# Presentation: 707791

## CMS: Electromagnetic calorimetry and e/gamma performance

- G. Dissertori
- ETH Zürich
- LHC Symposium, FNAL, Chicago
- May 1, 2002

- on behalf of the
- CMS ECAL collaboration

- LHCS03,  CMS ECAL

- May 1, 2003

## Contents

- Setting of the stage
- Construction status
- Crystals, APDs, VPTs
- The new electronics layout
- Results from the 2002 test beam
- e/gamma performance
- Calibration, reconstruction
- Preshower
- Summary

- LHCS03,  CMS ECAL

- May 1, 2003

## The setting of the stage

## The CMS electromagnetic     calorimeter

- Choice of crystals:
- Excellent energy resolution
- Structural compactness
- Tower structure facilitates event reconstruction (cluster algorithms)
- Choice of PbWO4:
- LHC rate (25 ns)
- Radiation hardness
- Longitudinal containment (X0)
- Choice of Photodetectors (APD, VPT)
- |B|=4 T
- Intrinsic gain (low light yield)
- Radiation level

-                           **|********| < 1.48**
**                            ****61.2k crystals**
**    ****~22x23x230 mm****3 ****(17 types)**

**25.8 X****0**

- LHCS03,  CMS ECAL

- May 1, 2003

## Focus on energy resolution

-      If you want precision, you have to take a lot of care...
- Longit. and lateral shower containment
- Light production, collection uniformity
- Nuclear counter effect
- Stability of PD gain
- Channel to channel intercalibration
- Electronic noise
- Temperature stability and uniformity
- Radiation damage
- Pileup
- ...

- LHCS03,  CMS ECAL

- May 1, 2003

## Production status

## Crystals production

**Barrel**
**1996**

**44 mm**

**65 mm**

**Endcap**
**1999**

**Barrel**
**end 2000**

**4 Barrel **
**2 Endcap**
**2003**

**85 mm**

- Technological steps in Bogoroditsk

**Longitudinal wire cut**
**after annealing, ok**

- Growing of large ingots well mastered
- All 138 ovens upgraded for 85 mm ingot production
- Fine-tuning of cutting technology going on

- see also talk by M. Della Negra

- LHCS03,  CMS ECAL

- May 1, 2003

## Crystal  production: Status

- Same quality obtained with new tech.
**Barrel** : overall 16300 crystals received
- Further 3000  crystals expected for Q2 03
**Endcap** : First batch of 100 pre-production crystals studied, waiting for 2. batch
**Super Module production**:
-      Bare/Dressed scheme

**Crystal  production: Status**

- LHCS03,  CMS ECAL

- May 1, 2003

## Avalanche Photo Diodes

- APDs optimized with extensive R&D programme
- Strict Q&A applied, want 99.9% reliability
- Production (Hamamatsu) well under way, already > 50 % finished

**Avalanche Photo Diodes**

**Two APDs per capsule**

-       Issues:
- Contributions to all resolution terms
-       (C, Idark, excess noise factor, gain stability)
- Nuclear counter effect
- Radiation hardness

**Internal gain=50 for V=380 V**

- LHCS03,  CMS ECAL

- May 1, 2003

## Vacuum Photo Triodes (Endcaps)

- All VPTs are measured at 0 < B < 1.8 T and -300 <  < 300 at RAL
- Sample VPTs checked at B=4T and =150 at Brunel, in addition faceplate irradiation
- Measured performance matches EE design objectives, but ‘sorting’ might be needed to accommodate  a spread in anode response
- Production well under way
-      >25% delivered

**Vacuum Photo Triodes (Endcaps)**

**Single stage photomultiplier tube**

-  = 26.5 mm

- MESH ANODE

**Gain 8-10 at B=4T, QE ≈ 20% at 420 nm**

- LHCS03,  CMS ECAL

- May 1, 2003

## ECAL electronics

## Read out chain 

**PbWO****4**
**Crystal**

**APD**
**VPT**

**Floating-Point **
**Preamplifier**
**4 gain ranges**
**analog gain selection**

**Fiber**
**Readout**

**ADC**
**12-bit**
**40 MHz**

**Upper-Level Readout**
**≈ ****1000**** boards, **
**in counting room**

**one optical link**
**per crystal**
**800 Mbit/s**

**Very Front End Board,  1/5 chan**

- On-detector
-       Light-to-Light readout
- All radiation hard
- High dynamic range
-      (50 MeV  2 TeV)

- LHCS03,  CMS ECAL

- May 1, 2003

## Read out chain / NEW

**Read out chain / NEW**

**PbWO****4**
**Crystal**

**APD**
**VPT**

**Floating-Point **
**Preamplifier**
**new version 2001**
**4 gain ranges**
**analog gain selection**

**ADC**
**12-bit**
**40 MHz**

**Very Front End Board,  1/5 chan**

- On-detector
-       Light-to-Light readout
- All radiation hard
- High dynamic range
-      (50 MeV  2 TeV)

- see also talk by M. Della Negra

- LHCS03,  CMS ECAL

- May 1, 2003

## Alternative solution

**Crystals and APD**

**5 x **
**VFE board**

**FE board**

- Goal
- Replace FPPA (Harris) + ADC (ADI) with new chips in 0.25 m techn.
- FPPA considered to be main risk factor
- MGPA : 3 parallel ampl, i.e. 3 gains
- ADC : 4 parallel 12-bit ADCs
- + digital gain selection
- Features
- All on-detector electronics in same technology, with details known to us
- Facilitates LV supply
- Reduction of power consumption
- Cost reduction
- Situation
- Chips submitted
- Will be studied asap, in lab, if possible, in beam
- Decision in summer .... !!

**MGPA**** ****: Multi-Gain Pre-Amplifier**

**new ADC**** ****in 0.25 ********m technology**

- see also talk by M. Della Negra

- LHCS03,  CMS ECAL

- May 1, 2003

## Test beam resultsM0’, 2002

## M0’ in 2002

- M0’
- First complete barrel system test
- Uniform construction procedure
- 100 channels of a module type 2
- “Old” electronics,  noisy FPPA
- Final Laser monitoring
- Services (Cooling, HV, LV, DCS)
- H4 test beam area
- Scanning table with automatic positioning of crystals in front of beam (electrons, pions)
- Online monitoring (laser, beam data)

**module on scanning table**

**100 channels, VFE cards**

- LHCS03,  CMS ECAL

- May 1, 2003

## Objectives

- Large scale system test
- VFE, HV, LV, DAQ, DCS
- Cooling for a large number of channels
- Step towards ECAL calibration
- System readiness for testbeam in 2003 and calibration in 2004
- DAQ and online software
- Moving table
- Understand laser monitoring system
- Stability checks (laser, temperature)
- Preparation for offline analysis
- Crystal behaviour under irradiation
- Compare laser with beam response, many crystals
- Universality
- Calibration
- Compare lab measurements with beam data

- LHCS03,  CMS ECAL

- May 1, 2003

## Cooling system

- Why is temperature stability
- so important?

-   Strong dependence of crystal
-     light yield with T, -2%/0C at 180C
-   Strong temperature dependence
-     of APD gain,  dM/dT = -2.4%/0C

- Thus the requirements are:
-  Long term stability of xtals and APDs < 0.1 0C

- LHCS03,  CMS ECAL

- May 1, 2003

## Laser monitoring

- Why is the laser monitoring
- so important?

**Light transmission**

-           Thus the idea is:
-  Inject laser light to monitor crystal transparency
-   Follow signals from beam and laser
-   Determine slope  laser vs. beam
-   Check universality

- LHCS03,  CMS ECAL

- May 1, 2003

## Laser monitoring

**slope :**
****** ****= 1.55 **

- LHCS03,  CMS ECAL

- May 1, 2003

## Calibration

- Idea:
- Obtain preliminary crystal intercalibration from light yield measurements (and comparison to reference crystal) in the **LAB**
- Previously expected: 6% achievable, as starting point for calibration
- Put crystals in test beam and check intercalibration
- Then compare  **LAB - BEAM**

- LHCS03,  CMS ECAL

- May 1, 2003

## Test beam: Conclusions

- Learned a lot, still a lot to learn
- Important achievements:
- Stability of cooling system and laser monitoring system
- Behaviour of APDs,  HV, LV, VFE electronics
- Universality of irradiation behaviour
- Intercalibration from LAB measurements
- To be improved/changed/foreseen for 2003, 2004:
- Final electronics  (noise level, auto-gain switching)
- Test larger system (up to 400 channels in 2003)
- Quick online/offline analysis of incoming data

- LHCS03,  CMS ECAL

- May 1, 2003

## e/gamma performance(calibration and reconstruction)for trigger issues, see talk by C. Seez

## Calibration steps

- intercalibration goes directly into
- constant term (most of the energy in a single crystal)

-   Precalibration:
-  Lab measurements, **< 5%**
-  Test beam,               **< 2%**
-    but only a fraction of ECAL will be calibrated

- LHCS03,  CMS ECAL

- May 1, 2003

## -symmetry  calibration

- Total transverse energy deposited from a large number of events is the same for all crystals at fixed 
- Correct **∑E****T** in a xtal to ****** ∑E****T**** ****** in a ring
- Reduce number of calibration constants from 60k (in barrel) to 170 (-rings in barrel)

******-symmetry  calibration**

- Limitations:
****** ****symmetry not exact**: tracker material not homogeneous
- With increased knowledge of the tracker material :  precision down to 1% in the whole barrel region
**Worries**: non-Gaussian noise (spikes), large lever arm of extrapolation to high energies
- Rates:
- If 1kHz of L1 bandwidth assigned, handled by HLT farm:
- 1 kHz = 3.6M evts/hour. For L=1033  this corresponds to 6M minimum-bias crossings/h
- Future:
- Look at jet triggers
- High tresholds to avoid trigger bias

- LHCS03,  CMS ECAL

- May 1, 2003

## Electron reconstruction

**Main difficulty** : tracker material    **bremsstrahlung **
-                            Ebreams/E = 43.6 %, Pt = 35 GeV,  || < 1.5
- Recover by reconstructing clusters of clusters ( **super-clusters **)
- Essential for Z ee and W  e reconstruction, find compromise between statistics and little bremsstrahlung-loss

- LHCS03,  CMS ECAL

- May 1, 2003

## Preshower

## CMS Preshower – Overview

**Idea of **
**Preshower:**

- Single incident
- photon

**Shower profile measured by ****2mm-pitch silicon strip sensors**

- LHCS03,  CMS ECAL

- May 1, 2003

## CMS Preshower – Current highlights

- Active part of the Preshower are 4300 “**micromodules**”based on 6.3x6.3cm2 **silicon sensors**, with 32 strips,equipped with high dynamic range analogue readout (**PACE3**)

**25% of sensors have been produced** (in Russia). Remainder will be produced in Russia, India and Taiwan this year

- Front-end electronics (0.25 m “**PACE3**” and “**K-chip**”) submitted in March. **Will be tested in Summer 2003**

- Large mechanical pieces being fabricated in 2003

- Full-scale production of **micromodules** on schedule to start in mid-2004

- LHCS03,  CMS ECAL

- May 1, 2003

## Summary

- Construction of the CMS ECAL is progressing well
- Improved technology for crystal production (larger ingots)
- > 50% of APDs , > 25% of VPTs  already there
- Major re-design of the electronics readout scheme
- Remarkable progress in the project, under high pressure with little time
- In summer decision  if  0.25 m solution instead of FPPA
- Test beam in 2002
- Several essential tests carried out (temperature stability, laser monitoring, precision of the lab intercalibration < 5%)
- Calibration and reconstruction
- Method identified which allows to achieve in-situ a quick intercalibration in using minimum bias events
- Knowledge of tracker material and bremsstrahlung-recovery essential for good reconstruction

- LHCS03,  CMS ECAL

- May 1, 2003

## Acknowledgements

- Many thanks to all those who helped me for the preparation of this presentation
-     D. Barney, P. Bloch, J. Cogan, M. Dejardin, M. Diemoz, S. Gascon-Shotkin, P. Lecomte, P. Lecoq, A.v.Lysebetten, F. Nessi-Tedaldi, M. Paganoni, R. Paramatti, C. Seez,  ...
- Thanks to the organizers of the symposium

- LHCS03,  CMS ECAL

- May 1, 2003

## Crystal  production: Status

- Same quality obtained with new tech.
**Barrel** : overall 16300 crystals received
- Further 3000  crystals expected for Q2 03
**Endcap** : First batch of 100 pre-production crystals studied, waiting for 2. batch
**Super Module production**:
-      Bare/Dressed scheme

**Crystal  production: Status**

**Transmission  at 420 nm**

**Light Yield**

**260 barrel Xstals**
**  ****standard tech.**
**40 barrel Xtals, **
**     ****new tech.**

- LHCS03,  CMS ECAL

- May 1, 2003

## Read out Chain / OLD

- Advantages
- High level of flexibility
- minimal amount of radiation hard electronics
- Drawbacks
- High volume of data transfer and storage
- many Upper-Level readout (ULR) boards (> 1000 boards, 60 crates)
- very many optical links,  > 91000
- Problems
- FPPA 2000: excess noise (factor 4), gain switching
- Cost of digital data links (no cost reduction as anticipated)
- Very high costs of ULR

- LHCS03,  CMS ECAL

- May 1, 2003

## Read out chain / NEW

**Crystals and APD**

**5 x **
**VFE board**

**FE board**

- Features
- use L1 latency to transport data of triggered events from all 25 crystals in a trigger tower over a single link
- tracker technology for links and control
- maintains functionality
- nr. of links              / 8
- nr. of ULR boards  / 4
- reduce cost
- revised integration and cooling scheme
- new FPPA version 2001
- low yield, but first tests show improved behaviour

- see also talk by M. Della Negra

- LHCS03,  CMS ECAL

- May 1, 2003

## Recorded data

- more than 300 Gbytes recorded
- 25 time samples, all 100 crystals for each trigger
- continuous high rate data taking
- data sets
**calibration** mainly with 120 GeV electrons
**energy scan** (20 to 280 GeV) on about 9 crystals
- very fine **position scan** across 5 crystals
**irradiation** of 20 crystals with 120 GeV e- beam for several hours, then monitor recovery, simulate LHC cycle
- some runs with **pions**
- a few forced temperature steps (extract time constants)

- LHCS03,  CMS ECAL

- May 1, 2003

## -symmetry  calibration

- Idea:
- Total transverse energy deposited from a large number of events is the same for all crystals at fixed 
- correct **∑E****T** in a xtal to ****** ∑E****T**** ****** in a ring
- Aim:
- reduce number of calibration constants from 60k (in barrel) to 170 (-rings in barrel)
- First Study:
- 18 M minimum bias crossings simulated
- ≈ **few hours** at 2x 1033 cm-2 s-1 for 1 kHz L1 bandwidth for calibration

**|********| = 0.23, ****18M min-bias events  **

- LHCS03,  CMS ECAL

- May 1, 2003

## Electron reconstruction

- LHCS03,  CMS ECAL

- May 1, 2003