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Development of Advanced Gaseous Detectors for Muon
Tracking and Triggering in Collider Experiments
Liang Guan 1,2
16-10-2014 Dissertation Defense
Supervised byProf. Xiaolian Wang1, Prof. Zhengguo Zhao1 and Prof. Junjie Zhu2
1 University of Science and Technology of China2 University of Michigan
Outline
Introduction
Thermo-bonded MICRO-MEsh GAseous Structure (Micromegas)
Thin gap Resistive Plate Chamber (RPC)
Small-strip Thin Gap Chamber (sTGC)
Summary
Liang Guan ([email protected]) Dissertation Defense 16 October 2014
Outline
Introduction
Thermo-bonded Micromegas (Micromegas)
Thin gap Resistive Plate Chamber (RPC)
Small-strip Thin Gap Chamber (sTGC)
Summary
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 1
Physics of Collider Experiments
…
Standard model Dark matter Super symmetryLiang Guan ([email protected]) Dissertation Defense 16 October 2014 2
• Collider experiments, utilizing high energy accelerators and large spectrometers, are unique to discover new particles, resonances, phenomena … Changing our understanding of fundamental building blocks of the nature and their interactions
• Very broad physics topics: Standard Model, SUSY, Extra dimension etc…
• Hunting for heavy new particles relies on capturing high momentum secondary particles from their decays via different channels. (decay to muons is one of the important channel. e.g. H ZZ* 4µ)
New!
Muon tracking and trigger in collider experiments
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 3
ATLAS CMS
• Examples:
Drift tube (DT), Resistive plate chamber (RPC), Cathode Strip Chamber (CSC)
Monitored drift tube (MDT), Resistive plate chamber (RPC), Thin gap chamber (TGC) and Cathode Strip Chamber (CSC)
• Muon trigger and tracking based on large scale gaseous detectors. • Trigger and tracking are performed with separate detectors
Challenges of muon tracking and triggering in future experiments
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 4
• Take ATLAS as an example
• High backgrounds environment (expected ~ 15 kHz/cm2 at the hottest region at end-cap @ lumi. 7x1034 cm-2s-1) results in
» Low detector efficiency» Higher probability of generate fake trigger» Reduced tracking accuracy (space charge effect)
• Stringent requirements on rate capability, timing and localization precision simultaneously for on-line trigger and off-line muon reconstruction!
Rate vs. radius
R&D of Three Advanced Gaseous Detectors
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 5
• In the context of ATLAS muon upgrade program, we performed extensive studies on three advanced gaseous detectors for muon tracking and trigger in future collider experiments.
• Studies are carried out on Micro-mesh gaseous structure (Micromegas) (Part I), Resistive plate chamber (RPC) (Part II) and Thin gap multi-wire chamber (TGC) (Part III).
• Researches are focused on addressing critical issues of applying these detectors for muon detection in harsh high rate environment and understanding their basic characteristics which affect the timing and tracking.
• Research approaches: simulation, calculation, lab and beam tests …
Garfield, Magboltz, HEED: electron transportation ...Ansys Maxwell 3D, neBEM: electric field
Outline
Introduction
Part I Thermo-bonded MICRO-MEsh GAseous Structure (Micromegas)
Thin gap Resistive Plate Chamber (RPC)
Small-strip Thin Gap Chamber (sTGC)
Summary
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 6
• Thermo-bonded Micromegas
• Basic performance parameters
• Simulation
• High resistivity anode Micromegas
• Parallel ionization multiplier (PIM)
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Introduction
• bulk-Micromegas* photolithography• microbulk-Micromegas** Kapton etching
* Giomataris et al. NIMA 560.2 (2006): 405-408.1.** Andriamonje et al. JINST 5.02 (2010): P02001.
• Fabrication• Micromegas structures
• Key advantages:• High rate capability: 105 Hz/mm2 *
• Spatial resolution: < 100 µm
• Present challenging • Scale to large size• Spark resistance in hadron
environment * Y. Giomataris, NIMA 419 (1998) 239
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 8
Thermo-bonded Micromegas
• Thermo-bond film: excellent insulating spacer
• Fabrication of thermo-bonded Micromegas
• An novel approach to construct avalanche gap: thermally bond woven meshes to anode PCB using thermo-bond film spacers
°C
No photolithography process Easier to build small prototyped in Univ. labs. with simple tools.
Potential to go to at least a few hundreds of cm2 size.
Measurement of Basic Performance Parameters
4.5 cm x 4.5 cm Thermo-bonded Micromegas
9 cm x 9 cm Bulk Micromegas
• Energy resolution for 5.9 keV X-rays
• Gas gain and energy resolution in Ar/iC4H10
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 9
I. Giomataris et al. NIM A560 (2006) 405
Measurement of Basic Performance Parameters
• Uniformity:
• Gain non-uniformity due to:
» PCB warping
» Avalanche gap non-uniformity
» Mesh sagging
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• ± 20% across ~ 4.5 x 4.5 cm2
unsupported active area
Sufficiently for tracking and triggering applications
Simulation optimization
• Optimizing gas to improve uniformity• Electron transparency optimization
> 50% optically transparent woven wire meshes should be used
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Various simulations studies on operational mechanism, among them are:
Micromegas with High Resistivity Anode
Micromesh
PCB Anode Pads
Thermo-bond film
Resistive sheet
Resistive adhesive film
Cathode
Signals1 MΩ
collimator
X-ray source• Attempting an alternative ways to make Micromegas spark-tolerant: attaching a thick layer of high resistive sheet directly on the anode
• Standard Micromegas is vulnerable to discharge when highly ionizing particles are present. Coating a thin resistive layer on the metal anode (separated by thin insulating layer and grounded at its periphery).
• High resistive materials studied
» High gain» Lateral charge spread in thick
resistive layer» Spark-protection
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13
Micromegas with High Resistivity Anode (cont.)• Basic performance measurements
Gas Gain Charge up
Polycarbonate anode
Fe-55 spectra
Energy resolution
Rate capability
Illuminated area:2 mm x 0.3 mm
Semi-condu. glass
Polycarbonate
105
Regular glass
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 13
Semi-conductive
glass
Micromegas with High Resistivity Anode (cont.)
~ 2 x 104 ~ 3 x 104 ~ 4 x 104
• “Spark” signals recorded directly using 50 Ω terminated oscilloscope:
Gain
• Spark amplitudes: mostly < 100 mV; up to 0.5 V at high gain, rate less than ~10-4
per detected photon count • Spark signal duration : < 200 ns• Charge released: less than few nC; mostly at few tens of pC effective to protect front-end
electronics
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Parallel Ionization Multiplier
• Parallel ionization multiplier (PIM): multiple mesh layers and multi-stage of avalanches. Originally intended to be used for tracking low energy beta rays.
• Attempt to design a structure and operate PIM at GEM-mode: only electrons extracted to the bottom induction gap. fast signal, fast timing!
• Prompt electron signal component:
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 15
Fast signal: 50% Fast signal: 17%
Parallel Ionization Multiplier
• Can we extract enough electrons from the bottom mesh to the induction gap?
• Fast signal is preferable, but …
E2
E1
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Parallel Ionization Multiplier (cont.)
• Experimental study
Prototype photo Signals
Fe-55 spectrum Effective gain on anode
~ 15 % of amplitude on mesh(Sim: 10%)
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Part I Summary
Development of a novel method to fabrication Micromegas: thermal bonding. Good energy resolution, basic performances parameters comparable to bulk Micromegas. Reasonable gain uniformity (< 20%).
Many simulation studies for optimizing thermo-bonded Micromegas with woven wire mesh.
Attempts made to develop high resistivity anode Micromegas for spark tolerance High resistivity material significantly reduce discharge amplitude.
Attempts made to develop fast timing parallel ionization multiplier (PIM) Analysis of prompt charge concentration; experimentally assesses the viability to operate PIM at “GEM-mode”.
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 18
Outline
Introduction
Thermo-bonded MICRO-MEsh GAseous Structure (Micromegas)
Part II Thin gap Resistive Plate Chamber (RPC)
Small-strip Thin Gap Chamber (sTGC)
Summary
• Introduction
• Beam test setup
• Beam test results (spatial resolution … )
• Rate capability measurements
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Introduction - RPC for muon triggering
Aielli et al., NIM A 456.1 (2000): 77-81.
ATLAS CMS
Carrillo, NIMA 661 (2012): S19-S22.
• RPC in muon spectrometers of present experiments» Timing: 1-2 ns» Spatial resolution: a few mm to a few cm » Rate capabilities: up to 1 kHz/cm2
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Introduction – Benefit of good timing for trigger
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Introduction- Proposed fast tracking trigger system based on RPC
• Thin gap RPCs for excellent timing, fine pitch readout strips for precision coordinate measurements, dual end readout to make RPCs as mean-timers and also for second coordinate measurement
• Ideas need to be assessed Beam tests
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• Glass electrode RPC» ~ 1 mm glass electrodes» 1.15 mm gas gap» Resistive paint: 1-5 MΩ/» Size: 96 cm x 32 cm» 1.27-mm-pitch readout strips at the
ground side
• Bakelite RPC» 2-mm-thick Bakelite electrodes,
1010 Ω∙cm bulk resistivity (same as used for ATLAS RPC)
» 1mm gas gap» Size: 20 cm x 20 cm» 1.27-mm-pitch readout strips at
the ground side • Gas mixture : Ar (94.7%):iC4H10(0.5%):SF6 (0.3%)
96 cm
20 cm
Thin gap Resistive Plate Chamber
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• CERN SPS H8 beam line (180 GeV/c muon beam)
Reference for spatial resolution measurements: small-diameter (15 mm) Monitored Drift Tube Chamber (sMDT)
• Glass RPCs: horizontal strips reading from both ends
• Bakelite RPC: with vertical readout strips provide reference hit position along glass RPC r/o strips.
Beam Test Setup
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Bakelite RPC
Glass RPC
180 GeV/c muon
180 GeV/c muon TGC Quad.
sMDT
Glass RPC
Beam Test Setup (cont.)
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ATLAS MDT Front-end
Low noise electronics with Amplifier, Shaper and Discriminator (ASD)Zin=120 Ω. ENC = 6000 e- rms
Bipolar shaping, 15ns shaper peaking time
Sensitivity: 8.9 mV/fC
ALICE NINO Front-end
Fast electronics with differential in/out puts
40 Ω<Zin<75 Ω. ENC = 5000 e- rms
1 ns peaking time
Threshold: 10fC to 100fC
F. Anghinolfi et al., IEEE TNS 51(2004)Yasuo Arai et al., IEEE TNS 51 (2004)
• TDC chips with 0.78 ns least countused
• 100 ps resolution VME TDC modules (CAEN v1190A)used
Precision coordinate measurements Timing and 2nd coordinate measurements
Readout Electronics
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• With MDT readout electronics
• With NINO readout electronics
HV @6.5 kV
HV @6.8 kV
1.15 mm gap glass RPC
1.15 mm gap glass RPC
Efficiency and Cluster Size
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• Charge centroid (1.27-mm-pitch):- Resolutions: ~ 200 µm (Best) and ~ 220 µm (Average)- Limited by the nonlinear charge representation and small cluster size (~2.3)
• Using timing information only (1.27-mm-pitch): - Hit position determined to be the average center of strips in the cluster- Resolutions < 290 µm Useful for fast tracking at trigger level. (ATLAS NSW requires 300 µm online resolution per detector layer)
Precision Coordinate Spatial Resolution
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• Over all time jitter from RPC and Scintillator
• Overall time jitter after time walk correction
After de-convolution:𝜎𝜎𝑅𝑅𝑅𝑅𝑅𝑅 ≅ 453 ±15 ps
𝜎𝜎 ≅ 613 ±16 ps
𝜎𝜎𝑅𝑅𝑅𝑅𝑅𝑅 ≅ 562 ±18 ps
𝜎𝜎 ≅ 697 ±18 ps
After de-convolution:
time jitter of reference scintillator: 413 ps
Time Resolution -1.0 mm gap RPC
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 29
• Over all time jitter from RPC and Scintillator
• Overall time jitter after time walk correction
After de-convolution:
𝜎𝜎𝑅𝑅𝑅𝑅𝑅𝑅 ≅ 510 ±13 ps
𝜎𝜎 ≅ 656 ±14 ps
𝜎𝜎𝑅𝑅𝑅𝑅𝑅𝑅 ≅ 574 ±15 ps
𝜎𝜎 ≅ 707 ±16 ps
After de-convolution:time jitter of reference scintillator: 413 ps
Time Resolution -1.15 mm gap RPC
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Bonus of excellent timing
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• Maximum charge strip off-line time jitter
Time
Strip ID
σ = 400 ps
• Good timing after off-line corrections Trigger RPC act as Time of flight detector. Could be used for searching slow exotic particles.
• 2nd Coordinate measurements• Hit position determine from signal arrival time difference from two ends of a strip• Resolution: ~1 cm (w/ 100 ps resolution TDCs) and ~ 7 mm if averaging the
reconstructed positions from multiple strips.
Mean-time and 2nd Coordinate
v ~15 cm/ns
• Mean-time: Average signal arrival time from two ends of a strip measured to be independent of hit position
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Bakelite RPC Rate Capability Measurements
• Critical issue with RPC: rate capability limitations due to voltage drop across the high resistive electrodes.
Rate
Charge per countElectrode bulk resistivity
Electrode thickness
• A bi-gap Bakelite RPC (constructed by Univ. of Rome II) tested under intense 137Cs source at CERN GIF.
• RPC basic parameters: 2 x 1 mm gaps, 2 x 1010 Ω∙cm and 2 mm thick Bakelite plates as electrodes
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filters
Bakelite RPC Rate Capability Measurements (cont.)
• Results: » fully efficient to muons @ > 18 kHz/cm2 detected photon rate. » charge per count: ~ 2 pC (compared with 30 pC for present ATLAS 2 mm
gap RPCs)
Current, charge per count vs. HVEfficiency vs. HV
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Part II Summary
We proposed a fast tracking trigger scheme based on thin gap RPCs.
Several beam tests to study thin gap RPC on-line/off-line spatial resolution, timing etc. possibility to construct (sub-ns x sub-mm x sub-cm) trigger logic cells. It will be very powerful to handle muon triggering in an unexpected high rate environment.
Rate capability tests: critical to reduce delivered charge per count. RPC with 1 mm gaps and 1010 Ω∙cm resistive electrodes can be fully efficient to muons at > 18 kHz/cm2.
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 35
Outline
Introduction
Thermo-bonded MICRO-MEsh GAseous Structure (Micromegas)
Thin gap Resistive Plate Chamber (RPC)
Part III Small-strip Thin Gap Chamber (sTGC)
Summary • Introduction: ATLAS NSW upgrade
• sTGC Simulation – basic parameters
• sTGC Simulation – timing
• sTGC Simulation – charge production and sharing
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Motivations for upgrading present muon Small Wheel:• Remove the “fakes”• Improve muon pT resolution and sharpen the trigger “turn-on” curve after the
Phase-II upgrade when the BW segment angle resolution is improved to ~ 1 mrad
New Small Wheel (NSW) structure: 2 x 4 planes of Micromegas (Primary tracking) sandwiched by 2 sTGC quadruplets (Primary trigger)
Introduction – ATLAS New Small Wheel
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Similar structure as TGC in the present end-cap muon system except:
• Strip readout (3.2 mm x 1-2 m): precision measurement of track position in η• Pad segmentation (8 cm x 8 cm): fast pattern recognition for selecting readout strips• Lower cathode resistivity (~1 MΩ/ 100 kΩ/)
Introduction – sTGC for NSW
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Introduction – sTGC Trigger Logic
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Understand sTGC operational parameters • Electric field, Electron transportation coefficients
Evaluate sTGC timing capability for LHC bunch crossing identification • Impact of particle incident angle, magnetic field and HV
Estimate total amount of charges collected on strips, pads and wires
Understand the charge sharing among readout strips
Motivations for the simulation studies
Strips, pads, wires from sTGC detectors are all read out and used for on-line trigger or off-line muon reconstructions. Key requirements:
Timing LHC BX discrimination
Tracking 1 mrad on-line angular resolution trigger
~ 100 µm off-line resolution
Rate Up to 15 kHz/cm2
It is essential to:
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 40
• Electric field simulated using neBEM and FEM methods consistent with analytical calculation
• Strong (>1 kV/cm) electric field over 97% of the detector volume @ 2.85 kV
sTGC Electric Field
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• Motions of electrons under E, B fields governed by
• Lorentz angle: the angle between the drift direction and the electric field
• Simulation of electron transport parameters: Magboltz package
Lorentz angleDrift velocity
Long. DiffusionTrans. Diffusion
Electron transportation in sTGC
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• Timing performance: mainly determined by earliest cluster arrival time (high gas amplification factor)
• B-field at Small Wheel: < 1 T
Earliest cluster arrival time under different HV
2.8 kV, 0 degree0 degree
Earliest cluster arrival time under B field
Timing – Impact of HV and B-field
• Non-degraded timing performance in NSW B-field and with reduced HV.
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• The earliest cluster arrival time: related to the track angle in the plane orthogonal to the wire plane.
• 16 sectors in the NSW φ direction. The track incident angle in the plane normal to wire plane: 0~11 degree.
• The simulation suggests an improved timing capability for inclined tracks.
Earliest cluster arrival time under different angles
Timing - Impact of Incident Angle
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• Full simulation of single-layer time spectrum: take into account the gain fluctuation, electronics and reference detector time jitters > 95% events within 25 ns
• Multiplayer timing performance improves by shifting wire positions wrt. adjacent layers minimize the probability of passing low eclectic field region
0 degree
(With arbitrary offset)
2.85 kV
Single layer time spectrum Time spectrum from 3/4 coincident
with shifted wires
Timing – Fully Simulated Time Spectrum
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• Avalanches develop within ~20 µm above the wire surface (Garfield sim.)
• Charge proportional to the logarithm of integration time
• Only ~ 20% of total charge will be collected within 25 ns int. gate
sTGC Charge Production
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<<Raw charge spread on the cathode>>
<<Point charge dispersion>>
• R: resistance of cathode resistive paint per unit length
• C: capacitance between cathode and readout strip layer per unit length
• σ: width of raw charge spread (from Garfield simulation)
wire
wire
<<Charge development with time>>
• C: normalization factor • t0: average arrival time of earliest cluster
wire
sTGC Charge Sharing
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(τ = RC)
• The charge density at position x and time t
𝜌𝜌′ 𝑥𝑥, 𝑡𝑡 = 𝐷𝐷(𝑥𝑥) ⊗𝜌𝜌(𝑥𝑥, 𝑡𝑡) ⊗𝑇𝑇(𝑡𝑡)
• The charge density at certain strip:
𝜌𝜌′ 𝑡𝑡 = 𝑥𝑥1
𝑥𝑥2𝜌𝜌′ 𝑥𝑥, 𝑡𝑡 𝑑𝑑𝑥𝑥
Strip charge density evolution
• Integration over time gives the collected charge on each strip
Important parameters to determine the charge spread:Resistive paint (cathode) resistivityStrip-cathode coupling capacitor (distance, dielectric constant)Electronics integration timeStrip width and pitch
sTGC Charge Sharing (cont.)
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 48
Distributions of the ratios of charges induced on various strips to the maximum charge
position charge
Maximum strip -x0 QC
2nd maximum strip p-x0 QR
3rd maximum strip -p-x0 QL
• Simulation procedures:» Vary hit position: (strip center,
half strip pitch).» Integrate charge density func.
between strip boundaries
sTGC Charge Sharing (cont.)
• Result: 2nd and 3rd max. charge strips get 60% and 20% of the charge on max. strip High dynamic front-end electronics required.
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Data from beam test
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Part III summary
Various simulations of sTGC electric field, electron transportation etc.
sTGC timing capability full-fills ATLAS NSW LV-1 trigger requirement (LHC 25 ns BX discrimination). Does not degrade with reduced HV, mag. field in NSW.
We have built an analytic model to describe charge dispersion in resistive layer and charge sharing among strips (still in developing):
• Could be implemented in ATLAS main software framework for sTGC digitization
• Very crucial to understand the impact of resistive paint non-uniformity to off-line muon reconstruction accuracy
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 51
Outline
Introduction
Thermo-bonded MICRO-MEsh GAseous Structure (Micromegas)
Thin gap Resistive Plate Chamber (RPC)
Small-strip Thin Gap Chamber (sTGC)
Summary
Liang Guan ([email protected]) Dissertation Defense 16 October 2014 52
Summary
• Extensive R&D on three gaseous detectors are carried out to explore theircapabilities for muon tracking and triggering in collider experiments.
• We developed a novel way of constructing Micromegas. Detailed simulation andexperimental studies are performed. Attempts are made to construct highresistivity anode Micromegas and parallel ionization multiplier to address sparkissues and to improve parallel mesh structure detector timing capability.
• Our studies indicate RPCs are capable of providing (sub-ns x sub-mm x sub-cm) high granularity logic trigger cells Powerful for rejecting backgrounds and improving muon selectively
• Simulation study suggest sTGC is capable to preform LHC BX discrimination inNSW environment. We developed an analytical charge sharing model for betterunderstanding the detector characteristics.
Thank you!
感谢各位评审老师的聆听!
不积跬步无以至千里,不积小流无以成江海
List of publications
(5 in total. 4 as primary author or contact person)
Contact person. Drafted the paper
Contact person. Drafted the paper
Primary author. Drafted the paper
Primary author. Drafted the paper
Second author
List of publications
(4 in total. 3 as primary author)
Primary author. Drafted the paper
Primary author. Drafted the paper
Primary author. Drafted the paper
Important contributor
NSW TDR 2013: sTGC simulation subsection
List of conferences and talks
• IEEE NSS , 2010, Knoxville, USA• RD51 mini week meeting, 2010, CERN• 第八届全国高能物理年会,2010 南昌• 第一届中国微结构气体探测器会议,2010,庐江• 第二届中国微结构气体探测器会议,2012,高能所
• “Studies on Fast Trigger and High Precision Tracking with Resistive Plate Chamber”, 2013 CPAD and Instrumentation Frontier Community meeting, Argonne, IL, USA (口头报告)
• “Development of 1 mm low resistivity Bakelite Plate for thin-gap Resistive Plate Chamber”, RPC 2012 Conference, Frascati, Italy (会议海报)
• “Simulation Studies of Characteristics and Performances of sTGC for ATLAS Muon New Small Wheel”, 2013 US ATLAS Workshop Upgrade Session, Argonne, IL, USA (口头报告)
8 oral talks in total in national and international conferences
Backup slides
hardware based trigger that searches for high transverse momentum leptons, photons, jets and large missing and total transverse energy. Reduce 40MHz rate to 75kHz.
ATLAS Level -1 Trigger
dN_mu vs PT
Hot roll and hot press
Hot roll and hot press
Trans. diffu. coefficient
• Typical Fe-55 spectrum
Characteristics of Mmegas in Argon based mixture Ar/CO2 93:7
• Gas Gain
• Electron transparency • (Fe-55) Energy resolution vs. Gain
Gain ~104
Vm [V]
Gai
nFW
HM[%
]
Ea/Ed Vm [V]
“knee” @80
Uniformity correction
PIM fast signal calculation
PIM bottom mesh electron extraction coefficient
Prompt charge signal from 1.15 m gap
Beam test (w/ NINO) trigger logic
RPC time resolution (w. MRPC as reference)
Magnetic field around the SW
Earliest Cluster Arrival Time Distributions
Degree 0 Degree 5 Degree 10 Degree 15
Degree 20 Degree 25 Degree 30 Degree 35
Degree 40 Degree 45 Degree 50
Earliest Cluster Arrival Time vs. Track Hit Position
Degree 0 Degree 5 Degree 10 Degree 15
Degree 20 Degree 25 Degree 30 Degree 35
Degree 40 Degree 45 Degree 50
Algorithm for timing determination
• Trigger: n out of 4 coincidence
• Timing tag is given after nth latest response of a layer
Layer 1
Layer 2
Layer 3
Layer 4
Time Trigger!
Layer 1
Layer 2
Layer 3
Layer 4
Time Trigger!
3/4 coincidence time spectrum – single layer efficiency effect
• For instance, wire displacement = 0.5 mm
Tail disappears as efficiency approaches 100%
From J. Dubbert’s Talk @ ATLAS muon week 27th,March,2013
sTGC big sector layout
• sTGC big sector is subdivided into 4detection areas in azimuthal direction.
• Maximum wire length ~1 m
• Signal propagation velocity: 27ns/cm 3.7 ns arrival time difference for 1m
3/4 coincidence time spectrum – including additional jitters
• Signal propagation jitter
• Electronics jitter
• Single layer time spectrum measured with SonyASD/VMM+TDC well reproduced assuming a total external time jitter of 3 ns
• The subtracting ~2ns jitter from largereference scintillator : ~2.3 ns
𝜌𝜌(𝑥𝑥, 𝑡𝑡) = 𝑅𝑅𝑅𝑅/4𝜋𝜋𝑡𝑡𝑒𝑒(−𝑅𝑅𝑅𝑅4𝑡𝑡 𝑥𝑥2)𝐷𝐷 𝑥𝑥 =
𝑄𝑄2𝜋𝜋𝜎𝜎
𝑒𝑒(− 𝑥𝑥22𝜎𝜎2)
𝜌𝜌′ 𝑥𝑥, 𝑡𝑡 = 𝐷𝐷(𝑥𝑥) ⊗𝜌𝜌(𝑥𝑥, 𝑡𝑡) =𝑄𝑄
2𝜋𝜋(2 𝑡𝑡𝑅𝑅𝑅𝑅 + 𝜎𝜎2)
𝑒𝑒(− 𝑥𝑥2
4 𝑡𝑡𝑅𝑅𝑅𝑅+2𝜎𝜎
2)
⇒ Charge density on readout strip
Initial charge spread Dispersion on resistive layer
Induced charge distribution on strip
Charge sharing
𝜌𝜌 𝑡𝑡 = 𝑤𝑤1
𝑤𝑤2𝜌𝜌′ 𝑥𝑥, 𝑡𝑡 𝑑𝑑𝑥𝑥 =
𝑄𝑄2
[𝐸𝐸𝐸𝐸𝐸𝐸𝑅𝑅𝑅𝑅
4𝑡𝑡 + 2𝑅𝑅𝑅𝑅𝜎𝜎2𝑤𝑤2 − 𝐸𝐸𝐸𝐸𝐸𝐸(
𝑅𝑅𝑅𝑅4𝑡𝑡 + 2𝑅𝑅𝑅𝑅𝜎𝜎2
𝑤𝑤1)]
Charge density of strip (w1,w2) vs. time
Strip width/pitch: 2.7/3.2mm
RC: 25 ns
σ: 1.12 mm
The charge sharing among strips depends on:• Dispersion time constant RC
• Charge integration time
Charge sharing
Validation: Garfield + Psipice
Initial charge spread:• Built wire chamber model and segmented
cathode to 1.5 mm pitch strips. Charge on cathode is the superimposition from each strip
Charge diffusion through resistive layer:• Built equielent1D RC network in Pspice
R47
rv arC47cv ar
R48
rv arC48cv ar
R49
rv arC49cv ar
C50cv ar
Charge sharing
Time
0s 5ns 10ns 15ns 20ns 25ns 30ns-I(Cstr1) -I(Cstr2) -I(Cstr3) -I(Cstr4) -I(Cstr5)
-20uA
-10uA
0A
Central strip
Neighbor to neighboring strip
Neighboring strip
Simulated current signals
RC=10ns
R(kΩ/mm) C (pF/mm) RC (ns) Calculation Garfield+Psipce
50 0.2 10 30.4% 31.8%
100 0.43 43 13.5% 16.8%
Q2nd/Qmax (muon hit in the center of the strip with Qmax charge)
Charge sharing