ICARUS T600 experiment
Yesterday, in the first afternoon session, Francesco Pietropaolo presented, for the ICARUS Collaboration, a talk on “ICARUS and Status of Liquid Argon Technology”.
Since it is similar to the one I gave at the LaThuile Conference 2 weeks ago, here you are a summary of mine:
ICARUS T600, now operating at LNGS (Laboratori Nazionali del Gran Sasso) after a long R&D and installation phase, is the biggest Liquid Argon Time Projection Chamber (LAr-TPC), containing more than 700 t of Liquid Argon in two 3.6 x 3.9 x 19.6 m3 cryostats. This kind of detector operates collecting the ultra-violet scintillation light and recording ionization electron signals produced by a charged particle in LAr; in particular, a 500 V/cm electric field is applied to make the ionization electrons drift along a 1.5 m path towards the wire array planes, where their signal can be continuously collected. Thus LAr-TPCs can be in a certain way considered an evolution of the bubble chambers, the famous detectors which 30 years ago played a crucial role in particle physics, allowing for the discovery of many particles and interaction mechanisms: indeed they mantain the excellent topological and calorimetric properties of the bubbles chambers with in addition the possibility of being continuously sensitive and self-triggering.
Icarus T600 is exposed to the CNGS muon neutrino beam, travelling for 732 km from CERN to LNGS at 17. 4 GeV medium energy, looking mainly for the tau neutrino appearance, but it can perform interesting research also in atmospheric and solar neutrino physics and in some background-free nucleon decay channels; furthermore, it can be considered a major milestone towards the realization of future much more massive LAr-TPC detector. The detector has taken CNGS data during 2010 in stable conditions from Oct. 1st to Nov. 22nd, collecting an overall number of neutrino interactions in agreement with expectations and demonstrating the feasibility of full event reconstruction and particle identification. Thus we are looking forward to the two next years of data taking with the CNGS beam (2011-2012), with the possibility of detecting a few nu-tau events with a full background rejection.
According to a recent proposal still under discussion, Icarus T600 has also the interesting perspective of beeing reused, in combination with a smaller 150 t LAr-TPC detector to be built ex novo, at a CERN-PS refurbished neutrino beam to solve a puzzle which is drawing the attention of many neutrino specialists: the possible existence of one, or event more, “sterile” neutrino states. It all started with the LSND short baseline experiment observing a nu-e bar excess signal from a nu-mu bar beam, later confirmed by the MiniBooNE experiment, hinting at a nu-mu bar –> nu-e bar oscillation beyond the 3 neutrino flavour oscillation as observed in solar/atmospheric neutrino experiments; recently, as a consequence of the nu-e bar reactor spectra re-evaluation, another anomaly has emerged as a nu-e bar deficit at several reactor experiment, hinting at some fast disappearance rate. In such a mess it is clear that a definitive experiment is needed, and the LAr-TPC technique is an optimal candidate. The idea is to use two strictly identical LAr-TPC detectors in near (127 m from target) and far (850 m from target) positions to look both for the LSND appearance signal and the disappearance reactor anomaly, accounting for a complete cross-sections and experimental biases cancellation in the comparison, thanks to the identical nu-e spectra in the two positions and the same technique of the two detectors. Sensitivities of this experiment are under study but seem to be really promising.
(posted by A. Fava)