1. 1 A Digitizer for Monolithic Active Pixel Sensors Christina Dritsa 1,2,3, Michael Deveaux 3 1 IPHC, Strasbourg, France 2 GSI, Darmstadt, Germany 2 GSI, Darmstadt, Germany 3 IKF, Goethe University Frankfurt/Main, Germany XLVIII International meeting in nuclear physics Bormio, 25-29 January 2010

2. 2 The Compressed Baryonic Matter Experiment Exploration of the QCD phase diagram at highest net baryon densities Experimental focus: rare diagnostic probes (i.e. open charm) Experimental focus: rare diagnostic probes (i.e. open charm) Needs: Vertex detector with sec. vtx resolution of 50µm Needs: Vertex detector with sec. vtx resolution of 50µm Uses Monolithic Active Pixel Sensors: Single point resolution: ~ 1µm Material budget: 0.05% X 0 MVD STS RICH TRD TOF ECAL S. Belogurov et al. Artistic view of the MVD The Micro-Vertex Detector Occupancy: Up to 40 tracks/mm²

3. 3 The simulation challenge MAPS are non-depleted Signal charge is collected via thermal diffusion. Conventional simulation models fail => wrong model assumptions Input for the simulation: 0°15°30° 45°60° 80° Beam test at CERN-SPS, 120 GeV/c pions Beam test at CERN-SPS, 120 GeV/c pions MAPS sensor MIMOSA 17 ( pitch of 30 µm ) MAPS sensor MIMOSA 17 ( pitch of 30 µm ) Different incident angles (0 o - 80 o ) Different incident angles (0 o - 80 o )

4. 4 Cluster Profile E Energy from measured Landau Energy from measured Landau Shape from measured Lorentz Shape from measured Lorentz Digitizer Summary and Conclusion: A digitizer for MAPS is available Cluster multiplicity and charge distributions reproduce reality with 10% accuracy.