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Beam Instrumentation Overview

November 14th, 2004 WG4 - Beam Delivery/Interaction Region First ILC Workshop KEK

Eric Torrence University of Oregon З Largely personal viewpoint З Re-written to remove head-on references

Eric Torrence

1/15

November 2004


Topics Beamline Laserwire BSL Monitor Polarimeter Spectrometer

Diagnostic

Physics

Pair Monitor Bunch Length Detector

Veto Bhabha Acol

Wide variety of topics Very broad overview...

Eric Torrence

2/15

November 2004


Forward Detector Overview

L*=4 m Proposal (Achim Stahl, Paris) З З З З Mask/Overlap Lumi Monitor Tagger Pair Monitor ~ ~ ~ ~ 50-100 mRad 20-50 mRad 5-20 mRad 5-20 mRad Critical for Hermeticity Outside pair backgrounds Identify electrons Machine diagnostics

Could be provided one detector Could optimize separately for each function
Eric Torrence 3/15 November 2004


Electron Hermeticity SUSY Two Photon

~~ e + e - Е Е Е + Е -

e+e- Е+Е-e+e

-

-

Min. forward angle e- veto determines m = m

-m



0

sensitivity

Veto - Inefficiency gives false signal To reach ~1 fb sensitivity need fakes < 0.1% or ( e - ) > 99.9 % Some cracks/holes are OK if they are well localized Bulk of detector must be very efficient Demonstrate in test beam

~~ (Bambade)

Veto

Personally not convinced of viability with variation in pair background

Eric Torrence

4/15

November 2004


Pair Monitor Head-on 20 mRad Crossing Angle

Pair distribution gives snapshot of beam collision On paper, powerful sensitivity to collision parameters (e.g. Lohmann, bunch width, length, offset, waist, etc.) Questions З Will this really work? Possible to extract orthogonal observables with realistic beam jitter, asymmetries, etc? З Is this mandatory for luminosity, or just icing on the cake? З Are distortions due to x-angle (even with dipole windings) catastrophic? Possible advantage of small crossing angle
Eric Torrence 5/15 November 2004


Laser Wire

Operational at PETRA, complimentary effort underway at ATF O(100 Еm) fast scan at PETRA Developing 6 Еm for ATF

Mandatory for operation as production diagnostic? Where does it go, how is it used? Design and sim. for BDS underway Defining real-estate critical, particularly around IP
Eric Torrence 6/15 November 2004


Diagnostic Instrumentation Proposed "exotic" diagnostics include Laserwire, SR monitor, pair monitor, bunch length, nBPM Question: which are strictly required, and which would simply be nice to have? Need to define instrumentation needs for both operations and tuning/startup phase

What is really needed? How is it to be used? Where does it go?

Also should consider useful main detector information З З З З Pair monitor, fast lumi monitoring Luminous region z from Е + Е - Background signals s profile

Design to be directly available to machine DB and feedbacks like any other beam instrumentation Same true in reverse...
Eric Torrence 7/15 November 2004


Physics Instrumentation Physics Needs З s understood to 100-200 ppm - m H , m t , m Beam energy necessary but not sufficient З Polarization P 0.25 % - A
LR X

at high energy

Goal for polarimeter, could use better З Absolute luminosity My view: L 0.2 % ("easy") Zeuthen view: L 0.01 % ("very hard") LEP expt. 3.4 з10
-4

Theory 5.4 з10
qq

-4

Motivations given are Z and Design Philosophy

Precision measurements require redundant information and meaningful cross-checks to be believable Use physics channels where possible Reduce dependence on beam-beam simulations
Eric Torrence 8/15 November 2004


Polarimetry
532 nm Frequency Doubled YAG Laser e- Mirror Box Pockels Cell Left or Right Circularly Polarized Photons Focusing and Steering Lens Mirror Box (preserves circular polarization) Compton Back Scattered e- Analyzing Bend Magnet
1-93 7268A1

Basic principle well understood

e+

SLD e-

Location and some design details missing

Laser Beam Analyzer and Dump "Compton IP"

Cerenkov Detector Proportional Tube Detector

Downstream Polarimeter З Measure collision effects (lumi-weighted ~ 1/4 of total depol.) З Significant effects at 1 TeV ( P lum ~ 0.5%, should be re-evaluated) Mitigated by W + W - , but lose cross-check P e + also helps, but only if fast reversals IP spin alignment З Longitudinal and parallel to polarimeter З Difficult with 2 IPs? Upstream polarimeter after final bend... З Need solenoid compensation to control orbit

Compatibility in extraction line with other diagnostics
Eric Torrence 9/15 November 2004


Collision Energy Observables Downstream Upstream

0.05 0.04 0.03 0.02 0.01 0

490

492

494

496

498

500

s e+eЕe+ee+e- Е

502 504 Root(s) (GeV)

e+e- Е ЕЕ

1 2

1

2 e+e- Еe+e-

Need coordinated effort to put the pieces together and demonstrate precision on a real physics analysis
Eric Torrence 10/15 November 2004


Spectrometer Designs

RF BPMs

1 mm

З З З З

Bends ~ 100 ЕRad, lengths 10 m, 1 mm bump Need 100 nm (or better) resolution and accuracy Move BPMs to the beam (keep same relative position) Calibrate alignment by turning off chicane Upstream only, very difficult to control all systematics WISRD-style SyncRad Detector Plane Wigglers

З З З З

Downstream only few mRad bends Detect SR Collision diagnostic?

Must operate in difficult x-line environment

Highly complimentary approaches Both challenging for 100 ppm absolute measurements Personally wouldn't believe either without full-scale prototype
Eric Torrence 11/15 November 2004


X-line layout

Difficult to please everyone Considering designs with separate polarimeter and spectrometer X-line must also extract beam safely with tolerable backgrounds... Need to understand if additional diagnostic instrumentation must be accommodated!

Eric Torrence

12/15

November 2004


Collision Biases
in s - 2 E b vs. Vertical Offset (truncated range)
Ecm (MeV) Ecm (MeV)

NLC 500
-800

TESLA 500
-1000 -1200

-1000

-1200 -2 -1 0 1 2 Offset (nm)

-1400 -2 -1 0 1 2 Offset (nm)

Bias sensitive to fine details of the collision process, not completely reflected in Bhabha dL / d s measurement (E vs. z vs. L correlations) Proposed Solutions (all speculative) З З З З Downstream spectrometer Calibrate with ZZ or Z (loose one cross-check) Monitor with Bhabha energy, muon curvature Accelerator solution Not an easy problem Would like a real observable, reduce simulation dependence
Eric Torrence 13/15 November 2004


Critical Questions Veto in Forward Detector З How well can this really work? З How significant is hole vs. other inefficiencies? More detailed detector designs/simulations + beam tests Diagnostic Instrumentation З What is really needed for operations and tuning? З Where does this go and how is it used? З Do all critical technologies exist? Specify requirements and develop instrumentation design Physics Instrumentation З What does downstream really buy you? З Can you survive without it (physics channels)? З What is the cost/risk of upstream vs. downstream? Design and simulation of complete BDIR region with all foreseen instrumentation Demonstration analysis with real physics observable Time for a philosophy shift inclusive inquiry -> directed, prioritized research
Eric Torrence 14/15 November 2004


Do we need spectrometers at all? Can we simply use L and s from physics reactions? Contrived Example - Lineshape Scan L s Measured True s N= s



dL ----- ( s ) ds not N = L З ( s ) ds

Need dL / d s spectrum including both inter-bunch and intra-bunch variations Some Observations З З З З No idea if this is significant, real study needed Depends upon variance in L and s Need to consider effects of IP feedbacks Could also be correlated to polarization... Fast spectrometer and luminosity monitor could be very useful (even relative)
Eric Torrence 15/15 November 2004