1. The Ohio State University CSC Detector Performance Group
Quick Study of Knock-on Electrons
Can we remove them ?
S. Durkin
The Ohio State University
CSC Detector Performance Group
Feb. 15, 2007
S. Durkin, CSC DPG, Feb. 15, 2007

2. Knock-on Electrons -PDG
Scale factor needed
Shape similar
Is the dE/dx for
testbeam same as
MTCC ?
Analysis will get
more difficult
MTCC LHC
Rays strongly peaked at
low kinetic energy
S. Durkin, CSC DPG, Feb. 15, 2007

3. Can we remove Knock-on Electrons?
Will concentrate on Knock-on electronics nearly contained within
one wire group or strip
Leave the energetic ones to Ingo
Today analysis use ME1/1 HV data sample (clean)
dE/dx – Charge on Strip: 
A mess to implement
Need to know Landau Peak
for each chamber e
Expect  rays in tail
S. Durkin, CSC DPG, Feb. 15, 2007

4. Can we remove Knock-on Electrons? (cont)
Anode Width – 2 Adjacent Hits: e
# 2 wire groups  dy/dz
Completely Hopeless at MTCC
Dominates 
S. Durkin, CSC DPG, Feb. 15, 2007

5. Can we remove Knock-on Electrons? (cont)
Cathode Width – Gatti Chi-Square:
Knock-on increases Gatti width
Chi-square has to be properly tuned
Tuning has been done for ME1/1 and ME3/2
Not included in CMSSW
Poor Chi-Square 
Depends on
Angle ! e
Typical Bad Chi-Square Event
chi-square = 667
charge = 7478
Note: Fast Algorithm can calculate
Chi-Square or Width
Data Fit
573
589
216
1145
1664
481
884
1535
387
442
625 50
1153
1670 83
1023
1566 33
S. Durkin, CSC DPG, Feb. 15, 2007

6. Investigation of the Tails
red points: Residual > 350m
black points: Residual < 350m
ME1/1
=120m
Cut line: 4500-Q-100*2<0
S. Durkin, CSC DPG, Feb. 15, 2007

7. Removal of Knock-on Electrons
Cut removes 1460/24974= 6%
Tail Details (truncated)
initial sample
initial sample
events cut
events cuts
Cut Remove ~ 50% of Residual Tail
S. Durkin, CSC DPG, Feb. 15, 2007

8. Conclusion We can identify 50% of Knock-on Electrons and Remove them
Difficult to implement (Landau peak, tuned 2 (or width))
Must remove remaining Knock-on Electrons with “Outlier” Cuts
Standard
Statisics theory
S. Durkin, CSC DPG, Feb. 15, 2007