  The INO collaboration is designing a cosmic muon veto detector (CMVD) to
cover the mini-ICAL detector which is operational at the IICHEP transit campus,
Madurai in South India. The aim of the CMVD is to study the feasibility of
building an experiment to record rare events at a shallow depth of around 100
m, and use plastic scintillators to veto atmospheric muons from those produced
by the rare interactions within the target mass of the detector. The efficiency
of such a veto detector should be better than 99.99% and false positive rate of
less than $10^{-5}$.
  The CMVD is being built using extruded plastic scintillator (EPS) strips to
detect and tag atmospheric muons. More than 700 EPS strips are required to
build the CMVD. Two EPS strips are pasted together to make a di-counter (DC)
and wavelength shifting fibres are embedded inside the EPS strips to trap the
scintillation light generated by a passing cosmic ray muon and transmit it as
secondary photons to the Silicon Photo-Multipliers (SiPMs) mounted at the two
ends of the DCs. Since the efficiency requirement of the veto detector is
rather high, it is imperative to thoroughly test each and every component used
for building the CMVD. A cosmic ray muon telescope has been setup using the DCs
to qualify all the DCs that will be fabricated. In this paper we will discuss
the details of the design and fabrication of the DCs, and the cosmic muon setup
and the electronics used for their testing and the test results.

Instrumentation and Detectors;High Energy Physics - Experiment