lum != Pbeam Collision-related · Sokoloff-Ternov spin flips · BMT spin precession Due to large fields seen in collision process Spin transport ( g ­ 2 ) E ( GeV ) ---------------- = -------------------2 0.441 At 250 GeV, 50 µRad bend 28 mRad spin Significant change to spin vector 99% 98.6% · Spin orientation · Spin diffusion (dispersion)

Equally important before/after IP Collision-related can only be studied post-IP
Eric Torrence 3/14 April 2003


Why Downstream Effects equally important before/after IP

Only way to verify/validate collision-based depolarization (in/out)

Can (potentially) study correlations of polarization with energy and dL/dE

But will it work?

Can always run out-of-collision (pulse stealing) for background reasons
Eric Torrence 4/14 April 2003


Tools Tools Needed · GuineaPig (or similar) with spin vectors + some physics · Liar (or similar) with spin transport Tools Available · Cain · Yokoya-Chen semi-analytic calculation K. Thompson study (2001) · MAT-Liar + A. Seyri (TRC code) Produce `realistic' incoming beam profiles · GuineaPig - collision simulation · MAT-Liar extraction line · GEANT + Takashi M. extraction line + backgrounds (g ­ 2) · = ---------------- 0 2 K. Moffeit + M. Woods
Eric Torrence 5/14 April 2003


Collision Effects
Depolarization [%]

60

40

P(%)
3 2 1

P vs. Efinal

Outgoing Bunch

NLC 1TeV

20

0

0

5

10

15

0

3
100 200 300 400 500 Electron energy [GeV]

Lumi Weighted S-T BMT Total

Lumi weighted ~ 25% of bunch average P
K. Thompson January 2001 SLAC PUB 8716
Eric Torrence 6/14

2 1 0 0

5

10

15 dy / y

April 2003


Some Numbers

Semi-Analytic NLC-B 500 1000 1500
Total Lumi Diff

Simulation
Total Lumi Diff

1.1% 0.3% 0.8% 0.9% 0.2% 0.7% 2.5% 0.7% 1.8% 2.0% 0.5% 1.5% 3.2% 0.9% 2.3% 2.7% 0.6% 2.1%

Agreement (0.1% level) between simulation and semi-analytic calculation

Significant effects, even at 500 GeV

Lumi-weighted polarization is closer to incoming beam than outgoing beam

Eric Torrence

7/14

April 2003


Chicane Layout

SLAC-PUB-8096 (Nosochkov) also SLAC-PUB-8871 (Nosochkov & Raubenheimer)

Secondary focus with 20mm dispersion
Eric Torrence 8/14 April 2003


Beam Envelope

Y Projection

Eric Torrence

9/14

April 2003


Chicane Distributions

Laser Spot

± 5 GeV

Eric Torrence

10/14

April 2003


Angular Dispersion at Chicane

1 mRad = 32 degrees

Laser Spot ~200 µRad x 10 GeV

Targeting Important Possible to sample spin

Eric Torrence

11/14

April 2003


Rough Guess

Spin diffusion due to angular dispersion NLC 500 simulations RMS x (µRad)
IP CIP

RMS y (µRad)
IP CIP

P
CIP-IP

1 2 3 4 5 6

240 230 230 210 240 220

330 280 320 240 320 320

99 53 98 52 88 118

42 30 49 27 44 59

0.17% 0.08% 0.16% 0.04% 0.15% 0.16%

Simple model (not simulation) of lumi-weighted polarization Plum ~ 1/4 P

Laser spot-size tends to mitigate this effect...
Eric Torrence 12/14 April 2003


But Wait... Don't take the dispersion numbers literally:

It was found recently that there was a bug in our FF optics deck.

All quad excitations are reversed

More H focusing, less V focusing `secondary focus' not really a focus at all

This is a `possible' deck, but not the currently foreseen extraction line...

Eric Torrence

13/14

April 2003


Conclusions Much work to be done, but at least somebody is working... Beam-Beam effects can lead to 0.2% level depolarization

Pure dispersion effects can reach similar levels.

Neither upstream or downstream polarimeters can directly sample lumi-weighted polarization

Downstream detectors can (possibly) allow direct measurements

Need to demonstrate feasibility...

Eric Torrence

14/14

April 2003