Calorimeters at CBM A. Ivashkin INR, Moscow

CBM setup: CBM includes two calorimeters: PSD – Projectile Spectator Detector (Very Forward Hadron Calorimeter) ECAL – Electromagnetic Calorimeter

Features of CBM calorimeters. ECAL: Two-arm “shashlik” type EM-calorimeter. PSD: Lead/Scintillator-tile sandwich hadron compensating calorimeter. Common features of calorimeters: Sampling calorimeters; Consist of Lead/ Plastic Scintillator sandwiches; The light readout from scintillators is provided by WLS-fibers; Transverse segmentation; Total weight is similar. Different features of calorimeters: Sampling is very different; PSD modules are a factor 20 heavier. The light readout from scintillators is quite different; Transverse segmentation is different; The photodetectors are different. 44 modules. ~22 tons. ~1000 modules. ~28 tons.

Common features of ECAL and PSD: because of general principles of calorimetry and particle detection.

Different features of ECAL and PSD: because of different types and tasks of calorimeters. Let’s start from PSD : Definition of detector: PSD is fully compensated (e/h=1) sampling Lead/Scintillator hadron calorimeter. Tasks of PSD: Characterization of the events (determination of the collision geometry): Impact parameter (centrality ); Reaction plane (event plane). Experimental task: Detection of projectile spectators (non-interacting fragments, protons and neutrons of beam ions).

a) Measurement of centrality Impact parameter b – two dimensional vector connecting the centers of ions. b can not be measured directly. Small b – central events; Large b – peripheral events. Experimental situation: centrality fraction for b by measuring the track multiplicity or energy of spectators in forward calorimeter. Track multiplicity PSD Energy

b) Reaction plane (direction of b) Ideal situation: Reaction plane crosses Z and b and points out the direction of b. Experimental situation: measurement of event plane: spectators (energy in PSD)

ECAL overview. Definition: ECAL is sampling “shashlik” type electromagnetic calorimeter. ECAL is intended for the detection of electrons and photons from the decays of neutral mesons. How electrons and photons are detected in calorimeter?

Photons in matter g e- e-* Ze e- g e-* Ze Rayleigh scattering Coherent, elastic scattering of the entire atom + atom  g + atom Compton scattering Incoherent scattering of electron from atom + e-bound  g + e-free Photoelectric effect absorption of photon and ejection of single atomic electron + atom  g + e-free + ion Pair production absorption of g in atom and emission of e+e- pair Needs Eg>2mec2 Ze e-* e- g Photons in matter Ze e- e-* g Bremsstrahlung Electrons create photons through:

Electromagnetic cascade (shower) in calorimeter. E(x) = E0 exp(-x/X0) Longitudinal profile of E-M shower. The development of em-showers, whether started by primary e or  is measured in X0. Radiation Length X0 of a medium is defined as: distance over which electron energy reduced to e times. Characterizes the shower depth. Critical Energy, when energy loss due to Brem and energy loss due to ionization are equal. Transverse shower dimension: multiple scattering of low energy e-: Moliere Radius: 90% of energy is inside of cylinder with radius of RM. 99% of energy is inside of cylinder with radius of 3RM.

Hadronic cascade (shower) in calorimeter. Hadronic shower consists of two parts, EM (e) and pure hadronic (h) π0   - EM shower, e-part Pure hadronic component, h-part: Charged hadrons; Nuclear excitation, spallation, fission; Heavy nuclear fragments; n can produce signals by elastic scattering in scintillator. Basically e-part is higher of h: e/h>1 ! Nuclear break-up (invisible) 42% Charged particle ionisation 43% Neutrons with TN ~ 1 MeV 12% Photons with E ~ 1 MeV 3%

Characterization of Hadron cascade Shower development is determined by the mean free path between inelastic collisions, the nuclear interaction length: λI = (NAσI / A)-1  A1/3 E(x) = E0 exp(-x/ λI) Comparison of X0 and λI. X0 is one order smaller! Nuclear interaction length λI characterizes both, longitudinal and transverse profile of hadronic shower. The lateral spread of a hadronic showers arises from the transverse energy of the secondary particles which is typically <pT>~ 350 MeV/c.

Properties of Hadronic Showers Hadronic Showers are: Much broader; Extend deeper in the calorimeter; Have significant event-by-event fluctuations. Individual Hadronic Showers in calorimeter.

Compensation ● As already stated, hadronic showers have electromagnetic component (e) strong interaction component (h) e/h ≠1 ● EM fraction increases with energy Non-linearities ● Event by Event fluctuations tend to be non-gaussian Affect the resolution ● What can be done ? Compensating calorimeters to achieve e/h=1: Reduce EM-Component or Boost hadronic response. Nuclear break-up (invisible) 42% Charged particle ionisation 43% Neutrons with TN ~ 1 MeV 12% Photons with Eg ~ 1 MeV 3% Normally, the compensation is provided by selecting an appropriate thickness of absorber and scintillator.

Calorimeter types Homogeneous Calorimeters have the best energy resolution, but the most expensive.

Sampling Calorimeters The smaller sampling fraction, the worse energy resolution because of smaller visible energy.

Energy Resolution (inaccuracy of energy measurement) Sampling fluctuations for sandwich calorimeters (!!). Statistical fluctuations eg number of photo-electrons or number of e-ion pairs. b) Electronic noise. Pile-up effects. Others Non-uniform response. Calibration precision. Dead material (cracks). Material upstream of the calorimeter. Lateral and longitudinal shower leakage. Parameterise resolution as a Statistical b noise c constant (where  denotes a quadratic sum) Resolution of E.-M. calorimeters: Resolution of hadron calorimeters:

Structure of ECAL (shashlik) module 4 cells 60x60 mm2. 124 lead/scintillator layers Lead – 1.0 mm Scintillator – 1.0 mm tiles. Length 22.1 X0. Light collection - 36 WLS fibers inside each cell. Expected resolution:

Technical drawing of ECAL module

Structure of PSD (Forward Hadron Calorimeter) Modular Lead/Scintillator sandwich compensating calorimeter. 44 modules, Each module 20x20cm2 , Length 5.6 λint Sampling ratio Pb:Scint=4:1, Weight – 22 Tons, Longitudinal segmentation, Central beam hole.

Structure of PSD module 23.06.2018 Structure of PSD module SiPMs and amplifiers. SiPM – silicon photomultiplier (avalanche photodiod) ~60 lead/scintillator sandwiches lead – 16 mm scintillator – 4 mm Light readout – WLS -fibers Expected resolution: A.Litvinenko VBLHEP JINR

Сonstruction of PSD module 60 lead/scintillator sandwiches 10 longitudinal sections 6 WLS-fiber/SiPMs per section 10 SiPMs/module Module size 20x20x160 cm3 Weight ~500 kg.

Calibration of the module by muons Spectra of energy depositions in each longitudinal section pedestals Muons after beam stopper have wide energy spectrum.

Energy deposition in 1, 1+2, 1+2+3,… 1+…+10 sections for protons at 2 GeV/c in 1 section in 2 sections in 3 sections in 4 sections in 5 sections in 6 sections in 7 sections in 8 sections At Ep=1.27 GeV practically there is no hadron shower but only proton ionization losses. In green: Hadron shower profile in 9 sections in module

Energy deposition in 1, 1+2, 1+2+3,… 1+…+10 sections for protons at 6 GeV/c in 1 section in 2 sections in 3 sections in 4 sections in 5 sections in 6 sections in 7 sections in 8 sections The contributions from proton ionization losses are visible in first 8 sections. Longitudinal profile. in 9 sections in module In green: Hadron shower profile

Energy resolution of calorimeter (test data at NA61/CERN) Protons 4-158 GeV/c Large size hadron calorimeter The constant term is still non-zero because of imperfect calibration and problem with readout electronics.

Forward lead calorimeter leads CBM forward! Thank You!