1. Lei Xia Argonne National Laboratory
Construction of a Digital Hadron Calorimeter with Resistive Plate Chambers
Lei Xia
Argonne National Laboratory

2. RPC DHCAL Collaboration
Argonne
Burak Bilki
Carol Adams
Mike Anthony
Tim Cundiff
Eddie Davis
Pat De Lurgio
Gary Drake
Kurt Francis
Robert Furst
Vic Guarino
Bill Haberichter
Andrew Kreps
Zeljko Matijas
José Repond
Jim Schlereth
Frank Skrzecz
(Jacob Smith)
(Daniel Trojand)
Dave Underwood
Ken Wood
Lei Xia
Allen Zhao
Boston University
John Butler
Eric Hazen
Shouxiang Wu
Fermilab
Alan Baumbaugh
Lou Dal Monte
Jim Hoff
Scott Holm
Ray Yarema
IHEP Beijing
Qingmin Zhang
University of Iowa
Burak Bilki
Edwin Norbeck
David Northacker
Yasar Onel
McGill University
François Corriveau
Daniel Trojand
UTA
Jacob Smith
Jaehoon Yu
IIT
Guang Yang
Daniel Kaplan
RED = Electronics Contributions
GREEN = Mechanical Contributions
Yellow = Students
BLACK = Physicist
RPC 2012

3. Motivation: physics at the next lepton collider
– Physics Benchmarks for the ILC Detectors
Required: excellent Jet energy/mass resolution Solution: Particle Flow Algorithm (PFA)
RPC 2012

4. Particle Flow Algorithms
Need new approach
Particle Flow Algorithms
ECAL
HCAL γ π+ KL
The idea…
Charged particles Tracker
measured with the
Neutral particles Calorimeter
Particles in jets
Fraction of energy
Measured with
Resolution [σ2]
Charged
65 %
Tracker
Negligible
Photons
25 %
ECAL with 15%/√E
0.072 Ejet
Neutral Hadrons
10 %
ECAL + HCAL with 50%/√E
0.162 Ejet
Confusion
≤ Ejet
18%/√E
Required for 30%/√E
Requirements for detector system
→ Need excellent tracker and high B – field
→ Large RI of calorimeter
→ Calorimeter inside coil
→ Calorimeter as dense as possible (short X0, λI)
→ Calorimeter with extremely fine segmentation
→ Single particle energy resolution not critical
thin active medium
Opens up new
possibilities
RPC 2012

5. Digital Hadron Calorimeter (DHCAL) and Choice of active medium
Requirement of PFA hadron calorimeter
Extremely fine segmentation (~1x1cm2 readout cell)  simple hit counting provide sufficient energy resolution  1bit readout/Digital Hadron Calorimeter (DHCAL)
DHCAL  counting charged particles in hadronic showers (instead of measuring dE/dx in the active medium)  the active medium can have poor, or even no dE/dx resolution
Thin active medium, embedded readout
Cost …
What RPC can offer
Good position resolution  great for fine segmentation
Excellent efficiency for charged particles  great for counting charged particles
Large charge fluctuation for single MIP  no dE/dx resolution, poor particle counting on single pad  but this is exactly NOT needed for a DHCAL
Can be made very thin
Low cost
RPC is a perfect choice for a Digital Hadron Calorimeter!
RPC 2012

6. 1 m3 – Digital Hadron Calorimeter Physics Prototype
Description
Readout of 1 x 1 cm2 pads with one threshold (1-bit) → Digital Calorimeter
38 layers in DHCAL and 14 in Tail Catcher, each ~ 1 x 1 m2
Absorber: 18mm Fe + 2mm Cu in DHCAL, thicker Fe plates in Tail Catcher
Each layer with 3 RPCs, each 32 x 96 cm2
~480,000 readout channels
Purpose
Validate DHCAL concept
Gain experience running large RPC systems
Measure hadronic showers in great detail
Validate hadronic shower models (Geant4)
Status
Started construction in 2008
Completed in January 2011
Test beam runs started in Oct at Fermilab
More test beam runs in 2011
Analysis on-going
Critical for PFA validation
RPC 2012 6 6 6

7. RPC Construction RPC design RPC production Resistive paint spraying
Glass
Pad board
Frame
RPC design
2 – glass RPCs (chosen for construction)
1 – glass RPCs (developed at Argonne)
Gas gap size 1.1mm
Well arranged gas flow (by fishing line + sleeve spacer)
Total RPC thickness < 3.4mm
Dead area ~5% (frame ~3%, spacer ~2%)
RPC production
~114 for DHCAL + 42 for TCMT + spares  at the end, produced ~ 205 RPC’s
Resistive paint spraying
Uses two-component artist paint
Built dedicated spraying booth
Accept plates with value 1 – 5 MΩ/□
Achieved a yield of ~60% overall
Gap assembly
Developed precision cutting/gluing fixtures
Production rate 1RPC/day/tech
RPC 2012 7 7 7

8. Quality Assurance Pressure tests Gap size measurement HV tests
All RPC’s are tested with 0.3 inch of water pressure
Gap size measurement
Thickness of 1st batch RPC’s measured along the edges
(Gap size away from the edges is assured by spacers)
Gap sizes along edges vary within 0.1 mm
Corners typically thicker (up to 0.3mm, but limited effect)
HV tests
ALL RPC’s tested up to 7.0 kV before placing readout
board on top (nominal operating voltage is 6.3 kV)
Cosmic ray test
9 of the 1st batch RPC’s were tested on a cosmic ray test
stand for performance (efficiency, multiplicity, uniformity)
All other RPC’s were later tested in vertical position
with cosmic rays, after assembled into cassettes
Overall yield: ~95%
RPC 2012 8 8

9. Design consideration for readout system
System is built around a custom ASIC (DCAL chip)
Designed to handle huge number of channels + low channel density
(1cm2 pad, 1m2 planes, planes  480K channels)
64ch, handling 8x8 RPC active area
System tailored for test beam / prototype tests, NOT for real colliding beam detector
Facilitates all possible tests (test beam, cosmic ray test, noise runs, system diagnostics, etc)
Avoided cutting-edge technology and fancy functionality
Didn’t optimize for minimum power consumption, minimum data links, minimum thickness, etc.
Compromises aimed at proving detector concept  key in getting system up quickly and running reliably
Two basic running mode
External triggering mode  primary method for beam events, also used for cosmic ray test
20-stage pipeline  2μs 100ns clock cycle
Deadtimeless readout (within rate limit)
Self triggering mode primary method for noise runs, also used for cosmic ray, beam runs
Powerful running mode for monitoring RPC condition
Equally powerful for cosmic ray running and some beam running as well
RPC 2012

10. Readout system overview
VME Interface
Data Collectors – Need 10
Timing Module
Double Width
- 16 Outputs
Ext. Trig In
master IN
6U VME Crate
To PC
Data
Concentrator
Front End Board
with DCAL Chips
& Integrated DCON
Chambers – 3 per plane
Data Collectors – Need 10
VME Interface
master IN
Ext. Trig In
To PC
Timing Module
Double Width
- 16 Outputs
Communication Link
- 1 per Front-End Bd
6U VME Crate
Square Meter Plane
RPC 2012 10

11. The DCAL Chip Developed by Input Threshold Readout Versions
FNAL and Argonne
Input
64 channels
High gain (GEMs, micromegas…) with minimum threshold ~ 5 fC
Low gain (RPCs) with minimum thrshold ~ 30 fC
Threshold
Set by 8 – bit DAC (up to ~600 fC)
Common to 64 channels
Readout
Triggerless (noise measurements)
Triggered (cosmic, test beam)
Versions
DCAL I: initial round (analog circuitry not optimized)
DCAL II: some minor problems (used in vertical slice test)
DCAL III: no identified problems (final production: used in current test beam)
Production of DCAL III
11 wafers, 10,300 chips, fabricated, packaged, tested
Hits/100 tries
Threshold (DAC counts)
RPC 2012
Threshold (DAC counts) 11 11 11

12. FrontEnd/DCON board + Pad board
Resistive paint
Mylar
1.2mm gas gap
Aluminum foil
0.85mm glass
1.1mm glass
Signal pads HV
ASIC
Front-End PCB
Pad Board
Conductive Epoxy Glue
Communication Link
8.6 mm
Fishing line spacers
Build FE and pad boards separately to avoid blind and buried vias (cost and feasibility issue)
Each board contains 1536 channels and 24 ASICs
The data concentrator is implemented into the same board
Glue the two boards together with conductive epoxy
FE board need to pass computer test before gluing
Extensive tests (S-curves, noise rates…)
3 – 6 hours/board
Accepted boards with less than 4/1536 dead channels
RPC 2012 12

13. Timing and Trigger Module (TTM) Data Collector DCOL
Power supply systems
Low voltage system
High voltage system
Back end electronics
Timing and Trigger Module (TTM)
Data Collector DCOL
Gas System
RPC 2012 13

14. Cassette Assembly Assembly Cassette Testing
- FEB’s are placed onto RPC’s directly (no gluing), positioning and
contact is assured by pressure asserted from cassette
- Cassette is compressed horizontally with a set of 4 (Badminton) strings
- Strings are tensioned to ~20 lbs each, very few broken strings
Cassette Testing
- Cassettes were tested with CR
before shipping to test beam
38+14 cassettes assembled
RPC 2012 14

15. Digital calorimeter: will it work?
During the time we were busy with the DHCAL construction (2010), Richard Wigmans, who wrote a well-known book on calorimeter, claimed at a calorimeter conference:
“ ‘Digital’ calorimetry was tried and abandoned for good reason (1983) ”
Unfortunately, this was said too late – we were very close to finishing the DHCAL construction
Even more unfortunately, it only took us a short while in the test beam to prove him wrong!
RPC 2012

16. The DHCAL in the Test Beam
Fermilab test beam
run dates
DHCAL layers
RPC_TCMT layers
SC_TCMT layers
Total RPC layers
Total layers
Readout channels
10/14/2010 – 11/3/2010 38 16 54
350,
1/7/2011 – 1/10/2011 8 46
350,
1/11/2011 – 1/20/2011 4 42 50
387,
1/21/2011 – 2/4/2011 9 6 47 53
433,
2/5/2011 – 2/7/2011 13 51
470,016+0
4/6/2011 – 5/11/2011 14 52
479,232+0
5/26/2011 – 6/28/2011
11/2/2011 – 12/6/2011
460800
Run I
Run II
Run III
Run IV
Run V
More test beam in 2012, at CERN
~ 480K readout channels
~ 35M events
RPC 2012
DHCAL
Tail Catcher (TCMT)

17. RPC 2012 17

18. First beam: muons One muon Three muons Four muons A lot of muons
RPC 2012 18

19. Next: pions
60 GeV pions measured in DHCal
RPC 2012 19

20. And also positrons
32 GeV
25 GeV
20 GeV
16 GeV
RPC 2012
12 GeV 20

21. And occasionally, neutral hadron
RPC 2012 21

22. Summary
The construction of the DHCAL prototype (+Tail Catcher) is complete
Test beam at Fermilab started in October 2010
Had 5 successful test beam campaigns in 2010/11
DHCAL prototype (+Tail Catcher) works extremely well
A lot of good data collected, analysis is on-going
First look at data is very encouraging!
More test beam/more data is on the way
2012 : At CERN with Tungsten absorber
For more details of the DHCAL performance and preliminary physics results
Please see:
Next talk, by Jose Repond (Analysis of DHCAL Events)
Poster, by B. Bilki (Response of the DHCAL to Hadrons and Positrons)
RPC 2012 22