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

2. EM showers vs Hadron cascadesg 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

3. Development of hadron cascadesX0 lI
X0, λI [cm] Z
Fluctuations due
to po production
2 scales for hadronic
cascade development:
- lI for strong interactions
- Xo for EM interactions

4. 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

5. 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

6. 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 /

7. “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?

8. Cherenkov Calorimeters
b > 1/n qC
cos qC = 1/(bn)
Radiator n qC Tkin (MeV)
e± p p
Lead glass o
Water o
Quartz o
PbWO o

9. “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

10. 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

11. 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

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

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

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

15. ~ 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 )

16. HF Cross-section and front view

17. p/e values for SPACAL and HF

18. 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%.

19. 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.)

20. 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

21. 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 )

22. 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

23. 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

24. 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

25. Differentiating Cherenkov and Scintillation light in PBWO4

26. Angular dependence and L-R asymmetry

27. Studies with pions
Preliminary results