The CALICE collaboration has constructed highly granular sampling calorimeter prototypes that were tested in test beams at DESY, CERN and FNAL. The CALICE setup consisted of a silicon-tungsten ECAL (since mid-2008: a scintillator-tungsten ECAL), a scintillator-steel HCAL with analog readout with silicon photomultipliers (SiPMs) and a tail catcher/muon tracker (TCMT) with scintillator strips read out by SiPMs. Beam tests of a digital hadron calorimeter using RPCs are coming up at FNAL, and preparations for a test of an HCAL using Tungsten absorbers to allow a more compact detector suitable for a multi-TeV collider at CERN are under way.

The goal of the test beam program is to identify the most promising calorimeter technologies for future collider detectors which base their event reconstruction on the particle flow concept.

The CALICE setup at Fermilab, with the SiW ECAL (black front face), the HCAL (grey structure) and the TCMT (orange support frame).

Within CALICE, the junior research group focuses on the analog hadron calorimeter. The physics prototype currently in operation is a 1 m3 steel/scintillator sampling calorimeter with a total of 38 active layers with a lateral size of 90 x 90 cm2 sandwiched between 2 cm thick absorber plates. The active layers consist of small scintillator tiles with a size of 3 x 3 cm2 in the center of the detector, and large tiles (6 x 6 cm2 and 12 x 12 cm2) in the outer regions of the detector. For more detail on the detector, see the reference list at the bottom of the page, or the DESY CALICE HCAL webpage.

Within this project, we work on the analysis of the test beam data and participate in the data taking at Fermilab. The group produces the detector simulations for all CALICE detectors and contributes to the study of these simulated events and their comparison to real data. We also study silicon photomultipliers in detail, investigate the direct coupling of SiPMs to scintillator tiles without the use of wavelength shifting fibers, and work together with the Semiconductor Laboratory of the Max-Planck-Society to evaluate novel SiPM prototypes. Further details on these activities are given below.

Our group covers a broad range of analysis topics, focusing on the analog HCAL but also extending to the complete CALICE setup. New ideas are also always welcome. Current topics include:

Energy resolution for single hadrons: Improvement of the resolution with weighting techniques, development of software compensation procedures. Transfer the results from the detector prototypes to the PandoraPFA particle flow algorithm, study this in full detector simulations.

Identification of track segments within hadronic showers, detector calibration studies using these track segments, and detailed comparisons with simulation.

For the next generation of detectors, we study the properties of silicon photomultipliers and investigate the coupling of these devices to small scintillator cells.

Coupling of SiPMs to Scintillator Tiles

Since the latest generation of SiPMs are blue sensitive, they cover the spectral range of the scintillation light of plastic scintillators. It is thus possible to couple the SiPM directly to the scintillator tile, without using a wavelength shifting fiber embedded in the scintillator material. However, the fiber also serves as means of collecting the light, and improves the uniformity of the response across the tile surface.

We investigate different tile geometries, different coupling positions and various surface treatments to improve the uniformity of the signal across the scintillator cell without the use of a fiber embedded in the plastic. We are also studying the effects of non-uniformities on the calorimeter performance in simulations performed with GEANT4.

Study of Silicon Photomultipliers

We use a setup with a highly focused, short-pulsed infrared laser to investigate the properties of silicon photomultipliers in detail. The optical setup contains a lens system that can focus the laser spot to a size of less than 2 µm on the SiPM surface. With a three dimensional moving stage with micrometer precision the laser can be scanned across the surface of the device, enabling us to study single pixels of the SiPMs in detail. The signals of the SiPM are recorded with a fast-sampling oscilloscope and then analyzed by computer.

This setup is used to investigate for example:

- relative efficiency as a function of position on the device surface

- pixel to pixel cross talk, as a function of the starting point - of the avalanche process within a pixel

- afterpulsing

Test setup for silicon photomultipliers. The device under study is placed under the lens which focuses the laser on the SiPM surface. The SiPM can be moved in three dimensions with micron precision.

Selected Publications for further Information

Setup for detailed studies of the response of scintillator tiles: A 90Sr source, emitting electrons with an energy of up to
2.2 MeV, is scanned across the the scintillator. A trigger scintillator underneath the tile ensures that only fully penetrating electrons are studied. The response of the scintillator read out with a SiPM is monitored as a function of the source position.

Cell-by-Cell calibration of the analog HCAL proposed for the ILD detector concept (a detector concept for the future ILC) using identified minimum-ionizing track segments in hadronic events. This study is based entirely on simulated data.

More details on these analyses can be found in publications listed below.

The power of highly granular calorimeters: Detailed image of a hadronic shower in the CALICE HCAL, with tracks of the primary and of secondary particles identified in the detector.

The CALICE Detectors:

Software Compensation, Track Finding in Hadronic Showes and Calibration
(Studies done in the Munich CALICE Group):

Hardware Development (performed by the Munich CALICE Group):

F. Simon [CALICE Collaboration], Energy Reconstruction of Hadron Showers in the CALICE Calorimeters,
arXiv:0911.4575 [physics.ins-det]

F. Simon [CALICE Collaboration], Track Segments in Hadronic Showers: Calibration Possibilities for a Highly Granular HCAL, arXiv:0902.1879 [physics.ins-det]

F. Simon [CALICE Collaboration], Calibration of a Highly Granular Hadronic Calorimeter with SiPM Readout,
arXiv:0811.2431 [physics.ins-det]

F. Simon and C. Soldner, Uniformity Studies of Scintillator Tiles directly coupled to SiPMs for Imaging Calorimetry,
arXiv:1001.4665 [physics.ins-det].

M. Anduze et al.[CALICE Collaboration], Design and Electronics Commissioning of the Physics Prototype of a Si-W Electromagnetic Calorimeter for the International Linear Collider, JINST 3, P08001 (2008).

G. Eigen  [Calice Collaboration], The CALICE scintillator HCAL testbeam prototype, AIP Conf. Proc. 867, 565 (2006).

A. Dyshkant  [CALICE Collaboration], Tail Catcher Muon Tracker for the CALICE test beam, AIP Conf. Proc. 867, 592 (2006).