1. CMS Preshower: Startup procedures: Reconstruction & calibration
C-M. Kuo & D. Barney

2. Contents of presentation
Preshower reconstruction scheme
Data flow
Digits
RecHits
Clusters
Inter-calibration of silicon strips etc.
Prior to installation
In-situ
Inter-calibration with EE
Startup procedure

3. Data Flow Detector Front-end  ES-DCC  global DAQ
pedestal subtracted
CMN corrected
zero suppressed data
“final version” of unpacker will be ready soon
VME spy memory  local DAQ
non-zero suppressed data
pedestal, noise, dead channel

4. ES Digits & RecHits Estrip = W0S0+W1S1+W2S2
PACE 3 Pulse Shape S1 S2 S3
Estrip = W0S0+W1S1+W2S2
Apply MIP calibration at RecHit level

5. ES Clusters EEndcap SC = Σ(Ebci+Epreshi) Epresh = γ(EPlaneX+EPlaneY)
See CMS IN 2001/056 (C. Palomares & D. Barney)
Use the EE basic cluster to extrapolate back to preshower planes
4 ES clusters matching each EE basic cluster
Each ES cluster contains 5 strips
Search area : 3 x 31 strips
EEndcap SC = Σ(Ebci+Epreshi)
Epresh = γ(EPlaneX+EPlaneY)

6. Intercalibration Preshower is a sampling calorimeter
Only “reference point” is the minimum-ionizing particle (MIP)
Response to a MIP varies from strip to strip due to:
Silicon thickness (known)
MIP Incidence angle (~known from placement in ES)
Gain of the electronics (constant with radiation)
Charge collection efficiency – varies with radiation damage
Required accuracy of MIP calibration is about 5% (corresponds to ~0.25% contribution to overall EE+ES energy resolution as about 5% electron/photon energy deposited in ES)
Switchable gain of electronics
High Gain (0  60 MIPs dynamic range) for MIP calibration
Low Gain (0  450 MIPs dynamic range) for physics running
Need for gain inter-calibration – done with internal electronic injection pulse

7. MIP Pre-calibration
All ES modules undergo “cosmic-ray calibration” for 24 hours (also serves as a first burn-in)
Not optimum as:
cosmic-rays are asynchronous with the 40MHz clock
Range of incidence angles – but ES modules arranged in a vertical stack so “tracking” can be performed
Reference data sets taken over 4 days
MIP calibration accuracy estimated to be better than 2% for 24-hours of running

8. ES Cosmic Ray Test

9. MIP Pre-calibration: examples
S. W. Li et al

10. MIP Pre-calibration: alternative method
Detector capacitance (known) is a good measure of the MIP to about 2%

11. In-situ MIP calibration
Main use is to follow change of charge collection efficiency with radiation damage
Use MIPs from triggered events
MUON events
Min-bias events (charged pions)
Can use the L1 (100 kHz) triggers
See CMS-NOTE 2006/052 (I. Evangelou)
Time required depends on luminosity
At high L expect ~1 week needed

12. ES-EE inter-calibration
Start by using inter-calibration constants found from beam tests and simulations
Ideally use monochromatic electrons/photons (e.g. electrons from Z0)
γ= GeV/MIP
γ= GeV/MIP
2007 H2 test beam E = 50 GeV (Prelim.) S. W. Li et al
2007 H2 test beam E = 20 GeV (Prelim.)

13. p0 rejection training
Present p0 rejection algorithms based on Neural Networks (A. Kyriakis et al)
Require training
Use constants from simulation to start with
Low-energy p0 can be used as a starting point – also used for EE calibration
Iterative procedure
THIS PART NEEDS SOME THOUGHT!!!

14. Startup Procedure Ensure data readout from all modules
Use charge-injection pulse
Set trigger latency (i.e. time-in the beam) using triggered events
High-gain mode
Single parameter required for all modules
Pedestal runs to measure:
Pedestals for each channel (~ strips)
Intrinsic noise level
Common-mode noise level
 will use “spy memory” of ES-DCC (off-detector readout) i.e. no zero-suppression
Pedestals, noise, thresholds fed-back into ES-DCC via conditions database
Start training NN and perform ES-EE inter-calibration