The MOLLER experiment at Jefferson Laboratory is aimed at a precision measurement of the parity-violating asymmetry APV in polarized electron-electron (Møller) scattering.

According to the Standard Model, APV results from the interference between the electromagnetic amplitude and the weak neutral current amplitude, the latter being mediated by the Z0 boson. At the proposed experimental kinematics, 11 GeV incident electron beam and 5mrad < lab < 20mrad, APV

is predicted to be ≈ 35 parts per billion (ppb) at an average Q2 of 0.0056 (GeV/c)2. The goal is to measure APV, and thus the electron's weak charge (Qw

e), to a precision of 0.73 ppb or 2.3%.

Dustin McNultyIdaho State University

Introduction Motivation: Precision Electroweak Tests—sin2W and MHiggs Constraints

Motivation: Search for New Contact Interactions Beyond Standard Model

Experiment Design

Status and Future Plans

Very challenging measurement requiring:

Characterizing new dynamics using 4-electron contact interactions gives corresponding sensitivity/g ~ 7.5 TeV

This underscores importance of low energy measurements of Q

W

e: E158, Qweak, PVDIS, and MOLLER.

World data avg: sin2W = 0.23122(17)

—> mH = 89 GeV

(favors SUSY, rules out Technicolor)

Proposed measurement is sensitive to new neutral current amplitudes as weak as ~10-3 ⋅ GF from as yet undiscovered high energy dynamics—providing indirect access to new physics with multi-TeV scale sensitivity.

Proposed measurement precise enough to effect the central value of sin2W and its implications for mH, as well as test the electroweak theory at the quantum loop level.

Tracking and Integrating Detectors

The MOLLER Project at Jefferson Lab

This significantly extends the reach beyond current best limits—LEP2 probed /g ~ 5 TeV but was insensitive to |g2

RR – g2

LL|.

Near the Z resonance, new physics interactions (e.g. Z 'X

exchange) don't visibly mix with standard model AZ (which is the case for high energy collider experiments).

Avg dominated by two measurements separated by 3:

--Afb0,1: 0.2322(3)—>mH = 480 GeV

The Search for the Higgs

Current and Future sin2W Measurements

Weak mixing angle measurements vs. the energy scale . The three future measurements are located at appropriate values of , but the vertical locations are arbitrary.

(rules out SUSY, favors Technicolor)

(rules out SM!)--A1(SLD): 0.2310(3)—>mH = 35 GeV

Summary of 1 bands from various precision measurements. The red ellipse is the 90% Confidence Level contour of all precision electroweak data. Green regions are excluded by direct collider searches. The strongest constraint on the width of the dotted contour (Q2 << MZ

2) is E158 (QW(e)), while its shape and location are influenced by NuTeV (-DIS). The proposed APV measurement would dominate the future width and location of the dotted contour.

Layout of Target, Spectrometer and Detectors in Hall A

Optimized Spectrometer (~100% Acceptance)

Shadows of 7 Toroid Coils

The combination of a toroidal magnet system with an odd number of coils together with the symmetric, identical particle scattering nature of the Møller process allows for ~100% azimuthal acceptance.

Toroid Magnets

Unpolarized Target:

1.5m liquid hydrogen target capable of handling ~5kW heat load from beam. E158 target cell is basis for design.

Polarized Electron Beam:

11GeV, 85A, ~85 – 90% longitudinally polarized with pseudo-random helicity reversals at ~2kHz.

Spectrometer employs two back-to-back toroid magnets and precision collimation: The upstream toroid has a conventional coil geometry, while the downstream “hybrid” toroid is quite novel—the design was inspired by the need to focus Møller electrons, with a wide range of momenta, at the detector ring, while separating them from the e-p (Mott) scattering bkgd.

~30 m

~3m

Long and Skinny Design

Single Hybrid coil shown with 1/10 scale in z direction. Note the 4 current returns give successively higher downstream fields.

Projected radial coordinate of scattered Møller electron trajectories. Colors represent lab(rad). Magnet coils (grey) and collimators (black) are overlaid.

Perspective view of integrating detector assembly

BeamLuminosity Monitors

Auxiliary “pion” Detectors

Lead Shielding

Main Integrating Quartz Detector Rings (colored);

6 radial x 28 azimuthal

GEM Tracking Detector Arrays

Transverse distribution of Møller (black) and ep (red) electrons 28.5 m downstream of target. Note the phi defocusing of spectrometer optics.

Radial rate distribution of Møller (black), elastic ep (red), and inelastic ep (green) electrons at main detector location.

Cutaway View of Detectors

Møller and ep trajectories beamline

...are collected over here.

The rays that are blocked here...

~150GHz integrated

rate

Evacuated Beampipe

Krishna KumarUniversity of Massachusetts

•Unprecedented precision matching of electron beam characteristics for Left versus Right helicity states.

•Precision non-invasive, redundant continuous beam polarimetry.

•Precision knowledge of luminosity, spectrometer acceptance (Q2) and backgrounds.

Feynman diagrams for Møller scattering at tree level.

– Z mixing diagrams and W-loops. “Hard” radiative corrections involving the massive vector bosons--modify the tree level prediction quite significantly.

GEM

MOLLER received full approval with a strong endorsement from JLab PAC34.

This endeavor represents a 4th generation JLab parity violation experiment with a collaboration consisting of ~100 physicists from 30 institutions.

Currently working with lab management to prepare funding requests (DOE, NSF, and international funding agencies).

Construction/Installation: 2012 - 2015 Commissioning/Running: 2016 -

Approved request of 344 PAC days for production running and 13 commissioning weeks over three running periods.

(on behalf of the MOLLER collaboration)

List of key subsystems and institutions who are interested in their design, construction, and implementation: --Polarized source: UVa, JlLab, Miss St. --Hydrogen Target: Jlab, VaTech, Miss St. --Spectrometer: Canada, ANL, MIT, Umass, UVa --Focal Plane Detectors: Syracuse, Canada, Jlab, UNC A&T, VaTech --Luminosity Monitors: VaTech, Ohio --Pion Detectors: Umass, LATech, UNC A&T --Tracking Detectors: William & Mary, Canada, Umass, UVa, INFN Roma --Electronics: Canada, JLab --Beamline instrumentation: Umass, Jlab, VaTech --Polarimetry: UVa, Syracuse, Jlab, CMU, ANL, Miss St., Clermont- Ferrand, Mainz, William & Mary --Data Acquisition: Ohio, Rutgers --Simulations: Idaho State, UMass/Smith, Berkeley, LATech, UVa