Parity Violation in Deep Inelastic Scatteringpeople.virginia.edu/~kdp2c/pubpage/talkarchive/Spin08_Paschke... · Parity Violation in Deep Inelastic Scattering ... SUSY RPV SUSY 12

Parity Violation in Deep Inelastic

Scattering

Kent Paschke

Figures and slides from E. Chudakov, K.Kumar, T. Londergan, P. Souder, X.Zheng

Kent Paschke SPIN ’08 October 9, 2008

• The couplings gT depend on electroweak physics as well as on the weak vector and axial-vector hadronic current • For PVDIS, 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

Weak Neutral Current (WNC) Interactions at Q2 << MZ2

Longitudinally Polarized Electron Scattering off

Unpolarized Fixed Targets

PV Asymmetries

! = |M! + MZ |2

APV =!L ! !R

!L + !R" MZ

M!" GF Q2

4 " #

!ge

AgTV + $ge

V gTA

"


e-

NX

e-

Z* γ*

fi(x) are quark distribution functions

PV in Deep Inelastic Scattering

A

V

V

A


e-

NX

e-

Z* γ*

fi(x) are quark distribution functions

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

Above x~0.5, APV/Q2 becomes independent of x, W, and depends only on y

Deuterium PVDIS

a(x) =310

!2C1u

"1 +

2c+

u+ + d+

#!C1d

"1 +

2s+

u+ + d+

#+ · · ·

$

b(x) =310

[2C2u !C2d]!

u! ! d!

u+ + d+

"+ · · ·


Fundamental Parameters in PVDISAPV !

3GF Q2

10"

2!"[(2C1u #C1d) + f(y)(2C2u #C2d)]

2C2u !C2d

2C1u !C1d" 0.136

Isovector weak charge

Isos

cala

r wea

k ch

arge

Young et. al

C1u and C1d will be determined to high

precision by Qweak, Cs

C2u and C2d are small and poorly known,combination accessible in PV DIS

Useful precision on C2‘s requires dA/A~0.5%

X. Zheng, 2008 Hall C Summer Workshop

Current Knowledge on C1,2q

MIT/ Bates

SLAC/Prescott

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

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

C1u

+C1d

Tl APV

Qweak (expected)

Figure from X.Zheng


Comprehensive Search for New Neutral Current Interactions

�

Lf1 f2= 4π

Λ ij2 ηij

i, j= L ,R∑ f 1iγµ f1i f 2 jγ

µ f2 j

Consider

�

f1 f 1 → f2 f 2

�

f1 f2 → f1 f2or Λ’s for all f1f2 combinations and L,R combinations

Eichten, Lane and Peskin, PRL50 (1983)

Many new physics models give rise to neutral ‘contact’ (4-Fermi) interactions: Heavy Z’s, compositeness, extra dimensions…

Important component of indirect signatures of “new physics”

One goal of neutral current measurements at low energy AND colliders: Access Λ > 10 TeV for as many f1f2 and L,R combinations as possible

Covers a unique corner of parameter space, and is a

crucial component of a comprehensive search for

new physics

RPC SUSY

RPV SUSY 12 GeV

Møller

PVDIS


Sensitivity to QCD and Nucleon Structure

NuTeV result on Paschos-Wolfenstein ratio deviates from SM expectation; suspicion focuses on hadronic and

nuclear effects

Electroweak studies in nuclear systems require control of QCD effects

Sensitivities to QCD or hadronic/nuclear structure provide an opportunity to study:

• partonic charge symmetry violation• higher twist

The well-defined kinematics of electron scattering provide an advantage


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

• u-d mass difference• electromagnetic effects

• 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:

Search for CSV in PV DIS

!APV

APV! 0.28

!u" !du + d


MRST Phenomenological PDFs (2004)include CSVMartin, Roberts, Stirling, Thorne (03):

Chose restricted form for parton CSV:

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

CSV predictions

MRST ADEL

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

90% conf limit (κ)

Bag model

Phenomenological Parton CSV PDFs

Slide from T.Londergan


Effects at high-x are predicted to be very large, but Q2 evolution not predicted

from Londergan, using MRST fit

RC

SV [

%]

CSV and PV-DIS

x

RC

SV

x

δd

δu

bag model (solid) Radionov et al.QED splitting (dashed) Glueck et al.

x


(Does not Evolve)

Evolves accordingTo DGLAP equations

Higher Twist iswhat is left over

Higher Twist is anyQ2-dependent deviationFrom the SM prediction

Higher Twist Coefficients


x D(x) D(x) Q2min D/Q2

min(%) D/Q2min(%)

LO NNNLO LO NNNLO

0.1-0.2 -0.007 0.001 0.5 -14 2

0.2-0.3 -0.11 0.003 1.0 -11 0.0

0.3-0.4 -0.06 -0.001 1.7 -3.5 -0.5

0.4-0.5 0.22 0.11 2.6 8 4

0.5-0.6 0.85 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)

PV-DIS might show higher twist at high x without needing QCD evolution.

MRST, PLB582, 222 (04)

Higher Twist Coefficients Large at High x


Observing a clean higher twist operatormay become very interesting.

Interpretation of Higher Twist

• Many higher twist effects will cancel in ratio • APV sensitive to diquarks: ratio of weak to electromagnetic

charge depends on amount of coherence• Do diquarks have twice the x of single quarks?

≠+

+


To achieve a high precision constraint on axial-vector quark couplings, first study

hadronic physics

• Measure AD in NARROW bins of x, Q2 with 1% precision

• Cover broad Q2 range for x in [0.3,0.6] to constrain HT• Search for CSV with x dependence of AD at high x

• Use x>0.4, high Q2, and Y dependence to measure C2q’s

Requires precise kinematics and broad range

x y Q2

New Physics no yes no

CSV yes no no

Higher Twist yes no yes

Coherent Program of PV-DIS Study


PVDIS w/ Base Equipment

Prescott et al(SLAC)

PDG Best Fit

Young Full Fit

Sample

6 GeV PVDIS 3% Ad measurement:Bands correspond to central values of either PDG

best fit or Young et al.’s best fit.

StandardModel

SHMS

HMS

Proposal approved for 11 GeV:Factor of ~ 2 to 3 improvement

E08-011: PVDIS off 2H at 6 GeV

• 08-011 provides first look, at x~0.25-0.3

• Insensitive to CSV, HT, but possibly sensitive to the quark sea?

• 11 GeV, allows greater precision at higher x, but doesn’t provide lever arm to fully separate QCD effects


• High luminosity with thick (40 cm) cryotargets• Better than 1% errors• x-range 0.25-0.75• Q2 range a factor of 2 for each x• W2 well over 4 GeV2

• Moderate running times

A Design for Precision PV DIS Physics

A large solenoidal spectrometer works •need BaBar, CDF or CLEOII Solenoid•fast tracking, particle ID and “parity” counting electronics•polarimetry ~ 0.5%


• 20o - 35o, E’~ 1.5 - 5 GeV• δp/p ~ 2% • some regions 10’s of kHz/mm2

• Pion rejection with Cerenkov + segmented calorimeter.• Asymmetric yoke, detectors in magnetic field

Design for PVDIS Physics

Figure from E.Chudakov

trackingE-calgas Cerenkovcollimator


Collimation


Reconstruction

For an idealized solenoid (constant field within, zero field without), two points outside magnet and beam position give analytic expressions for θ, E, zvertex, φ

y

x

End-on view

Beam position Magnet-exit tracker

Last trackerSimulation•Regression training for tracking parameters•radiation in target•slit scattering•simple “chamber resolution” smearing is added

Δp

/p

Δθ/θ

θ, deg θ, deg


Good Resolution Prevents Bin Migration

simulatedSimulated x,

reconstructed Q2, W2


Broad Kinematic Acceptance

Q2 Q2

x x

11 GeV 8.8 GeV

Q2

x

• 11 GeV Solenoid• 8.8 GeV Solenoid• 11 GeV HMS/SHMS

35 days at each energy,

85% pol

Error bars in each

[x,Q2] bin


•Allows d/u measurement on a single proton!•Vector quark current (electron is axial-vector)

+ small corrections

APV in DIS on 1H


Uncertainty in d/u at High x

•LD2 studies can control higher twist, SM coupling

• 35 days on proton can pin d/u at x~0.75

• No nuclear corrections!


OutlookProposed design provides sufficient acceptance, resolution, and shielding for broad PVDIS program• charge symmetry violation• C2q’s and new physics• higher twist and quark correlations• d/u• new structure functions• PV analog of EMC• SIDIS, spin structure fcns

Proposal planned for

Jan ‘09

Fall ’08: INT workshop, Seattle


Design II (very preliminary)

Features:•Simpler Detectors•Better resolution

Double Toroidal Spectrometer

Tracking Chambers

Custom Toroids

Cerenkov

E-cal

Drawbacks:•Reduced coverage•Longer runs

Documents

Parity Violation in Deep Inelastic Scatteringpeople.virginia.edu/~kdp2c/pubpage/talkarchive/Spin08_Paschke... · Parity Violation in Deep Inelastic Scattering ... SUSY RPV SUSY 12