1. M. Poli Lener1 Developments of an Active target GEM-TPC for the AMADEUS experiment Outline: Micro-Pattern Gas Detector (MPDG) era; GEM: principle of operation; GEM-TPC in the AMADEUS experiment; Active target TPC: GEANT simulation; Prototype construction & PSI beam test ; GEM-TPC performances: efficiency, spatial resolution, dE/dx; New development: resistive anode GEM detector; Conclusions Achievements and Perspective in Low-Energy QCD with Strangeness

2. M. Poli Lener2 Achievements and Perspective in Low-Energy QCD with Strangeness MPGDs: THE EARLY DAYS GEM: F.Sauli, NIMA A386 (1997) 531 MICROMEGAS (MM) : Y. Giomataris et al, NIMA A376 (1996) 29 200 mm MSGC MicroStrip Gas Chamber MSGC - MicroStrip Gas Chamber High E-values at the edge between insulator and strips  damages Charge accumulation at the insulator  gain evolution vs time A. Oed, NIMA 263(1988) 351 Later (~ 1999-2000): Passivation of the cathode edges  MSGD operational !  t ~9 ns  t ~12 ns

3. M. Poli Lener3 Achievements and Perspective in Low-Energy QCD with Strangeness MPGDs: THE EARLY DAYS GEM: F.Sauli, NIMA A386 (1997) 531 MICROMEGAS (MM) : Y. Giomataris et al, NIMA A376 (1996) 29 200 mm MSGC MicroStrip Gas Chamber MSGC - MicroStrip Gas Chamber High E-values at the edge between insulator and strips  damages Charge accumulation at the insulator  gain evolution vs time A. Oed, NIMA 263(1988) 351 Later (~ 1999-2000): Passivation of the cathode edges  MSGD operational !  t ~9 ns  t ~12 ns Why MPGDs? High rates (granularity & occupancy, signal formation time) Fine space resolution  Moving towards high luminosity / high precision experiments, i.e. towards the future MPGDSphoto-lithography technology MPGDS are realized by photo-lithography technology, the same used for standard PCBs.

4. M. Poli Lener4 Achievements and Perspective in Low-Energy QCD with Strangeness MPGDs @ LHC (I-Run) LHCb LHCb has been the first LHC experiment using GEM detectors for triggering purpose 24 triple-GEM 20x24 cm 2 active area TOTEM TOTEM uses GEM detectors for tracking purpose Half-Moon Triple-GEM chambers Inner Ø: 80 mm Outer Ø 300 mm 40 Detectors (Helsinki-CERN) The LNF group started the work on GEM in the 2000:  Non-standard gaps: 3/1/2/1 mm  Innovative gas mixture: Ar/CO2/CF4 = 45/15/40  high time resolution (high efficiency ≈ 96% - in 25 ns)  No aging effects observed up to 2.2 C/cm2 during R&D

5. Small Wheel Rates in Hz/cm 2 Rates at inner rim 1–2 kHz/cm 2 M. Poli Lener5 Achievements and Perspective in Low-Energy QCD with Strangeness MPGDs @ LHC (Upgrades) # chambers / size (w/out spares) Total GEM foil area M2R1 M3R1 n.48 –> ~ 30x25 cm 2 n.48 –> ~32.x27 cm 2 ~12 m 2 ~13 m 2 LHCb upgrade GE1/1 GE2/1 ME0 Alice-TPC

6. Achievements and Perspective in Low-Energy QCD with Strangeness GEM Principle of operation M. Poli Lener

7. 7 Gas Electron Multiplier By applying a voltage between the two copper sides an electric field as high as 100 kV/cm is produced in the holes acting as multiplication channels. Voltage ranging between 400 - 500 V Field lines induction amplification conversion and drift Anode Readout Cathode Achievements and Perspective in Low-Energy QCD with Strangeness

8. M. Poli Lener8 Pads Detector peculiarities:  The regions of conversion, multiplication and signal induction are physically distinct  freedom in readout design choice;  Signal is purely due to the motion of electrons in the induction region  no ion tail, fast signal;  Ions are quickly removed from multiplication region  high rate capability  Multiplication is divided in 3 steps  robustness to discharges;  Light detector ( 3 ‰ X 0 /GEM foil) Triple-GEM detector Cartesian Small angle

9. Achievements and Perspective in Low-Energy QCD with Strangeness AMADEUS EXPERIMENT M. Poli Lener

10. 10 AMADEUS Experiment A novel idea of using an active target GEM-based TPC as a low mass target & tracker/PID detector at the same time is investigated Achievements and Perspective in Low-Energy QCD with Strangeness

11. M. Poli Lener11 Diameter: 40 cm Length: 20 cm Solid angle coverage: Up to |cos θ| = 0.98 Size About 120 measurement point per track rφ p oint resolution < 200 µm Momentum resolution: <1*10 -2 / GeV/c rz point resolution < 500 µm dE / dx resolution ≈ 10 % Other performance requirements 0.5 X0 in the barrel 1.5 X 0 in the endcaps Material budget Active target GEM-TPC requirements GEANT Simulation GEM-TPC in AMADEUS Achievements and Perspective in Low-Energy QCD with Strangeness

12. GEANT Simulation in Hydrogen gas target M. Poli Lener

13. 13 Elastic Scattering: K ± p  K ± p Kinematics for a 127 MeV/c kaon elastic scattering Both backward & forward scattering can be tracked in the target GEM-TPC Forward Scattering Forward Scattering proton Kaon Backward Scattering proton Kaon Achievements and Perspective in Low-Energy QCD with Strangeness

14. M. Poli Lener14 Performances in a pure H 2 Active Target GEM-TPC Kaon Multiple-scattering  z = 0.085+-0.003 mm @ radius = 20 cm Angular distribution of diffused kaons < 1 mrad Particle ID with dE/dx for Kaon & proton proton kaon (a.u) Achievements and Perspective in Low-Energy QCD with Strangeness

15. GEM-TPC prototype M. Poli Lener

16. 16 GEM-TPC R&D design A prototype of 10x10 cm 2 active area and 15 cm drift gap has been realized in a class 100 clean room. The detector is encapsulated inside a gas tight box (PERMAGLASS material) which allow to simply change the geometry and/or replace with new GEMs. The water contamination is below 100 ppmv No value for O 2 contamination Field Cage GEMs Foil Cathode Gas Tight Box Windows Achievements and Perspective in Low-Energy QCD with Strangeness

17. M. Poli Lener17 GEM-TPC construction: Assembly Cathode electrode GEMs Field Cage support 10 cm

18. M. Poli Lener18 PAD  3x3 mm 2 4 Rows of 32 PADs GEM-TPC construction: Readout Pads readout by CARIOCA- GEM chip (Digital FEE) THR= 2 fC

19. Achievements and Perspective in Low-Energy QCD with Strangeness GEM-TPC Performances M. Poli Lener

20. 20 Test beam @ PSI The PSI  M1 beam is a (quasi) continuous high- intensity secondary beam: Pions/proton arrive in 1 ns-wide bunches every 20 ns. The trigger consisted of the coincidence of three scintillators placed at the edge of the detector (  20 cm) and covering an area of about 12x20 mm 2. Another scintillator, 5 m far from the detector, allowed to perform the measurement of particle momentum by mean Time of Flight. An external tracker (  100 μm) improves the tracking Characteristics of the piM1 beam line: Momentum range 100-500 MeV/c Momentum resolution 1 % Spot size on target (FWHM): 15 mm (H)- 10 mm (V) Pion Momentum range Proton momentum

21. Achievements and Perspective in Low-Energy QCD with Strangeness M. Poli Lener21 Laboratory Measurements Gas Mixture Drift Vel @ 200 V/cm [µm/ns] Long. & Tran. Diff. @ 200 V/cm [µm/  cm] Cluster/cm PSI 170 MeV/c Pion PSI 440 MeV/c Proton DAFNE 127 MeV/c Kaon Ar/Iso = 90/10 39±2282±7359±18 40.2±2.0122.2±3.4 Helium = 1004.4±0.5383±15778±5 4.0±0.712.1±1.131.1±1.8 Hydrogen = 100 4.41±0.1210±11280±12 78.0±2.7 GEM: Ionization & Gain Successfully Tested @ PSI The use of pure helium (no quencher) allows to work in stable operation until to gain of 3*10 4

22. High ionizing particle & high yield gas allow to reach higher detection efficiency at lower gain (E ff =1-e -np (*) ) Detector Efficiency The curves are fitted with negative exponential function  for different efficiency values the relative gain is reported as function of the simulated primary clusters (G=n tot /n p (*) ) M. Poli Lener Helium Hydrogen (*) F. Sauli. Yellow Report CERN 77-09, 1977

23. Spatial Resolution M. Poli Lener Achievements and Perspective in Low-Energy QCD with Strangeness σ core  200 μ m Spatial Resolution=√(σ 2 RES –σ 2 trackers ) Double Gaussian fit due to particles scattering in the detector gas volume/field cage walls

24. Time Over Threshold measurement The measurement of signal pulse width above a discriminator threshold may be used as a determination of the charge  Landau distribution as expected Accepting the 40% lowest values, the most probable value of the track charge is correctly reproduce  for higher values of the accepted fraction, the resolution gets worse due to inclusion of hits from the Landau tail  for smaller values, the effect is related to the loss in statistics. dE/dx resolution = 15% M. Poli Lener Achievements and Perspective in Low-Energy QCD with Strangeness

25. PID & dE/dx measurements (Isobutane gas mixture) By simultaneously measuring the momentum of proton & pion (by means the time of flight) and the deposited energy (by means the mean value of the truncated distribution), an estimation of the prototype to identify the particle crossing the detector has been performed The dE/dx resolution is usually parametrized (*) as: σ dE/dx ∝ N a *x b N=# of samples and x their length (3 mm). Assuming an average track length of 100 hits in AMADEUS, with 100 MeV/c pion and 40% of accepted fraction, we expect to measure a dE/dx resolution of 10%. (*) W. Allison, J.H. Cobb., Ann. Rev. Nucl. Part. Sci 30 (1980) 253. Resolution Limit (*) M. Poli Lener

26. PID & dE/dx measurements Separation power n  E Particle Momentum (MeV/c) e/  K/  K/p M. Poli Lener Estimation with a dE/dx  10%

27. M. Poli Lener The physics limit of TPC resolution comes from transverse diffusion: N eff = effective electron statistics. For best resolution, choose a gas with smallest diffusion LlMIT ON ACHIEVABLE TPC RESOLUTION For small diffusion, less precise centroid for wide pads Micro Pattern Gas Detector Anode pads width w Direct signal on the MPGD anode pad Pad width would limits MPGD TPC resolution Proportional wire Cathode pads width w Induced cathode signal determined by geometry Accurate centroid determination possible with wide pads ExB systematics limits wire/pad TPC resolution 27

28. M. Poli Lener28 Achievements and Perspective in Low-Energy QCD with Strangeness Modified GEM anode with a high resistivity film bonded to a readout plane with an insulating spacer Charge dispersion in a GEM with a resistive anode R.K.Carnegie et.al., NIM A538 (2005) 372 K. Boudjemline et.al., NIM A574 (2007) 22 GEM with direct charge readout GEM with charge dispersion readout 2 mm wide pads

29. M. Poli Lener29 Conclusions The GEM-TPC prototype is successfully tested at the  M1 test beam facility of PSI with isobutane-based gas mixtures and pure Helium:  Efficiency > 99% and spatial resolution ≈ 200 μ m with isobutane-based gas mixture have been measured;  With pure Helium gas a detector stability up to 3*10 4 has been achieved  efficiency  97% & spatial resolution  270 µm;  Particle Identification capability & dE/dx resolution  10% with isobutane gas mixtures have been achieved  High separation µ/  /K/p in AMADEUS environment;  Charge Dispersion Technique by means of resistive anode will be soon validated in order to reach a better spatial resolution and to decrease the number of FEE channels; Achievements and Perspective in Low-Energy QCD with Strangeness

30. THANKS

31. M. Poli Lener31 Achievements and Perspective in Low-Energy QCD with Strangeness

32. Field Cage Effect on detector performance Detector Efficiency Efficiency per Row Field Cage Edge effect M. Poli Lener

33. 33 Garfield GEM Detector Simulation GARFIELD is a powerfull simulation tool: primary ionization, diffusion, attachment,multiplication, E-/ion drift, induced & direct signal, ecc Garfield Achievements and Perspective in Low-Energy QCD with Strangeness

34. M. Poli Lener34 GEANT Simulation of a pure H 2 Active Target GEM-TPC Berylium beam pipe: 20 mm - 20.5 mm Plastic Scintillator : 40 mm - 40.5 mm Kapton target wall : 49.95 mm - 50. mm Copper Cage : 49.94 mm - 49.95 mm Hydrogen gas : 50 mm - 200 mm Copper Kapton Hydrogen gas:1 atm Kapton Scintillator 20 cm 40 cm 0.6 tesla Performed with H. Shi

35. M. Poli Lener35 Field Cage Effects All these effects are fully reduced drifting away from the field-cage by 5 mm Low and/or not full detection efficiency has been measured on the edge of each pad rows. - the first and the last pad of each rows collect about 2/3 of the charge with respect to the other pads of the row; - the primary electrons produced in the drift gas and drifting toward the first GEM can be collected by the internal strips of the field-cage. Garfield

36. M. Poli Lener36 GEM-TPC construction: Field Cage 30 cm 15 cm 100 M  resistor 32 copper strips on both sides of Kapton foil (strip pitch 2.5 mm) Cylindrical mould of the Field cage in vacuum bag The Field Cage has been produced with the same C-GEM technique (*) (*) G. Bencivenni et al., NIM A 572 (2007) 168