1. The DHCAL – An overview José Repond Argonne National Laboratory
Presented by
Katja Krüger
Deutsches Elektronen Synchrotron
CALICE Meeting
Santander, Spain
June 1, 2016
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2. The DHCAL Description 54 active layers
Resistive Plate Chambers with 1 x 1 cm2 pads
→ ~500,000 readout channels
Main stack and tail catcher (TCMT)
Electronic readout
1 – bit (digital)
Digitization embedded into calorimeter
Tests at FNAL
with Iron absorber in 2010 – 2011
without absorber plates 2011
Tests at CERN
with Tungsten absorber 2012
1st time in calorimetry

3. Current situation
Funding from DOE-HEP completely stopped on September 30, 2014
Directed to cease any activity immediately

4. The Electron – Ion Colliders EICs
eRHIC
250 GeV/nucleon protons/ions
1.3 – 21.2 GeV electrons
√sep= 36 – 146 GeV
Luminosity ~ 4 x 1033 cm-2s-1
JLEIC
GeV/nucleon protons/ions
3 – 12 GeV electrons
√sep= 10 – 69 GeV
Luminosity ~ 5.6 x 1033 cm-2s-1
For comparison HERA
√sep= 318 GeV
Luminosity (peak) ~ 1032 cm-2s-1

5. The Electron – Ion Collider or EIC
Nuclear Science Advisory Committee (NSAC) Long Range Plan
In this context, submission of proposals for support for DHCAL studies
A) Laboratory Directed Research and Development (LDRD)
→ as part of larger proposal to develop a detector concept for the EIC
B) EIC detector R&D
→ specifically for DHCAL studies
Recommendation III
“We recommend a high-energy high-luminosity polarized EIC as the highest priority for new facility construction following the completion of FRIB.”
Initiative for Detector and Accelerator R&D
“We recommend vigorous detector and accelerator R&D in support of the neutrinoless double beta decay program and the EIC.”

6. Proposed studies for the EIC I
Long-term tests of 1-glass RPCs
Novel RPC design: readout pads in gas volume
Advantages: thinner, pad multiplicity constant and around 1 (easy to calibrate!),
higher rate capability
Design validated: JINST 10 (2015) P05003
Chemical stability of anode plane in gas volume?
Long-term tests with cosmic rays needed
Long-tem tests of fast RPCs
Use of semi-conductive glass as resistive plates
Rate capability improved by 2 orders of magnitude: JINST 10 (2015) P10037
Chemical stability of glass plates over time, with prolonged periods of HV?
Long-term tests with cosmic rays needed

7. Proposed studies for the EIC II
3. Development of a gas recycling system
Typical RPC avalanche gas harmful for the environment (green house gas)
Challenge: capture gas without changing the gas pressure in the chambers
Designed system which captures exhaust gas: ‘Zero Pressure Containment’ system
Assembled system and tested successfully
Implementation of filtering system and test with RPCs
4. Development of a High Voltage distribution system
An RPC based HCAL needs approximately 3,000 chambers with individual HV
Requires a HV distribution system
Each channel: option to turn on/off, monitor current and voltage,
adjust voltage to within ±100 V
First prototype designed, built (by University of Iowa) and tested successfully
1 channel, no monitoring, no voltage adjustment yet
Implement all features and test

8. The Min-DHCAL Special tests Fermilab test beam Analysis
Use of DHCAL layers (0.29 X0)
No absorber plates between layers
50 layers in total
Fermilab test beam
Mixture of e+, μ+, π+
Momentum range of 1 – 10 GeV
Data with extremely fine spatial segmentation
Analysis
Positron data published
Pion data being analyzed
Analysis performed by Benjamin Freund (McGill)
MC samples by Burak Bilki (Iowa)
8 GeV e+ shower in the Min-DHCAL

9. Test Beam and Data Samples
Min-DHCAL placed in secondary beam
at Fermilab’s FTBF
Secondary beam mixture of electrons,
muons, pions in 1 – 66 GeV/c momentum
range
Particles arrive every minute in 4 s spills
Cerenkov counter to tag electrons
Data collected in November 2011
Momentum range limited to 1 – 10 GeV/c (due to shallow depth of Min-DHCAL)

10. Analysis of Min-DHCAL Events
Quality cuts
Reject multiple particles, cosmic rays, fake triggers, out of time events…
Equalization of the response of RPCs
Use through-going muons to equalize response of RPC i
(εi = efficiency, μi = average pad multiplicity of RPC i)
MC Simulation of the set-up
GEANT4 and digitizer (RPC_sim)
Digitizer tuned to muon and e+ data
Complete study of experimental systematic errors
Equalization (dominant), rate limitation,
contamination from other particles (negligible), noise hits (negligible)
Systematic errors of the simulation
No meaningful systematic error for e+ simulation (used in the tuning process)
Systematic error of π+ simulation calculated from the deviations between data
and simulation observed with e+

11. Selection of Min-DHCAL Positron Events
Entries = percentage of surviving events
Data
Momentum [GeV/c] 1 2 3 4 6 8 10
Timing cuts
99.9
99.8
99.95
99.96
Requirements on first layer
88.5
87.0
80.3
88.1
86.6
88.2
At least 6 active layers
86.4
80.0
79.8
88.0
86.5
Čerenkov signal
60.3
31.7
40.0
30.7
53.9
41.7
33.0
Simulation
100.0
98.3
97.9
97.6
97.2
97.1
96.8
Cleaning cuts
PID provided by Cerenkov
(not simulated)
Only 2 – 3 % of events rejected

12. Min-DHCAL Positron Results I
Published in JINST (2016) 11 P05008
Main messages from paper
Default simulation of electromagnetic interaction not adequate
Need detailed simulation of electromagnetic interactions (Option 3 or _EMY)
High precision data → Well reproduced by simulation
Response in number of hits
Non-linear (saturation)
Fit to power law
m = 0.76 ± 0.02 (m = 1 would be perfectly linear)
Invert power law to reconstruct energies

13. Min-DHCAL Positron Results II
Energy spectra
Fit to Gaussian within ± 2σ
No evidence of contamination
from muons/pions
Response
Linear by construction
Resolution
Well reproduced by _EMY
Significantly worse with default simulation
Fit to standard formula
c [%]
α[%]
Data
6.3±0.2
14.3±0.4
FTFP_BERT_EMY
6.2±0.1
13.2±0.2

14. Min-DHCAL Positron Results III
Precision shower shapes
Longitudinal shape
Fit to Gamma distribution
Small leakage observed
Radial shower shape
Covering 6 orders of magnitude in hit density
Hit density
Distribution of number of neighbors to a given hit
Some differences between data and simulation

15. Selection of Min-DHCAL Pion Events
Cleaning cuts
Positrons rejected by Cerenkov (not simulated)
Muons rejected by requesting interaction
Rejects positrons and minimizes leakage
Final efficiency between 8 and 18%
Positrons in data of course rejected by Cerenkov (not simulated)
Muons efficiently rejected

16. GEANT4 Physics Lists Hadronic Shower Models
Physics list combine various hadronic shower models
Models cover different energy ranges
Linear transition between ranges

17. Min-DHCAL Pion Results I
These results are not yet preliminary
Distributions of number of hits
Not well reproduced by simulation
Fit to the Novosibirsk function
(works well for data, not so much for simulation)
Response in number of hits
In average more hits (~15%) in simulation
Discontinuities for some physics lists
Very linear response
Fit to power law
m = 1.00 ± 0.04 (m = 1 is perfectly linear)
Invert power law to reconstruct energies

18. Min-DHCAL Pion Results II
Energy spectra
Distinct differences for different physics lists
Simulated spectra different from data

19. Min-DHCAL Pion Results III
Radial shower shape
High precision data
Results based on different physics lists differ from each other
None of the simulations agree with the data

20. Min-DHCAL Pion Results IV
Longitudinal shower shape
High precision data
Results based on different physics lists more or less agree with each other
None of the simulations agree with the data
Simulated showers deeper into the calorimeter
(remember the longitudinal shower shapes for positrons were well simulated!)
Notice the agreement between data and simulation before the shower start

21. Min-DHCAL Pion Results V
Distribution of density of hits
High precision data
Results based on different physics lists more or less agree with each other
None of the simulations agree with the data (but not too bad)

22. The Fe-DHCAL Data set Collected at Fermilab Covering 2 – 60 GeV/c
About 13M events
Both main stack and TCMT with RPCs
Data analysis
Performed by Coralie Neubüser (Hamburg)
Tuning digitizer
Different operating conditions from Min-DHCAL
6 Parameters to tune
Spread of charge on anode plane: σ1, σ2, and relative weight R
Scale of charge distribution: Q0
Threshold for hit definition: T
Radius of inefficiency for additional avalanches: dcut

23. Tuning of Fe-DHCAL Digitizer
Data sets
10 GeV muons
10 and 20 GeV positrons
Tuning
Quite good agreement already
Further improvements to come

24. Fe-DHCAL Positron Results
Distribution of hits
Nice agreement at low energies
Increasing difference at higher energies
Response in number of hits
Very non-linear (as expected)
Simulation significantly fewer hits at high energies
Further improvements to the simulation to come

25. Summary Overall situation
Not easy to make strident progress without support from the funding agencies
Possibility to revive DHCAL effort with support from Nuclear Physics (EIC)
Min-DHCAL positron paper
High precision measurement of electromagnetic showers
Results published in JINST (2016) 11 P05008
Min-DHCAL pion analysis
Analysis well advanced
Paper draft in preparation
Fe-DHCAL analysis
Tuning of digitizer almost complete
Results soon