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

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

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.

Machine-Detector Interface - v2 vs v3

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.

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

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

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

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

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

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

Where Background Hits Nozzle INNER surface-v3 2.2 105 decay e+- through Be beam pipe (25 GeV/c)

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

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

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

Where Background Hits Nozzle INNER surface -III v3 nozzle: 2.2 105 decay e+- through Be beam pipe (25 GeV/c) reduced v3 nozzle: 106 decay e+- through Be beam pipe (25 GeV/c)

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

Nozzle geometry – considered setups

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

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

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

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

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

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

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

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

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

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

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 - 100 keV, muon – 1 MeV, charged hadron - 1 MeV, gamma, e± - 200 keV.

Where is Background Produced? Number of Particles Entering Detector

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

Where is Background Produced? Energy Flow Entering Detector

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

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

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

Where is Background Enters Detector? v3 and v7

Where is Energy Enters Detector? v3 and v7

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

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!

Nozzle geometry – 2 vertex setups

Vertex Barrel

Vertex Endcup

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

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

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

V7x2 setup – time

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.

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

Occupancy in vertex detector (3 keV threshold) name hit/cm2 5x5 μm, % 10x10 μm,% 20x20 μm,% Barrel 1 2.3 104 1.2 4.8 19.2 Barrel 2 2.2 103 0.11 0.44 1.8 Barrel 3 542 0.43 Barrel 4 559 0.45 Endcup 1 8.9 103 0.2 0.8 3.6 Endcup 2 5.7 103 0.57 2.26 Endcup 3 3.6 103 0.36 1.45 Endcup 4 1.2 103 0.5

Occupancy in vertex detector (10 keV threshold) name hit/cm2 5x5 μm, % 10x10 μm,% 20x20 μm,% Barrel 1 1.3 104 0.66 2.64 11 Barrel 2 1.3 103 0.06 0.24 9.6 Barrel 3 300 Barrel 4 142 0.1 Endcup 1 4.9 103 0.49 1.96 Endcup 2 3.1 103 0.31 1.64 Endcup 3 1.9 103 0.20 0.80 Endcup 4 662 0.26

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.

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.

Backup

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 30% 2.8% 10 μm 15% 1.4% 20 μm 8% 0.7% 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. .

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

Where is Background Produced? Energy Flow Entering Detector 1.5 TeV

Energy Spectra Entering Detector 1.5 TeV