1. Higgs Factory Backgrounds
Fermilab
Accelerator Physics Center
Higgs Factory Backgrounds
Sergei Striganov
Nikolai Mokhov and Igor Tropin
Fermilab
MAP 2014 Spring Workshop
Fermilab
27-31 May, 2014

2. Outline
Introduction
Background spectrum and fluxes at central part of detector
Basic characteristics of backgrounds coming into detector
Hits in vertex detector
Conclusion

3. v0 - minimal 7.6 deg, 5σ nozzles
HF MDI Versions – MAP12
No nozzles, no other MDI shielding
v0 - minimal 7.6 deg, 5σ nozzles
v1 - minimal 7.6 deg, 5σ tungsten nozzles, tungsten collimator in IR and concrete collars in IR
v2 - thicker 15 deg, 4σ tungsten nozzles in BCH2 cladding, 5 sigma tungsten collimator in IR, concrete colars in IR, new magnets geometry, magnetic field maps
v3 – additional shielding installed around first quad.
Tungsten collimators reduced to 4 sigma. Beam pipe
radius near IP enlarged from 3 to 5 cm. Minor
changes in inner nozzle surface.

4. Machine-Detector Interface - v2 vs v3

5. Where is Background Enters Detector? V2 – MAP13
70% gamma, 80% e+-, 60% of hadrons coming into detector through quad (Z>350cm and R > 50 cm) – more than 15 ns from IP.

6. Gamma Flux (1/cm2/bunch X)
without nozzle v3

7. Gamma Flux in Plane Perpendicular to Beam at IP (1/cm2/bunch X)
without nozzle v3

8. Electron/Positron Flux (1/cm2/bunch X)
without nozzle v3

9. Electron/Positron Flux in Plane Perpendicular to Beam at IP (1/cm2/bunch X)
without nozzle v3

10. Neutron Flux (1/cm2/bunch X)
without nozzle v3

11. Neutron Flux in Plane Perpendicular to Beam at IP (1/cm2/bunch X)
without nozzle v3

12. Where Background Hits Nozzle INNER surface-v3
decay e+- through
Be beam pipe (25 GeV/c)

13. Angle between electron/positron and beam as function of nozzle entrance point

14. Momentum spectra of electron from muon decay and momentum spectra of electron entered into nozzle (|z|<120 cm)

15. Where Background Hits Nozzle INNER surface -II
v3 nozzle
Reduced v3 nozzle

16. Where Background Hits Nozzle INNER surface -III
v3 nozzle: decay e+- through Be beam pipe (25 GeV/c)
reduced v3 nozzle: 106 decay e+- through Be beam pipe (25 GeV/c)

17. How to choose minimal nozzle radius?
electron distribution after first quad
350 cm from IP
minimal nozzle radius

18. Nozzle geometry – considered setups

19. Where Background Hits Nozzle INNER surface -IV
v4 nozzle- no decay electron through Be beam pipe
v7 – no decay electron through Be beam pipe

20. Electron flux near IP for different nozzle inner shape in accelerator plane
v3 nozzle: electron/cm2/BX
v7 nozzle: electron/cm2/BX

21. Electron flux at IP in Plane Perpendicular to Beam
v3 nozzle: electron/cm2/BX
v7 nozzle: electron/cm2/BX

22. Gamma flux near IP for different nozzle inner shape in accelerator plane
v3 nozzle: gamma/cm2/BX
v7 nozzle: gamma/cm2/BX

23. Gamma flux at IP in Plane Perpendicular to Beam
v3 nozzle: gamma/cm2/BX
v7 nozzle: gamma/cm2/BX

24. Neutron flux near IP for different nozzle inner shape in accelerator plane
v3 nozzle: neutron/cm2/BX
v7 nozzle: neutron/cm2/BX

25. Neutron flux at IP in Plane Perpendicular to Beam
v3 nozzle: neutron/cm2/BX
v7 nozzle: neutron/cm2/BX

26. Gamma Flux in Plane Perpendicular to Beam at IP (1/cm2/bunch X)

27. e+- Flux in Plane Perpendicular to Beam at IP (1/cm2/bunch X)

28. Neutron Flux in Plane Perpendicular to Beam at IP (1/cm2/bunch X)

29. Background File Simulation
Simulation of background particles coming into detector takes a lot of CPU. To look at detector background in detail file with particles on some interface surface is prepared. Different detector geometries and different codes (Geant4, Fluka) can be used in further studies starting from this file. Muon decay points are simulated randomly from -23 to 23 m from IP using MARS code. Electron/positron shower in accelerator structure is simulated. Calculation is stopped at interface surface. Following results were obtained with cutoff energies (±23 m from IP): neutron keV, muon – 1 MeV, charged hadron - 1 MeV, gamma, e± keV.

30. Where is Background Produced? Number of Particles Entering Detector

31. Number of particles entering detector per bunch X-ing
10deg
(750 GeV) v2
(62.5 GeV) v3 V v4 v7 v
Photon
1.8 x 108
3.2x109
7.4x108
9.2x108
5.6x108
Electron
1.0 x 106
1.2x108
9.6 x 106
4.7x106
3.5 x 106
Neutron
4.1 x 107
1.7x108
3.8 x 107
7.4x107
6.4 x 107
Charged hadron
4.8 x 104
1.0x105
1.6 x 104
2.4x104
1.7 x 104

32. Where is Background Produced? Energy Flow Entering Detector

33. Energy (TeV) entering detector per bunch X-sing
Particle
10deg
(750 GeV) v2
(62.5 GeV) v3 v4
(62.5GeV) v7
Photon
1.6 x 102
1.2x104
5.7x103
8.0x103
4.6x103
Electron
5.8
9.0x103
5.3x103
107
100
Neutron
1.7 x 102
3.0x102 84
122
112
Charged hadron 12 26
2.1 15
6.4

34. Momentum Spectra of Particles Entering Detector: v3 and v7
v7: 92% of e+- momentum < 0.5 MeV/c

35. Average momentum (MeV/c) of particle entering detector
10deg
(750 GeV) v2
(62.5 GeV) v3 v4 v7
Photon
0.9
3.7
7.7
8.7
8.1
Electron 6 75
789 23 29
Neutron 45 38 33 35
Charged hadron
513
460
354
909
629

36. Where is Background Enters Detector? v3 and v7

37. Where is Energy Enters Detector? v3 and v7

38. Where background enters to nozzle - v7?
Distance from IP
gamma
positron
electron
neutron #
0 to 50 cm 9% 1% 6%
55%
energy
11%
0.02%
0.4%
43%
50 to 87 cm
51%
82%
70%
14%
48%
85%
100%
10%
87 to 150 cm
37%
15%
25%
26%
47%
20%
28%
Most of electrons/positrons are produced from nozzle jaws

39. Gamma flux: entrance to detector vs entrance to nozzle
Gamma flux: entrance to detector vs entrance to nozzle. Beam pipe – 5 cm radius, nozzle minimal radius – 2 cm
vertical coordinate
horizontal coordinate
Maximum at positive (negative) entrance to nozzle and negative (positive) entrance to detector – backscattering from nozzle jaws!

40. Nozzle geometry – 2 vertex setups

41. Vertex Barrel

42. Vertex Endcup

43. Number of particles entering detector per bunch X-ing. ch
Number of particles entering detector per bunch X-ing. ch. Hadron > 1 MeV; γ,e > 0.2 MeV; neutron> 0.1 MeV
Particle
10deg
(750 GeV) v2
(62.5 GeV) v3 V v4
v7x2s4 v
Photon
1.8 x 108
3.2x109
7.4x108
9.2x108
2.8x108
Electron
1.0 x 106
1.2x108
9.6 x 106
4.7x106
2.0 x 106
Neutron
4.1 x 107
1.7x108
3.8 x 107
7.4x107
5.2 x 107
Charged hadron
4.8 x 104
1.0x105
1.6 x 104
2.4x104
1.0 x 104

44. Energy (TeV) entering detector per bunch X-sing
Particle
10deg
(750 GeV) v2
(62.5 GeV) v3 v4
(62.5GeV)
v7x2
Photon
1.6 x 102
1.2x104
5.6x103
8.0x103
2.2x103
Electron
5.8
9.0x103
7.4x103
107 32
Neutron
1.7 x 102
3.0x102 84
122 86
Charged hadron 12 26
2.2 15
2.3

45. V7x2 setup – origin and spectra (low energy thresholds!!!)

46. V7x2 setup – time

47. Hit calculations
MARS improvements : all weights equal 1 and EGS5 simulation up to 1 keV. We can simulate hits now!
Hit definition: charged track left sensitive volume + charged
track is stopped in sensitive volume. To estimate occupancy we
need to perform simulation for chosen pixel size. Appropriate
electron transport threshold should be determined as function of
pixel size.
In MARS minimal energy of produced δ-electron Ed= electron
transport threshold. Number of produced δ-electron ~ 1/Ed . Low energy
δ-electron are produced with large angle to δ-electron direction.
Electron ranges in silicon: 3 keV – 0.14 μm and 10 keV – 1.5 μm.
With 3 keV threshold most of δ-electrons are stopping in same pixel as
outgoing track - double counting! 10 keV threshold looks like more
realistic.

48. ILC experience – Tatsuya Mori (Tohoku University)
Important numbers: pixel size 5-10 μm and occupancy < 3%

49. Occupancy in vertex detector (3 keV threshold)
name
hit/cm2
5x5 μm, %
10x10 μm,%
20x20 μm,%
Barrel 1
1.2
4.8
19.2
Barrel 2
0.11
0.44
1.8
Barrel 3
542
0.43
Barrel 4
559
0.45
Endcup 1
0.2
0.8
3.6
Endcup 2
0.57
2.26
Endcup 3
0.36
1.45
Endcup 4
0.5

50. Occupancy in vertex detector (10 keV threshold)
name
hit/cm2
5x5 μm, %
10x10 μm,%
20x20 μm,%
Barrel 1
0.66
2.64 11
Barrel 2
0.06
0.24
9.6
Barrel 3
300
Barrel 4
142
0.1
Endcup 1
0.49
1.96
Endcup 2
0.31
1.64
Endcup 3
0.20
0.80
Endcup 4
662
0.26

51. Summary
Improved shielding (v7x2s4) reduces numbers of background particles to same order of magnitude as we had for 1.5 TeV collider.
Background electrons and gammas have about 10 times larger
average momentum at Higgs Factory than at collider.
Main source of background – decay electrons entered inner nozzle surface near IP.
Optimization of nozzle significantly reduces background in
comparison with MAP 2013: 10 times for gammas, 60 times for
electrons, 3 times for neutrons. Total energy of background
electrons was reduced by 300 times.

52. Summary - II
Particle fluxes, energy depositions in vertex and tracker are presented.
Pixel occupancy of background in vertex detector is estimated. Even with very conservative calculation occupancy requirement
can be reached for ILC type Fine Pixel CCD detector.

53. Backup

54. Simple estimate of occupancy
Simulations were performed with MARS background files in EGS5
mode with 3, 10, 20, 30 keV thresholds. Number of charged tracks
leaving detector weakly depends on Ed , number of stopped tracks is
proportional ~ 1/Ed . Low energy δ-electron are produced with large
angle to δ-electron direction. Part of them is stopped in same pixel as
track going from this pixel. To avoid double counting we need to choose
adequate electron transport threshold. Electron ranges in silicon:
3 keV – 0.14 μm, 10 keV – 1.5 μm, 20 keV – 5 μm, 30 keV – 10 μm.
Probability to stop in neighbor pixel:
energy < 10 keV energy < 3 keV
5 μm % %
10 μm % %
20 μm % %
10 keV is close to estimated from above
20 kev is minimal estimate for 5 μm
30 kev is minimal estimate for 10 μm
10 keV estimate is only 30% large than 30 keV estimate in simulation. .

55. Where is Background Produced. Number of Particles Entering Detector 1
Where is Background Produced? Number of Particles Entering Detector 1.5 TeV

56. Where is Background Produced? Energy Flow Entering Detector 1.5 TeV

57. Energy Spectra Entering Detector 1.5 TeV