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Kent Paschke
International Workshop on Neutrino Factories, Super Beams and Beta
BeamsJuly 25, 2012
Strangeness Content of the Nucleon
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
“Static” Strange Quarks in the Nucleon
Strange quarks exist in the nucleon at short distance scales.
Momentum ~ 4%
Magnetic moment, charge radiusMass 0-30% ,
Spin 0 - -10%
Strange contributions to nucleon matrix elements
are unsettled
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Strangeness Nucleon Sigma Term The spin-independent neutralino-nucleon
scattering cross section as a function of ΣπN.Strange quarks coupling to the Higgs is much higher than that of the u/d flavors.The spin independent neutralino-
nucleon coupling varies by an order of magnitude depending on the strange condensate of the nucleon
Ellis et al, Phys.Rev. D77 (2008) 065026, arXiv:0801.3656
Dark Matter Searches
= 36 ± 7 MeV
Analyses of experimental data (πN scattering) implied large values of ΣπN ~ 65 MeV-> Large but uncertain σs ~ 350 MeV
σ0 estimated from known SU(3) breaking in the baryon octet: 36 ± 7 MeV
R.D. Young and A.W. Thomas, Nuclear Physics A 844 (2010) 266c
Recent lattice results claim high precision with small values for strange
quark mass contribution 15-60 MeV
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Other Open Questions in Nucleonic Strangeness
NuTeV published a 3σ deviation from the standard model A leading hypothesis is that a signficant fraction is explained by an asymmetry in the strange sea:
NuTeV Anomaly
The spin dependent neutralino-nucleon coupling depends on Δs
Strange SpinOriginally motivated by the “spin problem”, but remains an important question in nucleon structure
Do the strange quarks in the sea play a significant role in the
electric/magnetic charge distributions in the nucleon?
?
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Extracting the Strange Vector Form Factor
Two equations and three unknowns
Measuring all three enables separation of up, down and strange contributions
Measure neutral weak proton vector form-factor
Three equations and three unknowns
The weak form factor is accessible via parity violation
Charge Symmetry
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Strange Form Factors in PVeSγ Z0
γ 2
€
~10−4Q2
GeV2
GsE only!
Spin=0,T=0 (4He):nuclear corrections: forward angle, low Q2 only
Deuterium:Enhanced GA
Back-angle quasi-elastic.
~ few parts per million
Forward angle Backward angle “Anapole” radiative corrections are
problematic
Proton:
p
Asymmetry of longitudinal polarized electron beam from unpolarized target
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
The Axial Term and the Anapole Moment
Axial form-factors GAp, GA
n
• Determined at Q2=0 from neutron and hyperon decay parameters (isospin and SU(3) symmetries)
• Q2 dependence often assumed to be dipole form, fit to ν DIS and π electroproduction
• Includes also Δs, fit from ν-DIS data (with significant uncertainties)
€
˜ G Ap,n = −τ 3 1+ RA
T = 1( )GA
( 3)
+ 3RAT = 0GA
( 8) + Δs
Anapole Moment Correction: Multiquark weak interaction in RA
(T=1), RA
(T=0) Zhu, Puglia, Holstein, Ramsey-Musolf, Phys. Rev. D 62, 033008•Model dependent calculation, with large uncertainty (~30% Model dependent calculation, with large uncertainty (~30% on axial FF)on axial FF)
•Dominates Uncertainty in Axial TermDominates Uncertainty in Axial TermDifficult to achieve tight experimental constraint Difficult to achieve tight experimental constraint Reduced in importance for forward-angle measurementsReduced in importance for forward-angle measurements
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Axial Strange Form-FactorStrange axial form-factor related to integral over spin-dependent strange PDFs via QCD sum rule
Extrapolation of measurements of spin dependent structure functions are ambiguous:
Phys. Rev. D75 012007 (2007)
= −0.085 ± 0.013(th) ± 0.008(exp) ± 0.009(evol) HERMES (inclusive)
= 0.028 ± 0.033(stat) ± 0.009(ev) HERMES (semi-inclusive)
COMPASS (semi-inclusive)~ -0.01 ± 0.012 (exp)
DSSV helicity PDF fit reflects the HERMES SIDIS dominance: positive above x~0.05, with inclusive data dominating at lower xde Florian, Sassot, Stratmann and Vogelsang, Phys. Rev. D80 034030
(2009)
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Neutrino NC elastic measurements for GA
s
G. Garvey et al., Phys. Rev. C48, 761 (1993).
= −0.21 ± 0.10 (exp) ± 0.10 (FF)
Fitting cross-section data from NC scattering in E734
L. A. Ahrens et al., Phys. Rev. D35, 785 (1987).
Very sensitive to Q2 dependence (axial mass MA)
Limited precision and moderately high Q2 reduce precision of bound on
Finesse Would have provided a precise, low Q2 measurement using a ratio of NC and CC quasi-elastic cross-sections, projected
In any case, this is a small contributor to the axial uncertainty due to radiative corrections for the vector strange FF measurements
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Lead - Lucite Cerenkov Shower Calorimeter•phototube current integrated over fixed time periods
Hall A Parity: Integrating in the High Resolution Spectrometers
parts per million
Psuedo-random, rapid helicity flip
Very clean separation ofelastic events by HRS optics
no PID needed; detector sees only elastic events
Elastic
Inelastic
detector
Q Q
Dipole
Quad
target
Techniques for high flux, to get few percent precision on 1-20 parts per million asymmetry
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Experimental Overview
SAMPLE
HAPPEX Precision spectrometer, integrating
A4
open geometry, integrating, back-angle only
Open geometry
Fast counting calorimeter for background rejection
Forward and Backward angles
G0
Open geometry
Fast counting with magnetic spectrometer + TOF for background rejection
Forward and Backward angles over a range of Q2
Forward angle, also 4He at low Q2
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Forward-angle proton scattering
• ANS error: precision of EMFF (including 2γ), Anapole correction, and γZ box diagrams• Using experimental determination for axial form factor would increase total Ans uncertainty about 50%• Additional data at backward angles, and 2H and 4He target
Combining results from forward-angle proton scattering (similar beam energies):
“No net vector strangeness” line
Significant background challenges in G0 measurement
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
World Data at Q2 ~0.1 GeV2
Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account.
For somewhat more careful treatment, see published fits by:R. Gonzalez-Jimenez, J.A. Caballero, T.W. Donnelly, arXiv:1111.6918orR. Young et al., Phys. Rev. Lett 97, 102002 (2006) orJ.Liu et al., Phys. Rev. C 76, 025202 (2007)
~3% +/- 2% of proton magnetic moment
~0.2 +/- 0.5% of Electric FF
95%
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
World data on Gs
all forward-angle proton data
At Q2 ~ 0.1 GeV2, Gs < few percent of Gp
Q2 ~ 0.22 Q2 ~ 0.62
Leading Order Fit
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Simple fit
Fit includes only data Q2 < 0.65 GeV2 G0 Global error allowed to float with unit constraint
Simple fit:
GEs = ρs*τ
GMs = μs
• Simple fit (including all data, even if not shown)• Parameterization doesn’t matter... just “no bumps” • Data consistency is good (~20% confidence level)• Slight positive preference but low statistical significance• Contributions smaller than few percent of proton electric/magnetic form factors
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Parameterizations
Fit includes all world data Q2 < 0.65 GeV2 G0 Global error allowed to float with unit
constraint
GEs = ρs*τ
GMs = μs
GEs = ρs*galster
GMs = μs*dipole
GEs = ρs* τ + a2*τ2
GMs = μs + m2*τ
Models would need “bumps” to find significant strange effects
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Considering only the 4 HAPPEX measurements
• High precision• Small systematic error• ε>0.95 - relatively clean theoretical interpretation
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Model guidance is unclear: kaon loops, vector dominance, Skyrme model, chiral quark model, dispersion relations, NJL model, quark-meson coupling model, chiral bag model, HBChPT, chiral hyperbag, QCD equalities, …
- Dong, Liu, Williams PRD 58(1998)074504 - Lewis, Wilcox, Woloshyn PRD 67(2003)013003 - Leinweber, et al.,PRL 94(2005) 212001; 97 (2006) 022001- Lin, arXiv:0707:3844- Wang et al, Phys.Rev. C79 (2009) 065202- Doi et al., Phys.Rev. D80 (2009) 094503
QCD models
Recent significant progress in Lattice QCD:
these all suggest very small effects with precision an order of magnitude beyond empirical constraints - predictions are
experimentally indistinguishable from zero
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
The Axial Term and the Anapole MomentAnapole Moment
Correction: Multiquark weak interaction in RA
(T=1), RA(T=0)
Difficult to improve on theoretical bound€
˜ G Ap,n = −τ 3 1 + RA
T = 1( )GA
( 3)
+ 3RAT = 0GA
( 8) + Δs
Uncertain Q2 dependence
G0 results
Young et al., Phys.Rev.Lett. 97 (2006) 102002, nucl-ex/0604010
Worse, if you assume that the correction might independently affect GA
p and GAn
G0 Collaboration, Phys.Rev.Lett. 104 (2010) 012001
Zhu
Leinweber
Zhu
(preliminary)
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Proton Weak Charge
Proton weak charge precisely known from EW gauge theory and precision EW at the Z-pole
If measurement at low energy comes up different, indicates proton charged for some other (parity-violating) interaction
slope due to proton structure
Global fit of existing strange-quark program data provides constraint on Standard Model
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Bounding the vector weak charge
SM value
R. Young et al., PRL 99 122003 R. Young et al., PRL 99 122003 (2007)(2007)
With this parameterization for hadronic effects, what can be said about the Standard Model parameters?
QpW = 2 C1u + C1d
These “form factor” measurements offer a
powerful constraint on new physics
Neutral weak charge of Up, Down quarks
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Proton Weak Charge with QWeak
δQWp=4%
- Non-perturbative theoryNon-perturbative theory g g ~~ 2 2ππ ΛΛ ~~ 29 TeV 29 TeV
- Extra Extra Z’Z’ g ~ 0.45 g ~ 0.45 Z’Z’ ~~ 2.1 2.1 TeVTeV
Figure: R.Young
Dedicated proton form-factor at very low Q2: proton weak charge to 4%
Run concluded this May. Analysis underway. First results at October DNP!
Kent Paschke
LNS Colloquium, September 2011
Precision Electroweak Physics with e- beam
Steady progress in technology:
• part per billion systematic control
• 1% systematic control
• Major developments in
- photocathodes ( I & P )- polarimetry- high power cryotargets- nanometer beam stability- precision beam diagnostics- low noise electronics- radiation hard detectors
• pioneering• recent• next generation• futurePioneeringStrange Quark Studies3rd GenerationFuture Future:
•Qweak-electron (MOLLER at JLab)•Quark axial charges + nuclear studies (SOLID at JLab)•super Qweak-proton (P2 at Mainz)
SOLID: significant interplay with ν studies
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Vector Strange Form Factors are Small
Q2 ~ 0.1
Q2 ~ 0.22
Q2 ~ 0.62
• Global results are consistent with strangeness contributions less than a few percent of the electromagnetic structure of the nucleon
• Recent lattice results indicate values smaller than these uncertainties
• Further improvements in precision on strange form factors would require additional theoretical (radiative corrections) and empirical (vector FF) input for interpretationVector strange quark program is winding down...
...nuclear and fundamental interaction studies with parity-violating electron scattering
continue
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Backup
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
γZ box contributions
Tjon, Blunden, Melnitchouk (2009)
Also results from Zhou, Kao, Yang, Nagata (2010)
~10-3 for APV
Q2 dependent, but incomplete resonant states
1%-few% for APV
Sibirtsev, Blunden, Melnitchouk, Thomas (2010)
Also results from: Rislow, Carlson (2010),Gorchtein, Horowitz, M. Ramsey-Musolf(2011)
Complete calculations, but only at Q2 =0
Recent interest in radiative corrections which remain significant at low Q2
Current status: few% uncertainty over measurement range, from 20-50% of Ans error. Precision will be
improved.
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
SAMPLEBates Laboratory, 1998-2001Backward angle, H and 2H Q.E. at low Q2
Mirrors focus Cerenkov light from backscattered particles into shielded PMTs
Analog integration of PMT during beam burst
No magnetic or T.o.F. spectrometer; background is not excluded
Background Dilution:Non-light background 15-30%Non-Cerenkov background 10-15%Pion decay background 5-10%
Measured in specialized runs
GEANT simulation
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
PVA4 at MainzCalorimeter:1022 PbF2 crystals
10 cm LH2 target
20 A, 80% polarized beam
LuMo
MAMI Microtron, 2000-presentForward and backward angles, Hydrogen, D2 Q2 = 0.6, 0.23, 0.1 GeV2
1022 PbF2 calorimeter crystals distinguish elastic via energy resolution
Specialized fast counting electronics self-trigger and histogram energy distributions in overlapping 3x3 modules
Elastic rate: 10 MHz, total rate 100 MHz
Scintillator paddles in coincidence to tag charge in backangle studies
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
G0JLab, 2004 Forward angle H
Duty factor of 499 MHz CEBAF beam reduced to 31 MHz
Recoil protons detected in scintillators, segmentation defines Q2 point
T.o.F through toroidal spectrometer,Time histogram from specialized electronics
Simultaneous Q2 = [0.16,1] GeV2
pions,background elastic protons
inelastic protonslead collimators
elastic protons
detectors
targetbeam
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
G0 Backward Angle
Electron detectionTurn magnet/detector package aroundAdd Cryostat Exit Detectors (“CEDs”) to define electron trajectoryAdd aerogel Cerenkovs to reject pions
JLab, 2006
Back angle H, D2
One Q2 point for each beam energy
“tracking+PID” from magnetic spectrometer
Kent Paschke
NuFACT, Williamsburg, Virginia, July 25, 2012
Combining with PVeS
S. Pate et al., Phys.Rev. C78 (2008) 015207
Subtracting off the CC axial term
Simultaneous fit E734 with PVeS to control vector strange form factor contributions
How well is Q2 dependence known? (recent Miniboone and K2K results raise questions)
Robust over models of Q2 dependence?Anapole corrections to PVeS?