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@PHDTHESIS{Malygina:218538,
      author       = {Malygina, Hanna},
      othercontributors = {Senger, Peter and Stroth, Joachim},
      title        = {{H}it reconstruction for the {S}ilicon {T}racking {S}ystem
                      of the {CBM} experiment},
      school       = {Johann Wolfgang Goethe-Universität},
      type         = {Dissertation},
      reportid     = {GSI-2019-00457},
      pages        = {155},
      year         = {2018},
      note         = {Dissertation, Johann Wolfgang Goethe-Universität, 2018},
      abstract     = {The mission of the Compressed Baryonic Matter (CBM)
                      experiment is to investigate the phase diagram of strongly
                      interacting matter in the region of high net-baryon
                      densities and moderate temperatures. According to various
                      transport models, matter densities of more than 5 times
                      saturation density can be reached in collisions between gold
                      nuclei at beam energies between 5 and 11 GeV per nucleon,
                      which will be available at FAIR. The core detector of the
                      CBM experiment is the Silicon Tracking System (STS), which
                      is used to measure the tracks of up to 700 particles per
                      collision with high efficiency $(>95\%)$ and good momentum
                      resolution $(<1.5\%).$ The technological and experimental
                      challenge is to realize a detector system with very low
                      material budget, in order to reduce multiple scattering of
                      the particles, and a free-streaming data readout chain, in
                      order to achieve reaction rates up to 10 MHz together with
                      an online event reconstruction and selection. The STS
                      comprises 8 tracking stations positioned between 30 cm and
                      100 cm downstream the target inside a magnetic field,
                      covering polar emission angles up to 25 degrees. A station
                      consists of vertical structures with increasing number
                      (between 8 and 16, depending on station number), each
                      structure carrying between 2 and 10 double-sided microstrip
                      silicon sensors, which are connected through low-mass
                      microcables to the readout electronics placed at the
                      detector periphery outside the active detector area. The
                      work presented in this thesis focuses on the detector
                      performance simulation and local hit pattern reconstruction
                      in the STS. For efficient detector design and reconstruction
                      performance, a reliable detector response model is of utmost
                      importance. Within this work, a realistic detector response
                      model was designed and implemented in the CBM software
                      framework. The model includes non-uniform energy loss of an
                      incident particle within a sensor, electric field of a
                      planar p-n junction, Lorentz shift of the charge carriers,
                      their diffusion, and the influence of parasitic
                      capacitances. The developed model has been verified with
                      experimental data from detector tests in a relativistic
                      proton beam. Cluster size distributions at different beam
                      incident angles are sensitive to charge sharing effects and
                      were chosen as an observable for the verification. Taking
                      into account parasitic capacitances further improves the
                      agreement with measured data. Using the developed detector
                      response model, the cluster position finding algorithm was
                      improved. For two-strip clusters, a new, unbiased algorithm
                      has been developed, which gives smaller residuals than the
                      Centre-Of-Gravity algorithm. For larger clusters, the
                      head-tail algorithm is used as the default one. For an
                      estimate of the track parameters, the Kalman Filter based
                      track fit requires not only hit positions but their
                      uncertainties as an input. A new analytic method to estimate
                      the hit position errors has been designed in this work. It
                      requires as input neither measured spatial resolution nor
                      information about an incident particle track. The method
                      includes all the sources of uncertainties independently,
                      namely: the cluster position finding algorithm itself, the
                      non-uniform energy loss of incident particles, the
                      electronics noise, and the discretisation of charge in the
                      readout chip. The verification with simulations shows
                      improvements in hit and track pull distributions as well as
                      x²-distributions in comparison to the previous simple
                      approach. The analytic method improves the track parameters
                      reconstruction by $5-10\%.$ Several STS module prototypes
                      have been tested in a relativistic proton beam. A signal
                      to-noise ratio was obtained at the level of 10-15 for
                      modules made of 30 cm long microcable and of either one or
                      two 6.2 x 6.2 cm² CiS sensors. First simulations have shown
                      that this signal-to-noise ratio is sufficient to reach the
                      required efficiency and momentum resolution. The
                      high-radiation environment of CBM operation will deteriorate
                      the sensor performance. Radiation hardness of sensors has
                      been studied in the beam with sensors irradiated to 2 x
                      10[hoch 14] 1MeV [neq/cm²], twice the lifetime dose
                      expected for CBM operation. Charge collection efficiency
                      drops by $17-25\%,$ and simultaneously noise levels increase
                      1.5-1.75 times. The simulations show that if all sensors in
                      the STS setup are exposed to such a fluence uniformly, the
                      track reconstruction efficiency drops from $95.5\%$ to
                      $93.2\%$ and the momentum resolution degrades from $1.6\%$
                      to $1.7\%.$},
      cin          = {CBM / CBM@FAIR},
      cid          = {I:(DE-Ds200)CBM-20080821OR102 / I:(DE-Ds200)Coll-FAIR-CBM},
      pnm          = {612 - Cosmic Matter in the Laboratory (POF3-612) /
                      SUC-GSI-Frankfurt - Strategic university cooperation GSI-U
                      Frankfurt/M (SUC-GSI-FR) / HGS-HIRe - HGS-HIRe for FAIR
                      (HGS-HIRe)},
      pid          = {G:(DE-HGF)POF3-612 / G:(DE-Ds200)SUC-GSI-FR /
                      G:(DE-Ds200)HGS-HIRe},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:hebis:30:3-464018},
      url          = {https://repository.gsi.de/record/218538},
}