1. EKLM: Progress and prospects
P. Pakhlov (ITEP)
SiPM operation
Strip quality check
Data bases
Start of mass production
Bg/software/reconstruction/physics
Material status/Plans
Conclusion

2. SiPM operation for cosmic tests and Belle-II run ΔHV = 1.4 V
Need strategy how to choose optimal HV for each of SiPMs, and how to tune HV during Belle-II operation under temperature variation
~ 70 V
1 – 1.5 V
HV = HVbreak down + ΔHV
HVbreak down strongly depends on temperature: ~ 57mV/°C;
all important SiPM characteristics (gain, efficiency, xtalk, noise) depends only on ΔHV – independently of temperature!
ΔHV = 1.4 V
choose working point:
efficiency < saturation
noise (at 0.5 p.e.) < 1 MHz
xtalk < 20%
to have maximum efficiency but staying in linear region (robustness against quick temperature changes) ~
SiPM noise 8 p.e. threshold)
< 1kHz << neutron bg rate ~

3. SiPM data base
For 200 SiPMs available at ITEP main characteristics measured and put to SiPM db
HVbreak down varied within 1 V range,
but optimal ΔHV is almost identical for all 200 SiPM.
No big spread of gain (RMS<10%) found;
Data base for 18k (+ 3.5k BKLM) SiPM’s is welcomed before start of assembly and installation at KEK
SiPM’s properties vary from one to another
some SiPM’s can be bad (T2K experience 0.1%)
Univ. of Tabuk applied for a grant in SA with proposal to develop and produce calibration device (Belle-II DAQ boards+LED) The decision is expected in mid – too late!
Strategy to find optimal point and stay their with Belle-II DAQ:
Find HVbreak down by scanning HV and calculating gain ( ≡amplitude of 1p.e. peaks) – can be done instantly during local run.
Fix gain at optimal ΔHV=1.4V.
To stay at the operation point it is sufficient to adjust HV to keep gain constant at chosen value

4. Quality check & strip data base
On line test of the production quality & strip db with cosmics set up and NIM/CAMAC electronics
covered by black film to protect from external light

5. t h e n e a r e s t t o S i P M r e g i o n
Cosmics tests
10 strips of the same length:
20 minutes cosmic run → triggers at each point
light yield statistical error ~ 2%
systematic error:
environment (temperature etc) after gain adjustment ~ 2%
optical connection ~ 6%
t h e n e a r e s t t o S i P M r e g i o n
m i d d l e o f s t r i p
Light yield: remove pedestal (due to non perfect trigger strips alignment) discard 10% low and 30% high (Landau tail); find average/gain
f a r e n d
Light yield then corrected for
non-perpendicular incidence: × 0.86
cross talk: × 1/(1+xtalk)

6. Mass production technique
pushing gel inside closed groove vs filling the groove from the top
push inside groove through a needle
strip
SiPM
housing
rubber press over groove
pneumatic press
fill from the strip top
gel two components
moving
carriage
gel stopper
Because of large gel viscosity there is high pressure inside the groove (>10 atm at speed 1m/min). For P>5 atm incidental gel leakages from the top of the strip occur. No stable operation was reached at reasonable speed of production.
While gel filling is automatic, more manual manipulations with fiber required. However, they take less time than gel filling.

7. Mass production Optimize speed of carriage moving and gel feed:
gel pump
Optimize speed of carriage moving and gel feed:
optimal speed ~ 1m/min – uniform gel spread in the groove;
<1min to change the strip;
fiber insertion during gel filling of the next strip;
1-layer sector (75 strips ~150m)/day is produced without rush
speed (pumping &moving) control
Need 220 working days (1 year) to produce all EKLM sectors
moving
carriage

8. Schedule & plans Delay in machinery Original plans:
start mass production in March’2012
for 2 months
at low speed;
produce & test ~ 5-8% of strips (~ of 220 one layer sectors)
3 month break of the strip production
select good strips (light yield from the far end > required threshold) for further use.
use bad strips to study the reasons of defects and improving the production scheme
June’2012
2 days
normal speed
1% of strips (= 2 sectors)
good Gaussian distribution with perfect average & reasonable RMS
resume mass production in September’2012

9. Improved performance near end Module-0 near end far end far end
to reduce air gap between fiber end and SiPM modify the SiPM-fiber connector
TDR value
<LY>=48
RMS=14%
200 μ
Fiber holder
near end
Module-0
near end
TDR value
TDR value
<LY>=28
RMS=12%
far end
TDR value
far end

10. Data bases SiPMs: temperature HVbreak down gain/ΔHV Strips: efficiency
noise (at working HV)
xtalk (at working HV)
Strips:
production time
length
light yields at three points (two points for short strips < 1m) + reference to test result n-tuple
# segment (filled during segment gluing)
# SiPM (filled during assembly)
Segments:
production time
type (1-5)
#s of strips
# of the sector (filled during assembly)
Sectors:
assembly time
#s of segments
cosmic run at KEK results + reference to test result n-tuple
position (filled during installation)
Preamplifiers:
production time
15-gains
#s of segment
# of motherboard

11. Background and radiation hardness
Neutrons in EKLM from far sources |z|>4m are still missing in the generator.
Innermost EKLM layers effectively shields the others from neutrons.
Z, cm
r, cm
Strip #
Hit rate, kHz
Neutrons
Photons/electrons
Innermost layer (the highest occupancy)
Deposited energy >0.5MeV
TDR estimation: 160 kHz (max), 60 kHz (average)
Strip occupancies are well below the TDR estimates -> good for DAQ and for physics.
Double x-y superlayer hits are of critical importance for physics (possibility to use loose KL-reconstruction) -> to be checked soon.
No one neutron hits found in the SiPM region -> good for radiation issues but suspicious (this is >order of magnitude estimates):
Does the simulation incorporate all possible background sources?

12. Account for absorption in fiber
Software & physics
Simulation of light transfer, SiPM response & DAQ signal fit – done by T. Uglov
DAQ
Account for mirror
Account for absorption in fiber
SiPM response
RawEKLM
# photons ~ energy deposited
Fit signal for
t & A
1D & 2D hit reconstruction (including 2D time consistency check) – done by T. Uglov
KL-reconstruction: compromise between efficiency (loose cuts) & backgrounds
soft KL momentum measurement (KLM=TOF)
MuID is being implemented by L. Piilonen:
similarly to Belle use two variables (χ2 & Δlayer= observed – expected)
possibility to use extra information: time, amplitude, ECL
matching delayed electron from the stopped muon decay – possibility to measure μ-polarization: previous/next layer to the last muon hit.
Optimize number of required superlayers in the backward: replace 2-4 outermost layers with neutron shield – to be done after reconstruction codes ready
innermost bg
muons
outermost

13. Purchase, production Scintillator (need (10 + 2 spare) tones)
4 tones produced and delivered to ITEP
+4.5 tones paid
2.5 tones to be purchased this year
all to be delivered to ITEP by September’2013
Fiber (need (30 +3 spare) km)
12,5 km sent to ITEP;
18 km at KEK to be sent to ITEP by the end of 2012
SiPMs (need spare) – all available
I-bars for support structure: 4.5 km – all available;
Miscellaneous supplies (gel, substrate, 3M scotch, silver shine) – all available
Documents
MoU between KEK & NRC KI (head organization for ITEP and IHEP) signed in June’12 (Suzuki-Kovalchuk) with Belle-II as a pilot project for collaboration
Intergovernmental agreement including BINP, ITEP & IHEP as Russian participants of Belle-II signed in July’12
Need final paper: memorandum between ITEP – Belle-II

14. Schedule & plans Strip (segment) mass production:
September‘12 – November’13 (3 spare months)
Support structure: Processing of I-bars & fasteners (at ITEP)
September‘12 – July’13
Welding I-bar net (at KEK)
March’13 – December’13
Transportation to KEK in 3-4 batches; the first delivery in December’12
First assembly and installation ~ March’ 13
Mass assembly and installation after September’13
Electronics: Preamplifiers to be produced by VPI by December’13;
DAQ mother boards need only for start of data taking, except for 4-6 mother boards (not obligatory final design) for cosmic tests at KEK by January’13

15. Conclusion
Improved performance of light collection reproduced with mass production provides large safety margin.
Mass production to be started in September’12, lasts for one year + 3 spare month
Strategy of SiPM operation for tests and Belle-II run developed; needs to be implemented with DAQ mother board
Quality check + data bases to start mass production are ready
Software development is in good shape; need to run MC for optimizing # of layers - shielding