1. Backgrounds using v7 Mask in 9 Si Layers at a Muon Higgs Factory
T. Markiewicz & T. Maruyama / SLAC
MAP Detector Group Meeting
8 August 2014

2. Masks v2 versus v7
8 Aug MAP at SLAC
T. Markiewicz

3. Comparison with Striganov (2 bunches, 1 BX)
Striganov |Z|<600cm
FLUKA |Z|<600 cm
FLUKA |Z|<350 cm
Striganov |Z|<??? 
3.2×109
4.0×109
2.1×109
5.6×108
6.7×108 e
1.2×108
1.6×108
8.7×107
3.5×106
4.0×107 n
1.7×108
1.4×108
7.3×107
6.4×107
6.6×107 h
1.0×105
2.0×105
7.7×104
1.7×104
2.5×104
8 Aug MAP at SLAC
T. Markiewicz
Seems anomalous

4. 320um Silicon Conversion/Scoring Planes
Barrel Detector
Radius (cm)
Half Length (cm)
VXD
5.5
20.5
Tracker
50.0
91.0
ECAL
131.0
200
Barrel Detector
Radius (cm)
Half Length (cm)
VXD
7.7
28.7
Tracker
50.0
91.0
ECAL
131.0
200
Endcap
Z (cm)
Rin (cm)
Rout (cm)
VXD
24.8
6.7
18.4
Tracker
92.0
25.2
53.3
ECAL
200.1
38.0
130.9
Endcap
Z (cm)
Rin (cm)
Rout (cm)
VXD
30.0
6.7
18.4
Tracker
92.0
25.2
53.3
ECAL
200.1
38.0
130.9
8 Aug MAP at SLAC
T. Markiewicz

5. Pythia timing to set a timing gate for each layer Timing resolution not considered
Barrel 1
Barrel 2
Barrel 3
1.5-4ns
4-10ns
0-1ns
Time (ns)
Z (cm)
Endcap 3
Endcap 1
Endcap 2
6.5-9ns ns
3-4ns
8 Aug MAP at SLAC
T. Markiewicz
R (cm)

6. Converted Photons
8 Aug MAP at SLAC
T. Markiewicz

7. Time and z of converted photon background All Si Layers
X100 to get background associated with one bunch
8 Aug MAP at SLAC
T. Markiewicz

8. V7 Hit multiplicity (all layers)
nh-1 counts all charged “children” hits of a photon leaving the mask
The long tail (cut in GEANT at 200) skews the mean multiplicity
What is the correct multiplicity to use?
NB: (γ that conv.) x 200 / 6.7E8 (FLUKA γ) = 0.59% conv. eff.
8 Aug MAP at SLAC
T. Markiewicz

9. What is the best way to simulate detector hits?
Setup massless scoring plane, score photon crossings and apply fixed conversion efficiency x hit multiplicity(2%).
Under estimate spirals.
Technique for ILC studies
Setup Si layer and massless scoring plane, and score only charged particle crossings.
There are very low energy spirals inside the scoring volume .
There are low energy electrons that don’t come out of Si.
Setup only Si layer and score only energy depositions. 
8 Aug MAP at SLAC
T. Markiewicz

10. Photon conversion prob. in 320 m Si from EGS
Approx. range of gamma energies
Edep > 8 keV
Edep > 30 keV
8 keV is assumed E_dep to produce a signal on a VXD pad
0.6% is observed eff.
LOG10(E(MeV))
LOG10(E(MeV))
8 Aug MAP at SLAC
T. Markiewicz

11. Z Distribution of Photons in Innermost Barrel VXD
All hits
First hit only
Inner VXD:
γ Conversion eff: 6581/1,121,001=0.587%
Hit Multiplicity = 89207/6581 =
8 Aug MAP at SLAC
T. Markiewicz

12. Innermost VXD Layer Separation between Hits that stay on the layer
20 um bins
Adjacent Hits
20 um bins
Most probable length of string of hits ~ 1mm
Average separation between adjacent hits ~2mm (??)
Both >> 20um pixel pitch -> non adjacent pixels will be hit
8 Aug MAP at SLAC
T. Markiewicz

13. Numerology for hits on Innermost VXD Layer
Set MaxHit=2
Inner VXD:
1,121,001 photons make a hit on this layer
There are a total of hits seen
6581 photons make one or more hits on this & other layers
In 5872 cases all the hits stay on this Inner VXD layer;
In cases the last hit in the n-tuple is on a different layer
1053 of 6581 (or 5872) events only have one e- hit on the layer
In 4819 of 5872 events, all the hits stay on the inner VXD layer
When >1 hit, the max. probability of separation between first and last hit is 1mm
Conversion eff: 6581/1,121,001=0.587%
Hit Multiplicity = 89207/6581 =
This is ~ 3.1x the mean number of hits when histogram truncated at 20 hits.
8 Aug MAP at SLAC
T. Markiewicz

14. Innermost VXD Layer-Converted Photons
34.4% in 0-1ns
<>=311;
Peak/<>~2
8 Aug MAP at SLAC
T. Markiewicz

15. Cut nh-1<20 37% hits left after cut 58.3% in 0-1ns
1.7x as many hits are left after the timing cut
8 Aug MAP at SLAC
T. Markiewicz

16. Converted photon hits on r=50cm Barrel
50.8% in 1.5-4ns
82.8% in 1.5-4ns
After nh cut
<>=301;
Peak/<>~2
25% hits left after nh cut
8 Aug MAP at SLAC
T. Markiewicz

17. Time Distribution of photon hits on r=131cm Barrel
95.3% in 4-10ns
After nh cut
92.3% in 4-10ns
<>=131;
Peak/<>~2
34% hits left after nh cut
8 Aug MAP at SLAC
T. Markiewicz

18. Time Distribution of photon hits on 2 VXD disks at z=25 or 30cm, 6
Time Distribution of photon hits on 2 VXD disks at z=25 or 30cm, 6.7<r<18.4
After nh<21 cut
78.6% in
Gate 0.5<t<1.5ns
<>=14;
Peak/<>~10
97% hits left after nh cut
Peak due to inner barrel VXD layer
8 Aug MAP at SLAC
T. Markiewicz

19. Time Distribution of photon hits on 2 disks at z=92cm, 25.3<r<53.3cm
67.3% in
Gate 3<t<4ns
<>=4.4;
Peak/<>~5
Peak due to inner barrel tracker layer
8 Aug MAP at SLAC
T. Markiewicz

20. Time Distribution of photon hits on 2 disks at z=200cm, 38<r<130
Time Distribution of photon hits on 2 disks at z=200cm, 38<r<130.9cm
59% in
Gate 6.5<t<9ns
<>=4.2;
Peak/<>~6
8 Aug MAP at SLAC
T. Markiewicz

21. e- backgrounds Good comparison v2 versus v7
8 Aug MAP at SLAC
T. Markiewicz

22. e+e- backgrounds: All scoring planesv7 v2
8 Aug MAP at SLAC
T. Markiewicz

23. e+e- backgrounds: All scoring planesv7 v2
8 Aug MAP at SLAC
T. Markiewicz

24. Time Distribution of e+e- hits on Innermost Barrel
5.3%
time=time_parent+time_child
0-1ns gate v7 v2
<>=162
Peak/<> ~ 5.5
8 Aug MAP at SLAC
T. Markiewicz

25. Relatively few e+/e- Backgrounds make it to the r=50cm barrel but those hits are “in time” with physics events v7 v2 v7 v2
8 Aug MAP at SLAC
T. Markiewicz

26. Relatively few e+/e- Backgrounds make it to the r=131cm surface of the barrel Ecal, but those hits are “in time” with physics events v7 v2 v7 v2
8 Aug MAP at SLAC
T. Markiewicz

27. time=time_parent+time_child
Time Distribution of e+e- hits on z=25cm Disks Many, many spirals before hitting disk delays arrival v2 v7
time=time_parent+time_child
ns gate
1% in ns gate v7
<>=113
Peak/<> ~ 4.4 v2
8 Aug MAP at SLAC
T. Markiewicz

28. Relatively few e+/e- Backgrounds make it to the z=92cm fwd tracker the tighter time cuts help further as e+/e- source is far up the cone, away from the IP at large z v7 v2
<>=2.5
Peak/<> ~ 4 v2 v7
2% in 3-4ns gate
8 Aug MAP at SLAC
T. Markiewicz

29. Relatively few e+/e- Backgrounds make it to the z=200cm surface of the Endcap Ecal the tighter time cuts help further as e+/e- source is far up the cone, away from the IP at large z v7 v2 v2 v7
4% in ns gate
8 Aug MAP at SLAC
T. Markiewicz

30. Neutrons
8 Aug MAP at SLAC
T. Markiewicz

31. Detector hits simulation for neutrons
Setup simple fluka geometry.
Score all particles produced inside Si
Look at energy deposition per incident neutron.
320 m
neutron
8 Aug MAP at SLAC
T. Markiewicz

32.  106 25 MeV neutrons p 4He e- Neutron energy d e+ t 3He E (MeV)
Particle type
8 Aug MAP at SLAC
T. Markiewicz

33. Energy deposition per incident
MeV neutrons
MeV neutrons
0.1%
0.07%
Energy deposition in Si (MeV)
8 Aug MAP at SLAC
T. Markiewicz

34. Neutrons
In this simulation, neutrons do not interact with Si in layers but can hit the layer more than 1 time or can hit more than 1 layer
8 Aug MAP at SLAC
T. Markiewicz

35. Parent Neutrons Leaving Mask
8 Aug MAP at SLAC
T. Markiewicz

36. Z and Time Distribution of all Parent Neutrons
Transition to B-CH2
8 Aug MAP at SLAC
T. Markiewicz

37. ALL Layers-Children of Parent Neutrons
8 Aug MAP at SLAC
T. Markiewicz

38. All Layers--Children of Parent Neutrons
Digitization of neutron energy <20MeV in FLUKA
Momentum (MeV)
8 Aug MAP at SLAC
T. Markiewicz

39. Innermost VXD Layer-Neutrons
<>=43;
Peak/<>~5
8 Aug MAP at SLAC
T. Markiewicz

40. Innermost Tracker Layer at r=50cm Neutrons
6.7E-4 in 1-4ns
<>=1287;
Peak/<>~2
8 Aug MAP at SLAC
T. Markiewicz

41. OuterMost Ecal Layer at r=131cm Neutrons
1.8E-3 in 4-10ns
<>=711;
Peak/<>~1.7
8 Aug MAP at SLAC
T. Markiewicz

42. InnerMost VXD Disk at z=30cm Neutrons
4.3E-4 in ns
<>=100;
Peak/<>~1.2
8 Aug MAP at SLAC
T. Markiewicz

43. First Tracker Disk at z=92cm Neutrons
<>=105;
Peak/<>~1.1
4.7E-4 in 3-4ns
8 Aug MAP at SLAC
T. Markiewicz

44. ECAL Disk at z=200cm Neutrons
1.5E-3 in 6.5-9ns
<>=72;
Peak/<>~1.4
8 Aug MAP at SLAC
T. Markiewicz

45. Charged Hadrons
8 Aug MAP at SLAC
T. Markiewicz

46. Charged Hadrons
8 Aug MAP at SLAC
T. Markiewicz

47. Parent Hadrons Leaving Mask
8 Aug MAP at SLAC
T. Markiewicz

48. Z and Time Distribution of all Parent Charged Hadrons
8 Aug MAP at SLAC
T. Markiewicz

49. ALL Layers-Children of Parent Charged Hadrons
8 Aug MAP at SLAC
T. Markiewicz

50. All Layers--Children of Parent Hadrons
8 Aug MAP at SLAC
T. Markiewicz

51. Innermost VXD Layer-Hadrons
<>=22;
Peak/<>~1.5
8 Aug MAP at SLAC
T. Markiewicz

52. Innermost Tracker Layer at r=50cm Charged Hadrons
<>=27;
Peak/<>~1.5
20% in 1-4ns
8 Aug MAP at SLAC
T. Markiewicz

53. OuterMost Ecal Layer at r=131cm Charged Hadrons
36% in 4-10ns
<>=6;
Peak/<>~1.8
8 Aug MAP at SLAC
T. Markiewicz

54. InnerMost VXD Disk at z=30cm Charged Hadrons
16% in ns
<>=12;
Peak/<>~1.3
8 Aug MAP at SLAC
T. Markiewicz

55. First Tracker Disk at z=92cm Charged Hadrons
20% in 3-4ns
<>=8.3;
Peak/<>~1.5
8 Aug MAP at SLAC
T. Markiewicz

56. ECAL Disk at z=200cm Charged Hadrons
35%
in 6.5-9ns
<>=12.9;
Peak/<>~2.3
8 Aug MAP at SLAC
T. Markiewicz

57. Background Summary
8 Aug MAP at SLAC
T. Markiewicz

58. Contributions to Average Hit Density per Read Out Unit per 1000 Bx Before Timing Cuts
8 Aug MAP at SLAC
T. Markiewicz

59. Contributions to Average Hit Density per Read Out Unit per 1000Bx After Timing Cuts
8 Aug MAP at SLAC
T. Markiewicz

60. Sum of all Background Sources after Timing Cuts Average Background per Silicon Layer Peak/Average Ignored (can be up to x10 for γ in Endcap VXD)
8 Aug MAP at SLAC
T. Markiewicz

61. Sum of all Background Sources after Timing Cuts Peak Background per Silicon Layer Ignore density variation in Phi
8 Aug MAP at SLAC
T. Markiewicz

62. Conclusions
Change to the version 7 conic mask design with larger beampipe radius reduces backgrounds x2-3
We do not see the x30 reduction in the e- channel shown by MARS
Irreducible backgrounds in the photon and electron channels emanate from the IP area, predominately from the downbeam cone tip, and are thus largely in time with the collision
Nonetheless, timing in tight gates can reduce these backgrounds ~x2
Neutrons and charged hadrons emanate from the body of the conic mask
Timing can reduce the charged hadron background by x3-10
The neutrons, which dominate the hit density outside the barrel VXD, are very slow and are very effectively eliminated by timing: only % remain after cuts
An accurate determination of hit density requires a detailed detector model, ideally with clustering. The simplified model used in this analysis has shown
Photon backgrounds convert with 0.6% probability in 320um layers of Silicon
While the “most probably” number of hits per converted photon is 2-3, there is a long tail (artificially cut at 200) that drives the mean number of hits to >10.
The average separation of these hits is ~1mm, so it seems like they would “count” in the tracking & vertex detectors
ILC analyses assumed 2% for the product of conversion probability and hit multiplicity; the analysis here results in ~ 6%
As all the neutrons are cut by the timing gate, we habe only SCORED them in this analysis
Separate studies indicate that these low energy neutrons will produce visible hits in thin Si 0.1% of the time
Signal in calorimetry has not been studied
Timing cuts not particularly effective given (in this IR geometry) proximity of cone tips to the IP (±0.7ns away)
Silicon strip tracker (50um x 1cm) show 100%-500% occupancy per BX to be compared to ILC performance of 1-2%. Can argue what is max. allowed (10%), but 100% does not work.
Hits per readout unit per train (1000 BX) >> 4 buffers designed for the ILC Readout architecture (“KPIX”)
Reading each readout element each bunch crossing probably required
Barrel backgrounds more important than endcap backgrounds
Endcap hits caused by spiraling e+e- are out of time when they hit endcap trackers
Tracker backgrounds with 50um x 1cm strips >> VXD backgrounds with 20 um x 20um pixels
Barrel and Endcap ECAL need to passively absorb ~1 MeV photons/pad/BX without showing a hit
8 Aug MAP at SLAC
T. Markiewicz