Xiaochao Zheng, International Workshop on Positrons at JLab 1/64 C 3q Measurement Using Polarized e...

Xiaochao Zheng, International Workshop on Positrons at JLab 1/64

C3q Measurement Using Polarized e+/e- Beams at

– Introduction — Standard Model of Electroweak Interaction

– Neutral Weak Coupling Constants

– C3q Measurements

– Summary

Xiaochao ZhengUniv. of VirginiaMarch 27, 2009

Four Interactions of Our Nature

Electron scattering has been widely used to study

Structure of the nucleon — strong interactions, pQCD;

(Recently) parity violation electron scattering:

strange-quark content of the nucleon (elastic)

Electroweak interactions (DIS)

Gravitational General relativity Well understood at large distances

Electro-Magnetic 1/137

Strong SU(3), QCD less understood, no analytical calculation

SU(2)L X U(1)

EM, weak: almost fully understood,

but there is room for New Physics10-5

10-1~100

Electroweak Interaction – Charged Currents

1932, charged pion and muon decay indicate a fourth type of interaction:

−. −.

−. e−. e

Much longer than strong (10-23 s) or electromagnetic (10-16 s) decays

1932, based on QED, Fermi proposed:

=2.6×10−8 s

=2.2×10−6 s

M = e u p u

p −1

q2 −e ue u

e = −e2

em p j em, e

M = G u n u

1956, when Parity violation was first proposed (and test by experiments), the only modification needed is: 1−5

MCC =4G

If further assume that weak interaction occurs by exchanging a (W) particle, similar to the photon in electromagnetic interactions, then

21− 5 u 1

2 −q2 g

21−5ue

if q2<<MW

2 then G

1973, with developement of beams, found:

e−. e−. N X N Xcannot be explained by CC;

magnitude of strength indicate Neutral Currents.

Electroweak Interaction – Neutral Currents

M NC =4 G

NC J NC ,

If further assume that weak interaction occurs by exchanging a (W) particle, similar to the photon in electromagnetic interactions, then

21− 5 u 1

2 −q2 g

21−5ue

J NC =

21−5u J

NC q = uq

q −cA

1961, construct a SU(2)L group using charged currents, quantum number:

Weak isospin T.

Linear combination of the two is a neutral current, but it couples only to Left-handed fermions,

while experimentally observed NC couples to both R- and L-handed,

On the other hand, EM [U(1)] also couple to both R- and L-H fermions.

Can combine NC from SU(2)L and UEM(1) to construct:

⇔ J 3

completes SU(2)L

U(1)Y, Y: weak hyper

charge

Q = T 3Y

W −.

A = B cosW

W 3 sin

Z = −B sin W

W 3 cos

Wm≠0

SM works well at present energy range;

Conceptual reasons for new physics:

What happens in the “high-energy desert”?

ElectroWeak Standard Model

Data exist: cannot be explained by the SM ( m, NuTeV

anomaly...);

(250 GeV ~ 5 x 1014 GeV ~ 2.4 x 1018 GeV)?

Exploring Nucleon Structure Using Electron ScatteringElastic, quasi-elastic, resonances, deep inelastic

(Quasi-) elastic – the nucleus (nucleon) appears as a rigid body

Resonance region – quarks inside the nucleon react coherently

Deep Inelastic Scattering (DIS):

Quarks start to react incoherently (start to see constituents of the nucleon)

(Can test pQCD)

Q2=2MT N

Weak Interaction in DIS (Parity Violating DIS)

study hadron structure

elastic scattering: strange form factors A4(MAINZ), G0, HAPPEX (JLab), SAMPLE (MIT/Bates)

DIS: higher twist effects, charge symmetry violation... PVDIS

test the electroweak standard model E158(SLAC), Qweak(JLab)

Electromagnetic observables — , A...

Weak observables — parity violating asymmetries (APV)

(polarized beam + unpolarized target)

≡ r− l

r l≈

2≈120 ppm

at Q2=1GeV /c2

Parity Violating Electron Scattering

Data exist: cannot be explained by the SM ( m, NuTeV

anomaly...);

(250 GeV ~ 5 x 1014 GeV ~ 2.4 x 1018 GeV)?

indirect searches:

E158, NuTeV, Qweak, PVDIS

High energy direct searches:

LEP, LHC

Search for Physics beyond the Standard Model

(250 GeV ~ 5 x 1014 GeV ~ 2.4 x 1018 GeV)?

Testing the EW Standard Model – Running of sin2W and the NuTeV Anomaly

(expected)

Current Knowledge on Weak Coupling Coeffecients

Facility Process Result SM Value

SLAC 1.39 -0.7185

SLAC 1.39 -0.0983

CERN 34 1.4351

CERN 66 1.4204

MAINZ 0.20 -0.8544

Bates 0.0225 0.1528

Bates 0.1 -0.0624

Bates 0.04 -0.0624

0.03 approved -0.0357

0 -73.16

0 -116.8

Fit low 0.1528

All -0.5297

PVES -0.0095

Data -0.0621

Q2 Ciq Combination

e--D DIS 2C1u

-C1d -0.90± 0.17

e--D DIS 2C2u

-C2d 0.62± 0.81

m±-D DIS 0.66(2C2u-C2d)+2C3u

-C3d 1.80± 0.83

m±-D DIS 0.81(2C2u

)+2C3u

-C3d 1.53± 0.45

e--Be QE 2.68C1u

-0.64C1d

+2.16C2u

-2C2d -0.94± 0.21

e--C elastic C1u

+C1d 0.138±0.034

e--D QE C2u

-C2d -0.042± 0.057

e--D QE C2u

-C2d -0.12± 0.074

JLab e--p elastic 2C1u

133Cs APV -376C1u

-422C1d -72.69±0.48

205Tl APV -572C1u

-658C1d -116.6±3.7

e--A C1u

+C1d 0.1358±0.0326

-C1d -0.4659±0.0835

+C2d -0.2063±0.5659

-C2d -0.0762±0.0437

J. Erler, M.J. Ramsey-Musolf, Prog. Part. Nucl. Phys. 54, 351 (2005) R. Young, R. Carlini, A.W. Thomas, J. Roche, PRL 99, 122003 (2007) & priv.

PDG2002 (best): (2C2u-C2d)=±0.24

Current Knowledge on C1,2q

MIT/ Bates

SLAC/Prescott

Qweak (expected)

R. Young (PVES)

R. Young (combined)

PDG best fit

Cs APV

PDG 2006 fitSAMPLE

SLAC/ Prescott

R. Young (combined)

all are 1 limit

Best: PDG2002 (2C2u-C2d) = 0.24

C2u-C2d

- 0.2 0.40.20- 0.4

C1u-C1d

- 0.4- 0.6- 0.8

Tl APV

Neutral Weak Couplings in Electron DIS

PV =−G

2e e∑q

C2q q 5 q

axial electron * vector quark :

vector electron * axial quark :

PV=−G

2e 5 e ∑q

C1q q q

2−2 sin2

u =−1

22 sin 2

u =−1

3sin 2

q gVq −g A

e g Ve −g A

Deuterium:

PVDIS Asymmetries

= 540 ppmQ22 C

C x ]−C

S x ]Y 2 C

2u−C

5RS x 4 R

Deuterium:

PVDIS Asymmetries

= 540 ppmQ22 C

C x ]−C

S x ]Y 2 C

2u−C

5RS x 4 R

PV LNEW

PV =−G

2e e∑q

C2q q 5 q L

PV =g2

4 2e e∑ f

q q 5q

g: coupling constant, : mass limit, hAq: effective coefficient

New physics sensitivity:

Deuterium:

PVDIS Asymmetries

= 540 ppmQ22 C

C x ]−C

S x ]Y 2 C

2u−C

5RS x 4 R

PV LNEW

PV =−G

2e e∑q

C2q q 5 q L

PV =g2

4 2e e∑ f

q q 5q

g: coupling constant, : mass limit, hAq: effective coefficient

New physics sensitivity:

g≈ [8G

F∣ 2 C2u

−C 2d∣]−1/ 2

Sensitive to: Z' searches, compositeness, leptoquarks

Mass limit:

PV DIS and Other SM Test ExperimentsE158/Moller (SLAC)

NuTeV (FNAL)Atomic PV

PVDIS (JLab)Qweak (JLab)

2 (2C1u+C1d)

Coherent quarks in the proton

Purely leptonicWeak CC and NC differenceNuclear structure?Other hadronic effects?

Coherent Quarks in the Nucleus- 376C1u - 422C1d

Nuclear structure?

(2C1u-C1d)+Y(2C2u-C2d)

Isoscalar quark scattering

Cartoons borrowed from R. Arnold (UMass)

Different ExperimentsProbe Different

Parts of Lagrangian,

PVDIS is the only one accessing C2q

2 [s x s x ]

u xu xd x d x

PVDIS Asymmetries

2 [c xc x]

u xu x d x d x R

u xu x d x d x

Deuterium:

= 540 ppmQ22 C

C x ]−C

S x ]Y 2 C

2u−C

5RS x 4 R

Also sensitive to:

quark-gluon correlations (higher-twist effects)

Charge symmetry violation

up x ≠dn x d px ≠un x

PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV ...... However, hasn't been done since 1978.

1970's, result from SLAC E122 consistent with sin2W=1/4,

established the Electroweak Standard Model;C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978)

PVDIS Experiment – Past, Present and Future

(Re)start PVDIS at JLab 6 & 12 GeV

Difficulty: separate New Physics and hadronic effects

Do a first measurement at JLab 6 GeV:

If observe a significant deviation from the SM value, it will definitely indicate something exciting;

Indicate either electroweak new physics, or current understanding of strong interation is worse than we thought.

New electroweak Physics

Non-perturbative QCD (higher-twist) effects

Charge symmetry violation

Likely to be small, but need exp confirmation

Small from MRST fit (90% CL ~1%)

At the 6 GeV precision:

Do a first measurement at JLab 6 GeV:

If observe a significant deviation from the SM value, it will definitely indicate something exciting;

Indicate either electroweak new physics, or current understanding of strong interation is worse than we thought.

At 12 GeV, a larger, well-plannedwell-planned PVDIS program could separate all three: New Physics, HT, CSV, important information for both EW and Strong interaction study.

JLab 6 GeV Experiment 08-011

Use 85mA, 6 GeV, 80% polarized beam on a 25-cm LD2 target;

Two Hall A High Resolution Spectrometers detect scattered electrons;

Measure PV asymmetry Ad at Q2=1.10 and 1.90 GeV2 to 2.7% (stat.);

Ad at Q2=1.10 will limit the higher twist effects;

If HT is small, can extract 2C2u-C2d from Ad at Q2=1.90 to ±0.04 (or

with reduced precision if higher twists are un-expectedly large)

Co-spokesperson & contact: X. ZhengCo-spokesperson: P.E. Reimer, R. Michaels

(Hall-A Collaboration Experiment, approved by PAC27, re-approved by PAC33 for 32 days, rated A-)

Current Knowledge on C1,2q

MIT/ Bates

SLAC/Prescott

Qweak (expected)

R. Young (PVES)

R. Young (combined)

PDG best fit

Cs APV

PDG 2006 fitSAMPLE

SLAC/ Prescott

R. Young (combined)

all are 1 limit

Best: (2C2u-C2d) = 0.24

C2u-C2d

- 0.2 0.40.20- 0.4

C1u-C1d

- 0.4- 0.6- 0.8

Tl APV

C2q from JLab E08-011

MIT/ Bates

SLAC/Prescott

Qweak (expected)

R. Young (PVES)

R. Young (combined)

PDG best fit

Cs APV

PDG 2006 fitSAMPLE

SLAC/ Prescott

R. Young (combined)

all are 1 limit

Best: (2C2u-C2d) = 0.24 0.04 (factor of six improvement);

New physics mass limit:

C2u-C2d

- 0.2 0.40.20- 0.4

C1u-C1d

- 0.4- 0.6- 0.8

Tl APV

JLab E08-011 (PDG

JLab E08-011 (R. Young's

≈ [8 GF∣ 2 C

2u−C

2d∣]

−1 /2≈ 0.9 TeV

Higher precision, possibly sensitive to 1) New Physics beyond the SM; 2) Charge Symmetry Violation (CSV)

Two approaches (conditionally approved):

Hall C “baseline” SHMS+HMS: PR12-07-102 (P.E. Reimer, X-C. Z, K. Paschke)

1% on Ad, extraction of C2q, sin2W (if higher-twist and CSV are

negligible);

PVDIS Program at JLab 12 GeV

Hall A large acceptance “solenoid” device: PR09-012

Measure Ad to 1% for a wide range of (x,Q2,y), clean separation of

New Physics (via C2q and sin2W), HT and CSV possible;

Extract d/u at large x from PVDIS on a proton target, free of nuclear effects;

Other hadronic physics study possible: A1n at large x, Semi-inclusive

negligible);

Xiaochao Zheng, International Workshop on Positrons at JLab

Measurement of neutron asymmetry A1n in the valence quark

region at JLab 12 GeV

Flagship experiment

Will be one of the first experiments to run (~2014?)

PVDIS at 12 GeV

Ultimate goal: clean separation of New Physics and CSV (2015 or later?)

Summary (2013 - )

Xiaochao Zheng, International Workshop on Positrons at JLab 1/64 C 3q Measurement Using Polarized e...

Documents

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Undulator-Based Production of Polarized Positrons Status Report on E-166 Undulator-Based Production of Polarized Positrons K.T. McDonald Princeton University

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PVDIS at 6 GeV JLabweb.mit.edu/pavi09/talks/Zheng.pdf · 2009-07-08 · PVDIS at 6 GeV JLab X. Deng, R. Michaels, K. Pan, P. Reimer, R. Subedi, D. Wang Xiaochao Zheng University of

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