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Beam Polarisation at the ILC:Physics Case and Realisation.
Annika VauthSPIN 2014, Beijing
Introduction Physics case Realisation Conclusion
Introduction: the ILC
Physics case for beam polarisation
Realisation at the ILC
Conclusion
Introduction Physics case Realisation Conclusion
Introduction: the ILC.
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 1 / 24
Introduction Physics case Realisation Conclusion
Motivation for a linear lepton collider.
Electron positron collidersI pointlike particlesI well defined initial stateI precision machinesI discovery potential
e+e− → HZAdvantage of linear colliderI no energy loss due to synchrotron radiationI extendable (length→ energy)
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 1 / 24
Introduction Physics case Realisation Conclusion
ILC history.
Since early 90s different LC studiesTESLA (SCRF)
NLC/JLC (normal conducting)
2004 technology decision: SCRF
2004 ILC Global Design Effort founded
2007 ILC Reference Design Report
2009 LOI for detector concepts
2012/13 ILC Technical Design Report
since 2012/13: Linear Collider CollaborationI ILC: Higgs/Top factory
possible realisation in JapanI CLIC: multi-TeV, on longer timescale
(next energy frontier project in Europe?)
2013
2011
2007
2009
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 2 / 24
Introduction Physics case Realisation Conclusion
ILC in Japan.
Japanese HEP community put the ILC high on their roadmap
Japanese government is interested to host ILC in Japan:
I Support for ILC in Japanese parliament (Diet) is multi-partisanI government has started international initiativeI MEXT has assigned 50 MJPY project money to ILC
2010: two candidate sites (Sefuri and Kitakami)
August 2013: Kitakami site chosen
北上Kitakami
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 3 / 24
Introduction Physics case Realisation Conclusion
ILC overview.
I Planned e+e− collider (length ≈ 30 km)I Energy up to
√s = 500 GeV , potential upgrade to 1 TeV
I Technology: superconducting RF-cavities
damping rings IR & detectors e+ bunchcompressor
e- source
central region5 km
positron main linac
11 km
electron main linac
11 km2 km
e- bunchcompressor
e+ source
2 km
[ILC
TDR
vol.
1,20
13]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 4 / 24
Introduction Physics case Realisation Conclusion
Detectors for physics measurements.
[line
arco
llide
r.org
]
Two detector concepts: ILD and SiD
Use push-pull system at interaction region
Both detectors use particle flow algorithm:I measure each particle type in the
most appropriate subdetector(charged particles→ tracker,photons→ ECAL,neutral hadrons→ HCAL)
I low material budget for thevertex detector and tracker
I high granularity calorimeters
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 5 / 24
Introduction Physics case Realisation Conclusion
Physics case for beam polarisation.
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 6 / 24
Introduction Physics case Realisation Conclusion
Precision physics at ILC.
ä Cleanliness calculability
ä Tune-able center-of-mass energy
ä Polarised beams: P(e+) & 30%, P(e−) ≈ 80%
I polarisation asymmetry as observable
I enhanced rates and background suppression fore−L e+R (Standard Model) or e−R e+L (new physics searches)
I access to chirality of new particles
e⁻ he- he+ cross section
J=0
e⁺
-1
+1
+1
-1
σLL
σRR
σRL
σLR
J=0
J=1
J=1
-1
+1
-1
+1
[LC
-RE
P-2
013-
017]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 6 / 24
Introduction Physics case Realisation Conclusion
ILC physics program.
Polarisation benefits for major physics studies:
Energy Reaction Physics Goal91 GeV e+e− → Z ultra-precision electroweak160 GeV e+e− → WW ultra-precision W mass250 GeV e+e− → Zh precision Higgs couplings350 - 400 GeV e+e− → t t̄ top quark mass and couplings
e+e− → WW precision W couplingse+e− → νν̄h precision Higgs couplings
500 GeV e+e− → f f̄ precision search for Z’e+e− → tth Higgs coupling to tope+e− → Zhh Higgs self-couplinge+e− → χ̃χ̃ search for supersymmetrye+e− → AH,H+H− search for extended Higgs states
700 - 1000 GeV e+e− → νν̄hh Higgs self-couplinge+e− → νν̄VV composite Higgs sectore+e− → νν̄t t̄ composite Higgs and tope+e− → t̃ t̃∗ search for supersymmetry [IL
CTD
Rvo
l.2,
2013
]
polarisation asymmetry as observable opposite polarisations enhance luminositySM: e+
R e−L enhance rates / suppress BG NP: e+L e−R enhance rates / suppress BG
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 7 / 24
Introduction Physics case Realisation Conclusion
Top electroweak coupling.
Top quark production at ILC throughelectroweak processesno competing QCD production
→ small theoretical errors
Polarised beams allow to testchiral structure at ttX vertex
I cross sectionsI forward-backward asymmetryI helicity angle distribution
→ precision on form factorssensitive to new physics
)hel
θcos(-1 -0.5 0 0.5 1
0
0.2
0.4
0.6
0.8
1R+e
L-e
L+e
R-e
Generator - Whizard
Reconstructed
1V
γF~
1VZF~
2V
γF~
2VZF~
1AZF~
Unce
rtainty
-310
-210
-110
1ILC (preliminary)
LHC (hep-ph/0601112)
[LC
-RE
P-2
013-
007]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 8 / 24
Introduction Physics case Realisation Conclusion
Trilinear gauge boson couplings (TGC).
Current experimental statuson charged TGCs in WW production:few percent precision from single parameter fits (LEP & LHC)
Study of WWZ and WW γ at ILC:
Beam polarisation increases sensitivity to deviations from thestandard model & allows to disentangle couplings→ resolutions of few 10−4 in simultaneous fit
γ Z⁰
W⁺
W⁻
W⁺
W⁻
aTGC Parameter Limit
[hep
-ex/
1406
.773
1]pol+30% epol
-80% e
[LC
-DE
T-20
09-0
03]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 9 / 24
Introduction Physics case Realisation Conclusion
Model distinction.
Polarisation can improve distinction between physics models.
Example: R-parity violating SUSY (spin 0) or Z’ (spin 1)?
Ñ ×
Î ℄
Ø
Ó
Ø
Ô
Ô
℄
¼ ¼ ââ ¼ ¼¼ ¼ ¼¼ ¼ ¼¼ ¼ ¼¼ ¼ â¼ ¼
â
â
¿
¾
½
¼
600 620 640 660 680 700
√s �GeV�
σto
t�pb�
e+ e− → ν̃τ → µ+ µ− e+ e− → Z’ → µ+ µ−
500
√s �GeV�800600 700
0
10
20
5
15
25
σto
t�pb�
0
1
5
2
3
4
(-80%, +60%)
(P , Pe- e+ )
(-80%, -60%)
(-80%, +60%)
(P , Pe- e+ )
(-80%, -60%)
Z’
[hep
-ph/
0509
099]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 10 / 24
Introduction Physics case Realisation Conclusion
Precision observables.
What if nothing beyond the standard model is found?sin2 θeff can be crucial quantity to reveal effects of new physics
LEP:sin2 θeff(Ab
FB) = 0.23221± 0.00029
SLC:sin2 θeff(ALR) = 0.23098± 0.00026
World average:sin2 θeff = 0.23153± 0.00016
Goal ILC “GigaZ” (√
91 GeV):∆ sin2 θ = 1.3 · 10−5
[hep
-ph/
1310
.670
8]
Precision measurement via left-right cross-section asymmetry
ALR =
√(σRR + σRL − σLR − σLL)(−σRR + σRL − σLR + σLL)
(σRR + σRL + σLR + σLL)(−σRR + σRL + σLR − σLL)
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 11 / 24
Introduction Physics case Realisation Conclusion
Realisation at the ILC.
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 12 / 24
Introduction Physics case Realisation Conclusion
Electron source.
Requirements: 1312 bunches of 3 · 1010 electrons at 5 Hzwith polarisation >80 %
Polarisation, charge & lifetime already reached at SLC in the past
photocathodes with GaAs/GaAsPstrain-compensated superlatticeat least 85% polarisation,
quantum efficiency typically >0.4%
Active Region
GaAs0.64P0.36
Buffer
GaAs(1-x)Px
Graded Layer
GaAs Substrate
GaAsP
strained GaAs
GaAsP
GaAsP
strained GaAs
strained GaAs
30 Å
40 Å
1000 Å
25μm
25μm
[ILC
TDR
vol.
3.2,
2013
]
Primary challenges at ILC:I long bunch train→ laser system developementI high RF-power on the normal-conducting pre-accelerator
both demonstrated in R&D prototypes
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 12 / 24
Introduction Physics case Realisation Conclusion
Positron source.
Electromagnetic showers to generate positrons:multi-MeV photon beam onto thin metal targetalternative: e− driven source (“300 Hz scheme”), but no polarisation
Options for generation of the photons:I Compton backscatteringI Helical undulator - generates circularly polarised photons,
which in turn generate longitudinally polarised positrons147 m long undulator, space reserved for upgrade
[ILC
TDR
vol.
1,20
13]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 13 / 24
Introduction Physics case Realisation Conclusion
Positron source (2).
Positron yieldI requirement Y = 1.5 e+/e−
I polarisation and yield stronglycoupled to e− beam energy
I below 150 GeV: “10 Hz scheme”with dedicated drive beam(tuning of undulator and collimator parameters -
possible to go to 120 GeV without this)
Polarisation upgradeI nominal design ∼ 30 % e+ polI for 60 %: 73.5 m longer undulator &
photon beam collimation
[ILC
TDR
vol.
3.2,
2013
][IL
CTD
Rvo
l.3,
2,20
13]
R&D work remains (e.g. target design, photon collimator)Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 14 / 24
Introduction Physics case Realisation Conclusion
Spin rotators.
Spin rotators before / after damping rings to preserve polarisation
Fest helicity reversal→ cancellation of time-dependent effects
ä Electron polarisation: switch at source by changing laser polarity
ä Positron polarisation:I depends on direction of undulator windingsI helicity reversal: use spin flipper near the damping ringI beam is kicked into one of two parallel transport lines
Kicker magnet
Dipole + FODO
Solenoidspin
directionfrom polarised
positron sourceB=+Bo
B=-Bo
to damping ring
line with positive solenoid field
line with negative solenoid field
[LC
-RE
P-2
013-
016]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 15 / 24
Introduction Physics case Realisation Conclusion
Polarimetry concept.
ILC polarimetry: per mille level precision by combining
1650m
150m
e⁻ e⁺spin tracking
e⁺e⁻collisionsupstream
polarimeter
downstreampolarimeter
ä Compton polarimeter measurements upstream anddownstream of the e+e− interaction point
ä Spin tracking studies to relate these measurements to thepolarization at the e+e− interaction point
ä Long-term average determined from e+e− collision data asabsolute scale calibration
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 16 / 24
Introduction Physics case Realisation Conclusion
Compton polarimeters.
I O(103) Compton scatterings/bunchI Energy spectrum of scattered e+/e− depends on polarisationI Magnetic chicane: energy distribution→ position distributionI Measure number of e+/e− per detector channel
Upstream polarimeter:
e⁺/e⁻ IP
125 GeV
25 GeV2
4 c
m
inout
LaserIP
Dipole 2 Dipole 3
Dipole 4Dipole 1
total length: ~75 m
250 GeV
[JIN
ST
4(20
09),
1001
5]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 17 / 24
Introduction Physics case Realisation Conclusion
Compton polarimeters (2).Downstream Polarimeter
I located at secondary focusI 6-magnet chicane kicks Compton e± out of synchrotron fan
15 c
m27
.4 c
m
z~46.8m1E
3Ez~55.2m
vacuumchamber
+dz=20m2P 4P
+dz=20m+dz=12m
1G
+dz=10m2G
+dz=10m
Polarimeter Chicane3P
z~175m
SR− limit forCherenkov detector
250 GeV
44 GeV
25 GeV
Cherenkov Det.
Energy Chicane
7Ez~68.8m
10 m
10 c
m
Horizontal BendMagnets z~147.7m, y=15.3cm
Synchrotron Strip Detectorz~147.7m, y=−19.9cm
2mrad energy stripes
z~120.7m1P
z~52.2m z~65.7m
SR−shielding forCherenkov det.
Synchrotron Strip Detector
energycollimator
[JIN
ST
4(20
09),
1001
5]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 18 / 24
Introduction Physics case Realisation Conclusion
Polarimeter detectors.
Simple, robust, fast: Cherenkov detectorsI Cherenkov light emission proportional to number of electronsI independent of electron energy (once relativistic)I successfully used in best polarimeter sofar at SLCI gas or quartz option for Cherenkov medium
Goal: total uncertainty ∆P/P ≈ 0.25 %, of whichI laser: 0.1 %I analysing power (i.e. asymmetry at P = 1 ): 0.2 %I detector linearity: 0.1 %
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 19 / 24
Introduction Physics case Realisation Conclusion
Cross-calibration of Polarimeters.
Polarimeter locations 1650 m before and 150 m after the IP
Spin tracking studies to understand spin transport in-between
Without collisions: cross-calibration of polarimeters
effect on P[10−3]Beam and detector alignment at polarimeters 0.72(∆θbunch = 50 mrad,∆θpol = 25 mrad)Beam parameter variations (10% in emittances) 0.03Bunch rotation to compensate crossing angle < 0.01Longitudinal precession in detector magnets 0.01Emission of synchrotron radiation 0.005random misalignments (10 µm) 0.35Total 0.80
JIN
ST
9(2
014)
P07
003
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 20 / 24
Introduction Physics case Realisation Conclusion
Collision Effects.
zlo
ng. p
olar
izat
ion
P
0.79
0.795
0.8 ]-3
rela
tive
ch
ang
e [1
0
-10
-5
0
UPbefore collisionlumi-weightedafter collisionDP(0.1/0.2/0.5/1.0 mm) -e
w/o collisions
w/o beamstr.
with coll. effects
I beamstrahlung (energy loss, radiative depolarisation):difference downstream measurement vs. 〈P〉IP increases
I energy loss limits refocusing of the beam:laser spot at the polarimeter affects measurement
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 21 / 24
Introduction Physics case Realisation Conclusion
Polarisation Average from Collision Data.
Direct extraction from collision data:any abundant, well-known, polarisation dependent process
〈| Pe± |〉IP =
√(σ−+ + σ+− − σ−− − σ++)(±σ−+ ∓ σ+− + σ−− − σ++)
(σ−+ + σ+− + σ−− + σ++)(±σ−+ ∓ σ+− − σ−− + σ++)
(assumes P+(e−) = −P−(e−) and P+(e+) = −P−(e+) )
Methods studied so farI total cross-sections:
WW at 500 GeV and 1 TeVI single-differential cross-sections:
WW at 500 GeV and 1 TeVI double-differential cross-sections:
WW at 1 TeV1Luminosity fb
0 200 400 600 800 1000 1200
% e
rro
r p
ola
riza
tio
n
0
0.2
0.4
0.6
0.8
1 pol
pol 80% e
+30% e
positron Blondel
electron Blondel
positron Fit
electron Fit
[LC
-DE
T-20
09-0
03]
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 22 / 24
Introduction Physics case Realisation Conclusion
Impact of Polarimeter Precision.
What happens if P+(e−) 6= −P−(e−) and P+(e+) 6= −P−(e+)?I let all P vary independently⇒ δP/P in percent regimeI better: difference to ±δP/P|pol = 0.25% with polarimetersI limits ultimate precision on P(e−)!
Luminosity [fb⁻¹]0 200 400 600 800 10000
1
0.2
0.4
0.6
0.8
error on polarisation [%]
80% e⁻ pol30% e⁺ pol
e⁻ (with polarimeters)e⁺ (with polarimeters)
e⁺ fit (2 parameters)e⁻ fit (2 parameters)
[thes
isI.
Mar
ches
ini2
011]
→ need polarimetry at permille-level and fast helicity reversal
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 23 / 24
Introduction Physics case Realisation Conclusion
Conclusion.
Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 24 / 24
Introduction Physics case Realisation Conclusion
Conclusion.
I Beam polarisation is a key ingredientfor ILC physics studies
I Polarised electron and positron sourcesmore R&D on e+ source necessary, no show-stoppers
I Permille-level polarimetry from acombination of
I up- and downstream polarimetersI spin tracking, collision effectsI scale calibration from e+e− data
I Site for ILC selected,government negotiations ongoing
⇒ Exciting times ahead!
Backup Slides.
Push-Pull concept.
Beam delivery system(Accelerator tunnel)
Access to damping ring
SiD detector(parked)
ILD detector(on beamline)
ILD garage
[ILC
TDR
vol.
1,20
13]
Possible construction schedule.
[ILC
TDR
vol.
1,20
13]
Beam size.
[AFT
2]
44 nm reached in July 2014(different beam energy→ 37 nm at ATF will correspond to < 5 nm at ILC)
Sin Theta.
Connection between ALR and sin2 θeff:
ALR =1〈Peff〉
σL − σR
σL + σR=
2veae
v2e + a2
c
ve
ae= 1− 4 sin2 θeff
Peff =Pe+ + Pe−
1 + Pe+Pe−
With positron polarisation:
ALR =
√(σRR + σRL − σLR − σLL)(−σRR + σRL − σLR + σLL)
(σRR + σRL + σLR + σLL)(−σRR + σRL + σLR − σLL)
0LRA
0.10 0.12 0.14 0.16
92
93
94-95
96
97-98
Average
SLD
resu
lts[h
ep-e
x/05
0900
8]
Electron source parameters.
Parameter Symbol Value UnitsElectrons per bunch (at gun exit) N− 3×1010 NumberElectrons per bunch (at DR injection) N− 2×1010 NumberNumber of bunches nb 1312 NumberBunch repetition rate f b 1.8 MHzBunch train repetition rate f r ep 5 (10) HzFW Bunch length at source ∆ t 1 nsPeak current in bunch at source I avg 3.2 AEnergy stability σE /E <5 % rmsPolarization Pe 80 (min) %Photocathode Quantum Ef ciency QE 0.5 %Drive laser wavelength λ 790±20 (tunable) nmSingle bunch laser energy ub 5 µJ
[ILC
TDR
vol.
3.2,
2013
]
Electron source system.
SC e- LINAC (5.0 GeV)
Damping Ring
L-band (b = 0.75) TW Bunching
and Pre-Acceleration
DC Gun (2x)
DriveLaser
(aboveGround)
Spin Rotation
Faraday Cupand Mott
Polarimeter(13.5W)NC tune-up dump
(11.3 kW)
SC tune-up dump (311 kW)
3.2 nC
140 keV - 76 MeV76 MeV - 5.0 GeV
Energy Collimation(Vertical Chicane)
10 MW8 x 10 MW 10 MW
325
MH
z
325
MH
z
5 nC
Energy Compression
10 MWSPARE
SHB
2 x 5 MW(1 + 1 spare)
[ILC
TDR
vol.
3.2,
2013
]
Positron source parameters.
Parameter Symbol Value UnitsPositrons per bunch at IP nb 2 × 1010 numberBunches per pulse Nb 1312 numberPulse Repetition Rate f r ep 5 HzPositron Energy (DR injection) E 0 5 GeVDR Dynamic Aperture γ(Ax + Ay ) <0.07 m radDR Energy Acceptance ∆ 0.75 %DR Longitudinal Acceptance Al 3.4 x 37.5 cm-MeVElectron Drive Beam Energy† Ee 150/175/250 GeVUndulator Period λ 1.15 cmUndulator Strength‡ K 0.92/0.75/0.45 -Undulator Type - Helical -Undulator Length L u 147 mPhoton Energy (1st harm cutof ) Ec10 10.1/16.2/42.8 MeVPhoton Beam Power Pγ 63.1/54.7/41.7 kWTarget Material - Ti-6%Al-4%V -Target Thickness L t 0.4 / 1.4 r.l. / cmTarget Absorption - 7 %Incident Spot Size on Target σi 1.4/1.2/0.8 mm, rmsPositron Polarisation P 31/30/29 %† For centre-of-mass energy below 300 GeV, the machine operates in 10 Hz mode where
a 5 Hz 150 GeV beam with parameters as shown in the table is a dedicated drive beampositron source.
‡ K is lowered for beam energies above 150 GeV to bring the polarisation back to 30 % with-out adding a photon collimator before the target. [IL
CTD
Rvo
l.3.
2,20
13]
Compton cross-subsection.
(dσ
dy
)Compton
=
(dσ
dy
)unpol
+2πro
x· λP · rx(1− 2r)(2− y)
Compton electron energy [GeV]
0 50 100 150 200 2500
1
2
3
4
Pλ=−1.0
Pλ=+1.0
Pλ= 0.0
[mb]
Compton
(dσ/d
E)
x =4E0ω0
m2 cos2(θ0/2), y = 1− EE0
, r =y
x(1− y),
(dσ
dy
)unpol
=2πro
x
[1
1− y+ 1− y − 4r(1− r)
]
Polarimetry - gas detector concept.
e⁻ beam
Čerenkovphotons
Photomultiplier
LED calibration system
gas-filled Al-channel
beam
aluminum tubes
photodetectors
LED calibration system
[arX
iv:1
011.
6314
]
Beam Energy Spectrum After Collision.
-1 -0.8 -0.6 -0.4 -0.2 0
# of
par
ticle
s
1
10
210
310
410
510
610
710
particle energy [GeV]0 50 100 150 200 250
before collisionafter collision
Downstream Polarimeter: y vs E .
-0.4 -0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
1
10
210
310
410
510
610
particle energy [GeV]160 180 200 220 240ve
rt. p
artic
le p
ositi
on y
[mm
]
-20
-10
0
10
-0.05 -0.04 -0.03 -0.02 -0.01 0
-0.4
-0.2
0
0.2
0.4
-310×
1
10
210
310
410
510
particle energy [GeV]238 240 242 244 246 248 250ve
rt. p
artic
le p
ositi
on y
[mm
]
-0.5
0
0.5
Blondel scheme.
Blondel scheme:
〈| Pe± |〉IP =
√(σ+− + σ−+ − σ−− − σ++)(∓σ−+ ± σ+− + σ−− − σ++)
(σ−+ + σ+− + σ−− + σ++)(∓σ−+ ∓ σ+− − σ−− + σ++)
included assumption:P+(e−) = −P−(e−) and P+(e+) = −P−(e+)
If not: assume | P | equal up to 2ε±
measure ε±with polarimeters.
Correction to modified Blondel scheme.
P+(e±) = P± + ε± and P−(e±) = P± − ε±
Correction to P(e+)
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-0.06
-0.04
-0.02
0
0.02
0.04
0.06
ε-/%
ε+/%
Luminosity Sharing.
How much running time needed for ++ and −−?
I like-sign combinations less interesting for SM phyicsI 10% to 20% like-sign lumi rather close to optimum (50%)I even 2% halfs already total lumi needed for 0.2% precision
1Luminosity fb200 400 600 800 1000
pola
rization
%
err
or
e
0
0.2
0.4
0.6
0.8
1 pol
pol 80% e+60% e
0% ++
2% ++
5% ++
10% ++
20% ++
50% ++ [thes
isI.
Mar
ches
ini2
011]
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