The Group Activities

December 2006

During the first months of its existence the group (composed of one post-doctorate and three PhD students, in addition to the group leader, Dr. Erika Garutti) has taken an active role in the commissioning and test of a hadronic calorimeter prototype for the ILC. For this prototype innovative silicon-based photo-detectors (Silicon-Photomultiplier) have been used. The photo-detectors are produced and characterized in Moscow, Russia as a combined effort of the company Pulsar and the physics institutes MEPHI and ITEP.

The calorimeter prototype equipped with more than 5000 Silicon-Photomultiplier has been tested this summer at the CERN SPS test beam, as a collaborative effort of an international collaboration with 39 institutes in 12 countries and more than 150 participants.
The operation of the detector, mainly driven by the photo-detectors, has proved to fulfill expectations and the analysis of the physics data collected is at present in full swing.

As a project for the coming year the DESY group in collaboration with the Shinshu group has decided to further the application of Silicon-Photomultiplier in calorimetry taking advantage of a new Hamamatsu product available on the market since Nov '06.
Hamamatsu (Japan), one of the world largest producer of photo-detectors, has recently developed a new blue-sensitive version of Silicon-Photomultiplier better suited to applications.
Five pieces have been already characterized by the group at DESY, 20 more pieces have been studied at the Shinshu university, all the results indicate very good performances and high stability of the photo-detectors.

The next aim of the group is to substitute 6 out of 38 active layers of the existing hadronic calorimeter prototype with layers read out via the new Hamamatsu Silicon-Photomultiplier.
This is the minimum amount of channels to provide a meaningful physics comparison of the two technologies on the basis of hadronic shower reconstruction. In order to make a serious impact in the field and to support the Japanese partner of the young investigator group I would like to ask for financing half of the purchase of the new photo-detectors, amounting to a total of 650 pieces (1300 being the total number needed to equip 6 active detector layers). This purchase exceeds the possibility of the young investigator grant, though being vital to its objective.

December 2007

During year 2007 a new PhD student has joined the group from the university partner Heidelberg, A. Kaplan (supervised by Prof. H.-C. Schultz-Coulon) and two of the PhD students have concluded their doctoral work. In October the postdoctoral fellow Dr. M. G\"ottlich has joined the group.

Main commitments of the group:

- The CALICE collaboration
After the commissioning run in 2006, the fully equipped calorimeter prototype has been tested this summer at the CERN SPS test beam.
The operation of the detector, mainly driven by the photo-detectors, has proved to fulfill expectations. The analysis of the physics data 2006 has been presented at conferences and reported in internal CALICE
notes. The analysis of 2007 data has posed severe challanges to the software, not only for the larger number of channels to handle, but
also for the increased volume of data to be processed. A test beam at Fermilab, Chicago, is currently in preparation for the year 2008.

- The PET experiment
During 2007 the group has intensified the laboratory activities of tests of new photo-detectors and their application to new
fields. The main challenges posed by the design of future Positron Emission Tomography machines are the improvement of the spatial and timing
resolution and the combined operation with magnetic resonance. The Micro Pixel Photon Counter by Hamamatsu is a good candidate for this
application. Its small size (down to 1\times 1~mm2) and the high photo-detection efficiency in the blue spectral region allow the
direct readout of a highly segmented scintillator matrix improving the spatial resolution of the machine.
The group has tested the energy resolution at the 511 keV and the time response of a basic, but innovative, PET system made
of two LSO crystals coupled to two MPPC photo-detectors.

- The ALPS experiment
The group is also involved in the ALPS (Axion-Like Particle Search) experiment, a joint-venture of DESY, Laserzentrum Hannover e.V. and Hamburger Sternwarte. Scope of the experiment is detection of laser photons penetrating an optical barrier with very high sensitivity. Observation of these kind of signals can only be explained by so far undiscovered light particles, which emerge in beyond-standard-model theories. The sensitivity achievable depends on a combination of the laser power, the measurement time, and the quality of the photon detector. ALPS has been approved and commissioned in 2007 and continues to take data.

December 2008

- Commissioning of the hadronic calorimeter prototype
The year 2008 has seen the installation of the AHCAL calorimeter prototype at Fermilab, Chicago, for the start of a new campaign of test beam at the Meson Test Beam Facility (MTBF). After a successful commissioning time in April the entire CALICE experiment was operational and the collaboration has taken data for three beam periods of approximately one month each. The members of the group have played a key role in the installation, commissioning and running of the experiment.
In the third period the Silicon-Tungsten based electromagnetic calorimeter has been replaced by a Scintillator-Tungsten based one provided by the Japanese group members of the collaboration. Our group has supported the installation and provided expertise for the integration of the new detector.
E. Garutti has taken an active role in support of the run coordination as in the previous years. N. Meyer was appointed software coordinator of the CALICE collaboration and has supervised the software aspects of installation and operation.
A. Kaplan and N. Feege have acted as AHCAL experts on-call during the test beam periods. All group members have taken shifts in Fermilab and in the remote control room at DESY.

- Remote control room for ILC test experiments
Thanks to the HGF Sonderf\"orderung SO-NG-064 the group has made a significant contribution to the realization of a remote control room, located at DESY, for the control of the ILC test beam activities around the world. The new control room has been equipped and was functional by the start of the Fermilab campaign. A fraction of the shifts have been taken remotely from DESY.
  The control room ensures the capability to run the experiment remotely with the help of highly sophisticated tools like high-resolution steerable cameras and a web-accessible oscilloscope. The easy exchange of information with the local crew in Fermilab is ensured by a high quality audio conferencing system, which acts as an open window between the two control rooms.
This project had a very positive impact on the work of the collaboration, and most general on the ILC R\&D projects.
An interesting press article on this project can be found at:
http://www.linearcollider.org/newsline/readmore\_20080605\_atw.html

- Software development and analysis of CALICE data
The group is active in the development of software tools for the calibration and in the analysis of the test beam data collected with the AHCAL prototype.
N. Meyer has accepted the role of software coordinator for the CALICE collaboration and is driving the software development effort. The whole group is involved in data analysis. The following topics are covered by group members:
muon calibration and muon physics in the AHCAL, temperature correction of the detector response, electromagnetic shower studies, validation of MC models for hadronic showers.
Three diploma students working within the group have finalized their theses work on analysis of CALICE data during 2008.

- Research and study of new photo-detectors
A new set-up has been established for the precise characterization of SiPM devices at Heidelberg. The set-up allows measurements of dark-rate, of gain and most important of photo-detection efficiency. A high precision movable support and a highly collimated beam of monochromatatized light allow the scan of each pixel in a SiPM with micrometer resolution. This offers a sharp view on the detector geometry as well as the possibility to investigate surface defects.
New photo-detectors both from Hamamatsu and from SenseL have been tested in this set-up, as well as the SiPM from MEPHI/Pulsar used already in the CALICE calorimeter prototype.

- The PET experiment
In the DESY laboratory set-up for PET tests of the readout of inorganic scintillators crystals via the new silicon photo-detector produced by Hamamatsu (MPPC) have been performed.
It has been demonstrated that MPPC devices are very suitable for this type of application. The good energy resolution (12\% FWHM) allows to distinguish between Compton and photo-electric events, allowing to reject scattered events with high efficiency as it is necessary for PET application.
The achieved time resolution of 460 ps FWHM is important to reduce the number of random coincidences and to use time-of-flight information to considerably improve the signal to background ratio of the reconstructed images.
The very good performance of the gamma-detectors motivated the next step toward building a gamma camera consisting of a matrix of MPPC devices and scintillator crystals. The construction and test of the gamma camera is planned for the year 2009.
With funds from the HGF Sonderf\"orderung SO-NG-064 100 LFS crystals have been bought and tested. The homogeneity of the crystal production is satisfactory.
The first studies on the properties of the ASIC chip which could be used for the multi-channel readout of the camera are ongoing. The Heidelberg group has proposed to develop an ad-hoc designed chip for PET application. The Heidelberg group is also contributing with engineering support, providing the mechanical structure and the motor-driven rotation system for the camera.
The photo-detector needed for the matrix readout have been ordered and are also financed through the Sonderf\"orderung SO-NG-064.
Simulation studies are ongoing at DESY to fix the main parameters of the camera and determine the expected spatial resolution.