GEM Module Design for the ILD TPC. Astrid Münnich

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1 GEM Module Design for the ILD TPC Astrid Münnich RD-51 collaboration meeting Zaragoza, Spain July 2013 Astrid Münnich (DESY) GEM Module Design for the ILD TPC 1

2 Overview A TPC for ILD Simulations GEM Module Design Measurement Setup Field Distortions Point Resolution Astrid Münnich (DESY) GEM Module Design for the ILD TPC 2

3 A TPC for ILD Requirements: Momentum resolution σ(1/p t) = /GeV for Higgs mass measurement (TPC alone 10 4 /GeV) Tracking efficiency close to 100% down to low momentum to fulfill Particle Flow Algorithm (PFA) requirements. Minimum material in front of the highly segmented calorimeter Solution: TPC 200 continuous position measurements along each track Single point resolution of σ rφ < 100 µm Lever arm of around 1.2 m in the magnetic field of T Astrid Münnich (DESY) GEM Module Design for the ILD TPC 3

4 The Large Prototype The Large Prototype has been built to compare different detector readouts under identical conditions and to address integration issues LP field cage parameters: L = 61 cm D = 72 cm up to 25 kv E drift 350 V/cm Made of composite materials 1.24 % X 0 Modular endplate Space for 7 modules Area cm 2 Astrid Münnich (DESY) GEM Module Design for the ILD TPC 4

5 Simulation: GEM Module Previous measurements showed field distortions at the border of the module. Simulation study to understand the observed behavior and optimize module design: Use finite element based software to simulate electrostatic fields (CST TM ) Use Garfield++ to drift electrons in that field and add constant B-field Astrid Münnich (DESY) GEM Module Design for the ILD TPC 5

6 Simulation: Field Distortions Module without modification With field shaping wire Study distortion of electron path: Start 200 electrons from start points which have a distance of 0.1mm and have the same distance to the module With 50 start positions you can cover the first 6 rows (first start point is 0.6 cm in front of the 1st row) Pad height: hpad = cm (corresponds to the row height) Astrid Münnich (DESY) GEM Module Design for the ILD TPC 6

7 Field Distortions: Electron Position B=0T Unmodified module B=1T Distortion [μm] Distortion [μm] Number of electrons Distance to first row [cm] Distance to first row [cm] Module with field shaping wire Distortion [μm] Distortion [mum] [μm] Number of electrons Distance to first row [cm] Distance to first row [cm] Astrid Münnich (DESY) GEM Module Design for the ILD TPC 7

8 Field Distortions: Comparison Charge collection eff. [%] Modified module - simulation Modified module - experiment Unmodified module - simulation Unmodified module - experiment row Good qualitative agreement: Improvement of charge collection of 30% both in simulation and mesasurement Absolute values different, both for charge efficiency and size of distortions, due to the simplifications in the simulation Astrid Münnich (DESY) GEM Module Design for the ILD TPC 8

9 Module Development: DESY GEM Module Goals: Minimal dead space Minimal material budget Smooth and even surface of GEM Stable HV operation Solution: Divide anode side of GEM into 4 sectors HV stability No division on cathode side better field homogeneity Thin ceramic mounting grid good flatness of GEM Triple GEM stack Fully sensitive readout board 4829 pads ( mm2 ) Field shaping wire Astrid Mu nnich (DESY) GEM Module Design for the ILD TPC 9

10 DESY Testbeam Measurements Magnetic field of 0 or 1 T, electron beam up to 6 GeV 3 modules, half equipped 7200 channels ALTRO readout electronics Lever arm of 50 cm along the beam Astrid Mu nnich (DESY) GEM Module Design for the ILD TPC 10

11 Measurement: Module Boundaries Field distortion are observed at the boundaries of the modules. This leads to charge loss on the outer rows and bending of the drift path of the electrons due to E B effects. Astrid Münnich (DESY) GEM Module Design for the ILD TPC 11

12 Measurement: Hit Efficiency Hit efficiency proves to be close to >95% Dips are due to dead channels Independent on drift distance or guard ring potential Retrieved up to 30 % compared to measurements without a guard ring Astrid Münnich (DESY) GEM Module Design for the ILD TPC 12

13 Measurement: Charge Efficiency Charge Efficiency still reduced at the border of the modules Reduced electron collection efficiency or gas gain No charge calibration of the electronic channels possible Substructure may hint towards GEM uniformities (needs electronics calibration first) Astrid Münnich (DESY) GEM Module Design for the ILD TPC 13

14 Measurement: Resolution Preliminary result with simple track fit Not cuts, all points used Correction of field distortion is important Astrid Münnich (DESY) GEM Module Design for the ILD TPC 14

15 Summary & Outlook Summary Successful test beam campaign Lots of data to analyze Constantly improving reconstruction Understand distortions better, study systematic effects from reconstruction and tracking Work ongoing on calibration and correction procedures Outlook Next goal: Momentum resolution Needs external reference (between magnet and TPC) Momentum distribution dominated by beam spread and energy loss in magnet Entries GeV 2 GeV 3 GeV 4 GeV 5 GeV Entries GeV 2 GeV 3 GeV 4 GeV 5 GeV reconstructed momentum [GeV] /p [1/GeV] T Astrid Münnich (DESY) GEM Module Design for the ILD TPC 15