Документ взят из кэша поисковой машины. Адрес оригинального документа : http://zebu.uoregon.edu/~uochep/talks/talks01/SM01_Ecal.pdf Дата изменения: Wed Sep 5 01:51:23 2001 Дата индексирования: Tue Oct 2 11:06:52 2012 Кодировка: ISO8859-5 Поисковые слова: m 80

Precision Energy Measurements for Linear Colliders
Snowmass 2001 July 13th, 2001 Snowmass, Colorado

Eric Torrence University of Oregon

З Spectrometer З Spin Precession З Kinematic
http://www.cern.ch/torrence/talks/SM01_Ecal


LC Energy Needs Weak Mixing Angle
sin
2 eff W

E

beam

[MeV]

E

beam

[ppm]

SLD e- only Blondel

0.00027 0.00005 0.00002

25 ~5 ~2

500 100 40

W Threshold E
beam

< 5 MeV [50 ppm]

Top Mass 40 MeV in 10fb-1 [230 ppm]

Higgs Mass ~ 50 MeV (Direct Reconstruction)


LEP Spectrometer Project
Bend Angle

BPM Triplet

LEP Dipole

BPM Triplet =

АB dl-------------E
Beam

З Use dipole which ramps with LEP З З BPM Triplets measure bend angle

АB

dl from Local NMR and precision Field Map

= 4.8 mRad x

BPM

1Еm

Relative Energy Measurement
З Calibrate Spectrometer using RDP З Ramp immediately to Physics Energy З Direct Measurement of E Beam in ratio E B dl 100 E Beam 100 --------------- = -------------------50 E Beam B dl
50 50 Beam 100

А А

Measure

------------------ +

RDP Few Hours

Time


LSP Magnet Mapping
NMR Probe Hall Probe

Steel Dipole

Marble Bench

1m

Precision Stage Carbon Fiber Arm

Hetrodyne Ruler

Need B dl as f ( B Field (kG) 3 2 1 0

А

Ref

)

NMR Probe Locks

-4

-3

-2

-1

0

1 2 3 Position (meters)
-6

NMR Probe: B / B 10 Hall Probe: B / B 10

over 90% over 10%

-4

Precision of ~ 3 x 10-5 achieved in 1999


SLC WISRD Spectrometer
Spectrometer Magnet Quadrupole Vertical Doublet eHorizontal Bends for Synchrotron Radiation

E

beam

l = -- B dl x



Dump Synchrotron Light Monitor

e+

SLC Parameters at 50 GeV
= 0.3 GeV T-1 m-1



B dl = 3.05 Tesla meters

l = 15 meters x = 27 cm at 50 GeV

Systematic Errors per Beam
B dl : Alignment: 190 ppm Detector - IP: 135 ppm Total: 250 ppm 12.5 MeV at 50 GeV 1998 SLC mZ scan implies a ~ 40 Б 20 MeV offset in ECM



100 ppm


Spectrometer Limits Magnetic Field
З B dl : 100 ppm achieved at SLC З Error is relative: Not affected by increasing З Dominated by absolute scale error s



Relative accuracy of ~ 30 ppm achieved at LEP

Detector Alignment
З Magnet to Detector distance irrelevant: dl / l = 17 ppm З Transverse detector precision dominates: Wire Screen #1 Wire Screen #2

p

d Pitch Error: p = 10 Еm

Relative detector distance: d = 25 Еm 93 ppm at 50 GeV (d=27 cm) 370 ppm at 500 GeV! (assuming single screen) Better detector possible for high energy/small d? Intrinsic Synchrotron stripe width ~1mm at SLC...


Spin Precession Resonant Depolarization
High Precision technique used extensively at LEP ge - 2 Spin Precession Frequency: s = -------------- E 2 2 me c Intrinsic Resolution: E
Beam Beam

200 keV

Linear Collider?

P z = P sin ( s b )

At E

beam

= 0.5 TeV s = 1135

= 5.56 mRad for 1 precession
B dl g-2 ----------- ----------- s b = 2



invariant!

Could use

Pz 1 - s = ----- ---P b

Need / and P / P at < 100 ppm


M?ller Scattering
Silicon Microstrip Detector (SMD) Hydrogen Gas Jet (GJT) Scattered electron 1 LEP beam Recoil Proton Tracker 2 Electromagnetic Calorimeter (ECAL) E1

L

E2

E

beam

8 me 1 = ----------------------------------------- -------------- - m ( tan 1 + tan 2 ) 2 1 - 2

e

tan 1 - tan 2 E1 - E2 = --------------------------------- or = -----------------tan 1 + tan 2 E1 + E2 З Use angles only (need IP position) З Use energy and angles (independent of IP position)

LEP II Study

(LEP II Yellow Report)

l = 30 meters = 2 - 6 mRad angular acceptance E / E = 3.37 / E ( GeV ) 1 / 4 % resolution

E E

stat syst

= 2 MeV in 30 minutes 2 MeV (dominated by Fermi

motion)

Complete study for LC needed... (also Compton)


Radiative Returns f e+e- Е f f Statistics
Channel Ebeam

1 f
Number of Events / 1 GeV

2

sin 1 + sin 2 - sin ( 1 + 2 ) s' -- = -----------------------------------------------------------------------sin 1 + sin 2 + sin ( 1 + 2 ) s

300

Data qq M.C. reweighted M.C. background 183 GeV Data MZ = 91.172 Б 0.098 GeV

L3

qq ЕЕ ee

~ 18 MeV ~ 40 MeV ~ 70 MeV

200

LEP Potential Statistics Only 2.7 fb-1

100

0 70

80

90

100

110

m

inv

[ GeV]
Estimates Ebeam ~ 70 MeV Ebeam ~ 20 MeV Ebeam ~ 80 MeV

Systematics
З Theoretical Description З Hadronization Uncertainties З Detector Understanding Need absolute measurement! Opal qq ЕЕ ee


Other Energy Concerns Need Ebeam at IP З Synchrotron energy loss З Beamstralung З Luminosity-weighted energy

IP Typical values (2 Ebeam - ELum) SLD NLC-90 Tesla-90 GigaZ 40 125 44 ~1 MeV MeV MeV MeV

Low dispersion machine settings needed Lumi-weighted energy spectrum З Needed for energy-sensitive measurements З Best to measure directly from data More difficult than radiative returns?


Conclusions Beam Energy Needs ЗdEbeam < 50 ppm at GigaZ ЗdEbeam ~ 100 ppm at High Energy WISRD spectrometer З Most likely option for general use З Needs detector ideas/R&D M?ller scattering З Only possibility for 50 ppm? З Major project in effort/cost Radiative returns З Intrinsic precision adequate for m W З Measures exactly what is needed З Must be planned in detector from beginning Other methods (SR, Stimulated Emission) З Intriguing possibilities out there З More thought/R&D necessary З Not obviously applicable to High Energy