Crossing Angle:

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Crossing Angle Impact on Physics
!!! Warning !!! Physics Case based on ultimate
precision Even small systematic problems can
damage it

• Overview of potential impact
• Study a few examples in more details

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Overview
Crossing Angle 10 mrad
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Overview

• Events are boosted horizontally
• Modified beamstrahlung
• Acceptance holes near z-axis
• Changes in machine background
• Diagnostics behind the IP

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The Boost
10 mrad ? 5 GeV at vs 500 GeV
vs 2 Eb v(1 sin2?c) 0.99995 vs ? sin ?c
0.01 ? 1 / v( 1 sin2?c) 1.00005
All events can be boosted back into
the center-of-mass system
Detector operates in the boosted frame
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The Boost
In the direction of the boost

1. Phasespace compressed
2. Angular resolution reduced
3. Momentum increased

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Boost Example
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Boost
MC-Study by Thorsten Kuhl
ee- ? Z0 H
anything
µ µ (recoil mass)
No visible effect, even for large systematics
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Precision Luminosity
From Bhabha scattering Nbhabha ? Lint Goal
10-4 precision d?/d? 1 / ?3
Sensitiv to beam offset?
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0.00212
0.00252
no visible effect
0.00257
0.00238
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0.0129 / µm
0.0133 / µm
no visible effect
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Beamstrahlung
Beam direction and direction of magnetic field no
longer aligned
Potential risc of higher background through
backscattered particles
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Acceptance Hole
2-Photon Events ee- ? ee- µµ- Veto on final e
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pT(µ-) pT(µ)
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Opportunities
Beam diagnostics behind the IP
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No Conclusions yet