1. Non-Prompt Tracks with SiD BeamCal Radiation Damage Studies (Proposal)
Two R&D Topics
Non-Prompt Tracks with SiD
BeamCal Radiation Damage Studies (Proposal)
SiD Collaboration Workshop
November

2. Non-Prompt Tracking with the SiD
Explore performance via explicit signature: Metastable stau NLSP (Gauge-Mediated SUSY)

3. Reconstructing Metastable Staus w/ SiD
Gauge-Mediated SUSY
Large tract of parameters space as stau NLSP
Metastable (cstau ~ centimeters) is in cosmologically preferred region
Process is
with

4. Reconstructing Metastable Staus w/ SiD
Start with:
5+1 layers for inside track
4 layers for outside track
 Restricted range in rdecay for now; will expand soon

5. Measuring Staus with the SID
Stau sample:
11.1 fb-1 of e+e- stau pairs with
mstau = 75 GeV
Ecm = 500;  = 90 fb
c = 23 cm
Background sample:
5.3 fb-1 combined SM background

6. Reconstructing Metastable Staus w/ SiD
Focus initially on rdecay = cm…
Reconstruct decays by requiring:
    - Outer hit of primary track on first tracker layer
    - Inner hit of non-prompt track on second tracking layer
   - Both tracks be on the same side of the Barrel (in z)
    - The sign of the track curvatures match
    - Non-prompt track curvature larger than the primary
    - Tracks have a geometric intersection in the x-y plane
Of 294 staus with 22<rdec<27 and |cos| < 0.5, 239
staus are reconstructed, of which 232 truth-match

7. Stau Reconstruction Efficiency
Truth-Matched Staus

8. Signal to Background for 10 fb-1
Truth-matched stau: 210
Background kinks:
Perhaps slight preference for background kinks
to show up at material layers at 22 and 47 cm
47cm
22cm

9. Signal to Background (10 fb-1)
Curvature ratio
Kink angle

10. Signal to Background (10 fb-1)
pT of prompt track
#Tracks/event
Good separation between signal and background for #tracks/event and track pt

11. Extend Region of Search: First Look
Require prompt track end on
VTX L5 or
Tracker L1
Require non-prompt track start on Tracker L1 or L2 [L2 only for b)]

12. Stau Reconstruction Efficiency
Truth-Matched Staus
Tracker L1

13. S/B; Extended Region (10 fb-1)
pT of prompt track
Kink Radius
Separation can still be made, but distinction between signal and background in prompt track pt somewhat degraded by reduced lever arm

14. Plans for Radiation Damage Studies for Si Diode Sensors Subject to 1 GRaD Doses
CERN Linear Collider Workshop
October

15. But: Are electrons the entire picture?
G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993)
NIEL e- Energy
2x MeV
5x MeV
1x MeV
2x MeV
Damage coefficients less for p-type for Ee- < ~1GeV (two groups); note critical energy in W is ~10 MeV
But: Are electrons the entire picture? 15 15

16. Hadronic Processes in EM Showers
There seem to be three main processes for generating hadrons in EM showers (all induced by photons):
Nuclear (“giant dipole”) resonances
Resonance at MeV (~Ecritical)
Photoproduction
Threshold seems to be about 200 MeV
Nuclear Compton scattering
Threshold at about 10 MeV;  resonance at 340 MeV
 Flux through silicon sensor should be ~10 MeV e/, but also must appropriately represent hadronic component 16 16

17. Rates (Current) and Energy
Basic Idea:
Direct electron beam of moderate energy on Tungsten radiator; insert silicon sensor at shower max
For Si, 1 GRad is about 3 x 1016/cm2, or about 5 mili-Coulomb/cm2
Reasonably intense moderate-energy electron or photon beam necessary 17 17

18. 5.5 GeV Electrons After 18mm Tungsten Block
Not amenable for uniform illumination of detector.
Instead: split 18mm W between “pre” and “post” radiator separated by large distance
Caution: nuclear production is ~isotropic  must happen dominantly in “post” radiator!
Boundary of 1cm
detector
Fluence (particles per cm2)
Radius (cm) 18 18

19. 5.5 GeV Shower Profile e+e- (x10) All  E > 100 MeV (x20)
“Pre”
“Post”
e+e- (x10)
All 
Remember: nuclear component is from
photons in MeV range.
Fluence (particles per cm2)
E > 100 MeV (x20)
E > 10 MeV (x2)
Radius (cm) 19 19

20. Proposed split radiator configuration
5mm Tungsten “pre”
13mm Tungsten “post”
Separated by 1m
Fluence (particles per cm2)
1.0
2.0
3.0 20
Radius (cm) 20

21. Rastering
Need uniform illumination over 0.25x0.75 cm region (active area of SCIPP’s charge collection measurement apparatus).
Raster in 0.05cm steps over 0.6x1.5 cm, assuming fluence profile on prior slide (see next slide for result)
Exposure rate:
e.g. 10 GRad at 50 nA 5.5 GeV e-  ~ 30 Hours

22. Irradiation Plan Use existing Micron sensors from ATLAS R&D
n-type and p-type
Standard float-zone and Magentic Czochralski
Runs of up to 1 GRad for each sample
Runs with samples far from radiator (no hadronic effects)
Total integrated dose of ~10 Grad
Will assess the bulk damage effects and charge collection efficiency degradation.
Sensors
Sensor +
FE ASIC
DAQ FPGA
with Ethernet 22 22

23. Wrap-Up
Non-Prompt Tracks with SiD:
Reconstructing clean metastable stau signature between first and second tracking layer with high efficiency. Backgrounds have low primary track momentum. Region between VTX and tracking L1 looks promising; needs more work. Between L2 and L3 requires dedicated tracking algorithm (exploring).
Radiation Damage for ~1 GRad EM Showers
Some evidence that p-bulk sensors will be most robust. Need to worry about nuclear effects. Looking for facility (SLAC ESA beam would require 2-4 weeks of exposure when available)

24. NIEL (Non-Ionizing Energy Loss)
Conventional wisdom: Damage proportional to Non- Ionizing Energy Loss (NIEL) of traversing particle
NIEL can be calculated (e.g. G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 [1993])
At EcTungsten ~ 10 MeV, NIEL is 80 times worse for protons than electrons and
NIEL scaling may break down (even less damage from electrons/positrons)
NIEL rises quickly with decreasing (proton) energy, and fragments would likely be low energy
 Might small hadronic fractions dominate damage? 24 24

25. BeamCal Incident Energy Distribution2 4 6 8 10
e+/e- ENERGY (GEV) 25 25

26. Wrap-up Worth exploring Si sensors (n-type, Czochralski?)
Need to be conscious of possible hadronic content of EM showers
Energy of e- beam not critical, but intensity is; for one week run require Ebeam(GeV) x Ibeam(nA) > 50
SLAC: Summer-fall 2011 ESA test beam with Ebeam(GeV) x Ibeam(nA)  17 – is it feasible to wait for this? 26 26

27. Shower Max Results
Photons with
E > 100 MeV per electron, x 100
Photons with
E > 10 MeV per electron, x10
Photons per electron
Electrons, per GeV incident energy
1.0
2.0
3.0 27
 Photon production ~independent of incident energy! 27

28. Proposal: JLAB Hall B Beam Dump (Plan to run 0
Proposal: JLAB Hall B Beam Dump (Plan to run 0.05 A through next May)  Total power in beam ~250W.
Oops – too much background for Hall B! Look elsewhere…

29. Fluence (e- and e+ per cm2) per incident 5.5 GeV electron
(5cm pre-radiator 13 cm post-radiator with 1m separation)
mm from center 1 2 3 4
13.0
12.8
11.8
9.9
8.2
13.3
12.9
12.0
13.1
12.6
11.7 5
12.3 6
11.6
10.7 7
10.4 8
8.6
8.0
6.4
Center of irradiated area
¼ of area
to be measured
¼ of rastoring area (0.5mm steps)