Maria Laach Summer School Maria Laach Abbey 9

Maria Laach Summer School Maria Laach Abbey 9 -18 September, 2015 Principles of Detection for Particle Physics Part 3: High-Energy Calorimetry Bruce A. Schumm Santa Cruz Institute for Particle Physics and the University of California, Santa Cruz

High-Energy Calorimetry Introduction Two basic types of calorimetry • Electromagnetic • Make use of compact, collimated showers induced by pair-production and brehmstrahlung • Relatively well-understood (EGS shower MC) and precise • For incident electrons, positrons, and photons (but remember: 0 ) • Hadronic • For hadronic particles, of course • I longer that LRAD, so much less compact (and less precise) • More and more, integrated into “energy flow” approach to measure jet, rather than individual particle, properties. Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 2

Electromagnetic Shower Development Incoming photon pair-converts; daughter e+e- pair radiate (brehm), leading to more pair-production Shower generated almost solely by pairs production and brehm ~ LRAD Power-law growth stops as particle energies degrade to critical energy Ec PDG Incoming electron starts process with brehm, but same overall shower characteristics. “Electromagnetic Shower” Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 3

Transverse Shower Development (Moliere Radius) Substance LRAD (cm) RM (cm) Iron 1. 76 Copper 1. 43 1. 44 Lead 0. 56 1. 6 Tungsten 0. 35 0. 93 Crystal Scintillators 1 -2. 5 2 -4 Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 4

Shower Monte Carlos Electromagnetic • EGS (electron gamma shower) Monte Carlo • Developed at SLAC • Maintained at KEK and/or (? ) Canada’s National Research Council • http: //rcwww. kek. jp/research/egs/ • http: //www. nrc-cnrc. gc. ca/eng/solutions/advisory/egsnrc_index. html Hadronic • • GEANT (Geometry And Tracking) MC Developed at CERN Maintained by international GEANT collaboration http: //www. geant 4. org/geant 4/ Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 5

Electromagnetic Calorimetry: Types • Total absorption, for which the entire shower is absorbed within the active medium • Doped “glasses” (transparent materials with significant fractions of heavy elements • Lead glass, Cs. I, lead tungstate (Pb. WO 4), … • Sampling, for which the shower is largely absorbed in passive radiator material, but the shower is periodically “sampled” with thin layers of active medium N. B. : All hadronic calorimeters are sampling calorimeters ( I >> LRAD) • Lead/Liquid Argon, Iron/Scintillator, Si/W, … Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 6

Total Absorption Calorimetry Figure of merit: light output Material Deposited Energy per Photon Plastic Scintillator ~100 e. V Crystal Scintillator (Na. I, Pb. WO 4) ~25 e. V Crystalline Silicon 3. 5 e. V 2. 2 x 23 cm CMS Lead Tungstate crystal with readout (avalanche photodiode detectors) Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 7

Electromagnetic Calorimetry: Stochastic Term Bruce Schumm Calorimeter Type b ( Ge. V) for EM Resolution Na. I . 027 Pb. WO 4 . 035 Pb Glass . 05 Pb/Liquid Argon . 075 Pb/Scintillator . 09 Iron/Gas MWPC . 23 Maria Laach 2015, Part 3: High Energy Calorimetry 8

EM Calorimetry: Energy Resolution Full Picture Generally, energy resolution of calorimeters parametrized as a: Electronic noise. Fixed size; relative contribution falls linearly with calorimeter signal (i. e. , with energy) b: Stochastic term. See last slide… c: Systematic effects, such as light collection uniformity, shower leakage, crystal uniformity (resolution won’t go to 0 as E ). D. V. Alexsandrov et al. , A High Resolution Electromagnetic Calorimeter Based on Lead-Tungstate Crystals, Nucl. Inst. And Meth. 550, 169 (2005). a = 0. 013 Ge. V b = 0. 036 Ge. V c = 1. 1% Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 9

The CMS Detector (Slice) Last component to discuss: hadronic calorimetry… Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 10

Hadronic Calorimetry: Shower Fluctuations Question: How accurately can we measure the energy of, say, a +? Consider two scenarios for the first scatter, each resulting in a dominant “leading particle”: + N Upper scenario: K 0 p • Energy remains hadronic • Response is lower (“h”) due to energy lost in breaking up nuclei … + + 0 N … K + p Lower scenario: • Energy becomes primarily electromagnetic • Response is higher (“e”) Thus, the single-particle resolution of the hadronic calorimeter is tied to the intrinsic fluctuations of the hadronic shower Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 11

Hadronic Calorimetry: Compensation R. Wigmans, High Resolution Hadron Calorimetry, Nucl. Instr. & Meth. A 265, 273 (1988) Idea: Compensation • Heavy elements that produce neutrons upon fragmentation • Active materials with large response to neutron absorption • Need not be exotic – just need to pay attention (iron/scintillator in right proportion, for example) • ZEUS lead/scintillating-fiber “SPACAL” achieved 30%/ E, approaching the performance of some EM calorimeters. Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 12

The New(ish) Development: Energy Flow What do you really want to do with your calorimeter? For example… m = 91 Ge. V/c 2 Z 0 m = 80 Ge. V/c 2 W For W/Z separation (International Linear Collier Physics), need to optimize jet energy resolution, not individual particle resolution. What’s in a jet? Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 13

What’s in a Jet? Average content of hadronic shower (according to GEANT) Shower Component Particle Species Charged particles , K , p , e , … Fraction of Energy Ideal Detector System Energy Resolution 64% Tracking System O(10 -3) Photons 0 25% EM Calorimeter (5 -10)%/ E Neutral hadrons K 0, n, … 11% Hadronic Calorimeter ~50%/ E Goal: measure each object with subsystem best tailored to it (pions not measured in hadronic calorimeter!) “Energy Flow Calorimetry” Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 14

Energy Flow Calorimetry 1. Identify EMCal deposits associated with photons; measure in EM calorimeter and remove deposits from collection 2. Reconstruct charge tracks and measure energy of each track. Identify associated calorimeter deposits (both EM and Hadronic) and remove 3. Remaining deposits are from neutral hadrons. Assemble deposits into objects (particle candidates) and measure energy In principle, resulting jet is well measured. For example, consider measuring the dijet mass for the following ILC reaction: e+e- q qbar at Ecm = 200 Ge. V Bruce Schumm Approach Resolution ( Mjj) Ideal Compensation 9. 2 Ge. V/c 2 Ideal Energy Flow 2. 6 Ge. V/c 2 Maria Laach 2015, Part 3: High Energy Calorimetry 15

Calorimeter Design Basic Compensation • Match absorber and active layers so that • Nuclear fragments from absorber must excite active layers to an extent that brings hadronic response up to that of EM Cal. Energy Flow • Hadronic Calorimeter resolution does not play critical role • Instead, must minimize “confusion terms” that mix objects and lead to missing or redundant energy measurements • Highly pixelated hadronic calorimetry “digital” calorimeter of 1 cm 2 pixels, each of which reports out simple “hit/no-hit”? Subject of substantial R&D, especially in context of proposed ILC Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 16

Wrap-up We’ve just scratched the surface and laid out general principles. Each of the three topics could be the subject of a week’s lecture A significant amount of R&D is underway • Active/monolithic pixel sensors • Precise (high resolution, low-mass) silicon strip tracking • Digital calorimetry • Advanced compensating calorimeters • Novel sensor designs (edgeless, HV CMOS, …) • Application-optimized electronic readout • Radiation hardness • Applications • Gaseous tracking and TPCs… A rewarding area of inquiry! Bruce Schumm Maria Laach 2015, Part 3: High Energy Calorimetry 17