Comparison of Two Highly Granular Hadronic Calorimeter Concepts

The CALICE collaboration develops hadron calorimeter technologies with high granularity for future electron-positron linear colliders. These technologies differ in active material, granu- larity and their readout and thus their energy reconstruction schemes. The Analogue Hadron Calorimeter (AHCAL), based on scintillator tiles with Silicon Photomultiplier readout, mea- sures the signal amplitude of the energy deposition in the cells of at most 3 × 3 cm$^2$ size. The Digital, Resistive Plate Chamber (RPC) based, HCAL (DHCAL) detects hits above a certain threshold by firing pad sensors of 1 × 1 cm$^2$. A 2 bit readout is provided by the, also RPC based, Semi-Digital HCAL (SDHCAL), which counts hits above three different thresholds per 1×1cm$^2$ pad. All three calorimeter concepts have been realised in 1m$^3$ prototypes with in- terleaved steel absorber and tested at various test beams.The differences in active medium, granularity and readout have different impacts on the energy resolution and need to be studied independently.This analysis concentrates on the comparison between these technologies by investigating the impact of the different energy reconstruction schemes on the energy resolution of the AHCAL testbeam data and simulation. Additionally, a so-called software compensation algorithm is developed to weight hits dependent on their energy content and correct for the difference in the response to the electromagnetic and hadronic sub-showers (e/h $\neq$ 1) and thus reduce the influence of fluctuations in the π$^0$ generation. The comparison of the energy resolutions re- vealed that it is mandatory for the AHCAL with 3×3cm$^2$ cell size to have analogue signal readout, to apply the software compensation algorithm and thus achieve the best possible en- ergy resolution.The effect of the granularity is studied with a simulation of the AHCAL with 1×1cm$^2$ cell size, and it has been found that to achieve the best possible energy resolution the semi-digital energy reconstruction is sufficient.To study the impact of the active medium, the DHCAL testbeam data was calibrated and the simulation was tuned using the muon and positron data. The energy resolutions, achieved by the DHCAL data and simulation and achieved by the 1 × 1 cm$^2$ AHCAL simulation using the digital energy reconstruction, are successfully used to investigate the influence of the active medium. Finally, the energy resolutions of the data and simulations of the AHCAL, DHCAL and SD- HCAL are compared and the influences discussed.