beyond the standard model - uvacollab : gateway : … · •higher twist effects ... october 8 2008...

October 8 2008 Beyond the Standard Model: Parity-Violating Electron Scattering 1

Beyond the Standard Model:Precision Low Energy Weak Neutral Current Measurements

Krishna KumarUniversity of Massachusetts, Amherst

Acknowledgement:E. Chudakov, A. Deshpande, W. Marciano, K. Paschke, F. Petriello, M.J. Ramsey-Musolf, P. Souder

October 8, 2008

SPIN 2008Charlottesville, VA


Outline• Beyond the Standard Model at Low Energy• Weak Neutral Current Interactions• Parity-Violating Electron Scattering

– Past Results– Experiments in Preparation at Jefferson Laboratory– The Potential of the 12 GeV Upgrade– The Frontier: High Luminosity at an EIC

The Standard Model of Strong, Weak and Electromagnetic Interactions is an Effective Theory that describes precision experiments at and below the scale of the massive vector bosons extraordinarily well. Very reasonable and compelling theoretical arguments point to “new physics” at the 1 to 10 TeV scale, which will be directly explored at the Large Hadron Collider in the near future.

October 8 2008 Beyond the Standard Model: Parity-Violating Electron Scattering

Beyond the Standard Model

3

Low Energy: Q2 << MZ2High Energy Colliders as well as

Low Q2 offers complementary probes of new physics at multi-TeV scales:

• Neutrons: Lifetime, P- & T-Violating Asymmetries (LANSCE, NIST, SNS...)

• Muons: Lifetime, Michel parameters, g-2, Mu2e (PSI, TRIUMF, FNAL, J-PARC...)

• Parity-Violating Electron Scattering Low energy weak neutral current couplings, precision weak mixing angle (SLAC, Jefferson Lab, MIT-Bates, Mainz)

Low Energy Precision Electroweak Physics

• Neutrino mass and their role in the early universe 0νββ decay, θ13, β decay,…

• Matter-antimatter asymmetry in the present universe EDM, DM, LFV, 0νββ, θ13

• Unseen Forces of the Early Universe Weak decays, Parity-Violating Electron Scattering, gµ-2,…

LHC new physics signals likely will need additional indirect evidence

of Electroweak Interactions


Comprehensive Search for New Neutral Current Interactions

Many new physics models give rise to neutral ‘contact’ (4-Fermi) interactions: Heavy Z’s, compositeness, extra dimensions…

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

Important component of indirect signatures of “new physics”

LEPII, Tevatron access scales Λ’s ~ 10 TeVe.g. Tevatron dilepton spectra, fermion pair production at LEPII

- L,R combinations accessed are parity-conservingLEPI, SLC, LEPII & HERA accessed some parity-violating combinations but precision dominated by Z resonance measurements

€

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 f2orΛ’s for all f1f2 combinations and L,R combinations

Eichten, Lane and Peskin, PRL50 (1983)


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

Focus of this talk

Consider known weak neutral current interactions mediated by Z Bosons


Specific choices of kinematics and target nuclei probes different physics:

• In mid 70s, goal was to show sin2θW was the same as in neutrino scattering• Early 90s: target couplings carry novel information about hadronic structure• Now: precision measurements with carefully chosen kinematics can probe physics at the multi-TeV scale

(gAegV

T +β gV

egAT)

Parity-Violating (PV) AsymmetriesWeak Neutral Current (WNC) Interactions at Q2 << MZ

2

Longitudinally Polarized Electron Scattering off Unpolarized Fixed Targets

€

10−4 ⋅Q2

€

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

October 8 2008 Beyond the Standard Model: Parity-Violating Electron Scattering7

Experimental Technique

•Optical pumping of a GaAs wafer•Rapid helicity reversal: change sign of longitudinal polarization ~ 100 Hz to minimize drifts (like a lockin amplifier)•Control helicity-correlated beam motion: under sign flip, keep beam stable at the micron level

“Flux Integration”:Allows counting at high rates

Spectrometer directs flux to background-free region

APV in Deep Inelastic Scattering off liquid Deuterium: Q2 ~ 1 (GeV)2C.Y. Prescott et. al, 1978

APV ≈ 100 ± 10 ppm

In the mid-70s, Stanford Linear Accelerator Center produced the first suitable polarized electrons at a beam energy of ~ 20 GeV


Today: MeV to TeV Physics

• Steady progress in technology• part per billion systematic control• 1% normalization control• Intensive R&D on:

-Photocathodes-Polarimetry-High Luminosity cryotargets-Nanometer beam stability-Precision Beam Diagnostics-Counting Electronics-Radiation hard detectors

Four electron scattering laboratories: SLAC, MIT-Bates, Mainz & JLab

Parity-violating electron scattering has become a precision tool

•Many-body nuclear physics: Neutron skin of 208Pb•Nucleon structure: strangeness contribution to form factors•Valence quark structure: Deep inelastic scattering at high-x•Search for new TeV physics: Precision electroweak parameters

Physics over a range of energy scales: talk by Paul Kingyesterday afternoon


PV Møller Scattering

9

Purely leptonic reaction

€

APV ∝meElab (1− 4sin2ϑW )

€

δ(sin2ϑW )sin2ϑW

≅ 0.05δ(APV )APV

APV = (-131 ± 14 ± 10) x 10-9

PRL

50 GeV at SLAC: ~ 150 ppb!

Phys. Rev. Lett. 95 081601 (2005)

SLAC End Station Aspectrometerquadrupoles

target chamber

detector cart


SLAC E158 Implications

16 TeV17 TeV

0.8 TeV 1.0 TeV (Zχ)

0.01•GF

95% C.L.

Running of sin2θW established to 6σ

T

6σ•Czarnecki and Marciano •Erler and Ramsey-Musolf•Sirlin et. al.•Zykonov

Limits on “New” Physics


Lepton-Quark WNC Couplings•Atomic Parity Violation (APV)

•133Cs 6s to 7s transition•Future: isotope measurements

•Neutrino DIS: NuTeV•3 σ deviation•Many hadronic physics issues•Look at other l-q couplings?

A

V

V

A

€

δ(C1q )∝ (+ηRLeq +ηRR

eq −ηLLeq −ηLR

eq )

€

δ(C2q )∝ (−ηRLeq +ηRR

eq −ηLLeq +ηLR

eq )

APV in elastic e-p scattering:

€

Qweakp = 2C1u + C1d

€

∝1− 4sin2ϑW

Qweak at Jefferson Laboratory

•Design & Construction ongoing•Installation: late 2009•Data ~ 2010 thru mid-2012

PV elastic e-p scattering, APV

PV deep inelastic scattering

Contains GγE,M and GZE,M,Extracted using global fit of existing PVES experiments!

86 scientists from 25 institutions


Qweak

12

Isovector weak charge Is

osca

lar w

eak

char

ge

E = 1.165 GeV, θlab ~ 9o, Q2 = 0.026 GeV2

New, complementary constraints on lepton-quark interactions at the TeV scale

Talk by M. Gericke tomorrow

Young et. al


PV Deep-Inelastic Scattering (DIS)

€

APV =GFQ

2

2παa(x) + f (y)b(x)[ ]

For a 2H target, assuming charge symmetry, structure functions largely cancel in the ratio:

€

a(x) =310

(2C1u −C1d )[ ] +L

€

b(x) =310

(2C2u −C2d )uv (x) + dv (x)u(x) + d(x)

+L Q2 >> 1 GeV2 , W2 >> 4 GeV2

APV in Electron-Nucleon DIS:e-

N X

e-

Z* γ*

Must measure APV sub-1% fractional accuracy!

Feasible at 6 GeV at Jlabwell-suited for higher precision 11 GeV after the upgrade

luminosity > 1038/cm2/s

Need intermediate beam energies at moderately large scattering angle

With Qweak and APV, C1i’s measured, but C2i’s still unconstrained

•First experiment at 6 GeV, to run in Fall ’09•Approved Hall C proposal at 11 GeV using upgraded spectrometers•New large acceptance spectrometer proposal being developed


PVDIS w/ Base Equipment

14

Prescott et al(SLAC)

PDG Best Fit

Young Full Fit

Sample

6GeVPVDIS3%Admeasurement:Bandscorrespondtocentralvaluesof

eitherPDGbestfitorYoungetal.’sbestfit.

StandardModel

SHMS

HMS

Proposal approved for 11 GeV:Factor of ~ 2 to 3 improvement

E08-011: PVDIS off 2H at 6 GeV

Robust sensitivity to TeV scale physics will require detailed understanding of nucleon structure at high-x:

•d/u ratio at high-x•charge symmetry violation•higher twist effects•quark axial-current structure

Talk by R. Subedi this afternoon

(Similar to NuTeV anomaly concerns)


Dedicated Spectrometer

15

11GeV(solenoid)

8 GeV (solenoid)

11 GeV (Hall C)

Deuterium target

•Simulation and design development begun•Proposal targeted for Jan 2009 to JLab PAC

• High Luminosity on Liquid 1H & 2H• Better than 1% error• x-range 0.25-0.75• W2 well over 4 GeV2

• Q2 range a factor of 2 for each x bin• Moderate running times

Talk by Kent Paschke this afternoon

Talk by K. Paschke this afternoon

3 meter


Precision sin2θW at Any Scale

⇒ mH = 89 +38-28 GeV

ALR AFB (Z→ bb)

sin2θw = 0.2310(3)

↓mH = 35 +26-17 GeV

sin2θw = 0.2322(3)

↓mH = 480 +350-230 GeV

Rules out the SM! Rules out SUSY!

The Average: sin2θw = 0.23122(17)

3σ apart

•Precision sin2θW at colliders and neutrino facilities very challenging•Would like a third measurement of comparable precision!•No resolution of this issue in next decade in HEP facilities

Fundamental inputs to Electroweak theory are αem, GF and MZSo far, to search for TeV scale physics, sin2θW is a book-keeping parameter

Ultraprecise (0.1%) measurements of “derived” parameters (sin2θW and MW) are the most sensitive consistency checks of the EW theory


Møller Scattering at 11 GeVParity-Violating Møller Scattering: Luminosity and Stability at Jlab upgrade makes feasible a factor of 5 improvement over E158

sin2θW to ± 0.00025Λee ~ 25 TeV reach

Best new measurement until Linear Collider or Neutrino Factory

E158-like Quad concept: same quads provide focus; fits within 25 m

Design work in progress for the submission of a proposal in Jan 2009

δ(Aexp) = 0.6 ppb!

Rate ~ 200 GHz!

Mother of all PV measurements!

Toroidal spectrometer concept with similar acceptance being investigated


Complementarity of Low Q2Does Supersymmetry provide a candidate for dark matter?•B and L need not be conserved (RPV): neutralino decay

Kurylov, Ramsey-Musolf, Su RPC SUSY

RPV SUSY 12 GeV

Møller

PVDIS

Advertisement:2008 INT Program: Sept 22 - Dec 5, 2008

Low Energy Precision Electroweak Physics in the LHC EraV. Cirigliano, J. Erler, K. Kumar, M. Ramsey-Musolf

Suppose a 1 to 2 TeV heavy Z’ is discovered at the LHC•What are its vector- and axial-vector coupling?

F. PetrielloPV Moller

PV Moller LHC AFB


General EW Hadronic Tensor

19

QPM Interpretation

e-

N X

e-

Z γ*

Anselmino, Gambino and Kalinoski, hep-ph/9401264v2Anselmino, Efremov & Leader, Phys. Rep. 261 (1995)

A! =f(y)g!

1

F !1

APV =GF Q2

2!

2!"

!gA

F !Z1

F !1

+ gVf(y)

2F !Z

3

F !1

"

ATPV =GF Q2

2!

2!"

!gV

g!Z5

F !1

+ gAf(y)g!Z1

F !1

"


New Structure Functions

20

•Jefferson Lab 12 GeV can begin exploration•A high luminosity EIC (~ 1034 /cm2/s) is a new opportunity

★Enough y range to separate vector and axial-vector couplings★Could go down in x as low as 0.01 ★electroweak g1 is complementary to electromagnetic g1: weights of up, down and strange quark helicity distributions differently: could eliminate the need for input from Hyperon decays for extracting strange quark helicity distributions! ★effective polarization error might be significantly reduced: peculiarity of measuring parity-violating asymmetries between relativistic particles★All three asymmetries could be measured simultaneously

€

APV =GFQ

2

2παa(x) + f (y)b(x)[ ]

€

a(x) =

C1iQi fi(x)i∑

Qi2 f i(x)

i∑

€

b(x) =

C2iQi fi(x)i∑

Qi2 f i(x)

i∑

QED Double-spin Asymmetry polarized electron, unpolarized hadron

unpolarized electron, polarized hadrongV and gA are the electron vector- and axial-vector couplings


The “Take-Away” Message• Precision low energy weak neutral current

measurements have played a central role in constraining “new physics” models at the TeV scale

• Jefferson Lab experiments in progress and the ones being designed for 12 GeV will likely provide critical information in unraveling “new physics” signals at the LHC– JLab beam quality and luminosity critical!

• A new era of parity violation observables will become available at a polarized EIC, provided the ability will be built in to integrate 50 to 100 fb-1

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