The compressed baryonic matter (CBM) experiment will be one of the major scientific activities at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. The goal of the CBM research program is to explore the QCD phase diagram in the region of high-baryon densities using highenergy nucleus-nucleus collisions. This includes the study of the equation-ofstate of nuclear matter at high densities, and the search for the deconfinement and chiral phase transitions. The CBM detector is designed to measure both bulk observables with large acceptance and rare diagnostic probes such as charmed particles and vector mesons decaying into lepton pairs. The layout and the physics performance of the proposed CBM experimental facility will be discussed.
The energy-sensitive detection of heavy ions with calorimetric low temperature detectors was investigated in the energy range of E=0.1-1 MeV/amu, commonly used for accelerator mass spectrometry (AMS). The detectors used consist of sapphire absorbers and superconducting aluminum transition edge thermometers operated at T approximately 1.5 K. They were irradiated with various ion beams (13C, 197Au, 238U) provided by the VERA tandem accelerator in Vienna, Austria. The relative energy resolution obtained was DeltaE/E=(5-9) x 10(-3), even for the heaviest ions such as 238U. In addition, no evidence for a pulse height defect was observed. This performance allowed for the first time to apply a calorimetric low temperature detector in an AMS experiment. The aim was to precisely determine the isotope ratio of 236U/238U for several samples of natural uranium, 236U being known as a sensitive monitor for neutron fluxes. Replacing a conventionally used detection system at VERA by the calorimetric detector enabled to substantially reduce background from neighboring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of 236U/238U=6.1 x 10(-12) could be obtained, representing the smallest 236U/238U ratio measured at the time. In addition, we contributed to establishing an improved material standard of 236U/238U, which can be used as a reference for future AMS measurements.
The planned Compressed Baryonic Matter (CBM) experiment at the upcoming FAIR center at GSI, Darmstadt is aiming at the investigation of baryonic matter at high density produced in relativistic heavy-ion collisions. The research program comprises the exploration of the QCD phase diagram at high net baryon densities and moderate temperatures, the search for the de-confinement phase transition, and in-medium modifications of hadrons. The proposed key observables include the measurement of charmonia and low mass vector mesons which can be measured via their decay into the dilepton channel. In this paper, we discuss the physics motivation, detector concepts, and feasibility studies of the di-muon measurements.
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