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

JLab

– 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

Weak

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

10-38

SU(2)L X U(1)

Y

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

q2 j

em p j em, e

M = G u n u

p u e

ue

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


MCC =4G

2J J

.

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

M = g

2u

1

21− 5 u 1

MW

2 −q2 g

2ue

1

21−5ue

if q2<<MW

2 then G

2=

g2

8 MW

2


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

22 J

NC J NC ,

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

M = g

2u

1

21− 5 u 1

MW

2 −q2 g

2ue

1

21−5ue

J NC =

1

2 u 1

21−5u J

NC q = uq

1

2 c

V

q −cA

q 5uq


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:

jem

J NC

⇔ J 3

j Y

completes SU(2)L

U(1)Y, Y: weak hyper

charge

Q = T 3Y

2


W 1

W 2

W 3

B

⇔

W .

W −.

A

Z

A = B cosW

W 3 sin

Wm=0

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)

ALR

≡ r− l

r l≈

Q2

MZ

2≈120 ppm

at Q2=1GeV /c2

APV

= +

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

-C2d

)+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

+C1d

133Cs APV -376C1u

-422C1d -72.69±0.48

205Tl APV -572C1u

-658C1d -116.6±3.7

e--A C1u

+C1d 0.1358±0.0326

C1u

-C1d -0.4659±0.0835

C2u

+C2d -0.2063±0.5659

C2u

-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.

comm.

new

PDG2002 (best): (2C2u-C2d)=±0.24

Som

e N

ew

Ph

ysi

cs c

an

aff

ect

C2

q,

bu

t n

ot

C1

q

C3q

=gA

e gA

qC1q

=gA

e gV

q C2q

=gV

e gA

q


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

C2

u+C

2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u-C2d

- 0.2 0.40.20- 0.4

0.10

0.125

0.15

0.175

C1u-C1d

- 0.4- 0.6- 0.8

C1

u+

C1

d

Tl APV


Neutral Weak Couplings in Electron DIS

APV

= +

LSM

PV =−G

F

2e e∑q

C2q q 5 q

axial electron * vector quark :

vector electron * axial quark :

LSM

PV=−G

F

2e 5 e ∑q

C1q q q

C2d

=gV

e gA

d =1

2−2 sin2

W

C2u

=gV

e gA

u =−1

22 sin 2

WC

1u=g

A

e gV

u =−1

2

4

3sin2

W

C1d

=gA

e gV

d =1

2−

2

3sin 2

W

12

q gVq −g A

q 5q

12

e g Ve −g A

e 5e


Deuterium:

PVDIS Asymmetries

Ad

= 540 ppmQ22 C

1u[1R

C x ]−C

1d[1R

S x ]Y 2 C

2u−C

2d R

V x

5RS x 4 R

C x

APV

= +


Deuterium:

PVDIS Asymmetries

APV

= +

Ad

= 540 ppmQ22 C

1u[1R

C x ]−C

1d[1R

S x ]Y 2 C

2u−C

2d R

V x

5RS x 4 R

C x

+

L=LSM

PV LNEW

PV

LSM

PV =−G

F

2e e∑q

C2q q 5 q L

NEW

PV =g2

4 2e e∑ f

hA

q q 5q

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

New physics sensitivity:


Deuterium:

PVDIS Asymmetries

APV

= +

Ad

= 540 ppmQ22 C

1u[1R

C x ]−C

1d[1R

S x ]Y 2 C

2u−C

2d R

V x

5RS x 4 R

C x

+

L=LSM

PV LNEW

PV

LSM

PV =−G

F

2e e∑q

C2q q 5 q L

NEW

PV =g2

4 2e e∑ f

hA

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


RSx =

2 [s x s x ]

u xu xd x d x

PVDIS Asymmetries

RCx =

2 [c xc x]

u xu x d x d x R

Vx =

uV xd

V x

u xu x d x d x

APV

= +

Deuterium:

Ad

= 540 ppmQ22 C

1u[1R

C x ]−C

1d[1R

S x ]Y 2 C

2u−C

2d R

V x

5RS x 4 R

C x

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

C2

u+C

2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u-C2d

- 0.2 0.40.20- 0.4

0.10

0.125

0.15

0.175

C1u-C1d

- 0.4- 0.6- 0.8

C1

u+

C1

d

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:

C2

u+C

2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u-C2d

- 0.2 0.40.20- 0.4

0.10

0.125

0.15

0.175

C1u-C1d

- 0.4- 0.6- 0.8

C1

u+

C1

d

Tl APV

JLab E08-011 (PDG

fit)

JLab E08-011 (R. Young's

fit)

g

≈ [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

DIS.







DIS.





negligible);


Xiaochao Zheng, International Workshop on Positrons at JLab

33/64

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...

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