- Email: [email protected]
The FOXFIRE liquid xenon detector research and development project
Nuclear Instruments and Methods in Physics Research A 718 (2013) 110–111
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
The FOXFIRE liquid xenon detector research and development project G. Signorelli a,n, S. Dussoni a, A. Baldini a, C. Cerri a,1, M. Grassi a, A. Papa c, F. Tenchini a,b a b c
INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa, Italy Dipartimento di Fisica dell’Universita degli Studi di Pisa, Largo B. Pontecorvo 3, 56127 Pisa, Italy Paul Scherrer Institute PSI, CH-5232 Villigen, Switzerland
a r t i c l e i n f o
a b s t r a c t
Available online 29 August 2012
The FOXFIRE project (Feasibility Of a Xenon detector with Frontend for Ionization Real-time Extraction) aims at studying and developing new techniques for the detection of rare processes in elementary particle physics by means of condensed noble gases detectors. Particles in noble liquids release energy in both scintillation light and electron–ion pair formation. The combined usage of this information is being exploited by many research groups. We are studying the extension of these techniques towards high-rate, high-energy (tens of MeV) environments with particular emphasis on real-time event reconstruction. & 2012 Elsevier B.V. All rights reserved.
Keywords: Calorimetry Liquid xenon Scintillation Ionization detector TPC FPGA
1. Introduction Liquid xenon (LXe) presents a unique set of characteristics (high density and stopping power, high light yield, relatively high boiling temperature) which makes it an ideal choice as detector active material [1]. Particles interact in liquid xenon producing scintillation light and ionization charge. The vacuum ultra-violet (178 nm) light can be read by suitable photo-detectors, while electrons from ionized Xe molecules drift towards collection anodes under applied electric field and can give sub-millimeter position resolution. The main characteristics of liquid xenon are summarized in Table 1. Noble liquids find optimal application in particle physics at an intermediate energy range: at an energy of 50–100 MeV one has to maximize the light yield, the stopping power and homogeneity. At higher energies materials with intrinsecally lower light yield and poorer time resolution can be used, since the larger energy deposit reduces the fluctuations. At lower energies, since showers are smaller, it is easy to find homogeneous detectors also among crystals of reasonable size. Large LXe homogeneous scintillation detectors, such as the one of the MEG experiment, can detect photons of several tens of MeV with excellent energy, position and timing resolution [2]. In such experiments photons enter the detector from one specific side (the ‘‘entrance face’’) which is generally made of lower density materials, and it is instrumented to detect precisely the g-ray direction and position. When the photon conversion is very close to the entrance face the resolutions are degraded because of
spatial non-uniformities on dimensions of the order of the photosensor size. In the case of MEG, where 2 in. PMTs are used, resolution reach their optimum for photon conversions deeper than 2–3 cm. Resolutions for 50 MeV g–rays depend on its conversion depth and, for energy, are around sr ¼ 1:6% ð2:5%Þ for deep (shallow) events. Usage of smaller photo-sensors partially improves the performance, but comes to a larger cost. Collection of ionization electrons was used in the past in large volumes for energy or position reconstruction [3,4]. Such large drift volume detectors are too slow for high rate applications required in high energy physics experiments. Nevertheless LXe radiation length X0 is short enough that almost 65% of 50 MeV photons convert in the first 3 cm, a distance that drift electrons cover in few microseconds. Instrumenting only the first X0 with a segmented Time Projection Chamber (TPC) can therefore help in recovering the optimum resolutions also for this region in which most of the photons convert, keeping the dead time of the detector (dominated by the electron drift time) within a reasonable level. In a 3 cm thick TPC the dead time is kept low thanks to the reduced electron drift time ð o 5 msÞ and can be further improved by implementing a readout electronics capable of online multi-hit processing; the result is a higher precision 3D event reconstruction especially for the photon conversion point, with improvements in both time and energy resolution. The aim of the FOXFIRE project is to study an hybrid TPCscintillation detector based on these principles.
2. Photodetectors and front-end electronics n
Corresponding author. Tel.: þ39 0502214425. E-mail address: [email protected] (G. Signorelli). 1 Retired.
0168-9002/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nima.2012.07.063
The prototype detector is conceived as a volume of few liters of liquid xenon read by photo-detectors on all sides, and
G. Signorelli et al. / Nuclear Instruments and Methods in Physics Research A 718 (2013) 110–111
impedance discrete component amplifier showed a good behavior at liquid xenon temperature. Further optimization is needed to reduce the single channel heat load which is presently around 50 mW per channel (see Fig. 2).
Table 1 Main characteristics of liquid xenon as a detector material. Atomic number Z Density Boiling point Light yield Radiation length X 0 Electron drift velocity
111
54 3 g/cm3 165 K 40,000 phe/MeV 2.87 cm 3 105 cm/s (2 kV/cm)
3. Online event reconstruction Both light and charge information will be sampled by custom VME 100 MHz waveform digitizers evolved from those used in the MEG experiment trigger system (type 3 boards) [5]. These boards provide complete trigger and read-out capabilities. A customization of the input stage to match the different fast (scintillation) and slow (ionization) signals is possible thanks to the tunable dynamic input range, a flexible memory depth from 1 to 50 ms and a 1:10 downscale of the 100 MHz sampling speed. The firmware to be loaded on the on-board Field Programmable Gate Array (FPGA) will be tailored in order to provide online waveform analysis for complex trigger algorithms, as well as complete and effective data storage for full event reconstruction (energy, time and position).
4. Prototype detector A UHV cold chamber containing 2‘ of liquid xenon is being instrumented at INFN Pisa. Gas xenon is purified by means of circulation through a molecular sieve and a heated getter. This procedure has shown to yield sufficient purity of xenon to see the drift charge on the desided few-cm volume. XY charge read-out is provided by 32þ32 sense wires while light read-out and trigger are provided by 4Hamamatsu R8520-406 1 in. square PMTs, whose bleeder circuit was designed to withstand a high photon rate, based on the experience and design of the MEG PMTs base circuits. All material in contact with LXe is clean or tested for compatibility, in particular, CIRLEXs is used as a support material for the circuit boards of PMT bases, wire supports and preamplifiers.
Fig. 1. Sketch of a hybrid scintillation-TPC prototype. 1.2
1
g/g0
0.8
0.6
5. Schedule and plans
0.4
0.2
0 -120
-100
-80
-60
-40
-20
0
20
40
The project was financed in 2011. R&D on photo-detectors test with a small prototype and definition of geometry is being done in 2012. The construction and test of the final prototype are foreseen in 2013 and 2014, respectively.
Temperature (C)
Fig. 2. Gain of the preamplifier under test at different temperatures. The gain was evaluated by looking at the amplitude of an APD single photo-electron peak.
instrumented with a double TPC with 3D reconstruction capability on the photon entrance face, as schematically shown in Fig. 1. Various photo-detector candidates are presently under test for the final prototype. In particular we are considering 2 in. round Hamamatsu R9869 VUV sensitive photo-multiplier tubes (PMTs) presently used in the MEG liquid xenon detector, 1 in. square Hamamatsu R8520-406 PMTs, large area ð1 cm 1 cmÞ VUVsensitive avalanche photo-diodes (APDs) from Hamamatsu (S8664-1010VUV), and small area ð1 mm 1 mm to 4 mm 4 mmÞ silicon photo-multipliers (SiPM) from AdvanSiD. To minimize noise, the front-end pre-amplifiers for both photo-detector and ionization signals can be placed directly in the liquid at 165 K. Preliminary tests on a custom made trans-
Acknowledgments Discussions with G. Collazuol (Padua University) and F. Sergiampietri (INFN Pisa) are gratefully acknowledged. This project is supported by the Italian Ministry of University and Research (MIUR) under the project Future in Research (FIRB) grant RBFR08XWGN. References [1] E. Aprile, T. Doke, Reviews of Modern Physics 82 (2010) 2053. [2] S. Mihara, Journal of Physics: Conference Series 308 (2011) 012009. [3] G. Carugno, et al., Nuclear Instruments and Methods in Physics Research Section A 376 (1996) 149. [4] E. Aprile, et al., Nuclear Instruments and Methods in Physics Research Section A 412 (1998) 425. [5] L. Galli, IEEE Nuclear Science Symposium 2009 (2009) 205.
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
The FOXFIRE liquid xenon detector research and development project G. Signorelli a,n, S. Dussoni a, A. Baldini a, C. Cerri a,1, M. Grassi a, A. Papa c, F. Tenchini a,b a b c
INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa, Italy Dipartimento di Fisica dell’Universita degli Studi di Pisa, Largo B. Pontecorvo 3, 56127 Pisa, Italy Paul Scherrer Institute PSI, CH-5232 Villigen, Switzerland
a r t i c l e i n f o
a b s t r a c t
Available online 29 August 2012
The FOXFIRE project (Feasibility Of a Xenon detector with Frontend for Ionization Real-time Extraction) aims at studying and developing new techniques for the detection of rare processes in elementary particle physics by means of condensed noble gases detectors. Particles in noble liquids release energy in both scintillation light and electron–ion pair formation. The combined usage of this information is being exploited by many research groups. We are studying the extension of these techniques towards high-rate, high-energy (tens of MeV) environments with particular emphasis on real-time event reconstruction. & 2012 Elsevier B.V. All rights reserved.
Keywords: Calorimetry Liquid xenon Scintillation Ionization detector TPC FPGA
1. Introduction Liquid xenon (LXe) presents a unique set of characteristics (high density and stopping power, high light yield, relatively high boiling temperature) which makes it an ideal choice as detector active material [1]. Particles interact in liquid xenon producing scintillation light and ionization charge. The vacuum ultra-violet (178 nm) light can be read by suitable photo-detectors, while electrons from ionized Xe molecules drift towards collection anodes under applied electric field and can give sub-millimeter position resolution. The main characteristics of liquid xenon are summarized in Table 1. Noble liquids find optimal application in particle physics at an intermediate energy range: at an energy of 50–100 MeV one has to maximize the light yield, the stopping power and homogeneity. At higher energies materials with intrinsecally lower light yield and poorer time resolution can be used, since the larger energy deposit reduces the fluctuations. At lower energies, since showers are smaller, it is easy to find homogeneous detectors also among crystals of reasonable size. Large LXe homogeneous scintillation detectors, such as the one of the MEG experiment, can detect photons of several tens of MeV with excellent energy, position and timing resolution [2]. In such experiments photons enter the detector from one specific side (the ‘‘entrance face’’) which is generally made of lower density materials, and it is instrumented to detect precisely the g-ray direction and position. When the photon conversion is very close to the entrance face the resolutions are degraded because of
spatial non-uniformities on dimensions of the order of the photosensor size. In the case of MEG, where 2 in. PMTs are used, resolution reach their optimum for photon conversions deeper than 2–3 cm. Resolutions for 50 MeV g–rays depend on its conversion depth and, for energy, are around sr ¼ 1:6% ð2:5%Þ for deep (shallow) events. Usage of smaller photo-sensors partially improves the performance, but comes to a larger cost. Collection of ionization electrons was used in the past in large volumes for energy or position reconstruction [3,4]. Such large drift volume detectors are too slow for high rate applications required in high energy physics experiments. Nevertheless LXe radiation length X0 is short enough that almost 65% of 50 MeV photons convert in the first 3 cm, a distance that drift electrons cover in few microseconds. Instrumenting only the first X0 with a segmented Time Projection Chamber (TPC) can therefore help in recovering the optimum resolutions also for this region in which most of the photons convert, keeping the dead time of the detector (dominated by the electron drift time) within a reasonable level. In a 3 cm thick TPC the dead time is kept low thanks to the reduced electron drift time ð o 5 msÞ and can be further improved by implementing a readout electronics capable of online multi-hit processing; the result is a higher precision 3D event reconstruction especially for the photon conversion point, with improvements in both time and energy resolution. The aim of the FOXFIRE project is to study an hybrid TPCscintillation detector based on these principles.
2. Photodetectors and front-end electronics n
Corresponding author. Tel.: þ39 0502214425. E-mail address: [email protected] (G. Signorelli). 1 Retired.
0168-9002/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nima.2012.07.063
The prototype detector is conceived as a volume of few liters of liquid xenon read by photo-detectors on all sides, and
G. Signorelli et al. / Nuclear Instruments and Methods in Physics Research A 718 (2013) 110–111
impedance discrete component amplifier showed a good behavior at liquid xenon temperature. Further optimization is needed to reduce the single channel heat load which is presently around 50 mW per channel (see Fig. 2).
Table 1 Main characteristics of liquid xenon as a detector material. Atomic number Z Density Boiling point Light yield Radiation length X 0 Electron drift velocity
111
54 3 g/cm3 165 K 40,000 phe/MeV 2.87 cm 3 105 cm/s (2 kV/cm)
3. Online event reconstruction Both light and charge information will be sampled by custom VME 100 MHz waveform digitizers evolved from those used in the MEG experiment trigger system (type 3 boards) [5]. These boards provide complete trigger and read-out capabilities. A customization of the input stage to match the different fast (scintillation) and slow (ionization) signals is possible thanks to the tunable dynamic input range, a flexible memory depth from 1 to 50 ms and a 1:10 downscale of the 100 MHz sampling speed. The firmware to be loaded on the on-board Field Programmable Gate Array (FPGA) will be tailored in order to provide online waveform analysis for complex trigger algorithms, as well as complete and effective data storage for full event reconstruction (energy, time and position).
4. Prototype detector A UHV cold chamber containing 2‘ of liquid xenon is being instrumented at INFN Pisa. Gas xenon is purified by means of circulation through a molecular sieve and a heated getter. This procedure has shown to yield sufficient purity of xenon to see the drift charge on the desided few-cm volume. XY charge read-out is provided by 32þ32 sense wires while light read-out and trigger are provided by 4Hamamatsu R8520-406 1 in. square PMTs, whose bleeder circuit was designed to withstand a high photon rate, based on the experience and design of the MEG PMTs base circuits. All material in contact with LXe is clean or tested for compatibility, in particular, CIRLEXs is used as a support material for the circuit boards of PMT bases, wire supports and preamplifiers.
Fig. 1. Sketch of a hybrid scintillation-TPC prototype. 1.2
1
g/g0
0.8
0.6
5. Schedule and plans
0.4
0.2
0 -120
-100
-80
-60
-40
-20
0
20
40
The project was financed in 2011. R&D on photo-detectors test with a small prototype and definition of geometry is being done in 2012. The construction and test of the final prototype are foreseen in 2013 and 2014, respectively.
Temperature (C)
Fig. 2. Gain of the preamplifier under test at different temperatures. The gain was evaluated by looking at the amplitude of an APD single photo-electron peak.
instrumented with a double TPC with 3D reconstruction capability on the photon entrance face, as schematically shown in Fig. 1. Various photo-detector candidates are presently under test for the final prototype. In particular we are considering 2 in. round Hamamatsu R9869 VUV sensitive photo-multiplier tubes (PMTs) presently used in the MEG liquid xenon detector, 1 in. square Hamamatsu R8520-406 PMTs, large area ð1 cm 1 cmÞ VUVsensitive avalanche photo-diodes (APDs) from Hamamatsu (S8664-1010VUV), and small area ð1 mm 1 mm to 4 mm 4 mmÞ silicon photo-multipliers (SiPM) from AdvanSiD. To minimize noise, the front-end pre-amplifiers for both photo-detector and ionization signals can be placed directly in the liquid at 165 K. Preliminary tests on a custom made trans-
Acknowledgments Discussions with G. Collazuol (Padua University) and F. Sergiampietri (INFN Pisa) are gratefully acknowledged. This project is supported by the Italian Ministry of University and Research (MIUR) under the project Future in Research (FIRB) grant RBFR08XWGN. References [1] E. Aprile, T. Doke, Reviews of Modern Physics 82 (2010) 2053. [2] S. Mihara, Journal of Physics: Conference Series 308 (2011) 012009. [3] G. Carugno, et al., Nuclear Instruments and Methods in Physics Research Section A 376 (1996) 149. [4] E. Aprile, et al., Nuclear Instruments and Methods in Physics Research Section A 412 (1998) 425. [5] L. Galli, IEEE Nuclear Science Symposium 2009 (2009) 205.