1. Presented by Aldo Penzo, Calorimetric Techniques Session, 26 May 2008
LHC
The CMS - HF Calorimeters:
Radiation hard Quartz Calorimetry
Aldo Penzo
(INFN – Trieste, Italy)
Yasar Onel
(Univ. of Iowa, USA)
(On behalf of CMS HCAL)
Outline
LHC ( → SLHC): Huge radiation challenge
Quartz: Radiation – hard material
Cherenkov light: Filter – out junk
HF calorimeters in CMS: Forward physics at LHC
Rad – hard Quartz R&D for SLHC
INFN
CALOR 2008 – Pavia, Italy (26- 30 May 2008)
Presented by Aldo Penzo,
Calorimetric Techniques Session, 26 May 2008

2. LHC (SLHC) Experimental Challenges
For LHC:
Luminosity L = 1034 cm-2 s-1,
Bunch Crossing (BX) interval D = 25 ns,
High Interaction Rate
pp interaction rate ~109 interactions/s
Large Particle Multiplicity
~ 20 superposed events in each BX
~ 1000 tracks into the detector every 25 ns
High Radiation Levels
radiation hard detectors and electronics
In forward CMS region (h ~ 3-5) ~ 100 Mrad/year (~ 107 s)
[Activation of HF ~10 mSv/h (60 days LHC run/1 day cool-down) ]

3. LHC to SLHC
Assume SLHC luminosity L = 1035 cm-2s-1 (10 x LHC)
Possible bunch crossing intervals: 25 ns, 50 ns
Some parameters for comparison are (1 LHC year = 107 s) :
LHC SLHC
L (cm-2s-1)
BX interval (ns)
Nint / BX-ing ~ ~ ~ 400
dN/d / BX-ing ~ ~1000 ~1000
∫L dt (fb-1)
In forward CMS region (h ~ 3-5) ~ 10 MGy/year

4. Rad – hard Quartz Fibers
Quartz Fibers (QF) with fluorine-doped silica cladding (QQF) can stand ~20 Grads, with ≤ 10% light loss;
Plastic-clad fibers (QPF) may have ~75% losses after 5 years at LHC luminosity in high h region
Quartz Fibers respond to fast charged particles by producing Cherenkov light
PMT Photodetectors (low B) are sensitive to radiation mainly through PK windows with ≥ 30% transmission loss at 420 nm (glass)
Recovery mechanisms, for fibers and PMT, may reduce the effects of radiation damage, either in a natural way (self-repair in quiet periods after exposure), or artificially, for instance like thermo-(or photo-)bleaching.
Need to be understood to describe accurately the behaviour of the detector, and its history
Robust enough for a survival strategy of detectors in extreme SLHC radiation conditions…???

5. Typical spectral response of QF shows reduced damage
effects in the region around maximum (420 nm) of PMT
sensitivity (Quantum Efficiency); this is an important asset
of quartz-fiber calorimetry.

6. Characteristics of Cherenkov light from Quartz Fibers
In quartz (n=1.45) charged particles with b >1/n (0.7) emit Cherenkov light (Threshold 0.2 MeV for e, 400 MeV for p)
Cherenkov angle qc such that cos qc = (bn)-1 (~45o for b=1)
Optical fibers only trap light emitted within the numerical aperture of the fiber qT (~20o with axis of fiber)
qT ~ 20o
qC ~ 45o
b > 0.7
DRDC P54 (1994) - Development of quartz fiber calorimetry (A. Contin, P. Gorodetzky, R. DeSalvo et al.)

7. Sharper shower profiles
L. R. Sulak – Frascati Calorimetry Conf., 1996
R. Wigmans – Lisbon Calorimetry Conf., 1999
N. Akchurin and R. Wigmans – Rev. Sci. Instr. 74 (2003)

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

9. CMS – HF Calorimeters
2 Quartz Fiber Calorimeters for the forward region (3< h <5) of CMS
~ 250 tons iron absorber (8.8 lI)
~ 1000 km quartz fibers (0.8mm diam)
~ 2000 PMT read-out
36 wedges azimuthally; 18 rings radially
(Segmentation DhxDf = 0.175x0.175)
Test beam results of CMS quartz fibre calorimeter prototype and simulation of response to high-energy hadron jets - N. Akchurin et al. - Nucl.Instrum.Meth.A409:593,1998
Design, Performance and Calibration of CMS Forward Calorimeter Wedges – G. Bayatian et al. – Eur. Phys. J. C53, 139, 2008

10. Assembling the wedges Manual insertion of the fibers
Wedges completed with fibers

11. HF at SX5 ready for lowering to the cavern
Completely assembledHF module

12. HF in UX5 – at beam level
Since lowering to UX5, HFs were in garages, while the rest of CMS was lowered to UX5 & assembled;
in the garages HFs were commissioned
one module seen here was extracted and was brought to beam level temporarily

13. HF structure and properties

14. Energy resolution of HF
a – Statistical fluctuations
b - Constant term
(calibration, nonlinearity)
c - Noise, etc
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%.
Highly non-compensating: e/h ~ 5
Light yield ~ 0.3 phe/GeV
Uniformity (transverse) ± 10%
Precision in h ~ 0.03 and in f ~ 0.03 rad

15. HF in all global runs, since beginning 2007
2007 CMS Global Runs
As 2007 progressed an increasing number of the following subsystems participated in the global runs (in order of entrance) :
HF: forward hadron calorimeter
DT: drift tubes
EB: barrel electromagentic calorimeter
RPC: resistive plate chambers
CSC: cathode strip chamber
Trk FEDs/RIB: tracker front-end drivers/rod-in-a-box
Lumi: luminosity monitor
HB: barrel hadron calorimeter
HO: outer hadronic calorimeter
HE: endcap hadron calorimeter
HLT: high level trigger
HF in all global runs, since beginning 2007

16. HF calibrations solo and in GR
Events’ display of the HF+ calibration data
(by Ianna Osborne).

17. HF monitoring and calibration tools
Pedestals – long/short term stability; light-leaks
LED – stability, photoelectron response
Laser – timing
HV scans – gain
Co60 Source scan – calibration ~ ± 5%
Rad-dam monitoring – fiber attenuation damage by radiation

18. HF in CMS Total weight : 12500 t Overall diameter : 15 m
Overall length m
Magnetic field : 4 T

19. HF in the forward region of CMS
HF: 3. < h < 5.
T1: 3.1 < h < 4.7
T2: 5.3 < h < 6.5
10.5m
14m HF h 2p f
HF-
HF+ C A S T O R
CMS
ZDC
Almost complete
rapidity coverage at LHC

20. HF Physics Benchmark Processes
High Luminosity:
Higgs production via WW fusion :
pp → j j (WW) → H j j (tagging jets in HF)
Higgs decays to vector bosons :
H → ZZ (WW) → l l j j
- SUSY → jets + ETmiss (hermeticity)
Rapidity coverage needed: |h| up to 5 for ETmiss , 3 < |h| < 5 for ‘tagging’ forward jets

21. “Tagging” jets

22. Forward di-jets probe low-x QCD
Moderate Luminosity
Salim Cerci, David d’Enterria:
“Mueller-Navelet” Jets separated by several Δη

23. Luminosity Monitor Real time lumi monitoring with HF Offline
Count minimum bias events at low luminosity
Count “zeroes” at design luminosity
Use linear ET sum, which scales directly with luminosity.
Bunch by bunch
Update time: 0.1 s to 1.0 s or slower*
“Always on” operation, independent of main CMS DAQ
Offline
Robust logging
Easy access to luminosity records
Dynamic range (1028 ~ 1034cm–2s–1)
Absolute Calibration
Target 5% (or better)
Offline: TOTEM, W’s & Z’s
Simulations: Full GEANT with realistic representation of photostatistics, electronic noise and quantization, etc.
Minimal hardware requirements•Mezzanine board to tap into HF data stream
Autonomous (mini) DAQ system to provide “always on”operation

24. SLHC R&D on Rad-hard Quartz
University of Iowa
As a solution for SLHC conditions quartz plates are proposed as a substitute for the scintillators at the Hadronic Endcap (HE) calorimeter.
Castor uses Quartz Plates
A first quartz plate calorimeter prototype (QPCAL - I) was built with WLS fibers, and was tested at CERN and Fermilab test beams.
Geant4 simulations are completed
R&D studies to develop a highly efficient method for collecting Cerenkov light in quartz with wavelength shifting fibers.
• We are also constructing a prototype calorimeter, first 6 layers have been tested at Fermilab test beam. This summer whole prototype will be at Cern test beam.

25. Extracting Cherenkov light from Quartz plates
Studies and simulations
The real thing…

26. Preliminary results Light Enhancement Tools: Readout Options:
PTP and Ga:ZnO (4% Gallium doped) enhance the light production almost 4 times. OTP, MTP, and PQP did not perform as well as these.
PTP is easier to apply on quartz, we have a functioning evaporation system in Iowa, works very well. We also had successful application with RTV. Uniform distribution is critical!!
We tested gr/cm2, 0.01 gr/cm2, and gr/cm2 PTP densities on quartz surfaces, looks like 0.01 gr.cm2 is slightly better than the others.
ZnO can be applied by RF sputtering, we did this at Fermilab- LAB7. We got 0.3 micron, and 1.5 micron deposition samples. 0.3 micron yields better light output.
Readout Options:
Single APD or SiPMT is not enough to readout a plate. But 3-4 APD or SiPMT can do the job.
Test Beams: We have opportunity to test our ZnO and PTP covered plates, at CERN (Aug07), and Fermilab MTest (Nov 07, and Feb 08).
Blue : Clean Quartz
Green : ZnO (0.3 micron)
Red : PTP (2 micron)