Download Study of baryonic matter with the BM@N

The BM@N experiment at the Nuclotron.
Figure 1. BM@N experimental set-up.
BM@N (Baryonic Matter @ Nuclotron) is the first experiment at the accelerator
complex of NICA-Nuclotron-M. The aim of the BM@N experiment is to study
interactions of relativistic heavy ion beams with fixed targets [5]. The Nuclotron
will provide verity of beams from protons to gold ions with the kinetic energy
from 1 to 6 GeV per nucleon. The BM@N experimental zone is situated at the
far end of the building for extracted beams. The beam line between the Nuclotron
and the BM@N experiment is around 160 meter in length. It comprises 26
elements of magnetic optics: 8 dipole magnets and 18 quadruple lenses. The
planned intensity of the gold ion beam accelerated and accumulated in the
Nuclotron with the Booster and transported to the BM@N experimental zone is
up to 107 ions per second. The gold ion beam is expected in the end of 2018. The
xenon ion beam is planned for the end of 2017. The first technical run of the
BM@N detectors was performed with deuteron and carbon beams in spring 2015.
A sketch of the proposed experimental set-up is shown in figure 1. It combines
high precision track measurements with time-of-flight information for particle
identification and total energy measurements for the analysis of the collision
centrality. The charged track momentum and multiplicity will be measured with
the set of 12 two coordinate planes of GEM (Gaseous Electron Multipliers)
detectors located downstream of the target inside the analyzing magnet and
drift/straw chambers (DCH, Straw) situated outside the magnetic field. The GEM
detectors sustain high rates of particles and are operational in the strong magnetic
field. At the second stage of the BM@N experiment, at least 4 planes of twocoordinate silicon strip detectors will be installed between the GEM tracker and
the target. The magnetic field can be varied up to 1.2 T to get the optimal
BM@N detector acceptance and momentum resolution for different processes and
beam energies. The design parameters of the time-of-flight detectors based on
multi-gap Resistive Plate Chambers (mRPC-1,2) with a strip read-out allow us to
discriminate between hadrons (π,K,p) as well as light nuclei with the momentum
up to a few GeV/c produced in multi-particle events. The Zero Degree
Calorimeter (ZDC) is designed for the analysis of the collision centrality by
measuring the energy of forward going particles. The T0 detector, partially
covering the backward hemisphere around the target, is planned to trigger central
heavy ion collisions and provide a start T0 signal for the mRPC-1,2 detectors.
Optionally, an electro-magnetic calorimeter can be installed behind the mRPC-1
wall to study processes with electro-magnetic probes (γ, e±) in the final state.
At present, the activities on the detector and beam line construction are
complemented with intensive Monte Carlo simulation studies for optimization of
the detector set-up. A focus is made on the efficiency of the measurement of
strange hyperons and hyper-nuclei in Au+Au collisions at the maximal kinetic
energy of 4.5 AGeV. The simulation of Au+Au collisions is performed using the
URQMD and DCH-QGSM models of heavy ion collisions [2]. The products of
collisions are transported through the BM@N setup using the GEANT program
and reconstructed using track reconstruction algorithms for multi-particle events.
Figure 2. Left plot: distribution of primary protons generated in Au+Au collisions
at 4.5AGeV in the phase space of the transverse momentum and rapidity in the
laboratory frame. Right plot: acceptance of the GEM tracker for primary protons
as a function of the particle transverse momentum and rapidity.
Figure 3. Momentum resolution and vertex impact parameter resolution of
charged particles reconstructed in the GEM tracker shown as a function of the
particle momentum.
Figure 2 illustrates the distribution of primary protons generated in Au+Au
collisions at the beam kinetic energy of 4.5AGeV in the phase space of the
transverse momentum and rapidity in the laboratory frame. The acceptance of the
GEM tracker for primary protons for the same phase space is shown on the right
plot. Figure 3 presents the momentum resolution and vertex impact parameter
resolution of charged particles reconstructed in the GEM tracker. The results are
presented for the magnetic field in the center of the magnet of 0.44 T. Figure 4
presents the distributions of the invariant mass of decay products of -hyperon,
Ξ- hyperon and hyper-triton 3HΛ reconstructed with the GEM tracker in central
Au+Au collisions at the beam kinetic energy of 4.5 AGeV. The obtained results
indicate that the proposed set-up has a reasonable reconstruction capability for
strange hyperons produced in high multiplicity central Au+Au collisions. The
reconstructed signals of Ξ- hyperon and hyper-triton 3HΛ correspond to 0.9M and
2M of
central collisions, respectively. Taking into account the signal
reconstruction efficiency, data acquisition capacity (20 kHz of triggered events at
the 1st stage of the BM@N experiment) and the duty factor of the Nuclotron beam
(0.2), the expected statistics of Ξ- hyperons and hyper-tritons 3HΛ for a month of
the BM@N operation are 2.7M and 4M, respectively.
Figure 4. The distributions of the invariant mass of Λ-hyperon, Ξ- hyperon and
hyper-triton 3HΛ reconstructed with the GEM tracker in central Au+Au collisions
at 4.5 AGeV.
The expected statistics is sufficient to perform studies of strange hyperon and
hyper-nuclei production yields and ratios, transverse momentum spectra, rapidity
and angular distributions, as well as fluctuations and correlations of particles as a
function of the collision energy and centrality.
References
1. BM@N Conceptual Design Report.
http://nica.jinr.ru/files/BM@N/BMN_CDR.pdf
2. References to the URQMD and DCM-QGSM models.