Parity and the JLab 12 GeV Upgrade: The Program for Hall A

1
Parity and the JLab 12 GeV UpgradeThe Program
for Hall A

• Hadronic and Electroweak Physics
• Moller and DIS Parity

Thanks to Bosted, Brodsky, Kumar, Londergan,
Meziani, Michaels, Reimer, Ramsey-Musolf, Paschke
, Pitt, Zheng
P. A. Souder Syracuse University
2
Outline

• Parity-Violating Electron Scattering
• Brief Overview
• Weak Neutral Current Interactions at Q2ltltMZ2
• Parity-Violating Møller Scattering
• Ultimate Precision at Q2ltltMZ2 25 TeV Reach
• Complementary to Qweak
• Parity-Violating Deep Inelastic Scattering
• New Physics at 10 TeV in Semileptonic Sector
• Charge Symmetry Violation
• d/u at High x
• Higher Twist Effects

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PV Asymmetries
Weak Neutral Current (WNC) Interactions at Q2 ltlt
MZ2
Longitudinally Polarized Electron Scattering off
Unpolarized Fixed Targets
(gAegVT ? gVegAT)

• The couplings g depend on electroweak physics as
  well as on the weak vector and axial-vector
  hadronic current
• With specific choice of kinematics and targets,
  one can probe new physics at high energy scales
• With other choices, one can probe novel aspects
  of hadron structure

4
APV Measurements
APV
to
0.1 to 100 ppm

• Steady progress in technology
• part per billion systematic control
• 1 normalization control
• JLab now takes the lead
• New results from HAPPEX
• Photocathodes
• Polarimetry
• Targets
• Diagnostics
• Counting Electronics

E-05-007
e2e
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The Standard Model
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The Annoying Standard Model
(it just wont break!)
Nuclear Physics Long Range Plan What is the new
standard model?
Low Q2 offers unique and complementary probes of
new physics

• Rare or Forbidden Processes
• Symmetry Violations
• Electroweak One-Loop Effects

- Double beta decay.. - neutrinos, EDMs.. - Muon
g-2, beta decay..
Input
G0
Output

• Precise predictions at level of 0.1
• Indirect access to TeV scale physics
• Extra probe of hadrons

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World Electroweak Dataon sin2?W
Most experts see the precision data as
remarkably consistent
Perhaps there are bigger deviations lurking
elsewhere???
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Electroweak Physics at Low Q2
Q2 ltlt scale of EW symmetry breaking
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WNC Low Q2 Processes

• Limited by theory Atomic structure Neutron Halo

• PV DIS experiment feasible within scope of
  HMS/SHMS upgrade
• Unique, complementary probes of New Physics
• Theoretical issues are interesting in themselves

• Reactor experiment cannot do better than SLAC
  E158
• Dedicated new apparatus at upgraded JLab can do
  significantly better

Best low energy measurement until Linear Collider
or ?-Factory
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Fixed Target Møller Scattering
Purely leptonic reaction Weak charge of the
electron QWe 1 - 4sin2?W
Unprecedented opportunity The best precision at
Q2ltltMZ2 with the least theoretical uncertainty
until the advent of a linear collider or a
neutrino factory
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Present Results and Future Experiments
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Qeweak Electron Weak Charge SLAC E158
Experiment
Parity-violating Moller scattering Q2 .026 GeV2
? 4 7 mrad E 48 GeV at SLAC End Station A
Final results hep-ex/0504049 APV -131 ? 14
(stat) ? 10 (syst) ppb
sin2?eff(Q20.026 GeV2) 0.2397 0.0010
0.0008 Running of sin2?eff established at 6?
level in pure leptonic sector
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Design for 12 GeV
APV 40 ppb
E 3-6 GeV
?lab 0.53o-0.92o
150 cm LH2 target
Ibeam 90 µA

• Beam systematics steady progress
• (E158 Run III 3 ppb)
• Focus alleviates backgrounds
• ep ? ep(?), ep ? eX(?)
• Radiation-hard integrating detector
• Normalization requirements similar
• to other planned experiments
• Cryogenics, density fluctuations
• and electronics will push the state-
• of-the-art

Mack, Reimer, at al
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New Physics Reach
JLab Møller
?ee 25 TeV
New Contact Interactions
LEP200
Kurylov, Ramsey-Musolf, Su
?ee 15 TeV
Examples
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The Qweak Apparatus (Calibration Mode Only -
Production Calibration Modes)
Quartz Cherenkov Bars (insensitive to
non-relativistic particles)
Region 2 Horizontal drift chamber location
Region 1 GEM Gas Electron Multiplier
Mini-torus
e- beam
Ebeam 1.165 GeV Ibeam 180 µA Polarization
85 Target 2.5 KW
Lumi Monitors
QTOR Magnet
Region 3 Vertical Drift chambers
Collimator System
Trigger Scintillator
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Qpweak Qeweak Complementary Diagnostics for
New Physics
JLab Qweak
SLAC E158
-
(proposed)
Run I II III (preliminary) 0.006

• Qweak measurement will provide a stringent
  stand alone constraint
• on Lepto-quark based extensions to the SM.
• Qpweak (semi-leptonic) and E158 (pure
  leptonic) together make a
• powerful program to search for and identify
  new physics.

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Running coupling constants in QED and QCD
QCD(running of ?s)
QED (running of ?)
137 ?
?s
What about the running of sin2?W?
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Running of sin2?W
QWe modified
sin2?W runs with Q2
?(sin2?W) 0.0003
Comparable to single collider measurements

• JLab measurement would
• have impact on
• discrepancy between
• leptonic and hadronic Z-pole
• measurements

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Parity Violation in Deep Inelastic Scattering
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Electron-Quark Phenomenology
V
A
A
V
C1u and C1d will be determined to high precision
by Qweak, Cs
C2u and C2d are small and poorly known one
combination can be accessed in PV DIS
New physics such as compositeness, new gauge
bosons
Deviations to C2u and C2d might be fractionally
large
Proposed JLab upgrade experiment will improve
knowledge of 2C2u-C2d by more than a factor of 20
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Parity Violating Electron DIS
e-
e-
?
Z
X
N
fi(x) are quark distribution functions
For an isoscalar target like 2H, structure
functions largely cancel in the ratio
Provided Q2 gtgt 1 GeV2 and W2 gtgt 4 GeV2 and x
0.2 - 0.4
Must measure APV to fractional accuracy better
than 1

• 11 GeV at high luminosity makes very high
  precision feasible
• JLab is uniquely capable of providing beam of
  extraordinary stability
• Systematic control of normalization errors being
  developed at 6 GeV

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2H Experiment at 11 GeV
E 5.0 GeV 10
?lab 12.5o
60 cm LD2 target
Ibeam 90 µA

• Use both HMS and SHMS to increase solid angle
• 2 MHz DIS rate, p/e 2-3

APV 217 ppm
xBj 0.235, Q2 2.6 GeV2, W2 9.5 GeV2

• Advantages over 6 GeV
• Higher Q2, W2, f(y)
• Lower rate, better p/e
• Better systematics 0.7

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Physics Implications
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Why should we believe DISparitywhen no one
Believes NuTeV?
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Measuring sin2?W with NuTeV
Paschos Wolfenstein ( PR D7, 91 (73)) PW
ratio ? minimizes sensitivity to PDFs,
higher-order corrections
Result is off by 2.8 s
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The NuTeV Experiment
Features very large kinematic acceptance
µ
Charged current
Neutral current
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Assumptions for the Paschos-Wolfenstein Ratio

• PW Ratio depends on the following assumptions
• Isoscalar target (NZ)
• include only light (u, d) quarks
• neglect heavy quark masses
• assume isospin symmetry for PDFs
• no nuclear effects (parton shadowing, EMC, .)
• no higher twist effects
• radiative corrections OK? (?-W boxes?)
• no contributions outside Standard Model

JLab 12 GeV issues
Nobody believes that this is the problem
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PV DIS can Address Issues Raised by NuTeV

• Analysis assumed control of QCD uncertainties
• Higher twist effects
• Charge Symmetry Violation (CSV)
• d/u at high x
• NuTeV provides perspective
• Result is 3? from theory prediction
• Generated a lively theoretical debate
• Raised very interesting nucleon structure issues
  cannot be addressed by NuTeV
• JLab at 11 GeV offers new opportunities
• PV DIS can address issues directly
• Luminosity and kinematic coverage
• Outstanding opportunities for new discoveries
• Provide confidence in electroweak measurement

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Search for CSV in PV DIS

• 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

Sensitivity will be further enhanced if ud falls
off more rapidly than ?u-?d as x ? 1
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Phenomenological Parton CSV PDFs
MRST Phenomenological PDFs include CSV for 1st
time Martin, Roberts, Stirling, Thorne (03)
Choose restricted form for parton CSV
90 conf limit (?)
f(x) 0 integral matches to valence at small,
large x
Best fit ? -0.2, large uncertainty ! Best fit
remarkably similar to model CSV predictions
ADEL
MRST
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Higher Twist Coefficients in parity conserving
(Di) and nonconserving (Ci) Scattering
(Does not Evolve)
?

• APV sensitive to diquarks ratio of weak to
  electromagnetic charge depends on amount of
  coherence
• If Spin 0 diquarks dominate, likely only 1/Q4
  effects
• Some higher twist effects may cancel in ratio, so
  APV may have little dependence on Q2.

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Going from LO to NNNLO Greatly Reducesthe
Extracted Higher Twist Coefficients
F2(x,Q2)F2(x)(1D(x)/Q2)
Q2(W2-M2)/(1/x-1)
Q2minQ2(W2)
If D(x)C(x), Parity might show higher twist At
high x without needing QCD evolution.
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APV in DIS on 1H
small corrections

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

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

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Uncertainties in d/u at High x, and the Errors we
Would Like to Achieve with PV Measurements
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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Complete PV DIS Program (Including 12 GeV)

• Hydrogen and Deuterium targets
• Better than 2 errors
• It is unlikely that any effects are larger than
  10
• x-range 0.25-0.75
• W2 well over 4 GeV2
• Q2 range a factor of 2 for each x point
• (Except x0.7)
• Moderate running times

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

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Apparatus Needed for PVDIS
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E05-007 Start PVDIS at 6 GeV (Approved)
R. Michaels (JLab), P. Reimer (ANL), X. Zheng
(ANL) and the Hall A Collaboration

• Asymmetry to be measured

• Experimental Setup
• 85uA, 6 GeV, parity-quality 80 pol. beam
• 25-cm LD2 target
• Two HRS detect scattered electrons.

• Measure Ad at Q21.10 and Q21.90 (GeV/c)2 to 2
  (stat.)

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Goals at 6 GeV

• From Ad at Q21.90 (GeV/c)2, can extract
  (2C2u-C2d) to an uncertainty of 0.03 (factor of 8
  improvement compared to PDG)
• provide constraints on new physics test of the
  Standard Model up to 1 TeV mass limit
• Z' Searches
• Compositeness (4-fermion contacts)
• Leptoquarks.

• The Ad at Q21.10 (GeV/c)2 will help to
  investigate if there are significant hadronic
  (higher-twist) effects (12 GeV, NuTeV...)

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Reaching Large x and Large Q2 at 12 GeV
Need Large ? for large x and Q2
6 GeV
HMS and SHMS are fine for small ?
50 azimuthal coverage assumed
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• 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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Details on Kinematics and p/e Backgrounds
Cut on 0.6ltylt0.8

• 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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Large Angle Large Acceptance Concept

• CW 90 µA at 11 GeV
• 40-60 cm liquid H2 and D2 targets
• Luminosity gt 1038/cm2/s

JLab Upgrade
Need toroid to block ?s and low energy ps
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d/u Measurements for Proton
(Kent Paschke simulation)
A couple weeks of beam time with toroid
spectrometer
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What Physics is Allowed by New Device?
Example d/u of Proton
Compare MAD Spectr. to Toroid Spectr.
Curves from Melnithouk and Thomas
d/u
off shell
on shell
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EMC effect in Parity Violation ?
Cross section data from J. Gomez et.al. PRD 49
(1994) 4348
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High x Physics Outlook Context

• 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
• A short run to probe TeV physics in PV DIS off
  2H Hall A or C
• The bulk of the program requires a dedicated
  spectrometer/detector
• CSV can also be probed via electroproduction of
  pions
• 6 GeV beam can probe x 0.45 (P-05-006, K.
  Hafidi contact)
• Should be able to go to higher x with 12 GeV beam
• Other vital physics topics could be addressed by
  dedicated spectrometer
• Transverse (beam-normal) asymmetries in DIS
• Polarized targets g2 and g3 structure functions
• Higher twist studies of A1p and A1n

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Summary

• 12 GeV Upgrade
• Opens unique opportunities for new PV
  measurements
• Hall configuration must support dedicated
  apparatus
• Large solid angle toroid/calorimeter for PV DIS
• Superconducting solenoid for Møller scattering
• Physics Highlights
• Unique Standard Model tests
• Unique, clean d/u for proton
• Test Charge Symmetry at the Quark level
• Observe clean higher twist effects
• New probe for EMC effect?

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Future Directions for PV Moller and APV
e2ePV Parity-Violating Moller scattering at 12
GeV JLAB (Mack, Reimer, et al.)

• Achieve Moller focus with long, narrow
  superconducting toroidal magnet,
• Radiation hard detector package
• E 12 GeV Q2 .008 GeV2 ,
• ? .53 - .92o , APV - 40 ppb
• In 4000 hours, could determine QeW to 2.5
• (compare to 12.4 for E158)

Atomic Parity Violation Future Directions

• Paris group (Bouchiat, et al.) more precise Cs
  APV
• Seattle group (Fortson, et al.) single trapped
  Ba APV 6S1/2 ? 5D3/2
• Berkeley group (Budker, et al.) isotope ratios
  in Yb APV
• Stony Brook group (Orozco, et al.) isotope
  ratios in Fr APV
• Note isotope ratios can eliminate large atomic
  structure theory uncertainties

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Overview of the QpWeak Experiment
Experiment Parameters (integration mode)
Incident beam energy 1.165 GeV Beam Current
180 µA Beam Polarization
85 LH2 target power 2.5 KW
Central scattering angle 8.4
3 Phi Acceptance
53 of 2p Average Q²
0.030 GeV2 Acceptance averaged
asymmetry 0.29 ppm Integrated Rate (all
sectors) 6.4 GHz Integrated Rate (per
detector) 800 MHz
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Running of sin2?W Current Status and Future
Prospects
12 GeV QW (e)
present d-quark dominated Cesium APV (QAW)
SM running verified at 4? level pure lepton
SLAC E158 (QeW ) SM running verified
at 6? level
future u-quark dominated Qweak (QpW)
projected to test SM running at 10? level pure
lepton12 GeV e2ePV (QeW ) projected to test
SM running at 25 ? level
51
Comparing Qwe and QWp
JLab at 12 GeV will do a factor of about 5 better!
Erler, Kurylov, R-M
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The Qweak Experiment
53
New Physics Reach
JLab Møller
?ee 25 TeV
New Contact Interactions
LEP200
?ee 15 TeV
Kurylov, Ramsey-Musolf, Su
95 C.L. JLab 12 GeV Møller
Examples
54
Relative Shifts in Proton and Electron Weak
Charges due to SUSY Effects
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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
56
EMC Effect ?
50 days running. 15 cm LD2 0.17 mm Fe
Targets
A(Fe)/A( H)
2
Ratio of Asymmetries (Iron to Deuterium)
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A Concept for PV DIS Studies

• Magnetic spectrometer
• would be too expensive
• Calorimeter to identify
• electron clusters and reject
• hadrons a la A4 at Mainz
• Toroidal sweeping field to
• reduce neutrals, low energy
• Mollers and pions
• Cherenkov detectors for pion
• rejection might be needed

• CW 100 µA at 11 GeV
• 20 to 40 cm LH2 and LD2 targets
• Luminosity gt 1038/cm2/s

• solid angle gt 200 msr
• Count at 100 kHz
• pion rejection of 102 to 103

58
APV Measurements
APV
to
0.1 to 100 ppm

• Steady progress in technology
• part per billion systematic control
• 1 normalization control
• JLab now takes the lead
• New results from HAPPEX
• Photocathodes
• Polarimetry
• Targets
• Diagnostics
• Counting Electronics

E-05-007
59
EMC Effect ?
50 days running. 15 cm LD2 1 RL C12 Targets
2
12
A( C)/A( H)
Ratio of Asymmetries (Carbon to Deuterium)
60
Parity Violation at Jlab

• Electron Beam Quality
• Simple laser transport system pioneers in PV
  experiments with high polarization cathodes
  (HAPPEX-I)
• CW beam alleviates many higher order effects
  especially in energy fluctuations
• HAPPEX-II preliminary result Araw correction
  60 ppb
• High Luminosity
• High beam current AND high polarization
• Dense cryogenic targets with small density
  fluctuations
• Progression of Precision Experiments
• Facilitates steady improvements in technology
• Strong collaboration between accelerator and
  physics divisions

?(APV)/APV ?1
?(APV) ?1 part per billion