# Presentation: 023044

## Catcher

- Scope of subsystem
- Current specification from physics
- Current design
- Open issues
- Resources

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## Scope of subsystem

**“****Photon veto inside/near the beam at downstream end”**
_**TASK**_
- Detect photons from KL decays passing through the beam hole
- Be insensitive to a vast amount of unwanted neutrons
_**SOLUTION**_  Utilize Cherenkov radiation
- Lead and **aerogel tile** sandwich counter inside the beam	named “aerogel catcher”
- Lead and **acrylic slab** sandwich counter near the beam	named “guard counter”

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## Specification from physics

_**Photon Efficiency**_
- Energy spectrum of photonswhich go into the catcher  after canonical kinematical cuts(K2; dominated by odd pairing events)
- >98% for 300MeV photons
- >99% for more energetic ones
_**Sensitivity to neutrons, K**__**L**__**s**_
- To avoid false vetoes by beam neutrons and surviving KLs...
- <0.3% for neutrons with Ekin=800MeV
- KL decaying in the catcher ends up to be detected,but false veto probability should be kept less than a few %

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## Current design  Overview

- _Current design__ __ Overview_

***Guard counter***

***Aerogel Catcher***

- beam

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## AEROGEL CATCHER  Principle of aerogel catcher

_**AEROGEL CATCHER**_
- Lead and **aerogel tile** counter
- Avoid detection of slow particlesfrom neutron interactions
- Distributed arrangement
- Coincidence along the beamhelps us catch forward  only

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## AEROGEL CATCHER Module - Elements / Optics

- _AEROGEL CATCHER__ __Module - Elements / Optics_

- TDR design

**Current design**

|  | TDR | Current |
| --- | --- | --- |
| Aerogel | 5cm-thick |  |
|  | 20cm sq. | 30cm sq. |
|  | n=1.03
(SP-30) | n=1.05
(IY-50) |
| Mirror | Parabolic | Flat |
| PMT /
Funnel | 5-inch dia. PMT |  |
|  | Winstone-type cone |  |
|  | Inclined | Upright |

_**Parameters of each module**_
- To get more Cherenkov lights
- To simplify optics for easy production

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## AEROGEL CATCHER Configuration

- _AEROGEL CATCHER__ __Configuration_

_**Distributed arrangement**_
- Module size: **30cm x 30cm**
- Pb converter: 2mmt per layer
- Number of modules: **420**
**12-21** in horizontal  with beam divergence
- 25 layers along beam(8.3 X0 in total)
- Z gap between layers: 35cm
- Coincidence condition
**>= 4 p.e.** in 1st layer (A)
**>= 2 p.e.** in 2nd layer (B)

- Top view

- Beam envelop

- 12m downstream of main detector

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## Expected performance of AEROGEL CATCHER Photon efficiency / Neutron sensitivity

- _Expected performance of AEROGEL CATCHER__ __Photon efficiency / Neutron sensitivity_

- Average over the whole position and angle

**Neutron sensitivity**

- 0.3% @ 0.8GeV

**Photon efficiency**

- >99% @ 300MeV

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## GUARD COUNTER  Principle of guard counter

_**GUARD COUNTER**_
- Lead and **acrylic slab** counter
- Slow particle doesn’t emit Cherenkov light
- Utilize the **total reflection angle**	in light transportation
- Cherenkov lights from slow particlesdon’t fulfill the total reflection condition

- Photon

- Neutron

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## Current design of GUARD COUNTER Guard counter

_**Counter to cover the halo region**_
- Soft but many neutrons around the beam
- Lead & acrylic slab sandwich
- Size: 15cm x 15cm
- 8 layers of 2mm Pb + 10mm acrylic
- Read by 5 inch PMT
- 3 modules along the beam
- Number of modules: 144

- Side View

- Front View

- beam

- Module

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## Expected performance of WHOLE CATCHER SYSTEM Efficiency map of catcher + guard counter

- _Expected performance of WHOLE CATCHER SYSTEM__ __Efficiency map of catcher + guard counter_

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005

## Justification of the conceptual design Prototypes so far

- _Justification of the conceptual design__ __Prototypes so far_

_**Prototype 1 (2001-2)**_
- 1/4 size, flat mirror
- light yield
_**Prototype 2 (2002-3)**_
- 1/4 size, parabolic mirror
- light yield
- response to proton (as substitute for neutron)
- Check **single layer eff.** / **two-layers’ coincidence**
**Good agreement ****with MC**(with gas scintillation)

- PT2

- PT1

- RSVP Project Director's Review, N. Sasao (Kyoto U.)

- January 18, 2005