Beam test of DIRC barrel segment for the PANDA Experiment by mikesanye

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									FAIR-EXPERIMENTS-04                                                                                                 GSI SCIENTIFIC REPORT 2008



                 Beam test of a DIRC-barrel-segment for the PANDA Experiment∗

                R. Hohler1,2 , D. Lehmann1 , K. Peters1,2 , G. Schepers1 , C. Schwarz1 , and C. Sfienti1,3
         1
             GSI, Darmstadt, Germany; 2 Goethe Universit¨ t Frankfurt, Germany; 3 Universit` degli Studi di Catania, Italy
                                                        a                                  a

       For the PANDA detector a DIRC-barrel (Detection of              data are in agreement considering that the position of the
    Internally Reflected Cherenkov photons) for particle iden-          two MCPs had an uncertainty of about 1 cm. Furthermore
    tification is planned around the interaction point [1]. The         for some pixel, especially for the left MCP, the electron-
    R&D process proceeds mainly at GSI. A prototype of a               ics was not fully working during the beam time (two dead
    segment of this Cherenkov counter was tested in a beam             columns). Next, a calibration for the whole setup with
    time in September 2008 at GSI. The proton beam had an              LEDs will be performed. Particularly, the signal-to-noise
    energy of 2.3 GeV.                                                 ratio will be investigated first in laboratory and then realis-
                                                                       tic experimental conditions.
               MCP
                                                                          spatial position [mm] (beta=0.9571)                                      gen.: 39600
                                                                                  100                                                              det.: 11141

                                                                                   80

                                                                                   60

                                                                                   40
                                                   scintillator                    20

                                                                                   0
      box                                                                         -20
     with oil           lens
                                                                                  -40
                                          57°
                          quartz bar                                              -60

                                                proton trajectory                 -80

                                                                             -100
                                                                                -150           -100         -50       0           50        100        150
              Figure 1: Schematic setup of the beam test.

       The setup for the beam time, shown in Figure 1, was in-         Figure 2: Simulation of the expected Cherenkov ring frag-
    stalled in a light-tight box. The proton beam hits the quartz      ments and the position of the two MCPs.
    bar with an angle of 57◦ at which two scintillator paddles
    act as a coincidence trigger. The focussing readout is re-
                                                                                                                                                            Hits
    alized by a lens attached at the bar end followed by a box




                                                                                                                                                                         Hits
    filled with oil to avoid optical image distortions. Two 8                       60
                                                                                                                                                                   103
    × 8 pixel MCP-PMTs (Burle 85011-501) at the rear side
    of the box, which corresponds to a distance bar–detector                       40

    of 23 cm, measure the incoming Cherenkov photons. The                                                                                                          102
                                                                         Y [mm]




    discriminators of each MCP-channel were set to 20 mV. A                        20

    single photon signal is about 50 mV after all amplification
                                                                                   0
    stages. Finally, for the data acquisition the HADES trigger                                                                                                    10
    and readout board (TRBv2) was used [2].
                                                                                  -20
       Figure 2 shows the expected Cherenkov ring fragments
    on the rear side of the box and the position of the MCPs on                                                                                                    1
                                                                                        -80   -60     -40     -20      0     20        40     60       80
    that drawn as rectangulars. For the simulation, a realistic                                                     X [mm]
    beam spot with a 1-σ-radius of 2 cm was assumed. The
    color of the markers corresponds with the wavelength of            Figure 3: Hits on the two MCPs. Color code is in a loga-
    the photons whereas for the ultraviolet range grey is used.        rithmic scale.
       A part of the recorded dataset after multiplicity- and
    time-cuts is shown in Figure 3. Both MCPs show roughly
    an accumulation in the region where it is expected. Due                                                   References
    to the count statistic we can identify these accumulations
    of hits as Cherenkov photons. So the simulation and the            [1] C. Schwarz et al., NIM A 595 (2008) 112, ”The barrel DIRC
                                                                           of the PANDA experiment”
       ∗ Work supported by the European Community RESEARCH INFRAS-
                                                                       [2] M. Traxler et al., Scientific Report 2006, ”A general purpose
    TRUCTURES ACTION under the FP6 program: Structuring the Euro-          Trigger and Readout board (TRB) for HADES and FAIR-
    pean Research Area - Specific Support Action - DESIGN STUDY (con-
                                                                           Experiments”
    tract 515873 - DIRACsecondary-Beams)



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