L. Rossi

A search for two neutrino and neutrinoless double beta decay of 136Xe in the Gran Sasso underground laboratory

Abstract We have searched for two neutrino and neutrinoless double beta decay of 136 Xe with a multicell proportional counter in the Gran Sasso underground laboratory. The search for the two neutrino channel has been based on the comparison of spectra obtained in runs with natural and enriched xenon and with xenon which had been specifically cleaned with an ultracentrifuge. Special dedicated runs have been carried out with the various gases to evaluate the background from the rate of α-particles. No evidence has been found for two neutrino or neutrinoless double beta decay. The corresponding lower limits on the lifetime are evaluated with a new statistical procedure.

State-of-the-art superconducting accelerator magnets

With the LHC the technology of NbTi-based accelerator magnets has been pushed to the limit. By operating in superfluid helium, magnetic fields in excess of 10 T have been reached in various one meter-long model magnets while full scale magnets, 15 meter-long dipoles, have demonstrated possibility of safe operation in the 8.3-9 tesla range, with the necessary, very tight, field accuracy. The paper reviews the key points of the technology that has permitted the construction of the largest existing superconducting installations (Fermilab, Desy and Brookhaven), highlighting the novelties of the design of the LHC dipoles, quadrupoles and other superconducting magnets. All together the LHC project will need more than 5000 km of fine filament superconducting cables capable of 14 kA @ 10 T, 1.9 K.

Progress on the conductor for the superconducting toroids of the ATLAS experiment

The production of the conductor for the superconducting toroids of the ATLAS experiment at LHC (CERN) is under way. The conductor is obtained by coextruding a big Rutherford cable with very pure aluminium. All toroids, one Barrel Toroid (BT) and two End Cap Toroids (ECT), require a conductor with a critical current of about 60 kA at 5 T, 4.2 K and a RRR in excess of 800 (at zero field), together with a very good bonding between cable and aluminum: 20 MPa for the BT and 15 MPa for the ECT. So far four long lengths, approximately 7 km out of the 90 km of the total need, have been successfully produced, thus demonstrating the feasibility of the process. The paper describes the results of the R&D phases and the results obtained in this first production. The critical current degradation due to cabling and coextrusion was found quite moderate (7-8% in total), despite the low copper content of the strands (Cu:NbTi=1.09-1.18). The bonding was also very good with values well in excess of the specification. A special control system based on continuous ultrasonic inspection was used in the coextrusion line to monitor the bonding quality in real time during production.

A search for lepton number non-conservation in double beta decay of 136Xe

Abstract We have searched for neutrinoless double beta decay of 136Xe with a multielement proportional chamber installed in the Gran Sasso Underground Laboratory. The chamber has been operated with natural xenon and with xenon enriched to 64% in the isotope 136. No evidence has been found in a preliminary analysis for neutrinoless double beta decay with a lower limit on the halflife of 1.4×1022 yr at 68% confidence level.

Multielement proportional chamber — a study of background in the Gran Sasso underground laboratory

We describe the counting and background characteristics of the multielement proportional chamber used for the search on two-neutrino and neutrinoless double beta decay of 136Xe in the Gran Sasso underground laboratory. Enriched xenon to 64% in the 136Xe isotope and natural xenon cleaned by ultracentrifugation were filled up to 9.5 bar and counted for 6210 and 5120 h, respectively. The reduction of chamber background using suitable software triggers is discussed in detail.

A multi-element proportional chamber used in an experiment on ββ-decay of 136Xe

The lower limits on the neutrinoless and two neutrino ββ-decay of 136Xe, obtained with a multi-element proportional chamber, are reported. The sensitivity of the experiment was limited by the level of the background contamination. The experimental apparatus, its performance and the background analysis are discussed in detail.

Production and qualification of the 60-kA, aluminum-stabilized conductor for the ATLAS B0 coil

For the toroidal ATLAS magnet system, some 90 km of aluminum stabilized conductor are required. The conductor is a Rutherford cable, coextruded with very pure aluminum. The main characteristics of the conductor are: (1) a very large critical current, 60 kA at 5 T and 4.2 K; (2) RRR of the stabilizing aluminum of at least 1000 on the finished conductor; (3) a good bonding between the Rutherford cable and the stabilizer: a shear stress of 20 MPa is required; and (4) 1750 m of unit length. To assure a good quality of the conductor all along the production and to minimize the risk of rejection of such expensive units, a strict quality assurance was established. The paper describes the results of the R&D phase to set all parameters to produce the first two unit lengths necessary for the winding of the B0 coil (a 9 m long model coil of the ATLAS Barrel Toroid). It also describes the control system based on continuous ultrasonic inspection, able to provide images of the cable inside the aluminum that is used to evaluate on line the quality of aluminum to cable bonding.