OPERA tau neutrino charged current interactions

Abstract

The OPERA experiment was designed to discover the v_τ appearance in a v_μ beam, due to neutrino oscillations. The detector, located in the underground Gran Sasso Laboratory, consisted of a nuclear photographic emulsion/lead target with a mass of about 1.25 kt, complemented by electronic detectors. It was exposed from 2008 to 2012 to the CNGS beam: an almost pure v_μ beam with a baseline of 730 km, collecting a total of 1.8·10²⁰ protons on target. The OPERA Collaboration eventually assessed the discovery of v_μ→v_τ oscillations with a statistical significance of 6.1 σ by observing ten v_τ CC interaction candidates. These events have been published on the Open Data Portal at CERN. This paper provides a detailed description of the v_τ data sample to make it usable by the whole community.

Fig. 1

OPERA detector (20 × 10 × 10) m³.

Fig. 2

Schematics of micro-tracks reconstruction. Each emulsion layer is scanned focusing at different depths, obtaining different tomographic images grabbed at equally spaced depth levels through the sensitive layer (left). The silver grain clusters are connected to form micro-tracks. On the right, micro-tracks are associated between two emulsion layers to form a base-track.

Fig. 3

Particle detection principle in a scintillating strip (left) and schematic view of an end-cap of a scintillator strip module (right).

Fig. 4

Schematic view of a v_τ CC interaction and the decay-in-flight of the final state τ lepton as it would appear in an OPERA brick, in the interface emulsion films (Changable Sheets), and in the scintillator trackers (Target Trackers).

Fig. 5

Schematic layout of the muon spectrometer. The six drift tube chambers (PT) are denoted by x₁, …, x₆. The brown bands represent the iron slabs of the magnets. With three chamber pairs the momentum can be extracted from two independent measurements of the deflection of the charged particle in the magnetic field.

Fig. 6

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 9190097972 (Brick 26670), (b) for nuclear emulsion films.

Fig. 7

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 9234119599 (Brick 72693), (b) for nuclear emulsion films.

Fig. 8

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 10123059807 (Brick 136759), (b) for nuclear emulsion films.

Fig. 9

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 11113019758 (Brick 29570), (b) for nuclear emulsion films.

Fig. 10

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 11143018505 (Brick 77152), (b) for nuclear emulsion films.

Fig. 11

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 11172035775 (Brick 27972), (b) for nuclear emulsion films.

Fig. 12

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 11213015702 (Brick 4838), (b) for nuclear emulsion films.

Fig. 13

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 12123032048 (Brick 23543), (b) for nuclear emulsion films.

Fig. 14

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 12227007334 (Brick 130577), (b) for nuclear emulsion films.

Fig. 15

Event displays (a) for electronic detectors data (top view on the left and side view on the right) for the v_τ candidate event 12254000036 (Brick 92217), (b) for nuclear emulsion films.