“tests of a proximity focusing rich with aerogel as radiator” toru iijima / nagoya university...

“Tests of a proximity focusing RICH with aerogel as radiator”

Toru Iijima / Nagoya [email protected]

for Belle Aerogel-RICH R&D group

Introduction for aerogel + proximity focusingSimulationResults from the 1st beam testDiscussionSummary

“Tests of a proximity focusing RICH with aerogel as radiator”, by Toru Iijima, June 8, 2002

RICH20025-10 June 2002Pylos, Greece

Collaborators

Belle Aerogel-RICH R&D group;

I.Adachi2, I. Bizjak5, A. Gorisek5, T. Iijima3, M. Iwamoto1, S. Korpar5,8, P. Krizan7,5, R. Pestotnik5, M. Staric5, A. Stanovnik5,6, T. Sumiyoshi4,

K. Suzuki2 and T. Tabata1

1 Chiba University, Chiba, Japan2 High Energy Accelerator Research Organization (KEK), Japan

3Physics Department, Nagoya University, Nagoya, Japan4Physics Department, Tokyo Metropolitan University, Tokyo, Japan

5 Jozef Stefan Institute, Ljubljana, Slovenia 6 Faculty of Electrical Engineering, University of Ljubljana, Slovenia

7 Faculty of Mathematics and Physics, University of Ljubljana, Slovenia8 Faculty of Chemistry and Chemical Engineering, University of Maribor, Slovenia



IntroductionSilica aerogels…

Collidal form of SiO2

=0.1g/cm3

Prosity ~ 95% (n=1.03)n=1.006~1.06

⇒useful for /K separation in GeV region

Applied in many particle/nuclear physics exp’s.But, mostly used in threshold mode (before).

Limitation for imaging Rayleigh scatteringCracks

Established techniqueSimple & reliable

Limited momentum coverageKaon ID in veto mode



KEK Aerogel

Development in 90’s for Belle-ACC at the KEK B factory.New single-step production method developed in collaboration with Matsushita E.W.CoGood optical quality:

• Transmission• Index uniformity

Long term stability• Hydrophobicity• Radiation hardness

Improved optical quality of aerogels →Break through for imaging (“Aerogel-RICH”).



Transmission of aerogels

Almost 3 times better transmission(dominated by Rayleigh scattering)



Index uniformity

n/(n-1) = ±3% (FWHM) in Belle-ACC experience



Ring viewed by IIT

Yes, rings are there !



RICH w/ aerogel radiatorLarger c between two particle species

Wider PID coverage ⇔ threshold/K separation@ higher momentum (~10GeV/c?) separation @ low momentum (<1GeV/c)

Note: /K sep.(5GeV/c) ~ sep.(1GeV/c)

Compact ring size ~ 13°for n = 1.03 / = 1

Small material thickness

Photodetection in the visible regionShort wave length component strongly suppressed by Ra ｙ leigh scattering.

Cherenkov Angle

0

10

20

30

40

50

60

0 1 2 3 4 5p(GeV/ c)

d(the

ta) [m

rad]

-K

K-p

n=1.47n=1.03



Proximity Focusing ?

Mirror focusingHERMES/LHC-B (open geometry exp.)Thick aerogel

⇒ Easier to obtain enough light yield.

Proximity focusingSuitable for collider exp.Aerogel must be thin enough not to deteriorate the angle resolution.

⇒ Light yield ?Never been considered well by other exp’s.

Talk by M.Buenerd (AMS)

Maybe difficult but CHALLENGING⇒Our R&D



Possibility at Future BellePresent Belle PID system

Combination of dE/dx + ToF + ACCKID eff.=88%/fake=8.5%.“Particle ID Holes”

• EACC works only for tagging• e/- separation at low momentum

Proximity focusing aerogel-RICH for the endcap to cover give /K sep.in 0.8<p(GeV/c)<4.5※photodetection is hard for Barrelphotoelectrons must drift perpendicular to the B filed axis.

TOP counter for Barrel Talk by T.Ohshima⇒



R&D HistoryBy 2000: Some preliminary studies Imaging test with IIT / Photodetection / Simulation

… busy years for Belle-ACC though,…

March 2001: “Proximity focusing aerogel-RICH” introduced as a possible Belle PID upgrade option by T.I.

J.Stefan institute joined the R&D

Discussion for Super-KEKB/Belle

June‐Oct. 2001: Cosmic ray test at IJS.

Nov.‐Dec. 2001: Beam test at KEK 12 GeV-PS



Simulation IngredientsProduction of Cherenkov photons ：　 F-T formulaChromatic dispersion ：　 Scaled from fused silica Rayleigh scattering ：

Mean free path based on transmission data (with correction of finite acceptance of photospectrometer)

Photodetection ：　Bialkari photocathode (QE = 25% at 400nm)

Pad size : 5mm/10mm



Simulation Result (I)Simulated Npe for unscattered photons.

Normal incidenceAssume 100% geometrical acceptance for photodetection

Higher n is preferred to have enough light yield for pions at 0.8 GeV/c.⇔Lower n gives better separation at high momentum (next slide).

Npe: Momentum DependenceAerogel thickness = 20mm

0

5

10

15

20

0 1 2 3 4 5 6Momentum (GeV/c)

Npe (

unsc

atter

ed&d

etecte

d)

pi 1.030pi 1.050pi 1.070K 1.030K 1.050K 1.070



Simulation Result (II)Simulation indicates:

Npe>12 possible for light velocity particlesN=1.030 gives better separation, but light yield at around threshold (p~0.8GeV/c) may be critical. Optimal n ~1.05⇒Separation @ 4GeV/c > 5 possible even with 10mm read-out pad.⇒Need verification with experiment.

pi/ K separation20mm thick / +-5mm reso.

0

5

10

15

20

25

0 1 2 3 4 5 6Momentum (GeV/ c)

Sigma

1.0301.0501.070

0.31

0.72

0.860.92

0.950.96

0.59

0.91

0.97

0.91

0.98

Numbers: Eff (Npe>=6) for K(not shown if >0.99)

4GeV/c

K

5.7 separation

Cherenkov angle



2cm thickn=1.03/1.05/1.07

p = 0.5~4.0Gev/c, p

Incident angle0 ~ 30 deg.

(Gas C to eliminate e)

1st Beam Test

Nov.25~Dec.2 @ KEK-PS, 2 beam line

Index Thickness(mm)

t(mm)

1.029 21 38

1.050 19.5 15

1.070 20.5 7.2

Aerogel sample



Photodetection

Coarse granularity

Fine granularity

6×6 Multi-anode PMT array based on Hamamatsu R5900-M16

36% photocathod coverage: □18mm / 30mm pitch

Two read-out configurationCoarse granularity:

Every 4 pads grouped together (144ch) ⇒optimum for light yield measurement

Fine granularity: only 1/3 sector connected to TDC (192ch) ⇒optimum for angular reso. measurement



Observed Ring Image

Coarse granularity, 3GeV/c -

n=1.029 (2cm thick)

2D hit distribution w.r.t beam Typical hits / event

Ring expected from tracking

Hit due to beam



Data @ p= 0.5GeV/ce-, -, - at low momentum with beam line polarity at negative

electron vetoby gas C



Typical distributionNdet & are obtained by fitting the distribution.

Gaussian + background NsNdet = Ns/#eventAlso checked Ndet by counting hits in ±3 window around the peak. is the single photon angular resolution.

Gaussian+background

Ndet = Ns/#event

Counting in ±3 window

＊ Poisson based on 0 hit bin



Detected photon / event

Ndet = 2.6/2.7 for n=1.029/1.050 samples (2cm thick).Note: n=1.050 has worse transmissionCorrection by PMT array acceptance applied (event-by-event).

C (in PMT acceptance)C (whole ring)

fcorr =

2cm coarse2cm fine2+2cm coarse

2.8cm Novosibirsk



Angular resolutionFine granularity (4.5mm pad)

⇒ ~ 10mrad at d = 20cm, 2cm thick, n=1.029/1.050.d: distance between radiator and photodetectorvaried depending on index: d=29cm (1.029), 21cm(1.050), 17cm(1.070)Right figure shows the results when normalized to d = 20cm.

Normalized at d=20cm

2cm fine gran.

d



Momentum dependence

Momentum dependence is as expected.Lines in figures are expected dependence fit to the data points.Effect of multiple scattering at low momentum ()

Ndet/ring (not normalized by d)



Incident angle dependence

Almost no dependence on incident angle.

Ndet/ring (not normalized by d)



Discussion

Comparison to expectation (2cm, 3GeV/c pions)index Ndet (coarse gran.) (mrad, fine)

Measured Expected Measured Expected

1.029 2.6 2.7 7.0 6.7

1.050 2.7 2.9 9.8 9.7

Assume: 36% effective area 70% correction eff.

Importatnt R&D issues: Improvement of aerogel quality

Better transmission Improvement of photodetection

Good effective area (36% 70%)Good efficiency for single photon



Improvement of aerogels

Significant increase in Ndet with n=1.050 Novosibirsk sample.Ndet = 4.6 (28mmt) 2.7 (20mmt) w/ KEK70% increase (40% increase when thickness difference accounted).

We aim at improving the quality at n~1.05 by revisiting;

Production method/procedurePrecursor materialSolvent

Other R&D issuesSizeFlatness etc.

Novosibirsk sample (48mm)

Large potential to improve

Talk by A.F.Danilyuk



Photodetection

Flat Panel PMT array for R&DNewly developed 8 ×8 multi-anode PMT by HPK.Effective area = □49mm for □51.7mm package (90% coverage)Single p.e. peak is observable.

Further performance studies and better understanding of the detector behavior.Optimization of design

In real application in 1.5T magnetic field at Belle,⇒Proximity focusing HPD with good effective area

Flat Panel HPD/HAPD?



Summary

Improved optical quality of aerogels in 90’s opened the window for aerogel-RICH.We have tested possibility of proximity focusing aerogel-RICH with beam

Angular resolution < 10mrad with ~5mm pad.Light yield ~ 2.7 with photodetection efficiency of 25% (=36×70%).

⇒ Good starting point;Results are reasonable and understood.They clarify the R&D targets.

– Further improvement of aerogel quality (n ~ 1.05)– Proximity focusing H(A)PD with good effective area.

×(1.5~2.0)×>2

Our hope for improvement factor.If achieved, K/ separation > 6 (@ 4GeV/c) possible



Thank you !!!



Backup Slides



Lens System

Optionally used in the beam test.



Importance of K/ separation remains unchanged also at the Super-Belle.Flavor tagging (p<2 GeV/c)

• For any CPV measurement in neutral B.Two-body decays (1.5<p<4GeV/c)

• B→/KB→/ K• B→DK/D• Others:’/’K etc.

Increased demand at the Super KEKB/Belleb→d/b→srequired reduction ~50?)

Good separation in inclusive measurements (multiple tracks)Full reconstruction tag (efficiency/purity)How about / charm ?

++ low momentum e/ separation (< 1 GeV/c)B→K(*)ll (b →sll) (especially in channel)

Good K/< 5 GeV/c good ⇒ < 1 GeV/c

Physics Requirement

Large impact of improved PID



Present Belle-PIDCombination of dE/dx + ToF + ACC

Performanceeff.=88%/fake=8.5%.

Concerns: Background immunity

• TOF dead time: O(10%)Material thicknessRadiation hardness“Particle ID Holes”

• EACC works only for tagging• e/- separation at low momentum

⇒Points of improvement @ upgrade



K*+

++0 K++0

B+ → / K*+ /KB0 → ++0 / K++0 Conditions:

Br(s) = 20×Br(d)Present eff/fake from data(open histograms)Improved eff/fake = 0.975/0.025~ 4 separation of two Gaussian(hatched histograms)

K/-ID Impact in b→d/b→s

Present 0.95/0.05 0.975/0.025 0.99/0.01

ds(2chg) 0.64 1.3 (1.1) 2.3 (1.8) 4.6 (2.6)

ds (3chg) 0.45 0.90 (0.78) 1.7 (1.2) 4.2 (1.9)

(): Endcap as it is.

PID w/ good eff/fake and hermeticity is important



Lepton/-ID Impact in b→sllForward-backward asymmetry (AFB)

Need to measure AFB as a function of Mll

May flip sign below and above 1.5GeVHowever,

In K channel, Mll<1.5GeV is difficultbecause (almost) no separation.

Present MUID + 97.5% @ p<1GeV/c by Cherenkov

⇒ ×2 events in Mll < 1 GeV ⇒ ×1.5 events in 1 < Mll < 2 GeV

A good Cherenkov detector will givesignificantly earlier finding of AFBand test of the sign flip.



‘Flat panel HPD’ Concept

Photon counting w/ hybrid PD(typical spectrum)



Dual Radiator SchemeInteresting option, if aerogel transmission is improved.Light yield can be increased without deteriorating the angular resolution.Need study effectiveness with simulation

“tests of a proximity focusing rich with aerogel as radiator” toru iijima / nagoya university...

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