Beam test of low index sillica aerogel

Yukiyoshi KonRCNP, Osaka University

Collaboration meeting @Tiwan2008/5/2

Low reflective index silica aerogel was developed by Chiba University group.

To use as AC veto Counter, we tested this sillica aerogel by beam at LEPS .– 2008/4/21,22– Tabata, Saito, Kawai, Chiba University, Kon

Detection efficiency and mean # of photoelectron was estimated about index n = 1.015, 1.0082 and 1.0027.

Method to estimate efficiency• Aerogel Counter:

– Cerenkov effect

– PhotomultiplierEmission of photoelectrons from cathode obey

Poisson statistics.

• Detection efficiency:

n

n

1

,1cos

eNe

e NN

NNNP exp

!),(

ee NNP exp1),0(1

S1 S2C

S1, S2: Scintillation countersC: Cerenkov Counter

Cerenkov counter(: C)’s signal is taken with S1, S2 coincidence trigger.

Beam is injected inside Cerenkov counter perfectly.

Pulse hight distribution obteined by ADC outputs forms Poisson distribution.

all

pedee

all

pedee

N

NN

N

NN

log

1exp1

I. Adachi et al./Nucl. Instr. and Meth. in Phys. Res. A 355 (1995) 390-398

Counter design

Light guide box: width 125 x hight 260 x thickness 65Covered by reflector Alminized mylar & Gore-tex sheet. 4 Photomultiplier: Fine mesh type (Hamamatsu

Photonics H6614-70)Aerogel was arranged by hangging in midair by strings.

Beam test

Beam: Converting LEP into e+e- shower by 10mm x 10mm lead sheet.

Trigger: Tag x !UP x (S1 x S2 x S3) S1, S2: front Scintillation Counters, S3: backward Scintillation Counter.

Set up

LEP

S1

S2

S3C

TOF Wall

Convertor

Index and Reflectorn = 1.015 n = 1.0082 n = 1.027

40 mmMylar

Mylar Mylar Mylar (Plane)Gore-tex

65 mmMylar

Mylar Gore-tex

Mylar (empty box)

Gore-tex (empty box)

100 mm

100 mm

20 mmScillica aerogeln = 1.0027 was first beam test in the world.But, Transmission was bad.

n = 1.015 n = 1.0082 n = 1.0027

π 0.802 GeV/c 1.088 GeV/c 1.898 GeV/c

e 0.00293 GeV/c 0.00695 GeV/c 0.00397 GeV/c

Threshold momentums

Cerenkov angle

• Cerenkov angle:

• Beam: electron

• In very low index point, Cerenkov angle is a few degrees.

n: smaller

β

θ [rad.]

n = 1.0027, 1.0082, 1.015, etc.

n 1cos 1

1

Aerogel arangement

e

40 mm 65 mm

20 mm

100 mm

Light‘s pass length is shorter.But emitted photon is less.

Emitted photon is larger than 40mm one.But path length is longer.

Version A:

e

40 mm

Cerenkov light mainly is ejected to forward direction. It is difficult to go out from aerogel in horizontal dirrection.

Version B:Only n = 1.0027, mylar

Index dependence

n=1.015 n=1.0082 n=1.0027Analyzed event #: 10000 for all samples.

Mylar, 40mm

Pulse hight distribution was selected to get correct photoelectron event by TDC cut.4 photomultiplier‘s event # was summed up.

Photoelectron’s number became smaller, as soon as index was smaller.

n=1.015 n=1.0082 n=1.0027

Pedestal 9163

All 39984

Npe = 0.640Eff. = 0.771

Pedestal 13898

All 40000

Npe = 0.451Eff. = 0.653

Pedestal 25794

All 40000

Npe = 0.191Eff. = 0.355

Estimation - The number of mean photoelectron and efficiency

Pass length dependence40mm 65mm

Npe = 0.640Eff. = 0.771

Npe = 0.994Eff. = 0.899

Npe and efficiency was increased , as pass length longer.

Difference of aerogel arrangemnt

Npe = 0.191Eff. = 0.355

Npe = 0.168Eff. = 0.321

A B

Npe and efficiency of version B was little worse.

Difference of reflecting materials

Npe = 0.639Eff. = 0.771

Npe = 1.061Eff. = 0.913

Gore-texmylar

Efficiency ofGore-tex counter was better- it’s suitable for random reflection in light guide box.

Empty Counter

Npe = 0.014 Npe = 0.181

Gore-texMylar

Little Cerenkov light was emitted• Air Cerenkov ?

Photon # was more than mylar.• Scintillation light from Gore-tex ?

Summary

We tested low index sillica aerogel with beam, and estimated detection efficiency.

For NTPC Experiment, counter coverd Gore-tex one is not suitable for e+e- beto counter because of over veto the hadron.

AC beto counter was exchanged to (n=1.0082, version B, mylar) from (n=1.01, version B, Gore-tex).

Efficiency should be rechaecked another method, beacause pedestal couldn’t from distribution perfectly.

- Fitting with poisson distribution conboluted gaussian function.

n = 1.015 n = 1.0082 n = 1.027

40 mm0.771

0.653 0.355 0.3210.913

65 mm0.899

0.788 0.975

Efficiency