1 Small GEM Detectors at STAR Yi Zhou University of Science & Technology of China

2 Structure of Gas Electron Multiplier foil Typical geometry: S: 5 µm T: 50 µm d: 60µm D: 80 µm P: 140 µ m Cu Kapton a thin metal (copper)-clad insulator (kapton) foil that is chemically perforated with a large number of small holes

3 Field Strength ： 55kV/cm Static E-Field in GEM Detector

4 The goals of this GEM project The MTD (Muon Telescope Detector) installed in Run9 is constructed by 3 long-strip MRPC modules. There are 6 strips with 2.5 cm width (φ direction) and 87 cm length (Z direction) on MTD readout PCB. The position resolution of MTD at φ direction is about 3 cm, it is the pitch of the strips. Along Z direction, the intrinsic resolution is about 1 cm. This is given by the Beam test in Fermi Lab. The hit positions of inject muons are calculated from time difference of the signal out puts from 2 ends of one strip. At STAR, the inject muon will interact with the materials before MTD, which result in a worse resolution, about 10 cm along Z direction. If pion injected, the resolution would be worse than 10 cm. To make the resolution be dominated by MTD, we need one more detector that provides an extra coincidence of the muon hit position. The detector should have a very good position resolution (better than MTD), fast response rate, and high efficiency for muon (same or better than MTD). Gas Electron Multiplier (GEM) detectors are suitable for this work.

5 The delay-line circuit is consist of many discrete LCs (inductor-capacitor). These LC cells connected to individual anode or cathode readout strips. The Localization information is determined by the propagation time of the induced signals traveling along the delay-line. The linearity and time response are depend on the time delay per cell and the distributed parameters of readoutPCB. Delay-line readout method Important parameters of Delay-line

6 Delay-line Design 1 1.The position resolution of the GEM detector should be less than 1cm(Better than resolution of MTD). 2.The max delay should be less than 30ns(Compatible with STAR trigger system). 3.The characteristic impedance should be 50 Ohm (To avoid the signal reflections). Requirements for Delay-Line

7 Delay-line Design 2 Total area of GEM: 10cm ＊ 10cm Pitch of Readout Strips: 2mm Total Readout Strips: 51 W: 1 mm Er1: 4.2 （ dielectrical constant) Zo: 50 Ohm Empirical formula:

8 In order to take into account the influence of the parasitical parameters of delay-line PCB routes, all parasitical parameter matrices can be calculated by the Finite Element method. To simplify the electric circuit model of the PCB route, the impedance, the mutual capacitance between two routes are ignored. Only the self-capacitances, inductance, characteristic impedance matrices are kept and used to construct the simplest electric circuit model (as the zero- order model). Delay-line Design 3

9 Delay-line Design 4

10 Delay-line Design 5

11 Delay-line Design 6

12 Delay-line Design 7 Input at Strip 1 Input at Strip 9 The input calibration signal is a pulse that has 2ns rise time and 20ns width

13 Delay-line Design 8 Simulatio n Test

14 Delay-line Design 9 Timing system Simulation Program

15 Delay-line Design 10 Constant Fraction Discriminator (CFD) Module

16 Delay-line Design 11 General Discriminator Module

17 Delay-line Design 12 TDC Module

18 Delay-line Design 13 Simulated Calibration Results of GEM Readout PCB+DelayLine

19 Delay-line Design 14

20 Delay-line Design ns/ch n ns/ch n ns/ch n ns/ch n ns/ch n ns/ch n

21 GEM Output Signals( 55 Fe) 3500V3600V3700V

22 Assemble work at BNL 1

23 Assemble work at BNL 2

24 Assemble work at BNL 3

25 Assemble work at BNL 4

26 Installation at STAR

27 Drift Velocity of the Electrons

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29 Summary A Delay-Line readout PCB has been designed for this GEM project. 2 GEM detectors have been assembled and installed in STAR. We have got very good signals, but there are some data acquisition problems.

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