger and veto scintillation counters, the coordinate drift chambers and the NaI calorimeter. In the experiment we measured the position of the track of 1 GeV/c electrons in the photon detection plane that gave us the radius of the detected Cherenkov photons. To suppress SiPM dark count rate contribution we selected hits within 73st of mean
Fig. 2. Density of photoelectrons on radius for SiPM 14.
Fig. 1. The test beam apparatus layout: 1 – the converter of Bremsstrahlung gammas to electron–positron pairs, 2 – the drift chambers, 3 – the dipole magnet, 4 – the trigger scintillation counters, 5 – the FARICH prototype, and 6 – NaI scintillation counter.
Please cite this article as: A.Yu. Barnyakov, et al., Nuclear Instruments & Methods in Physics Research A (2014), http://dx.doi.org/ 10.1016/j.nima.2014.04.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
A.Yu. Barnyakov et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
profile needs to be optimized. Also no significant improvement in the accuracy of the photon coordinate detection was achieved. The possible reason was that the GEM detectors were located outside the FARICH prototype box and, as a consequence, multiple scattering of electrons could worse the track position resolution in the photon detector plane. The coordinate system of the beam line will be upgraded for the next tests.
density (refractive index) gradient along the block depth. A specialized installation was used for automatic control of the reagents ratio during the synthesis process [8]. The dependence of the refractive index on the continuous density along the block depth for one produced aerogel sample is presented in Fig. 3. Three possible causes of focusion capability degradation of the aerogel sample are
The difference between actual and design values of the refractive index of the layers.
The difference between actual and design values of the thick-
5. Conclusion
ness of the layers.
The uncontrolled refractive index variations [8].
The development of focusing aerogel samples is progressing in two main directions: tuning the production technology of multilayer blocks and developing a new production method with continuous density (refractive index) gradient along the block depth. A beam test was carried out in December 2012–January 2013 at the electron beam test facility at VEPP-4 M. The goal of this test was to measure different single layer and focusing aerogel samples, both multilayer and gradient. Aerogel samples were tested with PDPC FARICH prototype. A part of DPC SPADs in each pixel were disabled to form an active area of 1 1 mm2 to improve photon coordinate resolution.
At the test beam the ’perfect’ focusing aerogel sample must produce a narrow distribution of photons on the Cherenkov ring radius. The effects of incomplete focusing must form structures in such a distribution like multiple peaks or smaller side peaks. To observe such structures we suggest to use a RICH detector with precise photon position detection.
4. The first test of FARICH prototype with precise photon position detection The beam test was carried out from December 2012 to January 2013 at the electron beam test facility at the VEPP-4 M e þ e collider. Several single layer and focusing aerogel samples, both multilayer and gradient, were tested at the beam with the PDPC FARICH prototype working in the mode of precise photon position detection. We used the unique feature of the DPC detector — the ability to inhibit individual micro-cells in a pixel. During the measurements, 92% of micro-cells in each pixel were inhibited. Thus, the active area was reduced from 3:2 3:9 mm2 to 1 1 mm2 . This corresponds to 300 μm photon position resolution. At the time of the test the total number of working pixels was 1088. In addition the beam line was upgraded, the drift chambers were replaced by GEM-based coordinate detectors with 70 μm resolution. The preliminary results on the density of photoelectrons on a radius for an aerogel sample with continuous gradient are presented in Fig. 4. The distance from the aerogel to the DPC detectors was 190 mm. The Cherenkov angle resolution of the gradient aerogel sample is about the same as for the 4-layer sample. The Cherenkov light is focused by the gradient sample, but the refractive index
Fig. 4. The density of photoelectrons on the radius for aerogel with a continuous gradient.
Refr. index vs X 1.043
nprofile Entries Mean Mean y RMS RMS y
1.042
Refractive index
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
3
1.041
676 16.81 1.039 9.757 0.00209
1.04 1.039
op357_f1
1.038 1.037 1.036 0
5
10
15
20
25
30
Thickness of aerogel block, mm Fig. 3. The dependence of the refractive index along the block depth measured by the digital X-ray detector [7].
Please cite this article as: A.Yu. Barnyakov, et al., Nuclear Instruments & Methods in Physics Research A (2014), http://dx.doi.org/ 10.1016/j.nima.2014.04.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
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Acknowledgments This work was partially supported by the Ministry of Education and Science of the Russian Federation and the Siberian Branch of Russian Academy of Sciences (Grant N103). References [1] Super CharmTau Factory CDR. 〈https://ctd.inp.nsk.su/docs/ScTau_CDR_en/CDR_en_ ScTau.pdf〉. [2] T. Iijima, et al., Nuclear Instruments and Methods in Physics Research Section A 548 (2005) 383; S. Korpar, et al., Nuclear Instruments and Methods in Physics Research Section A 553 (2005) 64.
16 [3] A.Yu. Barnyakov, et al., Nuclear Instruments and Methods in Physics Research Section A 553 (2005) 70; 17 A.Yu. Barnyakov, et al., Proceedings of SNIC 2006, eConf C0604032 (2006) 18 0045. 19 [4] A.V. Bobrov, A.E. Bondar, Nuclear Physics B (Proceedings Supplements) 225–227 20 (2012) 195. [5] T. Frach, G. Prescher, C. Degenhardt, B. Zwaans, IEEE Nuclear Science Sympo21 sium/Medical Imaging Conference (2010) 1722; 22 C. Degenhardt, T. Frach, B. Zwaans, R. de Gruyter, IEEE Nuclear Science 23 Symposium/Medical Imaging Conference (2010) 1954. [6] A.Yu. Barnyakov, et al., Nuclear Instruments and Methods in Physics Research 24 Section A 732 (2013) 352. 25 [7] E.A. Babichev, et al., Nuclear Instruments and Methods in Physics Research 26 Section A 513 (2003) 57. Q2 27 [8] A.Yu. Barnyakov, et al., Aerogel for FARICH Detector, these proceedings.
Please cite this article as: A.Yu. Barnyakov, et al., Nuclear Instruments & Methods in Physics Research A (2014), http://dx.doi.org/ 10.1016/j.nima.2014.04.086i
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Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Tests of FARICH prototype with precise photon position detection A.Yu. Barnyakov a, M.Yu. Barnyakov a,c, I.Yu. Basok a, V.E. Blinov a,c, V.S. Bobrovnikov a, A.A. Borodenko a, A.R. Buzykaev a, A.F. Danilyuk d, C. Degenhardt f, R. Dorscheid f, D.A. Finogeev e, T. Frach f, V.V. Gulevich a, T.L. Karavicheva e, P.V. Kasyanenko a, S.A. Kononov a,b, D.V. Korda a,c, E.A. Kravchenko a,b,n, V.N. Kudryavtsev a, A.B. Kurepin e, I.A. Kuyanov a, O. Muelhens f, A.P. Onuchin a,c, I.V. Ovtin a,c, N.A. Podgornov a,c, A.Yu. Predein d, V.G. Prisekin a, R.S. Protsenko d, V.I. Razin e, A.I. Reshetin e, R. Schulze f, L.I. Shekhtman a,b, A.A. Talyshev a,b, E.A. Usenko e, B. Zwaans f a
Budker Institute of Nuclear Physics SB RAS, Novosibirsk, Russia Novosibirsk State University, Novosibirsk, Russia c Novosibirsk State Technical University, Novosibirsk, Russia d Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia e Institute of Nuclear Research RAS, Moscow, Russia f Philips Digital Photon Counting, Aachen, Germany b
art ic l e i nf o
Keywords: Aerogel Ring imaging Cherenkov counter Particle identification
a b s t r a c t In June 2012 a FARICH prototype from Philips Digital Photon Counting (PDPC) based on a photon camera with dimensions of 200 200 mm has been tested at CERN. Remarkable particle separation has been achieved with a 4-layer aerogel sample: the π/K separation at a 6 GeV/c momentum is 3.5s, the μ=π separation is 5.3s at 1 GeV/c. The analysis of the data has shown that the main contribution to the accuracy of the ring radius measurement comes from aerogel. The development of focusing aerogels is proceeding in two main directions: tuning of production technology of multilayer blocks and development of a new production method with continuous density (refractive index) gradient along the block depth. The beam test was carried out in December 2012–January 2013 at the electron beam test facility at the VEPP-4 M e þ e collider. The goal of this test was to measure different single layer and focusing aerogel samples, both multilayer and gradient. Aerogel samples were tested with a PDPC FARICH prototype. A part of DPC SPADs in each pixel was disabled to form an active area of 1 1 mm2. The collected data proved that gradient aerogel samples focus Cherenkov light. & 2014 Published by Elsevier B.V.
1. Introduction Focusing Aerogel Ring Imaging Cherenkov (FARICH) detector is suggested for particle identification at a Super-cτ-factory (SCTF) in Novosibirsk [1]. The ’focusing aerogel’ refers to aerogel radiators for proximity focusing RICH detectors with a nonuniform refractive index. Basically, we distinguish two types of such radiators: multilayer and gradient aerogel radiators. The first one is done in such a way that rings from different layers having particular refractive indices overlap on the photon detection surface. Such radiators could consist of separate aerogel samples [2] or this could be a monolith aerogel sample with several (2–4) layers [3]. n Corresponding author at: Budker Institute of Nuclear Physics SB RAS, Novosibirsk, Russia. E-mail address: [email protected] (E.A. Kravchenko).
This concept was first proposed in 2004 to minimize the contribution of the finite radiator thickness to the Cherenkov angle error [2,3]. The second one is a monolithic aerogel sample, where refractive index inside the sample gradually changes in such a way that generated Cherenkov photons are projected to a ring with zero width on the photon detection surface. In a sense, a gradient radiator is a multilayer radiator with the infinite number of layers. One of the important physics cases of the SCTF is a search of τ-μγ lepton-flavor-violating decay. The ability of FARICH to separate muons and pions up to 1.7 GeV/c a 3s level combined with precise calorimetry and kinematic analysis should help to set an upper limit of the order of 10 9 on the corresponding branching fraction [4]. The main parameters of the FARICH for the SCTF detector are
4π geometry; 17 m2 of the radiator and 20 m2 of photon detectors;
http://dx.doi.org/10.1016/j.nima.2014.04.086 0168-9002/& 2014 Published by Elsevier B.V.
Please cite this article as: A.Yu. Barnyakov, et al., Nuclear Instruments & Methods in Physics Research A (2014), http://dx.doi.org/ 10.1016/j.nima.2014.04.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87
A.Yu. Barnyakov et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
silicon photomultipliers (SiPM) for photon detection, 3
3 mm2 , pitch 4 mm; 4-layer ‘focusing’ aerogel, nmax ¼ 1:07, total thickness 35 mm; and the expansion gap 200 mm.
SiPMs are promising candidates to be used as photon sensors in FARICH detectors due to their high gain, photon detection efficiency, immunity to magnetic field, compactness and potentially low cost. However, a high dark count rate of the order of 1 MHz/mm2 at room temperature of present SiPMs requires some challenging technical solutions such as cooling the detector and/or achieving a high photon timing resolution ( 100 ps) combined with a fast data acquisition. Several years ago the PDPC has developed a digital silicon photomultiplier called Digital Photon Counter (DPC) by integrating readout electronics on the same chip as the array of single pixel Avalanche diodes (SPAD) using conventional CMOS process technology [5]. Each cell (one SPAD), when it is hit, generates a logical signal that enables counting the number of fired cells and constructing coincidences of cell groups to produce the trigger signal and measure its timing. The DPC cardinally solves the problem of front-end electronics integration, offering an easily scalable solution for a high channel number and density. It has much lower dark counting rate and superior timing resolution than the conventional ’analogue’ SiPM. In 2012 a Focusing Aerogel RICH detector prototype based on DPC by Philips was tested at the CERN PS T10 beam line. The measured π =K separation at 6 GeV/c momentum was 3:5s, the μ=π separation was 5:3s at 1 GeV/c. We would like to note that these numbers for particle separation are 2.6 times worse than in the initial Monte Carlo simulation. One of the main reasons of such discrepancy is the difference of the actual parameters of focusing aerogel sample from the ideal design values [6].
Cherenkov photon timing for each channel. The timing resolution of channels st varies from 300 to 900 ps. The distance between the downstream face of the aerogel block and SiPMs (expansion gap) could be varied. According to calculations the minimum width (sr) of the Cherenkov ring should be observed for the expansion gap of about 62 mm. This value could be defined as a ‘focal’ length of the aerogel sample. The density of photoelectrons on radius measured at the 62 mm expansion gap for one SiPM is presented in Fig. 2. The measured spatial resolution for Cherenkov photons is equal to 1.1 mm which is comparable with a photon position resolution of about 0.7 mm. The measured sr is dominated by photon position resolution and track resolution. This restricts precise examination of uncertainty due to parameters aerogel samples. Based on the results from the FARICH prototype #1 and the PDPC FARICH prototype we made the conclusion that to investigate parameters of focusing aerogel samples and tune the production technology, we need to improve the coordinate resolution of the photon detection.
3. Focusing aerogel radiator development The development of focusing aerogels is going in two main directions: tuning of the production technology of multilayer blocks and developing a new production method with continuous Table 1 The refractive index and thickness of the layers of tested focusing aerogel sample. Layer number
1
2
3
4
Index of refraction Thickness (mm)
1.050 6.2
1.041 7.0
1.035 7.7
1.030 9.7
2. Test of FARICH prototype #1 A beam test with the first FARICH prototype was done in 2011 at the electron beam test facility at VEPP-4 M collider (Budker INP, Novosibirsk) (Fig. 1). The 4-layer focusing aerogel block was tested. The dimensions of the block were 100 100 31 mm3. The light scattering length in the sample was 43 mm at 400 nm wavelength. The index of refraction and thickness of the layers is presented in Table 1. The FARICH prototype used 32 SiPMs from the CPTA company (Moscow, Russia) as photon detectors. The SiPMs pixel size was 2.1 2.1 mm2. The custom made discriminator boards and the CAEN V1190B multihit TDC were used for the signal readout. The test beam apparatus also comprised the trigger and veto scintillation counters, the coordinate drift chambers and the NaI calorimeter. In the experiment we measured the position of the track of 1 GeV/c electrons in the photon detection plane that gave us the radius of the detected Cherenkov photons. To suppress SiPM dark count rate contribution we selected hits within 73st of mean
Fig. 2. Density of photoelectrons on radius for SiPM 14.
Fig. 1. The test beam apparatus layout: 1 – the converter of Bremsstrahlung gammas to electron–positron pairs, 2 – the drift chambers, 3 – the dipole magnet, 4 – the trigger scintillation counters, 5 – the FARICH prototype, and 6 – NaI scintillation counter.
Please cite this article as: A.Yu. Barnyakov, et al., Nuclear Instruments & Methods in Physics Research A (2014), http://dx.doi.org/ 10.1016/j.nima.2014.04.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
A.Yu. Barnyakov et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
profile needs to be optimized. Also no significant improvement in the accuracy of the photon coordinate detection was achieved. The possible reason was that the GEM detectors were located outside the FARICH prototype box and, as a consequence, multiple scattering of electrons could worse the track position resolution in the photon detector plane. The coordinate system of the beam line will be upgraded for the next tests.
density (refractive index) gradient along the block depth. A specialized installation was used for automatic control of the reagents ratio during the synthesis process [8]. The dependence of the refractive index on the continuous density along the block depth for one produced aerogel sample is presented in Fig. 3. Three possible causes of focusion capability degradation of the aerogel sample are
The difference between actual and design values of the refractive index of the layers.
The difference between actual and design values of the thick-
5. Conclusion
ness of the layers.
The uncontrolled refractive index variations [8].
The development of focusing aerogel samples is progressing in two main directions: tuning the production technology of multilayer blocks and developing a new production method with continuous density (refractive index) gradient along the block depth. A beam test was carried out in December 2012–January 2013 at the electron beam test facility at VEPP-4 M. The goal of this test was to measure different single layer and focusing aerogel samples, both multilayer and gradient. Aerogel samples were tested with PDPC FARICH prototype. A part of DPC SPADs in each pixel were disabled to form an active area of 1 1 mm2 to improve photon coordinate resolution.
At the test beam the ’perfect’ focusing aerogel sample must produce a narrow distribution of photons on the Cherenkov ring radius. The effects of incomplete focusing must form structures in such a distribution like multiple peaks or smaller side peaks. To observe such structures we suggest to use a RICH detector with precise photon position detection.
4. The first test of FARICH prototype with precise photon position detection The beam test was carried out from December 2012 to January 2013 at the electron beam test facility at the VEPP-4 M e þ e collider. Several single layer and focusing aerogel samples, both multilayer and gradient, were tested at the beam with the PDPC FARICH prototype working in the mode of precise photon position detection. We used the unique feature of the DPC detector — the ability to inhibit individual micro-cells in a pixel. During the measurements, 92% of micro-cells in each pixel were inhibited. Thus, the active area was reduced from 3:2 3:9 mm2 to 1 1 mm2 . This corresponds to 300 μm photon position resolution. At the time of the test the total number of working pixels was 1088. In addition the beam line was upgraded, the drift chambers were replaced by GEM-based coordinate detectors with 70 μm resolution. The preliminary results on the density of photoelectrons on a radius for an aerogel sample with continuous gradient are presented in Fig. 4. The distance from the aerogel to the DPC detectors was 190 mm. The Cherenkov angle resolution of the gradient aerogel sample is about the same as for the 4-layer sample. The Cherenkov light is focused by the gradient sample, but the refractive index
Fig. 4. The density of photoelectrons on the radius for aerogel with a continuous gradient.
Refr. index vs X 1.043
nprofile Entries Mean Mean y RMS RMS y
1.042
Refractive index
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
3
1.041
676 16.81 1.039 9.757 0.00209
1.04 1.039
op357_f1
1.038 1.037 1.036 0
5
10
15
20
25
30
Thickness of aerogel block, mm Fig. 3. The dependence of the refractive index along the block depth measured by the digital X-ray detector [7].
Please cite this article as: A.Yu. Barnyakov, et al., Nuclear Instruments & Methods in Physics Research A (2014), http://dx.doi.org/ 10.1016/j.nima.2014.04.086i
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Acknowledgments This work was partially supported by the Ministry of Education and Science of the Russian Federation and the Siberian Branch of Russian Academy of Sciences (Grant N103). References [1] Super CharmTau Factory CDR. 〈https://ctd.inp.nsk.su/docs/ScTau_CDR_en/CDR_en_ ScTau.pdf〉. [2] T. Iijima, et al., Nuclear Instruments and Methods in Physics Research Section A 548 (2005) 383; S. Korpar, et al., Nuclear Instruments and Methods in Physics Research Section A 553 (2005) 64.
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