Digital Calorimetry for FCC Detectors Yasar Onel1, Burak Bilki1,2 1 University of Iowa, Iowa City, USA 2 Beykent University, Istanbul, Turkey

Trend in Calorimetry Imaging calorimetry Tower geometry ET Large number of calorimeter readout channels (~107) Option to minimize resolution on individual channels Particles in a jet are measured individually Tower geometry Energy is integrated over large volumes into single channels Readout typically with high resolution Individual particles in a hadronic jet not resolved ET

Particle Flow Algorithms (PFAs) 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 If goal is to achieve a resolution of 30%/√E → ≤ 0.242 Ejet Attempt to measure the energy/momentum of each particle with the detector subsystem providing the best resolution Maximum exploitation of precise tracking measurement Large radius and length to separate the particles Large magnetic field for high precision momentum measurement “no” material in front of calorimeters (stay inside coil) Small Moliere radius of calorimeters to minimize shower overlap High granularity of calorimeters to separate overlapping showers Emphasis on tracking capabilities of calorimeters 3 High lateral and longitudinal segmentation

Digital Hadron Calorimeter Development of the Digital Hadron Calorimeter Develop a tracking Hadron Calorimeter Implement digital readout (1-bit) to maximize the number of readout channels Place the front-end electronics in the detector The active medium should: Be planar and scalable to large sizes Not necessarily be proportional (only yes/no for the traversing particle) Be easy to construct, robust, reliable, easy to operate, … Resistive Plate Chambers

The Digital Hadron Calorimeter (DHCAL) I Active element Thin Resistive Plate Chambers (RPCs) Glass as resistive plates Single 1.15 mm thick gas gap Readout 1 x 1 cm2 pads 1-bit per pad/channel → digital readout 100-ns level time-stamping Calorimeter 54 active layers 1 x 1 m2 planes with each 9,216 readout channels 3 RPCs (32 x 96 cm2) per plane Absorber Either Steel or Tungsten 9

The Digital Hadron Calorimeter (DHCAL) II DHCAL = First large scale calorimeter prototype with Embedded front-end electronics Digital (= 1 – bit) readout Pad readout of RPCs Extremely fine segmentation with 1 x 1 cm2 pads DHCAL = World record channel count for calorimetry World record channel count for RPC-based systems ~500,000 readout channels DHCAL construction Started in 2008 Completed in 2010 Test beam activities In the Fermilab testbeam (Steel absorber / No absorbers) In the CERN testbeams (Tungsten absorber) This is only a prototype For a colliding beam detector multiply by ×100 10

Resistive Plate Chambers (RPCs) Gas: Tetrafluorethane (R134A) : Isobutane : Sulfurhexafluoride (SF6) with the following ratios 94.5 : 5.0 : 0.5 High Voltage: 6.3 kV (nominal) Average efficiency: 96 % Average pad multiplicity: 1.6 Gap size and gas flow uniformity is maintained via fishing line channels 11

Resistive Plate Chambers (RPCs) All geometries probed Default design (32 cm x 96 cm) First generation RPCs (20 cm x 20 cm) 11 One-glass RPCs (32 cm x 48 cm)

DHCAL Construction Stages of Construction RPC Painting RPC Construction Front-end electronics Cassette Assembly Back-end electronics Gas System

RPC Painting Challenges/Requirements Provide uniform surface resistivity 1-5(10) MΩ/☐ on thin (thick) glass high R reduces rate capability low R increases multiplicity Maximize coverage of paint (HV) across RPC Produce ~ 500 sheets The Paint 2-component artist (airbrush) paint needs to be mixed and sprayed (paint booth and spray gun) Paint Booth: Large structure to exhaust fumes and instrument step motors for gun control Spray Gun: Commercial paint gun with fine control and rugged construction (easy to clean) Uses nitrogen (dry gas) to carry paint Production Procedure Mix paint Clean glass Mask rims Operate booth  8 sheets/day Clean tools

RPC Assembly and Quality Control Cut frames (sets gap size) Assemble and glue chambers 1 RPC/day/tech RPC Quality Control and Validation Pressure tests – chambers are sealed Gap size measurement – maintain uniform electric field in gas gap HV tests – tests connections in cassette environment Cosmic Ray Test Stand (9 RPCs stacked vert.) validate production test front-end electronics noise measurements HV scans  multiplicity and efficiency > 95% of the RPCs pass the quality control tests

Electronics Overview

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

The DCAL Chip Developed by Input Threshold Readout Versions Threshold (DAC counts) Hits/100 tries The DCAL Chip Developed by FNAL and Argonne Input 64 channels High gain (GEMs, micromegas…) with minimum threshold ~ 5 fC Low gain (RPCs) with minimum threshold ~ 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) Production of DCAL III 11 wafers, 10,300 chips, fabricated, packaged, tested Threshold (DAC counts) 14

Front-end Electronics and Gluing Front-end board (FEB) assembly Build electronics and pad boards separately to avoid blind and buried vias Each FEB contains 1536 channels A data concentrator is implemented Test electronics (noise rates, threshold curves,…) Glue Robot Glue is a conductive epoxy Robot precisely places glue dots 0.001” thick plastic film used as spacers dried in oven over night 10 boards/day >300 FEB fabricated

Cassette Design structurally hold RPCs within the absorber structure large copper and steel sheets 3 RPCs for each cassette 6 FEBs readout RPCs maintain FEB contact with RPC (badminton strings cool electronics (Cu)

Cassette Assembly Assembly Cassette Testing - Cassette is compressed horizontally with a set of 4 (Badminton) strings - Strings are tensioned to ~20 lbs each - ~45 minutes/cassette Cassette Testing - Cassettes are tested in the cosmic ray test stand

Peripheral Systems Gas System - HV mixer and bubbler racks 1 channel feeds 6 RPCs leaky layers have individual supply Wiener power supply with ISEG HV modules. Custom slow control software Low voltage distribution for FEBs Wiener power supply Back-end Electronics (2 VME crates) 2 Trigger and Timing Modules 20+ Data Collectors bubbler mixer TTM DCOL

DHCAL in Test Beams CERN May 12 June 12 July 12 Nov 12 > 40M events FNAL Oct 10 Jan 11 Apr 11 (w/ CALICE SiW ECAL) June 11 > 20M events FNAL Nov 11 ~ 2M events

Event Displays: Muons

Event Displays: Positrons 32 GeV 20 GeV 16 GeV 12 GeV

Event Displays: Pions 8 GeV 60 GeV 10 GeV

Event Displays: Protons 120 GeV

3D Event Display w/SiW ECAL 40 GeV π+

A Few Test Results 0.04 – 2 cc/min/RPC  1.2 – 60 vol/day JINST 5, 02007, 2010 Too many to list. Please see references in the last slide.

Recent R&D: 1-glass RPCs Offers many advantages Pad multiplicity close to one → easier to calibrate Better position resolution → if smaller pads are desired Thinner → t = tchamber + treadout = 2.4 + ~1.5 mm → saves on cost Higher rate capability → roughly a factor of 2 Status Built several large chambers Tests with cosmic rays very successful → chambers ran for months without problems Both efficiency and pad multiplicity look good Good performance in the test beam 65 Efficiency Pad multiplicity cm JINST 5, 05003, 2015

Rate capability of RPCs Measurements of efficiency With 120 GeV protons In Fermilab test beam Rate limitation NOT a dead time But a loss of efficiency Theoretical curves Excellent description of effect Rate capability depends Bulk resistivity Rbulk of resistive plates (Resistivity of resistive coat) 66 JINST 4 P06003, 2009

There is a gap between 10-9 and 10-3 Here is the problem There is a gap between 10-9 and 10-3 67 C. Pecharromán X. Workshop on RPC and related Detectors (Darmstadt)

Development of semi-conductive glass Co-operation with COE college (Iowa) and University of Iowa World leaders in glass studies and development Vanadium based glass Resistivity tunable! Procedure aimed at industrial manufacture (not expensive) 75 See M. Affatigato’s talk. International Journal Of Applied Glass Science, 6, 26, 2015

Development of semi-conductive glass 75 Soda-lime Soda-lime Schott SchottGlassTechnologiesInc., 400 York Ave, Duryea, PA18642, U.S.A. JINST 10 P10037, 2015

(trigger-less acquisition) High Voltage Distribution System Generally Any large scale system will need to distribute power in a safe and cost-effective way HV needs RPCs need of the order of 6 – 7 kV Specification of distribution system Turn on/off individual channels Tune HV value within restricted range (few 100 V) Monitor voltage and current of each channel Status Iowa started development First test with RPCs encouraging Work stopped due to lack of funding 77 Size of noise file (trigger-less acquisition)

Gas Recycling System DHCAL’s preferred gas Development of ‘Zero Pressure Containment’ System Work done by University of Iowa/ANL Status First parts assembled… Gas Fraction [%] Global warming potential (100 years, CO2 = 1) Fraction * GWP Freon R134a 94.5 1430 1351 Isobutane 5.0 3 0.15 SF6 0.5 22,800 114 Recycling mandatory for larger RPC systems 78 Work stopped due to lack of funding

Summary The Digital Hadron Calorimeter concept is validated. Extensive and unique experience with RPCs: We operated an RPC-based calorimeter for several years Many R&D issues ahead for future systems, mostly under control but all stopped due to lack of funds

References B. Bilki, et.al., Calibration of a digital hadron calorimeter with muons, JINST 3 , P05001, 2008. B. Bilki, et.al., Measurement of positron showers with a digital hadron calorimeter, JINST 4, P04006, 2009. B. Bilki, et.al., Measurement of the rate capability of Resistive Plate Chambers, JINST 4, P06003, 2009. B. Bilki, et.al., Hadron showers in a digital hadron calorimeter, JINST 4, P10008, 2009. Q. Zhang, et.al., Environmental dependence of the performance of resistive plate chambers, JINST 5, P02007, 2010. J. Repond, Analysis of DHCAL Muon Data, CALICE Analysis Notes, CAN-030, CAN-030A, 2011. L. Xia, CALICE DHCAL Noise Analysis, CALICE Analysis Note, CAN-031, 2011. B. Bilki, DHCAL Response to Positrons and Pions , CALICE Analysis Note, CAN-032, 2011. J. Repond, Analysis of Tungsten-DHCAL Data from the CERN Test Beam, CALICE Analysis Note, CAN-039, 2012. B. Bilki, The DHCAL Results from Fermilab Beam Tests: Calibration, CALICE Analysis Note, CAN-042, 2013. B. Bilki, et.al., Tests of a novel design of Resistive Plate Chambers, JINST 10, P05003, 2015. M. Affatigato, et.al., Measurements of the rate capability of various Resistive Plate Chambers, JINST 10, P10037, 2015. N. Johnson, et.al., Electronically Conductive Vanadate Glasses for Resistive Plate Chamber Particle Detectors, International Journal Of Applied Glass Science, 6, 26, 2015. B. Freund, et.al., DHCAL with minimal absorber: measurements with positrons, JINST 11, P05008, 2016. C. Adams, et.al., Design, construction and commissioning of the Digital Hadron Calorimeter — DHCAL, JINST 11, P07007, 2016.