Eric Torrence 1/27 May 2002
Linear Collider Beam Instrumentation Overview
Linear Collider R&D Opportunities Workshop
May 31
st
, 2002SLAC
Eric Torrence*University of Oregon
*with M.Woods and D.Cinabro
• BI Overview
• Beam Energy
• Polarization
• Luminosity
http://physics.uoregon.edu/~torrence/talks/
Eric Torrence 2/27 May 2002
Beam Instrumentation Topics
• Beam Energy Scale and Width• Beam Polarization• Integrated Luminosity and Spectrum
Instrumentation needed for physics...
State of Affairs
• Many conceptual ideas• Few concrete designs or detailed studies• First meeting of new study June 26
th
http://www.slac.stanford.edu/~torrence/ipbi/
Significant Overlap
• Detector/Physics groups• Beam delivery/Final focus activities• Accelerator instrumentation
BI Overview
Eric Torrence 3/27 May 2002
Production Threshold
Kinematic Fits
Common Scale Uncertainty
0
5
10
15
20
160 170 180 190 200 210Ecm [GeV]
σWW
[pb]
LEP Preliminary
RacoonWW / YFSWW 1.16
RacoonWWYFSWW 1.16
16
17
18
2C Kinematic Fit
Hadronic Mass
Invariant Mass (GeV)
WW � qqlν
0
500
1000
1500
2000
2500
3000
3500
40 50 60 70 80 90 100
δMW
MW-------------
δEBeam
EBeam------------------≈
Beam Energy at LEP II
Eric Torrence 4/27 May 2002
Hadronic Final States
Leptonic Final States
Combined
Still statistics limited...
ALR1
Pe------
NL NR–
NL NR+----------------------=
0
100
200
300
400
500
600
SLDe- Le- R
Z0→µ+µ- 97-98
even
ts
cosθ-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
θWeff2
sin 0.23098 0.00026±=
Polarization at SLC
Eric Torrence 5/27 May 2002
Beam Energy Scale
• m
t
from threshold• m
H
from direct reconstruction• m
new
from either
~ 100-200 ppm
Polarization
• SM asymmetries ( , ...)• Background suppression of • SUSY quantum numbers
~ 0.25 - 0.5%
Luminosity Spectrum
• m
t
from threshold• most every physics result! (at some level)
Know ~ 1%
➾
Very challenging in LC environment!
tt
δEb Eb⁄
l+l− qq WW,,WW
δP P⁄
tt
dL dE⁄
Linear Collider Requirements
Eric Torrence 6/27 May 2002
Weak Mixing Angle
where
WW Threshold
~ 6 MeV
➾
< 5 MeV
Also Needed
• Low beamstrahlung (separate IP)• Positron polarization• Theory improvements
➾
Very challenging for BI!
SLD 0.00026 25 MeV 0.50%
e
-
only 0.00005 ~ 5 MeV 0.25%
Blondel 0.00002 ~ 2 MeV 0.25% 0.10%
∆ θ2sin W
eff ∆Ebeam ∆P− P−⁄ ∆Peff Peff⁄
ALR1
Peff-----------
NL NR–
NL NR+----------------------= Peff
P− P++1 P−P++--------------------=
∆mW ∆Eb
GigaZ Requirements
Eric Torrence 7/27 May 2002
Measurement time scales
• Luminosity averaged - months• Operator tuning - minutes• Train-to-train - 10 ms• Bunch-to-bunch - 1 ns
Correlations between L, E, P need to be understood
Measurement Location
• At IP (luminosity weighted) • Near IP in final focus (upstream/downstream)• Elsewhere in machine
Measurement Frequency
• Every pulse - in collision • Sampled (dropouts?) • Dedicated runs
➾ How much time needed for calibration?
Must compare physics needs to operational needs...
General Issues
Eric Torrence 8/27 May 2002
Linear ColliderBeam Energy Measurements(E. Torrence)
Eric Torrence 9/27 May 2002
Energy needs
• 100-200 ppm absolute energy scale• pulse-by-pulse relative measurement?• Detailed width measurement also
Can calibrate at Z-pole ~ yearly?
Potential beam methods
• WISRD-style spectrometer• LEP-style BPM spectrometer• Møller/Bhabha scattering target• ‘Wire’ scanner at high dispersion• Your good idea???
Potential detector methods
• Radiative return ( ) kinematics• Mu-pair momenta?
µ+µ−γ
Energy Overview
Eric Torrence 10/27 May 2002
T m m cm at 50 GeV
Systematic Errors per Beam
: 100 ppm
Alignment: 190 ppmDetector - IP: 135 ppmTotal: 250 ppm ➾ 12.5 MeV at 50 GeV
➾ 1998 SLC mZ scan implies a ~ MeV offset in ECM
NLC Questions
• Stronger bend (and where)?• Better detector technology• Possible downstream (in collision)?• Also measure energy shape?
Horizontal Bends forSynchrotron Radiation
SynchrotronLight Monitor
Dump
e+
e-
QuadrupoleDoublet
SpectrometerMagnetVertical
Ebeam κ lx-- B ld∫⋅ ⋅=
B ld∫ 3.05= l 15= x 27=
∆ B ld∫
40 20±
Meet the WISRD
Eric Torrence 11/27 May 2002
LEPII Spectrometer
• Relies heavily on frequent calibrations• 1 micron stability for less than 8 hours• Operated within tight dynamic range• Beam position and bend held constant
➾ Very low duty factor for LC operations
RF Spectrometer
• Compact 1m RF BPM triplet blocks• Chicane layout for better alignment control• Magnet system more complicated
➾ 100 nm precision required...(assuming 1 mRad bending)
~1 meter
RF BPMTriplets
BPM Spectrometer
Eric Torrence 12/27 May 2002
or
• Use angles only (need IP position)• Use energy and angles (independent of IP position)
LEP II Study [LEP II Yellow Report]
meters mRad angular acceptance
% resolution
in 30 minutes (~600 Hz)
(dominated by Fermi motion)
➾ Complete study for LC needed...
L
Hydrogen Gas Jet (GJT)
Recoil Proton Tracker
Silicon Microstrip Detector (SMD)
Electromagnetic Calorimeter (ECAL)
LEP beam
Scattered electronθ
θ
1
2
E 1
E 2
Ebeam
8me
θ1tan θ2tan+( )2----------------------------------------- 1
1 κ2–-------------- me–=
κθ1tan θ2tan–
θ1tan θ2tan+----------------------------------= κ
E1 E2–
E1 E2+-------------------=
l 30=θ 2 6–=σE E⁄ 3.37 E⁄ GeV( )1 4/=
∆Estat 2MeV=
∆Esyst 2MeV∼
Møller Scattering
Eric Torrence 13/27 May 2002
Statistics
Channel ∆Ebeam
~ 18 MeV
~ 40 MeV
~ 70 MeV
LEP Potential
Statistics Only
2.7 fb-1
Systematics
• Theoretical Description• Hadronization Uncertainties• Detector Understanding
Need absolute measurement!
γf
f
θ1
θ2e+e- � f f γ
s's---
θ1 θ2sin+sin θ1 θ2+( )sin–
θ1 θ2sin+sin θ1 θ2+( )sin+-------------------------------------------------------------------------=
minv [GeV]
Num
ber
of E
vent
s / 1
GeV
L3Data qqM.C. reweightedM.C. background
MZ = 91.172± 0.098 GeV
0
100
200
300
70 80 90 100 110
183 GeV Dataqqγµµγeeγ
Opal Estimates∆Ebeam ~ 70 MeV∆Ebeam ~ 20 MeV∆Ebeam ~ 80 MeV
qqγµµγeeγθ
Radiative Returns at LEP
Eric Torrence 14/27 May 2002
Symmetric production: ,
Need precision and accuracy at small
% per event ( limit)
Collision Energy (mRad)
2 mW 0.522 1000
2 mt 0.875 500
500 GeV 0.937 360
1 TeV 0.984 180
Collision Energy (GeV)
cos
Θ
0.5
0.6
0.7
0.8
0.9
1
200 300 400 500 600 800 1000
γ θ1
θ2e+e- � µµγ
s′ mZ2= Θ1 Θ2=
Θcos Θ
Θ
δΘ 0.1≈ ΓZ
Radiative Returns at NLC
Eric Torrence 15/27 May 2002
Linear ColliderPolarimetry(M. Woods)
Eric Torrence 16/27 May 2002
Polarization Needs
• ~ 0.25 - 0.5%• Each helicity state separately • In vs. out of collision difference?
➾ e+ polarization a big help!
Location and Technology
• Source - Mott scattering• Damping ring - Synchrotron?• DR - IP - Laser Wire?• Interaction point - WW pairs or Blondel (e+)• Post IP - Compton scattering
Other issues
• Significant depolarization during collisions• In-collision measurements desired• Post-IP environment very difficult
δP P⁄
Polarimetry Overview
Eric Torrence 17/27 May 2002
Multiple Detectors
• Çerenkov counter - scattered e- asymmetry• Photon counter - integral γ E asymmetry• Quartz fiber calorimeter - transverse γ asym.
Unique systematics help reduce errors
SLD
MirrorBox
Mirror Box(preserves circularpolarization)
FocusingandSteering Lens
AnalyzingBend Magnet
Laser BeamAnalyzer and Dump Compton
Back Scattered e–
532 nmFrequency DoubledYAG Laser
Pockels CellLeft or Right CircularlyPolarized Photons
“Compton IP”
1-937268A1
e–
e+
e–
CerenkovDetector
ProportionalTube Detector
Compton Polarimetry
Eric Torrence 18/27 May 2002
45° Al coated Stainless Mirrors
Phototubes (Hamamatsu R1398)
Cherenkov Detector
10-927268A6
Window 0.5 cm Al
250 µm Al walls in radiator region. All reflective surfaces coatedwith 1000 Å pure Alwith 1000 Å pure Al
45° Al coated Stainless Mirrors
Phototubes (Hamamatsu R1398)
250 µm Al walls in radiator region. All reflective surfaces coatedwith 1000 Å pure Al
Electron (Beam Pipe)
Proportional Tube Detector
Preradiator7 mm Pb
Pb ShieldingPb Shielding
Çerenkov Detector
Eric Torrence 19/27 May 2002
Improvements
• Better segmentation in Cherenkov counter • Better design to define active volume • Additional e- detectors?
Kinematics at high energy are favorable!
Outstanding Issues
• Extraction line design• Background tolerance• NLC bunch structure/timing
➾ 1-2% depolarization in collision process!
UncertaintySource SLD LC
Analyzing Power 0.40% 0.20%
Detector Linearity 0.20% 0.10%
Laser Polarization 0.10% 0.10%
Electronic Noise 0.20% 0.05%
Total Uncertainty 0.50% 0.25%
IP Corrections 0.15% < 0.05%
δP P⁄ δP P⁄
NLC Polarimetry Goals
Eric Torrence 20/27 May 2002
vs. Efinal
K. ThompsonJanuary 2001
SLAC PUB 8716
vs.
Total Outgoing Bunch ➾
Lumi weighted ~ 25% of bunch average
Lumi Weighted ➾
How well can this be determined???
100 200 300 400 5000
20
40
60
Electron energy [GeV]
Dep
olar
izat
ion
[%]
∆P
TotalS-TBMT
0 5 10 15
0 5 10 15
0
1
2
3
0
1
2
3
∆P ∆y σy⁄
∆P
Depolarization Effects
Eric Torrence 21/27 May 2002
pb at GeV
[K. Mönig, Snowmass 2001]
% for 500 fb-1 at 350 GeV (9/1 L ratio)
➾ Similar with e- only
Z/γW
W
W
Wν
σ 12 7–= s 350 500–=
0.4
0.6
0.8
1
-1 -0.5 0 0.5 1
κγ = 1.007κZ = 1.01SM
cos θ
AL
R
√s = 800 GeV
δP P⁄ 0.1<
Direct Polarization
Eric Torrence 22/27 May 2002
Linear ColliderLuminosity Issues
(D. Cinabro)
Eric Torrence 23/27 May 2002
Luminosity Needs
• Precise knowledge of (~ 1%)• Need to know incoming energy distribution• Want relative lumi monitor pulse-to-pulse?
Beam Instrumentation
• Beamstrahlung monitors • Spot size/bunch length/deflection scans • Pair monitor • Radiative Bhabha • Two photon monitor • ?????
Detector Instrumentation
• Low angle e+e- tagger • Forward tracker (e+e- acolinearity)
dL dE⁄
Luminosity Overview
Eric Torrence 24/27 May 2002
➾
Luminosity spectrum highly dynamic!
350 GeV Machine + ISR + Beamstrahlung + 0.3% Linac
300 310 320 330 340 350 360Collision Energy (GeV)
10-4
10-3
10-2
10-1
1
Assuming Gaussian energy spreadPandora
dn dE⁄
E
Beyond ISR
Eric Torrence 25/27 May 2002
Simple Model (D. Cinabro June 26th)
Flat tail + Gaussian core
= 40 MeV / 1%
= 100 MeV / 1%
Comparable to other systematics
335 340 345 350 3552*Ebeam (GeV)
0.00
0.25
0.50
0.75
1.00σ(
tt) (
pb)
Γ = 1.42 GeV, β = 1)Bare (Peskin+Strassler, m = 174.0 GeV,
+ISR
+Beamstrahlung
+Linac
R Atail Acore⁄=
dmt dR⁄
dΓt dR⁄
Physics Example tt
Eric Torrence 26/27 May 2002
Bhabha rates
• Forward (180-300 mRad) ~ 200 R• Intermediate (300-800 mRad) ~ 100 R• Barrel (> 800 mRad) ~ 8 R
Need rates from forward events, but not too far ...
Tracking Based (silicon)
• Excellent angular resolution %?
• Backgrounds and radiation?
Calorimeter Based (energy balance)
• % at 100 GeV• Need well understood acceptance/uniformity • Need segmentation (backgrounds)
➾ Detailed studies with backgrounds needed
θ0
∆θ
σs
σ∆θEb θ0sin⁄∼
σs
0.1∼
σE E⁄ 1<
Bhabha Acolinearity
Eric Torrence 27/27 May 2002
General Thoughts
• Many conceptual ideas• Need more concrete planning• IPBI meeting June 26th to kick this off
Beam Energy
• Where to put spectrometer device?• Detector requirements for radiative returns• Other clever ideas???
Polarization
• Possible during collisions?• Detailed polarimeter design• Depolarization model
Luminosity
• Very challenging problem• Large overlap with machine side• Impacts detector design• Detailed studies needed now!
BI Wrap-up