Spin Tracking Studies for Polarimetry at the ILC
Transcript of 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
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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
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Simulation
• This study: ILC
• Could be used for other projects (e.g. CLIC) as well, if fedwith corresponding beamline design / parameters
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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
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Beam Delivery System des ILC
Latest available beamline design (SB2009 Nov10 lattice)
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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
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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
UP/DP: up-/downstream polarimeter
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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?
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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
UP/DP: up-/downstream polarimeter
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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
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Static Misalignments (corrected)
, beam axis)bunch
p angle(≈>/(250 GeV) t
<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
+1)γ(a⋅precession
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
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Static Misalignments (corrected)
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
longitudinal polarization at IP0.79 0.792 0.794 0.796 0.798 0.8
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
Entries 1000Mean 1.002RMS 0.003945
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Static Misalignments (corrected)
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
longitudinal polarization at IP0.79 0.792 0.794 0.796 0.798 0.8
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
Entries 1000Mean 1.002RMS 0.003945
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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
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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)
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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)
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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
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Idealized Lattice
, beam axis)bunch
p angle(≈>/(250 GeV) t
<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
+1)γ(a⋅precession
IP
UP
DP
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Idealized Lattice
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%±
1000 of 1000 entries
longitudinal polarization at IP0.79 0.792 0.794 0.796 0.798 0.8
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
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