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A Study of Proximity Focusing RICH
with Multiple Refractive Index Aerogel Radiator
Adachi, 2I. Bertović, 3K.Fujita, 4T. Fukushima, 2A. Gorišek, 3D. Hayashi, 3T. Iijima, 3K.Ikado, 5M.Iwabuchi,
4H. Kawai, 6,2S. Korpar, 3Y. Kozakai, 7,2P. Križan, 4A. Kuratani, 8T. Matsumoto, 3Y. Mazuka, 8T. Nakagawa,
1S. Nishida, 5S. Ogawa, 2R. Pestotnik, 8T. Seki, 8T. Sumiyoshi, 4M. Tabata, 1Y. Unno
1I.
1:IPNS, KEK, Tsukuba, Japan / 2:J.Stefan Institute, Ljubljana, Slovenia / 3:Dept. of Physics, Nagoya Univ., Nagoya, Japan /
4:Dept. of Physics, Chiba Univ., Chiba, Japan /5:Dept. of Physics, Toho Univ., Funabashi, Japan
6:Faculty of Chemistry and Chemical Engineering, Univ. of Maribor, Maribor, Slovenia
7:Faculty of Mathematics and Physics, Univ. of Ljubljana, Ljubljana, Slovenia / 8:Dept. of Physics, Tokyo Metropolitan Univ., Tokyo, Japan
presented by Peter Križan ([email protected])
Proximity Focusing RICH with Aerogel Radiator
Performance Test at 2002 Beam Experiment
Developed for a new particle ID device in the Belle forward region
• improve /K separation up to 4 at 4 GeV/c
• limited space
• operational under 1.5 Tesla magnetic field
Key components
• Hydrophobic aerogel with refractive index of ~1.050 as a
Cherenkov radiator
Aerogel radiator
n=1.05
• Position sensitive photodetector with ~5x5mm2 pixel size
• Electronics for read-out
RICH prototype counter
n=1.05 aerogel radiator
“K”4.0GeV
 =14mrad
4 separation confirmed
Npe = 6
typical event
Position sensitive PD
with B=1.5Tesla
Hamamatsu Multi-anode
Flat-Panel PMT(H8500)
200mm
/K 4 separation at 4 GeV/c achieved with a prototype counter
need more photoelectrons for a further improvement as well as
for more robustness
HOW ?
R&D project since 2000
Belle detector
 4.0GeV
Concept Validation in Beam
Innovative idea to Get More Photoelectrons w/o Degrading Resolution
Employ multiple layers with different indices so that
Cherenkov images from individual layers overlap on
the photon detector.
4cm-thick single index aerogel
2001 sample
n1
q(1p.e.) = 22 mrad
Npe ~ 10.6
Simple accumulation of aerogel layers allows
to detect more Cherenkov photons, however
it deteriorates overall resolution.
n2
q(track) = 6.9 mrad
Focusing by 2cm+2cm aerogel (n1:1.047, n2:1.057)
n1 n2
q(1p.e.) = 14.4 mrad
Npe ~ 9.6
n1<n2
q(track) = 4.8 mrad
Novel idea of dual radiator “focusing scheme” has been proven
 Only possible because refractive index of aerogel radiator can be adjusted in the production
 Require further improvement of aerogel transparency not only for n=1.050 but for other indices
Progress in Aerogel Radiator Production
Extension of the new concept: multiple layer radiator
refractive index control
Transmission length at 400nm(mm)
Transparency improvement for samples with n=1.040~1.060
With new aerogels provided, we have examined the
performance by stacking more layers during a 2005 beam test
n = 0.0003
High accuracy of index is
advantageous for dual/multiple
layer radiator configurations
Transmission length at  = 400nm
more than doubled
Single index radiator
n = 1.045 only
Multiple layer
radiator
n1 = 1.045
n2 = 1.050
n3 = 1.055
n4 = 1.062
index deviation from average
1.045 1.055
1.050 1.062
Crack-free large sample has been made
Comparison between single index and multiple radiator schemes(3.0 GeV/c pion beam)
old synthesis method
n =1.050
# of photoelectrons
single photon resolution
resolution per track
Measured index
Target index
Averaged transmission
length at 400nm
1.045
46.6  1.4
1.050
40.4  1.1
1.055
32.8  1.1
1.060
28.9  0.7
4th
Progress on aerogel optical quality has
been examined in test beam
3rd
best (track) = 4.2 mrad
2nd
Npe
2005 sample
1st
110x110x20mm3
2001 sample
radiator thickness(cm)
150x150x20mm3
Significant increase of
Npe observed for 2005
sample, while old
sample gets saturated
around Npe~4.5
|q()-q()|/(track) ~5.5
separation achieved for 4
GeV/c with Npe= 9.1
▲：single index layer
●：multiple layer
1st
2nd
3rd
4th
▲：single index layer
●：multiple layer
We have succeeded in getting more Npe without an increase in the single photon uncertainty.
Conclusions
Additional feature: RICH+TOF
Idea: Make use of the fast photon detectors and measure time-of-flight
with Cherenkov photons from aerogel and from the PMT window
Beam test data:
50ps resolution
per single photon
 ~20ps per track
1. In 2004 we have introduced and tested a new technique which uses multiple
aerogel tiles with different indices so that Cherenkov photons can be
imaged to overlapping rings. With this configuration, we have demonstrated
a 5.5   separation with ~9 photoelectrons in the 2005 beam test.
2. Optical quality of aerogel tiles has been significantly improved. As a result,
photoelectron yield has been doubled. The radiator size can be enlarged by
86% and crack free sample was obtained.
10mV
~38ps per track
The Cherenkov photons from the window: can be used for
particles below the threshold in aerogel 
The separation in Belle should be even better: flight distance
~2m (instead of 0.7m in the beam test set-up).
Separation of pions and protons at 2 GeV,
flight distance 0.7m.
3. We have tested additional time-of-flight capabilities of such a counter. Both
Cherenkov photons from the aerogel radiator as well as from the PMT
window can be used. The latter would allow to extend the PID capabilities of
the counter to particles which are below the Cherenkov threshold in aerogel.
References
1.
2.
3.
4.
5.
T.Iijima et al., NIM A543(2001)321.
T.Matsumoto, S.Korpar et al., NIM A521(2004)367.
T.Iijima, S.Korpar et al., NIM A548(2005)383.
I.Adachi et al., NIM A553(2005)146.
P.Križan et al., physics/0603022, to be published in NIM A.