Parity-Violating Electron-Electron (Møller) Scattering … · Parity-Violating Electron-Electron (Møller) ... •Change sign of longitudinal polarization ... Precision Measurement

The MOLLER Project at Jefferson Laboratory

Krishna S. KumarUniversity of Massachusetts, Amherst

Parity-Violating Electron-Electron (Møller) Scattering

K. Kumar The MOLLER Project at Jefferson Laboratory

OutlinePhysics Motivation

• Physics Context★ Low Energy Neutral Current Interactions & TeV Physics

★ Parity-Violating Electron Scattering

• Møller Scattering★ The MOLLER Project at Jefferson Laboratory

★ Physics Reach

Experimental Design• Main Components of the Apparatus

• Statistical & Systematic Errors

Status and Outlook

An ultra-precise measurement of the parity-violating asymmetry in fixed target electron-electron (Møller) scattering

2


Physics Context

3


145 150 155 160 165 170 175 180 185 190mt [GeV]

10

20

30

50

100

200

300

500

1000

MH [G

eV]

LEP 2

Tevatron excluded (95% CL)

excluded

all data (90% CL)

(95% CL)

ΓZ, σhad, Rl, Rq

Z pole asymmetriesMWlow energymt

courtesy: Jens Erler

Precision EW PhysicsStart with 3 fundamental inputs needed: αem, GF and MZ

Other experimental observables predicted at 0.1% level: sensitive to heavy particles via higher order quantum corrections

4th and 5th best measured parameters: sin2θW and MW

Allows searches for new physics at the TeV scale via

small measurement deviations

All weak neutral current amplitudes are functions of sin2θW

W

W Z

Zt b t t

Muon decay Z production

4


Colliders AND Low Q2Neutral Current Amplitude at Low & High Energy

Low Q2 Processes with TeV-scale Sensitivity•Parity-violating electron scattering•opposite parity transitions in heavy atoms•Neutrino deep-inelastic scattering

5

One goal of neutral current measurements at low energy AND colliders: Access Λ > 10 TeV for as many f1f2 and L,R combinations as possible

€

Lf1 f2=

4πΛ ij2 ηij

i, j= L ,R∑ f 1iγµ f1i f 2 jγ

µ f2 j

Consider

€

f1 f 1→ f2 f 2

€

f1 f2 → f1 f2orMany new physics models give rise to such terms:

Heavy Z’s, compositeness, extra dimensions, SUSY…

At colliders, one studies Z boson production and decay

At low energies, one studies neutral weak scattering

Both methods have complementary access to new neutral interactions

at the TeV scale


PV Electron Scattering

(gAegV

T +β gV

egAT)

€

10−4 ⋅Q2

€

APV ~ 10−5 ⋅Q2 to gV and gA are function of sin2θW

At very forward angles, APV ∝ gVT, the target vector coupling, called

the weak charge QW

Thumb rule: measure or better to access the multi-TeV scale

!(sin2 "W) ! 0.002

•One of the incident beams longitudinally polarized•Change sign of longitudinal polarization•Measure fractional rate difference

The pioneering experiment was SLAC E122 in the mid-70s: PV Deep-Inelastic Scattering off Liquid Deuterium

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-810 -710

-610

-510 -410

-310

-1010

-910

-810

-710

-610

-510

-410

PVeS Experiment Summary

100%

10%

1%

G0

G0

E122

Mainz-Be

MIT-12C

SAMPLE H-I

A4

A4

H-II

H-He

E158

H-III

PV-DIS

PREX

Qweak

(12GeV)PV-DIS

Moller(12GeV)

PVA

)PV

(A!

Rich Physics

•photocathodes, polarimetry, high power cryotargets, nanometer beam stability, precision beam diagnostics, low noise electronics, radiation hard detectors

•Beyond Standard Model•Strange quark form factors•Neutron skin of a heavy nucleus•QCD structure of the nucleon

• part per billion systematic control• 1% normalization control

Parity-violating electron scattering has become a precision tool

Mainz & MIT-Bates in the mid-80s

JLab program launched in the mid-90s: focus on strange quarks

History of attracting & training excellent students & postdocs7

SLACMIT-Bates

MainzJLab


Fundamental Symmetries & Nuclear Physics

Direct and Indirect Searches for Physics Beyond the Standard Model

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

A comprehensive search for clues requires:

Compelling arguments for “New Dynamics” at the TeV Scale

Neutrino Physics: 0νββ decay, accelerator/reactor experiments

Rare or Forbidden Processes: EDMs, Violation of CP, T, Lepton Flavor

Dark Matter SearchesPrecision Electroweak Measurements

• weak neutral currents at low energy, muon g-2, weak decays

Topics critically need nuclear experimentalists and theorists 8


SLAC E158

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Purely leptonic reaction

LH24-7 mrad

45 & 48 GeV Beam85% longitudinal polarization

Standord Linear Accelerator Center (SLAC) Major technical challenges

Final Result:APV = (-131 ± 14 ± 10) x 10-9

Phys. Rev. Lett. 95 081601 (2005)

16 TeV17 TeV

0.8 TeV 1.0 TeV (Zχ)

0.01•GF

95% C.L.

Limits on “New” Physics

0.001 0.01 0.1 1 10 100 1000µ [GeV]

0.23

0.234

0.238

0.242

0.246

sin

2!

W(µ

)

QW

(APV)Q

W(e)

"-DIS

LEP 1

SLC

Tevatron

e-DIS

MOLLER

Qweak

screening

anti-screening

SM

current

proposedCzarnecki and Marciano (2000)Erler and Ramsey-Musolf (2004)


Fundamental Symmetries and the Long Range Plan

• We recommend a targeted program of experiments to investigate neutrino properties and fundamental symmetries. These experiments aim to discover the nature of the neutrino, yet unseen violations of time-reversal symmetry, and other key ingredients of the new standard model of fundamental interactions. Construction of a Deep Underground Science and Engineering Laboratory is vital to US leadership in core aspects of this initiative

Experimentalists and theorists pursuing neutrino physics, particle EDMs, double-beta decay, weak decays, and parity-violating electron scattering

collaborated to articulate a grand theme: searches for clues to the early universe that are complementary to the highest energy colliders

while making new discoveries about atoms, nuclei & nucleons

The proposed physics program led to the 3rd recommendation:

The combination of physics potential, technical feasibility, new accelerator capabilities, & a seasoned community have conspired to make MOLLER especially compelling at this time

Ideal training ground for the next generation of scientists for future intiatives in Fundamental Symmetries as well as Hadron Physics

The MOLLER and SOLID experiments are part of the broad initiative above:

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Specific LRP Excerpts

These recommendations were the result of:•Endorsement of the physics goals by the larger NP community•Technical success and physics impact of recent parity-violation experiments

The SLAC E158 result was highlighted as one of the 4 major results from the previous seven years in the area of Fundamental Symmetries

E158 made the first measurement of parity-violation in Møller scattering:We propose to improve the result by a factor of 5 with the 11 GeV JLab beam

Page87What are the unseen forces

that were present at the dawn of the universe but

disappeared from view as the universe evolved?

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MOLLER Physics Reach

Measurement of Lepton-Lepton Electroweak Reaction

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MOLLER Goal

APV = 35.6 ppb δ(APV) = 0.73 ppb δ(QeW) = ± 2.1 (stat.) ± 1.0 (syst.) %

75 μA

δ(sin2θW) = ± 0.00026 (stat.) ± 0.00012 (syst.)

48 weeks

€

δ(sin2ϑW )sin2ϑW

≅ 0.05δ(APV )APV

LH25-17 mrad

11 GeV Beam80% longitudinal polarization

APV !meElabQeW ! (1" 4 sin2 !W)

Precision Measurement of the Electron Weak Charge using Electron-Electron (Møller) Scattering

!!|g2

RR ! g2LL|

= 7.5 TeVLe1e2 =!

i,j=L,R

g2ij

2!2ei!µeiej!

µej

best contact interaction reach for leptons at low OR high energy

To do better for a 4-lepton contact interaction would require: Z factory, linear collider, neutrino factory or muon collider

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MOLLER Goal

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0.001 0.01 0.1 1 10 100 1000µ [GeV]

0.23

0.234

0.238

0.242

0.246

sin

2!

W(µ

)

QW

(APV)Q

W(e)

"-DIS

LEP 1

SLC

Tevatron

e-DIS

MOLLER

Qweak

screening

anti-screening

SM

current

proposed


New Physics Example

Does Supersymmetry provide a candidate for dark matter?•B and/or L need not be conserved (RPV): neutralino decay•neutralino then unlikely to be a dark matter candidate•neutrinos are Majorana

MSSM sensitivity if light super-partners, large tanβ

PR = (!1)3(B!L)+2s

RPV SUSY

MSSM

MOLLER

Ramsey-Musolf and Su, Phys. Rep. 456 (2008)

SUSY Sensitivity

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Qw

eak

Such probes become even more important if LHC sees an anomaly consistent with SUSY


Experimental Design

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MOLLER Apparatus28 m

DetectorAssembly

Target

Chamber

Hybrid

First

Toroid

Toroid

“Pots” for insertabletracking detectors

Polarized Beam• Unprecedented polarized luminosity

• unprecedented beam stability

Liquid Hydrogen Target• 5 kW dissipated power (2 X Qweak)

• computational fluid dynamics

Toroidal Spectrometer• Novel 7 “hybrid coil” design

• warm magnets, aggressive cooling

Integrating Detectors• build on Qweak and PREX

• intricate support & shielding

• radiation hardness and low noisecompact structure: plan to make

apparatus and sheilding easily removable17


Statistics & Systematicsparameter MOLLER E158 Qweak

Rate 135 GHz 3 GHz 6 GHz

pair stat. width 82.9 ppm 200 ppm 400 ppm

δ(Araw) 0.544 ppb 11 ppb 4 ppb

δ(Astat)/A 2.1% 10% 3%

δ(sin2θW)stat 0.00026 0.001 0.0007

• 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±0.4% correction– variation of APV with r and φ

Irreducible Backgrounds:source of error % errorabsolute value of Q2 0.5beam second order 0.4

longitudinal beam polarization 0.4inelastic e-p scattering 0.4elastic e-p scattering 0.3

beam first order 0.3pions and muons 0.3

transverse polarization 0.2photons and neutrons 0.1

Total 1.018

Accuracy goals are factors of 2 to 10 beyond those of

E158 & Qweak


Technical Challenges• ~ 150 GHz scattered electron rate

– Design to flip Pockels cell ~ 2 kHz– 80 ppm pulse-to-pulse statistical fluctuations

• Electronic noise and density fluctuations < 10-5

• Pulse-to-pulse beam jitter ~ 10s of microns at 1 kHz• Pulse-to-pulse beam monitoring resolution ~ 10 ppm and few microns at 1 kHz

• 1 nm control of beam centroid on target– Modest improvementin polarized source laser controls– Improved methods of “slow helicity reversal”

• > 10 gm/cm2 target needed– 1.5 m Liquid Hydrogen target: ~ 5 kW @ 85 μA

• Full Azimuthal acceptance with θlab ~ 5 mrad– novel two-toroid spectrometer– radiation hard, highly segmented integrating detectors

• Robust and Redundant 0.4% beam polarimetry– Plan to pursue both Compton and Atomic Hydrogen techniques

•Currently, design and R&D being done with students and postdocs part-time•One dedicated postdoc focused on spectrometer (thanks!)•Engineering advice is “pro-bono” right now

Collaboration is preparing a

prioritized R&D plan, but the

spectrometer is at the top of the list

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K. Kumar The MOLLER Project at Jefferson Laboratory!"""#$%

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Spectrometer Concept

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K. Kumar The MOLLER Project at Jefferson Laboratoryr (m)

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Spectrometer Concept

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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• beam & target density fluctuationsneutrals

‘pion’

luminosity

• Auxiliary Detectors– Tracking detectors

• 3 planes of GEMs/Straws• Critical for systematics/

calibration/debugging

– Integrating Scanners• quick checks on stability

Moller Peak Detectors

ee’s

ep’s

CAD design in progress

optimized for robust background subtraction

Collaboration physicists will continue to define and optimize

the full suite of detectors 21


Status and Outlook

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– Polarimetry

– Electronics/DAQ

– Simulations

G. CatesM. Pitt

K. Kumar

M. Gericke and D. MackD. Armstrong

K. PaschkeR. Michaels

D. McNulty

• Steering Committee:– D.Armstrong, R.Carlini, G.Cates, K.de Jager, Y.Kolomensky, K.Kumar (chair),

F.Maas, D.Mack, K.Paschke, M.Pitt, G.Smith, P.Souder, W.van Oers, J. Gomez

• Working Groups & Conveners– Polarized Source– Beam & Beam Instrumentation– Target– Spectrometer– Integrating Detectors– Tracking Detectors

J-P Chen & G. Smith

Recent Evolution•Project received PAC approval: Jan ’09•Director’s review of physics goals and concept: Jan ’10•Collaboration planning targets installation late 2015•Ranking and beamtime in PAC37: Jan ’11 (3 run periods requested)

sub-system Institutionspolarized source UVa, JLab, Miss. St.

Target JLab, VPI, Miss. St.

Spectrometer Canada, ANL, MIT, UVa

Integrating Detectors

Syracuse, Canada, JLab, FIU, UNC A&T, VPI

Luminosity Monitors VPI, Ohio U.

Pion Detectors UMass/Smith, LATech

Tracking Detectors William & Mary, Canada, INFN Roma

Electronics Canada, JLab

Beam Monitoring VPI, UMass, JLab

Polarimetry UVa, Syracuse, JLab, CMU, ANL, Miss. St., Claremont-Ferrand, Mainz

Data Acquisition Ohio U., Rutgers U.

Simulations LATech, UMass/Smith, Berkeley, UVa(Canada: UBC, Manitoba, Winnipeg, TRIUMF)

expression of interest:not yet formalized

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~ 100 Physicists~ 30 institutions


– Polarimetry

– Electronics/DAQ

– Simulations

G. CatesM. Pitt

K. Kumar

M. Gericke and D. MackD. Armstrong

K. PaschkeR. Michaels

D. McNulty

• Steering Committee:– D.Armstrong, R.Carlini, G.Cates, K.de Jager, Y.Kolomensky, K.Kumar (chair),

F.Maas, D.Mack, K.Paschke, M.Pitt, G.Smith, P.Souder, W.van Oers, J. Gomez

• Working Groups & Conveners– Polarized Source– Beam & Beam Instrumentation– Target– Spectrometer– Integrating Detectors– Tracking Detectors

J-P Chen & G. Smith

Recent Evolution•Project received PAC approval: Jan ’09•Director’s review of physics goals and concept: Jan ’10•Collaboration planning targets installation late 2015•Ranking and beamtime in PAC37: Jan ’11 (3 run periods requested)

sub-system Institutionspolarized source UVa, JLab, Miss. St.

Target JLab, VPI, Miss. St.

Spectrometer Canada, ANL, MIT, UVa

Integrating Detectors

Syracuse, Canada, JLab, FIU, UNC A&T, VPI

Luminosity Monitors VPI, Ohio U.

Pion Detectors UMass/Smith, LATech

Tracking Detectors William & Mary, Canada, INFN Roma

Electronics Canada, JLab

Beam Monitoring VPI, UMass, JLab

Polarimetry UVa, Syracuse, JLab, CMU, ANL, Miss. St., Claremont-Ferrand, Mainz

Data Acquisition Ohio U., Rutgers U.

Simulations LATech, UMass/Smith, Berkeley, UVa(Canada: UBC, Manitoba, Winnipeg, TRIUMF)

expression of interest:not yet formalized

Two categories of design and R&D

National lab driven: target, spectrometer, beam instrumentationUser driven: source control, detectors, polarimetry

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~ 100 Physicists~ 30 institutions


Director’s Review

• Primary Recommendation:– “The Review Committee unanimously recommends that the Director

undertake planning for MOLLER now, to be ready for the 12 GeV Upgrade era.”

• Physics Motivation:– “MOLLER, by exploiting the best qualities of the JLab beam, brings

new information to bear on, and to constrain interpretations of, any new physics that may result at the LHC and elsewhere.”

• Technical Feasibility:– “The Committee could find no technical reasons the goals of MOLLER

could not be reached.”

Doug Beck (Illinois), Dave Hertzog (Illinois), Bob Kephart (Fermilab), Bill Marciano (BNL), Matt Poelker (JLab), Charles Prescott (SLAC, Chair), Michael Schmitt (Northwestern), Glenn Young (JLab), John Weisend (SLAC)

Jan 14-15, 2010: 1.5 days of talks, Homework, Q&A

24


Director’s Review

• Primary Recommendation:– “The Review Committee unanimously recommends that the Director

undertake planning for MOLLER now, to be ready for the 12 GeV Upgrade era.”

• Physics Motivation:– “MOLLER, by exploiting the best qualities of the JLab beam, brings

new information to bear on, and to constrain interpretations of, any new physics that may result at the LHC and elsewhere.”

• Technical Feasibility:– “The Committee could find no technical reasons the goals of MOLLER

could not be reached.”

Doug Beck (Illinois), Dave Hertzog (Illinois), Bob Kephart (Fermilab), Bill Marciano (BNL), Matt Poelker (JLab), Charles Prescott (SLAC, Chair), Michael Schmitt (Northwestern), Glenn Young (JLab), John Weisend (SLAC)

Jan 14-15, 2010: 1.5 days of talks, Homework, Q&A

A number of detailed recommendations:

First and foremost, bring engineering to bear on the spectrometer design NOW

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Spectrometer Engineering• Magnet Advisory Committee formed

– George Clark (TRIUMF), Ernie Ihloff (MIT-Bates), Vladimir Kashikhin (Fermilab), Jim Kelsey (MIT-Bates), Dieter Walz (SLAC) & Robin Wines (JLab)

We face the usual “chicken and egg” story: No funding yet, but need engineering before we fine-tune optics, define footprint, estimate cost and risk

Optics Optimization and Engineering Feasibility

Proposal field map achieved with buildable coil configuration

One dedicated postdoc under my supervision with occasional free engineering advice

The hybrid toroid is the heart of the apparatus

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Spectrometer Engineering• Magnet Advisory Committee formed

– George Clark (TRIUMF), Ernie Ihloff (MIT-Bates), Vladimir Kashikhin (Fermilab), Jim Kelsey (MIT-Bates), Dieter Walz (SLAC) & Robin Wines (JLab)

We face the usual “chicken and egg” story: No funding yet, but need engineering before we fine-tune optics, define footprint, estimate cost and risk

Optics Optimization and Engineering Feasibility

Proposal field map achieved with buildable coil configuration

One dedicated postdoc under my supervision with occasional free engineering advice

The hybrid toroid is the heart of the apparatus

Could use real engineering effort by Summer 2011

25


MOLLER Project

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A small volume apparatus• heavy on engineering design• careful attention must be paid to tolerances• conventional technologies pushed to limits

★ build on previous experience wherever possible

Cost and scheduling exercise begun• aim for a 3 year construction project• availability of technical manpower an issue

A zeroth-order subsystem cost estimate• Currently being checked for completeness• escalated (AY ‘13-’15) ~ 15M$ + contingency


Summary and Outlook• Projected Result from an APV measurement in Møller Scattering

• Opportunity with high visibility and large potential payoff– The weak mixing angle is a fundamental parameter of EW physics– A cost-effective project has been elusive until now

• expensive ideas reach perhaps 0.2% (reactor or accelerator ν’s, LHC Z production...)• sub-0.1% requires a new machine (e.g. Z- or ν-factory, linear collider....)

– physics impact on nuclear physics, particle physics and cosmology• pin down parameter for other precision low energy measurements• decipher potential LHC anomalies at the TeV scale• shed light on feasibility of SUSY dark matter via search for R-Parity violation

• NSAC Long Range Plan strongly endorsed the physics– part of fundamental symmetries initiative to tune of 25M$– beginning to attract foreign participation

• 11 GeV JLab beam is a unique instrument that makes this feasible• A motivated collaboration with plenty of experience• Sustains/expands/trains community: feed future nuclear physics needs

δ(sin2θW) = ± 0.00026 (stat.) ± 0.00012 (syst.)

APV = 35.6 ppb δ(APV) = 0.73 ppb δ(QeW) = ± 2.1 (stat.) ± 1.0 (syst.) %

~ 0.1%

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Documents

Parity-Violating Electron-Electron (Møller) Scattering … · Parity-Violating Electron-Electron (Møller) ... •Change sign of longitudinal polarization ... Precision Measurement