1. Use of the BeamCal to Constrain ILC IP Beam Parameter
ECFA Linear Collider Workshop
Palacio de la Magdalena
Santander, Cantabria, Spain
May 30 – June 5, 2016
Bruce Schumm
UC Santa Cruz Institute for Particle Physics
Don’t forget x,y recon results
X2 background effect
Description of algorithm
Segmentation strategy study 1

2. Contributors Goal Luc D’Hauthuille, UCSC Undergraduate (thesis)
Anne Schuetz, DESY Graduate Student
Christopher Milke, UCSC Undergraduate
With input from Glen White, Jan Strube, B.S.
Goal
Idea is to explore the sensitivity of various beamstrahlung observables, as reconstructed in the BeamCal, to variations in IP beam parameters. The sensitivity will be explored with various different BeamCal geometries.

3. IR Layout
Low-Z Mask
M1 Mask
BeamCal L* 3 3 3

4. BeamCal Pixellation (Cartoon)

5. Of these, we believe the following can be reconstructed in the BeamCal:
Total energy and its r, 1/r moment
Mean depth of shower
Thrust axis and value (relative to barycenter; could also use mode of distributions. What is wise choice though? Maybe just (0,0)?)
Mean x and y positions
Left-right, top-bottom, and diagonal asymmetries

6. BeamCal Face Geometry Options
“plugged”
Wedge cutout
Circle cutout
“wedge” cutout
Plug
Insert plug here
“circle” cutout 6 6 6

7. IP Parameter Scenarios
Thanks to Anne Schuetz, GuneaPig expert
Relative to nominal:
Increase beam envelop at origin (via -function), for electron and positron beam independently, by 10%, 20%, and 30%
Move waist of electron and positron beam (independently) back by 100m, 200 m, 300 m.
Change targeting angle of electron and positron beam (independently) by 5 mrad and 20 mrad (in retrospect, isn’t this a bit much?)
Details at

8. First (Early) Results Luc has coded the following observables:
Deposited energy, mean depth of shower, L/R and up/down asymmetries, thrust (relative to barycenter) value.
He has taken eight beam crossings (working on larger sample soon!) and explored the following “trajectories”:
Beam envelope for electrons
Beam envelope for positrons
Electron waist position
Following are a core-dump of plots of these observables over those trajectories.

9. (Electrons and Positrons)
Beam Envelope Scan
(Electrons and Positrons)

10. Total Deposited Energy e+ and e- beam envelope scan

11. e+ and e- beam envelope scan
Mean Depth
e+ and e- beam envelope scan

12. e+ and e- beam envelope scan
L/R Asymmetry
e+ and e- beam envelope scan

13. e+ and e- beam envelope scan
Up-Down Asymmetry
e+ and e- beam envelope scan

14. e+ and e- beam envelope scan
Thrust Value
e+ and e- beam envelope scan

15. Waist Scan
(Electrons Only)

16. Total Deposited Energy
e- waist scan

17. Mean Depth
e- waist scan

18. L/R Asymmetry
e- waist scan

19. Up-Down Asymmetry
e- waist scan

20. Thrust Value
e- waist scan

21. Summary and Conclusions
First look at BeamCal observables and IP parameter dependence
Need to finish coding observables (thrust definition question)
Need to increase statistics (~100 pulses generated; working on simulation)
Need to develop some more interesting IP parameter variations (discussion!)
Need to explore sensitivity to BeamCal geometry
But this should be a good foot in the door for now…