Workshop on Synergy between High Energy and High Luminosity Frontiers.
January 10-12, 2011 Tata Institute of Fundamental Research, Mumbai, India
Detector Upgrade from Belle to
Belle II
Toru Tsuboyama (KEK) 12 Jan. 2011
The purpose of the B factories

Explore the CP violation of B meson decay through the
particular decay chain



e+ e–  ϒ(4S)  Bo Bo  (CP mode decay) + (tag mode
decay)
ϒ(4S) decays into a coherent Bo Bo pair.
Only the vertices of Bo and Bo can be measured.


No particles from the decay vertex of ϒ(4S).
The tasks of a B factory detector:




Record the B meson decay reactions as efficient as possible.
Identify the B and B in the final state.
Measure the decay position of B and B mesons.
Combining these information, investigate the difference of
particles and antiparticles.
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Method of CP violation measurement
t2
electron
(8GeV)
ϒ(4S)
resonance B1
electron
B2
(3.5GeV)
CP mode decay
t1
m+
m-
B0
B0
n
Tag mode decay
bg = 0.425
p+ K–
m-
ACP 
0
0
0
 ( B ( D t )  f CP ) -  ( B ( D t )  f CP )
 ( B ( D t )  f CP ) +  ( B ( D t )  f CP )
p+
D0
DZ~200mm
0
Ks
 S sin( D m d D t )
S: mixing induced CP parameter
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Belle Detector
CsI(Tl) 16X0
Super conducting
solenoid 1.5T
s/E=1.8%@1 GeV
Eid eff=30 % (0.1% fake)
Aerogel Cherenkov
Counter n=1.015~1.030
3.5 GeV e+
Kid eff = 90 % (6% fake)
Central Drift Chamber
TOF conter
small cell +He/C2H6
st = 95 ps
(spt/pt)2 [%2]
= (0.19 pt)2+(0.34)2
8 GeV em / KL detector
Silicon Vertex detector
4 layer silicon strip sensors
14/15 lyr. RPC+Fe
s(Dz) = 100 mm
Muon ID eff>90 % (2% fake)
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Belle Detector
Tasks
SVD
CDC
TOF
ACC
CsI
KLM
Record the B meson Events
Efficiently
Full
reconstruction
of B meson
Tracking
✔
✔
✔
Calorimetry
✔
Particle ID
Measure the decay vertex
position of B mesons
B flavor Tagging (Particle ID)
TRG
CMP
DAQ
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
High performance data
processing:
✔
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The adopted technology

Full reconstruction of B meson




Tracking: Central Drift Chamber and Uniform
Solenoid field.
Calorimetry: CsI(Tl) for good energy resolution.
Particle Identification: dE/dx in CDC, TOF,
Aerogel Cerenkov counters (Barrel/Forward),
KL/MU detector in the return yoke.
B flavor tagging



bc + lepton: Lepton identifications by E/p,
dE/dx, KL/MU:
bcs: Kaon identifications by ACC/TOF and
BD* X, D*  pD: Slow pions reconstruction by
CDC.
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The adopted technology

Measurement of the positions of two B decay
vertices.

Asymmetric Energy e+e– collider.



The B mesons travel significant distance in the
laboratory frame before decay.
The decay time of B can be measured by the
respective decay position.
Silicon vertex detector



The sensors are placed at 18 mm from the beam
collision point.
The intrinsic position resolution is 5-10 mm.
B meson decay vertices are reconstructed with enough
position resolution.
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More physics channels

As the B factory detector is general
purpose, we can explore following modes
with high precision and high statistics.

Other important channels





B  tn, B KsKsKs, BKsp0g …
B+/B–, charmed mesons, baryons
Leptons especially t.
Two photon processes.
New baryon/meson states
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Why Belle should be upgraded?

To accommodate 8x1035 /cm2/sec luminosity.





Belle was designed for 1x1035 /cm2/sec.
Physics rate amounts to 10 kHz
Beam background increases accordingly.
Beam energy asymmetry 8+3.5 GeV  7+4GeV
To Improve the detector performances

Better Tracking:




Beam pipe radius: 1.5cm  1.0 cm
Inner radius of vertex detector: 1.8 cm  1.3 cm
Outer radius of CDC 863 cm  1111 cm
Better PID performance

Threshold Cherenkov  Ring image Cherenkov
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The Belle detector upgrade
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IR (Interaction Region)
SC Quads
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Beam Pipe

The nano-beam option




The beam is squeezed to 60 nm thick at the collision point.
Beam current: 1.2 A 2.6 A(HER), 1.6 A  3.6 A(LER)
The beam pipe radius is reduced from 1.5 cm to 1 cm.
The e+ and e– beams collide with crossing angle, 83 mrad.

The two beams are separated significantly at 50 cm from the
collision point. The beam pipe will have a crotch.
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Silicon Vertex detector

Background hit occupancy reduction



APV25 ASIC with faster shaping time.
Pixel detector in the first 2 layers 
Smaller sensitive area per readout.
Improve physics performance




Vertex reconstruction and resolution
Recover the smaller energy asymmetry.
Sensor at smaller radius.
Lager acceptance for Ks vertexing. 
larger radius.
Belle
Belle2
Beam pipe
Radius (cm)
1.5
1.0
Vertex detector
Radius (cm)
1.8 < R < 9.6
1.4 < R < 14,0
Layers
4 layer DSSD
2 Layer Pixel
13 +
4 layer DSSD
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DEPFET pixel detector



2 layer DEPFET pixel detector
Located at R=14 mm and 22 mm.
The sensor are thinned to 50 mm
thick, in contrast to the hybrid pixel
sensors (>500 mm thick, including
sensor, readout chip, cables and
cooling).
•The DEPFET group originally started the R&D for
the ILC vertex detector.
•Converting from ILC design to Belle2 design is a
challenge.
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DEPFET pixel detector
The charge collected in each
pixel is scanned by external
clocks and sent to subsequent
signal processing ASICs.
 Reduction of huge
data size due to
background hits
is a big challenge.

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Silicon strip vertex detector


4 layer with doublesided silicon strip
detectors.
3.8 cm < R < 14.0 cm
Layer
R (mm)
Ladders
Sensors
RO chips
3
38
8
16
850
4
80
10
30
560
5
115
14
56
300
6
140
17
85
192
49
187
1902
Sum
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Silicon strip vertex detector


3 types of DSSD sensors are
used.
Made from 6” (15 cm) diameter
wafers, that became popular in
the constructions of silicon
trackers for Atlas, CMS, LHCb.
DSSD
Large
Wedge
Small
Dimension (mm2)
124.88x59.6
125.58x(41.0-60.63)
124.88x40.4
# strips (p)
768/1535
768/1535
768/1535
# strips (n)
511/1023
511/1023
768/1535
Strip pitch (p)
75
50-75
50
Strip pitch (n)
240
240
160
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Activity at Tata Institute



Working with a foundry in Bangalore.
Double sided detector prototypes have been produced.
For the first time truly Microstrip Detector developed in India.
On 300 mm thin n-type bulk
silicon wafer of 4-inch diameter
A clean room in Tata institute for the
sensor characterization
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Performance (I)




Fourth Batch : <111>, 2 to 4 kΩ-cm
Single sided Microstrip Detectors, 1024 Strips
Two different processing cycles
Delivered : March 2009
< 1 nAm per strip (Meets the specification)
I - V characteristics of SSD
Better Photolithography
4
3.5
current ( µamps)

Two class of processings
3
2.5
8004-5*
8018-1*
8018-2*
8018-3
8004-7
8004-8
2
1.5
Single Level
Double Level
1
0.5
0
0
100
200
300
Reverse voltage ( volts )
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Performance (II)



Response to 1064nm pulsed laser
Directly observed with an oscilloscope
Expected responses are observed.
P – side response
N – side response
Rise-time 5ns
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Silicon strip vertex detector



Readout chip: APV25 developed for
the CMS Silicon tracker.
Its 192 stage pipeline and dead-time
free readout fits the Belle2 DAQ
scheme.
Belle2 group utilizes the analog data
in the pipe line for a wave form fit. A
100 times background rejection
compared with Belle SVD is
expected.
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Central Drift Chamber



Small cell structure and improved
readout electronics for immunity
against high background rate.
Longer lever arm for better track
momentum resolution, thanks to
thinner Particle ID device.
14,336 sense wires and 42,240
field wires.
22
Belle
Belle2
Radius of Inner Cylinder (mm)
77
160
Radius of Outer Cylinder (mm)
880
1130
Radius of innermost wire (mm)
88
168
Radius of outer most wire (mm)
863
1111
Number of Layers
50
56
Number of sense wires
8,400
14,336
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Central Drift chamber



The new electronics has been designed and
tested.
The drift time is measured with a TDC built-in in
an FPGA.
A slow FADC (around 30MHz) measures the
signal charge.
X-T relation
HV (kV)
s~100mm
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Residual distribution
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SEL 2011 meeting at Mumbai
Particle ID




Belle/Belle2 has the CsI calorimeter
for full acceptance 15<q<150o.
In order to keep its hermeticity,
Belle adopted Threshold Aerogel
Cherenkov counter for K/p separation.
Thanks to recent developments of new
type photo tubes, ring image Cherenkov Counters
can be installed to Belle2.
Significant improvement of K/p separation is
expected.
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TOP: Barrel Cherenkov counter

Time of Propagation Counter:

The Cherenkov angle of radiated photons is
measured with position (X, Y) and detection timing
T.
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TOP: Barrel Cherenkov counter

Prototype quartz bar
The Cherenkov angle
of radiated photons is
measured with
position (X, Y) and
detection timing T.
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TOP: Barrel Cherenkov counter

Square-shape multi-anode MCP-PMT






Multi-alkali photo-cathode
Single photon detection
Fast raise time: ~400ps
Gain=1.5x106 (B=1.5T)
T.T.S. (single photon): ~35ps (B=1.5T)
Position resolution: <5mm
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ARICH: Forward Ring Image Cherenkov counter

Proximity focusing Cerenkov
counter with:


2 layer Aerogel photon
radiators
Readout with Pixilated HADP
Package size
72x72x30 mm3
Pixels
12x12
Pixel size
4.9x4.9 mm2
Effective are
67 %
QE (typical)
25 %
Gain
~ 105
Mass
220 g
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CsI Calorimeter

Extrapolation of
background of Belle




Present status: Energy
deposit in random event: 0.5
MeV/Crystal or 3 GeV/ECL.
“Probably” proportional to
Beam current
3–10x background in Super
KEKB.
Fine segment in time will
be necessary
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CsI Calorimeter

Upgrade Plan:




The CsI (Tl) of present Belle is used again.
Shorten shaping time from 1μs to 0.5μs
Waveform sampling (18 bit, 2 MHz)
On board waveform fitting with FPGA.
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CsI Calorimeter

Physics simulations show the performance is close to
that of the ultimate upgrade with pure CsI crystals
readout with PMT.
Efficiency
Cases
B  J/ΨKs, Ks p0p0
has two p0 reconstructed.
CsI performance is
essential.
B  tn
requires no activities in
CsI except for t decay
particles. Sensitive to
beam background.
31
Current Belle
12.4 ± 0.2 %
Current Belle with 10x BG
7.8 ± 0.2 %
DAQ upgrade
12.0 ± 0.2 %
(Pure CsI + PMT readout )
12.3 ± 0.2 %
# BKG hits in B  tn
+
+
DAQ upgrade
Pure CsI + PMT
Eth (MeV)
SEL 2011 meeting at Mumbai T.Tsuboyama
KLM: KL and m detector


Belle  RPC (resistive plate
chamber): hit rate < 1Hz/cm2
Endcap part will be replaced with
Scintiilator + MPPC (SiPM)
Hit rate (Hz/cm2) expected of
KLM at SuperKEKB
Longest
strip
2820 mm
32
Layer
Barrel
Forw
ard
Back
ward
0
3.6
2.4
3.4
1
2.3
2.4
2.9
2
1.6
2.4
2,8
3
1.1
2.0
2.8
4
0.67
2.2
2.8
5
0.60
2.7
2.9
6
0.63
2.7
1.5
7
0.43
3.3
2.6
8
0.73
3.1
3.0
9
0.47
3.9
2.8
10
0.29
4.7
3.5
11
0.39
5.3
3.0
12
0.44
3.7
NA
13
0.42
NA
NA
14
0.48
NA
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KLM
HPK 1.3×1.3 mm 667
pixels
Vladimir (Russia)
(used in T2K ND)
Kuraray Y11 MC
No other competative option
High efficiency; long atten. length
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Trigger



The collision luminosity will
be 40 times larger than the
present Belle experiment.
Physics event rate will be
10 kHz at 8x1035/cm2/s.
The trigger system should
be tunable to accommodate
the physics rate for given
DAQ and computing
performances.
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DAQ


At the full luminosity, the data rate amounts
to 600 MB/sec.
A high performance DAQ system is
designed.
Belle
Belle2
0.3-0.5
20-30
40
300
Data rate
(MB/s)
20
6000
Reduction
1/ 2
1/10
20
600
Trigger rate
(kHz)
Level 1 Event size
Trigger (k Byte)
High
Level
Trigger
Storage
Band Width
(MB/s)
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Computing


Belle  computing resource is concentrated to
KEK.
Belle2  50-100x larger computation power
and storage is necessary



Highly distributed computing environment:
GRID with help of CLOUD is necessary.
GRID technology established by LHC computing
will be utilized.
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Computing


Belle  computing resource is concentrated to
KEK.
Belle2  50-100x larger computation power
and storage is necessary

Highly distributed computing environment: GRID
with help of CLOUD is necessary.
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Belle2 detector
CsI(Tl) with wave sampling
readout
PID: New Cherenkov Detectors
Barrel: Time of Projection counter
Forward: Aerogel RICH counter
(s/E)2 = (0.2/E)2+(1.6/√E)2 +(1.2)2 %2
Eid eff=30 % (0.1% fake)
TOP: Kid eff = 99 % (1 % fake)
ARICH: Kid eff = 96 % (1 % fake)
KL/m detector:
Barrel: RPC
End cap: Scintillator
readout with MPPC
Central Drift Chamber
Small cell layout
Muon ID eff>90 % (2% fake)
TRG/DAQ: New Dead
time free readout
COMP: High performance
computer systems
(spt/pt)2 = (0.1 pt)2+(0.3)2 %2
(with SVD)
Vertex detector:
2 layer DEPFET pixel detector
4 layer Si vertex detector
Impact parameter resolution sz = 20 mm
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Belle II Collaboration http://belle2.kek.jp
13 countries/regions, 53 institutes
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Summary


The Super KEKB is approved.
Improve the detector performances








Capability for data acquisition of 8x1035 luminosity.
Immunity to expected 30x beam background
Beam pipe radius: 1.5 cm  1.0 cm
Vertex detector: 4Layer DSSD  4Layer DSSD + 2layer
DEPFET
Lever arm of Vertex Detector + CDC: 210 cm  250 cm
PID: Threshold Cherenkov  Ring image Cherenkov.
KID efficiency (Barrel): 90 %  99 %.
Disintegration of Belle2 has started Oct. 2010
Commissioning of Belle2: 1 October 2014.
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Belle upgrade started

Dismantling of Belle detector components
Central Drift chamber on 6 Jan 2011
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And more ….




We still need more human resources or
collaborating institutes to construct our
detector and stable operations.
We welcome new group to join Belle 2.
Please contact our spokes persons if you are
interested.
Thank you for attention!
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