1. The silicon detector of the muon g-2 experiment at J-PARC
Vertex 2011, Rust
June 24, 2011
Tsutomu Mibe (KEK)
for the J-PARC muon g-2/EDM collaboration

2. Particle dipole moments
Hamiltonian of spin 1/2 particle includes
Magnetic dipole moment
Electric dipole moment
Magnetic dipole moment
　g = 2 from Dirac equation, in general g≠2 due to quantum-loop effects
Example : electron ＝ ＋ ＋
＋　…
a “anomalous magnetic moment”

3. Anomalous magnetic moment : g-2
Standard model can predict g-2 with ultra high precision
Useful in searching for new particles and/or interactions
Experiment has reached the sensitivity to see such effects...
Dal(exp)/al
Dal(SM)/al
0.24ppb
0.54ppm
4.5 ppb
0.41ppm
a exp – a SM =
(296 ± 81)  10 –11
(259 ± 81)  10 –11
 3.2~3.6 ”standard deviations“
HLMNT,Tau 2010 workshop
DHMZ, Tau 2010 workshop
 To be confirmed by
new experiments

4. Muon anomalous spin precession in B and E-field
Muon spin rotates “ahead” of momentum due to g-2 >0.
Precession frequency
BNL E821
Focusing electric field to confine muons.
At the magic momentum
g = 29.3, p = GeV/c  (am -1/(g2-1) ) = 0
Safely be neglected with current upper limit on EDM
Continuation of the experiment at FNAL is planned.

5. Our approach Compact storage ring
Suited for precision control of B-field
Example : MRI magnet , 1ppm local uniformity
Completely different systematics than the BNL E821 or FNAL
BNL E821 (FNAL )
J-PARC g-2
80 cm
14m
P= 3.1 GeV/c , B=1.45 T
P= 0.3 GeV/c , B=3.0 T
Hitachi co.

6. Our approach (cont’) Zero Focusing Electric field (E = 0 )
Equations of spin motion is as simple as at the magic momentum
Ultra-cold muon beam (pT/p < 10-5) by utilizing the laser resonant ionization of muonium makes it possible to realize such experimental condition.

7. BNL, FNAL, and J-PARC BNL-E821 Fermilab J-PARC Muon momentum
3.09 GeV/c
0.3 GeV/c
gamma
29.3 3
Storage field
B=1.45 T
3.0 T
Focusing field
Electric quad
None
# of detected m+ decays
5.0E9
1.8E11
1.5E12
# of detected m- decays
3.6E9 -
Precision (stat)
0.46 ppm
0.1 ppm

8. Material and Life Science
J-PARC Facility
(KEK/JAEA)
LINAC
3 GeV
Synchrotron
Neutrino Beam
To Kamioka
Material and Life Science
Facility
Main Ring
(30 GeV  50 GeV)
Hadron Hall
Bird’s eye photo in Feb. 2008

9. New Muon g-2/EDM Experiment at J-PARC with Ultra-Cold Muon Beam
Surface muon
Ultra Cold m+ Source
Muon
storage
Muon LINAC (300 MeV/c)
New Muon g-2/EDM Experiment at
J-PARC with Ultra-Cold Muon Beam

10. New Muon g-2/EDM Experiment at J-PARC with Ultra-Cold Muon Beam
3 GeV proton beam
( 333 uA)
Graphite target
(20 mm)
Surface muon beam
(28 MeV/c, 4x108/s)
Muonium Production
(300 K ~ 25 meV⇒2.3 keV/c)
Surface muon
Ultra Cold m+ Source
Muon
storage
Resonant Laser Ionization of Muonium (~106 m+/s)
Muon LINAC (300 MeV/c)
New Muon g-2/EDM Experiment at
J-PARC with Ultra-Cold Muon Beam

11. New Muon g-2/EDM Experiment at J-PARC with Ultra-Cold Muon Beam
3 GeV proton beam
( 333 uA)
Graphite target
(20 mm)
Silicon Tracker
Surface muon beam
(28 MeV/c, 4x108/s)
66 cm diameter
Muonium Production
(300 K ~ 25 meV⇒2.3 keV/c)
Surface muon
Super Precision Magnetic Field
(3T, ~1ppm local precision)
Ultra Cold m+ Source
Muon
storage
Resonant Laser Ionization of Muonium (~106 m+/s)
Muon LINAC (300 MeV/c)
New Muon g-2/EDM Experiment at
J-PARC with Ultra-Cold Muon Beam

12. Injection, kicker and positron detector
Muon beam is injected here
Magnet coil
kicker mm
detector

13. Expected time spectrum of me+nn decay
High energy positron tends to be emitted in the direction of muon spin.
Parasitic EDM search
in up-down asymmetry
g-2 precession spectrum wa
dm=2E-20 e・cm
Up-down asymmetry
∝EDM
Time

14. Requirements Detector should be efficient for
Positron track with p = MeV/c in 3T solenoidal B-field
Immune to early-to-late effect
The decay positron rate changes by two orders of magnitude.
1.6 MHz/strip  10kHz/strip for 200 um pich Silicon strip.
The positron detector must be stable over the measurements.
Zero E-field (<<10-2 V/cm) at muon storage area
Not spoil the precision B-field ( <<0.1ppm) at muon storage area
Analyzing
power
Number of event
Above threshold
pth(e+)
100MeV/c
200MeV/c
300MeV/c
rate per
200 mm strip
1.6 MHz
0.01 MHz
Muon life time 6.6 ms

15. g-2 silicon tracker
Tracking vanes made of Double-sided Silicon strip sensor
Anticipating excellent stability and high granularity
Number of sensors
384 for 24 vanes*
Number of channels
0.2 mm pitch
288k for 24 vanes
Detector area
0.12 * number of vanes [m2]
2.9 m2 for 24 vanes
* design studies in progress to determine these parameters
576 mm
580 mm
g-2 silicon tracker
front
back
g-2 silicon vane

16. The detector model
A GEANT4 model made of DSSD sensors (300mm thick) has been developed.
Dynamical Si response yet to be implemented (as discussed by Zbynek Drasal on Wed)
Track-finding performance is a key in the tracker design
Maximum ~10 tracks/10 ns
Algorithm based on the Hough transform in “zf” plane is being explored.
Example event display
Top view
Side view
Signal e+ (>150MeV)
BG e+ (<150MeV)
Lead developers:
Kazu Ueno (RIKEN)
Hiromi Iinuma (KEK)

17. Evaluation of DSSD sensor
HPK’s Belle-II DSSD sensor (discussed by Markus Fridel on Tue)
was used to evaluate timing response of the sensor.
A fast shaping ASD was wire-bonded to a part of strips (3x16 strip)
ASD
Special thanks to
Toru Tsuboyama (KEK)
and Belle-II SVD group
ASD
Belle-II
DSSD
Bias
XY stage
p-side

18. Sensors from HPK Technical details (layers 4,5,6):
Dimensions: 59.6 x mm2
p-side:
Readout pitch: 75 µm
768 strips
n-side:
Readout pitch: 240 µm
512 readout strips n-side
Atoll p-stop scheme
21 June 2011
Markus Friedl

19. First look at signal from sensor
Test pulse (7fC)
20 mV/div
40 ns/div
IR laser (1060nm), n-side
Full depletion above 60 V
Well identified signals from 90Sr as well as IR laser with a rise time of 10 nsec
Plan to investigate timing response as a function of bias voltage, instantaneous rate, and temperature.
Plan to perform a beam test at CERN in collaboration with the SiLC.

20. Front-end electronics
Muon spill comes in every 40 msec. We measure decay positrons for first 33 msec.
Data acquisition sequence resembles to that of LC. The SiLC collaboration led by Aurore Navarro-Savoy (Paris) has been developing FEE for LC.
R&D started to adopt the SiLC front-end technology to this experiment (French-Japan collaborative research program, ).

21. Summary A new muon g-2/EDM experiment at J-PARC:
Off magic momentum
Ultra-slow muon beam + compact g-2 ring
Start in 2016
Complementary to FNAL g-2
Silicon tracker for g-2
Not quite a vertex detector, but a tracker for incoming low energy positrons
Stringent requirements on early-to-late effect, E-field and B-field
Conceptual design and R&D are in progress