Emulsion sheet doublets as interface trackers for the OPERA experiment

TL;DR

This paper presents novel emulsion sheet doublets as interface trackers for the OPERA neutrino experiment, improving track matching, background rejection, and alignment procedures for detecting neutrino oscillations.

Contribution

Introduction of emulsion sheet doublets and associated methods for enhanced interface tracking and background reduction in the OPERA experiment.

Findings

Successful track-matching with automated microscopes

Effective background rejection using emulsion doublets

Improved alignment through electron track pattern matching

Abstract

New methods for efficient and unambiguous interconnection between electronic counters and target units based on nuclear photographic emulsion films have been developed. The application to the OPERA experiment, that aims at detecting oscillations between mu neutrino and tau neutrino in the CNGS neutrino beam, is reported in this paper. In order to reduce background due to latent tracks collected before installation in the detector, on-site large-scale treatments of the emulsions ("refreshing") have been applied. Changeable Sheet (CSd) packages, each made of a doublet of emulsion films, have been designed, assembled and coupled to the OPERA target units ("ECC bricks"). A device has been built to print X-ray spots for accurate interconnection both within the CSd and between the CSd and the related ECC brick. Sample emulsion films have been extensively scanned with state-of-the-art automated optical microscopes. Efficient track-matching and powerful background rejection have been achieved in tests with electronically tagged penetrating muons. Further improvement of in-doublet film alignment was obtained by matching the pattern of low-energy electron tracks. The commissioning of the overall OPERA alignment procedure is in progress.