dis-parity 12 gev - university of...

DIS-Parity 12 GeV Physics opportunities in PVeS

with a Solenoidal Spectrometer

Many slides liberated from: P. Souder, K. Kumar (… and their sources)

Kent Paschke

University of Massachusetts

June 14, 2006 DIS Parity at 12 GeV Kent Paschke

•  The couplings gT depend on electroweak physics as well as on the weak vector and axial-vector hadronic current •  For DIS-Parity, both new physics at high energy scales as well as interesting features of hadronic structure come into play •  A program with a broad kinematic range can untangle the physics

(gAegV

T + gV

egAT)

PV Asymmetries Weak Neutral Current (WNC) Interactions at Q2 << MZ

2

Longitudinally-Polarized Electrons Scattering off Unpolarized Fixed Targets


PVeS and Physics Beyond the SM: Qweak and Møller

Examples:

Kurylov, Ramsey-Musolf, Su

To be relevant, new SM tests must have small enough errors to show

up on plots like this


10%

10%

-10%

Add DIS-Parity: ±

20 15 10 5 0 5 10 2

1.5

1

0.5

0

0.5

1

(QWe )

SUSY/(Q

We )

SM (%)

(A d) SUSY/ (A d) SM (%)

(a)

15 10 5 0 5 10 15 2

1.5

1

0.5

0

0.5

1

(QWp )

SUSY/(Q

Wp )

SM (%)

(A d) SUSY/ (A d) SM (%)

(b)

DIS-Parity requires a factor of 5-10 improvement In δA/A to be competitive with Qweak, Møller

No 1-4sin2θW suppression of APV

20 15 10 5 0 5 10 2

1.5

1

0.5

0

0.5

1

(QWe )

SUSY/(Q

We )

SM (%)

(A

d) SU

SY/ (

Ad) S

M

(%

)

(a)

15 10 5 0 5 10 15 2

1.5

1

0.5

0

0.5

1

(QWp )

SUSY/(Q

Wp )

SM (%)

(A

d) SU

SY/ (

Ad) S

M

(%

)

(b)

1.0%


!"

#$%

&+

+'=)()(

)(154)2(

103)( 11 xdxu

xsCCxa du

Parity Violating Electron DIS

[ ])()()(2

2

xbyfxaQGA FPV +=

!"

)()()( 2

1

xqQxqQCxa

ii

iii=)()()( 2

2

xqQxqQCxb

ii

iii=

iV

eAi ggC 21 ! i

AeVi ggC 22 !

e-

N X

e-

Z* * EEy /1 !"#Bjorkenxx !

!"

#$%

&++'=

)()()()()2(

103)( 22 xdxu

xdxuCCxb VVdu

as x gets large, the sea is negligible

For an isoscalar target like 2H, structure functions largely cancel in the ratio:


[ ])2(103)( 11 du CCxa !=

New Physics: measuring sin2(qW)

[ ])2(103)( 22 du CCxb !=

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

Hall C “Standard”

Upgrade


What happened to NuTeV?

Hall C “Standard”

Upgrade

NuTeV result on sin2qW is 3s from standard model… why isn’t everyone more excited?

Various problems in interpretation, mostly in the hadronic physics…

PV-DIS will have the same problem! Too bad if you want to test the Standard Model…

…but very cool if you like hadronic physics!

PV-DIS Standard Model test interpretation might be “clouded” by:

•  Isospin-symmetry violation for PDFs •  Contributions from higher twist

The silver lining: one can study the clouds!


In principle, PV-DIS is sensitive to: •  Contributions from higher twist •  Isospin-symmetry violation for PDFs •  d/u PDF ratio as x->1 •  Nuclear effects (parton shadowing, EMC, ….)

PV-DIS and hadronic physics

What is needed: •  Large kinematic range (Q2 range at fixed, moderate xBj) •  Large acceptance •  High luminosity •  Excellent background suppression


Higher Twist Coefficients in parity conserving (Di) and nonconserving (Ci) Scattering

F2(x,Q2) = F2(x)(1+ D(x) /Q2)

Evolves according To DGLAP equations

Higher Twist is what is left over

APV (x,Q2) = APV (x)(1+ C(x) /Q2)

(Does not Evolve)

Higher Twist is any Q2-dependent deviation From the SM prediction

!"

#$%

&+

+'=)()(

)(154)2(

103)( 11 xdxu

xsCCxa du !"

#$%

&++'=

)()()()()2(

103)( 22 xdxu

xdxuCCxb VVdu

Remember: for 2H at moderate x, structure functions largely cancel in APV


Interpretation of Higher Twist

•  APV sensitive to diquarks: ratio of weak to electromagnetic charge depends on amount of coherence

•  Do diquarks have twice the x of single quarks? •  If Spin 0 diquarks dominate, likely only 1/Q4

effects

Clean observation of a higher twist operator may be possible.


Probing Higher Twist with PVeS

Sacco, R-M preliminary

APV Q2

y

Looking beyond the parton description PV Deep Inelastic eD (J Lab 12 GeV)

~0.4%

E=11 GeV q=12.50

Different PDF fits

x ~ 0.2

Slide from Ramsey-Mulsolf


Higher Twist unlikely at (moderately) low x, possible at high x

x D(x) Q2min D/Q2

min(%)

LO NNNLO LO NNNLO

0.1-0.2 -.007 0.01 0.5 -14 2

0.2-0.3 -.11 0.003 1.0 -11 0.0

0.3-0.4 -.06 -0.01 1.7 -3.5 -0.5

0.4-0.5 .22 0.11 2.6 8 4

0.5-0.6 .85 0.39 3.8 22 10

0.6-0.7 2.6 1.4 5.8 45 24

0.7-0.8 7.3 4.4 9.4 78 47

F2(x,Q2)=F2(x)(1+D(x)/Q2) Q2=(W2-M2)/(1/x-1) Q2min=Q2(W=2)

If C(x) acts like D(x), PVeS might show higher twist at high x without needing QCD evolution.

MRST ‘04


Charge Symmetry Violation

)()()()(xuxd

xdxunp

np

==

)()()()()()(xuxdxd

xdxuxunp

np

!=!=

""

Charge symmetry

quark mass difference: n-p mass difference:

Charge symmetry Violation (CSV)

Sather: Analytic Quark Model Approximation for Valence Parton CSV.

Leads to analytic results (model-dependent)

Londergan,Murdock,Thomas hep-ph/0603208 MRST, Eur.Phys.J. 39, 155 (05); Glueck, Jimenez-Delgado, Reya, PRL95, 022002 (05)

Contributes even if mu = md and Mn= Mp •  add to quark model CSV term •  MRST incorporate QED splitting with PDFs in global fit to high energy data

Figures from T.Londergan -0.01

-0.005

0

0.005

0.01

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x

Q2 = 10 GeV2

x uv

x dv

QEDbagQEDbag

“QED Splitting”


Phenomenological Parton CSV PDFs MRST PDFs from global fits include CSV for 1st time: Martin, Roberts, Stirling, Thorne [Eur Phys J C35, 325 (04)]:

Choose restricted form for parton CSV:

Best fit: κ = -0.2, large uncertainty ! Best fit remarkably similar to quark model CSV calculations

MRST (2004) ADEL (1994)

[f(x): 0 integral; matches to valence PDFs at small, large x]

90% conf limit (κ)

Slide from T.Londergan


Search for CSV in PV DIS

Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as x 1

Strategy: •  constrain higher twist effects at x ~ 0.5 - 0.6 •  precision measurement of APV at x → 0.7 to search for CSV

• Direct observation of parton-level CSV would be very exciting! • Important implications for high energy collider pdfs • Could explain significant portion of the NuTeV anomaly

For APV in electron-2H DIS: dudu

AAPV

PV

+!= """ 3.0

MRST fit suggests ~1% effect at x = 0.7

(QED + bag) says ~6% effect!


APV in DIS on 1H

APV = GFQ2

2!"a(x) + f (y)b(x)[ ]

a(x) = u(x) + 0.91d(x)u(x) + 0.25d(x)

Strategy: •  Determine that higher twist is under control •  Determine standard model agreement at low x •  Obtain high precision at high x

Allows d/u measurement on a single proton!

a(x) = 322C1uu(x) !C1d (d(x) + s(x))

4u(x) + d(x) + s(x)" # $

% & '

b(x) = 322C2uuv (x) !C2d dv (x)4u(x) + d(x) + s(x)

" # $

% & '

+ small corrections


d/u at High x

Deuteron analysis has nuclear corrections

APV for the proton has no such

corrections

Must simultaneously constrain higher twist effects!

The challenge is to get statistical and systematic errors ~ 2%


Scorecard

x y Q2 p d

Higher twist Yes No Yes X

Isospin Yes? No No X

d/u Yes No No X

New Physics No Yes No X


Coherent PV DIS Program (Including 12 GeV)

•  Hydrogen and Deuterium targets •  Better than 2% errors •  x-range 0.25-0.75 •  W2 well over 4 GeV2 •  Q2 range a factor of 2 for each x point

–  (Except x~0.75) •  Moderate running times

• With HMS/SHMS: search for TeV physics • With larger solid angle apparatus: higher twist, CSV, d/u…

EMC effect in PVeS

Cross section data from J. Gomez et.al. PRD 49 (1994) 4348

This study might be done with

8.5 GeV beam, 50 µa beam

50 days running. Targets:

15 cm LD2 0.17 mm Fe Targets 1% RL C12 Targets


Summary and Outlook •  Parity-Violating DIS can probe exciting new physics at high x •  One can start now (at 6 GeV)

–  Do 2 low Q2 points (P-05-007, X. Zheng contact) •  Q2 ~ 1.1 and 1.9 GeV2 •  Either bound or set the scale of higher twist effects

–  Take data for W<2 (P-05-005, P. Bosted contact) •  Duality •  Could help extend range at 11 GeV to higher x

•  Probe TeV physics in PV DIS off 2H: Hall C at 12 GeV

•  The bulk of this coherent program requires a dedicated spectrometer/detector •  Higher twist must be controlled (or exploited) •  CSV can be probed at high x •  Standard Model test is interpretable when coupled with hadronic studies •  Uniquely clean d/u at high x •  EMC effect in PVeS •  Additional physics topics could be addressed by dedicated spectrometer

–  Transverse (beam-normal) asymmetries in DIS –  Polarized targets: g2 and g3 structure functions


0.4<y<0.8, E’<7GeV

•  Large range in Q2 for HT study •  High x (>0.7) accessible with W2>4 •  Large acceptance allows feasible runtime requests •  p/e ratio is not extreme, but cannot integrate

Details on Kinematics

0.4<y<0.8, E’<5GeV

Solenoid SHMS


0.4<y<0.8, E’<7GeV

•  Large range in Q2 for HT study •  High x (>0.7) accessible with W2>4 •  Large acceptance allows feasible runtime requests •  p/e ratio is not extreme, but cannot integrate

Details on Kinematics and π/e Ratio

0.4<y<0.8, E’<5GeV

Solenoid SHMS


Exp. Constraints on C1u, C1d, C2u and C2d

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

From P. Reimer, describing PV-DIS possible with “standard” upgrade


Reaching Large x at 11 GeV

22

/

48.06.0

44020

GeVWyGeVE

><<

<<< !

50% azimuthal coverage assumed

6 GeV

Need Large θ for large x and Q2

HMS and SHMS are fine for

small θ

(and large y)

W<2


• 2 to 3.5 GeV scattered electrons • 20 to 40 degrees • Factor of 2 in Q2 range at moderate x • High statistics at x=0.7, with W>2

Range of W and Q2


Charge Symmetry Violation

)()()()(xuxd

xdxunp

np

==

)()()()()()(xuxdxd

xdxuxunp

np

!=!=

""

Charge symmetry

We know the origins of parton CSV: o  quark mass difference:

o  n-p mass difference:

Charge symmetry Violation (CSV)

Sather: Analytic Quark Model Approximation for Valence Parton CSV.

Leads to analytic results (model-dependent)


MRST, Eur.Phys.J. 39, 155 (05); Glueck, Jimenez-Delgado, Reya, PRL95, 022002 (05)

“QED evolution”, quark radiates photon Evolve in Q2

•  qualitatively similar to quark model CSV •  QED varied while quarks “frozen” •  contributes even if mu = md and Mn= Mp •  add to quark model CSV term à •  increase CSV ~ factor 2 •  MRST incorporate QED splitting with PDFs in global fit to high energy data

-0.01

-0.005

0

0.005

0.01

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x

Q2 = 10 GeV2

x uv

x dv

QEDbagQEDbag

Slide from T.Londergan

“QED Splitting”: a New Source of Isospin Violation

dis-parity 12 gev - university of...

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