Reducing the occupancies in the calorimeter endcaps of the CLIC detector Suzanne van Dam Supervisor: André Sailer CERN, 6 March 2014

Introduction Beam-beam interactions Background incoherent pairs Scatter in forward region of CLIC detector High occupancy in HCal Suzanne van Dam, 6 March CERN-THESIS

Occupancy reduction Suzanne van Dam, 6 March The high occupancy has to be reduced Support tube can provide shielding Optimize support tube material and thickness

Suzanne van Dam, 6 March Simulation of occupancy Simulate background for each geometry Estimate the occupancy – Need data from a few bunch trains (312 BX/train) Find number of particles passing through support tube – Correlated to occupancy – Need data from ~10 BXs Geometrical adaptations to the detector model: – Introduce a scoring plane around support tube – Make support tube geometry variable

Simulation of occupancy Simulate background for each geometry Estimate the occupancy – Need data from a few bunch trains (312 BX/train) Find number of particles passing through support tube – Correlated to occupancy – Need data from ~10 BXs Geometrical adaptations to the detector model: – Introduced a scoring plane around support tube – Made support tube geometry variable through text file Suzanne van Dam, 6 March 20145

Contributions to occupancy Occupancy per particle type: – Photons and neutrons contribute Compare to number of hits from different particles in the scoring plane: – Photons have a relatively large impact Reflect this in the relation between hits in the scoring plane and the occupancy Suzanne van Dam, 6 March Energy deposits in HCal endcap Hits in scoring plane

Figure of merit To minimize the occupancy, minimize neutron (n) and photon ( γ ) hits ( H ) with a relative weight ( w ) Assume linear dependence on each particle type This can be expressed in a figure of merit ( FOM ): Weights follow from the ratio of: – Number of energy deposits above threshold and within timing cut in the HCal endcap ( N ); – Number of hits in the scoring plane ( H ). Suzanne van Dam, 6 March 20147

Energy Energy spectrum for hits in the scoring plane HCal endcap threshold is 300 keV Suzanne van Dam, 6 March 20148

Support tube material Iron Suzanne van Dam, 6 March photons neutrons

Iron based: – Iron – Stainless steel – Cast iron – Borated steel Suzanne van Dam, 6 March Support tube material photons neutrons

Iron based: – Iron – Stainless steel – Cast iron – Borated steel Neutron moderating and absorbing: – Pure polyethylene (PE) – PE + Li2CO3 – PE + H3BO3 Suzanne van Dam, 6 March Support tube material photons neutrons

Suzanne van Dam, 6 March Support tube material Iron based: – Iron – Stainless steel – Cast iron – Borated steel Neutron moderating and absorbing: – Pure polyethylene (PE) – PE + Li2CO3 – PE + H3BO3 Short radiation length: – Tungsten – Lead photons neutrons

Combine materials Polyethylene for neutron shielding Iron-based materials for photon shielding Tungsten for further photon shielding To shield both photons and neutrons, materials should be combined. Suzanne van Dam, 6 March

Combine materials Polyethylene & stainless steel Suzanne van Dam, 6 March Total thickness of support tube 100 mm

Combine materials Polyethylene & stainless steel Tungsten & stainless steel Suzanne van Dam, 6 March Total thickness of support tube 100 mm

Summary and conclusions The high occupancy due to incoherent pairs in the HCal Endcap is caused by neutrons and photons Photons have relatively more impact on the occupancy Minimization of the occupancy is based on minimizing the number of particles passing the support tube Therefore a figure of merit is defined that reflects the higher impact of photons: Simulations show that – Tungsten is suitable for photon shielding – Polyethylene is suitable for neutron shielding – To shield both neutrons and photons materials should be combined – A high contribution from photon shielding materials is needed Suzanne van Dam, 6 March

Outlook Maximize shielding by reducing inner radius of support tube Use as much tungsten as structural strength allows For neutron shielding add polyethylene to a structure of tungsten and stainless steel Suzanne van Dam, 6 March