1. C.Lazzeroni, University of Birmingham
CEDAR Working Group CERN - 02/09/2008
Status and News
C.Lazzeroni, University of Birmingham

2. Situation in UK
Statement of Interest (first step) submitted to 22nd July PPAN-STFC meeting : “Search for New Physics beyond the Standard Model with the NA62 experiment at CERN” and the CEDAR
Feedback:
PPAN agreed that there was good and exciting science likely to emerge from the project and the proposal built upon the strong science role that the applicant has established.
However PPAN was concerned by the lack of a developed science consortium for what was a significant package of research. For the project to be viable, PPAN believed that a stronger research community in the UK would need to be identified.
Effort is now concentrating on identifying other interested institutes:
few universities already contacted - process will take some time...

3. From last meeting
At the last meeting, 2 principal tasks were identified :
choice of hydrogen gas and related infrastructure
choice of photo-detectors

4. K12 Beam Working Group – CEDAR Status
Why hydrogen:
Absolute necessity to minimize material on beam line
The hope is that the 4x lower pressure allows thinner windows (we hope 100 instead of 400 mm Al)
L.G., 22 July 2008
K12 Beam Working Group – CEDAR Status 4

5. K12 Beam Working Group – CEDAR Status
List of points to be addressed:
Provide SC-GS with construction drawings and material certificates or definitions of the materials used. This includes the type of steel, the windows material and thickness (SC-GS may provide design input or help) and the type of seals.
The insulation material should not produce toxic black smoke. Note that polyurethane foam is acceptable in small quantities whereas polystyrene is forbidden. A sample of the insulation material should be made available for analysis by SC-GS.
Provide drawings and/or details of all electrical equipment (HV, motors).
Look at all possible leak scenarios and propose actions. This includes leaks into the beam line, which must therefore use hydrogen rated pumps.
A hydrogen venting system must be available in TCC8 to cope with pressure changes (including unforeseen pressure rises) and the placing of the hydrogen supply bottle must be considered.
The relevant parts of the CEDAR counter should be housed in an inert enclosure. It should be small enough (local !) that it does not become a confined space problem in itself. Its walls should be thin to avoid danger in case of explosion.
Provide draft hydrogen filling and shutdown procedures, including emergency scenarios
L.G., 22 July 2008
K12 Beam Working Group – CEDAR Status 5

6. K12 Beam Working Group – CEDAR Status
- MC
L.G., 22 July 2008
K12 Beam Working Group – CEDAR Status 6

7. K12 Beam Working Group – CEDAR Status
Cedar-West (H2 filled)
- MC
Resolution is ok!
100.0±0.48 mm
102.3±0.45 mm
L.G., 22 July 2008
K12 Beam Working Group – CEDAR Status 7

8. Hydrogen CEDAR Need to identify:
- changes to be done(if any) to the CEDAR itself in order to
use hydrogen gas rather than current gas
- consequences in general infrastructure,
connected to safety aspects
Decision to proceed to a First step:
Prepare a CEDAR, as it is now, but filled with hydrogen
Test it on beam line, at low intensity
Negotiation with beam division will start soon,
to establish division of efforts and competences

9. K12 Beam Working Group – CEDAR Status
Original light spots
20 x 7 mm2
Y (mm)
Y (mm)
X (mm)
X (mm)
L.G., 22 July 2008
K12 Beam Working Group – CEDAR Status 9

10. Photo-detector for the CEDAR
Current optics condenses the Cherenkov light from the diaphragm into 8
rectangular light spots ~10x30 mm2 each
Kaon rate = 50 MHz and ~100 photons per Kaon
photon rate = 100 ph x 50 MHz / (300 mm2 x 8)
~ 2 MHz / mm2 (rate of singles from accidentals,
after-pulses, dark noise not included)
Key points for the new detector:
Single photon counting application
Stand very high photon rate / unit area (occupancy in time and space)
Reduced active area (beam activity)
(minimum ~150 mm2 / spot due to optics phase space)
UV/Blue light sensitivity with the highest efficiency (PDE)
Excellent timing resolution on single photon
Exposition to the halo of intense hadron beam (radiation damage)

11. PMTs: R2248 vs R7600 R2248 seems to be the best choice -
R R7600U/P
square x10mm(8x8mm) x30mm(18x18mm)
fill factor % %
peak sens nm nm
range nm nm can be extended in UV
QE % % normal angle of incidence
Gain (at 800 V) x x 106
Rise time ns ns
Transit time ns ns
TTS ~450 ps ps
Pulse width ~3 ns ~3 ns
Av. current mA mA
Dark current max nA nA or 500 counts
cost (per 250) CHF ??
R2248 seems to be
the best choice -
test started by Placci
R M R M R M64
square x26 (18x18)mm x26(18x18)mm x26mm (18x18mm)
fill factor % % %
peak sens nm nm nm
range
QE % % %
Gain (at 800 V) x x x 105
Rise time ns ns ns
Transit time ns ns ns
TTS ps ps ps
Pulse width ~3 ns ~3 ns ~3 ns
Av. current mA mA mA
Dark current max nA/ ch nA/ ch nA /ch
cross talk ? ? %
cost (per 250) ? ? CHF

12. PMTs options
R2248: 64 mm2 , 0.1 A/mm2 -> 6 A -> 1/5 max rated current
Which is the limiting factor: cathode / divider / anode current ?
Is a safety factor needed ?
Example: Assume we need to reduce the current by a factor of 6:
from 3 PMT per spot to 18 PMT per spot (144 PMT in total)
light spot (30x10mm2) enlarged x 6 / 0.64 ~ x 9 with cones (100%eff.)
Photo-electon rate per spot:
(12 photons per 50 MHz) x QE ~ 3 50 MHz
3 p.e. / 18 channels x 50MHz = 8.3 MHz per channel (R2248)
Would need optic system to increase the spot...
But can we work with no safety factor - with no additional optics ??
Test needed

13. ToDo measure the limiting factors of the candidate PMT R2248:
max anode/cathode currents
2) PMT single photo-electron pulse response:
signal width, after-pulse features, time lag features
3) PMT performances as a function of high voltage (DV):
timing features, collection efficiency, signal shape
working at low G possible ?
Some data already exist, analysis in progress
More data needed

14. See G.Collazuol talk at
SORMA WEST 08 conf.
Comparison SiPM vs PMT
for applications of photon counting and timing at high rates
PMT
HPK R7600
(18x18 mm2)
SiPM
HPK S C (1x1 mm2 )
Reference
device (eff. area)
Gain (G)
≥106
≥106
V/V for G/G=1%
3 x 10-4
6 x 10-4
20MHz limit to avoid signal pileup. Not mandatory: can
use proper shaping.
SiPM can stand at least x10 more rate per unit area
than PMT
T for G/G=1%
5o C
0.3 o C
Max average anode current
100 A
(350 mm2 )
3 A
(1 mm2 )
Efficiency
(on active area)
400nm
~40% (UBA)
400nm
Fill Factor
36%
40% to 80%
cell geometry
Time resolution
~300ps
50ps to 100ps
Dark noise (1 p.e.)
few kHz
0.5 T
After-pulse
1 p.e.)
1 % level
10 % level
B-field immunity No
Yes
Radiation damg.
No (also at single photon level ?)
Yes

15. SiPM very good rate capabilities and granularity
excellent efficiency and timing resolution for single photons
very good rate capabilities and granularity
cooling is necessary to reduce counts under control
keep devices in the peripheral beam halo to reduce radiation damage
dark count rate scales with active surface - small light spot

16. ToDo Test performances in the UV/Blue region: Optics/cooling:
From Francois:
1 Hamamatsu SiPM is being tested which
blue laser (405 nm) and connect to the NINO chip
- analysis in progress
Optics/cooling:
Assume to collect light on a spot area of 12x12 mm2
covered by a matrix of 4x4 square SiPM's each
of dimension 3x3mm2 and 900 cells (100x100 mm2) -
New design of suitable optics to concentrate Cherenkov light on 12x12 mm2 (about 1/2 of the original)
Design cooling system

17. FE electronics Need actual test of the chain with R2248 / SiPM -
pre-ampli + FADC + TELL1
pre-ampli + NINO + TDC + TELL1
Need actual test of the chain with R2248 / SiPM -
firstly in Lab, then on beam line
Richard Stanley, electronic engineer from Birmingham,
will visit Pisa in September with the aim of firstly learning
what has been done already, and then helping with the
readout electronic, especially with the TELL1 FPGA programming

18. Next Steps 1) Test CEDAR prototype with Hydrogen (at low intensity)
Test Beams
1) Test CEDAR prototype with Hydrogen (at low intensity)
2) Continue characterization of photo-detectors
3) Illumination with Cherenkov light for measuring : p.e. Yield and timing
4) Compare two solutions for electronics
5) Exposition of SiPM to K12 beam halo for measuring the radiation effects

19. Spares

20. PMTs for dummies...
Limiting Currents: average/peak Anode ∝ p.e. Rate x Gain ~ exp (DV)
average Cathode
1 photo-electron (p.e.) x Gain x qe = 1 x 106 x = 200 fC
 Anode Current = rate/mm2 x QE x = 2 MHz/mm2 x 0.25 x = 0.1 A/mm2
Transit time (TT) -> Pulse width ~ 1/ √DV
- to be compared to photo-electron rate/channel
- double pulse resolution: to be compared to rate/channel
TT spread (TTS) ∝ fluct. of flight time Cathd.-1stdynd. ~active Surf./ √DV
-> time resolution ~ TTS/ √p.e.
- to be compared to 100 ps necessary for tagging kaons
Rise time: ~ exp (-DV)
- to be matched by FE electronics bandwidth
Detection efficiency:
Sensitivity wavelength range: compare with Cherenkov spectrum
angle of incidence (photons)
collection efficiency (p.e.) ~DV first stage
Noise:
Dark current (uncorrelated)
After-pulses (correlated)
Cross-talk in Multi-Anode PMT (MAPMT) (correlated)

21. Fast FE Electronics for counting and timing
Ideal FE for a high rate system:
1) current amplifier or I-V converter: smallest Zin (to exploit the fast component)
need low Gain ~ x20 (especially if SiPM working at low gain) high bandwidth
inherently fast (time resolution of the device not to be spoiled)
2) RC shaper
minimize signal occupancy (pile-up) per channel
maximize the double pulse resolution (DPR < 5ns)
3) sampling with FADC
sampling (8 bits) at 1GHz: time resolution better than 20 ps rms
and DPR better than 5ps are easy to obtain
cost/channel < 180 $
to minimize the Kaon tagging inefficiency
Minimum number of channels to be evaluated on the basis of:
Max level of inefficiency in kaon tagging due to pile-up:
eg: DPR~5ns with Mhz (signal) + Mhz (noise) on 16 ch.
 inefficiencly due to pile-up ~ 5%
Limit on time resolution: worsens with rate
NOTE:
1. up to now our tests with voltage amplifier + FADC sampling were successful
even at very high rates (20MHz)
2. now we are testing the Time Over Threshold discrimination
technique by exploiting the NINO chip (ALICE TOF, NA62 RICH)
as an alternative FE chain: SiPM + Preamplif. + ToT Discrim. + TDC