DISParity 12 GeV

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DIS-Parity 12 GeV

• Physics opportunities in PVeS
• with a Solenoidal Spectrometer

Kent Paschke University of Massachusetts
Many slides liberated from P. Souder, K. Kumar
( and their sources)
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PV Asymmetries
Weak Neutral Current (WNC) Interactions at Q2 ltlt
MZ2
Longitudinally-Polarized Electrons Scattering off
Unpolarized Fixed Targets
(gAegVT ? gVegAT)

• 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

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PVeS and Physics Beyond the SM Qweak and Møller
Kurylov, Ramsey-Musolf, Su
To be relevant, new SM tests must have
small enough errors to show up on plots like this
Examples
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Add DIS-Parity
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DIS-Parity requires a factor of 5-10
improvement In dA/A to be competitive with Qweak,
Møller
No 1-4sin2?W suppression of APV
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Parity Violating Electron DIS
e-
e-
?
Z
X
N
For an isoscalar target like 2H, structure
functions largely cancel in the ratio

as x gets large, the sea is negligible

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New Physics measuring sin2(qW)
Note that each of the Ciq are sensitive to
different possible S.M. extensions.
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Exp. Constraints on C1u, C1d, C2u and C2d
From P. Reimer, describing PV-DIS possible with
standard upgrade
Combined result significantly constrains
2C2uC2d. PDG 2C2uC2d 0.08 0.24 Combined
d(2C2uC2d) 0.014
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What happened to NuTeV?
NuTeV result on sin2qW is 3s from standard
model why isnt 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!
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PV-DIS and hadronic physics

• In principle, PV-DIS is sensitive to
• Contributions from higher twist
• Isospin-symmetry violation for PDFs
• d/u PDF ratio as x-gt1
• Nuclear effects (parton shadowing, EMC, .)

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

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Higher Twist Coefficients in parity conserving
(Di) and nonconserving (Ci) Scattering
Evolves according To DGLAP equations
Higher Twist is what is left over
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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.
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Probing Higher Twist with PVeS
x 0.2
Slide from Ramsey-Mulsolf
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Higher Twist unlikely at (moderately) low x,
possible at high x
Q2(W2-M2)/(1/x-1)
Q2minQ2(W2)
F2(x,Q2)F2(x)(1D(x)/Q2)
MRST 04
If C(x) acts like D(x), PVeS might show higher
twist at high x without needing QCD evolution.
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Charge Symmetry Violation
Charge symmetry
Charge symmetry Violation (CSV)
Sather Analytic Quark Model Approximation for
Valence Parton CSV.
Leads to analytic results (model-dependent)
QED Splitting
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
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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
90 conf limit (?)
f(x) 0 integral matches to valence PDFs at
small, large x
Best fit ? -0.2, large uncertainty ! Best fit
remarkably similar to quark model CSV
calculations
ADEL (1994)
MRST (2004)
Slide from T.Londergan
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Search for CSV in PV DIS

• 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
Sensitivity will be further enhanced if ud falls
off more rapidly than ?u-?d as x ? 1
(QED bag) says 6 effect!
MRST fit suggests 1 effect at x 0.7

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

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APV in DIS on 1H
small corrections
Allows d/u measurement on a single proton!

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

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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
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Scorecard
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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 x0.75)
• Moderate running times

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

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EMC effect in PVeS
This study might be done with 8.5 GeV beam, 50 µa
beam
Cross section data from J. Gomez et.al. PRD 49
(1994) 4348
50 days running. Targets 15 cm LD2 0.17 mm Fe
Targets 1 RL C12 Targets
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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 Wlt2 (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

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Details on Kinematics
Solenoid
SHMS
0.4ltylt0.8, Elt7GeV
0.4ltylt0.8, Elt5GeV

• Large range in Q2 for HT study
• High x (gt0.7) accessible with W2gt4
• Large acceptance allows feasible runtime
  requests
• p/e ratio is not extreme, but cannot integrate

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Details on Kinematics and p/e Ratio
Solenoid
SHMS
0.4ltylt0.8, Elt7GeV
0.4ltylt0.8, Elt5GeV

• Large range in Q2 for HT study
• High x (gt0.7) accessible with W2gt4
• Large acceptance allows feasible runtime
  requests
• p/e ratio is not extreme, but cannot integrate

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Reaching Large x at 11 GeV
Wlt2
Need Large ? for large x and Q2
(and large y)
6 GeV
HMS and SHMS are fine for small ?
50 azimuthal coverage assumed
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Range of W and Q2

• 2 to 3.5 GeV scattered electrons
• 20 to 40 degrees
• Factor of 2 in Q2 range at moderate x
• High statistics at x0.7, with Wgt2

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Charge Symmetry Violation
Charge symmetry
Charge symmetry Violation (CSV)
Sather Analytic Quark Model Approximation for
Valence Parton CSV.
Leads to analytic results (model-dependent)
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QED Splitting a New Source of Isospin Violation
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 ?
• increase CSV factor 2
• MRST incorporate QED splitting with PDFs
• in global fit to high energy data

Slide from T.Londergan