OPERA tau neutrino candidate event 12227007334

Description

This neutrino candidate occurred on August $14^{th}$ 2012 in the second super-module, in the $24^{th}$ wall, 7 brick walls upstream of the spectrometer. No muon track was reconstructed by the electronic detectors and the event was classified as ${0\mu}$. The activity in the Target Trackers was limited to the 8 walls downstream of the vertex brick. The interaction was fully reconstructed in the brick, looking for tracks within an angular acceptance defined by $\tan \vartheta = 3$. The visible energy of the event was measured to be ${(12\pm 4)}$~GeV.

In the analysis of the interface emulsion films, 15 tracks were detected, six of which showed a converging path, thus validating the brick extraction and development. By following back these tracks with the scan-back procedure, the neutrino interaction was located between the $15^{th}$ and $16^{th}$ emulsion films, 42 plates from the downstream face of the brick. Its vertex consisted of two charged tracks, one of which exhibits a kink topology with ${\theta_{kink}=(90\pm 2)}$~mrad, after a flight length of ${(960 \pm 30)}$~${\mu}$m. The distance of closest approach between the ${\tau}$ candidate and the other primary track is 0.1~${\mu}$m.

In addition to these two tracks, four forward-going and two backward-going nuclear fragments pointing to the primary vertex were observed.

The ${\tau}$ daughter interacted after having crossed 22 plates, producing four charged particles and a photon, and it could thus be unambiguously identified as a hadron. Its measured momentum is ${11.0^{+13.9}_{-3.9}}$~GeV/c, while its impact parameter w.r.t.~the primary vertex is ${(83 \pm 5)}$~${\mu}$m.

The second primary track measured momentum is ${(1.1\pm 0.2)}$~GeV/c and it was classified as a proton from its energy loss in the emulsion target. The linear density of grains along the track left by a particle, indeed, is correlated with its energy loss. The ratio between the grain density of this track and that of the ${\tau}$ daughter track is ${(1.45 \pm 0.06)}$, to be compared with ${(1.38 \pm 0.14)}$ expected for a proton/m.i.p.~ratio. Therefore, the second primary track was likely produced by a proton.

This event was thus interpreted as a $\nu_{\tau}$ charged-current interaction with the $z\tau$ lepton decaying into a single hadron. A detailed description of the event is given in 10.1103/PhysRevLett.115.121802.

Related datasets

This event is part of OPERA Electronic Detector tau appearance dataset

Electronic detector data for tau neutrino appearance studies

This event is part of OPERA Emulsion Detector tau appearance dataset

Emulsion data for neutrino tau appearance studies

Dataset characteristics

1 events. 14 files. 9.2 kB in total.

Dataset semantics

Variable	Description
amplL	PMT amplitude measured from the "left" side of a scintillator strip (in photo-electrons)
amplR	PMT amplitude measured from the "right" side of a scintillator strip (in photo-electrons)
amplRec	PMT amplitude reconstructed from the "left" and "right" side amplitudes of a scintillator strip taking into account light attenuation in a WLS fiber (in photo-electrons)
clLength	cluster length (in cm)
driftDist	drift distance (in cm)
enHad	energy of a hadron jet (in GeV)
enNeu	energy of a neutrino (in GeV)
enVis	visible energy (in MeV)
evID	event Id (10- or 11-digit number)
globPosX	X position of a vertex in the OPERA detector system of reference (in cm)
globPosY	Y position of a vertex in the OPERA detector system of reference (in cm)
globPosZ	Z position of a vertex in the OPERA detector system of reference (in cm)
muMom	momentum of a muon (in GeV/c)
posX	For Electronic Detector events, X position of a drift tube, RPC, Target Tracker hit in the OPERA detector system of reference (in cm). For Emulsion Detector events, X position of a track/vertex in the OPERA brick system of reference (in micrometers).
posX1	X position of the beginning of a line in the OPERA brick system of reference (in micrometers)
posX2	X position of the end of a line in the OPERA brick system of reference (in micrometers)
posY	For Electronic Detector events, Y position of an RPC hit in the OPERA detector system of reference (in cm). For Emulsion Detector events, Y position of a track/vertex in the OPERA brick system of reference (in micrometers).
posY1	Y position of the beginning of a line in the OPERA brick system of reference (in micrometers)
posY2	Y position of the end of a line in the OPERA brick system of reference (in micrometers)
posZ	For Electronic Detector events, Z position of a drift tube, RPC, Target Tracker hit in the OPERA detector system of reference (in cm). For Emulsion Detector events, Z position of a track/vertex in the OPERA brick system of reference (in micrometers).
posZ1	Z position of the beginning of a line in the OPERA brick system of reference (in micrometers)
posZ2	Z position of the end of a line in the OPERA brick system of reference (in micrometers)
primary	flag of a vertex: 1 - primary vertex; 0 - not primary vertex
slopeXZ	tangent of a track angle in XZ view
slopeYZ	tangent of a track angle in YZ view
timestamp	event time in milliseconds since 01/01/1970
trType	type of a track: 1 - muon; 2 - hadron; 3 - electron/positron; 8 - tau lepton

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