moller - University of Massachusetts Amherst

118 Pages·2011·10.5 MB·English

The MOLLER Experiment
Measurement Of a Lepton Lepton Electroweak Reaction
An Ultra-precise Measurement of the Weak Mixing Angle
using Møller Scattering
An MIE proposal to
The United States Department of Energy
TheMOLLERCollaboration
September12,2011
The MOLLER Collaboration
J.Benesch,P.Brindza,R.D.Carlini,J-P.Chen,E.Chudakov,S.Covrig,C.W.deJager,A.Deur,D.Gaskell,
J.Gomez,D.W.Higinbotham,J.LeRose,D.Mack,R.Michaels,B.Moffit,S.Nanda,G.R.Smith,P.Solvignon,
R.Suleiman,B.Wojtsekhowski
JeffersonLab
H.Baghdasaryan,G.Cates,D.Crabb,D.Day,M.M.Dalton,C.Hanretty,N.Kalantarians,N.Liyanage,
V.V.Nelyubin,B.Norum,K.Paschke,M.Shabestari,J.Singh,A.Tobias,K.Wang,X.Zheng
UniversityofVirginia
P.Decowski,S.Johnston,K.S.Kumar[Contact∗],J.Mammei,L.Mercado,R.Miskimen,S.Riordan,J.Wexler
UniversityofMassachusetts,Amherst
J.Birchall,M.T.W.Gericke,W.R.Falk,L.Lee,R.Mahurin,S.A.Page,W.T.H.vanOers,V.Tvaskis
UniversityofManitoba
V.Bellini,A.Giusa,F.Mammoliti,G.Russo,M.L.Sperduto,C.M.Sutera
INFNSezionediCataniaandUniversita’diCatania
D.S.Armstrong,T.D.Averett,W.Deconinck,J.Katich,J.P.Leckey
CollegeofWilliam&Mary
K.Grimm,K.Johnston,N.Simicevic,S.Wells
LouisianaTechUniversity
L.ElFassi,R.Gilman,G.Kumbartzki,R.Ransome,
RutgersUniversity
J.Arrington,K.Hafidi,P.E.Reimer,J.Singh
ArgonneNationalLab
P.Cole,D.Dale,T.A.Forest,D.McNulty
IdahoStateUniversity
K.Aulenbacher,S.Baunack,F.Maas,V.Tioukine
JohannesGutenbergUniversitaetMainz
W.Duvall,A.Lee,M.Pitt
VirginiaPolytechnicInstituteandStateUniversity
E.Fuchey,F.Itard,C.Mun˜ozCamacho
LPCClermont,Universite´ BlaisePascal
J.H.Lee,P.M.King,J.Roche
OhioUniversity
E.Cisbani,S.Frullani,F.Garibaldi
INFNGruppoCollegatoSanita’andIstitutoSuperiorediSanita’
R.DeLeo,L.Lagamba,S.Marrone
INFN,SezionediBariandUniversitydiBari
F.Meddi,G.M.Urciuoli
DipartimentodiFisicadell’Universita’laSapienzaandINFNSezionediRoma
R.Holmes,P.Souder
SyracuseUniversity
G.Franklin,B.Quinn
CarnegieMellonUniversity
C.A.Davis,W.D.Ramsay
TRIUMF
J.A.Dunne,D.Dutta
MississippiStateUniversity
A.T.Katramatou,G.G.Petratos
KentStateUniversity
A.Ahmidouch,S.Danagoulian
NorthCarolinaA&TStateUniversity
S.Kowalski,V.Sulkosky
MassachusettsInstituteofTechnology
J.Napolitano,P.Stoler
RensselaerPolytechnicInstitute
O.Glamazdin,R.Pomatsalyuk
NSCKharkovInstituteofPhysicsandTechnology
J.Erler
UniversidadAuto´nomadeMe´xico
M.J.Ramsey-Musolf
UniversityofWisconsin,Madison
Yu.G.Kolomensky
UniversityofCalifornia,Berkeley
K.A.Aniol
CaliforniaStateU.(LosAngeles)
J.W.Martin
UniversityofWinnipeg
E.Korkmaz
UniversityofNorthernBritishColumbia
T.Holmstrom
LongwoodUniversity
S.F.Pate
NewMexicoStateUniversity
G.Ron
HebrewUniversityofJerusalem
D.T.Spayde
HendrixCollege
P.Markowitz
FloridaInternationalUniversity
F.R.Wesselmann
XavierUniversityofLouisiana
C.Hyde
OldDominionUniversity
F.Benmokhtar
ChristopherNewportUniversity
E.Schulte
TempleUniversity
M.Capogni
IstitutoNazionalediMetrologiadelleRadiazioniIonizzantiENEAandINFNGruppoCollegatoSanita’
R.Perrino
INFNSezionediLecce
∗[email protected]
ExecutiveSummary
We present the physics case and experimental design for the MOLLER project, in which we propose
to measure the parity-violating asymmetry A in polarized electron-electron (Møller) scattering. In the
PV
StandardModel,A isduetotheinterferencebetweentheelectromagneticamplitudeandtheweakneutral
PV
currentamplitude,thelatterbeingmediatedbytheZ0 boson. A ispredictedtobe≈ 35partsperbillion
PV
(ppb) at our kinematics. Our goal is to measure A to a precision of 0.73 ppb. The result would yield a
PV
measurement of the weak charge of the electron Qe to a fractional accuracy of 2.3% at an average Q2 of
W
0.0056GeV2.
The measurement is sensitive to the interference of the electromagnetic amplitude with new neutral
current amplitudes as weak as ∼ 10−3 · G from as yet undiscovered high energy dynamics. Such a
F
level of sensitivity is unlikely to be matched by any experiment measuring a flavor- and CP-conserving
process over the next decade, and results in a unique window to new physics at the multi-TeV scale in a
manner complementary to direct searches at high energy colliders. Some examples of physics beyond the
StandardModeltowhichourmeasurementextendssensitivitywellbeyondrecentandongoinglowenergy
measurementsincludenewZ(cid:48) bosons,electroncompositeness,supersymmetryanddoublychargedscalars.
IntheStandardModel,theQe measurementyieldsadeterminationoftheweakmixinganglesin2θ
W W
with an uncertainty of ±0.00026(stat) ± 0.00013(syst), similar to the accuracy of the single best such
determination from high energy colliders. Thus, our result could potentially influence the central value of
this fundamental electroweak parameter, a critical input to deciphering signals of any physics beyond the
StandardModelthatmightbeobservedattheLargeHadronCollider(LHC).
ThemeasurementwouldbecarriedoutinHallAatJeffersonLaboratory,wherea11GeVlongitudinally
polarized electron beam would be incident on a 1.5 m liquid hydrogen target. Møller electrons (beam
electrons scattering off target electrons) in the full range of the azimuth and spanning the polar angular
range5mrad< θ <19mrad,wouldbeseparatedfrombackgroundandbroughttoaringfocus∼ 30m
lab
downstream of the target by a spectrometer system consisting of a pair of toroidal magnet assemblies and
precision collimators. The Møller ring would be intercepted by a system of quartz detectors; the resulting
Cherenkovlightwouldprovidearelativemeasureofthescatteredflux.
Longitudinally polarized electrons are generated via photoemission on a GaAs photocathode by circu-
larly polarized laser light, enabling rapid polarization (helicity) reversal and suppression of spurious sys-
tematic effects. A would be extracted from the fractional difference in the integrated Cherenkov light
PV
response between helicity reversals. Additional systematic suppression to the sub-ppb level would be ac-
complishedbyperiodicallyreversingthesignofthephysicsasymmetrybythreeindependentmethods.
Simultaneouslywithdatacollection, thefluctuationsintheelectronbeamenergyand trajectory andits
potential systematic effects on A would be precisely monitored, active feedback loops would minimize
PV
beam helicity correlations, and detector response to beam fluctuations would be continuously calibrated.
Background fractions and their helicity-correlated asymmetries would be measured by dedicated auxiliary
detectors. TheabsolutevalueofQ2 wouldbecalibratedperiodicallyusingtrackingdetectors. Thelongitu-
dinalelectronbeampolarizationwouldbemeasuredcontinuouslybytwoindependentpolarimetersystems.
Astrongcollaborationwithextensiveexperienceinsimilarexperimentsiscommittedtothedesign,con-
structionanddeploymentoftheapparatusandtodatacollectionandanalysis. Itisenvisionedthatconstruc-
tion and assembly will take three years, to be followed by three data collection periods with progressively
improvedstatisticalerrorsandsystematiccontroloverasubsequentthreetofouryearperiod.
TheMOLLERExperiment p.i
Contents
ListofFigures v
ListofTables viii
1 Introduction 1
1.1 PhysicsContext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 DefinitionsandPrecisionGoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 PhysicsMotivation 3
2.1 NewContactInteractions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1 Supersymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Z(cid:48) Bosons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.3 Doubly-ChargedScalars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 PrecisionElectroweakMeasurementsandsin2θ . . . . . . . . . . . . . . . . . . . . . . . 8
W
3 ExperimentalDesign 10
3.1 PolarizedBeam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 LiquidHydrogenTarget. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3 ToroidalSpectrometer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.3.1 KinematicalConsiderations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3.2 ConceptualDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3.3 HybridCoilDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4 Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4.1 MainIntegratingDetectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.2 AuxiliaryDetectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4.3 TrackingDetectorsandScanner . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.5 ElectronicsandDataAcquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.5.1 RapidHelicityFlip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.5.2 IntegratingElectronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.5.3 OnlineCalibrationsandFeedbacks . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.6 HallAInfrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 SystematicControl 23
4.1 BeamFluctuations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.1.1 Helicity-CorrelatedBeamFluctuations . . . . . . . . . . . . . . . . . . . . . . . . 24
4.1.2 BeamSpotSizeDifferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 LongitudinalBeamPolarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.2.1 ComptonPolarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.2.2 MøllerPolarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.3 TransverseBeamPolarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.4 AbsoluteValueofQ2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.5 Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.5.1 ElasticepScattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.5.2 InelasticepScattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.5.3 HadronsandMuons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.5.4 PhotonsandNeutrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
TheMOLLERExperiment p.ii
5 BeamTimeRequestandRunGoals 31
5.1 TheThreeRuns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.1 RunI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.2 RunII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.3 RunIII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2 SpecialBeamConsiderations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2.1 TransversePolarizationRunning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2.2 WienAngle“Tweaks” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2.3 TheDouble-Wien . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2.4 BeamEnergy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6 Collaboration 34
6.1 Subsystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.2 Governance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7 ResearchandDevelopmentTopics 35
7.1 PolarizedBeam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1.1 PolarizedLaserLight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1.2 BeamlineInstrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1.3 BeamTransport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.2 TargetDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.3 SimulationsandSoftware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.4 SpectrometerDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.4.1 ToroidDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.4.2 CollimationandShielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.5 DetectorDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.5.1 QuartzandLightGuide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.5.2 MechanicalAssembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.5.3 PionBackground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.5.4 TrackingDetectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.6 Polarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.6.1 ComptonPolarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.6.2 MøllerPolarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
8 TheMOLLERProject 41
9 Conclusions 41
A PolarizedBeam 43
A.1 PolarizedElectronSource. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A.2 OperationalExperience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A.3 AdiabaticDamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
A.4 Slowreversals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
A.5 Requirementsfor11GeV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
A.5.1 RapidHelicityFlip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
A.5.2 MeasurementandControlofHCBAs . . . . . . . . . . . . . . . . . . . . . . . . . 47
A.5.3 Beamjitterandmonitorresolution . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.5.4 PositionFeedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
TheMOLLERExperiment p.iii
A.5.5 Beamspot-sizeasymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
A.6 StrategyforcontrolofHCBA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
B DetailedDiscussionoftheHydrogenTarget 54
B.1 ComparableTargets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
B.2 TargetParameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
B.3 DensityVariation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
B.4 CellDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
B.5 Refrigeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
B.6 QweakTargetExperienceandExpectedMOLLERPerformance . . . . . . . . . . . . . . . 60
C ToroidalSpectrometer 64
C.1 HybridToroidConcept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
C.2 DetailedDescriptionofCoilDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
C.2.1 ConductorLayout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
C.2.2 SuggestionsfromtheMagnetAdvisoryCommittee . . . . . . . . . . . . . . . . . . 66
C.2.3 SummaryofCoilSpecifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
C.3 SimulatedPropertiesoftheSpectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
C.3.1 PropertiesoftheIdealizedHybridField . . . . . . . . . . . . . . . . . . . . . . . . 68
C.3.2 PropertiesoftheActualConductorLayout . . . . . . . . . . . . . . . . . . . . . . 69
D IntegratingDetectorConsiderations 74
D.1 Current-ModeSignalMagnitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
D.2 Event-ModeSignalMagnitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
D.3 RadiationHardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
E Electronics 76
E.1 TheTRIUMFElectronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
E.2 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
F ComptonPolarimetry 79
F.1 TheHallAComptonPolarimeterBaselineUpgrade . . . . . . . . . . . . . . . . . . . . . . 79
F.2 UpgradesBeyondtheBaseline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
F.2.1 LaserSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
F.2.2 AlternativeLaserSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
F.2.3 ChicaneMagnetModification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
F.2.4 PhotonDetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
F.3 SystematicUncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
F.3.1 SourcesofCorrelatedError . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
F.3.2 SystematicErrorsfortheElectronDetector . . . . . . . . . . . . . . . . . . . . . . 86
F.4 SystematicErrorsforthePhotonDetector . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
F.5 SummaryofComptonPolarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
G MøllerPolarimetry 91
G.1 MøllerScattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
G.2 WaystoHigherAccuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
G.3 AtomicHydrogenTarget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
G.3.1 HydrogenAtominMagneticField . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
G.3.2 StorageCell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
TheMOLLERExperiment p.iv
G.3.3 GasProperties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
G.3.4 GasLifetimeintheCell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
G.3.5 UnpolarizedContamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
G.3.6 BeamImpactonStorageCell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
G.3.7 BeamRFGeneratedDepolarization . . . . . . . . . . . . . . . . . . . . . . . . . . 96
G.3.8 ContaminationbyFreeElectronsandIons . . . . . . . . . . . . . . . . . . . . . . . 97
G.3.9 ApplicationoftheAtomicTargettoMøllerPolarimetry . . . . . . . . . . . . . . . 97
G.4 MøllerPolarimeterinHallC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
References 102
TheMOLLERExperiment p.v
List of Figures
1 FeynmandiagramsforMøllerscatteringattreelevel(reproducedfromRef.[6]) . . . . . . . 2
2 γ −Z mixingdiagramsandW-loopcontributiontotheanapolemoment(reproducedfrom
Ref.[6]) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Relative shifts in the electron and proton weak charges due to SUSY effects. Dots indicate
therangeofallowedMSSM-loopcorrections. Theinteriorofthetruncatedellipticalregions
give possible shifts due to R-parity violating (RPV) SUSY interactions, where (a) and (b)
correspondtodifferentassumptionsonlimitsderivedfromfirstrowCKMunitarityconstraints. 5
4 90% C.L. exclusion regions for a 1.2 TeV Z(cid:48) (E gauge group) for MOLLER, Qweak and
6
SOLID, assuming they obtain exactly the SM predictions. Also shown is the contour from
theE158result. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5 90% C.L. exclusion regions for a 1.2 TeV Z(cid:48) from the E gauge group for E158, and
6
MOLLER,assumingtheMOLLERcentralvalueishalf-waybetweentheE158centralvalue
andtheSMprediction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6 Summary of 1σ bands from various precision measurements. The red (filled) ellipse is the
90% C.L. contour of all precision electroweak data. The colored regions are excluded by
direct colliders searches. The strongest constraint on the width of the purple (dotted) con-
tour (Q2 (cid:28) M2 measurements) is E158, while its shape and location are influenced by
Z
NuTeV [23, 24] (deep inelastic ν-scattering): large values of M are favored, similar to
H
theA (b)band. Incontrast,theA (had)andM bandsfavorverylowvaluesofM
FB LR W H
which are already ruled out by direct searches. The proposed A measurement would
PV
dominatethefuturewidthandlocationofthedottedcontour. . . . . . . . . . . . . . . . . . 8
7 Current and proposed weak mixing-angle measurements vs. the energy scale µ. The three
futuremeasurementsarelocatedatappropriateµvaluesbuttheverticallocationsarearbi-
trary. NotethatthePDGvalueofν-DIShasbeenadjustedfromthepublishedvalue. . . . . 9
8 Layoutofthetarget,spectrometeranddetectors. . . . . . . . . . . . . . . . . . . . . . . . 10
9 The SLAC E158 target loop is shown; MOLLER proposes to use the same concept. Liquid
flows clock-wise in the picture (downstream to upstream). The liquid-gas interface is just
belowthemotor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10 A CAD drawing of the SLAC E158 target chamber. The target loop is remotely movable
6 in in the vertical direction. A table containing optics targets can be moved in and out
horizontally. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
11 Θ vs E(cid:48) for E = 11 GeV, and E(cid:48) vs θ are depicted by the two plots on the
COM lab beam lab lab
left. On the right is shown the proposed concept for the primary acceptance collimator,
whichisabletoachieve100%acceptancewithjudiciouslychosenφ-sectors. . . . . . . . . 14
12 Projected radial coordinate of scattered Møller electron trajectories. Colors represent
θ (rad). Thespectrometercoils(grey)andcollimators(black)areoverlaid. . . . . . . . . 15
lab
13 Singlehybridcoilwithactualconductorlayout,with1/10scaleinthezdirection. . . . . . 15
14 TransversedistributionofMøller(black)andep(red)electrons28.5mdownstreamoftarget 17
15 RadialdistributionofMøller(black)andep(red)electrons28.5mdownstreamoftarget. . . 17
16 Layout of the main integrating and tracking detectors. Elastically scattered electrons off
targetprotons(blue)andelectrons(green)arealsoshown. . . . . . . . . . . . . . . . . . . 18
TheMOLLERExperiment p.vi
17 Plan cutaway view, along with the main elastic Møller (green) and ep (blue) trajectories.
The quartz detectors are color coded. The main Møller events predominantly hit the red
quartz,whiletheelasticeptrajectorieshittheyellowquartz. Theblueandgreendetectorsin
betweenwillbeimportanttoestimatetheinelasticepbackgroundcorrection;seeSec.4.5.2.
Note the two back-to-back red detectors that will simultaneously measure the flux of the
Møllerpeak. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
18 Aperspectiveviewoftheintegratingdetectorassembly . . . . . . . . . . . . . . . . . . . . 19
19 Proposed radial segmentation of the scattered electron flux, shown both in linear and log
scale. The vertical lines correspond to the radial segmentation of the quartz detectors as
showninFig.17. Theblack,redandgreencurvesareforelectronsfromMøller,elastice-p
andinelastice-pscattering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
20 Band structure of GaAs, showing how circularly polarized laser light produces polarized
electrons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
21 Schematic of the laser transport line that allows for rapid reversal of the electron beam
polarization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
22 Beam position and differences, plotted for all 27×106 pairs of the HAPPEX-II analysis.
Arithmetic means, widths, and centroid uncertainty due to random noise are shown. The
systematiccorrelationtohelicitywasmeasuredtobeconsistentwithzerowithintherandom
beamnoise. Gaussianfitsareincludedforreference. . . . . . . . . . . . . . . . . . . . . . 45
23 Schematicoftheconceptofthe“Double-Wien”filter,whichallowsafull“slow”flipofthe
electron beam polarization with minimal disruption to the front end electron beam optics.
Theflipisaccomplishedbyadjustingthesecondsolenoid, withoutchangingthesettingsof
thetwoWienrotators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
24 Typical position measurement resolutions from the Qweak experiment for 480 Hz window
pairsfor“stripline”beampositionmonitors. Theresidualsfromacomparisonofthemea-
suredbeampositiontotheprojectedpositionfromtwoupstreammonitorsareshown. . . . . 49
25 Typical X and Y position and angle difference distributions for 480 Hz window pairs from
theQweakexperimentat160µAbeamcurrent. TheRMSvaluesfromtheGaussianfitsare
therandombeamnoise(“jitter”)intheseparameters.. . . . . . . . . . . . . . . . . . . . . 50
26 Typical intensity asymmetry and energy difference distributions for 480 Hz window pairs
fromtheQweakexperimentat160µAbeamcurrent. TheRMSvaluesfromtheGaussianfits
aretherandombeamnoise(“jitter”)intheseparameters. . . . . . . . . . . . . . . . . . . 51
27 TargetdensityfluctuationwidthsversushelicityflipfrequencyfromrecentQ beamstudies. 58
weak
28 E158-type target cell design. Note that the fluid flow (left to right) is opposite the electron
beamdirection(righttoleft). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
29 CFDsimulationsofaE158-typecellinnominalconditions. . . . . . . . . . . . . . . . . . . 60
30 Qweak target performance: density fluctuation widths versus beam current from recent
Q measurements. The blue points are measured data. The red curve is a fit to the
weak
data. Thegreencurveisanotherfit,providingameasureoftheuncertainties. . . . . . . . . 61
31 CFDstudyoffilmboilingatthealuminumwindows: windowheatfluxforthreeexperiments
(G0, Qweak and MOLLER). The blue points are the convective part of the heat flux, which
is mainly responsible for the film boiling. The red points are the total heat flux. The first
(red)datapointshowsthethresholdforfilmboiling.. . . . . . . . . . . . . . . . . . . . . . 62
32 Schematicofthehybridtoroiddesignconcept. . . . . . . . . . . . . . . . . . . . . . . . . . 64
33 Layoutofindividualconductorswithintheallowedspaceatlowradius(trapezoidalshapes)
inTOSCAfor0.1819inchODsquareconductor(a). Diagramshowingthelayoutfor0.2294
inch OD square conductor, color-coded and labeled by how they are wound in individual
“double-pancakes”(b). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65