Hadronic Calorimetry Urs Langenegger (Paul Scherrer Institute) Fall 2015 ALEPH Hadronic showers Compensation Neutron detection
Hadronic showers simulations 50 GeV proton into segmented iron (simulation) 2
Hadronic showers Hadronic interactions: h + N π, K, p, n,... hard soft Consequences electromagnetic component roughly 1/3 of pions are π 0 π 0 γγ, e + e γ η γγ hadronic cascade weak hadron decays π µν invisible component K L neutrons Large fluctuations spatial development em component energy loss 3 pions into copper (4 different events )
Measurement of hadronic showers nuclear interaction length e.m. radiation length hadronic calorimeters are more massive and larger than electromagnetic calorimeters Hadronic calorimeters are sampling ( 10λ for decent measurement) Hadronic calorimeter: E = E ch + E em + E n + E nucl + E lost E ch charged pions, kaons, protons E em electromagnetic component (π 0, η) E n low-energetic neutrons E nucl energy loss through nuclear dissociation energy loss through neutrinos and muons E lost γ 100 GeV proton in lead n e + e γγ Each component with its own sampling fraction hadr. sampling: E vis = he ch + ee em + ne n + NE nucl depending on energy with different contribution 4 e N(n, γ) π
Time structure of showers SPACAL measurement Em and hadronic showers scintilating fibers for fast measurements Electrons no tails Hadrons exponential tail with time constant 10 ns neutrons 5
ECAL vs. HCAL at the LHC 6
CMS hadron calorimeter Barrel HB 5.82λ i / sin θ 40 mm steel, 8 50.5 mm + 6 56.5 mm brass (CuZnX), 75 mm steel scintillator plates η φ = 0.087 0.087 (9 mm, 3.7 mm,... 3.7 mm, 9 mm) Endcap HE 10λ i (incl ECAL) 79 mm brass, 3.7 mm sci scintillator plates η φ = 0.17 0.17 Tail catcher HO 1.4λ i / sin θ 195 mm iron scintillator plates η φ = 0.087 0.087 (ca 35 cm) 7
Hadronic shower: longitudinal shape Longitudinal shape for various energies roughly similar 8
Hadronic shower: transverse shape Transverse hadronic scale: Λ QCD 300 MeV Fermi momentum of quarks in hadrons 2 components: core and halo r M from π 0 mesons λ i from hadronic interactions transverse shower shape dependent on shower depth core: 95% with r < λ i High granularity (SPACAL) precise measurement of core improved position resolution 9
Hadronic vs. e.m. component Differences of calorimeter signal R on shower components electromagnetic vs. hadronic fractions f e and f h with different efficiencies ε e, ε h measurable: R = R e + R h = ε e f e E + ε h f h E = ε e (f e + ε h εe f h )E Ratio of measurable signal for e.m. and hadronic showers E h E e = 1 (1 ε h ε e )f h because (f h + f e = 1) The goal would be ε e /ε h = 1 normally not fulfilled (most often ε e /ε h > 1) Remarks calorimeter signal not linear because E e /E π depends on energy (normally) energy resolution σ(e) E = a E + b ε e 1 ε h 10
Compensation? Variable detector response to hadronic showers depends strongly on e.m. component Type A only photons (π 0 ) no neutrons/hadrons Type B hadrons and neutrons (nearly) no photons For best resolution same response to Type A And B compensation 11
Compensation! For a compensating calorimeter e/h 1 Increase h uranium absorber n, γ fraction increased through (induced) fission requires high n efficiency (scintillators!) Decrease e combination of absorber with high Z detector with small Z inefficiency for low-energetic γ Shower weighing in software e.m. shower in front part scaling of this energy 12
Compensating calorimeters CDHS (CERN-Dortmund-Heidelberg-Saclay) calorimeter finely grained Fe/Scint calorimeter good longitudinal shower reconstruction interpretation of plot electrons do follow E 1/2 (cf. HELIOS e ) raw hadron resolution does not follow E 1/2 s/w weighting improves resolution Hadrons Electrons 13
Calorimeters of various experiments Even at same collider mixture of sampling homogeneous calorimeters: Experiment e.m. calorimeter had. calorimeter CMS PbWO 4 crystals brass/scintillator ATLAS Pb/lAr Fe/scintillator and Cu/lAr BABAR (and Belle) CsI(Tl) crystals - H1 Pb/lAr Pb/lAr ZEUS U/scintillator U/scintillator SLD Pb/lAr Pb/lAr + Fe/Gas ALEPH Pb/Al tubes Pb/plastic tubes DELPHI Pb/TPC Fe/plastic tubes L3 BGO crystals U/brass tubes OPAL Pb glass Fe/proportional chambers 14
Detection of neutrons Issues with neutron detection no electric charge only strong/nuclear force Interactions of neutrons E n < 20 MeV n + 6 Li α + 3 He n + 10 B α + 7 Li n + 3 He p + 3 H E n < 1 GeV n + p n + p neutron-induced fission E n 1 40 ev hadronic cascades E n > 1 GeV Detection of secondary charged particles gas detectors scintillators semiconductor detectors 15
Neutron detectors Gaseous detectors large de/dx of slow protons gas pressure 8-10 bar, tube diameter 2-5 cm relatively bad position and time resolution rates limited to 10 khz/ cm 2 Improvements MWPC (multi-wire proportional chamber) MSGC (micro-strip gas chamber) Scintillation detectors light scintillator material with n-converter photo-detector e.g. CCD or MCP rate limited n 1 H Kathode Anode 3 He Abschirmung Detektor semiconductor detectors semiconductor detectors coated with n-converter: 6 Li or 156 Gd very good position resolution Optik n +HV Szintillator Spiegel 16