Searches for Physics Beyond the Standard Model

The MOLLER Experiment at Jefferson Laboratory

Willem T.H. van Oers CSSM – February 15-19, 2010

Information taken from the introductory talk by Krishna Kumar at the JLab Directors Review of the MOLLER experiment on January 14-15, 2010

Outline

• Global Physics Context

• MOLLER Objective and Physics Impact

• Experimental Technique– High Flux Parity Violation Experiments– MOLLER Design Choices– Technical Challenges/Requirements– Statistical and Systematic Errors

Nuclear/Atomic systems address several topics; complement the LHC:• Neutrino mass and mixing decay, 13, decay, long baseline neutrino expts

• Rare or Forbidden Processes EDMs, charged LFV, decay

• Dark Matter Searches

• Low Energy Precision Electroweak Measurements:

Worldwide Experimental Thrust in the 2010s: New Physics Searches

Lower Energy: Q2 << MZ2Large Hadron Collider as well as

• Neutrons: Lifetime, Asymmetries (LANSCE, NIST, SNS...)

• Muons: Lifetime, Michel parameters, g-2 (BNL, PSI, TRIUMF, FNAL, J-PARC...)

• Parity-Violating Electron Scattering Low energy weak neutral current couplings, precision weak mixing angle (SLAC, JLab)

Complementary signatures to augment LHC new physics signals

A comprehensive search for clues requires:Compelling arguments for “New Dynamics” at the TeV Scale

Colliders vs Low Q2

Window of opportunity for weak neutral current measurements at Q2<<MZ2

2

Processes with potential sensitivity:- neutrino-nucleon deep inelastic scattering- atomic parity violation (APV)- parity-violating electron scattering

NuTeV at Fermilab 133Cs at Boulder

Consider known weak neutral current interactions mediated by Z Bosons

E158@SLAC

The Standard Model: Issues• Lots of free parameters (masses, mixing angles, and couplings) How fundamental is that?

• Why 3 generations of leptons and quarks? Asks for an explanation!

• Insufficient CP violation to explain all the matter left over from Big Bang Or we wouldn’t be here.

• Doesn’t include gravity Big omission … gravity determines the structure of our solar

system and galaxy

Starting from a rational universe suggests that the SM is only a low order approximation of reality, as Newtonian gravity is a low order approximation of general relativity.

QED s (QCD)

Measured Charges Depend on Distance(running of the coupling constants)

1/137

1/128

Electromagnetic coupling isstronger close to the bare charge

Strong coupling isweaker close to the bare charge

far close far close

“screening” “anti-screening”

“Running of sin2W” in the Electroweak Standard Model

• Electroweak radiative corrections sin2W varies with Q + +

• All “extracted” values of sin2W must agree with the Standard Model prediction or new physics is indicated.

MOLLER Objective

Ebeam = 11 GeV

APV = 35.6 ppb

δ(APV) = 0.73 ppb

δ(QeW) = ± 2.1 (stat.) ± 1.0 (syst.) %

75 μA 80% polarized

δ(sin2θW) = ± 0.00026 (stat.) ± 0.00012 (syst.) ~ 0.1%

(~ 2.5 yrs)

•Comparable to the two best measurements at colliders•Unmatched by any other project in the foreseeable future•At this level, one-loop effects from “heavy” physics

Compelling opportunity with the Jefferson Lab Energy Upgrade:

not just “another measurement” of sin2W

APV me E lab (1 4 sin2 W )

Derman and Marciano (1978)

(sin2 W )

sin2 W

0.05(APV )

APV

Møller Scattering

Purely leptonic reaction

APV me E lab (1 4sin2 W )

1

E lab

Figure of Merit rises linearly with Elab

(sin2 W )

sin2 W

0.05(APV )

APV

Small, well-understood dilution

SLAC: Highest beam energy with moderate polarized luminosityJLab 11 GeV: Moderate beam energy with LARGE polarized luminosity

Derman and Marciano (1978)

JLab QweakJLab Qweak

Run I + II + III ±0.006

(proposed)-

• Qweak measurement will provide a stringent stand alone constraint on lepto-quark based extensions to the SM.

• Qpweak (semi-leptonic) and E158 (pure leptonic) together make a

powerful program to search for and identify new physics.• MOLLER (pure leptonic) is intended to do considerably better.

SLAC E158SLAC E158

Qpweak & Qe

weak – Complementary Diagnostics for New Physics

Erler, Kurylov, Ramsey-Musolf, PRD 68, 016006 (2003)

Experimental Technique:Technical Improvements over three Decades

Parity-violating electron scattering has become a precision tool

Steady progress in technology towards:

• part per billion systematic control

• 1% systematic control

• major developments in- photocathodes ( I & P )- polarimetry- high power cryotargets- nanometer beam stability- precision beam diagnostics- low noise electronics- radiation hard detectors

• pioneering• recent• next generation• future

11 GeV MOLLER Experimentdouble toroid configuration

MOLLER Hall LayoutLeft HRS

Right HRS

Beam Direction

TargetChamber

FirstToroid

HybridToroid

DriftRegion

contains primary beam & Mollers

DetectorRegion

Mollers exit vacuum

10 ft28 m

meters

met

ers

first toroidhybridtoroid

Asym

met

ry (p

pb)

Center of Mass Angle

Highest figure of merit at θCM

= 90o

Center of Mass Angle

cros

s-se

ction

(mb)

ECOM = 53 MeV

identical particles!

• Avoid superconductors– ~150 kW of photons from target– Collimation extremely challenging

• Quadrupoles a la E158– high field dipole chicane– poor separation from background– ~ 20-30% azimuthal acceptance loss

• Two Warm Toroids– 100% azimuthal acceptance – better separation from background

Odd number of coils: both forward & backward Mollers in same phi-bite

Parity-Violating Electron-Electron Scattering at 11 GeV

• Qeweak would tightly

constrain RPV SUSY (ie tree-level)

One of few ways to constrain RPC SUSY if it happens to conserve CP (hence SUSY EDM = 0).

Direct associated- production of a pair of RPC SUSY particles might not be possible even at LHC.

Theory contours 95% CL Experimental bands 1σ

ΔQeweak

ΔQpweak

(QeW)SUSY/ (Qe

W)SM

Optical Pumping•Optical pumping of a GaAs wafer•Rapid helicity reversal: change sign of longitudinal polarization ~ kHz to minimize drifts (like a lockin amplifier)•Control helicity-correlated beam motion: under sign flip, keep beam stable at the sub-micron level

C.Y. Prescott et. al, 1978

Beam helicity is chosen pseudo-randomly at multiple of 60 Hz• sequence of “window multiplets”

Example: at 240 Hz reversal

Choose 2 pairs pseudo-randomly, force complementary two pairs to follow

Analyze each “macropulse” of 8 windows together

any line noise effect here will cancel here

MOLLER will plan to use ~ 2 kHz reversal; subtleties in details of timing

Noise characteristics have been unimportant in past experiments:Not so for PREX, Qweak and MOLLER....

MOLLER Parameters

•Comparable to the two best measurements at colliders•Unmatched by any other project in the foreseeable future•At this level, one-loop effects from “heavy” physics

Compelling opportunity with the Jefferson Lab Energy Upgrade:

Ebeam = 11 GeV

APV = 35.6 ppb

δ(APV) = 0.73 ppb

δ(QeW) = ± 2.1 (stat.) ± 1.0 (syst.) %

75 μA 80% polarized

δ(sin2θW) = ± 0.00026 (stat.) ± 0.00012 (syst.) ~ 0.1%

~ 38 weeks

(~ 2 yrs)

not just “another measurement” of sin2W

Target: Liquid Hydrogen

parameter value

length 150 cm

thickness 10.7 gm/cm2

X0 17.5%

p,T 35 psia, 20K

power 5000 W

E158 scatteringchamber

• Most thickness for least radiative losses• No nuclear scattering background• Not easy to polarize

•Need as much target thickness as technically feasible•Tradeoff between statistics and systematics•Default: Same geometry as E158

Detector Systems

• Integrating Detectors:– Moller and e-p Electrons:

• radial and azimuthal segmentation

• quartz with air lightguides & PMTs

– pions and muons:

• quartz sandwich behind shielding

– luminosity monitors

neutrals

‘pion’

luminosity

• Other Detectors– Tracking detectors

• 3 planes of GEMs/Straws

• Critical for systematics/calibration/debugging

– Integrating Scanners

• quick checks on stability

Signal & Backgrounds parameter value

cross-section 45.1 μBarn

Rate @ 75 μA 135 GHz

pair stat. width (1 kHz) 82.9 ppm

δ(Araw) ( 6448 hrs) 0.544 ppb

δ(Astat)/A (80% pol.) 2.1%

δ(sin2θW)stat 0.00026

• Elastic e-p scattering– well-understood and testable with data

– 8% dilution, 7.5±0.4% correction

• Inelastic e-p scattering– sub-1% dilution

– large EW coupling, 4.0±0.4% correction

– variation of APV with r and φ

• photons and neutrons– mostly 2-bounce collimation system

– dedicated runs to measure “blinded” response

• pions and muons– real and virtual photo-production and DIS

– prepare for continuous parasitic measurement

– estimate 0.5 ppm asymmetry @ 0.1% dilution

• Statistical Error– 83 ppm 1 kHz pulse-pair width @ 75 μA

– table assumes 80% polarization & no degradation of statistics from other sources

– realistic goal ~ 90 ppm

– potential for recovering running time with higher Pe, higher efficiency, better spectrometer focus....

Backgrounds:

Outlook• Aggressive physics goal

– conservative design choices– reasonable extrapolations on existing/planned third generation

technologies

• Strong, committed collaboration– Experience from previous E158, G0, HAPPEX experiments– Major roles in Qweak and PREX (the best kind of MOLLER R&D!)

• No engineering yet– Spectrometer design is the heart of the apparatus

• launching physics/engineering efforts

• Cost range: 12-16 M$

– Very generous on engineering/design manpower and contingency projections

• Begun process of devising a coherent R&D Plan– Assuming green light from Doe and JLab, launch parallel effort to CD0

process in 2010

• Completed low energy Standard Model tests are consistent with Standard Model “running of sin2W”

SLAC E158 (running verified at ~ 6 level) - leptonicCs APV (running verified at ~ 4 level ) – semi-leptonic, “d-quark

dominated” NuTEV result in agreement with Standard Model after corrections have been applied

• Upcoming QpWeak Experiment

• Precision measurement of the proton’s weak charge in the simplest system.• Sensitive search for new physics with CL of 95% at the ~ 2.3 TeV scale.• Fundamental 10 measurement of the running of sin2W at low energy.• Currently in process of 3 year construction cycle; goal is to have multiple runs in 2010-2012 time frame

• Future 11 GeV Parity-Violating Moller Experiment Qeweak at JLAB

• Conceptual design indicates reduction of E158 error by ~5 may be possible at 11 GeV JLAB. Experiment approved with A rating; JLab Directors review took place in early 2010 with very positive outcome.

weak charge triad (Ramsey-Musolf)

Summary

To Note:

• ECT Workshop, November 8 – 12, 2010 –

“Precision Tests of the Standard Model: from Atomic

Parity Violation to Parity-Violating Electron Scattering”