# Presentation: 709491

## Concept of 

- Tianchi Zhao
- University of Washington

**Concept of **
**an Active Absorber Calorimeter**
- A Summary of LCRD 2006 Proposal
_**A Calorimeter Based on Scintillator and Cherenkov Radiator Plates Readout by SiPMs**_
**Tianchi Zhao**
**University of Washington**
**Adam Para**
**Fermilab**

- March 12, 2006, LCWS06 Bangalore, India

## Energy Compensation

**Reference:**
**1. “Compensating hadron calorimeters with Cerenkov light**”
-           Winn, D.R.   Worstell, W.A. , IEEE Trans. NS Vol 36 (1989) 334
**2. “Hadron Detection with a Dual-Readout Calorimeter”**
-           N. Akchurina et al., NIM A 537 (2005) 537-561
**3. “Cherenkov Compensated Calorimetry”**, Yasar Onel et al., 2004 LCRD Proposal

- Hadron energy Eh is given by:

- Eh : Compensated hadron energy
- Esc : Energy measured by plastic scintillators
- Ech : Energy measured by cherenkov radiators

## Basic Idea of Active Absorber Calorimeter

**Basic Idea of Active Absorber Calorimeter**
**In a sampling calorimeter based on active detector (scintillator) **
**+ absorber layers, partially replace absorber plates **
**by cherenkov radiator and**
**read out both ****scintillation**** light and  ****cherenkov**** light.**

- Thin plastic scintillator plates:
-      Measure energy of both hadron and EM components of hadron showers as in a standard sampling calorimeter

- Cherenkov radiator

- Plastic scintillator

- Heavy structural layer

- Thick Cherenkov radiator plates:
-       Measure mostly energies of EM components in hadron showers in an active absorber calorimeter

- Both readout by WLS fiber and SiPM/MPPC

## Configuration Example 

**Consider a 40 layer arrangement**

| Material | Layers | T 
(cm) | Layer   Thickness
(cm) | No. of  T |
| --- | --- | --- | --- | --- |
| Plastic scintillator | 40 | 80 | 40  0.5 = 20 | 0.25 |
| Lead glass  | 30 | 30 | 30  2 = 60 | 2 |
| Iron | 30  | 16.8 | 30  0.5 = 15 | 0.89 |
| Iron | 10 | 16.8 | 10  2.5 = 25 | 1.49 |
| TOTAL | 40 |  | 120 | 4.63 |

- 20 mm lead glass

- 5 mm steel

- ~1.3 X0

- 25 mm steel

- Last 10 layers

- First 30 layers

-  5 mm plastic scintillator

## Options for EM Calorimeter Section

- 15 mm PbF2

- 3 mm scintillator

- 2 mm tungsten

- 15 mm PbF2

- 3 mm scintillator

- 2 mm tungsten

- 20 layers

-  Good EM energy
-     resolution
-  Maintaining energy
-      compensation

- Any other EM calorimeter considered for ILC
- A segmented active absorber calorimeter with dual energy readout

**Example**

## Transverse Segmetation

-  Need Monte Carlo simulation to optimize the choice of
-    segmentation for
-  	- EM section
-  	- Front part of hadron section
-  	- Back part of hadron section
-  Minimum size of plates mainly limited cost considerations
-             3 cm × 3 cm (?)

## Cherenkov Light Readout by WLS Fiber 

- Lead glass: **  **2.4  0.5 p.e.
- Bicron 408:  27  4 p.e.                                 _**Ralph Dollan, 2004 Thesis**_

**Cherenkov Light Readout by WLS Fiber **

** ****Groove along 40 mm length**
** ****White paper wrapped**
** ********1 mm BCF-91AWSL fiber **
** ****One end open**
**  ****XP1911 PMT **
- (Average Q.E. ~ 13% for BCF-91A )

**Bicron 408**
**6 x 6 x 30 mm****3**

- P.E. yield of lead glass is about 5% of plastic scintillator

**Lead glass SF57**
**10 x 10 x 40 mm****3**

## Cherenkov Light Yield of 1 Charged Particles

**Forward**

| Cherenkov Radiator | Density |  X0 
(cm) |   
(cm) | Index of 
refraction |  Absorption Edge (nm) |
| --- | --- | --- | --- | --- | --- |
| SF2 lead glass | 3.85 | 2.76 | 38 | 1.65 | 330 |
| SF6 lead glass | 5.2 | 1.7 | 30 | 1.81 | 360 |
| SF57 lead glass | 5.5 | 1.5 | 28 | 1.85 | 370 |
| PbF2 crystal | 7.8 | 0.93 | 20 | 1.82 | 250 |
| UVT acrylic | 1 | 40 | 80 | 1.5 | 250 |

** ****Lead glass was popular calorimeter material in LEP experiments**
** ****Cast or extruded lead glass has the same light yield as cut/polished crystals**

**Plastic scintillator light yield**
**     ****~ 10,000 photons/cm**

**Chrenkov light yield:**
**     ****200 – 300 photons/cm **

**Isotropic**

## Cherenkov Plate Readout by MPPC or SiPM

- MPPC or SiPM

- WLS fiber

- Cherenkov Radiator

- 2 cm

- Target: Combined efficiency = η1 × η2 × η3  × η4   >1%

** ****η****1** **:** **probability of a photon hitting the core of a WLS fiber **
** ****η****2**** :**** ****conversion efficiency of WLS fiber **
** ****η****3**** : light trapping efficiency in WLS fiber **
** ****η****4**** : MPPC/SiPM quantum efficiency**

**Cherenkov photon ******** Photoelectrons**

## Signals from a   1 Charged Particle

**Number of P.E. = N****0**** x ****η****1**** x ****η****2**** x ****η****3 **** x ****η****4 ****= 400 x 1.6 % = 6.4 **

** ****Cherenkov light yield: N****0**** = 400 ********’s in 2cm radiator**
** ****Light collection efficiency by WLS fiber: ****η****1**** ~ 50% **
** ****WLS fiber efficiency: ****η****2**** ~ 80% **
** ****Assume ****η****3**** ~ 10% with mirror at far end of fiber**
** ****MPPC Q.E.: ****η****4**** ~ 40 % (100 pixel device may be sufficient)**

** **

**MPPC**

**Mirror**

**WLS fiber: high efficiency for blue light; emits green/yellow light to match MPPS**

**WLS fiber**

**Should be able to make reasonable measurements for high energy EM showers**

## An Alternative Configuration

**An Alternative Configuration**

| Material | Layers | T 
(cm) | Layer   Thickness
(cm) | No. of
T |
| --- | --- | --- | --- | --- |
| Plastic scintillator | 40 | 80 | 40  0.5 = 20 | 0.25 |
| UVT Lucite | 30 | 70.3 | 30  2 = 60 | 0.85 |
| Uranium | 30  | 10.5 | 30  0.5 = 15 | 1.43 |
| Iron | 10 | 16.8 | 10  2.5 = 25 | 1.49 |
| TOTAL | 40 | 30 | 120 | 4.02 |

- 20 mm lucite

- 5 mm uranium

- 25 mm steel

- Last 10 layers

- First 30 layers

-  5 mm plastic scintillator

## Potential Advantages

- Energy compensation for hadron showers on event by event basis as demonstrated by the DREAM Project, _but allowing for fine transverse and longitudinal segmentation__ _
- Performance should be better than the dual r eadout calorimeter of Dream project since cherenkov radiator in our implementation is 2/3 of total volume!!
- Energy resolution should be better than a calorimeter based only on scintillator plates and should achieve the “required” jet energy resolution
- Tighter spatial spread of hadron showers recorded by Cherenkov radiator may help correctly assigning energy clusters in HCal to tracks that produced them, therefore, improving the results of PFA.
- Very flexible design options for material choices and segmentations

## Disadvantages

- Significant cost increase compared to HCal that uses plastic scintillator plates only
- Density of calorimeter is reduced compared to a design that uses passive absorber only. Using a heavy metal such as uranium or tungsten may solve this problem.