Conceptual design report of the MPD Cosmic Ray Detector (MCORD)
Authors: Bielewicz M. , Bancer A. , Barabanov M. , Chlopik A. , Czarnynoga M. , Dabrowski D. , Dudzinski A. , Dziedzic A. , Grodzicka-Kobylka M. , Grzyb J. , Grodzicki K. , Jaworska E. , Kankiewicz P. , Kasprowicz G. , Kisiel A. , Kolasinski P. , Kowalski S. , Krakowiak M. , Kuich M. , Kutyla M. , Lukasik J. , Maksiak B. , Marzec J. , Matulewicz T. , Mianowski S. , Milewicz-Zalewska M. , J. Peryt M. , Piatek M. , Pollo A. , Pozniak K. , Protoklitow F. , Pszczel D. , Pulawski S. , Romaniuk R. , Roslon K. , Rybczynski M. , Rzadkiewicz J. , Satybaldyeva S. , Shchegolev D. , Shmyrev I. , Sitek M. , Sowinski M. , Stefanek G. , Stepaniak J. , Strugalska-Gola E. , Swiderski L. , Syntfeld-Kazuch A. , Szczesniak T. , Szuta M. , Vodopyanov A. , Wielanek D. , Wlodarczyk Z. , Wojcik K. , Zabolotny W. 
Published: November 2021

This report presents a concept of constructing a detector
dedicated for detection of muons observed during measurements
carried out at the MPD (Multi-Purpose Detector) detector that is
currently under construction at the NICA facility, Russia, Dubna. It
has been proposed to design and build an additional detector that
will complement the current MPD set and increase its measurement
capabilities. The main goal of this project is to provide
information from cosmic muons that pass the MPD detector in both
in-beam and off-beam experiments. Hence, the detector is called the
MPD COsmic Ray Detector (MCORD).The conceptual design of MCORD is
proposed by a Polish consortium NICA-PL comprising several Polish
scientific institutions.

The data from cosmic ray muons could be used as a trigger for
calibration of other detection systems comprising the MPD
detector. Large surface covered by the MCORD offers also possibility
for efficient registration of muons generated in expanding
atmospheric showers induced by distant sources. Moreover, beyond
some energy threshold, observation of muons originating from decays
of collision products will also be possible. In this report examples
of the MCORD functionality as a part of the MPD detector are
presented.

The MCORD is designed as a universal, fast triggering system built
as a modular reconfigurable construction. The detection system will
be based on plastic scintillators equipped with wavelength shifting
fibers, and silicon photomultipliers (SiPM) will be used for
scintillation readout. The online analysis of received signals will
be performed using digital FPGA modules. Due to the modular design,
the same system (its small part) can be used for both laboratory
testing of other MPD sub-detectors, and the calibration of these
detectors after placing them inside the MPD in off-beam mode. The
full detector will support these systems as an additional trigger,
calibrator, and muon identifier during the normal operation of the
MPD detector with the beam. Thanks to its unique construction, it
will expand the possibilities of collecting scientific data of the
MPD detector with astrophysical observations.

The publication will show the assumptions of the mechanical
structure and electronic systems of the planned detector. The
installation site of the detector as part of the MPD detector will
be described in detail. In the following, the results of simulations
made in preparation for this project will be presented. In
particular, simulations with the CORSIKA code present angular
distributions of particles in cosmic showers in the Dubna city
region. Since muons dominate the cosmic ray showers, the MPD
detector response to expected cosmic muon flux was also
simulated. The results provide information about the muon cut-off
thresholds depending on the MPD detector composition during the
installation campaign. Simulations of muon events that could be used
for MPD subsystems calibration were also performed. The results
shown for various configuration of MCORD detector modules will
enable the estimation of the time necessary to perform such tests in
the future.

Simulations with UrQMD model shows the muon abundances due to
beam-beam collisions. Approximately 90% of muons are created from
pions, whereas the number of muons that reach the MCORD detector is
10 times greater than the number of pions. The MPD detector response
was also simulated under the influence of a stream of various
particles, especially muons. It shows energy dependence of muon
transmission coefficient for MPD with and without ECal
assembled. Assuming requirement for muon transmission above 95%,
the muon cut-off thresholds are 1.6 GeV and 2.0 GeV, respectively.

MCORD detector performance evaluation is also reported. In the case
when we used scintillators with one fiber with a diameter of 1 mm,
the time resolution of about 1.0 ns was recorded, which corresponds
to the positional accuracy (σx) of 7.1 cm. The results of
laboratory tests show that application of a 2 mm diameter WLS fiber
instead of the previously used 1 mm diameter fiber improves the
time resolution to 0.80 ns.