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Beam Parameter Measurements

New Physics at TeV Scales and Precision EW Studies

Eric Torrence University of Oregon

Eric Torrence

1/14

March 2005


Beam Instrumentation Introduction
0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 490 492 494 496 498 500 502 504 Root(s) (GeV)

( -, - ), ( +, + ), ... dL -----dE L

0

s Fundamental Goal Spin-dependent absolute collision energy spectrum Typical Components · · · · · Beam Energy Beam Energy Width Beam Polarization Absolute Luminosity Differential Luminosity Spectrum

All are intrinsically related in fundamental goal
Eric Torrence 2/14 March 2005


Instrumentation Design Challenge

Physics

Detector

Accelerator

Must optimize between three often competing goals Better performance is always preferred, but resources are not infinite Hard Questions · What is mandatory? · What has high benefit/cost? · What is less compelling?

May be soon in a position to set priorities and make some difficult decisions Need solid input from the physics side ...
Eric Torrence 3/14 March 2005


Instrumentation Goals

Goals often defined by what is considered "achievable" · s understood to 50-100 ppm - m H , m t , m Beam energy necessary but not sufficient · Polarization P 0.25 % - A
LR X

at high energy
+

Goal for polarimeter, could use better, 0.1% with P · Absolute luminosity ALCPG view: L 0.2 % ("easy") Tesla view: L 0.01 % ("very hard") LEP expt. 3.4 â10
­4

Theory 5.4 â10
qq

­4

Motivations given are Z and

Baseline goals for high energy, high luminosity running Use mixture of beam-based and physics-based observables Redundancy is key to precision
Eric Torrence 4/14 March 2005


Special Configurations Dedicated runs can be taken with "special machine configurations" Examples · tt threshold scan · Mega/Giga Z running Reduced energy spread, beam-beam effects in return for reduced luminosity

With new ILC parameters table, should seriously look at specific running and instrumentation scenarios

Word of Warning Also must be ready for alternate situation: Worse beam conditions for higher luminosity Luminosity will trump almost all other considerations!

Eric Torrence

5/14

March 2005


Beam 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

e+

SLD e­ Laser Beam Analyzer and Dump "Compton IP"

Cerenkov Detector Proportional Tube Detector

Basic principle understood, many details missing · · · · Upstream/downstream polarimeter or both? Depolarization effects Spin transport with 2 IPs Benefit of P + and helicity reversal time

Eric Torrence

6/14

March 2005


IP-Polarimeter differences
P(%)
3 2 1 0
0
NLC 1TeV

Depolarization in collision · Sokolov-Ternov and BMT precession · Overall lumi-weighted ~ 1/4 total depol. · P lum ~ 0.5%, should be re-evaluated IP-polarimeter spin precession (g ­ 2) = ---------------- 2

Outgoing Bunch

0

5

10

15

· 1000x amplification, need spin vector longitudinal and parallel to ~ 50 µRad · Harder with 2 IPs (double spin rotators) · Must worry about solenoid in x-angle

3 2 1 0 0

Lumi Weighted S-T BMT Total

5

10

Downstream-Upstream argument

15 dy /

y

· Downstream allows direct measurements of depolarization effects · Upstream closer to lum-weighted polarization · Need separate polarimeter per IP, too expensive to do both? New IP simulation (GuineaPig) with spin transport may help guide arguments here.
Eric Torrence 7/14 March 2005


Positron Polarization Error Propagation P
eff

P- + P+ = --------------------- ~ 93% [80%/50%], P 1 + P- P+

eff

0.1 %

Blondel Scheme · Can directly extract P eff from ++, --, +-, · Assumption that P = P - ­ P + , L are zero With undulator production, windings determine photon helicity - difficult to reverse P + Longer time between P + reversals means effectively independent beams Increased reliance on absolute polarization scale... Personal belief: only fast reversals will realize benefits of Blondel scheme
Eric Torrence 8/14 March 2005

-+


Physics Inputs
ALR

1

W

Z/



W W

W

0.8

Use t-channel WW or single-W as lumi-weighted polarization monitor. P ~ 0.1% independent of P
+

s = 800 GeV

0.6

= 1.007 Z = 1.01 SM

0.4

-1

-0.5

0

0.5

[K. MÆnig]

1 cos

Directly measures P , could be used for central value No more cross-check (precision) No information about correlations (e.g. P vs. L) Experimental systematic uncertainties?

Eric Torrence

9/14

March 2005


Spectrometer Design

RF BPMs

1 mm

· · · ·

Bends ~ 100 µRad, 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

· · · ·

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
Eric Torrence 10/14 March 2005


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) · · · · 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 11/14 March 2005


Radiative Returns

T. Barklow Possible to separately fit s and tracker momentum scale? K. MÆnig also presenting results from Arnd Hinze 100 ppm looks achievable, need separate tracking of variation, need to worry about possible correlations, systematics Probably the only hope for WW threshold scan... Other possibilities: ZZ, full energy µ+µ-, ...
Eric Torrence 12/14 March 2005


Absolute Luminosity

Re-design of forward region (partly) motivated by precision luminosity Is this motivated at high energy, or only Giga-Z? Is L ~ 0.1% good enough for all HE measurements?

Higher precision is always better, but question of cost/benefit and resource allocation. Should the lumi-monitor simply be replaced for Giga-Z running?

Eric Torrence

13/14

March 2005


Difficult questions

· Do we need beam-based polarimetry better than 0.5% (absolute), or are we satisfied to use physics channels. Relative is much easier than absolute... · Will the improved precision available in P + ever be realized, or will this be limited by switching time? · How important fundamentally are Lumi - Energy Polarization correlations? · Is it worth the effort to achieve L ~ 0.01%? · Are we satisfied to rely upon physics-based collision energy measurements? · How do our assumptions evolve with realistic running conditions? What are the relative risks?

Meaningful input from the physics groups most welcome on these issues...

Eric Torrence

14/14

March 2005