The JLab Parity Violation Deep Inelastic Scattering (PVDIS) … · 2018-10-16 · PVDIS at 6 GeV...

1X. Zheng, Nuclear Physics Symposium – Exploring the Heart of Matter, September 2014

The JLab Parity Violation Deep Inelastic Scattering (PVDIS) Experiment

Xiaochao Zheng (Univ. of Virginia)

September 26, 2014

Electron scattering basics – elastic, resonance, DISPVDIS and electron-quark effective couplingsThe 6 GeV PVDIS experiment– DIS results – electron-quark effective VA couplings– Resonance results – duality in EW sector?

Outlook for the 12 GeV Program – PVDIS with SoLID

2

W 2=P' 2

Q 2=−q 2

P= M,0

Inclusive Electron Scattering Basics

x

t

x

k '=E ' ,k '

k= E ,k

q= ,q

“Elastic”: W=Mp

(form factors)

“Resonance”: 1<W<2GeV (structure functions)

“Deep Inelastic”: W>2 GeV, (structure functions, parton

distribution functions)

Inclusive: only scattered electron is detected


Parity-Violating Electron Scattering

To study nucleon structure not accessible in electromagnetic interaction:

elastic PVES: nucleon strange form factors; “neutron skin” in heavy nucleus

To test the electroweak Standard Model:Moller – E158PVDIS e eee

Z0


Parity Violation in the Standard Model

In weak interaction, all elementary fermions behave differently under parity transformation

They have a preferred chiral state when coupling to the Z0


Unlike electric charge, need two charges (couplings) for weak interaction: gL, gR

or “vector” and “axial” weak charges:


fermions

u, c

d, s

e

e-, -

g Vf= I 3−2Q sin2W

12

12

−122sin

2W

12−43sin

2W

−1223sin

2W

g Af= I 3

−12

12

−12

Z0

e e

−ig Z

2

[ g V

e−g A

e5]

gV~(gL+gR) gA~(gL-gR)



or “vector” and “axial” weak charges:PVES asymmetry comes from V(e)xA(targ) and A(e)xV(targ)


Z0

e e


V-A -V-A

-V-A

e e

V-A



or “vector” and “axial” weak charges:PVDIS asymmetry comes from:

Effective Couplings in the Standard Model

Z0

e e


V-A -V-A

-V-A

e e

V-A

C1q≡2 g Ae g V

q , C 2q≡2 gVe g A

q

q q q q

“electron-quark effective couplings”




Effective Couplings and New Contact Interactions


C1q≡2 g Ae g V


q

“electron-quark effective couplings”V-A

V-A

e e

q q

-V-A

-V-A

e e

q q





C1q≡2 g Ae g V


q

“electron-quark effective couplings”V-A

V-A

e e

q q

-V-A

-V-A

e e

q qC1q=g AV

e q ,C2q=g VAe q

Erler&Su, Prog. Part. Nucl. Phys. 71, 119 (2013)

Effective Couplings and New Contact Interactions


Accessing C1q,2q

Need electron beam on hadronic targetIn elastic PVES– directly probes C1q, electrons' parity-violating

property;– quarks' parity-violation is represented by the nucleon

axial form factor GA, and extracting C2q from GA is model-dependent

Only in PVDIS, electron probes the quark and PVDIS asymmetry depends on C2q directly.


Formalism for Parity Violation in DIS

For an isoscalar target (2H), structure functions

largely simplifies:

0 1If neglecting sea quarks, asymmetry is no longer

sensitive to PDFs “static limit”→

APV=GF Q 2

2[a x Y y b x ]

q i−. x =q i

V x≡q i x−q i. x

a x =310

2C1u−C1d 1 0.6 s.

u.d. b x =

310

2C 2u−C 2d uVd V

u.d.

q i. x ≡q ix q i

. x

a x =12

g Ae F1

Z

F1=12

∑iC1iQ i q i

. x

∑iQi2q i

. x b x =gV

e F 3Z

F 1=12

∑iC2iQi qi

−. x

∑iQi2qi

. x

x≡x Bjorken=Q 2

2M


Still, C2q are more difficult to access than C1q

APV=GF Q 2

2[a x Y y b x ]

y≡E−E '

E=E

Y =[ r 2

1R ] 1−1− y 2

11− y 2− y2[1− r2

1R ]−xyME

r 2=1Q 2

2

The term sensitive to the quark spin is kinematically suppressed due to angular momentum conservation.C2q are much smaller than C1q:

C1u=−1243sin2W

C2u=−122sin

2W

C1d=12−23sin

2W C2d=

12−2sin

2W


Best Data on C1q (eq AV couplings) from PVES+APV

Androic et al., PRL 111, 141803 (2013);


Projecting to C1q vs C2q (e-q AV vs. VA couplings)

2C1u-C1d

2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

5

4

3

2

1

0

-1

15X. Zheng, Nuclear Physics Symposium – Exploring the Heart of Matter, September 20142C1u-C1d

2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

5

4

3

2

1

0

-1

Add E122 – the first PVES (1978)


2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

5

4

3

2

1

0

-1

and combine them


2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

5

4

3

2

1

0

-1

then zoom in

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4

0.2

0.1

0.0

-0.1

-0.2

-0.3

-0.4

-0.5


PVDIS at 6 GeV (JLab E08-011)


Staff: ~700User community: ~1300

A CB

Beam first delivered in 10/95 In full operation for since 11/97 >300 PhDs to date and >200 in

progress (~1/3 of US PhDs in Nuclear Physics)

Energy: 6 GeV, 12 GeV (starting 2014)

“Continuous beam”, provides the highest polarized luminosity of the world


PVDIS at 6 GeV (JLab E08-011)Ran in Oct-Dec 2009, 100uA, 90% polarized electron beam, 20-cm liquid deuterium targetTwo High Resolution Spectrometers (HRS pair) detected electrons in the inclusive mode at DIS Q2=1.1 and 1.9 GeV2, and five resonance kinematics.Spokespersons: Robert Michaels, Paul Reimer, X. Z.Students: Xiaoyan Deng, Kai Pan, Diancheng WangPostdoc: Ramesh Subedi


E08-011 Kinematics


It's not easy to count electrons! — Our customized fast counting DAQ with online particle identification

total cost: $200k

X. Zheng, Nuclear Physics Symposium – Exploring the Heart of Matter, September 2014

Data Quality

pull=Ai−⟨ A⟩

Ai

(pair-wise asymmetry pull plots):


From Measured to Physics Asymmetry

A phys= Araw

Pb

−∑iAi f i

1−∑if i

A phys≈Araw

Pb

i 1 f i

f i≡ f i 1− Ai

Araw P b

correcting for background fi with asymmetry Ai:


From Measured to Physics Asymmetry

AQ 2

=1.085, x=0.241

raw =−78.45±2.68±0.07 ppm


From Measured to Physics AsymmetryA

Q 2=1.901, x=0.295

raw =−140.30±10.43±0.16 ppmLHRS

AQ 2

=1.901, x=0.295

raw =−139.84±6.58±0.46 ppm RHRS


Compare to Standard Model?

AQ 2

=1.085, x=0.241

phys =−91.10±3.11±2.97 ppm

AQ 2

=1.901, x=0.295

phys =−160.80±6.39±3.12 ppm

ASM=2.022×10−4 [ 2C1u−C 1d 0.594 2C2u−C2d ]=−158.9 ppm

ASM=1.156×10−4 [ 2C1u−C1d 0.348 2C2u−C 2d ]=−87.7 ppm

uncertainty due to PDF: 0.5% 5%uncertainty due to HT: 0.5%/Q2, 0.7ppm

uncertainty due to PDF: 0.5% 5%uncertainty due to HT: 0.5%/Q2, 1.2ppm


Previous data: Elastic PVES + APV

2C1u-C1d

5

4

3

2

1

0

-1

2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50


5

4

3

2

1

0

-1

2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

Add JLab PVDIS


5

4

3

2

1

0

-1

2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

zoom in

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4

0.2

0.1

0.0

-0.1

-0.2

-0.3

-0.4

-0.5


5

4

3

2

1

0

-1

2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

best fit

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4

0.2

0.1

0.0

-0.1

-0.2

-0.3

-0.4

-0.5

Wang et al., Nature 506, no. 7486, 67 (2014);


5

4

3

2

1

0

-1

2C2u

-C2d

-1.50 -1.25 -1.0 -0.75 -0.50

best fit

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4

0.2

0.1

0.0

-0.1

-0.2

-0.3

-0.4

-0.5

Marciano., Nature 506, no. 7486, 43 (2014);


BSM Mass Limit on eq VA contact interaction

(2C1u-C1d) (TeV)15 10 5 0 5 10 15

15

10

5

0

5

10

15

(2

C 2u-

C 2d)

(TeV

)

Wang et al., Nature 506, no. 7486, 67 (2014);


I II III

IV

DIS1

DIS2

I II III

IV

Four setting covered the full resonance region;“Grouping” of lead glass blocks allowed a reasonable study of the W-dependence;

Q2=1.085Q2=1.085 Q2=1.901Q2=1.901

Resonance Background Data Coverage

Q2 Q2

W W

Monte Carlo Simulation

35X. Zheng, Nuclear Physics Symposium – Exploring the Heart of Matter, September 2014Wang et al., PRL 111, 082501 (2013);

Resonance PV Asymmetry ResultsA: Matsui, Sato, Lee, PRC72,025204(2005)B: Gorchtein, Horowitz, Ramsey-Musolf, PRC84,015502(2011)C: Hall, Blunden, Melnitchouk, Thomas, Young, PRD88, 013011 (2013)


Coherent PVDIS Program with SoLID @ 11 GeV

““SoLID” spectrometerSoLID” spectrometerSoLID Physics topics:

PVDIS deuteron (180 days) – C2, sin2W, CSV, diquarks,

PVDIS proton (90 days) – d/u

PV with 3He (LOI)

SIDIS

J/



Goal on C2q: one order of magnitude improvement over 6 GeV


6 GeV PVDIS Timeline

2003 – Letter of Intent to JLab PAC

2003-2005 – main proposer was distracted by other physics topics

2005 – Full proposal to JLab PAC, partially approved (E05-007) with A-rating

2008 – Jeopardy review, approved 32 days (E08-011) with A-rating

2009, Oct-Dec – Running of Experiment

2010-2013 – Data analysis

2013-present – publishing results (1 NIM, 1 PRL, 1 Nature, 1 PRC long paper ongoing)


6 GeV PVDIS Timeline

2003 – Letter of Intent to JLab PAC

2003-2005 – main proposer was distracted by other physics topics

2005 – Full proposal to JLab PAC, partially approved (E05-007) with A-rating

2008 – Jeopardy review, approved 32 days (E08-011) with A-rating

2009, Oct-Dec – Running of Experiment

2010-2013 – Data analysis

2013-present – publishing results (1 NIM, 1 PRL, 1 Nature, 1 PRC long paper ongoing)

I was at ANL-MEP


Summary and PerspectivesThe 6 GeV PVDIS from JLab:

Improved world data on the eq VA effective coupling term 2C2u-C2d by factor of five; agrees with the SM; and showed 2C2u-C2d is 2 from zero – indicating a nonzero contribution to PVDIS asymmetry due to quark's chirality preference; BSM mass limits complimentary to collider experiments.

Resonance PV asymmetries seem to indicate duality in the electroweak observables for the first time.

“New construction” experiments at JLab 12 GeV:PVDIS @ 11 GeV (SoLID) will improve C2q by another order of magnitude.

Subedi et al, NIM-A 724, 90 (2013); Wang et al., PRL 111, 082501 (2013);Wang et al., Nature 506, no. 7486, 67 (2014); long paper draft available.


Pion Asymmetries


Pair Production Background

Took reversed-polarity runs, mostly to determine e+/e- ratio. Positron asymmetry from those runs have very large error;Assumed positron asymmetry to be similar to - asymmetry;Effect on the measurement is about 10 times larger than - background.


SLAC E122 (1978) JLab E08-011 (2009)

Beam 37%, 16.2-22.2 GeV 90%, 6.0674 GeV, 100uATarget 30-cm LD2, LH2 20-cm LD2Spectrometer 4o 12.9o and 20o

Q2 1-1.9 GeV2 1.1 and 1.9 GeV2

Data collection Integrating gas Cerenkov and lead glass detectors, independently

Counting DAQ using both GC and lead glass for PID at the hardware level

Deuteron results

Proton results

SLAC E122 vs. JLab E08-011

A/Q2=(-9.7±2.7)x10-5 (GeV/c)-2

(two highest energies only)A/Q2=(-9.5±1.6)x10-5 (GeV/c)-2

±0.86x10-5(stat)±5%(Pb)±3.3%(beam)±2%( contamination)

±3%(radiative corrections)

±(3-4)%(stat)±syst.sin2W=0.20±0.03


SAMPLE

C2u+C

2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2uC

2d

- 0.25 0.50.250- 0.5

Some Older Plotswith recent PVES data and Qweak (projected) without JLab data

all are 1 limit

PDG best fit

SLAC/ Prescott

(original results)

Qweak in Hall C (2010-May 2012): factor of 5 improvement in the proton weak (vector) charge Qp

W=-2(2C1u+C1d)

1H + e → e’ + p

47

“Elastic” and “Resonance”

“Deep Inelastic”

Electron Scattering Basics

The JLab Parity Violation Deep Inelastic Scattering (PVDIS) … · 2018-10-16 · PVDIS at 6 GeV...

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