Diapositiva 1

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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

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MPGDs THE EARLY DAYS
st 9 ns
st 12 ns
GEM F.Sauli, NIMA A386 (1997) 531
MICROMEGAS (MM) Y. Giomataris et al, NIMA A376
(1996) 29
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MPGDs THE EARLY DAYS

• Why MPGDs?
• High rates (granularity occupancy, signal
  formation time)
• Fine space resolution
• Moving towards high luminosity / high precision
  experiments, i.e. towards the future
• MPGDS are realized by photo-lithography
  technology, the same used for standard PCBs.

st 9 ns
st 12 ns
GEM F.Sauli, NIMA A386 (1997) 531
MICROMEGAS (MM) Y. Giomataris et al, NIMA A376
(1996) 29
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MPGDs _at_ LHC (I-Run)
LHCb has been the first LHC experiment using GEM
detectors for triggering purpose
TOTEM uses GEM detectors for tracking purpose

• 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
  RD

Half-Moon Triple-GEM chambers Inner Ø 80 mm
Outer Ø 300 mm 40 Detectors (Helsinki-CERN)
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MPGDs _at_ LHC (Upgrades)
LHCb upgrade
chambers / size (w/out spares) Total GEM foil area
M2R1 M3R1 n.48 gt 30x25 cm2 n.48 gt 32.x27 cm2 12 m2 13 m2
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GEM Principle of operation
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Gas Electron Multiplier
Cathode
Field lines
conversion and drift
amplification

• 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

induction
Anode Readout
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Triple-GEM detector
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 X0 /GEM foil)

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AMADEUS EXPERIMENT
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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
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Active target GEM-TPC requirements
GEM-TPC in AMADEUS
GEANT Simulation
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GEANT Simulation in Hydrogen gas target
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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
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Performances in a pure H2 Active Target GEM-TPC
Kaon Multiple-scattering
Particle ID with dE/dx for Kaon proton
(a.u)
proton
Angular distribution of diffused kaons lt 1 mrad
kaon
?z 0.085-0.003 mm _at_ radius 20 cm
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GEM-TPC prototype
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GEM-TPC RD design
A prototype of 10x10 cm2 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 O2 contamination
Windows
Cathode
Field Cage
GEMs Foil
Gas Tight Box
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GEM-TPC construction Assembly
10 cm
Field Cage support
GEMs
Cathode electrode
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GEM-TPC construction Readout
Pads readout by CARIOCA-GEM chip (Digital FEE)
THR 2 fC
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GEM-TPC Performances
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Test beam _at_ PSI
The PSI ?M1 beam is a (quasi) continuous
high-intensity secondary beam Pions/proton
arrive in 1 ns-wide bunches every 20 ns.
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)
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
mm2. 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
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GEM Ionization Gain
Gas Mixture Drift Vel _at_ 200 V/cm µm/ns Long. Tran. Diff. _at_ 200 V/cm µm/?cm Long. Tran. Diff. _at_ 200 V/cm µm/?cm Cluster/cm Cluster/cm Cluster/cm
Gas Mixture Drift Vel _at_ 200 V/cm µm/ns Long. Tran. Diff. _at_ 200 V/cm µm/?cm Long. Tran. Diff. _at_ 200 V/cm µm/?cm PSI 170 MeV/c Pion PSI 440 MeV/c Proton DAFNE 127 MeV/c Kaon
Ar/Iso 90/10 392 2827 35918 40.22.0 122.23.4
Helium 100 4.40.5 38315 7785 4.00.7 12.11.1 31.11.8
Hydrogen 100 4.410.1 21011 28012 78.02.7
Successfully Tested _at_ PSI
Laboratory Measurements
The use of pure helium (no quencher) allows to
work in stable operation until to gain of 3104
M. Poli Lener
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Detector Efficiency
High ionizing particle high yield gas allow to
reach higher detection efficiency at lower gain
(Eff1-e-np ())

• The curves are fitted with negative exponential
  function
• for different efficiency values the relative
  gain is reported as function of the simulated
  primary clusters
• (Gntot/np ())

() F. Sauli. Yellow Report CERN 77-09, 1977
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Spatial Resolution
Double Gaussian fit due to particles scattering
in the detector gas volume/field cage walls
Spatial Resolutionv(s2 RES s2 trackers)
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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
dE/dx resolution 15

• 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.

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PID dE/dx measurements (Isobutane gas mixture)
By simultaneously measuring the momentum of
proton pion (by means the time of ?ight) 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
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PID dE/dx measurements
Estimation with a dE/dx ?10
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LlMIT ON ACHIEVABLE TPC RESOLUTION

• The physics limit of TPC resolution comes from
  transverse diffusion
• 
  Neff effective electron statistics.
• For best resolution, choose a gas with smallest
  diffusion

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Charge dispersion in a GEM with a resistive anode
Modified GEM anode with a high resistivity film
bonded to a readout plane with an insulating
spacer
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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 gt 99 and spatial resolution 200 µm
  with isobutane-based gas mixture have been
  measured
• With pure Helium gas a detector stability up to
  3104 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

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THANKS
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Field Cage Effect on detector performance
Detector Efficiency
Field Cage Edge effect
Efficiency per Row
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GEM Detector Simulation
Garfield
GARFIELD is a powerfull simulation tool primary
ionization, diffusion, attachment,multiplication,
E-/ion drift, induced direct signal, ecc
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GEANT Simulation of a pure H2 Active Target
GEM-TPC
0.6 tesla
Kapton
Kapton
Copper
Scintillator
Hydrogen gas1 atm
40 cm
20 cm
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
Performed with H. Shi
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Field Cage Effects
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
All these effects are fully reduced drifting away
from the field-cage by 5 mm
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GEM-TPC construction Field Cage
32 copper strips on both sides of Kapton
foil (strip pitch 2.5 mm)
15 cm
Cylindrical mould of the Field cage in vacuum bag
30 cm
The Field Cage has been produced with the same
C-GEM technique ()
100 M? resistor
() G. Bencivenni et al., NIM A 572 (2007) 168