Spin Tracking Studies for Polarimetry at the ILC

Spin Tracking Studies for Polarimetry at the ILC

Moritz Beckmann, Jenny List

DESY - FLC

visiting SLAC May-August 2010

LC-Forum

July 14, 2011

IntroductionPolarization

• Here: longitudinal polarization (alongbeam axis)

• P = pR − pL ∈ [−1,+1]

• Beam with 90% R (and thus 10% L)→ 80% polarization

Moritz Beckmann LC-Forum July 14, 2011 2/ 16

IntroductionPolarimetry at the ILC

• Polarization measurement with 0.25 % uncertainty

• Calibration to 0.1% using collision data

• Must understand spin diffusion/depolarization to 0.1%(further) spin tracking studies required


Simulation

• This study: ILC

• Could be used for other projects (e.g. CLIC) as well, if fedwith corresponding beamline design / parameters


Spin tracking

• Spin propagation in electromagnetic fields isdescribed by T-BMT equation

d

dt~s = ~Ω

(~E (~r , t), ~B(~r , t), ~p ,m , a

)×~s

• Approximation (~B⊥ only): precession

θspin = (aγ + 1) · θorbit

Electrons at 250 GeV: aγ + 1 ≈ 568 B

a ≡ g−22 : anomalous gyro-magnetic moment

γ = Em


Beam Delivery System des ILC

Latest available beamline design (SB2009 Nov10 lattice)


Idealized Lattice

• 10 000 simulated particles, spins parallel to z-axis

• Perfect magnet alignment, no collision effects

• In the following: look only at polarimeters und IP

distance from IP [m]-3000 -2500 -2000 -1500 -1000 -500 0

lon

g. p

ola

riza

tio

n

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

UP IP,DP

doglegcollimation energy

UP/DP: up-/downstream polarimeter


Idealized Lattice

• 10 000 simulated particles, spins parallel to z-axis

• Perfect magnet alignment, no collision effects

• No significant depolarization at the points of interest

distance from IP [m]-1680 -1660 -1640 -1620

lon

g. p

ola

riza

tio

n

0.6

0.7

0.8

UP

distance from IP [m]0 20 40 60 80 100 120 140

0.6

0.7

0.8

IP DP



Misalignments

• Magnets between polarimeters misaligned⇒ particles see field 6= design field⇒ affects spin orientation

• Static and time-dependent misalignments

• Beam orbit correction systems (operate on bunch time scales,required for luminosity)

• Automatic correction of spin alignment as well?


Static Misalignments (uncorrected)

Now: elements misaligned

• Random shifts in x and y for each element (some splitted!)

• Gaussian-distributed random numbers, σx ,y = 5 µmσx ,y = 50 nm in final focus region (0-50m in front of IP)

• Plots shows three exemplary samples

• Ignore collimators (beam loss)

distance from IP [m]-1680 -1660 -1640 -1620

lon

g. p

ola

riza

tio

n

0.6

0.7

0.8

UP

distance from IP [m]0 20 40 60 80 100 120 140

0.6

0.7

0.8

IP DP

not misaligned misaligned



Static Misalignments (uncorrected)

, beam axis)bunch

p angle(≈>/(250 GeV) t

<p0 0.001 0.002 0.003 0.004

lon

git

ud

inal

po

lari

zati

on

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

+1)γ(a⋅precession

IP

UP

DP

• Same misalignments as before (σx ,y = 5 µm)

• Deviation from dashed line still under investigation


Static Misalignments (corrected)

, beam axis)bunch


<p0 0.5 1 1.5 2 2.5 3 3.5 4

-610×

lon

git

ud

inal

po

lari

zati

on

0.77

0.775

0.78

0.785

0.79

0.795

0.8


IP

UP

DP

• Now: correct orbit in front of UP and at IP to < pt >= 0

• Even perfect orbit correction does not fix polarization at IP



longitudinal polarization at IP0.79 0.792 0.794 0.796 0.798 0.8

lon

git

ud

inal

po

lari

zati

on

at

UP

0.797

0.7975

0.798

0.7985

0.799

0.7995

0.8

y=x 0.1%±

968 of 1000 entries


lon

git

ud

inal

po

lari

zati

on

at

DP

0.797

0.7975

0.798

0.7985

0.799

0.7995

0.8

y=x 0.1%±

968 of 1000 entries

hzpol_UPIPEntries 1000Mean 1.003RMS 0.003915Underflow 0Overflow 0

pol(UP) / pol(IP)0.95 1 1.05 1.10

50

100

150

200

250

300

350

Entries 1000Mean 1.003RMS 0.003915

hzpol_DPIPEntries 1000Mean 1.002RMS 0.003945Underflow 0Overflow 0

pol(DP) / pol(IP)0.95 1 1.05 1.10

50

100

150

200

250

300





lon

git

ud

inal

po

lari

zati

on

at

UP

0.797

0.7975

0.798

0.7985

0.799

0.7995

0.8

y=x 0.1%±

968 of 1000 entries


lon

git

ud

inal

po

lari

zati

on

at

DP

0.797

0.7975

0.798

0.7985

0.799

0.7995

0.8

y=x 0.1%±

968 of 1000 entries

hzpol_UPIPEntries 1000Mean 1.003RMS 0.003915Underflow 0Overflow 0

pol(UP) / pol(IP)0.95 1 1.05 1.10

50

100

150

200

250

300

350


hzpol_DPIPEntries 1000Mean 1.002RMS 0.003945Underflow 0Overflow 0

pol(DP) / pol(IP)0.95 1 1.05 1.10

50

100

150

200

250

300



Summary

• A spin tracking framework for high energy linear colliders hasbeen set up

• ILC: understanding of polarization to permille-level required

• Implemented spin tracking through misaligned elements andhigher-order magnets

• Polarization in presence of misalignments: deviation fromsimple spin precession → investigate

• Assuring same beam angles at polarimeters and IP might notbe enough to fulfill polarimetry precision requirements


Outlook: Other To-Do’s

• Insert missing beamline elements:• Detector magnets• Crab cavities & travelling focus (to enhance luminosity)

• Simulate collision effects (GP++/CAIN):

• Deflection (∼ 10−4 rad) fromcolliding bunch (T-BMT)

• Spin flip by emission ofbremsstrahlung (Sokolov-Ternov)


Thanks for your attention!

Thanks for support and useful discussions to:

• David Sagan (Cornell)

• Deepa Angal-Kalinin (Daresbury)

• Anthony Hartin (DESY)

• Andrei Seryi (JAI)

• Kenneth Moffeit, Yuri Nosochkov, Michael Woods (SLAC)

• Jeff Smith (formerly SLAC)


Backup slides


Upstream Polarimeter Chicane

• Constant magnetic field

• Dispersion (depending on beam energy): 1-11 cm

• Compton scattering: ∼ 1000 electrons per bunch

• Energy distribution → spatial distribution

• Cherenkov gas detector counts electrons per channel


Idealized Lattice

, beam axis)bunch


<p0 0.5 1 1.5 2 2.5 3 3.5 4

-610×

lon

git

ud

inal

po

lari

zati

on

0.77

0.775

0.78

0.785

0.79

0.795

0.8


IP

UP

DP


Idealized Lattice


lon

git

ud

inal

po

lari

zati

on

at

UP

0.797

0.7975

0.798

0.7985

0.799

0.7995

0.8

y=x 0.1%±

1000 of 1000 entries


lon

git

ud

inal

po

lari

zati

on

at

DP

0.797

0.7975

0.798

0.7985

0.799

0.7995

0.8

y=x 0.1%±

1000 of 1000 entries

hzpol_UPIPEntries 1000Mean 1.001RMS 4.76e-09Underflow 0Overflow 0

pol(UP) / pol(IP)0.95 1 1.05 1.10

200

400

600

800

1000Entries 1000Mean 1.001RMS 4.76e-09

hzpol_DPIPEntries 1000Mean 0.9994RMS 4.772e-09Underflow 0Overflow 0

pol(DP) / pol(IP)0.95 1 1.05 1.10

200

400

600

800

1000Entries 1000Mean 0.9994RMS 4.772e-09


Documents

Spin Tracking Studies for Polarimetry at the ILC