1 Muon Collider Backgrounds Steve Geer Fermilab Steve Geer MC Detector & Physics Briefing @ DOE June...

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Muon ColliderBackgrounds

Steve Geer

Fermilab

Steve Geer MC Detector & Physics Briefing @ DOE June 24, 2009

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INTRODUCTION

Muon Collider detector backgrounds were studied actively 10 years ago (1996-1997). The most detailed work was done for a 22 TeV Collider → s=4 TeV.

Since muons decay (2TeV=42ms), there is a large background from the decay electrons which must be shielded.

The electron decay angles are O(10) microradians – they typically stay inside the beampipe for about 6m. Hence decay electrons born within a few meters of the IP are benign.

Shielding strategy: sweep the electrons born further than ~6m from the IP into ~6m of shielding.


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2 x 1012 muons/bunch

2 x 105 decays/m

Electron decay angles are O(10) rad

Mean electron energy = 700 GeVMean energy= 700 GeV

2 2 TeV Collider

As the decay electrons respond to the fields of the final focus system they lose 20% of their energy by radiating on average 500 synchrotron photons with a mean energy of ~500 MeV … & are then swept out of the beampipe.

DECAY BACKGROUNDS


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Shielding Simulations

• Shielding design group & final focus design group worked closely together & iterated

• Used two simulation codes (MARS & GEANT), which gave consistent results

• Shielding design & simulation work done by two experts (Mokhov & Stumer) in great detail, & involved several person-years of effort.


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Final Focus/Shielding Geometry


Beam-Beam region (* = 3mm): length = 3 mm, radius = 3 m (rms), Tbunch = 10 s

Fate of electrons born in the 130m long straight section: 62% interactupstream of shielding, 30% interact in early part of shielding, 2% interact in last part, 10% pass through IP without interacting.

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Shielding Details


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More Shielding Details


r=4cm

Z=4m

Designed so that, viewedfrom the IP, the inner shielding surfaces are notdirectly visible.

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Background calculations & shielding optimization was performed using(independently) MARS & GEANT codes … the two calculations were inbroad agreement with each other (although the designs were different in detail).

Results from Summer 1996

GEANT MARSI. Stumer N. Mokhov


4 TeV Collider Backgrounds

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Particles/cm2 from one bunch with 2 1012 muons (2 TeV)

r (cm) n p e 5 2700 120 0.05 0.9 2.3 1.7

10 750 110 0.20 0.4 0.7

15 350 100 0.13 0.4 0.4

20 210 100 0.13 0.3 0.1

50 70 120 0.08 0.05 0.02

100 31 50 0.04 0.003 0.008

calo 0.003

muon 0.0003

GEANT (I. Stumer) Results from LBL Workshop, Spring 1997


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Consider a layer of Silicon at a radius of 10 cm.

GEANT Results (I. Stumer) for radial particle fuxes per crossing:

750 photons/cm2 2.3 hits/cm2

110 neutrons/cm2 0.1 hits/cm2

1.3 charged tracks/cm2 1.3 hits/cm2

TOTAL 3.7 hits/cm2

0.4% occupancy in 300x300 m2 pixels

MARS predictions for radiation dose at 10 cm for a 2x2 TeV Collider comparable to at LHC with L=1034 cm-2s-1

At 5cm radius: 13.2 hits/cm2 1.3% occupancy


VERTEX DETECTOR HIT DENSITY

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Occupancies


TOTAL CHARGED PARTICLES

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S. Geer, J. Chapman: FERMILAB-Conf-96-375

Photon & neutron fluxes in inner tracker large but

mean energies O(MeV) & radial fluxes ~ longitudinal fluxes ( isotropic)

Clock 2 layers out at variable clock speed (tomaintain pointing) &take coincidence.

Blind to soft photon hits& tracks that don’t come

from IPSteve Geer MC Detector & Physics Briefing @ DOE June 24, 2009

PIXEL MICROTELESCOPE IDEA

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PIXEL MICROTELESCOPE SIMULATION - 1


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PIXEL MICROTELESCOPE SIMULATION - 2


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Electromagnetic: Consider calorimeter at r=120 cm, 25 r.l. deep, 4m long,22 cm2 cells:

GEANT 400 photons/crossing with <E> ~1 MeV <ETower>~400 MeV

E ~ (2<n>) <E> = 30 MeV

For a shower occupying 4 towers: <E> = 1.6 GeV and E = 60 MeV

Hadronic: Consider calorimeter at r=150 cm, 2.5m deep (~10), covering30-150 degrees, 55 cm2 cells:

<ETower> ~ 400 MeV

E ~ (2<n>) <E> = O(100 MeV)

These estimates were made summer 1996, before further improvements tofinal focus + shielding reduced backgrounds by an order of magnitude … so guess background fluctuations reduced by 3 compared with above.


Calorimeters

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Bethe-Heitler Muons (Z Z+-)

Special concern: hard interactions (catastrophic brem.) of energetic muons travelling ~parallel to the beam, produced by BH pair production.

Believe that this back-ground can be mitigated using arrival-times, pushing calorimeter to larger radius, & spike removal by pattern recognition … but this needs to be simulated


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Muon collider physics, backgrounds & detectors have not been intensely studied for 10 years. Since then a few things have happened:

-A decade of detector development driven by LHC & ILC requirements- Physics landscape has evolved-Community expectations for detector performance have evolved-Muon Collider baseline design details have evolved

New design studies for the final focus require, in the near future, a new shielding design study (final focus magnet configuration is changing) - started to rebuild the needed physics/detector/ background/final focus team.

Later this year we are planning to hold a workshop at FNAL on Muon Collider physics, detectors, and backgrounds:

-Revisit theoretical motivation-Explore detector R&D synergies with ILC/CLIC-Prepare the way for an eventual apples-to-apples comparison with CLIC


New Work

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Comparison with CLIC

• We are not yet in a position to make an apples-to-apples comparison with CLIC, but …..


hits/mm2/bunch train

30mm O(1) hit/mm2/bunch train

FROM CLIC Machine-Detector interface studies:

CLIC

NOT AN APPLES-to-APPLES COMPARISON … BUT … Background hit densities appear to be similar to MC … so there may be many detector design issues in common between the 2 machines

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Summary

• Background levels at a 4 TeV Muon Collider are expected to be similar to those at the LHC with L=1034 cm-2 s-1

• Detailed studies were done 10 years ago, and things have evolved. New studies to update the picture are beginning.

• We believe there is much synergy with CLIC physics, detector, & backrgound studies.Steve Geer MC Detector & Physics Briefing @ DOE June 24, 2009

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