The T600 ICARUS detector, with a mass of about 600 tons of liquid argon (LAr), is the largest LAr Time Projection Chamber (TPC) ever built. It has been successfully tested in Pavia/Italy in 2001. More than 29,000
cosmic rays events have been collected during about 100 days of continuous data taking. It was demonstrated that large mass scale LAr TPC technique is operational. The T600 ICARUS test run results are briefly reported in
this paper

Kisiel, Jan

Acta Physica Polonica B

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Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Present status of the ICARUS experiment  Author: Jan Kisiel  Citation style: Kisiel Jan. (2005). Present status of the ICARUS experiment. "Acta Physica Polonica B" (Vol. 36, no. 11 (2005), s. 3227-3234).   Vol. 36 (2005) ACTA PHYSICA POLONICA B No 11PRESENT STATUS OF THE ICARUS EXPERIMENT∗Jan KisielInstitute of Physics, University of SilesiaUniwersytecka 4, 40-007 Katowice, Polandfor the ICARUS Collaboration†(Received November 2, 2005)The T600 ICARUS detector, with a mass of about 600 tons of liquidargon (LAr), is the largest LAr Time Projection Chamber (TPC) ever built.It has been successfully tested in Pavia/Italy in 2001. More than 29,000cosmic rays events have been collected during about 100 days of continuousdata taking. It was demonstrated that large mass scale LAr TPC techniqueis operational. The T600 ICARUS test run results are briefly reported inthis paper.PACS numbers: 29.40.–n, 29.40.Gx1. IntroductionThe LAr TPC was proposed by Rubbia in 1977 [1]. Its operational prin-ciple exploits the fact that, in highly purified LAr, ionization charge (elec-trons) can drift practically undistorted, in an electric field, over distancesof meters. The non-destructive readout of electron signals, by subsequentanode wire planes, provides three dimensional imaging of tracks and allowsfor calorimetric measurements. Many years of the ICARUS Collaborationextensive R&D studies, construction of several prototypes of smaller massof 50 liters, 3 tons and 14 tons, proved the feasibility of the LAr TPC tech-nique. The successful tests of the cryogenics of the 14 tons LAr resultedin the construction of an ‘industrial’ T600 module, filled with about 600tons of LAr. The T600 ICARUS experimental set-up was assembled on the∗ Presented at the XXIX International Conference of Theoretical Physics, “Matter tothe Deepest”, Ustroń, Poland, September 8–14, 2005.† ICARUS Collaboration: Univ. and INFN of: L’Aquila, Frascati, Gran Sasso, Milano,Napoli, Padova, Pavia, Pisa, IFSI Torino, Politecnico di Milano, ETH Zurich, Univ.of Granada, CERN, Ciemat Madrid, UCLA Los Angeles, Inst. of Nucl. PhysicsCracow, Univ. of Technology Cracow, Univ. of Science and Technology Cracow,Univ. of Silesia Katowice, Warsaw Univ., Wroclaw Univ., SINS Warsaw.(3227)3228 J. KisielEarth surface in Pavia/Italy. All its components (cryogenics, argon purifi-cation, high voltage, wire chambers, electronics, data acquisition, ...) havebeen successfully tested during three months of technical run in 2001. Thedetailed description of the T600 ICARUS detector design, construction andtests, can be found in [2]. With the use of the LAr technology new im-portant contributions to studies of neutrino signals and matter stability areexpected. The physics program of the ICARUS experiment has been pre-sented at many conferences, also in Ustroń/Poland [3]. In this paper a briefdescription of the T600 ICARUS module and a summary of some resultsobtained during the 2001 test run are given.2. The T600 ICARUS detectorThe T600 ICARUS detector is composed of two identical half-modulesT300 (see Fig. 1). Each of them has internal dimensions of 3.6m (width)× 3.9m (height) × 19.6m (length). Each half-module houses two TPCswith common cathode placed in the middle, the electric field shaping sys-tem, monitors and probes, and photomultipliers for the LAr scintillationlight detection. The external thermal insulation and liquid nitrogen coolingcircuit allow to keep the LAr temperature uniform and stable. The LArpurification system completes the detector layout. Along the longest sidewalls of each half-module three parallel planes of anode wires are located.They are oriented at 60 degrees with respect to each other, 3mm apart,with wire pitch of 3mm. The instrumented volume in the T600 detector is340.3m3 (476.5tons) of LAr with the total number of wires equal to 53248.The ionization electrons travel, in an uniform electric field perpendicular tothe wires planes, toward them. The maximum electron drift length is 1.5m,whereas the maximum drift time is about 1ms, when the nominal voltageof 75kV is applied. Thanks to an appropriate voltage biasing, the elec-trons induce a signal on two first Induction wire planes, whereas the chargeis collected on the last Collection plane. This type of read-out allows fora three-dimensional event reconstruction: two-dimensional projections areprovided by each pair of wire planes, whereas the position along the driftdirection is obtained from the signal timing with respect to the trigger. Theprompt detection of scintillation light in LAr defines the time of the event.The Čerenkov light has also been identified during the T600 detector testrun [4] in 2001. The LAr purification system [5] was able to keep impuritiesat a very low level. Therefore, the ionization electrons could drift safelytoward the anode wires. The electrons drift life time τe has been measuredwith the purity monitors and with long ionizing tracks. The value of τe wasincreasing during the test run, reaching about 1.8 ms at the end of the datataking, with no sign of saturation. This allows for a drift distance of almost3m for ionization electrons.Present Status of the ICARUS Experiment 3229Fig. 1. The inner view of one of Time Projection Chambers (TPC) of the T600ICARUS module.More than 29,000 cosmic-ray events have been collected during the testrun of the T600 ICARUS detector on the Earth surface in Pavia/Italy in2001. Some examples, representing selected topologies, are given in Fig. 2.The overall detector performance is illustrated by long (up to 18m) horizon-tal muon tracks. They were detected with the use of a trigger system madeout of two external plastic scintillators working in coincidence. The T600ICARUS test run data were used at first for the development and optimiza-3230 J. Kisieltion of event reconstruction procedures. It was also demonstrated that theiranalysis can lead to physics results, confirming therefore the capabilities ofthe ICARUS LAr technique. Different aspects of the T600 ICARUS test runhave already been presented in a series of papers [4-7].Fig. 2. Examples of cosmic ray induced events collected during the T600 ICARUStest run.3. Examples of the analysis of the T600 ICARUS data3.1. Measurement of the µ decay spectrumThe measurement of the µ decay spectrum and the determination ofits Michel ρ parameter represent the first physics results obtained with theT600 ICARUS detector. The detailed analysis of the sample of stopping µPresent Status of the ICARUS Experiment 3231events is given in [7]. Here, only the main steps of the data selection, theevent reconstruction and the extraction of Michel ρ parameter are presented.The data selection starts with a visual scanning of the recorded events. Thetopology of the stopping and decaying µ event consists of two tracks: a min-imum ionizing track entering the detector, for which the energy depositionin LAr increases, and a minimum ionizing electron track with length smallerthan 23 cm, starting at the end of the first track. Only events with µ and etracks fully contained in the detector sensitive volume have been accepted.The T600 ICARUS data reconstruction means a three dimensional, spa-tial reconstruction of tracks with a subsequent calorimetric reconstruction.The search for wire signals above a local baseline (hits) on every wire be-gins the spatial reconstruction. For each hit its position, height and areaare calculated. Next, neighboring hits, within each wire plane, are groupedtogether, forming two-dimensional clusters. Finally, the three-dimensionalposition of each hit is computed exploiting the fact, that each wire planeconstrains two spatial coordinates: one common to all wire planes (the driftcoordinate) and one specific to the wire (the wire coordinate). The aim ofthe calorimetric reconstruction is to determine the deposited energy Ehit ofeach identified hit . Summing up all hit energies one can obtain the energyof spatially reconstructed track or shower. The Ehit is proportional to the:(1) ionization charge which is measured at the collection wire plane, (2) anexponential term involving electron’s drift and life times, and (3) calibrationand electron-ion recombination factors. All quantities needed to obtain Ehithave been extracted from the T600 test run data. The detailed descriptionof the reconstruction algorithm can be found in [2].The determination of the Michel ρ parameter of the µ decay spectrumwas based on the comparison of the measured energy spectrum of electronsfrom µ decays with the Monte Carlo simulated spectrum. The data sampleconsisted of 1858 events which passed the reconstruction procedure describedabove. For all of them, the electron energy lost by ionization had been mea-sured and is represented by dots in Fig. 3. The FLUKA package [8] hadbeen used to generate 10,000 muon decays in LAr. The simulated spectrum,obtained with the Standard Model V –A interaction parameters (ρ = 0.75and η = 0) is presented by solid line in Fig. 3. The best fit to the experi-mental points (dotted histogram in Fig. 3) gives the following value of theMichel parameter ρ = 0.72 ± 0.06 ± 0.08, where the first (second) error isstatistical (systematical). This value of ρ is in a very good agreement withthe V –A Standard Model predictions.Taking the advantage of the excellent agreement between the experimen-tal and simulated µ decay spectra, the energy resolution of the detector forthe measurement of electrons of E < 50MeV has been determined. Thefollowing contributions to the final energy resolution have been taken into3232 J. KisielFig. 3. Energy spectrum of electrons from muon decays in the T600 ICARUSdetector. For details see text. Figure taken from [7].account [7]: reconstruction effects (signal extraction procedure), calorimet-ric calibration and electronic noise. The first two are energy independent,whereas the last one gives smaller contribution at higher energies. The esti-mated energy resolution is the following:(Emease− EMCe)/EMCe= 11%/√E[MeV]⊕ 2% , (1)where the Emease(EMCe) is the measured (Monte Carlo simulated) energy ofthe electron track, assuming that electrons loose their energy only by theionization of Ar atoms.3.2. Calorimetric measurement of pi0 massThe CERN CNGS muon neutrino beam will have an unavoidable con-tamination (about 0.6%) of electron neutrinos. Therefore, in order to mea-sure neutrino oscillation parameters, it is important to distinguish betweenνµ neutral current interactions (νµ + n → νµ + pi0 + X) and νe chargedcurrent interactions (νe + n → e− + p). This requires good identificationof electrons and pions. It is not straightforward because, both, the photonsfrom the pi0 decay (pi0 decays in 2γ with a branching ratio of 98.8%) andthe electron from the charged current interaction, may initiate an electro-magnetic shower. The precision of the measurement of the energy releasedPresent Status of the ICARUS Experiment 3233in LAr by electromagnetic showers can be extracted from the pi0 mass re-construction. The search for pi0 candidates, produced by cosmic ray inducedhadronic interactions in LAr, starts with visual scanning for the followingtopology: two or more electromagnetic showers pointing to a common vertexof a hadronic interaction.The calculation of the invariant mass mγγ of the γγ systemmγγ =√2E1E2(1− cos θ12) (2)requires the measurement of the electromagnetic showers’ energies E1, E2,and the angle θ12 between these two gammas. The energy deposited byphotons, visible as electromagnetic showers, is evaluated by using the calori-metric method described in the previous section. The angle θ12 is obtainedfrom the spatially reconstructed vertex of the hadronic interaction and thestarting points of electromagnetic showers. An example of a pi0 candidate isgiven in Fig. 4. With the reconstructed shower energies E1 = 223± 24 MeV,E2 = 350 ± 43 MeV, and θ12 = 29 ± 1, the value of 139 ± 13 MeV for theinvariant mass mγγ was found.Fig. 4. Two views of an example of a pi0 decay event candidate (‘Left’ TPC of oneof T300 ICARUS half-modules). Energy depositions from electromagnetic showersare marked in the collection view, whereas the interaction vertex and the startingpoints of electromagnetic showers are visible in both (collection and induction)projections. The horizontal (vertical) axis is in wire (time sample) coordinates(wire pitch 3 mm, one time sample is 400 ns which corresponds to about 0.624 mmdrift length).3234 J. Kisiel4. ConclusionsThe test run results of the T600 ICARUS detector have been brieflysummarized. The analysis of the µ decay spectrum has been discussed. Theobtained value of the Michel ρ parameter of the electron energy spectrumis fully compatible with the Standard Model one. The samples of measuredand Monte Carlo simulated µ decays were used to determine the energy res-olution of the detector for low energy (E < 50 MeV) electrons. Also, thecalorimetric reconstruction of the γγ invariant mass has been presented. Itwas applied to the pi0 candidate events from hadronic interactions in LAr.This is a method to determine the energy resolution of the detector forthe measurements of electromagnetic showers. The analysis of cosmic-rayevents validated the method of Liquid Argon Time Projection Chamber(LAr TPC). During the test run it was demonstrated that a large LArcryostat can work for months giving high quality images of interactions ofdifferent types. In December 2004, the T600 ICARUS detector has beensuccessfully transported to the Gran Sasso underground laboratory and isbeing installed.REFERENCES[1] C. Rubbia, CERN-EP/77-08 (1977).[2] S. Amerio et al. ( ICARUS Coll.), Nucl. Instrum. Methods A527, 329 (2004.)[3] J. Kisiel, Acta Phys. Pol. B 34, 5385 (2003.)[4] M. Antonello et al. (ICARUS Coll.), Nucl. Instrum. Methods A516, 348(2004.)[5] S. Amoruso et al. (ICARUS Coll.), Nucl. Instrum. Methods A516, 68 (2004.)[6] F. Arneodo et al. (ICARUS Coll.), Nucl. Instrum. Methods A508, 287 (2003.)[7] S. Amoruso et al. (ICARUS Coll.), Eur. Phys. J. C33, 233 (2004.)[8] A. Fasso, A. Ferrari, J. Ranft, P.R. Sala, Electron–Photon Transport inFLUKA: Status, Proc. of Monte Carlo 2000 Conf., Lisbon, 23-26 October2000, edited by A. Kling et al., Springer, Berlin 2001.

Present status of the ICARUS experiment

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Present status of the ICARUS experiment

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