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Status and early events from ICARUS T600
Available online at www.sciencedirect.com
Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346 www.elsevier.com/locate/npbps
Status and early events from ICARUS T600 A. Guglielmi, for the ICARUS Collaboration Istituto Nazionale di Fisica Nucleare and Dep. of Physics “G. Galilei”, via Marzolo 8, 35131 Padova, Italy
Abstract The ICARUS T600 detector, a ∼ 600 t liquid Argon (LAr) TPC with unique imaging and calorimetric capabilities, is presently data taking at LNGS underground laboratory for a rich physics programme, covering cosmic neutrinos, nucleon decay search and neutrino oscillations with the CNGS neutrino beam.The successful detector commissioning and operation and the ongoing analysis of the recorded events show the excellent performance of this LAr-TPC, and opens the way to constructing very massive high quality detectors. Keywords: Liquid Argon, TPC, Neutrino Physics, Astroparticle Physics
1. Introduction The new superior bubble-chamber-like features of ICARUS T600 liquid Argon (LAr) TPC detector at LNGS is expected to provide additional and fundamental contributions to both neutrino physics and studies of nucleon stability. The operational principle of the LAr-TPC is based on the fact that in highly purified LAr ionization tracks can be transported practically undistorted by a uniform electric field over macroscopic distances [1]. Imaging is provided by a suitable set of electrodes (wires) placed at the end of the drift path continuously sensing and recording the signals induced by the drifting electrons. Non-destructive read-out of ionization electrons by charge induction allows detecting the entire signal of electrons crossing subsequent wire planes with different orientation. This provides simultaneously several projective views of the same event, hence allowing a precise reconstruction of the recorded particle trajectory and a precise calorimetric measurement. The ICARUS T600 detector presently in operation underground in Hall B of LNGS in a neutrino beam from the CERN-SPS, is the largest liquid Argon TPC ever built, with a size of about 600 t of imaging mass. The design and assembly of the detector relied on industrial support and represents the application of concepts 0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.053
matured in laboratory tests to the kton scale. In the following the installation and completion of T600 detector in Hall B at LNGS underground laboratory and the detector commissioning are presented as well as the first CERN to Gran Sasso (CNGS) neutrino beam interactions recorded in LAr-TPC. 2. The ICARUS-T600 LAr-TPC The ICARUS-T600 detector [2] (see Fig.1) consists of a large cryostat split in two identical, adjacent halfmodules, with internal dimensions 3.6 × 3.9 × 19.9 m3 each. Each half-module houses two Time Projection Chambers (TPC) separated by a common cathode, a field shaping system, monitors and probes, and two arrays of photo-multipliers. Externally the cryostats are surrounded by a common thermal insulation layer, which is realized by evacuated NomexT M honeycomb panels (0.4 m thick) to form a closed vacuum-tight box, with nominal heat losses of about 10 W/m2 . The detector layout is completed by a cryogenic plant made of a liquid Nitrogen cooling circuit based on 10 Stirling compressors circulating boiling Nitrogen to cool down the apparatus and to compensate the heat losses through the thermal insulation box. The circulation speed is defined by the request to maintain a thermal uniformity within 1 K in the LAr bulk.
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
343
Figure 1: The ICARUS T600 detector.
The LAr cryostat is operating at a slight overpressure of 100 mbar at a temperature of about 89 K. The cryostat is filled with ultra-pure Argon obtained starting with commercial liquid (with a typical content of H2 O, O2 , N2 of the order 1 ppm) purified at the cryostat input by means of commercial filters. To ensure an acceptable initial LAr purity, the detector is evacuated to a pressure of the order of 10−4 mbar, before filling, in order to perform an appropriate out-gassing of the cryostat internal walls and all the detector materials. Moreover, each semi-module is equipped with two gas and one liquid recirculation systems, both required to attain a very high free-electron lifetime (several ms) in less than one month. The continuously active gas recirculation units (25 GAr Nm3 /h each at maximum rate) collect the gas from the chimneys that host the cables for the wire chamber read-out on top of the detector.The re-condensed gas drops into Oxysorb/HydrosorbT M filters placed below the re-condenser and is sent back into the LAr container just below the LAr surface. Liquid recirculation units consist of an immersed, cryogenic, liquid transfer pump placed inside an independent dewar. The circulated LAr goes through standard Oxysorb/ HydrosorbT M filters before being re-injected into the cryostats (∼ 2 m3 /h, corresponding to a full volume recirculation in about 6 days).
Each TPC is made of three parallel planes of wires, 3 mm apart. The first faces the drift region, with horizontal wires, the other two have the wires at ±600 from the horizontal direction. By appropriate voltage biasing, the first two planes (Induction planes) provide signals in non-destructive way, whereas the charge is finally collected in the last one (Collection plane). The maximum drift path, i.e.the distance between the cathode and the wire planes, is 1.5 m and the nominal drift field 500 V/cm. The total number of wires in the T600 detector is about 54000. The signals coming from each wire are independently digitized every 400 ns. The electronics was designed to allow continuous read-out, digitization and independent waveform recording of signals from each wire of the TPC. The measurement of the time of the ionizing event, the “T 0 time” given by the prompt scintillation light produced by ionization in LAr, together with the knowledge of the electron drift velocity provide the absolute position of the tracks along the drift coordinate. Globally 74 photomultipliers coated with TPB wavelength-shifter to detect the UV scintillation light are directly installed in LAr behind the wire planes of TPCs [3]. The high resolution and ∼ mm granularity of the detector imaging allow a precise reconstruction of the event topologies identifying the particles produced in
344
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
Figure 2: A muon event recorded in ICARUS T600.
the interaction in LAr. The event reconstruction is completed by calorimetric measurement via dE/dx ionization signal in 1 MeV ÷ 50 GeV energy range. A 10−3 electron - π0 separation is expected in the CNGS neutrino energy range by gamma reconstruction, dE/dx signal comparison and π0 invariant mass measurement [4]. This will guarantee a powerful 90 % selection efficiency of the genuine electron neutrino interactions rejecting NC interactions to a negligible level. Moreover muon momentum measurement within ∼ 10 ÷ 15% accuracy is performed exploiting multiple scattering along the track [5]. The ICARUS-T600 can address both underground physics (proton decay search, solar and atmospheric neutrino measurements, supernova explosion detection) and long base-line and high precision neutrino physics [6].
3. Early operations of ICARUS-T600 in LNGS During the first months of 2010 the detector commissioning took place, leading to the successful filling with liquid Argon, DAQ electronic activation and the detection of the first CNGS neutrino events.
The cryogenic and liquefaction systems were put in operation and successfully tested. Sensors for the measurement of the thermal insulation and lateral panel deformations allowed to measure the thermal tightness on the panels, in agreement with the expectations. All the safety and technical requirements of LNGS laboratory were fulfilled leading to the start-up of the T600. The cryostats evacuation started on January 2010 reaching on April the residual vacuum pressure in the detector 4.5 10−5 mbar and 3.8 10−5 mbar in West cryostat and East cryostat. These values correspond to residual vacuum losses of 0.06 and 0.04 mbar l/s respectively mainly due to out-gassing. A large fraction of this was due to water, which is expected to freeze on the internal walls during the next detector cooling down phase, not affecting the LAr purity. Finally a mass-spectrometer residual gas analysis fixed the Oxygen contribution to at most 10% of the total pressure. In April the evacuation of the filters of the gaseous and liquid purification systems was performed as well as the tests of the vacuum tightness with helium leak detector and the starting of liquid nitrogen pumps and cryogenic emergency test. The laboratory SCADA (Supervisory Control & Data Acquisition) was correctly in-
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
terfaced, and the complete monitoring of the cryogenic plant was implemented in the ICARUS Control Room. 3.1. LAr filling phase The detector’s volume was filled with ultra-pure Argon gas at a slight overpressure on middle April and the cryostat cool-down started with 10 Stirling compressors fully operative through circulation of liquid Nitrogen in the cold screens. Periodic additions of Argon gas were performed, in order to maintain the correct overpressure in the process. The vapor not managed by Stirling compressors was exhausted in hall B through a 50 kW electrical heater and safely evacuated from hall B via the ventilation system. On April 23rd the LAr temperature (90 K) was reached at an average rate of about 1 K/hour. Finally cryostats were filled at a rate of ∼ 1m3 /hour/cryostat with 47 trucks in about 2 weeks for a total amount of 610511 Argon liters, including the 30 m3 storage tank filling. During the whole period the four gaseous re-circulations were operating at maximum speed. In steady state conditions 7/8 Stirling machines out of 10 are operating (32 KWatt) smoothly. The liquid recirculation became available on both cryostats (∼ 1 m3 /hour/cryostat) one month after the filling completion. 3.2. Detector commissioning and first signals DAQ and event builder architecture were deployed and tested including DAQ computers (10 server), storage (160 TB on disk and 100 TB on tape), networking (cabling, switches and fibers to control room and to external labs). Test pulse signals were injected to check the read-out electronic chain, measure the electronic noise, get a first calibration of the channels and test the response linearity. On May 18th , electronic racks were mechanically connected to the signal feed-throughs, and Faraday cages closed in order to shield the signal cables from the detector flanges to the decoupling boards from external noise. The cathode HV supplier of West cryostat was turned on: the -75 kV nominal voltage was reached with stable current flowing through the field shaping resistive dividers. Signals from the 21 internal photomultipliers in West module were exploited to build up a prompt trigger signal. Electronics for PMTs’ signal discrimination and trigger logic was also tested and commissioned during first data taking. On May 27th , nominal values were applied to wire biasing at (-220, 0, +280 V) on West cryostat. First c-ray ionization tracks and horizontal muons produced in the CNGS neutrino interactions in the upstream rock and CNGS neutrino interactions in
345
ICARUS-T600 were promptly recorded by DAQ system and visualized. In Figure 3 (top) is shown a ∼ 10 GeV νμ charged current interaction with a escaping muon (Collection view) and an atmospheric neutrino interaction with 910 MeV visible energy as determined by the charge deposition measurement. These events confirm the excellent detector performance which will allow to study in real-time neutrino interactions in a large mass detector with much more details that in the past experiments, opening “de facto” a new era for large mass neutrino and astroparticle detectors. Beginning of June, the second half module detector (East cryostat) was also switched on. Muon tracks are used to evaluate electron lifetime in real time (Figure 2). The starting value was measured to be τele ∼ 650 μs with only gaseous recirculation/purification system active, sufficient to visualize tracks over the full drift distance (1.5 m equivalent to 1 ms drift time). The LAr purity was steadily improving above 1 ms lifetime when liquid recirculation was turned on. The average electronic noise was measured to be well within expectations on practically all the 54000 channels: 1500 electrons rms to be compared with ∼ 15000 free electrons produced by m.i.p. over 3 mm (S /N ≥ 10). The event builder, including wire mapping and crate CPU’s synchronization, has been fully checked, exploiting the collected events. Synchronization of T600 detector with CERN early warning signal of the two 10.5 μs SPS spill proton extractions separated by 50 ms of distance, was performed by means of the 10 MHz atomic clock signal of LNGS. Packets containing the forseen proton extraction times and sent via web from CERN to LNGS about 80 ms before extraction, have been correctly decoded allowing the opening of a suitable gate signal to trigger CNGS neutrino events. The overall trigger system, based on PMT’s prompt signals and CNGS early warning information for both long-baseline and cosmic neutrino physics, is under refinement addressing mainly timing issues. 4. Conclusions: the Renaissance of the Bubble chamber neutrino physics Cryogenic noble liquids and Argon in primis have recently regained a strong interest in the scientific community. The successful assembly and operation of the ICARUS-T600 LAr-TPC at the Gran Sasso underground INFN laboratory demonstrate that the technology is mature for a full physics exploitation. The wide
346
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
Figure 3: A CNGS muon neutrino CC event (top) and a low energy NC neutrino interaction (bottom) recorded in ICARUS T600.
physics potentials offered by its high granularity imaging and extremely high resolution will address already with the T600 detector both underground physics and long base-line and high precision neutrino physics. In particular ICARUS-T600 will allow with few year data taking to study the atmospheric neutrino oscillations in the most relevant region of the spectrum below 200 MeV and investigate the nucleon stability with a new complete different way than the present experiments. In fact the T600 detector is well suited for nucleon decay channels not accessible to water Cherenkov detectors due to the complicated event topology, or because the emitted particles are below the Cherenkov threshold like in n → e− K + channel. The ICARUS-T600 detector is presently taking data receiving the CNGS neutrinos from CERN-SPS for νμ → ντ oscillations and sterile neutrino searches, smoothly reaching optimal working conditions. Data analysis of the recorded events is already on-going. The ICARUS experiment at the Gran Sasso Laboratory is so far the most important milestone for the LAr-TPC technology and acts as a full-scale test-bed located in a difficult underground environment. [1] C. Rubbia, The Liquid-Argon Time Projection Chamber: A new Concept for Neutrino Detector, CERN-EP/77-08 (1977).
[2] S. Amerio et al. [ICARUS Collab.], Nucl. Instr. and Methods A527 (2004) 329. [3] A. Ankowski et al. [ICARUS Collab.] Nucl. Instr. and Meth. A556 (2005) 146. [4] A. Ankowski et al. [ICARUS Collab.], Acta Phys. Polon. B41 (2010) 103. [5] A. Ankowski et al. [ICARUS Collab.], E. Phys. J. C48, (2006) 667. [6] F. Arneodo et al.[ICARUS Collab.], ICARUS initial physics program, LNGS P28/01, LNGS-EXP 13/89 add. 1/01; Cloning of T600 modules to reach the design sensitive mass, LNGS-EXP 13/89 add. 2/01.
Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346 www.elsevier.com/locate/npbps
Status and early events from ICARUS T600 A. Guglielmi, for the ICARUS Collaboration Istituto Nazionale di Fisica Nucleare and Dep. of Physics “G. Galilei”, via Marzolo 8, 35131 Padova, Italy
Abstract The ICARUS T600 detector, a ∼ 600 t liquid Argon (LAr) TPC with unique imaging and calorimetric capabilities, is presently data taking at LNGS underground laboratory for a rich physics programme, covering cosmic neutrinos, nucleon decay search and neutrino oscillations with the CNGS neutrino beam.The successful detector commissioning and operation and the ongoing analysis of the recorded events show the excellent performance of this LAr-TPC, and opens the way to constructing very massive high quality detectors. Keywords: Liquid Argon, TPC, Neutrino Physics, Astroparticle Physics
1. Introduction The new superior bubble-chamber-like features of ICARUS T600 liquid Argon (LAr) TPC detector at LNGS is expected to provide additional and fundamental contributions to both neutrino physics and studies of nucleon stability. The operational principle of the LAr-TPC is based on the fact that in highly purified LAr ionization tracks can be transported practically undistorted by a uniform electric field over macroscopic distances [1]. Imaging is provided by a suitable set of electrodes (wires) placed at the end of the drift path continuously sensing and recording the signals induced by the drifting electrons. Non-destructive read-out of ionization electrons by charge induction allows detecting the entire signal of electrons crossing subsequent wire planes with different orientation. This provides simultaneously several projective views of the same event, hence allowing a precise reconstruction of the recorded particle trajectory and a precise calorimetric measurement. The ICARUS T600 detector presently in operation underground in Hall B of LNGS in a neutrino beam from the CERN-SPS, is the largest liquid Argon TPC ever built, with a size of about 600 t of imaging mass. The design and assembly of the detector relied on industrial support and represents the application of concepts 0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.053
matured in laboratory tests to the kton scale. In the following the installation and completion of T600 detector in Hall B at LNGS underground laboratory and the detector commissioning are presented as well as the first CERN to Gran Sasso (CNGS) neutrino beam interactions recorded in LAr-TPC. 2. The ICARUS-T600 LAr-TPC The ICARUS-T600 detector [2] (see Fig.1) consists of a large cryostat split in two identical, adjacent halfmodules, with internal dimensions 3.6 × 3.9 × 19.9 m3 each. Each half-module houses two Time Projection Chambers (TPC) separated by a common cathode, a field shaping system, monitors and probes, and two arrays of photo-multipliers. Externally the cryostats are surrounded by a common thermal insulation layer, which is realized by evacuated NomexT M honeycomb panels (0.4 m thick) to form a closed vacuum-tight box, with nominal heat losses of about 10 W/m2 . The detector layout is completed by a cryogenic plant made of a liquid Nitrogen cooling circuit based on 10 Stirling compressors circulating boiling Nitrogen to cool down the apparatus and to compensate the heat losses through the thermal insulation box. The circulation speed is defined by the request to maintain a thermal uniformity within 1 K in the LAr bulk.
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
343
Figure 1: The ICARUS T600 detector.
The LAr cryostat is operating at a slight overpressure of 100 mbar at a temperature of about 89 K. The cryostat is filled with ultra-pure Argon obtained starting with commercial liquid (with a typical content of H2 O, O2 , N2 of the order 1 ppm) purified at the cryostat input by means of commercial filters. To ensure an acceptable initial LAr purity, the detector is evacuated to a pressure of the order of 10−4 mbar, before filling, in order to perform an appropriate out-gassing of the cryostat internal walls and all the detector materials. Moreover, each semi-module is equipped with two gas and one liquid recirculation systems, both required to attain a very high free-electron lifetime (several ms) in less than one month. The continuously active gas recirculation units (25 GAr Nm3 /h each at maximum rate) collect the gas from the chimneys that host the cables for the wire chamber read-out on top of the detector.The re-condensed gas drops into Oxysorb/HydrosorbT M filters placed below the re-condenser and is sent back into the LAr container just below the LAr surface. Liquid recirculation units consist of an immersed, cryogenic, liquid transfer pump placed inside an independent dewar. The circulated LAr goes through standard Oxysorb/ HydrosorbT M filters before being re-injected into the cryostats (∼ 2 m3 /h, corresponding to a full volume recirculation in about 6 days).
Each TPC is made of three parallel planes of wires, 3 mm apart. The first faces the drift region, with horizontal wires, the other two have the wires at ±600 from the horizontal direction. By appropriate voltage biasing, the first two planes (Induction planes) provide signals in non-destructive way, whereas the charge is finally collected in the last one (Collection plane). The maximum drift path, i.e.the distance between the cathode and the wire planes, is 1.5 m and the nominal drift field 500 V/cm. The total number of wires in the T600 detector is about 54000. The signals coming from each wire are independently digitized every 400 ns. The electronics was designed to allow continuous read-out, digitization and independent waveform recording of signals from each wire of the TPC. The measurement of the time of the ionizing event, the “T 0 time” given by the prompt scintillation light produced by ionization in LAr, together with the knowledge of the electron drift velocity provide the absolute position of the tracks along the drift coordinate. Globally 74 photomultipliers coated with TPB wavelength-shifter to detect the UV scintillation light are directly installed in LAr behind the wire planes of TPCs [3]. The high resolution and ∼ mm granularity of the detector imaging allow a precise reconstruction of the event topologies identifying the particles produced in
344
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
Figure 2: A muon event recorded in ICARUS T600.
the interaction in LAr. The event reconstruction is completed by calorimetric measurement via dE/dx ionization signal in 1 MeV ÷ 50 GeV energy range. A 10−3 electron - π0 separation is expected in the CNGS neutrino energy range by gamma reconstruction, dE/dx signal comparison and π0 invariant mass measurement [4]. This will guarantee a powerful 90 % selection efficiency of the genuine electron neutrino interactions rejecting NC interactions to a negligible level. Moreover muon momentum measurement within ∼ 10 ÷ 15% accuracy is performed exploiting multiple scattering along the track [5]. The ICARUS-T600 can address both underground physics (proton decay search, solar and atmospheric neutrino measurements, supernova explosion detection) and long base-line and high precision neutrino physics [6].
3. Early operations of ICARUS-T600 in LNGS During the first months of 2010 the detector commissioning took place, leading to the successful filling with liquid Argon, DAQ electronic activation and the detection of the first CNGS neutrino events.
The cryogenic and liquefaction systems were put in operation and successfully tested. Sensors for the measurement of the thermal insulation and lateral panel deformations allowed to measure the thermal tightness on the panels, in agreement with the expectations. All the safety and technical requirements of LNGS laboratory were fulfilled leading to the start-up of the T600. The cryostats evacuation started on January 2010 reaching on April the residual vacuum pressure in the detector 4.5 10−5 mbar and 3.8 10−5 mbar in West cryostat and East cryostat. These values correspond to residual vacuum losses of 0.06 and 0.04 mbar l/s respectively mainly due to out-gassing. A large fraction of this was due to water, which is expected to freeze on the internal walls during the next detector cooling down phase, not affecting the LAr purity. Finally a mass-spectrometer residual gas analysis fixed the Oxygen contribution to at most 10% of the total pressure. In April the evacuation of the filters of the gaseous and liquid purification systems was performed as well as the tests of the vacuum tightness with helium leak detector and the starting of liquid nitrogen pumps and cryogenic emergency test. The laboratory SCADA (Supervisory Control & Data Acquisition) was correctly in-
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
terfaced, and the complete monitoring of the cryogenic plant was implemented in the ICARUS Control Room. 3.1. LAr filling phase The detector’s volume was filled with ultra-pure Argon gas at a slight overpressure on middle April and the cryostat cool-down started with 10 Stirling compressors fully operative through circulation of liquid Nitrogen in the cold screens. Periodic additions of Argon gas were performed, in order to maintain the correct overpressure in the process. The vapor not managed by Stirling compressors was exhausted in hall B through a 50 kW electrical heater and safely evacuated from hall B via the ventilation system. On April 23rd the LAr temperature (90 K) was reached at an average rate of about 1 K/hour. Finally cryostats were filled at a rate of ∼ 1m3 /hour/cryostat with 47 trucks in about 2 weeks for a total amount of 610511 Argon liters, including the 30 m3 storage tank filling. During the whole period the four gaseous re-circulations were operating at maximum speed. In steady state conditions 7/8 Stirling machines out of 10 are operating (32 KWatt) smoothly. The liquid recirculation became available on both cryostats (∼ 1 m3 /hour/cryostat) one month after the filling completion. 3.2. Detector commissioning and first signals DAQ and event builder architecture were deployed and tested including DAQ computers (10 server), storage (160 TB on disk and 100 TB on tape), networking (cabling, switches and fibers to control room and to external labs). Test pulse signals were injected to check the read-out electronic chain, measure the electronic noise, get a first calibration of the channels and test the response linearity. On May 18th , electronic racks were mechanically connected to the signal feed-throughs, and Faraday cages closed in order to shield the signal cables from the detector flanges to the decoupling boards from external noise. The cathode HV supplier of West cryostat was turned on: the -75 kV nominal voltage was reached with stable current flowing through the field shaping resistive dividers. Signals from the 21 internal photomultipliers in West module were exploited to build up a prompt trigger signal. Electronics for PMTs’ signal discrimination and trigger logic was also tested and commissioned during first data taking. On May 27th , nominal values were applied to wire biasing at (-220, 0, +280 V) on West cryostat. First c-ray ionization tracks and horizontal muons produced in the CNGS neutrino interactions in the upstream rock and CNGS neutrino interactions in
345
ICARUS-T600 were promptly recorded by DAQ system and visualized. In Figure 3 (top) is shown a ∼ 10 GeV νμ charged current interaction with a escaping muon (Collection view) and an atmospheric neutrino interaction with 910 MeV visible energy as determined by the charge deposition measurement. These events confirm the excellent detector performance which will allow to study in real-time neutrino interactions in a large mass detector with much more details that in the past experiments, opening “de facto” a new era for large mass neutrino and astroparticle detectors. Beginning of June, the second half module detector (East cryostat) was also switched on. Muon tracks are used to evaluate electron lifetime in real time (Figure 2). The starting value was measured to be τele ∼ 650 μs with only gaseous recirculation/purification system active, sufficient to visualize tracks over the full drift distance (1.5 m equivalent to 1 ms drift time). The LAr purity was steadily improving above 1 ms lifetime when liquid recirculation was turned on. The average electronic noise was measured to be well within expectations on practically all the 54000 channels: 1500 electrons rms to be compared with ∼ 15000 free electrons produced by m.i.p. over 3 mm (S /N ≥ 10). The event builder, including wire mapping and crate CPU’s synchronization, has been fully checked, exploiting the collected events. Synchronization of T600 detector with CERN early warning signal of the two 10.5 μs SPS spill proton extractions separated by 50 ms of distance, was performed by means of the 10 MHz atomic clock signal of LNGS. Packets containing the forseen proton extraction times and sent via web from CERN to LNGS about 80 ms before extraction, have been correctly decoded allowing the opening of a suitable gate signal to trigger CNGS neutrino events. The overall trigger system, based on PMT’s prompt signals and CNGS early warning information for both long-baseline and cosmic neutrino physics, is under refinement addressing mainly timing issues. 4. Conclusions: the Renaissance of the Bubble chamber neutrino physics Cryogenic noble liquids and Argon in primis have recently regained a strong interest in the scientific community. The successful assembly and operation of the ICARUS-T600 LAr-TPC at the Gran Sasso underground INFN laboratory demonstrate that the technology is mature for a full physics exploitation. The wide
346
A. Guglielmi / Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 342–346
Figure 3: A CNGS muon neutrino CC event (top) and a low energy NC neutrino interaction (bottom) recorded in ICARUS T600.
physics potentials offered by its high granularity imaging and extremely high resolution will address already with the T600 detector both underground physics and long base-line and high precision neutrino physics. In particular ICARUS-T600 will allow with few year data taking to study the atmospheric neutrino oscillations in the most relevant region of the spectrum below 200 MeV and investigate the nucleon stability with a new complete different way than the present experiments. In fact the T600 detector is well suited for nucleon decay channels not accessible to water Cherenkov detectors due to the complicated event topology, or because the emitted particles are below the Cherenkov threshold like in n → e− K + channel. The ICARUS-T600 detector is presently taking data receiving the CNGS neutrinos from CERN-SPS for νμ → ντ oscillations and sterile neutrino searches, smoothly reaching optimal working conditions. Data analysis of the recorded events is already on-going. The ICARUS experiment at the Gran Sasso Laboratory is so far the most important milestone for the LAr-TPC technology and acts as a full-scale test-bed located in a difficult underground environment. [1] C. Rubbia, The Liquid-Argon Time Projection Chamber: A new Concept for Neutrino Detector, CERN-EP/77-08 (1977).
[2] S. Amerio et al. [ICARUS Collab.], Nucl. Instr. and Methods A527 (2004) 329. [3] A. Ankowski et al. [ICARUS Collab.] Nucl. Instr. and Meth. A556 (2005) 146. [4] A. Ankowski et al. [ICARUS Collab.], Acta Phys. Polon. B41 (2010) 103. [5] A. Ankowski et al. [ICARUS Collab.], E. Phys. J. C48, (2006) 667. [6] F. Arneodo et al.[ICARUS Collab.], ICARUS initial physics program, LNGS P28/01, LNGS-EXP 13/89 add. 1/01; Cloning of T600 modules to reach the design sensitive mass, LNGS-EXP 13/89 add. 2/01.