# Presentation: 070032

## The Lead TungstateElectromagnetic Calorimeterof CMS

- Q. Ingram
- on behalf of the CMS Electromagnetic Calorimeter Group
*Annecy, Demokritos, Belgrade, Bhabha, Bristol, Brunel, Caltech, CERN, Cyprus, Delhi, Dubna, Ecole Polytechnique, ETHZ, Imperial College, Ioannina, Lisbon, Lyons, Milan-Bicocca, Minnesota, Minsk, INR-Moscow, Lebedev Institute, Northeastern, Protvino, PSI, RAL, ENEA-Rome, La Sapienza U, Saclay, Split, Taiwan Central U, Taiwan U, Turin, Yale, Yerevan*
**	****	****	****   ****	****CMS, Goals, ECAL**
**	****	****	****   ****	****Lead Tungstate**
**	****	****	****   ****	****Photo-detectors & Electronics**
**	****	****	****   ****	****Assembly**
**	****	****	****   ****	****Calibration & monitoring**
**	****	****	****   ****	****Test beam results**

## Compact Muon Solenoid (CMS)

**21.6 m long x 15 m diameter;    12.5 k tonnes;    4 Tesla solenoid**

- 7 TeV protons

- 7 TeV protons

## Recent Photos of CMS Assembly

- Muon drift chambers mounted
- in barrel part of the yoke

- End-cap Muon cathode strip proportional chambers

## Inserting superconducting coil into vacuum tank

- Magnet inserted  into the outer tank September 2005
- Inner vacuum tank inserted October

**Coil is**
**12.5 m long**
**6 m ****Ø**

**Magnetic**
**Pressure**
**(4 Tesla):**
**60 bar**

## Standard Model Higgs (9/05)

**M****H ****< 186 GeV, 95% C.L**.

- Exclusion plot from LEP working group:
- http://lepewwg.web.cern.ch/LEPEWWG/plots/summer2005/

##    H        

**1 year at High Luminosity (1.10****34**** cm****-2****.s****-2 ****)**** **

- Background subtracted

**Background irreducible – need good energy resolution**

## Resolution Goal

_****__**E/E**__** = **__**a**__** **__**/**__****__**E**__**  **__****__**  **__**b**__**/E**__**  **__****__** **__**c**_

-  			    Aim:  Barrel	 End cap
**Stochastic term (a)      ****	****	****  ****2.7%         5.7% **
- (p.e. statistics, shower
- fluctuations, leakage, ...)
**Noise (b)****         ****	****         ****	****          ****155 MeV    770 MeV    **Low L
**                   ****	****         ****	****          ****210 MeV    915**** ****MeV    **High L
**Constant term (c)    ****	****	****  0.55%       0.55%**
- (gain stability, non-uniformities,
- inter-calibration,...)

## LHC/ECAL Conditions

_**Every 25 nsec:**_ 20 events, 1000 tracks in detector (high luminosity)
- 	****** ****fast, high granularity, triggering capability**** **
_**High radiation levels:**_ direct from collisions.  In ECAL Barrel ≤ 4 kGy
- 		           1 MeV neutron “soup”                          ≤ 2.1013 n cm-2
- 		                       (x 10 - 50 in End-caps)
- 	****** ****high radiation tolerance**
- ECAL detector is barely or practically _**unserviceable**_
- 	****** ****very high reliability**** **

## ECAL

## Lead Tungstate (PbWO4)

**	****	**

**Compact calorimeter:**
** ****CMS more compact, cheaper**

**Homogeneous calorimeter: excellent energy resolution**

**High density****	****	****8.28 g/cm****3**
**Short radiation length****	****0.89 cm**
**Small Moliere radius****	****2.19 cm**
**Short decay time****	****10 nsec**
**Cost ****	****	****    ****(was)****	****1.6 $ /cm****3**
**Peak light emission****	****430 nm**
**Temperature Coeff****	****- 2%/ oC**
**Refractive Index****	****	****ca 2.2 **
**Light yield****	****	****~ 5% of BGO**

**Radiation***** *****“hard”: scintillation and emission not affected, but transmission**
**         ****reduced by formation of colour centres ********constant monitoring**

## PbWO4 Quality Control

**	****	**

- Automatic testing of dimensions, transmission, light yield, longitudinal uniformity

- Sharpness of transmission edge indicator of radiation resistance
- (Crystals from Bogoroditsk, Russia)

- Crystals from Shanghai all
- tested after irradiation

## Photo-Detectors (APDs, VPTs)

_**Requirements:**_
** ****Gain (low light yield of PbWO****4****)**
** ****Operation in 4 Tesla field****	****	****	**
** ****Radiation hard (10 yrs: 2 10****13**** n/cm****2**** in Barrel, **
**                                           ****> 5 10****14**** n/cm****2** **in End-caps)**
**- High reliability (99.9%) over 10 years - unserviceable**
_**Solutions:**_
**Avalanche Photo-diodes (APDs) in Barrel: gain 50 **
**Vacuum Photo-triodes (VPTs) in End-caps (axial field): gain 8 - 10**
**Both specially developed for CMS**
**APDs: Hamamatsu  **
**         ****VPTs: RIE St Petersburg**

## APD Structure

**Photo-electrons from THIN 6 ****μ****m**
**p-layer induce avalanche**
**at p-n junction**
**Electrons from ionising particles**
**traversing the bulk NOT amplified**
_**(insensitive to shower leakage)**_

**2 APDs (each 5 x 5 mm)**
**mounted in capsule**
** ****for gluing to crystal**

##  Some APD Properties (Gain=50)

**Active area    ****	****	****	****	****5 x 5 mm**
**Charge collection within 20 nsec****	****	****99 ± 1%**
**Capacitance ****	****	****	****	****80 pF****	****         ****(fully depleted)**
**Dark Current (Id) before irradiation****	****< 50 nA****          ****(~ 5 nA typical)**
**Voltage sensitivity (1/M*dM/dV)****	****	****3.15 % / V**
**Temperature sensitivity (1/T*dM/dT)****	****- 2.4 % / ********C**** **
**Excess noise factor****	****	****	****2.1**

_**Radiation Hardness:**_ **After 10 years LHC equivalent hadron irradiation, ****	****	****                ONLY change is the dark current, ******** 5 μA **
**	**
_**Aging:**_**  ****No effect seen after ca 10 years’ equivalent in an oven.**

_**Acceptance tests:**_ **to ensure 99.9% reliability, **_***all***_** APDs screened by **
**5 kGy ****60****Co irradiation + 4 weeks cooking at 80********C **
**and tested to gain 300 (few % rejected)**

## Vacuum Photo-Triodes (VPTS)

-  B-field orientation favourable
-  Gain 8 -10 at B = 4 T
-  Radiation hard (UV glass window)
-  Active area of ~ 280 mm2/crystal
-  Q.E. ~ 20% at 420 nm

- Single stage photomultiplier tube with fine metal grid anode

- All tested at 1.8 T (10% at 4T)

## On-detector Electronics

- 800 Mb/soptical links to
- upper-level

- Custom designed ASICS in IBM 0.25 m technology

- multi-gain
- shaping
- amplifier.
- Gain 1, 6 & 12 for
- dynamic range
- of 20000

- 25 ns sampling
- 12-bit ADC with
- base-line detection.
- Selects gain

- Build, send
- trigger
- primitives;
- store data
- (3 s latency)

- Fast Xtal
- and
- photo-
- detector

## Electronics Performance

**Noise**

- 2003 data

-  - 44 MeV noise in single channel
-         (40 MeV in 2004 data)
-  - Negligible correlated noise

_**Resolution 120 GeV electrons**_** **
**Sum over 3 x 3 matrix. Only electrons entering centre of central crystal – minimises containment and cross-calibration errors**

- Excellent intrinsic resolution

## ECAL Barrel Assembly

**2 APDs in**
**capsule**

**Capsule mounted**
**on Xtal**

**10 Xtals in submodule alveolar (0.1 mm walls**
**glass-fibre/epoxy with Al lining) ****10 kg**

**4 modules in each of**
** ****36 “Supermodules”**
**(1700 Xtals, ****2 tons****)**

**40- 50**
**submodules**
**in a module**
**0.5 ton**

## Adding the Electronics

**Testing **

**Tidying**

## ECAL End-Caps and Pre-Shower

## Calibration

_**Pre-(inter)calibration**_**	**** ****	****	****	**rms
**	****	****	****	****	**
- Initial channel-to-channel variation:		 8%
- Apply crystal light yield lab data & APD gain 	 4%
- Calibrate in high energy electron beam	           < 2%      no beam till 6/06
- Calibrate with cosmic rays 			2-3%    in 1 week
_**In situ calibration**_
- Intercalibrate over Φ using jet energy deposit
-               with high (>120 GeV) ET triggers	2-3%    in 2 hours
- Calibrate over Φ and cross-calibrate
- 	over η with Z → e+e-			1%       in 1 day
- Final calibration with W → e ****
- 	(E/p comparison – needs Tracker)**       **   0.5%    in few months

## Pre-Intercalibration

## Laser Monitoring

**Radiation**** ****damage  ******** reduced crystal light transmission**
**Self-annealing        ******** (partially) restored light transmission**
**Net effect:  light reduction saturates depending on dose rate**
**                    ****light output varies with LHC beam conditions**

******Monitor transmission with laser **

- Light injected through fibres into each crystal

- Laser stability monitored by PN diode (< 0.1%)

## Laser Monitoring

- Electron/laser pulse comparison

- Electron (S) / laser (R) correlation:
-              S/S0   = (R/R0)1.6
- Power ≠ 1 because laser path shorter

## Performance in 2004 Test Beam

_**Resolution 120 GeV electrons**_** Sum over 3 x 3 matrix. Uniform **
**illumination of crystal front **

- Xtal 704

- 9 Crystals

## Schedule

**Schedule is very tight, driven by crystal production**
**	****	****	**
**But we expect that**
**	****Barrel will be installed for pilot run in late 2007**
**	****End-caps will be installed for first physics run in 2008**
**Dates are subject to the LHC schedule which is also very tight**

## Summary

**CMS Electromagnetic Calorimeter is **
**	****compact, precise, fast, highly granular, radiation tolerant**
**Major components**
**	****specially developed for ECAL**
**	****new technologies (PbWO****4****, APDs)**
**	****	****- now being used in other detectors**
**Test with beam and monitoring system show that**
**	****performance should meet design goals**
**	****H ******** ******** discovery possible in 2-3 years at low luminosity**
**Installation in CMS “just-in-time”**