The scientific mission of the CBM experiment [https://fair-center.eu/user/experiments/nuclear-matter-physics/cbm.html] is study of the phase diagram of the strongly interacting matter in more energetic collisions of 5 - 15 GeV per nucleon.

The scientific mission of the CBM experiment is study of the phase diagram of the strongly interacting matter (see figure). Such matter can be created in the laboratory by nucleus-nucleus high energy head on collisions. In particular the CBM research program is foreseen to provide answers to the following fundamental questions:

• What is the high-density equation-of-state of nuclear matter, which is relevant for our understanding of supernova, the structure of neutron stars, and the dynamics of neutron star mergers?

• Is there a phase transition from hadronic to quark-gluon matter, a region of phase coexistence, and a critical point? Do exotic phases of strongly interacting matter (QCD matter) like quarkyonic matter exist?

• Can we find experimental evidence for modification of hadron massed in dense and hot nuclear matter?

• How far can we extend the chart of nuclei towards the third (strange) dimension by producing single and double hypernuclei (nuclei with strange quarks inside)? Which role hyperons play in the core of neutron stars?

 

These questions will be addressed by measuring the following observables:

• The equation-of-state can be studied by measuring (i) the collective flow of identified particles, which is generated by the density gradient of the early fireball, and (ii) by multi-strange hyperons, which are preferentially produced in the dense phase of the fireball via sequential collisions.

• The existence of a phase transition from hadronic to partonic matter is expected to be reflected in the following observables: (i) the excitation function of multi-strange hyperons, which are driven into equilibrium at the phase boundary; (ii) the excitation function of the invariant mass spectra of lepton pairs which reflect the fireball temperature, and, hence, may reveal a caloric curve and a first-order phase transition; (iii) the excitation function of higher-order event-by-event fluctuations of conserved quantities such as strangeness, charge, and baryon number may be are expected to occur in the vicinity of the critical point (“critical opalescence”).

• Modifications of hadron properties in dense baryonic matter and the onset of chiral symmetry restoration will affect the invariant-mass spectra of di-leptons, which will be measured both in the electron and the muon channel with unprecedented precision.

• The discovery of new (double-Λ) hyper-nuclei, and the measurement of their life time will provide information on the hyperon-nucleon and hyperon-hyperon interaction, which will shed light on the hyperon puzzle in neutron stars.

An exhaustive review of the physics of hot and dense strongly interacting matter is presented in Ref. [1]. More information about CBM instrumentation and research program can be found in set of articles [2-4].

 

The CBM and HADES detector setups are shown in the figure below. The two setups will be operated alternatively. The CBM setup is a fixed target experiment which will be capable to measure hadrons, electrons and muons in heavy-ion collisions over the full FAIR beam energy range. In a central collision of two gold nuclei at FAIR energies, about 700 charged particles are emitted. The tracks of these particles will be measured by a Silicon Tracking System (STS) consisting of 8 layers of double-sided micro-strip sensors located in a magnetic field of a superconducting dipole magnet. Polish groups participating in the CBM experiment have particularly large contribution to STS. A group of physicist from the Department of Hot Matter Physics takes part in development of the CBM experiment since very beginning. The group will provide very important elements of the STS read-out system as well as contribute design and support of the experimental data base. The project is financed by the Polish Ministry of Science and Higher Education from in-kind contribution to FAIR.

The HADES detector (left) and the CBM experimental setup (right).

 

 

 

 

 

 

 

 

[1] B. Friman et al. "CBM Physics Book", 2011.
[2] C. Hohne at al. “The Compressed Baryonic Matter Experiment at FAIR”, Nuclear Physics News, Vol. 16, No. 1, 2006 .
[3] P. Senger (for the CBM Collaboration), arXiv:2005.03321 [nucl-ex].
[4] Ch. Simon, I. Deppner, and N. Hermann (for the CBM collaboration) "The physics program of the CBM experiment", PoS (CPOD2017) 014.