Calorimetry and Cherenkov Radiation Hadron cascades Aldo PENZO (INFN-Trieste) EM showers Cherenkov radiation red =e±/γ, green = μ±, blue = hadrons RICH2007 20 Oct 2007 Trieste 

EM showers vs Hadron cascades g e+ e- po p- p+ p Hadron cascades copiously produce po ‘s, which generate gg pairs, originating EM showers EM showers contain essentially e± and g’s Hadron cascades develop 2 components (hard and EM) evolving with different scales: - po → gg is ”one-way” process - po production stops when the energy available drops below pion production threshold

Development of hadron cascades X0 lI X0, λI [cm] Z Fluctuations due to po production 2 scales for hadronic cascade development: - lI for strong interactions - Xo for EM interactions

Hadron Cascade Composition Primary Energy (GeV) Fraction of Cascade Energy (%) EM Shower Particles Non-EM Charged Particles Bind Energy + Nucl. Fragm. 20 40 60 80 1 10 100 Protons Pions EM energy ~ 50% Visible non-EM energy (dE/dX) ~ 25% Invisible non-EM energy (nuclear breakup) ~25% Invisible escape energy (neutrinos) ~ 1% (Ranft ´72, Baroncelli ´74, Gabriel ´76) Barion number conservation implies EM fraction lower in proton - induced showers than in pion - induced ones

Predominance of SOFT particles (< 4 MeV) (< 1 MeV) (> 20 MeV) 10 GeV electrons Neutron yields Non-EM components in Lead: - Ionizing particles ~ 56% ~ 70% protons ~ 100 MeV (spallation) - Neutrons ~ 10% (37 neutrons/GeV) (Evaporation neutrons ~ 3 MeV) - Invisible 34% In Lead ~ 40% energy deposited by e± with E < 1 MeV

Hadronic vs EM response Not all hadrons’ energy is “visible”: Lost nuclear binding energy neutrino energy Slow neutrons, … Hadron calorimeters usually are, to various degrees, non – compensating: e/h = 1 /

“Compensation” virtues High precision hadron calorimeters should have equal response to electromagnetic and strongly interacting particles (compensation condition e/h =1) in showers generated by incoming hadrons, in order to achieve: linear response in energy to hadrons, gaussian energy distribution for mono-energetic hadrons, relative energy resolution (dE/E), improving as sqrt(1/E). This is of prime relevance for the measurement of jets, involving various particles of different energies, with a substantial fraction of neutral pions… However: not always virtue really pays… Any benefits with non-compensating calorimeters?

Cherenkov Calorimeters b > 1/n qC cos qC = 1/(bn) Radiator n qC Tkin (MeV) e± p p Lead glass 1.67 53o Water 1.33 41o Quartz 1.45 45o 0.2 190 400 PbWO4 2.2 63o

“Non-Compensation” Benefits In Cherenkov calorimeters, with e/h »1, only EM showers, (mainly low energy e±) contribute: Shower profiles thinner (rM), Better containment, Lower background As rad-hard materials for the active parts of calorimeters, quartz fibers are 1st choice: ZDC for Heavy Ions experiments at SPS, RHIC, LHC,… Large rapidity detectors at LHC (HF) Polarimeters e±: Compton back-scattering SLC, HERA, ILC

Quartz Fibers qT qT ~ 20o qC QF with fluorine-doped silica cladding (QQF) can stand ~20 Grads, with ≤ 10% light loss; MIP particle produces about 200 Cherenkov photons in 1 cm quartz (~ 500eV); same MIP particle deposits about 4.5 MeV by ionization

Quartz Fibers for Calorimetry DRDC P54 (1994) - Development of quartz fiber calorimetry (A. Contin, P. Gorodetzky, R. DeSalvo et al.) Directional properties of Cherenkov light in fibers 45o

Quasi-isotropy of soft shower particles R. Wigmans – Frascati Calorimetry Conf., June 1996

Sharper shower profiles L.R. Sulak – Frascati Calorimetry Conf., June 1996

Fast time response CMS HF Calorimeter 2003 Test Beam 25 ns Intrinsically very fast Y. Onel, Chicago Calorimetry Conf. , June 2006

~ 2000 PMT readout (magn. field ~ 0 ) CMS – HF Quartz Fiber Calorimeter ~ 1000 km quartz fibers 1 HF weights ~ 250 tons ~ 2000 PMT readout (magn. field ~ 0 )

HF Cross-section and front view

p/e values for SPACAL and HF

Energy resolution of HF c - Noise, etc b - Constant term (calibration, nonlinearity) a – Statistical fluctuations Electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form. The stochastic term a = 198% and the constant term b = 9%. Hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the EM case, a = 280% and b = 11%.

Challenge…. ….and DREAM… Improving the energy resolution? Mockett 1983 SLAC Summer Institute … A technique is needed that is sensitive to the relative fraction of EM energy and hadronic energy deposited by the shower. This could be done hypothetically if the energies were sampled by two media: one which was sensitive to the beta equals one electrons and another which was sensitive to both the electrons and other charged particles. For example one sampler could be lucite which is sensitive only to the fast particles, while the other sampler could be scintillator. See also Erik Ramberg et al. , Dave Winn et al. , … ….and DREAM… (R. Wigmans et al.)

DREAM = SPACAL + HF DREAM I L C Main theme: multiple measurements of every shower to suppress fluctuations Spatial changes in density of local energy deposit Fluctuations in EM fraction of total shower energy Binding energy losses in nuclear break-up fine spatial sampling with SciFi every 2mm clear fibers measuring only EM component of shower via Cherenkov light from electrons (Eth = 0.2 MeV) measure MeV neutron component of shower. Like SPACAL Like HF Triple Readout DREAM = SPACAL + HF DREAM 4 I L C

DREAM [Dual REAdout Module] prototype is 1.5 ton heavy Cell [basic element of detector] 2m long extruded copper rod, [4 mm x 4 mm]; 2.5mm hole contains 7 fibers:3 scintillator & 4 quartz(or acrylic plastic). In total, 5580 copper rods (1130Kg) and 90 km optical fibers. Composition (volume) Cu: S : Q : air = 69.3 : 9.4 :12.6 : 8.7 (%) Effective Rad. length (X0)=20.1mm;Moliere radius(rM)=20.35mm Nuclear Inter. length ( lint )=200mm;10 lint depth Cu. DREAM 4 I L C Filling fraction = 31.7%; Sampling fraction = 2.1% (S, Q fibers 0.8 mm f )

DREAM I L C Hexagonal shape with 270 cells (Fig. b); Fig. a : fiber bundles for read-out PMT; 38 bundles of fibers Fig b : front face of detector with rear end illuminated: shows 3 rings of honey-comb hexagonal structure.. Tower : readout unit Hexagonal shape with 270 cells (Fig. b); Readout 2 types of fibers to PMTs (PMT: Hamamatsu R580) (Fig. a) Detector : 3 groups of towers (Fig. b) center(1), inner(6) & outer(12) rings; Signals of 19 towers routed to 38 PMT DREAM 4 I L C

DREAM I L C DREAM calibrated with 40 GeV e- into center of each tower, recover linear hadronic response up to 300 GeV for p- and “jets” DREAM 4 I L C

New issues and options (Light-Emitting) Active Media Study Xstals, Cerenkov radiators, neutron sensitive scintillators (Photon-Sensing) Detectors Develop SiPM (popular objective… … need good technology partners) (Time-Domain) Signal Processing Fast Pulse Shape digitizer

Differentiating Cherenkov and Scintillation light in PBWO4

Angular dependence and L-R asymmetry

Studies with pions Preliminary results