In-beam tests of a new ToF wall for the R$^3$B setup

An important part of the RB setup will be the tracking system which allows the identification of mass and atomic number of the incoming beams as well as of the outgoing beam-like fragments and the emitted protons. Also, precise information on the momentum of the detected particles is required. The main design goals of the tracking system are: Measurement of the nuclear charge and mass with a resolution allowing separation of neighboring nuclei up to the Pb region; Total momentum measurement with a relative resolution of∆P/P<2x10−3 (σ); Operation in a high-rate mode (up to 1 MHz) and in a multi-hit mode with large acceptance; Detection efficiency of the combined system should exceed 85 %. These goals will be accomplished by using a series of detectors, see [1], placed before and after the large acceptance dipole magnet GLAD. Silicon detectors for energy-loss and position measurement, thin plasti c scintillator fiber detectors for position measurements, fa t scintillator detectors for timing and energy-loss measure ments (ToF wall), and large-area straw-tube gas detectors for evaporated protons flying at forward angles through the spectrometer into the proton arm. Several prototypes of the tracking detectors have been tested during the S438 experiment in 2014 using stable beams of Ni and Ca at 500 AMeV. Especially valuable was also the SOFIA experiment with FRS settings for Tl and Bi at ∼ 700 AMeV which could be used in a parasitic manner and allowed us to test the detector properties for heavy nuclei. In this report the main results of the Time-of-Flight (ToF) wall will be presented. A prototype of the new ToF wall was positioned about 13 m downstream of the target, behind the large-acceptance dipole magnet ALADIN. The ToF wall is based on a fast plastic scintillator material and the active part will cover an area of 120x80 cm 2 in the final stage. It will consist of 4 planes, each containing 44 vertic al scintillator paddles with a thickness of 5 mm. The scintilla tors are read out by photomultipliers on both far ends. The prototype which was used for the tests was equipped with only 6 paddles per plane. In all experiments we have been able not only to measure incoming beams but also their residues created in reactions of incoming particles at different materials situated in front of the detector prototyp e. Beside the time-of-flight, this detector gives also informa tion on the nuclear charge of the outgoing particles. In [4] we have reported on LED tests of the ToF wall prototype. Here, we will discuss results obtained with heavyion beams in the above-mentioned beam times. ∗Work supported by FAIR@GSI PSP code:1.2.5.1.2.1. Results