"R&D for the TESLA-Detector: Instrumentation of the very forward region "

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The goal of the R&D project is the development of calorimeter technologies to instrument the very forward region of the ILC detector. In the current design two calorimeters are planned, BeamCal adjacent to the beam pipe, covers polar angles between 5 and 28 mrad, and LumiCal covers the polar angle range from 28 to about 90 mrad. These calorimeters will have several functions. Both of them improve the hermeticity of the detector, a feature important for new particle searches, and they shield the central detectors from backscattered particles [1].

LumiCal is the luminometer of the detector. From the physics program an accuracy of the luminosity measurement of better that 10-3 is required. Small angle Bhabha scattering will be used for this measurement. Design studies are ongoing to optimise the structure of a silicon-tungsten calorimeter to reach the accuracy. For a small beam crossing angle the design is advanced [2]. We started to develop a design for 20 mrad beam crossing angle. Sensor tests, the mechanics design and the design of the readout electronics will be the next steps.

BeamCal is hit by a large number of low energy electrons and positrons originating from beamstrahlung, adding up to several 10 TeV per bunch crossing and about 10 MGy per year of operation. Hence radiation hard sensors are needed. Simulations of a highly compact and fine segmented diamond-tungsten calorimeter have shown that single high energy electrons can be detected even in areas with high depositions from beamstrahlung remnants with high efficiency.

The distribution of beamstrahlung depositions depends strongly on the beam parameters. We have shown that the analysis of these depositions allows determining beam parameters with very good accuracy. Beam diagnostics can be supported by the measurement of the tails of the beamstrahlung photons using a third downstream calorimeter at very low angles, called PhotoCal. PhotoCal is a multilayer heavy gas ionisation chamber. Test beam studies with single electron showers are promising. A more detailed design is under work. A concept for a fast luminosity optimisation feedback system will be the next step.

Large area diamond sensors from several manufacturers are investigated. Measurements are done on the dependence of the response to ionising particles from several operation parameters. The linearity of the response is tested using bunches containing between 10+3 and 10+6 particles within 10 ns. These studies are ongoing. The study of the performance as a function of the absorbed dose is done for low doses and will be continued to doses expected at the ILC.

These calorimeters are necessary for each detector concept. The R&D is independent on the concept.

A collaboration, FCAL, is formed to unify and structure the efforts in the participating laboratories. The results from design studies and possible technologies are published in IEEE transactions of nuclear science [3]. More recent results concern the requirements on the mechanical accuracy of LumiCal, the impact of the BeamCal performance on searches for supersymmetric particles, and testbeam measurements with diamond sensors. In a timescale of 2-3 years we will test sensor layer and readout electronics prototypes. In case the results are promising we will go to calorimeter prototype construction and test. Critical items are:

• The stability, homogeneity, linearity and dose dependence of the response of diamond sensors

• Integrated readout electronics (dynamic range >1000, 12 bit, data capture within 150 ns, fast buffer, sparsification, low material budget)

• Thin sensor planes with integrated bias supply and signal transmission

• The control of the mechanical frame of the LumiCal

• Homogeneity and stability of silicon sensors used in the LumiCal, and their radiation hardness if used in the BeamCal

The support of the project in all laboratories was not sufficient so far, however, it is growing. We hope that the EUDET framework will give a boost to our effort to improve the support by the laboratories.

[1] W. Lohmann, Instrumentation of the Very Forward Region of a Linear Collider Detector, Proc. of the Snowmass Workshop, (2005).

[2] H. Abramowicz, Luminosity Detector for the ILC, Proc. of the Snowmass Workshop, (2005).

[3] H. Abramowicz et al.,Instrumentation of the Very Forward Region of a Linear Collider Detector, IEEE Transactions on Nuclear Science, 51, 2983 (2004).

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Topic revision: 11 Jan 2006, WolfgangLohmann

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