DIS-Parity: Measuring sin2θW with Parity Violation in Deep Inelastic Scattering using Baseline

Spectrometers at JLab 12 GeV

Paul E. Reimer

2

Unification of Weak and E&M Force•SU(2)—weak isospin—Triplet of gauge bosons•U(1)—weak hypercharge—Single gauge boson

Electroweak Lagrangian:

J, JYisospin and hypercharge currents

g, g0 couplings between currents and fields

Weinberg-Salam model and sin2(W)

Rem

embe

r—I’

m n

ot t

he e

xper

t he

re. Gary Larson, The Far Side

Vector: giV= t3L(i) – 2qi sin2(W)

Axial: giA = t3L(i)

Charge

Weak isospin

Standard Model parameters:• Charge, e , em

• g , GF lifetime• MZ

• sin2(W)

3

Running of sin2(W)

Measurements of sin2(W)

– APV Cs– Møller Scattering (SLAC E-158)– DIS (NuTeV)

Clear indication of running of sin2(W)

Future Experiments– Q-Weak (JLab)– Møller (JLab 12 GeV)

DIS-Parity at JLab 12 GeV

4

DIS Formalism on unpolarized Deuterium Target

Note that each of the Cia are sensitive to different possible S.M. extensions.

Longitudinally polarized electrons on unpolarized deuterium target—Cahn and Gilman, PRD 17 1313 (1978).

C1q ) NC vector coupling to q £ NC axial coupling to eC2q ) NC axial coupling to q £ NC vector coupling to e

Cia provide sensitivity to sin2(W)e e

5

Sensitivity to sin2(W)

Large asymmetryQ2 = 3.7 GeV2, Ad = 0.0003

“Easy experiment”Gain factor of 2 in sin2(W)

over Ad

Look for interference between large photon term and New Physics

APV ~

e e

e

?

e

+

e e

Z

6

How does DIS-Parity fit in?

e e

Zp

n

W

Z+

e e

ee

Z

Møller Scattering

• Purely Leptonic—no quark interactions

• K Kumar/D. Mack

e e

Z

Q-Weak (JLab)

• Coherent quarks in Proton• Results in ~2008• 2(2C1u+C1d)• S Page

e

Z

Cs133

Atomic Parity Violation

• Coherent quarks in entire nucleus• Nuclear structure uncertainties• -376 C1u – 422 C1d

• A. Derevianko and Other talks

DIS-ParityNeutrino Scattering

• Isoscaler quark scattering• (2C1u-C1d)+Y(2C2u-C2d)• X Zheng/P. Souder

• Quark scattering (from nucleus)• Weak charged and neutral

current difference• Tim Londergan

Expt. Probe different parts of Lagrangian

7

Jefferson Lab at 12 GeV Upgrade

Currently:• 6 GeV CW beam• 3 exp. Halls (A, B, C)• 80% polarized beam

Upgrade (Completion date?):• 12 GeV (11 GeV to Hall A, B, C)• Addition of Hall D• 85A to Hall A, C

Figures from JLab web site

8

Criteria for DIS-Parity with baseline equipment

General Experimental Criteria: DIS regime:

– Maximize Q2 (3.0-4.0 GeV2)– Large W2 ( > 4GeV2)

Minimize uncertainty from parton distributions:– Deuterium target

(d/u ratio vs nuclear effects)– x<0.7

Maximize sensitivity to sin2W

– Large Y

Expt. Assumptions: 60 cm liquid deuterium target 11 GeV beam @ 90mA 85% polarization § 0.5% Rates which can be handled:

– 1MHz DIS– /e ¼ 1 ) 1 MHz pions– 2 MHz Total rate

Implementation /e separation ) gas Cherenkov

counters ¼ 6 GeV thresh. Rate requires flash ADC’s or

Scaler-based DAQ on Cherenkov and Calorimeters—this is a counting experiment!!

9

Hall C at 11 GeV

HMS spectrometer• Pmax¼ 7.4 GeV/c §10%• = 8.1 msr

SHMS spectrometer:• Design in progress• Pmax ¼ 11 GeV § 10% • = 5.2 msr

Figures from Hall C CDR

HMS

SHMS

10

JLab Hall C SHMS/HMS combination

Large asymmetry (3£ 10-4) implies short runtime

13 “perfect” days E0 = 7 GeV

(scattered electron momentum) = 13o

Average Range

x 0.51 0.41-0.68

Y 0.44 0.35-0.50

Q2 3.9 GeV2 3.5-4.3 GeV2

W2 4.7 GeV2 2.9-6.0 GeV2

General experimental criteria are met.

Statistical Precision Two independent spectrometer

measurements Combined statistical precision

– A/A = 0.5%

– sin2W/sin2W = 0.26%

What about Hall A? Smaller solid angle and lower E0

Ready for 11 GeV yearsyears sooner!

What about systematics?

11

Uncertainties in Ad

Beam Polarization:

– Q-Weak also needs 1% polarization accuracy.

– Hall C Møller has achieved 0.5% polarization accuracy at low intensity

Determination of Q2 significant Higher Twist will be studied by

– PV-DIS at 6 GeV

– Res-Parity

Source Uncertainty

Source A sin2W

Statistical 0.5% 0.26%

Beam polarization 0.5% 0.26%

Deadtime 0.3% 0.15%

Q2 0.2%

R = (L/T) 0.01%

Parton Distributions

0.05%

Radiative corr. ??

Higher Twist PV-DIS@ 6GeV

Res-Parity

EMC/Nuclear Effects in 2H Parity Violation

Res-Parity

Total Uncertainty 0.8% 0.45%

12

Expected sin2(W) Results (JLab)

Ad/Ad = §0.50% (stat) §0.58% (syst) (§ 0.78% combined)

sin2(W)/sin2W= § 0.26% (stat) § 0.36% (sys) (§ 0.45% combined)

What about Ciq’s?

13

Extracted Signal—It’s all in the binning

Fit Asymmetry data as fn. of Y

A = A0 [ (2C1u – C1d) + Y(2C2u – C2d

)]

intercept = 2C1u – C1d (QWeak) slope = 2C2u – C2d

14

Exp. Constraints on C1u, C1d, C2u and C2d

Present experimental constraints are wide open, except for APV(1 standard deviation limits shown)

Combined result significantly constrains 2C2u–C2d. PDG 2C2u–C2d = –0.08 § 0.24 Combined (2C2u–C2d) = § 0.014

15

DIS-Parity: Conclusions

Measurements of sin2(W) below MZ provide strict tests of the Standard Model.

DIS-Parity provides complementary sensitivity to other measurements.

DIS-Parity Violation measurements can be carried out in at Jefferson Lab– Asymmetry is Large!

Jefferson Lab:

sin2(W) = 0.0011

(2C2u – C2d) = 0.014

Waiting for 12 GeV upgrade!