A Study of Proximity Focusing RICH A Study of Proximity Focusing RICH with Multiple Refractive Index Aerogel Radiatorwith Multiple Refractive Index Aerogel Radiator

1I. 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

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 (peter.krizan@ijs.si)

Aerogel radiator

Position sensitive PDwith B=1.5Tesla

Cherenkov photon

200mm

n=1.05

Proximity Focusing RICH with Aerogel Radiator

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• Position sensitive photodetector with ~5x5mm2 pixel size• Electronics for read-out

Belle detector

Performance Test at 2002 Beam Experiment

n=1.05 aerogel radiator

=14mrad Npe = 6 4 separation confirmed

4.0GeV“K”4.0GeV

typical event

RICH prototype counter

Hamamatsu Multi-anode Flat-Panel PMT(H8500)

/K 4 separation at 4 GeV/c achieved with a prototype counterneed more photoelectrons for a further improvement as well asfor more robustness HOW ?

R&D project since 2000

Innovative idea to Get More Photoelectrons w/o Degrading Resolution

Simple accumulation of aerogel layers allows to detect more Cherenkov photons, however it deteriorates overall resolution.

n1 n2

n1<n2

Employ multiple layers with different indices so that Cherenkov images from individual layers overlap on the photon detector.

Concept Validation in Beam

4cm-thick single index aerogel

(1p.e.) = 22 mrad Npe ~ 10.6

(track) = 6.9 mrad

Focusing by 2cm+2cm aerogel (n1:1.047, n2:1.057)

n1 n2 (1p.e.) = 14.4 mradNpe ~ 9.6

(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

Measured index

Tra

nsm

issi

on le

ngth

at

400n

m(m

m)

old synthesis method

Transparency improvement for samples with n=1.040~1.060

Crack-free large sample has been made

110x110x20mm3 150x150x20mm3

n =1.050

refractive index control

n = 0.0003

index deviation from average

Extension of the new concept: multiple layer radiator

High accuracy of index is advantageous for dual/multiple layer radiator configurations

2001 sample

Target indexAveraged 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

1.0451.050

1.0551.062

# of photoelectrons

▲： single index layer

●：multiple layer

1st 2nd 3rd4th

1st

2nd

3rd

4th

▲： single index layer

●：multiple layer

With new aerogels provided, we have examined the performance by stacking more layers during a 2005 beam test

single photon resolution

Comparison between single index and multiple radiator schemes(3.0 GeV/c pion beam) resolution per track

best (track) = 4.2 mrad

We have succeeded in getting more Npe without an increase in the single photon uncertainty.

Single index radiator n = 1.045 only

Multiple layer radiator

n1 = 1.045

n2 = 1.050

n3 = 1.055

n4 = 1.062

|()-()|/(track) ~5.5separation achieved for 4 GeV/c with Npe= 9.1 Progress on aerogel optical quality has b

een examined in test beam

radiator thickness(cm)

Npe

2001 sample

2005 sample

Significant increase of Npe observed for 2005 sample, while old sample gets saturated around Npe~4.5

Transmission length at = 400nm more than doubled

10mV

Conclusions

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.

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. T.Iijima et al., NIM A543(2001)321.2. T.Matsumoto, S.Korpar et al., NIM A521(2004)367.3. T.Iijima, S.Korpar et al., NIM A548(2005)383.4. I.Adachi et al., NIM A553(2005)146.5. P.Križan et al., physics/0603022, to be published in NIM A.

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

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).

Beam test data:

50ps resolution per single photon ~20ps per track

~38ps per track

Separation of pions and protons at 2 GeV, flight distance 0.7m.