OPERA tau neutrino candidate event 10123059807

Description

This ${\nu_\tau}$ interaction occurred on May 3$^{rd}$ 2010 in the second super-module, in the 27$^{th}$ wall, 4 walls upstream of the muon spectrometer, well inside the target. No muon was identified by the reconstruction of the data provided by electronic detectors. All tracks possibly related to the interaction were searched for in the brick within an angular acceptance defined by $\tan\theta=3$.

After the analysis of the interface emulsion films, 4 tracks were found showing a converging path. This finding triggered the brick film development. By the scan-back procedure, the neutrino interaction was located with 7 tracks were reconstructed. The neutrino interaction vertex was located in the lead between the $19^{th}$ and $20^{th}$ emulsion films. One backward track was found in films 18-19 and a black segment in film 20. No $\gamma$ was detected. All tracks were identified as hadrons using their overall track length reconstructed along their path, the topology at their end-point and the correlation between their momentum and range.

It turned out that the 7 tracks did not originate from the same vertex because their impact parameters exceed the values expected according to the resolution: therefore, a particle decay must have occurred over a short flight length since it happened in the same lead plate. Looking at the impact parameters of the tracks, two hypotheses were made on the event topology: a primary vertex with 4 tracks and a trident decay or a primary vertex composed by 3 tracks and a secondary vertex with 4 tracks attached. Other hypotheses were discarded given their probability lower than $0.01\%$. The most probable hypothesis is the first one, with a vertex topological probability of $72.3\%$, according to the impact parameters, and corresponds to a $\nu_{\tau}$ charged-current interaction with the $\tau$ lepton decaying into three hadrons. In this configuration, the kink angle, evaluated as the mean kink angle for each daughter track, is 231~mrad. The hypothesis of a short decay of a heavy particle is supported also by the invariant mass measurement done with the three daughter tracks, 1.2~GeV, assuming the ${\pi}$ mass for all daughters.

The rejected hypothesis could be explained only by a $\nu_\mu$ charged-current interaction with charmed hadron production that would require the presence of a muon at the primary vertex, strongly suppressed by the hadron identification of the tracks.

The neutrino energy was measured to be $16.4$~GeV/c. This event was thus interpreted as a $\nu_{\tau}$ charged-current interaction with the $\tau$ lepton decaying into three hadrons.

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. 27.9 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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